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HomeMy WebLinkAboutHeritage Renton Hill Plat TECHNICAL INFORMATION REPORT Heritage Renton Hill Plat S.E. 7th Court and Beacon Way S.E. Renton, Washington City of Renton File Nos. LUA00-149, AAD and LUA00-053, PP, ECF Prepared for: Heritage Arnold Associates, LLC 2100 124th Avenue N.E., Suite 112 Bellevue, Washington 98005 January 2002 Our Job No. 7797 �C'HA 1�S V, � CIVIL ENGINEERING, LAND PLANNING, SURVEYING, ENVIRONMENTAL SERVICES _5 18215 72ND AVENUE SOUTH, KENT,WA 98032 . (425)251-6222 (425)251-8782 FAX www.barghausen.com U TABLE OF CONTENTS 1.0 PROJECT OVERVIEW 1.1 Technical Information Report(TIR)Worksheet 1.2 Vicinity Map 1.3 Assessor's Map 1.4 Aerial Topography 1.5 Aerial Photograph 1.6 Topographic Survey 1.7 Boundary Survey 2.0 CONDITIONS AND REQUIREMENTS SUMMARY 2.1 Preliminary Plat Maps 2.2 Hearing Examiner's Report dated January 25,2001 2.3 Mitigated Determination of Non-Significance dated October 19,2000 2.4 Summary of Hearing Examiner's Conditions 2.5 Summary of SEPA Conditions and ERC Advisory Notes 3.0 OFF-SITE ANALYSIS 3.1 Downstream Analysis by Peterson Consulting Engineers dated April 10,2000 4.0 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN 4.1 Existing Site Hydrology 4.2 Developed Site Hydrology 4.3 Tract A Infiltration Pond Sizing 4.4 Tract A Wet Pond Sizing 4.5 Tract A Infiltration Trench Sizing 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN 5.1 100-Year Conveyance Analysis 6.0 SPECIAL REPORTS AND STUDIES 6.1 Results of Subsurface Infiltration Testing by Geotech Consultants dated November 17,2000 6.2 Results of Test Pits for Fill Exploration by Geotech Consultants dated November 9,2000 6.3 Geotechnical Engineering Study by Geotech Consultants dated September 14, 1999 6.4 Phase 1 Environmental Site Assessment by Geotech Consultants dated September 9, 1999 6.5 Abandoned Mine Assessment by Hart Crowser dated August 23, 1999 6.6 Supplemental Geotechnical Recommendation by Geotech Consultants Dated March 28,2002 7.0 OTHER PERMITS 7.1 City of Renton Street Name and Address Approval 7.2 City of Renton Postmaster Approval 7.3 City of Renton Fire Hydrant Location Approval 7.4 Washington State Department of Natural Resources FPA Permit 7.5 Washington State Department of Ecology NPDES Permit Approval 7.6 City of Seattle Water Department Approval to Work Within Beacon Way S.E. 7.7 Water Line Easement through Falcon Ridge Plat dated March 22,2002 7797.006[RJA/jss/ca] 9.0 BOND QUANTITIES,FACILITY SUMMARIES,AND DECLARATION OF COVENANT 10.0 OPERATIONS AND MAINTENANCE MANUAL 7797.006[RJA/jss/ca] 1.0 PROJECT OVERVIEW The Heritage Renton Hill plat is located in a portion of the Northwest quarter of the Northeast quarter of Section 20,Township 23 North,Range 5 East,Willamette Meridian, City of Renton,King County, Washington. The project occupies approximately 10.35 acres and is situated east of Beacon Way S.E. and south of S.E. 7th Court,as shown on the Vicinity Map. To the north of the project is an existing single-family subdivision known as River Ridge. To the east of the project is an existing single-family subdivision known as Falcon Ridge. To the west of the project is the Seattle Water Department Cedar River Pipeline Easement and the City of Renton Philip Arnold Park. The project has received preliminary plat approval for 50 lots. The property is covered with young,second growth,mixed deciduous trees,except the northwest portion where filling has occurred in the past. The site is underlain with surface native topsoil overlying gravelly sand. There is an area in the northwest portion of the site where fill material was placed in the past. This fill is a mixture of soil,concrete rubble,construction debris,and household garbage. This garbage/fill will be screened on site and the soil will be retained on site while the garbage will be hauled away to an approved dump site. The entire site will be cleared and graded for individual lot pads. The proposed development for the site consists of a 50-lot single-family subdivision with roads and utilities serving each lot. The roadway sections used for this project are according to City of Renton standards, with a modification allowed to reduce the right-of-way width to 42 feet. Several private driveway tracts will be provided along with an emergency access tract. Tract A is a drainage facility containing a wet pond for water quality treatment and an infiltration pond for retention of stormwater on site. The wet pond is sized for Basic Water Quality treatment according to the 1998 King County Surface Water Design Manual(KCSWDM). The infiltration pond is sized for the KCRTS 100-year event according to the KCSWDM. The design infiltration rate used for the pond sizing is 30 minutes per inch based upon safety factors required by the KCSWDM and field measured infiltration tests by Geotech Consultants. Please refer to Section 6.0 ofthis Technical Information Report (TIR)for the Geotech Consultants reports. Roof drain infiltration trenches will be provided for each lot and equipped with an emergency overflow connection to the storm drainage system. This is in accordance with Section 5.1 of the 1998 KCSWDM. Drainage runoff from the roadways,driveway tracts, individual lot driveways, and front yards will be collected and conveyed by a series of catch basins and drainage pipes that run to the Tract A drainage pond. Individual lot drainage stubouts will be provided for each lot for the emergency overflow from the roofdrain infiltration trenches. This will provide a distribution of infiltration of stormwater runoff across the site. The storm drainage infiltration pond has been sized to handle the entire site,assuming a worst case scenario that the roof drain infiltration trenches are not functioning. This is the conservative approach. Please refer to Section 2.0 of this TIR for a detailed narrative response to each of the plat conditions and SEPA conditions for this project. 7797.006[RJA/jss/ca] Iti King County Department of Development and Environmental Services TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND Part 2 PROJECT LOCATION AND DESCRIPTION PROJECT ENGINEER Project Owner Heritage Arnold Associates, LLC Project Name Address 2100- 124th Avenue N.E., Suite 112 Heritage Renton Hill Plat Bellevue, Washington 98005 Location Phone Bill Sherman at(425)602-3700 Township 23 North Project Engineer Robert J. Armstrong, P.E. Range 5 East Company Barghausen Consulting Engineers, Inc. Section 20 Address/Phone 18215 - 72nd Avenue South Kent, Washington 98032/(425)251-6222 Part 3 TYPE OF PERMIT Part 4 OTHER REVIEWS AND PERMITS APPLICATION ■ Subdivision HPA ❑ DFW HPA ❑ Shoreline Management ❑ Short Subdivision ❑ COE 404 ■ Rockery I, Grading ❑ DOE Dam Safety ❑ Structural Vaults Commercial ❑ FEMA Floodplain ■ Other- Structural Wall ❑ Other ❑ COE Wetlands Part 5 SITE COMMUNITY AND DRAINAGE BASIN Community Renton Drainage Basin Cedar River Part 6 SITE CHARACTERISTICS ❑ River ❑ Floodplain ❑ Stream ❑ Wetlands ❑ Critical Stream Reach ❑ Seeps/Springs ❑ Depressions/Swales ❑ High Groundwater Table ❑ Lake ❑ Groundwater Recharge ❑ Steep Slopes ❑ Other 7797.006[RJA/jss/ca] in 7 SOILS Soil Type Slopes Erosion Potential Erosive Velocities Gravelly Sand 5% Minimal Minimal ❑Additional Sheets Attached See Geotech Consultants Reports in Technical Information Report Section 6.0 Part 8 DEVELOPMENT LIMITATIONS REFERENCE LIMITATION/SITE CONSTRAINT ■ Ch. 4 - Downstream Analysis ❑Additional Sheets Attached: See TIR Section 3.0 Part 9 ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION AFTER CONSTRUCTION ■ Sedimentation Facilities ■ Stabilize Exposed Surface Stabilized Construction Entrance ■ Remove and Restore Temporary ESC Facilities Perimeter Runoff Control ■ Clean and Remove all Silt and Debris ❑ Clearing and Grading Restrictions ■ Ensure Operation of Permanent Facilities ■ Cover Practices ❑ Flag Limits of SAO and open space preservation areas ■ Construction Sequence ❑ Other ❑ Other Part 10 SURFACE WATER SYSTEM ❑ Grass Lined Channel ❑ Tank ■ Infiltration Method of Analysis ■ Pipe System ❑ Vault ❑ Depression 100-Year KCRTS ❑ Open Channel ❑ Energy Dissipater ❑ Flow Dispersal Compensation/Mitigation of ■ Dry Pond ❑ Wetland ❑ Waiver Eliminated Site Storage ■ Wet Pond ❑ Stream ❑ Regional Detention Brief Description of System Operation Catch basins and pipes for collection and conveyance. Wet pond for water quality Infiltration pond for stormwater retention. _ Facility Related Site Limitations Reference Facility Limitation 7797.006[RJA/jss/ca] art 11 STRUCTURAL ANALYSIS Part 12 EASEMENTS/TRACTS ❑ Cast in Place Vault ■ Drainage Easement ■ Retaining Wall ■ Access Easement ■ Rockery> 4' High ❑ Native Growth Protection Easement ❑ Structural on Steep Slope ■ Tract ❑ Other ❑ Other Part 13 SIGNATURE OF PROFESSIONAL ENGINEER I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were incorporated into this worksheet a t at chments. 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SEC.2D-23-5 FOUND CASED CONC MON. RIVER RIDGE VOL. 163199-101 7/99 i �• NE CORNER SECTION FOUND 1/2'REBAR R CAP FOUND 1/2'REBAR k CAP FOUND 1/2'REBAR h CAP _ 20 23 5 I I TCA 9634/10358 D.1'N- OF TCA 9634/,0356 0.1'S OF TCA 9634/10356 0.1 N.OF 5 TM5'LE�HMO PROP. LINE PROP_UNE PROP.LINE 3/8'BRASS PIN NOT VISITED THIS SURVEY / 1 i 2 i 3 q ��� 5 s `� 7 S. 7TH ST. \\ / I FENS I FEN GE�`� N 89.56'37"�W \�\ 2659.62' 929.64' ,o�Do 4oa,r r -------'-'-----..-.----..-._-..-'-------- 1329.61 SEE ENCROACHMENT ENCROACHING AREA FROM \ DETAILLOT 3 OF RIVER RIDGE APPROK AREA= 3293t S.F. PUBLIC ROADWAY AND UTILITY �C'� EASEMENT REC NO. 9108190683. IQ \\ I(!1 w Iz o 9cl 01, \ no 100 0 100 200 300 v� �Fo \ FALCON RIDGE , 9� \ Z (CEDAR RIDGE) Scale 1" = 100 14 VOL. 129151—57 MERIDIAN: F9 PLAT OF FALCON RIDGE CEDAR RIDGE CURVE TABLE S'F � VOL. 129, PG. 51-57 ( > NUMBER262r12"IDELTA R25.00 662.08 ����' \ C2 134-a 25,00 StL88 MONUMENT SIGN \\ \ REFERENCES: 4.04 1. PLAT OF FALCON RIDGE(CEDAR RDGE1 VOL.129,PG 51-57 LINE TABLE \ 2. PLAT OF HIGHLAND ADOIDON,VOL 17.PG.32 NUMBER DIRECTION DISTANCE 25.95' 3 PLAT OF DAL USIBELI3 ADDITION,VOL 62.PG. 40 Lt N 0131'12"E 33AX L2 N 44'19 W 34.10 \ 4. PLAT OF RIVER RIDGE,VOL 163,PG. 99-101 L3 N 89363 W 100. BOUNDARY \ L4 N 183 1 W 15,43 LS N3T4/5 W 26.82 LINE •\ g604• L6 N 781534 W 22.66 \ 1 g 56 NOTES: L7 N Wlf4e w 45.o ENCROACHMENT DETAIL \ 1. EQUFUNT a PROCEDURE& A S'ELECTRONIC TOTAL STATION WAS L8 N l6.2TI2"E 45.18' USED FOR THIS FIELD TRAVERSE SURVEY ACCURACY MEETS OR l9 N 16'22'15"E 14.98' EXCEEDS W.A.C.332-130-090. TM OR` 2. 1HE INFORMATION DEPICTED ON THIS MAP REPRESENTS THE RESULTS SE $ OF A SURVEY MADE ON THE DATE INDICATED AND CAN ONLY BE O0N- SDERED AS WICATNNG THE GENERAL CONDITION OnTING AT THAT TIME. LEGAL DESCRIPTION 3. THIS MAP DOES NOT PURPORT TO SHOW ALL EASEMENTS OF RECORD, THAT PORTION of THE NORTHWEST QUARTER of THE NORTHWEST GARTER OF THE NORTHEAST QUARTER OF SECTION 20, TOWNSHIP 23 NORTH,RANGE 5 EAST,WI IN KING COUNTY.WASHIIGTON.DESK AS FOLLOWS: COMMENCING AT THE NORTHWEST CORNER OF SAD SUIWASION,SAID POINT Q,�bY•tv�Sk�F LEGEND BERG THE TRUE POINT OF BEGINNING`, THENCE SOUTH 891 EAST ,- ALONG THE NORTHERLY LIMITS OF SAID SUBDIVISION A DISTANCE OF 929.67 o. • SET REBAR AND CAP'MG 32+W UNLESS OTHERWISE NOTED. FEET 10 THE NORTHEAST CORNER of SAID sueavLSION: THENCE SOUTH (✓3n r,Z 01'43'38'WEST ALONG THE EASTERLY LUIS OF SAID SUBDIVISION A DISTANCE OF 818.33 FEET: THENCE SOUTH 71-05'12'WEST A DISTANCE ` OF 109.48 FEET TO A POINT ON THE NORTHEASTERLY MARGIN OF THE CITY OF SEATTLE'S CEDAR RIVER RPELINE RIGHT OF WAY. THENCE NORTH 44' �•.•R 32434 20'15'WEST ALONG SAID NORTHEASTERLY MARGIN A DISTANCE OF 1148.20 f�'JS.LC��4•: FEET TO A POINT ON THE WESTERLY LUIS OF SAID SUBDIVISION; THENCE �0 NORTH 01'46'20'EAST ALONG SND WESTERLY LUIS A DI IHE OF 33.14 FEET TO THE TRUE POINT OF BEGINNING. EXPIRES: 9/9/ NW1/4, NE1/4, SEC. 20, T. 23 N-, R. 5 E, W.M. KING COUNTY, WASHINGTON SURVEYOR'S CERTIFICATE RECORD OF SURVEY Se ad cylA/!)7cm IX. � vms� G RECORDERS CERTNF'KA1E ...........�___.�._. THIS MAP CORRECTLY REPRESENTS A SURVEY MADE BY ME OR for PROFESSIONAL LAND SURVEYORS FILED FOR RECORD THIS DAY OF 20_AT UNDER MY DIRECTION IN CONFORMANCE WITH THE REQUIREMENTS P.O_ BOX 289, WOODINVILLE, WA 98072 (425) 486-1252 OF 1}E SURVEY RECORDING ACT AT THE REQUEST OF M.IN BOOK OF SURVEYS AT PAGE �" T P• IN AQU' 1999 B E N N ETT DEVELOPMENT DRAWN BY; DATE JOB NO.: AT THE REQUEST OF OF EDA 3-21-00 99172 MANAGER SUPT. OF RECORDS EDWARD D.ANDERSON CHKD BY: SCALE: SHEET.- CERTIFICATE NO, 32434 9 LAKE BElEVUE DR. STE 100A BELUTAJE, WA 98005 JR 1 = 100' 1 OF 1 N O 2.0 CONDITIONS AND REQUIREMENTS SUMMARY Included within this section are the preliminary plat approval conditions and a narrative response describing how the conditions will be addressed prior to final plat recording. The basic and special requirements that govern this project have been listed below in a table that articulates how each ofthe core and special requirements have been addressed. These requirements come directly from the 1998 King County Surface Water Design Manual. DISCUSSION OF CORE REQUIREMENTS AND SPECIAL REQUIREMENTS OF THE 1998 KING COUNTY SURFACE WATER DESIGN MANUAL CORE REQUIREMENT How PROJECT HAS ADDRESSED REQUIREMENT: No. 1: Discharge at Natural The proposed infiltration pond will act as the natural discharge for the Location project,along with the individual lot roof drain infiltration systems. An emergency overflow connection to the catch basin in Beacon Avenue South will be provided. No. 2: Off-Site Analysis A Level 1 Downstream Analysis was prepared by Peterson Consulting Engineers, dated April 10, 2000. This analysis has been included in Section 3 of this Technical Information Report. No.3: Flow Control On-site infiltration will be provided to retain runoff. No.4: Conveyance System The conveyance analysis that was performed for the proposed storm drainage system is contained in Section 5.0 of this Technical Information Report and has been prepared according to the 1998 King County Surface Water Design Manual. No. 5: Erosion and Sediment Temporary erosion control measures for this project include temporary Control ditching,stabilized construction entrance,perimeter runoff control,cover practices,temporary sedimentation pond, and construction sequence. No.6: Maintenance and The drainage facility for this project will be maintained by City of Operations Renton,and has been designed in accordance with the 1998 King County Surface Water Design Manual requirements. No.7: Bonds and Liability Bonding will be completed as required by City of Renton. No. 8: Water Quality The project has provided a wet pond in accordance with the Basic Water Quality menu of the 1998 King County Surface Water Design Manual. SPECIAL REQUIREMENT How PROJECT HAS ADDRESSED REQUIREMENT: No. 1: Other Adopted Area This special requirement does not apply to this project. Specific Requirements 7797.006[RJA/jss/ca] No. 2: Floodplain/Floodway The 100-year floodplain boundary is not within the limits of this project, Delineation nor is it within the limits of any of the adjacent properties to this project. No.3: Flood Protection This project does not contain or abut a Class I or Class II Stream that has Facilities an existing protection facility;therefore,this requirement does not apply. No.4: Source Controls This project is not a commercial,industrial,or multi-family development, nor a redevelopment project proposing improvements to an existing commercial, industrial, or multi-family site; therefore,this requirement does not apply. No.5: Oil Control This site is not classified as a high use site given the criteria found in the 1998 King County Surface Water Design Manual;therefore,no special oil control treatment is necessary. 7797.006[RJA/jss/cal N 2.1 PRELIMINARY PLAT MAPS SEC. 20, TWP. 23 N., RGE, 5 E., W.M. ETERSON CONSULTING HE ITA E 4030 Lake Washington S RPOAT WAY �c��� Blvd. N.E., Suite 200 Kirkland, WA 98033 RENTON HILLs 2nd ST �9 y Tel(425)827-5874 S 3rd ST Fax (425) 822-7216 S 4fh ST SITE om �\ y� CT. = �.� a z z C \\ II \/ •� I � �\--�\ �,3 ADY WAY S GR PHILlP S. 7TH ST. C _1 S89 56 3 �_ 829.34' AIMWNVOLp Z a -1 F--fi 1- sroRMWATER 35 PARK O 3 s TRACT 43 42 47 40 39.38 37 36 SW 1634 fh ST m o 16 LA 7RA 1 '• 45 4 4 48 49 50 51 32 Z J J t I y 3 SB SS 54 JD -( J 200' 200 ° i \\ 4 5 _ 28 �� �T VICINITY MAP.• C7 c Q \ 6 sc 4/72/o00D' 1 - -I �A 6 9 to 11 12 27 NOT TO SCALE ' 4 s _ 17 1615 14 13 6 GENERAL NOTES: I ' \\ 24 I� - OWNER: RENTON SCHOOL DISTRICT �i c NUMBER DEL TA RADIUS LENGTH L/5 7RACT� fa „ 2J 1 L--.I C- ROfN70N WASHlNG70N 98055 ti Cl 13428'40" 25.00' 58.68 _ { C2 2827'12" 125.00' 6208' \ 22 I DEVELOPER.' BENNETT DEVELOPMENT l \\ 19 21 9 LAKE BELLEVUE A _ SU17E 100 A \/ BELLEVUE, WASHINGTON 98005 _ -- I --I I L/S TRACT / �( � (425) 709-6508 \ bs 0.41 \/ \ CONTACT., RYAN RKE m m t1�9 5\\/ ENGINEER NEERS 40JO LAKE WASHINGTON BL1VD N.E. SUITE 200 KIRKLAND, WASHINGTON 98033 (425)827-5874 D CONTACT: XIVNIFER SM7a P.E b r KEY MAP SURVEYOR., MEAD GILMAN&ASSOCIATES z E SCALE 1"=200' P.O. BOX 289 Vd WOOOINWLLE, WASHINGTON 98072 a (425) 486-1252 BENCHMARKS/DA TUM. CONTACT., EDWARD ANDERSON, P.L.S. 8 TOTAL AREA.(+/--) 10.35 ACRES(GROSS) o BENCHMARKS CITY OF RENTDN 1475- N1/4 COVL SEC. 20-23-5 CASED 4�4'CONC MON WITH t 1/2'BRASS DISC& -'; 80't E. OF TOTAL AREA R.O.W. 204 ACRES THE INIX OF S 77H ST. &JONES AVE S NET AREA 8.31 ACRES z�l ELEVA77ON= 341.34' CITY OF RENTON 1418 TOTAL LOTS 57 RESIDENTAL LOTS PROJECT A A CASED CONC MON WITH 1/4'BRASS PIN, 11 t S OF THE INTX OF MAX ALLOWABLE DENSITY: 8.00 DU/ACRE S 7TH ST. &RENTON AVE S DESIGNED: .L S7E/G ELEVA770N= 305.80' PROPOSED DENSITY.• 6.86 DU/ACRE CADD B. DENNEY DATUM: NAND 88(CITY OF RENTON) ZONING.` R-8, URBAN R£SIDETJD CIIECUD, d 57vcAL DAME: 4/10/00 PROPOSED USE., SINGLE-FAMILY, DETACHED FIE NAME: PP7HER25 LEGAL DESCRIPTION EXfS77NG USE 9NGLE-FAMILY, DETACHED THAT PORT70N OF THE NORTHWEST QUARTER OF THE NORTHWEST QUARTER OF 77E NORTHEAST BOUNDARY. FIELD SURVEYED BY MEAD GILMAN&ASSOCIATES QUARTER OF SEC77ON 20, TOWNSHIP 23 NORTH, RANG 5 EAST, WM IN KING COUNTY, WASHINGTON, DESCRIBED AS FOLLOWS: - TOPOGRAPHY. FIELD SURVEYED BY MEAD GILMAN&ASSOCIATES COMMENCING AT THE NORTHWEST CORNER OF SAID SURDIMSJON, SAID POINT BONG THE TRUE POINT �$R OF BEGINNING` THENCE SOUTH 89'5637'EAST ALONG THE NORTHERLY LIM17S OF SAID SUBDIVISION UTILITIES/PURVEYORS: ��! OF AS c9� A DISTANCE OF 929.67 FEET TO THE NORTHEAST CORNER OF SAID SUBDIVISIOA!• THENCE SOUTH 07 43'36' WEST ALONG THE EASTERLY LIMITS OFSAID SUBDIK90N A DISTANCE OF 81&33 FEET; THENCE SOUTH 71'05'12' WEST A DISTANCE OF 109.48 FEET TO A POINT ON THE NORTHEASTERLY SEWER/WATER: CITY OF RENTON ti MARGIN OF 7HE CITY OF SEATTLES CEDAR RIVER PIPELINE RIL44T OF WAY- THENCE NORTH 44' 20'15'WEST ALONG SAID NOR7HEAS7ERLY MARGIN A DISTANCE OF 114820 FEET TO A POINT ON THE STORM DRAINAGE. CITY OF RENTON n WESTERLY LIMITS OF SAID SUBDIVISION; THENCE NORTH 01 46'20'EAST ALONG SAID WESTERLY LIMITS 3 A DISTANCE OF 33.14 FEET TO THE TRUE POINT OF BEGINNING. CAS/POWER: PUGET SOUND&ENERGY `r`9rONAL LOT AREA'S (LSTED IN SQUARE FEET) TELEPHONE US WEST 3I d0 1. 5990 13 5,482 25. 4,750 37. 5,527 49. 4,750 CAS' AT&T EXPIRES: 9/9/00 2, 5,353 14. 4,965 26. 4,750 3& 5,500 50. 4,749 FIRE DISTRICT- aTY OF RENTON STAMP NOT VALID d 4,875 15. 4,750 2Z 4,750 39. 5,500 51, 5,825 44,625 16. 4,750 28 4,750 40. 5,500 52 5,863 UNLESS SIGNED AND DATED 5. 4,504 17. 6,090 29. 4,750 41, 5,500 5,£ 4,750 SCHOOL DISTRICT- REN70N SCHOOL DISTRICT,�403 6. 5,557 1& 7,584 30. 4,750 42 5,500 54, 4,750 7. 5,799 19. 7,3J9 31. 4,754 4-1 5,500 55. 4.750 JOBNUMBERHERM-0025 & 5,443 20. a318 32. 4,946 44. 5,500 56. 4,731 9. 4,750 21. 5;000 33 6,121 45. 4,750 57. 6,660 1a 4,750 22. 5,000 34. 5,549 46. 4,750 SHEET NUMBER 0 11. 4,750 23. 4,851 35. 6,905 47. 4,750 / OF T �O 1Z 5625 24. 4,750 36. 7,406 48 4,750 e SEC. 20, TWP. 23 N., RGE. 5 E., W.M. ETERSON (CONSULTING \ EX SS IH ! Nf/4 CDR. SEG 20-23-5 'v RIM 336. FOUND CASED CONC MON. \`/ ?. I - 1 CTR. CH 328.2(NW.SW) 4030 Lake Washington EX. CB TYPE ff ," ems• I T g CB 7 TYPE ll COULD44.4 NOT OPEN / // I I I Blvd. N.E., Suite 200 \ P IE 334.7(5W) Ex. ca TYPE/ Kirkland, WA 98033 1�2"IE 331.8(SE) TOP 343.5 i =X. SSA,( JI2"IE 331.6(NW) 12 1£340.4(S) I 1 { i{ Tel(425)827-5874 tIM 337.7 \\ I 12 IE 340.�� I I{ CHNL. 326.9\(,(V� W) \ 1 , { Fax (425)822-7216 PTUGA c 1, PM GS CA _ ' -FVC-v / $ R1* 46.6� ——— / I-_ __— - i .1.. 15' WGETATIV_E CT(t cHN��- 40.1 (NE,SWV �! "56'3-E44 Z ? — _ a — 6'WOOD FENCE 50' /� 50' — 50' ! Q a L _ �/ ——————— 1 ------ f AREA EX. <B TYPE R X \ 12 /E 44D9 N) ! I / i / i \ K\ 4 W > TOP 338.9 \\ fP1L \ \ \ •`? �. -` .'. /J f© y�2 I ! $rORMWATER_--' /! b`I\ \` ! \ ` ). ..ytr MACTice/ 1 I SOd\s.f._ —MSQa'��\ I 5500 af. <\ \\ \ /27982&f t I I 7 \ \\\� 191, / \ sorc 50' I / �\ I \ `, �`\ t Y• _ i s>?" � �,t z y h �<r � �. S. Ts` �,�.� `'' s ��' s>1 X V V _ I %. } \ ` \ \,\ > �p z ._ x ,may.�'�+G"r.-��•+�.ity, � 1'GT.-' �"a 6�d�-.�'�� - +.Q & �' .. W C 1'YM 1 ! \-0 / \1\\ � y. .y��� � .' � c3 d�'r �d .i "� *"'�.J��� ✓•4�� I :.;hi.,54>�; ^.,_. a� + r -� � � , uROAD �• ��`\ 9P01 `\ /6 \�� .S 5f' f _`p' 1 zr r 16 50' 6 5 14 PM \ \�� \ .\ t TRACT PARK NUMBER DELTA RADIUS LENGTH \ I �\�" I 5,4O2:r. / \ /t t >� 3042 of - Ci 13428'40" 25.00' S868' ( \ \ \ f.J 4,750 s 140,.f �7 C2 2827'12" 1125.00' \\ \ ' \y \\\ j �/ ^ U u U a \\� 30 \ ` ' /2 4 /.50' 50' > / 1 t' is \ \' t 5t353 4,875 s.t.� \\ r.\. _« SYE70 A, __ Dry A Smo CAM DENNEY ---- ---- � i \ \\ \ \\ 4825sf. ( / \ F DATE 4/10/b0 — I I '-�• \ \ `\♦ \ / \ _-- '- FIE NAM PP2Hvm SCALE: t"- 40' I I '" \ \\\\ \\ `\'• \\ <\ 4,50J4 sf. 4 ------ 5,55Zsf. 2236 EXPIRES: 9/9/00 STAMP NOT VAUD UNLESS SXM AND DATED I/S T 025 JRA Cr HERM-0 $ af SIM NUMM 2oF4 _ � SEC. 20, TWP. 23 N., RGE. 5 E., W.M. ETERSON (CONSULTING - \ ► / �\ I / \ 4030 Lake Washington Blvd. N.E., Suite 200 Kirkland,WA 98033 Tel(425)827-5874 I \ Fax(425)822-7216 SCALE: If= 40' gyp _ 15'VEGETA"W 38 '56'37'E 829.�5 50' 50' S0" ,.�- ♦ ♦ 50' S0' / 0' i" 60" di �I 16 �4, 2 l I 4f— t 3 _-5�� I I �J6 � ——-�—\� s�`�♦ ssoo x/. 15"s00�c I I t s .r. s s.c 07 40 ► T x cc . ` \ Q ��.:-- 'v .las .t.y.:- +_. k�+�>,T '� t - vy5 �^�:,Zxr- :1 �-. z �, ^� Yc S O• 1` 1 --� 50. Ll 16' 50 N•5OI `\\ \ M/ / 50 r max' > u \\\\ ► 6� s'f _ ) PARK I : I I / I\ \ , I / I 34 H 1 i A '46 r ,fir h � }i � // h I /"7 _j �+°_ _``♦_ d/ �7so a/. I I �7s0 s.f. l. J4/7so / I 4,749 ( 5,825 a r a7 L--t 1 L _—J L/ /I U► L---J L L --i �J- — �- — -- \ , t i s _ ._&.� b i• 1 50 / I j/ / 50 50. 50, 75' �± I.`\I� s /14•' �'•+�\ / S 50 -' 65 ?J a \ �n ——————— S l .T3\ �♦ / //"/ E j / ' \ BSBL / �� -3 I I 4`754 s1. l I T�, / / I z4444444444< � l I ( I � I � I - � \�i ) ► III / i 56 I 55 / 53__, I o yl I I ( t ► ,c sroc s./. 4,750 8f. 4,750 :t• :' i `♦ . ( i �' T' %�� i♦ I Ql ��J \ / Des► ED .c s1Erc tiy.,J n 4,625 a.►. / \\ s �',7 4r ► 2 so' DATE: 4/1o/m \ /> _ ' .. � ��.� s h I I y(�p�`1 ' / 1 / o \ �-� / FILE NAME:Pa.3wErr25 �zsi \ � 5 / s �. �.: �. `c+ �x- �F00..�hl x"`•�'� �vr`rk- 1,$�/7Qr�j �- + 3iz,_ �-�3j p / I // l \ \ 4.5o4 ►. �5 50 \ _ I z Q� I I / / 1 // �/' // $��o *, . /x " ✓r / / /I 1- — --s / sf. \ 4 �\ ti I' �; . n— s/. I I--�•5;443�I sl.I 4,7500 /. j'l- r�5i6�ZSf. L \I I `♦ I� /1p� ) / �` 9I0NAl. E*Ws: eke/66 STAWNMAM \ ♦ \ - v3 /i/�' _ _�- ,--�� UNM SIGNED AND DATM 5GC \ 4 - - - - - �NUWE M-0025 ACC i2 "EE U 4 3o' 4 .AOAO Ct / ol 41 34 ,' •y �is°'+1\, r r \\ ��/ I/ `„J\ l a //'C ��"kit'��;. �I.y. � 11 IK 1 • fib rn LJ 1-7 - 41/ '-—— I h1 C13 10 \ _`fir � l All 60" oN Iilp J L ;— _ 50, _ L_ Ol / _I / r / a�11�Q7 s IK \818.50 DATE REVISION BY G{ 81MA0 Pa cm•WMWN s aw As PRELIMINARY PLAT PLAN A JE Q `1. x 2-W ( Jr/ o * c�. O �. w a 0"i zz rn Q HERITAGE RENTON HILL N a 8 alb Q N000Nz �7 Q rn Aw00 n L� CITY OF RENTON. WASH/NGTON ••�•••• rw1 w� /1/flp Plot 9GNL 1-1' GAPER VAOC YU 6rA• JOB NO: Nm-0026 00: M1 om PIP, —1TfT CITY OF raO HERITAGE RENTON HILL a/z/oo J.sT _7` B. E1Q RENTON NEIGHBORHOOD DETAIL MAP 1 PER dT'COMMENTS gypit e�Tt/op 11$ arm SmG .�� DATUM Planning/Building/Public Works Dept. N0. REVISION BY DATE APPR � . AaaaoaY Gregg Zimmerman P.E., Administrator J.S'IflC g -A a T N \ \ T �1 s6 f -T-T -7 T777--1 1 1 21 I 11 1 1 1 1 1 1 1 1. y ��---- LLLL1111J1J --_ MAIN AVE 8 SR 400 ------------ / —————————MILL AVE S IfAi ; 7777777 FFTTTTT7777 / / w hI I I I I I I 111�ft 1 I I I I I I I y�L L1.L.L11J..�J a o yI�I III I I I I I I I I I g I I I I I I I I CEDAR AVE S--- ~LLLL1111J�J'' CEDAR AVE y --I f TTT—f--T—T'—T'1—'I T—I—T'l TTT—i It'! 1--1-r-'T--r-r--!- i J- r I I I I I I� I I I-3•�l / / I I I I I I i I, I I I :�••" I I I I I I I I I I I ��v►�''�T�I LJ_LJ_L_L I I RENTON AVE S tr iY RENTON AVE S I �-1-T•-f_� �-I--TT-7_T-7-1-T�1 1 (-T-1 f---I I I I I I I I I I I I I I :�:�: -17TT ('7-- 7-I-7r-7- / / I�1--1rT�l_� LJ_11 1 L-1J-i I / lY1 1 1 I I I� ,i I I- 1-i I I I rT- I;a I I I I f---i F---i I f�,i 1 1 I ► ;�' �� I I I I I I I I I -_J L_LL1_-j L;t,�:_1_L1-1--l--J L--LL_L`_LL�_L� \ I I I I I I I I 1 r_ .a_)-, — T — �� L�-,I_LlLJ_L L LL—. I ICI -�----r-r--, �U�i�fl---TT-T-T'�_�I r--��rTTrm-�-� -`\ \ � , L---L---!-->= i�I I:T`•'-•� I I I I 4--I Ir7-T---I - �LLL_l1_LLJ-J. �-�1 LLLI r__--- I I ICI I I 1 l y l �_r�_T_I -T-i���--Ti i i i i'-'� LJ._L lNoriAVE aL1—LJ I L—LLL1-I'► L��\L`L\LL\ /' I 11 r-i-77-77-7 I-7T-l- —I—�--�--I--r--I r--�—�°o,�_T-1' yro-77 vE s I III I I I I LJ \\\ L-1—L_I_1J_1—LLLLI—L�_1—V ✓ONES AV. S. / w \ I I\------------------ -—— / -- -- --�---� I T- j u, i 46 I----------------- INlERPACf'CORP. O/ At Aix Vgj r'v\\/vy '�j� \i0�9\ \\\ \\ I NOiSSIHS"ydai' g d.S.d�— ..uwu cmuecls/nrwlw�a/'oinwe Imnu: nlM PLOT DATE: a/k/W PLOT SOUG• 1'_1' PMlIt SPAC[: 1Q RN 408 N0: -00Y8 P F —TT17 HERITAGE RENTON HILL °4/2/00 CITY OF ° `J.OF7G RENTON DRAINAGE CONTROL PLAN Zi 1 PM 0/rY COMM£N7S SWD B/J)/OD J,15 aeon nu DATUM J.sma w Planning/Building/Public Works Dept. NO. REVISION BY DATE APPR • Gregg mmerman P.E., Administrator J.SiE7C L-----J I I I I I I I0 C I 110'; bun ay II I ----T----T--- ------�L-----+-- - -------I--- N o ---- w—I I e co \ � AV -M!R JONES AV. 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S. -------------- A "wn 4i6 Vl n ,oaf r V \ Vk iy ,f in ,49 .tz,:l.. \ 1 IL 4, /i _/ / \ \\ O, \ // \ % \ ^� ILIA, I /� i` In^rr,T 1 ( / 1\ \ \ L I / / k� \ / L , lkL S _/ a.iyySr4\a,r @r a { Yz�T+" Wl � 1 I I I V / \ V SE 8th DR \\i� N N January 25 ,2001 OFFICE OF THE HEARING EXAMINER CITY OF RENTON REPORT AND DECISION APPELLANT: Ruth Larson Appeal of ERC's Determination re Heritage Renton Hill File No.: LUA00-149,AAD LOCATION: Renton Hill, southeast of intersection of Beacon Way S with SE 7th Ct,Jones Ave S,and South 7th Street SUMMARY OF REQUEST: Subdivide an approximately 450,846 square feet(10.35 acre) property into 57 lots suitable for detached, single family homes SUMMARY OF APPEAL: Appeal of SEPA determination PUBLIC HEARING: After reviewing the Appellant's written request for a hearing and examining the available information on file,the Examiner conducted a public hearing on the subject as follows: MINUTES The following minutes are a summary of the November 14,2000 appeal hearing. The official record is recorded on tape. The hearing opened on Tuesday,November 14,2000,at 9:05 a.m. in the Council Chambers on the seventh floor of the Renton City Hall. Parties wishing to testify were affirmed by the Examiner. The following exhibits were entered into the record: Exhibit No. 1: Yellow file containing the appeal, Exhibit No.2: Yellow land use file, LUAOO- the Examiner's letter setting the hearing date,a map, 053,PP,ECF,containing the original application,proof photographs,and other documentation pertinent to the of posting,proof of publication and other appeal. documentation pertinent to this request. Exhibit No.3: Vicinity Map Exhibit No.4: Photo of Renton Ave S Exhibit No.5: Photo of telephone pole 6"from curb Exhibit No. 6: Photo of telephone pole 12-1/2" from curb Exhibit No.7: Photo of curb and gutters Exhibit No. 8: Photo of garbage truck on street Exhibit No. 9: Photo of garbage truck on street Exhibit No. 10: Photo of dip in street Exhibit No. 11: Photo of fire hydrant Exhibit No. 12: Ruth Larson's testimony Exhibit No. 13: Aerial photo from City Archives Exhibit No. 14: Plat map Exhibit No. 15: Phase I Environmental Site Exhibit No. 16: Jennifer Steig letter to Bennett Assessment Development Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25,2001 Page 2 Parties present: Appellant: Ruth Larson Renton Hill Community Association 714 High Ave S Renton, WA 98055 Representing applicant: Ann M. Gygi,Attorney Hillis Clark Martin &Peterson 500 Galland Building 1221 Second Avenue Seattle, WA 98101-2925 Applicant: Ryan Fike Bennett Development 9 Lake Bellevue Drive, Suite 100-A Bellevue, WA 98005 Representing City of Renton: Zanetta Fortes, City Attorney Elizabeth Higgins,Development Services -- 1055 S Grady Way Renton, WA 98055 Ms.Larson, appellant herein, reviewed each item contained in her written appeal of the ERC's Staff Report dated October 17,2000, and explained the reasons for her objections in each case. Particular emphasis was given to Renton Avenue South. Ms.Larson used photos to show the close proximity of telephone poles to the curbs,the narrowness of the street, the dips in the street and the tendency of garbage trucks to drive toward the center of the.street. She explained her concerns regarding safety issues when large trucks are using the street considering the narrowness of the street,the steep grade,and the limited sight distances. Becky Lamke,415 Cedar Ave S,Renton, WA 98055 expressed concern that the number of trips per day per single family household has been underestimated,based on informal surveys of her neighbors. Ms.Lamke questioned exactly what the landscaping would consist of in the 15-foot buffer along the north property boundary. She concluded by stating that the construction vehicles should be required to come onto the site off of Puget Drive. It is not considered safe for busses to come up the hill, so it should not be safe for large trucks to do so. Elizabeth Higgins Senior Planner, Development Services, 1055 S Grady Way, Renton, WA 98055 gave an overview of the nature of the project, its current status, and its progress through the ERC. Regarding the reason for the setbacks on Lot#35, Ms. Higgins stated the geotechnical engineer's report commented that the slopes at the rear of this lot are excessive. They recommended that the setback at the rear of Lot#35 be increased from Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF -anuary 25, 2001 ige 3 20 to 25 feet in order to further to protect the slope. Using a photograph from the City Archives,she clarified why an exemption to the requirement in the Critical Areas Ordinance that slopes above a certain grade be protected was granted to the project. Ms. Higgins also addressed the issues of groundwater, responsibility for landscaping,regulation of fences,and parks constructed on the property. Ms.Higgins discussed the issue of Metro service on Renton Hill. She also explained the State of Washington Growth Management Act requirements and how the City is required to plan for housing. The City Council has committed to provide as much single family housing as possible and not meet their target with apartments. Regarding the requirement that a note be placed on the face of the plat about former mining activities,Ms. Higgins stated this is the City's- way of insuring that a property owner is made aware of a potentially hazardous situation. Mining activity took place throughout the city, and there are very rudimentary maps of where these mine shafts might be.The note on the plat alerts the potential home owner to seek the consultation of a structural engineer and choose the construction method most appropriate for the site. The appeal hearing was adjourned at 12:30 pm.,to be continued on Thursday,November 16 at 9:00 a.m. ******************************** The continued appeal hearing opened on Thursday,November 16 at 9:02 a.m. in the Council Chambers on the seventh floor of the Renton City Hall. Kayren-Kittrick,Development Services, 1055 S Grady Way,Renton, WA 98055 explained her role regarding Land Use Applications and how these applications are reviewed by her office. Ms.Kittrick stated that the -eet Maintenance Plan requires that all arterials be evaluated annually and all other streets,which would __.elude Renton Avenue S, be evaluated every two years. Ms. Kittrick explained traffic mitigation fees and how they are reviewed and collected,resources available for street repair,and hauling times as allowed by code. Ms. Kittrick reviewed intersection distances,how they are measured,and under what circumstances intersections should be 110 feet apart vs. 150 feet apart. She also discussed the transportation study provided by the applicant, including levels of service at S 7th Ct and access to Renton Hill overall. Regarding the foundation of Renton Avenue S.,Ms. Kittrick stated that recent borings show four inches of asphalt over crushed rock. On cross examination,Ms.Kittrick responded to questions raised by Ms.Larson in her appeal letter. Ann M.Gygi,attorney representing applicant, Hillis Clark Martin&Peterson, 1221 Second Ave,Seattle,WA 98101-2925 opened by reiterating that in a SEPA appeal it is appellanfs burden to establish that the SEPA determination is clearly erroneous. This is a plat application that is based on an adopted comprehensive plan and zoning that slated this property for development at an urban scale. This parcel is among those that the City of Renton legislated to accommodate a certain amount of urban growth under the Growth Management Act. The general impacts associated with the conversion are impacts of the legislative decision. The specific and unique impacts of the plat proposal are what should be the subject of the SEPA consideration at this stage. Mark McGinnis,Geotech Consultants, 13256 NE 20th St. #16,Bellevue, WA 98005 reviewed his education, training and experience as a geotechnical engineer. He summarized what is contained in the Phase I Environmental Site Assessment prepared by his firm regarding coal mines under the site, including risk of excessive settlement, localized subsidence, and mine gas emissions.Mr. McGinnis discussed the mitigation measures recommended in the Geotechnical Report to address the two worked coal mine seams under the perty. He stated that it is his professional opinion that the recommended measures will adequately mitigate Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 Page 4 any potential risks associated with the two worked coal seams. Mr. McGinnis described the steep slope associated with Lot#35 in the northeast corner of the site. His firm investigated the slope, looked for slope problems, and did a test pit for exploration in the area to assess soil conditions near the top of the slope. Based on these observations, a 25 foot building setback from the crest of the slope is recommended. In addition to the 25 foot setback, it is recommended that there be no clearing and grading within 10 feet of the top of slope. Larry Hobbs, Transportation Planning and Engineering,Inc.,2223 112th Ave NE, Suite 101, Bellevue, WA 98004 reviewed his background,education and training as a traffic engineer. Mr. Hobbs stated that safety issues were considered as part of the traffic study that was prepared for the project. The city provided the last three years worth of accident data in the area,and it was found that there were no accidents recorded on Renton Hill itself for this period of time. In checking the data for the last five years, it was found that there were three traffic accidents throughout all of Renton Hill. Two of these accidents involved one vehicle backing into another,and the third was a vehicle striking a parked vehicle. There were no injuries or fatalities in any of the reported accidents. The record of reported traffic incidents is one of the main indicators of safety on a street system. Mr.Hobbs stated that it is his opinion that there will not be any increase in traffic accidents in the Renton Hill area as a result of the proposed development. Residents of the area would most likely be aware of anything that may be deficient and would drive accordingly to compensate for that. New residents moving into the area would rapidly gain familiarity with the street system. Jennifer Steig, Peterson Consulting Engineers,4030 Lake Washington Blvd NE, Suite 200,Kirkland, WA 98033 gave a summary of her training,education and experience as a civil engineer. Ms. Steig described the conceptual grading plan her firm prepared for the site. Once grades are set, computer programs to come up with cut and fill volume. Based on the conceptual grading plan, there would be approximately 55,000 cubic yards of cut material and 19,000 cubic yards of fill:.The applicant requested that we develop a plan with a closer balance so that all the cut and fill would be used on the site--there would not be any material hauled off the site as a result of grading. The conceptual plan was sent to a company used industry wide that has a computer program which can look at the site as it is graded in the conceptual plan and raise or lower the site in small increments to determine when a balance is reached. This information is used to develop a final grading plan for construction. In doing this, it was found that if the site is raised one foot from the conceptual grading plan,there would be a balance of the cut and fill material on the site. Based on further geotechnical studies, if the unsuitable fill were screened on site,the amount of fill that would need to be hauled off site could be reduced by approximately half. Ms.Steig discussed the number of truck trips that would be required to haul fill off the property based on the number of cubic yards of fill remaining. She explained under what conditions material must be worked so that it will be suitable for use in construction. In closing,Ms.Larson discussed the issues of preservation of vegetation and wildlife,compatibility of the new homes with the neighborhood, and the two crested vertical curves on Renton Ave S that do not meet city, county or state requirements for vertical curve design. Ms.Fontes, in closing,addressed issues raised by the appellant in the course of the hearing and discussed what the evidence has shown and what the process has been in each instance. Ms.Fontes reiterated that despite all the questions raised by the appellant,she has not shown evidence of significant adverse environmental impacts in any of these instances. Therefore, the decision made by the ERC must stand. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25,2001 'age 5 Ms. Larson responded that every question she asked was stated in the ERC's report. She responded to the questions because she felt there was clarification needed. Some of the issues have been clarified,others have not. In closing, Ms. Gygi stated that the applicant concurs with the City's closing arguments. She reviewed some of the issues raised by the appellant. Ms. Gygi summarized by stating that any project will alter the surrounding area. It is unrealistic to expect that there would be no effect from development. The law does not require that all adverse impacts be eliminated. If it did,no change in land use would ever be possible. Ms. Gygi reiterated that the burden is upon the appellant to prove adverse environmental impacts,which has not been done in this case. The Examiner called for further testimony regarding this appeal. There was no one else wishing to speak. The appeal hearing closed at 11:30 a.m. SEPA APPEAL FINDINGS, CONCLUSION & DECISION FINDINGS: 1. The appellant,The Renton Hill Community Association, represented by Ruth Larson, filed an appeal of a Determination of Non-Significance-Mitigated(DNS-M) issued for a proposed Preliminary Plat that would divide approximately 10.35 acres of R-8 (Residential: 8 units per acre)zoned property into 57 lots. The appeal was filed in a timely manner. 2. In processing the preliminary plat application the City subjected the application to is'ordinary SEPA review process. The City, in the course of and as a result of its SEPA review, issued a Determination of Non-Significance-Mitigated for the project. The Determination of Non-Significance-Mitigated (DNS-M)was conditioned by the City. 3. The subject site is located near the intersection of Beacon Way SE, S 7th Court and S 7th Street. The property is located immediately across from Philip Arnold Park. . 4. The subject site a triangular parcel approximately 1.114 feet by 818 feet by 829 feet. 5. The subject site is approximately 10.35 acres or 450,846 square feet in area. 6. The subject site has rolling and descending terrain with some steeper slopes that were determined to be manmade as part of past mining or quarrying activity. An exemption from steep slope regulations was issued administratively since the steeper slopes are not natural. 7. The ERC imposed five conditions related to erosion control,three conditions imposing mitigation fees for fire,parks and roads, three conditions related to geotechnical issues for building construction/foundation work, subsidence notice due to potential coal mines and setbacks from steep slopes,one condition dealing with the potential discovery of hazardous materials, one dealing with traffic control for construction vehicles and finally,a condition for access across the Seattle Pipeline for emergency, secondary access. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 Page 6 8. During the course of the public hearing staff noted that the gross vehicle weight of 26,000 was not intended to vary from that posted on the road signs and should have matched that posted along the road. 9. The appellants objected to the determination. The appellants objected to or raised concerns about: a. Modification of street standards to allow narrower roads in the plat. b. Protection for abutting Falcon Ridge and River Ridge properties. C. Weight limit on Renton Avenue differing from posted standard(that was an error not intended to vary from posted limits). d. Width and emergency access relating to the Pipeline road. e. The steepness and width of Renton Avenue South. f. Exception to Critical Areas Ordinance that permitted grading on previously disturbed slopes. g. The amount of grading and number of heavy truck trips were not fully evaluated for impacts on the community. (the applicant altered the plans to balance the cut and fill and substantially reduce material movements) h. Impacts on River Ridge. i. Air quality impacts of vegetation removal. j. The alteration of the base elevation and its impacts on water. k. The removal of 92%of the trees and retention of 32 trees, if possible. 1. The maintenance of installed landscaping strips and islands. M. Impacts on the deer population that frequents the subject site. n. The manner in which the rezone was adopted. o. The character of the homes. p. The consistency of fencing. q. The impacts of new light on the community. r. The impact of internal pocket parks. S. The impact on the Renton Hill community by this plat. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25,2001 age 7 t. Traffic impacts of new residents and construction vehicles on the existing road surfaces and the community. U. The use of mitigation funding. V. The development does not follow the policies of the City of Renton. 10. The subject site is located near the northeast corner of Renton Hill just where it begins its drop down to Maple Valley and the Cedar River. 11. The majority of property in the vicinity of the subject site is zoned R-8 (Residential; 8 dwelling units per acre). It has been developed with single family homes. The slopes north of and below the subject site are Resource Conservation. 12. Immediately north of the subject site is the River Ridge development that contains 11 lots. The proposed development would share an access roadway that now serves only River Ridge. East of the subject site is Falcon Ridge,and it contains 80 lots. Falcon Ridge is accessed from the east by a private roadway. 13. The subject site is covered by what is probably second or third growth trees and shrubs. As noted, the site has been disturbed by some form of extraction or quarrying in the past. 14. The applicant did an historical survey of the subject site using aerial photographs as well reviewing the permit history of the site. There also were reviews of the mining data for the subject site and vicinity. There were also borings to determine the nature of the soils and to expose potential dumping of hazardous or other materials. The US Geological Survey maps for the area show a mine symbol, although it does not specify the type of mine but it appears it was used as a gravel quarry. 15. An evaluation was made of potential mine hazards. Both the more shallow and deeper mines are located 200 feet to 600 feet deep. It is anticipated that most linear shafts would have subsided over time. Any collapse events in "horizontal"mines would be distributed over those 200 to 600 feet, causing little surface subsidence. The greater potential for dangerous collapses are old airshafts or vertical access shafts. Some of these were filled with jumbled lumber or other debris till it"caught" on the sides of the shaft and then filled. The"caught"materials can decay over time and lead to collapses. In most cases these latter actions cannot be predicted. The geotechnical information and studies have instructions on dealing with these if they are discovered during construction. In addition, there are governmental agencies that deal with such openings,although obviously,an opening occurring can still take parties by surprise. The geotechnical report also has construction methods to make sure homes constructed in this development follow certain prescribed foundation techniques. 16. The applicant and City emphasized stability in dealing with lots near the edge of slope areas. The only lot affected by steeper slopes is Lot 35 in the northeast corner of the subject site. Lot 35 will have a 25 foot setback for building and a 10 foot setback buffer that will remain undisturbed. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25,2001 Page 8 17. The Geotechnical information shows that areas that have 15%to 30% slopes are limited and most of the terrain is moderate and the underlying soils are suitable for construction. The ERC imposed conditions to deal with erosion. The professional analysis is that the measures suggested in the geotechnical report and the measures imposed by the ERC should prevent any problems. 18. There are approximately 250 to 300 acres of open space along the Cedar River and the slopes above the river in City ownership or open space. Although a large amount of this property is very steep slopes, there are a developed trail and park located along the river, and there are other level or more gentle areas. To accommodate roads and building pads, most of the vegetation will be removed from the subject site. It would appear that similar clearing probably has occurred for most development on the hill in the past with ornamentals replacing native trees. 19. There will be a loss of over 300 trees of six inches or greater in diameter. This loss of trees and habitat is an unfortunate but foreseeable result of development. Trees and vegetation may be maintained where possible. Open space tracts and ornamental landscaping generally occur as plats are developed and mature. 20. The project was reviewed for compliance with the Critical Areas Ordinance and the land clearing regulations. The exception approved for working on the man-made or altered slopes is not unusual and is a remedy available by code. Natural slopes will not be altered or would require special approvals. 1. The original plans called for a substantial grade and fill effort. This would have entailed a large number of dump trucks moving the materials to and from the subject site. The applicant further refined their grading plans and found that generally raising the elevation of the subject site by approximately one(1)foot would significantly reduce the needed trips. This would mean utilizing local materials on site in what is termed a "balanced cut and fill." There would still be export of unsuitable materials or debris that has been dumped on the subject site. It is not anticipated that raising the site by approximately one foot would create any problems with erosion or stability. The number of truck trips would probably be reduced to approximately 750 trips. The original estimate would have generated approximately 3,700 trips. The trucks would meet load limit requirements of the City. While this is not a:small number of trips, it is also not unusual where development is occurring, including in residential areas and the City urges that this is generally not a SEPA impact. 22. The existing public roads serving the subject site do not meet current standards. Similar undersized or steep roads serve other older or hilly areas of the City including roads serving areas west of Rainier. At the same time, these older roads serve their neighborhoods or communities. Renton Avenue seems to serve the existing population, and as new residents have moved to Renton Hill they have adjusted to the constraints and limitations. This does not discount the experiences of current residents and that fact that extra care seems necessary to negotiate the roadways and deal with events like snow and ice. The fact is,transportation impact analysis including LOS information and sight distance information shows that the existing road system can handle the additional traffic including the additional approximately 50 to 60 vehicle trips that would be generated during the peak hours. It appears that there may be an approximately 0.2 second delay in wait time at traffic lights. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos._ LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 'age 9 23_ The proposed intersection at SE 7th Court and the subject proposal's entry road will meet City standards for sight distance and angles. Anytime a new intersection is created residents have to accommodate the changes in traffic flow. 24. Renton Avenue South is approximately 26 feet wide and has an approximately 23 foot 2 inch driving surface. There is a 5 inch drop to the gutter. Both telephone poles and hydrants are located close to the right-of-way and driving surface. There are some dips in the road and the crest apparently creates difficult sight problems with traffic driving up and down the hill according the residents. The technical analysis would appear to show that at normal driving sitting position,the view is not significantly impaired. 25. A study of accident history showed no reported accidents during the last three years and three(3) accidents throughout Renton Hill during the last five years. They appeared to be minor accidents resulting in limited property damage but no personal injuries. Anecdotal evidence suggests that there have been a number of"near-miss"and minor accidents but that residents may not have reported some accidents. The assumption then would have to be that they were not major accidents if they remained unreported. 26. The evidence does suggest that curbs, gutters and sidewalks improve safety but there are areas along what would be the commute route where this is not possible. Limiting speed and driver caution serve to control conflicts. SEPA does not ask an applicant to rectify existing problems, whether traffic or storm water problems, but requires that impacts be appropriately disclosed. 27. The appellant challenged the traffic generation numbers used by the applicant. Those numbers estimate that each single family home generates approximately 9.55 trips. The 57 homes would generate 544.35 trips per day. The estimates also predict that approximately ten percent(10%)of the total trips would occur during each of the peak commuting times or approximately 55 trips. No basis for the challenge was provided. 28. The development, if approved in full,would add 57 homes to an existing inventory of approximately 200 homes,or an approximately 25% increase. There has been some infilling in the last few years,also adding to the inventory. At the same time, some homes were lost to the last expansion and straightening of I-405. The traffic report and City analysis demonstrate that while the roads are not standard,they have sufficient capacity to handle the additional traffic. There will be impacts,but they are not considered untoward. The LOS for the intersections on the hill will not change as a result of the development. 29. Intersection spacing was found to be able to meet standards for the new intersection,which will be controlled by a stop sign. 30. LOS of A and B exist for the critical intersections and those will not be changed by the development of the subject site,although as indicated, wait times may increase by a fraction of a second. 31. Street maintenance is accomplished as needed. No specific improvements outside the boundaries of the plat will occur other than some possible modification to the intersection at Beacon and 7th. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 Page 10 32. The City works with applicants to develop a construction management plan to deal with traffic, routes and times in order to control access by heavy trucks. This would be done in this case as well. 33. There is an approximately 30 foot wide strip of land between the proposed development and River Ridge,the residential site adjacent to the subject site. Fences are not generally an environmental issue. Setbacks between newer single family and existing single family uses is also not considered a SEPA issue. The project will be providing the required setbacks, and in some instances it intends to provide larger than required setbacks. Larger setbacks than code provides are not required(minimum impacts that would occur with any development and not untoward in any fashion). The additional light and glare created by the new homes is not expected to be out of the ordinary for single family communities. It is not particularly reviewed for single family development. 34. While there is no public bus route serving the hill, residents can apparently use a dial-up service for vans. 35. The proposed density of 6.78 is in the midrange permitted in the R-8 Zone. The R-8 Zone permits a density of between 5 and 8 single family units per acre. 36. There is an approximately 30 foot wide strip of land between the proposed development and Falcon Ridge,the other residential site adjacent to the subject site. 3.7. Mitigation fees for transportation are distributed after the City Council determines needs in its six year cycle. Maintenance is done as needed. 38. Construction activity and hauling is governed by code provisions limiting the impact on rush hour traffic and limiting it,generally,to daylight hours. In addition,there is the construction management plan. Trucks doing hauling are monitored and"weight tickets" and reports are required. Renton Avenue was checked and it is four inches of asphalt over crushed rock. The City found it acceptable for heavy loads. It currently serves large garbage trucks and fire trucks. 39. The-proposed reduction in street width from 50 feet to 42 feet for new roads within the plat boundaries is a code compliance issue and should not generally affect SEPA compliance. 40. The question of who builds the homes and what would be their quality is not a SEPA issue. The City does not control design of single family development nor who may develop such homes if they meet code standards. 41. The applicant and City, in response to the appeal, both noted that asking a series of questions, particularly if the answers are contained in existing studies or covered by existing regulations,does not provide a sufficient basis for overturning a SEPA decision. 42. All of the Findings and Conclusions of the companion Plat Report are incorporated into this report by reference. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 'age I CONCLUSIONS: 1. The decision of the governmental agency acting as the responsible official is entitled to substantial weight. Therefore, the determination of the Environmental Review Committee (ERC),the city's responsible official, is entitled to be maintained unless the appellant clearly demonstrates that the determination was in error. 2. The Determination of Non-Significance in this case is entitled to substantial weight and will not be reversed or modified unless it can be found that the decision is "clearly erroneous." (Hayden v. Port Townsend,93 Wn 2nd 870, 880; 1980). The court in citing.Norway Hill Preservation and Protection Association v. King County Council, 87 Wn 2d 267,274; 1976,stated: "A finding is'clearly erroneous' when,although there is evidence to support it,the reviewing court on the entire evidence is left with the definite and firm conviction that a mistake has been committed." Therefore,the determination of the ERC will not be modified or reversed if it can meet the above test. For reasons enumerated below, the decision of the ERC is affirmed. 3. The clearly erroneous test has generally been applied when an action results in a DNS,since the test is less demanding on the appellant. The reason is that SEPA requires a thorough examination of the environmental consequences of an action. The courts have, therefore,made it easier to reverse a DNS. A second test,the "arbitrary and capricious"test is generally applied when a determination of significance(DS) is issued.In this second test an appellant would have to show that the decision clearly flies in the face of reason since a DS is more protective of the environment since it results in the preparation of a full disclosure document,an Environmental Impact Statement. 4. An action is determined to have a significant adverse impact on the quality of the environment if more than a moderate impact on the quality of the environment is a reasonable probability.(Norway, at 278). Since the Court spoke in Norway, WAC 197-11-794 has been adopted, it defines "significant"as follows: a. Significant. (1) "Significant" as used in SEPA means a reasonable likelihood of more than a moderate adverse impact on environmental quality. b. (2)Significance involves context and intensity...Intensity depends on the magnitude and duration of an impact....The severity of the impact should be weighed along with the likelihood of its occurrence. An impact may be significant if its chance of occurrence is not great,but the resulting environmental impact would be severe if it occurred. Also redefined since the Norway decision was the term "probable." C. Probable. "Probable"means likely or reasonably likely to occur, ... Probable is used to distinguish likely impacts from those that merely have a possibility of occurring,but are remote or speculative. (WAC 197-11-782). 5. Impacts also include reasonably related and foreseeable direct and indirect impacts including short- term and long-term effects. (WAC 197-11-060(4xc)). Impacts include those effects resulting from growth caused by a proposal,as well as the likelihood that the present proposal will serve as precedent Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 Page 12 for future actions. (WAC 197-11-060(4)(d)). 6. Environmental impact is also related to the location. A development,whether an office building or a single family development, may or may not create impact depending on the existing surroundings. 7. There is no question that there will be changes in the neighborhood and there may definitely be inconvenience, particularly during construction. There will be clear changes to the subject site. But these changes do not necessarily rise to the level of impact mandated by SEPA to require the - preparation of an EIS. The development will not significantly alter the character of the community. It will be single family in character,just like the surrounding development. Adding additional single family homes to the existing single family community is not dramatic. It will not trigger changes to other undeveloped or low density sites and will not create any precedents generating calls for changes to the residential zoning already governing the area. Both the Comprehensive Plan and Zoning designated the area for urban densities. In addition, while additional traffic will flow through the main commute route into downtown Renton, the proposed community is located on the edge of the community, not in the midst of the existing community,and its overall impacts will not be very significant. 8. Traffic seems to be a key issue presented by the appellant,and traffic's associated issues such as narrow and steep roads,heavy construction traffic and stopping distance and sight distance on the hill and at the new intersection. These are legitimate concerns, but the evidence does not provide a basis for altering the ERC's decision. They will not have more than a moderate impact on the quality of the environment. The development will permanently add more traffic of a kind that traffic analysis shows the streets currently handle without appreciably'increasing commute times,overloading roads or increasing conflicts significantly in terms of SEPA impacts that would require more detailed information than has been prepared in the various technical studies reviewed by the ERC. It will not have more than a moderate impact on the quality of the environment. The development will generate impacts similar to those that now exist. 9. There definitely will be more traffic. That occurs anytime new development occurs. The streets leaving the hill are definitely steep and narrow. The various analyses demonstrate that the LOS will not be substantially changed. The analyses also demonstrate that while there are some constraints due to the steepness of the hill and the narrowness of the roadway, but that the additional traffic can be safely accommodated. 10. The most pronounced change will be the removal of the forest cover on the ten acres. This acreage has been cleared in the past and the site topography altered by what appears to have been quarrying activity. But clearing of trees alone is not sufficient to trigger the preparation of an EIS. Nothing in record suggests that this alone will create such a significant impact on the quality of the environment that additional information is needed. This acreage needs to be looked at in the context of the adjacent 200 to 300 acres of forest and habitat. It also needs to be looked at in terms of surrounding uses. The areas around the site are mostly urban and developed with single family homes such as proposed for the subject site. There is already a park located immediately across from the site. While animals will probably be displaced, there appears to be sufficient open space immediately adjacent to the site to provide habitat. Nothing in the record demonstrates the any large species or threatened species permanently inhabit the subject site. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 Page 13 11. Construction impacts will be irritating to those who live near the subject site and construction traffic will have impacts on the community as a whole,but they are not the type of impacts which have more than a short-lived impact and they are not the types of impacts that would throw the ERC's decision into doubt. In addition,code provides for construction management plans, and there remains the possibility that the pipeline road could serve some construction uses. In addition,the applicant has substantially reduced the amount of materials that would need to be transported either to or from the subject site. This will substantially reduce the originally anticipated truck traffic. 12. While there will be a series of impacts as there are in any development, they do not add up in a quantifiable manner to the type of impacts or long term precedents that result in more than a moderate impact on the quality of the environment. Issues such as quality or character of development, fencing, setback standards in excess of those required,code permitted exceptions to slope clearing or roadway width are not appropriately SEPA issues. Access to the site across the pipeline road is a condition of development,and if it were not granted,that would have a profound affect on the proposal and is not a SEPA issue. The creation of internal parks and open space and maintenance are not SEPA issues. The manner of adoption of the reclassification of the site is not a SEPA issue. 13. The reviewing body should not substitute its judgment for that of the original body with expertise in the matter, unless the reviewing body has the firm conviction that a mistake has been made. This office was not left with a firm conviction that the ERC made a mistake. There was a thorough review of geotechnical information that showed the site could be developed. There were two traffic reports, including slope analysis of sight distance issues,that demonstrated the current roads, while not meeting current standards have capacity for the additional traffic anticipated. 14. The appealing party has a burden that was not met in the instant case. The decision of the ERC must be affirmed. DECISION: The decision of the ERC is affirmed. MINUTES: PRELIMINARY PLAT The following minutes are a summary of the November 16 and December 12, 2000 preliminary plat hearing. The legal record is recorded on tape. The hearing opened on Thursday,November 16 at 11:35 a.m. in the Council Chambers on the seventh floor of the Renton City Hall. Because of time constraints,Mr. Mehlhaff,Ms.Liston, Mr. Giuliani,Mr. Ellis,Ms. Fulfer, Ms. Herman, Ms. Lamke,and Mr. Fulfer testified regarding the preliminary plat during the appeal portion of the hearing. Their comments appear later in the minutes. e following exhibits were entered into the record for the preliminary plat hearing: Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 Page 14 Exhibit No. 1: Yellow land use file,LUA00- Exhibit No.2: Overall plat plan 053,PP,ECF, containing the original application, proof of posting, proof of publication an other documentation pertinent to this request Exhibit No.3: Sheet 2 of 4, larger scale drawing of Exhibit No.4: Sheet 3 of 4, larger scale drawing of plat plan plat plan Exhibit No. 5: Sheet 4 of 4, preliminary plat plan . Exhibit No.6: Topographic survey Exhibit No. 7: Tree cutting and land clearing plan Exhibit No.8: Drainage control plan Exhibit No. 9: Generalized utilities plan Exhibit No. 10: Detailed grading plan Exhibit No. 11: Neighborhood detail map Exhibit No. 12: Zoning map Exhibit No."13: Plat map of lots along north border Exhibit No. 14: Timeline of project showing buffer Exhibit No.-15: Wildlife Report Exhibit No. 16: Original plat map of River Ridge Exhibit No. 17: Stopping sight distances drawing Exhibit No. 18: Stopping sight distances chart Exhibit No. 19: Stopping sight distances chart and Exhibit No.20: Renton Ave. S. stopping sight topographic distances Exhibit No. 21: Traffic Count Charts(6 sheets) Exhibit No.22: Aerial photograph of River Ridge Elizabeth Higgins, Senior Planner,Development Services, 1055 S Grady Way,Renton, WA 98055 presented the staff report. Bennett Development has proposed subdivision of an approximately 450,846 square feet(10.35 acre)property into 57 lots suitable for detached,single family houses. The triangular-shaped property is located on Renton Hill, southeast of the intersection of Beacon Way S with SE 7th Ct, Jones Ave S,and South 7th St. Although Renton Hill is a well established neighborhood, land abutting the proposed project to the; north has been developed fairly recently into River Ridge,an eleven lot subdivision. Falcon Ridge,a large(80 lot)subdivision, lies to the southeast. Philip Arnold Park is adjacent to the southwest. The Seattle Public Utilities Cedar River Pipeline, which is used occasionally for overflow parking from the park,separates the park from the proposed development property. The zoning designation for the property is R-8. Most of Renton Hill is zoned R-8 except for a strip of land on the west side above I-405 which is zoned R-10. Access would be from a new public street that would intersect with SE 7th Ct. The new street would terminate in a cul-de-sac. An emergency-only access would connect the cul-de-sac with the Seattle Public Utilities Cedar River Pipeline. A modification from street standards has been requested to reduce the width of the public right-of-way from 50 feet to 42 feet. This modification has been approved by the director of the Development Services Department. It would not reduce the pavement width,only the right-of-way width,and would not affect the ability to have sidewalks in the development. Ms Higgins continued by stating that the Environmental Review Committee(ERC) issued a Determination of Non-Significance- Mitigated on October 17, 200. One appeal was filed prior to the close of the appeal period. The ERC placed several mitigating measures on the project. The first four relate to erosion control on the project and are best management practices as required by the City. The applicant shall pay applicable Transportation, Fire and Parks mitigation fees. The applicant shall follow the recommendations of the Geotechnical engineers as they pertain to site development and building construction. A note shall be placed on the face of the plat prior to recording stating that a known potential for ground subsidence exists in the area and that building plans shall be designed in consultation with a structural engineer and shall conform to the recommendations of the Geotech report. The rear setback at the lot located in the northeast corner of the roperty, Lot#35, shall be increased to 25 feet from 20 feet. A note shall be placed on the title of the lot rohibiting building construction within 25 feet of the of the rear property boundary and prohibit land clearing Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 'age 15 within 10 feet of the rear property line. The applicant shall ensure that all construction debris and discarded items are excavated from the site and construction is ceased immediately, followed by notification of the City of Renton Development Services Division within 24 hours, should hazardous material be discovered during the removal. The Construction Traffic Control Plan shall include a condition that the construction vehicles in excess of 20,000 gvw associated with the project would be prohibited from operating on Renton Hill during a.m.and p.m. peak traffic hours as identified in the traffic report. The applicant shall obtain an access permit in order to use the Seattle Public Utilities Cedar River Pipeline Easement for a secondary, emergency only access. The permit shall be obtained prior to building permits. Ms.Higgins described the property and discussed how the proposal meets the various requirements of the Preliminary Plat Criteria. The proposed project meets the first objective of the Comprehensive Plan Land Use Element by providing new housing in what up to now has been underutilized land. It also provides a greater use of urban services and infrastructure. The proposed project would meet the policy of meeting net density levels by providing density of 6.86 dwelling units per acre. The lots are proposed at an average size of 5,350 square feet. The range of lot sizes is 4,504 to 8,318 square feet. Both the Development Standards and the Comprehensive Plan polices limit the height of building to two stories in the R-8 zone. The question of transportation and pedestrian connections between neighborhoods is difficult on Renton Hill due to its situation of being isolated from the rest of the city and having limited access. There will be pedestrian connections throughout the neighborhood from new sidewalks that are going to be added and the Cedar River Pipeline. Three areas in the proposed site plan in the proximity of the entryway are going to be set aside as commonly held open-spaces. It is not anticipated that the vegetation will be retained,but they will be landscaped. Staff ecommends that a landscape plan be submitted to Development Services for review prior to building permits. he Comprehensive Plan included a forecast of Renton's traffic increase for a twenty year period. In the plan, it was estimated that there would be a 52% increase in traffic in Renton between 1990 and 2010. The estimated traffic increase on Cedar and Renton Avenues on Renton Hill would be approximately 25% from the proposed project. This appears to be consistent with projected city-wide traffic volume increases. Ms.Higgins discussed how the project meets the Housing Mandates in the Comprehensive Plan. The Growth Management Act requires the City to plan how it will accommodate its share of the projected population growth. The projected population growth for a 20 year period is determined by the Puget Sound Regional Council, and it was distributed to all cities and counties in the Puget Sound region. The Comprehensive Plan has to address how the City will provide housing for all economic segments of the City's population,and delineates the strategies for doing that. Ms Higgins reviewed some of the policies of the Housing Element and explained how they are met by the proposal. Ms.Higgins continued by reviewing how the proposal meets the Environmental Element of the Comprehensive Plan. Some of the policies that staff felt were met by the proposed project are: minimizing erosion and sedimentation by requiring appropriate construction techniques; implementing surface water management systems which protect natural features; promoting the return of precipitation to the soil at natural rates near where it falls through the use of detention ponds,grassy swales, and infiltration; promoting development design which minimizes impenneable surface coverage; and managing the cumulative effects of storm water through a combination of engineering and preservation of natural systems. Slopes on the property were probably created by surface mining activity, and are therefore exempt from the -ritical Areas Ordinance. The stormwater control system would provide adequate protection of the City's ater resource. The applicant has estimated that approximately 389 trees sized 6 inches in diameter and greater Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 Page 16 and of various types would be removed from the property for construction. The applicant must adhere to the requirements of the Forest Practices Act. There are several areas in the project that are going to be preserved as "landscape tracts." The proposed project would meet all of the underlying zoning standards for the R-8 zone. The front, rear, and side setback lines indicated on the Preliminary Plat plan meet the minimum setback requirements for the R-8 zone. The maximum building coverage in the R-8 zone is 50% of lots 5,000 square feet or smaller and 35%of,or 2,500 square feet on, lots larger than 5,000 square feet. Compliance with the building coverage regulations would be a requirement of the building permit process. Ms. Higgins next reviewed the proposal's compliance with the subdivision regulations. All lots created by the subdivision would result in legal building lots according to the regulations for the R-8 zone. All parcels must have access-established to a public road,which would occur by either directly off the public roads that would be built or from the two private roads or driveway that would be placed on the property. Side lot lines shall be at right angles to street lines or radial to curved street lines--they would be in this project. All lot corners at intersections would have a radius of a minimum of 15 feet. Police and Fire have indicated they have sufficient resources to furnish services. The Parks and Recreation Department has also concurred that they could provide service. Renton School District has stated that new students, estimated to be approximately 25,could be accommodated in Talbot Hill Elementary School, Dimmitt Middle School, and Renton Senior High School. The School District further requested that the existing school busses be allowed to continue their route through the area, which would be allowed. The conceptual stormwater plan has been accepted by the Plan Review Division,as have the conceptual water and sanitary sewer plan. Staff recommends approval of the Heritage Renton Hill Preliminary Plat subject to the following conditions: (1)that the applicant comply with the ERC Mitigation Measures as they have been amended,(2)that all landscape tract areas,with the exception of the 5,402 square foot tract located at the entry,the private "park", and the landscape area adjacent to the storm pond be incorporated into lots already proposed,and(3) commonly held open space areas shall be enhanced prior to occupancy with landscaping including mixed deciduous and evergreen trees and plantings of native shrubs and groundcover,and the applicant shall submit a landscape plan to the Development Services Department for approval. An additional condition would be that a homeowners'association be established and that one of the requirements be that they would be responsible for maintaining-'the private stormwater system and the commonly held landscape area, including the 15 foot buffers. The Examiner stated that he will schedule an evening hearing to conclude this matter in order to accommodate those who have to leave due to prior commitments. The various parties will be notified of the date and time of the evening hearing. The hearing closed at 12:40 p.m. ********************************** The hearing opened on Tuesday, December 12,2000,at 6:00 p.m. in the Council Chambers on the seventh floor of the Renton City Hall. Ms. Higgins gave a brief review of the project based on the Staff Report,which was presented at the hearing on December 16. Ms.Higgins stated that staff has added a recommendation which was not presented at the last hearing, that a Hold Harmless Agreement shall be recorded that indemnifies the City of Renton from any damage resulting from subsidence that may occur due to previous subsurface mining activities. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 'age 17 Mr. Fike presented a timeline explaining how the design for the project developed. In March of 1999 Renton School District selected Bennett Development as the purchasers. In September 1999 the mandatory pre- application meeting was held with the City. At that time plans for a 69-lot subdivision were submitted, designed around access from Beacon Way S. It was subsequently determined that Beacon Way S could not be accessed off of, since it is an easement owned by the City of Seattle and they do not want it used as a public right-of-way. In January of 2000,another pre-application meeting was held with the City of Renton and a new design for the project was submitted, based on input from community groups and the Cities of Renton and Seattle. This new design eliminated the Beacon Way access and showed access off of S 7th Ct. A stub road - that would cross over the pipeline and go into Philip Arnold Park was included. The City of Renton determined that the stub road was not needed. A design was subsequently developed showing a buffer setback along the north border of the property In April of 2000 the developer sent a submittal package to Renton Hill community leaders showing them what was going to be submitted to the City of Renton. This showed a 56-lot subdivision. In May,the City of Renton deemed the application complete, but asked that the access road across the pipeline be removed. With the removal of the access road,the project went from 56 lots to 57. The City also asked the developer to do additional traffic counts. A three-week traffic study was done during the summer which took into consideration increased traffic from sports activities held in the area. Mr. Fike submitted a study which was done by a wildlife biologist in the period since the last hearing. The report shows that there are deer on the property;however,there were no signs of deer nesting there. An eagle that nests on the south tip of Mercer Island uses the Cedar River as a fishing ground. This may be the eagle that is seen over the Cedar River and approaching the property. There are no signs of an eagle nesting on the roperty. The wildlife report shows that the project has minimal,if any,wildlife assessments. Regarding the pipeline easement, Mr. Fike explained that the City of Seattle views pipeline usage as a privilege. In order to be good neighbors with the City of Renton,Seattle overlooks things such as possibly driving trucks over the pipeline rather than through the neighborhood,and school buses using the pipeline. The City of Seattle will only issue Conditional Use Permits for the pipeline. The developer has a verbal agreement with Seattle that they will be able to have emergency vehicle access on the pipeline. Ms Higgins entered an original plat map which shows the entry to River Ridge as it was proposed,crossing the School District property,then intersecting the pipeline. A letter in the files from the City of Renton's Utilities Systems Manager at the time to the Real Property Division of the Seattle Water Department explains why the entryway to River Ridge was moved into the present position, and shows further evidence that the Seattle Public Utilities does not want the pipeline to be used for general traffic. John Nelson,Peterson Consulting Engineering,4030 Lake Washington Blvd NE,Suite 200,Kirkland, WA 98033 explained what sight distance is and what kinds there are,using a sight distances drawing. Using charts and a topographic map, he explained stopping sight distance and how it is determined for different types of vehicles and several actual road slopes in the Renton Hill Area. Mr.Nelson stated that as a result of his analysis and actually driving the roads in question, he did not think there is any significant problem with sight distances on the roads in Renton Hill. Larry Hobbs,Transportation Planning and Engineering, Inc.,2223 112th Avenue NE, Suite 101, Bellevue, WA 98004 stated that typically intersections are made with three or four legs; however, five-legged intersections do xist. All of the legs of the intersection are stop controlled. There are no records of any accidents at the itersection over the past five years. There is no reason to believe this intersection does not operate safely and Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25,2001 Page 18 adequately. There is enough capacity in the intersection to handle the traffic that is there now, and the future development. The intersection itself is relatively flat. Sight distance criteria does not come into effect at the intersection, since all vehicles must stop. Ms. Higgins clarified the Zoning Code as it relates to the project. In the R-8 Zone,the City requests that a developer try to have at least five units per net acre,with a maximum of eight units per net acre. If for some reason a developer chooses not to develop to the maximum density,or if they are trying to develop below the minimum density,the City requests that the developer demonstrate that future lots could be developed on tl'ie property. The City asks for a technique called shadow platting which would create hypothetical lots that would have the proper setbacks and be conforming lots given the requirement of that zone so that in the future those lots could be developed. Mark Mehlhaff, 532 Grant Ave S, Renton, WA 98055 addressed the issue of road safety on Renton Avenue S. Many drivers tend to use excessive speed going up the hill because of the steepness of the grade. This, combined with limited sight distances and cars parked on the side of the street,creates a dangerous situation. Mr.Mehlhaff asked why Puget Drive and the pipeline cannot be opened up for use of construction vehicles and general traffic to alleviate the congested conditions on Renton Avenue S and Cedar Avenue. Nancy Liston, 1518 Beacon Way S,Renton,WA 98055 spoke to the issues of tranquility and quality of life on Renton Hill. Ms. Liston expressed concern that the tranquility of the area would be greatly impacted by the increased traffic, noise,dirt and dust generated by the large trucks and construction equipment. She stated that -the streets and parks on the hill were never intended for the increased number of vehicles and people who will be occupying 57 homes. Ms. Liston also discussed the issue of intersection safety. She has witnessed people not obeying the stop signs, and has seen many near-misses. Ms. Liston also expressed concern about deer crossing the street, particularly at night, and the safety of bicyclists on the streets. John Giuliani, 1400 South 7th Street, Renton, WA stated that the new exit off of Renton Hill has no bearing on the traffic on Renton Avenue, since it is necessary to travel on Renton Avenue to get to the new exit. Mr. Giuliani further-stated that when Renton Ave was repaved,he personally observed that all the asphalt was removed down to the dirt. New asphalt was placed directly on top of the dirt with no gravel base underneath to anchor it. Quentin Ellis,715 High Ave S., Renton, WA 98055 stated that there have been a lot of sophisticated studies made by the City and others regarding this project,but it all boils down to one word—infrastructure. The infrastructure that has to be maintained is not there. He cited a newspaper article regarding the Habitat program's plan to build low income housing on a ten acre parcel in Snoqualmie Ridge. They are only proposing to build 50 houses on those ten acres. This proposed project plans to build 57 homes in an area with only one street that is only 23.6 feet wide,as opposed to the normal 40 to 50 foot width. He expressed concern about the mine shafts in the area and the possibility of sink holes developing with the increased traffic on Renton Avenue S. Mr. Ellis challenged Bennett Development's traffic engineer to substantiate his statement that there would not be an increase in the number of accidents on Renton Hill. He questioned how, considering the 25% increase in traffic anticipated, the engineer could make that statement. Wendy Fuller, 1729 SE 7th Ct,Renton, WA 98055 stated she lives in River Ridge. The intersection where she comes out of her development is already a five-way intersection. Adding another street would only add to the iifficult situation at the intersection. Ms. Fulfer added that she personally makes eight to ten trips off the hill Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 age 19 every day. She expressed concern about the deer and other wildlife in the area, including nesting eagles, if the property is developed. Sharon Herman, 711 Jones Ave S,Renton, WA 98055 stated that the contractor of River Ridge had the opportunity to build 23 homes. He elected to build only 12 homes out of respect to the neighborhood and the residents of Renton Hill. Ms. Herman further stated that she feels the property value of her home will drop because of all the traffic and the smaller homes that will not fit in with the rest of Renton Hill. Becky Lamke,415 Cedar Ave S, Renton,WA 98055 stated that she feels the massive size of the project is an undue burden to the current residents of the Hill. The number of cars and speed of the vehicles on Cedar Ave is already excessive for the number of homes that are there. The project should be forced to have their entrance and exit off of Puget Drive. The increased traffic and safety issues due to the slope of the streets all lead to Puget Drive being the best alternative. Ms.Lamke asked why Renton School District is still listed as the owner. She questioned whether the property been sold,or if that is contingent on whether the project is approved. Ms. Lamke stated that a clear cutting of this ten acres of mature forest could be detrimental to the Cedar River and to salmon recovery. Mike Fulfer, 1729 SE 7th Ct,Renton, WA 98055 asked why the buffer on the north edge of the project was included in the setback of the homes and not separate from the lots. He asked who is responsible for providing and maintaining the vegetation in the buffer. He expressed concern about the increased number of trips per day as a result of the new homes. He further stated that the project will be out of place because of the density of the mes,and will change the character of the neighborhood and quality of life of the residents.Mr.Fulfer ;cussed stopping distances of vehicles and expressed concern that the stopping distances involved are right on the limit of safety. Being on the edge of safety should only be allowed in a controlled environment such as a race track,not on Renton Hill. Bentley Oaks, 1321 S 7th, Renton,WA 98055 addressed the sight distances issue. Most people drive in excess of 30-35 mph on Renton Ave. S. Considering the reaction time required, and trying to find a place to stop because of parked cars along the street, it can be a dangerous situation. It is important that the human factor be considered rather than just using an engineering study. Doug Brandt 610 Renton Ave. S, Renton,WA 98055 asked if Mr.Nelson made specific measurements on the two crests that exist on Renton Ave. S.or if he relied only on charts for his analysis. Mark Johnson.316 Renton Ave. S.,Renton, WA 98055 questioned the 6%grade, which is an average. The transition between 3% and 9% is sudden,so that close to the end of the 3%grade, it is effectively a 9%grade, not an average of a 6%grade. That would make a dramatic difference in the calculations. He expressed concern that cars are moving in both directions,the road is narrow, cars and trucks are parked on the side,and there is nowhere to go. Regarding speeds on the bridges,Mr.Johnson stated that speed limits are not observed. He feels that adding more cars is not something the road can handle safely. Dana Calhoun,433 Cedar Ave. S, Renton, WA 98055 stated that she feels the sidewalks, particularly on Renton Ave. S, are inadequate. The intersection at 7th and Beacon Way is very busy,especially during softball games. There are no crosswalks, and sometimes no sidewalks. Bicycling on the streets is dangerous. Ms. Calhoun said backs into her driveway because she does not want to have to back onto the street considering the erous conditions that exist. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25,2001 Page 20 Bill Collins,420 Cedar Ave. S., Renton WA 98055 entered traffic count charts that are a graphic version of traffic issues on Renton Hill. Using these charts,Mr. Collins explained how the increased number of cars would impact traffic conditions on various roads at various times of the day in the Renton Hill area. Rosemary Grassi,422 Cedar Ave. S,Renton, WA 98055 stated that this traffic count information was provided by Mr. Mar from the City. It is the City's latest official count of traffic on Renton Hill. The counts show that there would be 813 passes of vehicles on Cedar Avenue per day. On Renton Avenue S, there will be around 1,100 passes per day. There is also a problem of enforcement regarding stop signs. Ms. Grassi stated the Mr. Potter,who is president of the Falcon Ridge Homeowners Association, has signed a statement that he is opposed to this development. She also expressed concern that their appears to be an effort to"dump" affordable housing and apartments from other cities into Renton. Linda McManus, 530 Renton Ave. S., Renton, WA 98055 addressed the issue of accidents on Renton Ave. S. Ms.McManus stated that she was personally involved in an accident last summer on Renton Ave. S. The person coming down the hill failed to yield,and Ms. McManus' vehicle was forced into a telephone pole. She does not know why this accident wasn't recorded. Ms.McManus stated she has personally witnessed many near-accidents on Renton Hill S. She expressed her concern about safety issues in general in the Renton Hill area. Bart Bennett, 1800 SE A Ct., Renton, WA 98055 expressed concern that Lot#35 does not have the 15 foot -greenbelt that the other lots in the development have. He also expressed concern about the possibility of the S- way intersection being changed into a 7-way intersection. He questioned the distances of the stop signs from the intersection. Mr. Bennett also stated that the intersection of Renton Ave. S and 7th is a 3-way stop,which is also extremely dangerous because of the steepness of the hill. He feels that his project is too large for the street system to handle. Mr. Bennett stated that he lives on Lot#5 in River Ridge. He has a sink hole in his back yard which he has dumped about 50 bags of sand into,and it is still fairly deep. Ruth Larson, 714 High Avenue S, Renton, WA 98055 stated that the residents of Renton Hill did not oppose River Ridge because it brought sewer service to those people living above Renton Avenue S. They were not opposed to Falcon Ridge. The only problem with Falcon Ridge was that their original plan was to remove the gate and use<the pipeline for access. The residents did not want the gate removed because of traffic concerns. Falcon Ridge put in their own access road instead. Ms. Larson reviewed the safety issue on Renton Avenue S, and stated emphatically that this issue must be addressed before approval. Kayren Kittrick stated that there is an enforcement issue regarding traffic in the Renton Hill area. The City has programs in place for monitoring these things,and the Police Department should be made aware of the problem. If the City does improvements on Renton Avenue South,it means the streets and sidewalks will be widened,which will take away from front yards along the street and actually increase traffic speeds on the street will increase. The blocking off of the lane on Mill Avenue by Metro is temporary during the construction of the Transit Center. Regarding reports of accidents on Renton Hill,these were done by checking Police reports.The Police Department reported three accidents in five years. All of them involved hitting of stationery objects. Ms. Kittrick stated that pipeline is allowed to be used for emergency access only, not for general access. The pipeline is gated at the request of the local citizens in order to decrease traffic,and can be opened only for emergency access. Regarding sink holes, Ms. Kittrick stated that the City maintenance crews have peen monitoring the sink hole on Renton Avenue S. She has no other reports of sink holes in the area. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF anuary 25, 2001 age 21 Ms. Higgins stated that the Geotechnical Report indicates there is no surface evidence of former coal mines. The area is very inadequately mapped, so no one really knows if there are mines in the area or where they are located. Residents of the area have had problems with sink holes. That is the reason the City wanted to make sure that new residents would at least receive a warning that this could be a problem so that they could plan for it by having a structural engineer design the foundations of their house. Mr.Nelson discussed the enforcement issue on Renton Hill. The developer cannot and should not try to - accommodate people who do not follow the law. Mr.Nelson discussed reaction times and sight distances and stopping times of trucks. He also described the locations where measurements were made for the study and the relationship of road grades and sight distances. Mr.Nelson described how the intersections at 7th and Renton Avenue and 7th and Cedar Avenue are controlled with stop signs. Mark McGinnis Geotech Consultants, 13256 NE 20th Street#16,Bellevue, WA 98005 addressed the issue of coal mines and the question of a sink hole at Lot#5 in River Ridge. There is a deep mine under this area that is over 500 feet below ground surface. The shallower mine workings,which are the ones that seem to be giving the most problems on Renton Hill,do not extend that far to the east into the River Ridge development or into the proposed project's property. There are shallow mines under the western portion of Renton Hill,but they would not be under Lot#5. Regarding the subsidence on Renton Avenue S, Mr. McGinnis stated that he drove the street again and noticed many patches in the road, indicating some repaving and filling. The size of the catches is relatively small. Subsidence associated with a coal mine,related either to an air shaft or the collapse the tunnel itself,would be several thousand square feet in size. The small areas of subsidence and patching n Renton Avenue S appear to be related to utilities, improper compaction,or soft road sub-grade conditions that have been dealt with over time. Considering the depths of the mines, and the time that has elapsed since the last known workings under the property(at least 75 years) if large subsidence were to occur, it would have occurred already. Ms.Higgins discussed the issue of the increased setback on Lot#35 and the reasons for it. Ms.Higgins explained that we encourage quality development by looking at the layout of the plan and making sure it meets the requirements of the development standards that are set forth in the Code. Those are the minimal standards the City Council has felt should be applied in each neighborhood. Other factors that are looked at are the context of the project,development that has taken place in the past,and how the City plans to develop in the future. The City has housing goals that have been set by the Puget Sound Regional Council as to the amount of population that Renton,as well as other cities that are within the Growth Management Act,must meet. Regarding the question of stormwater drainage,Ms.Higgins stated that roof drains will be allowed to infiltrate. Stormwater from the driveways and streets would be collected in the stormwater pond,where it would receive treatment prior to release. It would be a controlled release,as there have been some stormwater problems in that area. Mr. Hobbs stated that the January 2000 Traffic Study was done based on the then current lot number count of 60 lots. This would mean a net reduction of 3 p.m. peak hour trips,and roughly 30 daily trips. The Traffic Report shows that there will be less than 1,500 trips per day on Renton Avenue S,which will be well below capacity for a one-way section. Mr. Hobbs stated that there would be an increased traffic volume on Renton Hill from this project. Regarding safety on Renton Hill, Mr. Hobbs said his statement that accidents should creased was based on accidents of record. The enforcement issue of people not obeying stop signs and speed tits is a consideration. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25,2001 Page 22 Mr. Giuliani stated that the air shafts from the underground mines are made of wood timbers and are approximately 14 to 15 feet in diameter. He expressed his concern that the wood timbers will rot over time. There have already been three incidents of cave-ins. One took place across the street from his home. The air shafts were not blocked off from the mines below,they were filled and blocked off 50 or 75 feet from the top. The passage of time makes the situation more dangerous,not less so. Mr.Brandt questioned exactly where Mr.Nelson made the sight distance measurements on Renton Hill. Mr.Nelson replied that graphical measurements were made on 7th Avenue from the project site all the way down to Renton Avenue S and Cedar, then all the way down Renton Avenue S and Cedar to the bottom of the hill. These were graphical measurements made on the computer. On-the-ground field work was done all the Way up Renton Avenue S. Jeff Schultek, 613 Grant Avenue S, Renton, WA 98055 stated that sometime between 1980 and 1982,a garage was taken down through a sink hole at 820 Renton Avenue S. Mr. Ed Gouch owned the property at that time. Mr. Schultek expressed his concern about safety issues on Renton Hill, particularly in regard to emergency vehicle access. Ms. McManus expressed her concern that the Geotechnical Report has a disclaimer on it. Ms. McManus stated that she has a sinkhole on the side of her property. Her neighbor, Marie Overman,has had to have coal mining engineers flown in from Montana because her driveway caved in. Ms. Gygi stated that Bennett Development does not object to the idea of a Hold Harmless agreement that would be a covenant against the land itself. Bennett Development does object to the idea of a bond being placed that would the hold the developer liable into the future. The Examiner called for further testimony regarding this appeal. There was no one else wishing to speak. The hearing closed at 9:00 p.m. PRELE IINARY PLAT FINDINGS CONCLUSIONS &RECOMMENDATION Having reviewed the record in this matter, the Examiner now makes and enters the following: FINDINGS: 1. The applicant,Ryan Fike, Bennett Development filed a request for approval of 57-lot Preliminary Plat together with Tracts for open space. 2. The yellow file containing the staff report,the State Environmental Policy Act(SEPA)documentation and other pertinent materials was entered into the record as Exhibit#1. 3. The Environmental Review Committee(ERC),the City`s responsible official, issued a Declaration of Non-Significance-Mitigated(DNS-M)for the subject proposal. An appeal of that determination was filed by the Renton Hill Community Association. A hearing on that appeal was consolidated with the hearing on this plat. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 age 23 4. The subject proposal was reviewed by all departments with an interest in the matter. 5. The subject site is located near the intersection of Beacon Way SE, S 7th Court and S 7th Street. The property is located immediately across from Philip Arnold Park. 6. The subject site a triangular parcel approximately 1.114 feet by 818 feet by 829 feet. 7. The subject site is approximately 10.35 acres or 450,846 square feet in area. 8. The subject site has rolling terrain but has steeper slopes along the northeast corner of the site. There are also some steeper slopes on the interior of the subject site that were determined to be manmade as part of past mining or quarrying activity. An exemption from steep slope regulations was issued administratively since the steeper slopes are not natural. 9. Although the slopes are not regulated by the Land Clearing and other development regulations,the ERC imposed a series of conditions to control erosion and deal with geotechnical issues. The subject site is located within Aquifer Protection Area 2. 10. The subject site was annexed to the City with the adoption of Ordinance 1861 enacted in February 1961. The subject site is currently zoned R-8 (Single Family-8 dwelling units/acre). It received this designation in June 1993. 12. The map element of the Comprehensive Plan designates the area in which the subject site is located as suitable for the development of single family uses. 13. The subject site is vacant. It currently is owned by the Renton School District but the applicant has an option to purchase the property. 14. The applicant proposes dividing the subject site into 57 single family lots. There would also be tracts for storm water detention and open space. Staff has recommended that most of these tracts be incorporated into adjacent lots to minimize potential maintenance issues. 15. The development of the subject site would require tree removal. Approximately 389 trees of 6 inches or greater diameter would be removed to allow for the construction of roads, building pads and storm drainage systems. A Class IV permit will be required to convert forest land to residential purposes. The applicant has indicated an intention to save some trees near the detention pond and property entrance if grading work permits. 16. The lots range in size from 4,504 square feet to approximately 8,318 square feet. Staff estimates that the average lot size would be approximately 5,350 square feet. The minimum lot size permitted in the R-8 zone is 4,500 square feet. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 Page 24 17. The Beacon Way Seattle Pipeline Road runs in a southeast to northwest diagonal along the southwest angle of the subject site. It connects to Puget Drive SE and Royal Hills Drive SE on the east. The roadway is not a public roadway and has a gated barricade to prevent through traffic. Philip Arnold Park is located on the southwest side of that roadway. The road does provide access to Philip Arnold Park from the east. School buses also use this road approaching from the east, and a school bus stop is located east of the barricade. School buses do not negotiate the steep hills from the I-405 side of Renton Hill. _ 18. Apparently,the pipeline road was open as a through-street in the past but was closed to reduce traffic passing across Renton Hill and down the steep roadways east of I-405. This also coincided with the then limitation of only one crossing of 1-405 that also crossed railroad tracks that could totally block access to the hill. Reconstruction and realignment of I-405 during the last decade provided a second crossing of I-405, and both crossings are elevated and therefore removed the railroad crossing. 19. The proposed layout would create a looped roadway in the interior of the plat with a cul-de-sac road providing access to the southeast corner of the subject site. A gated, emergency access connection would be installed between the dead end cul-de-sac and the Seattle Pipeline roadway, with Seattle's permission. 20. The proposed roadways would be 42 feet wide instead of the standard 50 feet, since the applicant requested an administrative modification to reduce width,which was approved. Road dimensions are determined by the Director administratively. 21. The lots would be located along the perimeter of the triangular shaped parcel as well as in the interior of the loop. The interior block would contain 13 single family lots as well as a"park"tract. 22. Eight lots would be served by either pipe stem or private roadways. Proposed Lots 14, 15, 16 and 17 would be served by private access easement or roads. Similarly,Proposed Lots 20, 21 and 22 would be served by private access roadway. Proposed Lot 35 would be located on a pipe stem driveway. 23. In order to prepare the site for the building pads and the new roads,the applicant will clear most of the vegetation from the site. Some trees may be preserved near the detention system. The slopes adjacent to Proposed Lot 35 would remain undisturbed, since there are steeper slopes that will be protected. 24. The applicant proposes open space and the storm water detention pond at the entrance to the plat. The road will pass through this open space. As the roadway splits to form the loop roadway,a small park will be located on the inside of the "Y" in the road. The applicant has proposed three triangular landscaped areas along the pipeline road to fill in between rectangular lots. Since the pipeline road runs at an angle,creating rectangular lots required these open space areas. As noted,staff recommended that these areas be incorporated into the adjacent lots to avoid maintenance problems. 25. Development of 57 single family homes will generate approximately 545 vehicle trips per day(based on approximately 9.55 trips per dwelling). It is anticipated that approximately 10%of the traffic trips will occur at each of the morning and evening peak hours. Staff has also estimated that the 57 homes will increase traffic on Renton Hill by approximately 25 percent. This is based on the fact that there Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25,2001 Page 25 are approximately 200 homes on the hill currently. The ERC imposed mitigation measures for fee generation. Staff noted that the City anticipated an increase in overall traffic of approximately 50 percent,and that the 25 percent increase was reasonable. 26. The traffic analysis shows that the major intersections serving this site,Main Avenue S and S 4th Street, Houser Way and Mill,Cedar and S 3rd and Renton Avenue and S 7th will suffer no degradation in LOS. The LOS for the first two intersections will remain at B, while the latter two intersections would remain at LOS A. 27. An analysis of historical traffic accidents showed only three minor accidents and no accidents resulting in injuries. Residents report that there have been a number of"near-misses"and residents living along Renton and Cedar must exercise diligence in using the driveways. 28. The width and slopes of Renton Avenue and Cedar and the other roads serving the subject site from downtown Renton, the only open access to the hill, do not meet current development standards. At the same time, staff reports that these roads have capacity to handle additional traffic and that these roads can also safely handle the additional traffic. Staff did suggest that new residents would have to adjust to the conditions of access just as other residents on the hi II have adjusted in the past, including other new residents. 29. The development of the subject site will generate approximately 25 school age children. These students would be spread among the different grades of the Renton School District. 30. The City will provide sanitary sewer service and domestic water. 31. The ERC imposed additional storm water detention requirements due to the topography and location of the subject site. The proposal will have to comply with the newest King County requirements. Staff reports that the conceptual drainage plan appears to adequately serve the subject site. Staff recommended a homeowners association be required to maintain the detention system. 32. While traffic and transportation issues were a main concern of the neighbors,the Transportation Division did not appear at the public hearing. Questions were handled by other planning and development staff. 33. In addition to the steep slopes along the northeast margins of the subject site, the subject site is located over old, abandoned coal mine tunnels and other workings. Old records and maps were also reviewed. The property was surveyed and inspected and did not show any evidence of mines or shafts. It does appear that the site was a quarry at one time. There are disturbed soils and slopes. A geotechnical analysis provides methods for preventing foundations from being affected if there should be subsidence. The studies also had other suggestions for dealing with the subject site, but indicated that there should not be any problems evident at the surface. Apparently,there have been incidents on the hill of subsidence in the past. The geotechnical information shows that the soils can bear development. The City did recommend that the applicant execute a "hold harmless"agreement regarding the coal mines in case some problems were to arise. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25,2001 Page 26 34. In order to develop the subject site, the applicant will be excavating and filling the subject site. Originally, the applicant was going to export and import materials to level the site. The applicant proposes to alter those plans and do a balanced cut and fill. This will reduce the amount of materials that need to be transported to or from the subject site, reducing the number of truck trips substantially. 35. Development of the subject site will not change the single family character of the area but will generate additional population and traffic as well as other attendant changes more people bring to an area. 36. The homeowners would be required to maintain the open space tracts at the entrance and the park area. 37. All of the Findings and Conclusions of the companion SEPA Appeal Report are incorporated into this report by reference. CONCLUSIONS: 1. The public interest in approving a preliminary plat depends on balancing a variety of interests. The City is bound by the Growth Management Act and has determined the appropriate density under that act for R-8 Districts is between 5 and 8 dwelling units per acre. For this parcel with a net site area of 8.31 acres,the 57 homes yields a density of 6.86 dwelling units per acre. At the same time, the increase in traffic projected for this project is approximately 25 percent over current traffic. This is not an issue that merely equates to LOS and technical issues. This means approximately 550 additional trips will be traveling up and down very steep, narrow roads. Staff noted that the Comprehensive Plan forecast a growth of 52 percent, but those projections would clearly have a lot of that traffic directed efficiently to arterial streets and not narrow streets with single family homes located on very steep streets. These narrow roads serve as collector arterials, but are in no way equal in width or slope to roads that would generally serve that purpose. Renton and Cedar and the streets nearest the subject site are local residential access streets. In fact,they are substandard streets in both width and slope angle. Five hundred additional trips per day is a substantial impact on the homes along the route from the subject site to the downtown area. The public interest sought to be served by approving a plat is not solely served by providing additional housing that meets density standards and growth management standards that do not consider the neighborhood characteristics, and particularly the street characteristics. The public interest is served when one balances density with the impacts of development on other homes and their residents. Engineering design standards to not measure or balance these impacts. They clinically decide that a certain pavement width is adequate to accommodate any additional 500 trips per day,without weighing the affects on adjacent residents. The number of trips will balloon from approximately 2,000 trips per day to 2,500 on Renton and Cedar. Similarly,engineering values on sight distance over the crest of a hill cannot discount the neighbors evidence of"near-miss" accidents as vehicles attempt to avoid each other when negotiating the steep, narrow streets. The engineering numbers do not necessarily account for slowed reaction time of elderly drivers or the impatience of teenage drivers. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 'age 27 Therefore, it seems that balancing the demands of growth management with the impacts on the residents along the commute route requires reducing the scale or scope of the project and the density of that project. The Zoning Code and Comprehensive Plan both provide a range. While it has been generally the case that the density should be as great as possible to meet the housing demands,there may be appropriate times when that density should be reduced modestly to effectuate a balancing of interests. While any reduction will be modest, it still would help to ameliorate the impacts on the existing community. Scaling the plat back to 50 homes would provide a density of 6.02 dwelling units per acre. This falls within the permissible range of 5 to 8 found in the regulations but reduces the - impacts. There would be approximately 50 less vehicle trips and while,not a substantial amount, it would go to lessen the impacts on the residential homes along the route and reduce the potential for vehicle conflicts somewhat. Reducing the density of this plat will reduce the unfoward impacts on the existing residents. 2. The applicant will probably be heard to argue that the SEPA review did not warrant this reduction and that no significant impacts having more than a moderate impact on the quality of the environment were found. "Significance" in terms of SEPA and whether it amounts to EIS threshold "significance" is entirely different than the localized but very consequential impacts of 500 to 600 additional vehicle trips on a local,residential street. Just because an issue is not so large or significant to trigger the need for EIS preparation does not mean it does have an impact which should not be mitigated when determining whether a plat serves the public use and interest. In this case,the additional traffic vis a vis the streets that would serve this traffic demand a density reduction. The applicant could choose to implement such a reduction by either maintaining the general lot size and increasing the open space and secondarily preserving additional trees or by modestly increasing the lot sizes of the remaining 50 lots. Rather then specify the method,the recommendation would be to allow the applicant flexibility in this redesign. 4. In general,with the proposed density reduction, the proposed plat appears to serve the public use and interest. It does provide additional housing choices in an area that can be adequately served by water and sewer and to a lesser extent,the steep narrow roads of Renton Hill. The plat is somewhat isolated from surrounding development and buffers between the subject site and adjacent properties have been provided. 5. The plans show that site can deal with its storm water runoff. As noted, it can be served by City water and sewer. 6. It would appear that there is a remote potential for instability due to the underlying coal workings. There remains the potential to discover overgrown or ineffectively sealed off shafts. The applicant will be required to follow the procedures outlined in the geotechnical reports to develop the site and home foundations. The recommendation of staff for a hold harmless agreement seems reasonable in the event a unforeseen settlement occurs in the future. Potential residents should be given adequate notice that their is some potential for a coal mine subsidence to occur. 7. The proposed layout appears reasonable. In most cases where "interior" lots would be accessed by easement or private roads or pipe stems, these lots are not sandwiched into compounds surrounded on Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 Page 28 four side by other homes. A number of these lots are located on the pipeline or at the open space edges of this site. 8. The ERC imposed conditions to avoid exacerbating drainage problems down stream and to avoid erosion. Storm water will be contained and diverted to avoid excessive flows. The development to R-8 density standards and the need to create building pads and streets means that most of the vegetation will be removed from the subject site. 9. The proposed plat will provide additional housing choices in an area in which urban services are r provided or can reasonably be provided. 10. Development of the site will introduce additional noise and population. 11. The plat provides reasonably rectangular lots and lots that meet the dimensional requirements of code. The open space between lots along the pipeline road does appear to be a potential maintenance problem, particularly with access to the pipeline road roundabout or circuitous from the main plat. These open space parcels should be absorbed into the adjacent lots. 12. The other open space parcels should be restricted by language on the face of the plat that preserves their open space characteristics and precludes selling them off for development in the future. 13. The plat will have its main access to a street which appears capable of providing a safe controlled intersection with appropriate sight and stopping distances. There will be a need to provide assurance that the Seattle pipeline road can be used for emergency access. 14. As a final recommendation,this office would recommend to the City Council that it explore providing the primary access to this plat from the pipeline road with a gated access to the remainder of Renton Hill. If such access could be granted,the narrow and steep streets would not be a issue and the plat could be built to full density. This office was not fully permitted to explore whether this was at all possible. This office only has anecdotal evidence that Seattle, at one time,permitted unobstructed access to Renton Hill from the east. This office does not suggest a full opening but again,recommends that primary access to this plat might be from the east with a gated emergency access at SE 7th Court to prevent through traffic movements. 15. In conclusion,the proposed preliminary plat should be approved by the City Council subject to the conditions noted below. RECOMMENDATION: The City Council should approve the Preliminary Plat subject to the following conditions: 1. The plat should be reduced from 57 to 50 single family lots with a density of 6.02 dwelling units per acre. This falls within the permissible range of 5 to 8 dwelling units per acre. 2. The applicant shall comply with the conditions imposed by the ERC. Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25,2001 Page 29 3. The plat shall contain language acceptable to the City Attorney regarding the recreational and open space respectively and precluding development of them. 4. All landscape tract areas, with the exception of the 5,402 sf tract located at the development entry,the 3,042 sf private"park", and the landscape area abutting the stormwater tract, shall be incorporated into lots already proposed within the plat. No additional building lots are to be created. A revised plan shall be submitted to the Development Services Division prior to receiving construction permits. 5. Commonly held open space areas shall be enhanced,prior to occupancy,with landscaping including r mixed deciduous and evergreen trees and plantings of native shrubs and groundcover. The applicant shall submit a landscape plan to the Development Services Department for approval. 6. A Hold Harmless Agreement shall be recorded that indemnifies the City of Renton from any damage resulting from subsidence that may occur due to previous subsurface mining activities. 7. The applicant will have to secure in writing permission to use the Seattle pipeline road for emergency access. 8. The homeowners would be required to maintain the open space tracts at the entrance and the park area. ,RDERED THIS 25th day of January, 2001. FRED J. KA HEARING EXAMINER TRANSMITTED THIS 25th day of January, 2001 to the parties of record: Zanetta Fontes Jennifer Steig Sharon Herman 1055 S. Grady Way Peterson Consulting Engineering 711 Jones Avenue S Renton, WA 98055 4030 Lake Washington Blvd NE, Renton, WA 98055 Suite 200 Kirkland, WA 98033 Elizabeth Higgins John Nelson Mike Fulfer 1055 S Grady Way Peterson Consulting Engineering 1729 SE 7th Ct. Renton, WA 98055 4030 Lake Washington Blvd NE, Renton, WA 98055 Suite 200 Kirkland, WA 98033 Kayren Kittrick Becky Lamke Bently Oaks 1055 S Grady Way 415 Cedar Avenue S 1321 S 7th .enton, WA 98055 Renton, WA 98055 Renton, WA 98055 Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 Page 3 0 Ruth Larson Mark Mehlhaff Doug Brandt 714 High Avenue S 532 Grand Avenue S 610 Renton Avenue S Renton, WA 98055 Renton, WA 98055 Renton, WA 98055 Ann M. Gygi Nancy Liston Mark Johnson Hillis Clark Martin & Peterson 1518 Beacon Way S 316 Renton Avenue S 500 Galland Building Renton, WA 98055 Renton, WA 98055 1221 Second Avenue Ryan Fike John Giuliani Dana Calhoun Bennett Development 1400 S 7th Street 433 Cedar Avenue S 9 Lake Bellevue Dr., Suite 100-A Renton,WA 98055 Renton, WA 98055 Bellevue, WA 98005 Larry Hobbs Quentin Ellis Bill Collins Transportation Planning& 715 High Avenue S 420 Cedar Avenue S Engineering,Inc. Renton, WA 98055 Renton, WA 98055 2223 112th Avenue NE, Suite 101 Bellevue, WA 98004 Mark McGinnis Wendy Fulfer Rosemary Grassi Geotech Consultants 1729 SE 7th Ct. 422 Cedar Avenue S 13256 NE 20th St., 416 Renton, WA 98055 Renton, WA 98055 Bellevue, WA 98005 Linda McManus Bart Bennett Jeff Schultek 530 Renton Avenue S 1800 SE 7th Ct. 613 Grant Avenue S Renton, WA 98055 Renton, WA 98055 Renton, WA 98055 This report was mailed to other Parties of Record. A complete list of the Parties of Record is available in the Hearing Examiner's office. TRANSMITTED THIS 25th day of January,2001 to the following: Mayor Jesse Tanner Gregg Zimmerman, Plan/Bldg/PW Admin. Members, Renton Planning Commission Neil Watts,Development Services Director Larry Rude, Fire Marshal Lawrence J. Warren,City Attorney Transportation Systems Division Jay Covington, Chief Administrative Officer Utilities System Division Councilperson Kathy Keolker-Wheeler Sue Carlson, Econ. Dev.Administrator Betty Nokes,Economic Development Director South County Journal Larry Meckling,Building Official Heritage Renton Hill Appeal and Preliminary Plat Hearings File Nos.: LUA00-149,AAD and LUA00-053,PP,ECF January 25, 2001 Page 31 Pursuant to Title IV, Chapter 8, Section 100G of the City's Code, request for reconsideration must be filed in writing on or before 5:00 p.m.,February 8,2001. Any aggrieved person feeling that the decision of the Examiner is ambiguous or based on erroneous procedure,errors of law or fact, error in judgment, or the discovery of new evidence which could not be reasonably available at the prior hearing may make a written request for a review by the Examiner within fourteen (14)days from the date of the Examiner's decision. This request shall set forth the specific ambiguities or errors discovered by such appellant,and the Examiner may, after review of the record,take further action as he deems proper. An appeal to the City Council is governed by Title IV,Chapter 8, Section 110,which requires that such appeal be filed with the City Clerk,accompanying a filing fee of$75.00 and meeting other specified requirements. Copies of this ordinance are available for inspection or purchase in the Finance Department, first floor of City Hall. If the Examiner's Recommendation or Decision contains the requirement for Restrictive Covenants,the executed Covenants will be required prior to approval by City Council or final processing of the file. You may contact this office for information on formatting covenants. The Appearance of Fairness Doctrine provides that no ex parte(private one-on-one)communications may occur concerning pending land use decisions. This means that parties to a land use decision may not communicate in private with any decision-maker concerning the proposal. Decision-makers in the land use process include both the Hearing Examiner and members of the City Council. A communications concerning the proposal must be made in public. This public communication permits all interested parties to know the contents of the communication and would allow them to openly rebut the evidence. Any violation of this doctrine would result in the invalidation of the request by the Court. The Doctrine applies not only to the initial public hearing but to all Requests for Reconsideration as well as Appeals to the City Council. N W • CITY OF R]ENTON" ' .A Planning/Building/Public Works Department Jesse Tanner,Mayor Gregg Zimmerman P.E.,Administrator October 19, 2000 Mr. Ryan Fike Bennett Development f�' 9 Lake Bellevue Drive, Suite 100-A`�' Bellevue, WA 98005 SUBJECT: Heritage Renton Hill Project No:LUA=00-053.PP,ECF Dear Mr. Fike: This letter is written on behalf of the Environ er tal pxpnw Committee (ERC) and.is to advise you that { they have com'.pleted their,review of Jec project ERC, on October 17; 2000; issued a areshold Determ�natronf Nori 5� i n i ited with jVli i �tion Measures See the`.enclosed c�a r Mitigation Measuresydotximeitf= ti U .Appeals of the environmental toi�iya ion must be filed m:wr�itin ion c .before;5 00 PM November 6r 2000 Appeals must be filed n. iti g ogether the require $75I application-fee:with Hearing Examiner, City of Renton,::10 5 S -Grey a b°' WA P8055,.- peals tq. the Examiner•are governed by City'of Renton N unicipal C,'ode Sec i n 4-8�1A =Additional info)oration regarding the appeal -process may be obtained from th ; .e ton�t- icy Y 425�430�51 D A Public Hearing �nnll be hel by'the Retfitb� nng miner t his regular;.meetir♦g in,the;Counal ` . Chambers on the seventti''floor of. 'a Hatl,`6n embe ,, , 2000 at 9 OOAM o consider the.proposed Preliminary Plat... The applican` r representatives)of the applicant is required to be present at the public hearing A copy of the staff report willitie ailed to you one wee 1?�fore the hearing If the Environmental Qeterminatiori is appealed,.the ap ail t e e rd s par(o is a ►i eanng The preceding infomiatton:Vwll ssist ptagkrn or i plem tion of>your p�oJect snd en2tslp yo�I:t4 exercise your__appeaf`nghts'Jnore::fu lyz, 1f yotJ,have apY queSbons or des S ;-clarification of the..above;:please.gll rfie at 42 .: :. FeEmRth v— onnbibtee; ww ')-�{;,.v;. F� jTi. zRro" • :'r . a .,� e-.x---r ;r.r :ca,:- S t, t.;^:., ,yv�:�' S 4-t`. ,r•J,p:••i'-''1.:7' ..t, Elizabeth Higgins,AICP ) J ` 4 SenlorPlanner. x cc "Renton Schdol Distddt 0310wners {- r , Parties of f tecord i z 1=rtcrosure . 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'¢{�z, '{i ,csZ �7�'; �a At ' " 1.Fy.':105 .South Grady Way Renton,Washnngtori?98055 This paper contains 50%recycled material.20%post consumer CITY OF RENTON DETERMINATION OF NON-SIGNIFICANCE (MITIGATED) MITIGATION MEASURES APPLICATION NO(S): LUA-00-053,PP,ECF APPLICANT: Bennett Development PROJECT NAME: Heritage Renton Hill DESCRIPTION OF PROPOSAL: The applicant proposes division of a 10.35 acre property, by means of the preliminary plat process, into 57 lots suitable for single family residential development. The,, property is zoned Residential 8 (R-8), which allows residential development of.between 5.0 and.8.0 dwelling units per net acre (du/a). The proposed density for this project would be 6.8 du/a... .Lot sizes would:range from.4,504 to 8,318 square feet each. The minimum lot size in the R-8 Zone is 4,500,sf The applicant has requested a modification of street standards to allow public street right-of-way widths of ` 42 (instead of 50).;The proposed project is subject two review,by the City of Renton Environmental Review Committee A public hearing before the City�of• enton�ear.i q Examiner will also_be required Y LOCATION OF PROPOSAL 1nte sects of Beaco aya E,S 7"-,Court,and S 7 Street 4";,� , r MITIGATION MEASURES: f 1 The applicant shall'install asittf rice alo the ownslo e ptne er,of the area that is to:be r 4- disturbed._ .The silt:fence sha�I be i pla efore Baring�a rid.gra ing.is initiated, and shall be constructed in conformance with the specs catidhs_presente�f in the King_Coupttyy Surface'Water; Design Manual (KCSWD]VI) phis wl x e :_ uireduri ;the.cons ctin of.both off site and on-site improvements was well 9s building 2 Shallow drainage swales hall 1 '71 cte Ito in t apt su ace water flow and route the flow.away from the construction area.to alsta��li discharge.point. ege ions growth shall be established in; the ditch.by seeding or placing sod: CZepending on site gr�I`de , I m be.necessary to line the ditch.. with rock;w.proteci the ditch• roi i `e o on and to redyce flov rate ,he design and construction flf {. drainage,swafes shall_ confo h .;s ecificattons; resnf.in.::the "most recent KCS�WD[VI Temporary pipe:sysfems caii s e sel-p:ponve s Wjvygt ..across.the.site These measures a 4 t will be required.during the cons of bo ff=s and =site imprs�vement5, fis well'as#�uddu> f ; == constructiort n i �r >'•i d �rS;n�+4 S ris lr', r. 3 The project.contractor shall perform daily.review..and maintenance Qf aN erosion and sedimentation .control measures at:the site during the.constrbceonof-bothvff-siteand�n-site improvemients,as nreti as building cons47, truction - 4 Weekly repoits'orl the:'status and condition.of the`erosion controi plan with any reaommen aborts of , � 3 .: change or revision to: aintenance schedules or:nstallation shall:be-s_ubm1ttedyth8 proje 1=ngjrZeew; � : of,Record:to the Public Works.Inspector_Ior the"construction:of the civil impro Monts 6f th�~plat. Certification of the::installation, mainteriance;and proper Yemo�al of'the'erosion-control facilitlesshall . ; _ be.required prior to recording of the.plat. s . t r . •. i --- :. `' ` irA �' •- } ♦�� ; ',fix � x"''.. 5 The applicant'shall part' the applicable Transporfatron Mitigabon Fee at the rote of;$75 00 per aaGl1 ?: new average weekd trip attributable to the;project,.estiimated to be 0.55.average weel�day trips new single family IoL e:'Transportation Mitigation Fee is due prior to the recording of the plat - t; Ti1erappliCant shah pay�therappropriate Fire,Mittgatio aFee t agate A $4:68,---pe -:e�a xie irig a .•Y e;��family Iqt created by the proposed plat 'The fee�e�dlue � tlaereccrdm f the 13at ' S': i+� yjp,.. ,�,, f sl;rkM S r+�hy�i��� � � 3°� � < r r �, r . ✓ ?tS3' r F r : 't`' � ri's � r } •l >r••'.t - _- ..fit q'S4rjj7�+SiP ''__yaa - �s „" .,w,L' S k~s' -� •.�ti �.w -'xy . -Yf � :.w ' yam+ ��.. Y�• -r,. ><i,IX ,�r a :.�x�aa. 7yTr'�ts ,. a^S. -r7r,J�.'F"'1't.,r`tt' ''�sk�,�"`,r7.r" •• t • ��K r3ii•,'y, y .s' n -:. iC'0 1. >�i.3' �y.•,. «.},t ^')+.�5♦ "`�e 'S �:v }y .. .i �4 y�,i�, ��' 'q'.>h -3`S •..F L t:�; ,y •'' "4t, 1 r t '1. , .,Sr..2.s -�`ra' f i'rti "_' +t.-i Heritage Renton Hill LUA-00-053,PP,ECF Mitigation Measures (continued) Page 2 of 2 7. The applicant shall pay the Parks Mitigation Fee at the rate of $530.76 per each new single family residential lot. The fee is due prior to the recording of the plat. 8. The applicant shall follow the recommendations of the geotechnical engineers, Geotech Consultants, Inc., (report dated September. 14, 19,99), as they pertain to site development and building construction. 9. A note shall be added to the face of the plat, prior to recording, stating that a known potential for ground subsidence exists in the area and that building plans shall be designed in consultation with a structural engineer and shall conform to the recommendations..of the Geotech Consultants, Inc., as found in their report dated September.14, 1999. 10. The rear setback at the lot located in the northwest comer of the property (Lot 35 as shown on the plan dated 8/31/00) shall be twenty-five feet. A note.shall be placed on. the title of the lot prohibiting building construction within.twenty-five feet�.apd;-fearing within ten feet of the rear:property line, as shown on the revised plan submitted b the.a plican�Yia diated 8/31/OOr :11 The applicant shall ensure that'l co :sfruction debris and.Aisca,cied items are excavated from;the-,Mte and construction is ceased J�Gd`djately; ollowed by;nott icai on.o the City,of Renton^Development Seances Division within.24 hours,Aould 7azardo is material be'dis _v."ered during said removal / ` '~ 12 The Construction Traffic,Control Tian.thalt a crude a condition iat nstruction vehicles in excess 26,000 gvw, associated with the proiec,woU fie" irohbited from operating on Renton Half during am and pm peak'traffic hours as identifiedCln e,report, Heritage Renton Hill 'Preliminary Plat Arnold Pro a Traffic Im act Anal" isiAddenduin,.No b .Trans"ortetiontPlannin & Engineering, Inc., -dated September 11,20 0 , g 13:The applicant shall obtai an a ss.perm% gin Orden o-use t e Seatt,e Public Utilities "Cedar River Pipeline Easement"for a se dairy' ern ency only access` ,. r a A.. . h- 'x r t .✓ s Vic.r r -.K t • - 4 y £ .� . 1 .�;_ •''+ c. >; - Wit,,:". y. t" 1 N�i� � •a � it2.!( r s_x ro�h s f ,� �.'f`^ " {,. .Y N�it�.� L. r.�.yr$y... �r .t('Fr.� -,'.'",.��`Y`:'"ri Y� i a;� ;;{� j ,�• ' !r „ins 'N ,�, rt �'�' •y44• .r i' �tt i 2� ,sf'S rt -}YY ^ X. .r•l }'ri�,TK wit '•az'v� ` 1�'y� mot', ° ri'.'Y» r '�. t 7y-t r�',j li `" a. 3)J`y 'T� a- a.fy'. .i+a�y -` �.Yt kl,.' ;�y'1 .ti1",•'�( ',=e�•.�r's -< -k .,Fvi'•."_7ar vay4•, ./1 f<7 _ }�" T .r L.. +'r "s 4 - •� t -. 2-.:xe v �, t r s -' `'a x r ,•j'�'� . xc w•V .=rt r� ..� h' rtx !i r,i'ry! h, �s �M.,y' ? ;,t''t {'_ 1z�s ,y -• :fit 1'- _x�- -j4 rL_.ki -a i ri t-`.s .rt ' = t - �• .i r, � #1 a+/ >3 ',,•c-%>!e / .� s. r.' r: � r_ •r { •1 stir ` t Z. 'M 'P -3 , - e 1 i�. , ,a e rf.�• ,�R'`�'''�"�}7?yyYt� crt*$S -r`r t tY-_ hF'+',v t-+�r� �•#i;c 4'"�t r i 7 .t {"r.#-tom - MrTMEAS +'l T `�r .r.�'k- c /�f �.h.`n.N ".tt:�S v T 4 � {• Iry '..4� { ) ( t CITY OF RENTON DETERMINATION OF NON-SIGNIFICANCE (MITIGATED) ADVISORY NOTES APPLICATION NO(S): LUA-00-053,PP,ECF APPLICANT: Bennett Development PROJECT NAME: Heritage Renton Hill DESCRIPTIOKOF PROPOSAL: The applicant proposes division of a 10.35 acre property, by means of the preliminary plat process, into 57 lots suitable for single family residential development:_ .The property1s; zoned Residential 8 (R-8). which allows residential development-of between •5.0 and: 8'0 ' dwelling units per, 31 net acre (du/a). The proposed density for this project would be 6.8 du/a. Lot sizes' would range from 4,504'to 8, 8 square feet each. The minimum lot size in.the R-8 Zone is-4,500 sf.. The applicant has requested a modification of street standards to allow public street right-of--way widths of 42'(instead of 50'). The proposed project is subjec_Ji to review by the City of.Renton Environmental Review Committee A public-heanng,before the Ciofa2e oebring Examiner will also be required :.; t LOCATION OF PROPOSAL Irate sectio of•:.Beacon a E,S 7.. Court,and;S 7"'ttreet Advisory Notes to Applicant , r The following notes are suppleMp at ' informa o ro �ded n`coijt�ri Iron with the environmental determination. -Because these notes are,pro:a -ass yif;rma>ion oral they are not subject to.the.. appeal process for environmental determmattons f Plan Review-Sanitary Sewer, � 1 There.is an existing 8" sewer,main."in SE 7 Court, adjacent p,.4t a "orth side of the proposed.plat. The new.project can'be served by'extending an 8 sewer main fro this existing main through the - proposed subdryision _the drawl submitted for:the foimal appi�cation ¢.=.2 2 The conceppteal sanitary sewer rsho�n fir► w` appears'to be in order: y _ L:.• 3 A sewer cleariout will need to be located five feet out from buildings: : :4 Separate side sewers will be required for each parcel (no dual sewers). Side sewer lines must have a 2 percent slope. ° " 5 Ai1:uUlity plans fnust comply with the City of Renton'Drafting Standards s. 6 Show firoshed floor elevations on the sewer constrii n plan sheet ..7 Tte vertical profle of the sewermain will be tequired _ <, 8 The protect is located in Aquifer.i'rotection Area Zone 2 , .: Any new:sewer mains are to be,separated from water lines by a minimum of 10 feet. Thete is a 7 5 , xr `" foot minimum separation frbm other utilities, �:Y.• - Y .• t i,1 fi a s•h �• t 1{'-s +t % 'J y H.x s a .. Ls 4•p�+Yh..,..-�;ia��_.'`s' �z. :-s•'y i„„.f rr< t , u3. . +•cep - --sx� ^a+�r*�e�'�v.�i rt r Sr•'"`^t :3 r 'rTiS�y��c�',yn4 �;' y -.f+ ' �Y.�,Sc'' �f *? "}'J'y)�cK' '`.,CC J°w-`..E ,,,,1t '•, 'v s! �r {'tt ��'f fL yt; t y„kn� ram•? - y�ir.;+.s`�':..r�'' �"r �r �'c �'"�. �-�.�� � �y.,. '''t 1' T kV^ '` f t t _ "t i' ti Y� .� �+f# .A ::K"n�4 ai��7i's �>`''• }? '.�r••� ,�s•; r •.1 4e .:d .s ..Y'. � 1 ry i:tiP f°s. �ft'S j _i.. Heritage Renton Hill LUA-00-053,PP,ECF Advisory Notes(continued) Page 2 of 2 10. Sewer Development Charges of$585.00 per single family residence will be required for this plat. The fee for this project would be $16,380.00. This fee must be paid prior to issuance of the construction permit for the preliminary plat. Plan Review—Water 1. There is an existing 6" water main in Jones Avenue S, an 8" water main in SE 7t' Court, and an 8" water main stub to the north boundary of this parcel. 2. The proposed project is located in the 490 foot water pressure zone. Static water pressure will range from approximately 40 psi at elevation 395 feet to 55 psi at elevation 360 feet. 3. Any new construction must have a fire hydrant capable of delivering a minimum of 1,000 GPM fire flow and shall be located within 300 feet of the structure. This distance is.measure along a travel route. Additional fire hydrants will be required as part of this project to meet this criteria. 4. The water main must be a looped system with two separate feeds. The conceptual utility plan needs to be modified to show the second feed to the existing 6"water main in Jones Avenue S. 5. Installation of 8"water mains in the interior"'streets ofthb-plat to serve the domestic water meters.and fire hydrants are`required 6. Connection to the 8"stub alog"th6.north-property lin is ru ri ed see plan W 208) 7. Connection to the existing 6"%ateti main-in-Jones Avenue S�s req `ire ,(see plan W=1156). The water conceptual utility plan shall beevised to show this connection AW &, � 8. Water System Development charges or-;;Oo per new rngl amity lob will be required for this: The charge for this plan would be,,48�450 4 is fe ust be paid prior tQ issuance of the construction Permit for the prelimina late t l Plan Review—Stormwater Drainage 1. A,conceptual drainage plan and drainage report was submitte�with the preliminary plat application for. this project and appears to bet order 2 `Drawings submitted to the City of`�e� n(on are�to be n:22�Irrx 34 inch sheets The information T pertaining to,the;;City of Renton should be moved from eitie block of the sheets submitted 3. Before any,construction or development activity occurs, apre-construction meeting must be held,with the+_City of Renton Development Services Division;Construction_Services_-f425-277-5570). .4. The.City of Renton-retains the right to restrict the timing of land;clearng and tree cutting activities to sped iicdates and/orseasons:when such restrictions may be necessary for the'public health,`safety, :and welfare or for the protection of,the environment 5 Surface Water System bevelopment.charges of$385 per new single family lot will be required for this Plat. The fee for-this project,.would be $21,945.00 This. fee must be paid prior to issuance,ofthe ;,construction permit for the preliminary plat Plan Review-Transportation and Street Improvements 1.: All electrical'and communication facilities to be underground behind the sidewalk: If right-of-way space is not available,then in a utility,easement. ,Construction of these franchise utilities must be' t _ inspected and approved#rya Ci,yof Renton publicworksJnspector pnorto recording of the plat , . '` �r`� :,- ,`s f ftS�j? '•4'a�.�r:;?t 5kF'w'v � ;:` ` •_," t =4 ";'S ` s:t�i f". S f r- 2 Streets over 700 feet m'Tength are required o have two means of access i 1 r S � vt C +1 i -, i : ADVISORYNOTES Heritage Renton Hill LUA-00-053,PP,ECF Advisory Notes(continued) Page 3 of 3 3. Street lighting is required to meet City standards. Minimum lighting level is 6:1 uniformity ratio and 0.2 foot candle level. The street lighting conduit to be located under the sidewalk. - 4. The minimum right-of-way width is 42 feet(modified from street standard width of 50 feet). 5. The cul-de-sac is required to have a minimum pavement radius of 45 feet and right-of-way radius of 55 feet. 6. A 5 foot sidewalk at the curb is required 7. Payment of a Transportation Mitigation fee of$75 per new average weekday trip, estimated at 9.55 new trips per single family lot,will be required prior to recording of the plat.- It has been estimated.that this 57 lot plat would result in approximately544.35 additional average(weekday)trips. The Transportation Mitigation Fee would be$40,826.25. Plan Review—General 1. All required utility,drainage,and street improvements will require separate plan submittals prepared according to City of Renton drafting standards by'a registered Civil Engineer. 2. The construction permit application(s)must include an itemized cost estimate for these _ improvements. ¢: 3 The fee for review and inspection these impr Apr is 5 percent of the first$100,000 of the estimated construction costs; percent of anythir.g over$ 00,d00; ut,less than $200,000;and 3 percent of anything over$200,000 'Half ofaiis fee mu°st�be l up i application for,construction permits (preliminary plat im vemen>s�, and the remamde y, of le construction permit is issued: There ma "be additional,fe�esf or water service elated ex enses 72Vt -� 3� -lY 'wit fu-1 SY�$, $ - - - 4. An easement that meets City standards for ing' ess egress, and:utilities shall be provided_ by the applicant to the property abutting the;east proe Moudary at a point within 200 feet of the northeast property comer of the proposed plat Parks Department Review h � . 1. Payment of a Parks Mitigation Jee of$530.76 for each new single family lot will be required prior to recording of the plat The parks fee wilhbe$30,253.32 2 : Building Department Review 1 Demolition pemiits will be required.•Fire Prevention Department Review 1 A fire hydrant with 1000 GPM fire flow is required within 300:feet of all new single family structures.' If the building square footage exceeds 3600 square feet in area, the minimum fire flow increases to 1500 GPM and requires two hydrants within 300 feet of the structure. 2t 'Provide a 20 foot paved secondary emergency,access from the cul-de-sac within the development to the Seattle,Public,Utilities Cedar River Pipeline Easement (Beacon -Way SE): This would be an emergency access only and can be gated or chained. I.' All building addresses shall be visible from a public street. 4: A Fire.Mitigation fee of $488 is required for all new Single family lots. Payment is required prior to recording of the plat. The Fire Mitigation fee for the proposed project would be$27,816.00:: *tPropertyServices Department Review "x C 1 Comments will be provided underseparate cover. " } ADVISORYNOTES Heritage Renton Hill LUA-00-053,PP,ECF Advisory Notes(continued) Page 4 of 4 Development Services Department Review 1. The site is designated Residential Single Family in the Comprehensive Plan. 2. The property is zoned Residential 8 (R-8). 3. Densities allowed in the R-8 Zone are 5.0 dwelling units per net acre (du/a) minimum and 8.0 du/a maximum. 4. Minimum lot size in the.R-8 Zone is 4500 sf, with minimum width of 50 for interior lots;and 60 for comer lots. The minimum permitted lot depth is 65 feet. Lot dimensions must be shown on the final site plan demonstrating that all lots meet these minimums. 5. Heights of buildings in the R-8.Zone are limited to 2 stories, or 30 feet. 6. Required setbacks in the R-8 Zone are 15 feet for houses and 20 feet for attached garages which . access from the front when houses front streets created after September 1;`1995, 20 foot rear yard setbacks; 5 foot side yard setbacks for interior lots and 15 feet sideyard setbacks for comer lots..All setbacks are minimums. Setback dimensionsshould be shown on the construction drawings, but setback lines must be removed prior tore�c`b�dmgthe finalplat. 7. The maximum building coveragefin the R-8 Zone,is 35 pe cent for lots`over 5,000 sf-or•50 percent fore lots 5,000 sf or less ; s° 8. Dead.end streets cannot exceed 706,,feet in length, measured,from:t a edge'of the connecting street to the end of the cul-de-sacs € F 9. Retaining walls in excess�of four�4)feet require engineered drawings anti a separate building permit. 10..Construction easements- obtained from.abuttmgproperty owners` ay be necessary, prior to construction of retainingrpalls on er nearpCopertylines. These agreeents'mustinclude protection measures for(or permission to potentially"d p age or;tremove),trees ocated on abutting properties within 20 feet of the property line 11. The. applicant shall draft and record 'a ,mamtenance,• agreement .or establish` a ,Homeowners' Association for the maintenance of all,.common impr�oveients (access and utility easements,:rights of-way;,and storm water facilities `draft of t'he docu en sha) ,be submitted,to the City of Renton for review and approval liy the City Attorney p%r o the r rd g f;the preliminary plat 12. Performance, Standards for Land Development Permits (RMC 4-4-130K), including "Protection Measures During Construction"'(RMC 4-4-130K7).relating to trees,-shall be followed.by the applicant. The applicant shall adhere to the definition of"tree"-a found an-RMC 4-1-1-200, "drip line"-asfound to RMC 4-11=040,and the measurement of trees as found in RMC.4-11 030 13. The Washington State.Department of Natural Resources may require'a Forest Practices Permit for .` the conversion of timber land to another use. . 14. The applicant should.:contact Paul Alexander of The King County Department of Transportation; Metro Transportation; Metro'TransitRoute.Facilities at 206-684-1599, regarding Metro's requirements for potential transit service in the area(no service is currently available to Renton Hill) ADVISORYNOTES N 2.4 SUMMARY OF HEARING EXAMINER'S CONDITIONS Heritage Renton Hill Plat City of Renton File Nos.LUA00-149,AAD Note: The following outline summarizes the Hearing Examiner's conditions for the preliminary plat approval,in italics,followed by a narrative response explaining how the Hearing Examiner's conditions have been met or will be met for this project. 1. The plat should be reduced from 57 to 50 single family lots with a density of 6.02 dwelling units per acre. This falls within the permissible range of 5 to 8 dwelling units per acre. Response: The final layout has been prepared for 50 lots. The final layout is nearly identical to the preliminary plat map except for the reduction in lot count and the elimination of some landscape tracts. 2. The applicant shall comply with the conditions imposed by the ERC. Response: Completed. See separate responses to ERC conditions in Section 2.5 of this TIR. 3. The plat shall contain language acceptable to the City Attorney regarding the recreational and open space respectively and precluding development of them. Response: Acknowledged as a final plat item. 4. All landscape tract areas,with the exception ofthe 5,402 sf tract located at the development entry, the 3,042 sfprivate `park", and the landscape area abutting the stormwater tract, shall be incorporated into lots alreadyproposed within theplat. No additional building lots are to be created. A revised plan shall be submitted to the Development Services Division prior to receiving construction permits. Response: Completed. The final layout is nearly identical to the preliminary plat map except for the reduction to 50 lots and eliminating the landscape tract areas described by this condition. 5. Commonly held open space areas shall be enhanced,prior to occupancy, with landscaping including mixed deciduous and evergreen trees and plantings of native shrubs and groundcover. The applicant shall submit a landscape plan to the Development Services Department for approval. Response: Acknowledged as final plat item. The landscape plans will be completed for approval prior to final plat approval. 6. A Hold Harmless Agreement shall be recorded that indemnifies the City of Renton from any damage resulting from subsidence that may occur due to previous subsurface mining activities. Response: Acknowledged as a final plat item. 7797.006[RJA/jss/ca] 7. The applicant will have to secure in writing permission to use the Seattle pipeline road for emergency access. Response: It is our understanding that the agreement has been written by the City of Seattle and is currently on file with the City of Renton awaiting approval by the Mayor. 8. The homeowners would be required to maintain the open space tracts at the entrance and the park area. Response: Acknowledged as a final plat item. 7797.006[RJA/jss/ca] N 2.5 SUMMARY OF SEPA CONDITIONS AND ERC ADVISORY NOTES Heritage Renton Hill Plat City of Renton Project No.LUA00-053,PP,ECF Note: The following outline provides the City of Renton's Determination of Non-Significance Mitigation Measures in italics, followed by a narrative response explaining how the mitigation measure will be addressed. Also, following the SEPA mitigation measures is each of the Advisory Notes in italics, followed by a narrative response indicating how the comment is addressed. 1. The applicant shall install a silt fence along the downslope perimeter of the area that is to be disturbed. The silt fence shall be in place before clearing and grading is initiated, and shall be constructed in conformance with the specifications presented in the King County Surface Water Design Manual(KCSWDM). Response: This condition will be satisfied with the approval of the grading and erosion control plan. A silt fence has been located along the downslope portions of the property boundary. 2. Shallow drainage swales shall be constructed to intercept surface water flow and route the flow away from the construction area to a stabilized discharge point. Vegetation growth shall be established in the ditch by seeding or placing sod. Depending on site grades, it may be necessary to line the ditch with rock to protect the ditch from erosion and to reduce flow rates. The design and construction of drainage swales shall conform to the specifications presented in the most recent KCSWDM. Temporary pipe systems can also be used to convey stormwater across the site. These measures will be required during the construction of both off-site and on-site improvements, as well as building construction. Response: This condition will be satisfied with the approval of the grading and erosion control plan. Temporary drainage ditches/swales with rock check dams have been designed to collect and convey drainage. 3. The project contractor shall perform daily review and maintenance of all erosion and sedimentation control measures at the site during the construction of both off-site and on- site improvements, as well as building construction. Response: This note has been placed on the grading and erosion control plan, Sheet T1. 4. Weekly reports on the status and condition of the erosion control plan with any recommendations of change or revision to maintenance schedules or installation shall be submitted by the project Engineer of Record to the Public Works Inspector for the construction of the civil improvements of the plat. Certification of the installation, maintenance and proper removal of the erosion control facilities shall be required prior to recording of the plat. Response: This note has been placed on the grading and erosion control plan, Sheet T1. 7797.006[RJA/jss/ca] 5. The applicant shall pay the applicable Transportation Mitigation Fee at the rate of$75.00 per each new average weekday trip attributable to the project,estimated to be 9.55 average weekday trips per new single family lot. The Transportation Mitigation Fee is due prior to the recording of the plat. Response: Acknowledged as a final plat item. 6. The applicant shall pay the appropriate Fire Mitigation Fee at a rate of$488.00 per each new single family lot created by the proposed plat. The fee is due prior to the recording of the plat. Response: Acknowledged as a final plat item. 7. The applicant shall pay the Parks Mitigation Fee at the rate of$530.76 per each new single family residential lot. The fee is due prior to the recording of the plat. Response: Acknowledged as a final plat item. 8. The applicant shall follow the recommendations of the geotechnical engineers, Geotech Consultants,Inc., (report dated September 14, 1999),as the pertain to site development and building construction. Response: This note has been placed on the grading and erosion control plan, Sheet T1. 9. A note shall be added to the face of the plat, prior to recording, stating that a known potential for ground subsidence exists in the area and that building plans shall be designed in consultation with a structural engineer and shall conform to the recommendations of the Geotech Consultants,Inc., as found in their report dated September 14, 1999. Response: Acknowledged as a final plat item. 10. The rear setback at the lot located in the northwest corner of the property(Lot 35 as shown on the plan dated 8131100)shall be twenty-five feet. A note shall be placed on the title of the lot prohibiting building construction within twenty-five feet and clearing within ten feet of the rearproperty line,as shown on the revised plan submitted by the applicant and dated 8131100. Response: This 25-foot setback is shown on the horizontal control plan,Sheet R1,as is the clearing limitation on the rear 10 feet of Lot 32 (please note that Lot 35 referenced in the condition has been renumbered to be Lot 32 as a result of the reduction from 57 lots down to 50 lots. 11. The applicant shall ensure that all construction debris and discarded item are excavated from the site and construction is ceased immediately,followed by notification of the City of Renton Development Serviced Division within 24 hours, should hazardous material be discovered during said removal. Response: This note has been placed on the grading and erosion control plan, Sheet T1. 7797.006[RJA/jss/ca] 12. The Construction Traffic Control Plan shall include a condition that construction vehicles in excess 26,000 gvw, associated with the project, would be prohibited from operating on Renton Hill during am and pm peak traffic hours as identified in the report, "Heritage Renton Hill Preliminary Plat Arnold Property Traffic Impact Analysis.Addendum No. 2." by Transportation Planning&Enizineerinz Inc., dated September 11, 2000. Response: This note has been placed on the grading and erosion control plan, Sheet Tl. 13. The applicant shall obtain an access permit in order to use the Seattle Public Utilities "Cedar River Pipeline Easement"for a secondary, emergency only access. Response: Acknowledged. The City of Seattle has prepared the agreement and it is on file with the City of Renton awaiting approval by the Mayor. 7797.006[RJA/jss/ca] Advisory Notes to Applicant. The following notes are supplemental information provided in conjunction with the environmental determination. Because these notes are provided as information only, they are not subject to the appeal process for environmental determinations. Plan Review-Sanitary Sewer 1. There is an existing 8"sewer main in SE 7th Court, adjacent to the north side of the proposed plat. The new project can be served by extending an 8"sewer main from this existing main through the proposed subdivision. Response: The final sanitary sewer design connects to the existing 8-inch PVC sanitary sewer main stub that was built to the property by the River Ridge plat. 2. The conceptual sanitary sewer main shown on the drawing submitted for the formal application appears to be in order. Response: Acknowledged. 3. A sewer cleanout will need to be located five feet out from buildings. Response: Acknowledged as a residential building permit item. The plat will stub side sewers 10 feet into each lot. 4. Separate side sewers will be required for each parcel(no dual sewers). Side sewer lines must have a 2 percent slope. Response: Each lot has been provided with an individual 6-inch side sewer stubbed 10 feet into the lot. S. All utility plans must comply with the City of Renton Drafting Standards. Response: Completed. 6. Show finished floor elevations on the sewer construction plan sheet. Response: The sewer plan shows lot pad elevations. The finish floor elevations will be determined at the time of individual house construction and will probably be approximately 1.0 foot higher than the lot pad elevation that will be graded with the plat construction. 7. The vertical profile of the sewer main will be required. Response: Completed on Sheets S2 and S3. 8. The project is located in Aquifer Protection Area Zone 2. 7797.006[RJA/jss/ca] Response: Acknowledged. Sanitary sewer is provided so that the aquifer is not impacted by any septic systems. 9. Any new sewer mains are to be separated from water lines by a minimum of 10 feet. There is a 7.5 foot minimum separation from other utilities. Response: Completed. We have designed the standard separation between water and sanitary sewer at 12 feet,as shown on Sheets W 1 and S 1,and in no case is the sewer closer than 10 feet separation as required. 10. Sewer Development Charges of$585.00persinglefamily residence willbe requiredforthis plat. The fee for this project would be$16,380.00. This fee must be paid prior to issuance of the construction permit for the preliminary plat. Response: Acknowledged as a final plat item. Plan Review- Water 1. There is an existing 6"water main in Jones Avenue S, an 8"water main in SE 7th Court, and an 8"water main stub to the north boundary of this parcel. Response: Acknowledged and shown on Sheet W1. 2. The proposed project is located in the 490 foot water pressure zone. Static water pressure will range from approximately 40 psi at elevation 395 feet to 55 psi at elevation 360 feet. Response: Acknowledged. 3. Any new construction must have afire hydrant capable of delivering a minimum of 1,000 GPM fire flow and shall be located within 300 feet of the structure. This distance is measure along a travel route. Additional fire hydrants will be required as part of this project to meet this criteria. Response: The water plan, Sheet WI,proposes three fire hydrants that comply with this spacing requirement. 4. The water main must be a looped system with two separate feeds. The conceptual utility plan needs to be modified to show the second feed to the existing 6"water main in Jones Avenue S. Response: The water plan, Sheet W1, proposes a water main loop connection to Jones Avenue South. It runs in an east/west direction approximately 140 feet south of S.E. 7th Court. 5. Installation of 8"water mains in the interior streets of the plat to serve the domestic water meters and fire hydrants are required. Response: Completed with 8-inch mains shown on the water plan, Sheet W l. 7797.006[RJA/jss/ca] 6. Connection to the 8"stub along the north property line is required(see plan W-2038). Response: Completed on the water plan, Sheet W I. 7. Connection to the existing 6"water main n Jones Avenue S is required(see plan W-1156). The water conceptual utility plan shall be revised to show this connection. Response: Completed on the water plan, Sheet W I. 8. Water System Development charges of$850.00 per new single family lot will be required for this. The charge for this plan would be $48,450.00. This fee must be paid prior to issuance of the construction permit for the preliminary plat. Response: Acknowledged as a final plat item. Plan Review-Stormwater Drainage 1. A conceptual drainage plan and drainage report was submitted with the preliminary plat application for this project and appears to be in order. Response: Acknowledged. 2. Drawings submitted to the City of Renton are to be on 22 inch x 34 inch sheets. The information pertaining to the City of Renton should be removed from the title block of the sheets submitted. Response: Completed. 3. Before any construction or development activity occurs, a pre-construction meeting must be held with the City ofRenton Development Services Division, Construction Services(425- 277-5570). Response: Acknowledged as a construction item. 4. The City of Renton retains the right to restrict the timing of land clearing and tree cutting activities to specific dates and/or seasons when such restrictions may be necessary for the public health, safety, and welfare, or for the protection of the environment. Response: Acknowledged. The applicant is requesting an early clearing and grading permit for approval of the grading and erosion control plan prior to approval of the road and utility plans. 5. Surface Water System Development charges of$385 per new single family lot will be required for this plat. The fee for this project would be$21,945.00. This fee must be paid prior to issuance of the construction permit for the preliminary plat. Response: Acknowledged as a final plat item. 7797.006[RJA/jss/ca] Plan Review- Transportation and Street Improvements 1. All electrical and communication facilities to be underground behind the sidewalk. If right- of-way space is not available, then in a utility easement. Construction of these franchise utilities must be inspected and approved by a City of Renton public works inspector prior to recording of the plat. Response: Acknowledged. The horizontal control plan,Sheet R1,provides a 10-foot-wide utility easement across all lots adjacent to right-of-way for the underground power, telephone, natural gas, and cable television. The street lighting has been designed on Sheet R9 and provides underground power service to the street lights. 2. Streets over 700 feet in length are required to have two means of access. Response: Emergency access is provided over Tract D for connection to Beacon Way S.E. The final layout is identical to the approved preliminary plat layout for the roads. 3. Street lighting is required to meet City standards. Minimum lighting level is 6:1 uniformity ratio and 0.2 foot candle level. The street lighting conduit to be located under the sidewalk. Response: Completed. The street lighting design is on Sheets R9,R10,and RI I. 4. The minimum right-of-way width is 42 feet(modified from street standard width of 50feet). Response: Completed. The road section is shown on Sheet R4 with 42 feet of right-of-way. 5. The cul-de-sac is required to have a minimum pavement radius of 45 feet and right-of-way radius of 55 feet. Response: The cul-de-sac has been designed with 50-foot radius at face-of-curb and 55-foot radius at right-of-way line. 6. A 5 foot sidewalk at the curb is required. Response: Completed. The road section on Sheet R4 shows that the 5-foot sidewalk width is provided between face-of-curb and back-of-sidewalk. 7. Payment of a Transportation Mitigation fee of$75 per new average weekday trip,estimated at 9.55 new trips per single family lot,will be required prior to recording of the plat.It has been estimated that this 57lotplat would result in approximately 544.35 additional average (weekday)trips. The Transportation Mitigation Fee would be$40,826:25. Response: Acknowledged as a final plat item. Plan Review-General 7797.006[RJA/jss/ca] 1. All required utility,drainage,and street improvements will require separateplan submittals prepared according to City of Renton drafting standards by a registered Civil Engineer. Response: Completed. The plans have been submitted to the City of Renton with separate plan sets for road,drainage,and street lights(R Sheets),water(W Sheets),sanitary sewer (S Sheets),and grading and erosion control(T Sheets). 2. The construction permit application(s) must include an itemized cost estimate for these improvements. Response: Completed. The permit application included the itemized cost estimate. 3. The fee for review and inspection of these improvements is 5 percent of the first$1000,000 of the estimated construction costs; 4 percent of anything over $100,000, but less than $200,000, and 3 percent of anything over$200,000. Half of this fee must be paid upon application for construction permit(preliminary plat improvements), and the remainder when the construction permit is issued. There maybe additional fees for water service related expenses. Response: Completed. The permit fee for the submittal has been paid. 4. An easement that meets City standards for ingress, egress, and utilities shall be provided by the applicant to theproperty abutting the eastproperty boundary at a point with 200feet of the northeast property corner of the proposed plat. Response: Completed as shown on the horizontal control plan, Sheet RI. Parks Department Review 1. Payment of a Parks Mitigation fee of$53076for each new single family lot will be required prior to recording of the plat. The Parks fee will be$30,253.32. Response: Acknowledged as a final plat item. Building Department Review 1. Demolition permits will be required. Response: Not applicable. There are no existing buildings on the property. Fire Prevention Department Review 1. Afire hydrant with 1000 GPMfire flow is required within 300 feet of all new single family structures.Ifthe building squarefootage exceeds 3600squarefeet in area,the minimum fire flow increases to 1500 GPM and requires two hydrants within 300 feet of the structure. Response: The water plan, Sheet W1,provides three fire hydrants that meet the spacing requirement and 8-inch water mains to convey the required fire flow. 7797.006[RJA/jss/ca] 2. Provide a 20 foot paved secondary emergency access from the cul-de-sac within the development to the Seattle Public Utilities Cedar River Pipeline Easement(Beacon Way SE). This would be an emergency access only and can be gated or chained. Response: Completed as shown on the road and drainage plan, Sheet R2, and the emergency access pavement section shown on Sheet R3. We have provided a gate at the west end of the tract along Beacon Way S.E. and a chain at the east end of the tract at the cul-de-sac. 3. All building addresses shall be visible from a public street. Response: Acknowledged as a building permit item. 4. A Fire Mitigation fee of$488 is required for all new single family lots. Payment is required prior to recording of the plat. The Fire Mitigation fee for the proposed project would be $27,816.00. Response: Acknowledged as a final plat item. Property Services Department Review 1. Comments will be provided under separate cover. Response: Acknowledged. Development Services Department Review 1. The site is designated Residential Single Family in the Comprehensive Plan. Response: Acknowledged. 2. The property is zoned Residential 8(R-8). Response: Acknowledged. 3. Densities allowed in the R-8 Zone are 5.0 dwelling units per net acre(du/a)minimum and 8.0 du/a maximum. Response: Acknowledged. 4. Minimum lot size in the R-8 Zone is 4500 sf, with minimum width of 50 for interior lots and 60 for corner lots. The minimum permitted lot depth is 65 feet. Lot dimensions must be shown on the final site plan demonstrating that all lots meets these minimums. Response: All lots have been designed to exceed 4,500 square feet and meet a minimum width of 50 feet for interior lots and 60 feet for corner lots. All lots are much greater than 7797.006[RJA/jss/ca] the minimum depth of 65 feet. The lot widths and areas are shown on the horizontal control plan, Sheet RI. 5. Heights of buildings in the R-8 zone are limited to 2 stories, or 30 feet. Response: Acknowledged as a residential building permit item. 6. Required setbacks in the R-8 Zone are 15 feet for houses and 20 feet for attached garages which access from the front when houses front streets created after September 1, 1995, 20 foot rear yard setbacks; 5 foot side yard setbacks for interior lots and 15 feet side yard setbacks for corner lots. All setbacks are minimums. Setback dimensions should be shown on the construction drawings,but setback lines must be removed prior to recording thefinal plat. Response: The required setbacks are shown on the horizontal control plan, Sheet R1. 7. The maximum building coverage in the R-8 Zone is 35 percent for lots over 5, 000 sf or 50 percent for lots 5,000 sf or less. Response: Acknowledged. For the drainage calculations,we have assumed the 50 percent maximum coverage for the buildings and an additional 20 percent impervious surface for driveways and patios to size the drainage facility. 8. Dead end streets cannot exceed 700 feet in length, measured from the edge of the connecting street to the end of the cul-de-sac. Response: Acknowledged. We have proposed Tract E as an emergency access connection from the end of the cul-de-sac to Beacon Way S.E. 9. Retaining walls in excess of four (4)feet require engineered drawings and a separate building permit. Response: Acknowledged. We have rockeries up to 6 feet in height along the east boundary of the project. 10. Construction easements obtained from abutting property owners may be necessary prior to construction of retaining walls on or near property lines. These agreements must include protection measures for(or permission to potentially damage or remove)trees located on abutting properties within 20 feet of the property line. Response: Not applicable. The project does not require construction easements from any abutting property owners. 11. The applicant shall draft and record a maintenance agreement or establish a Homeowners' Association for the maintenance ofall common improvements(access and utility easements, rights-of-way,and stormwater facilities). A draft of the document shall be submitted to the City of Renton for review and approval by the City Attorney prior to the recording of the preliminary plat. 7797.006[RJA/jss/ca] Response: Acknowledged as a final plat item. 12. Performance Standards for Land Development Permits (RMC 4-4-130K), including "Protection Measures During Construction"(RMC 4-4-130K7)relating to trees,shall be followed by the applicant. The applicant shall adhere to the definition of"tree"a found in RMC-4-11-200, "drip line"as found in RMC 4-11-040, and the measurement of trees as found in RMC 4-I1-030. Response: Not applicable. All trees on the property will be cleared for the small lot development. 13. The Washington State Department of Natural Resources may require a Forest Practices Permit for the conversion of timber land to another use. Response: Acknowledged as a construction permit item. We have sent a separate application for a FPA permit. 14. The applicant should contact Paul Alexander of The King County Department of Transportation, Metro Transportation, Metro Transit Route Facilities at 206-684-1599, regarding Metro's requirements for potential transit service in the area (no service is currently available to Renton Hill). Response: Acknowledged. We have sent a request to Metro Transit and verified that no service is currently available to Renton Hill. 7797.006[RJA/jss/ca] W O 3.0 OFF-SITE ANALYSIS A Preliminary Technical Information Report and Level 1 Downstream Analysis were prepared by Peterson Consulting Engineers,dated April 2000,for this project. The downstream analysis part of that report is contained in Section 3.1 of this TIR. We have reviewed the downstream analysis and completed a field verification at the time of final engineering design and found that conditions have not changed since the April 2000 report. The Heritage Renton Hill project will use an infiltration pond combined with individual lot rooftop infiltration systems to retain stormwater on site. The pond will be provided with an emergency overflow connection to the existing storm drainage system in Beacon Way S.E. Specifically, the pond emergency overflow will be piped to connect to existing City of Renton Catch Basin No. 17,E9-3 that is located at the northeast comer of the intersection of Beacon Way S.E.and S.E. 7th Court. This is a Type 1 Catch Basin that is 4.1 feet deep. From here,emergency overflow drainage is piped in a northwest direction along the easterly side of Beacon Way S.E. through a series of catch basins and 12-inch concrete pipes to the intersection of Beacon Way S.E.and High Avenue South to City of Renton Catch Basin No. 17,E84. Here,the drainage tightline flows north along the west side of High Avenue South through 12-inch concrete pipes to City of Renton Catch Basin No. 17,E8-6. From here, drainage flows through an 18-inch and then 16-inch HDPE tightline over the top of steep slopes down to a"bubble up"energy dissipater catch basin that is City of Renton Catch Basin No. 17,E7-1. We have obtained some as-built records from the City of Renton and included them in this section of the TIR. 7797.006[RJA/jss/cal ram♦ � �yt.�,11`�',`s�'�;a`•a:.���'�� ,1 � , .`' ♦,` `'' `' ' .,, /. ... `i ��' r 71 )•( N. rill ,Jt 1j111\\;1\L t'1\• ,\�r\�yd� (P� � : }M ✓ " '� �,�'�`. 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The City of Renton is not responsible for errors or omissions when this information is used for engineering purpose. Designers are to field verify this information. DWN DWN GRATE GRATE UPPER UPPER LOWER LOWER RAT CAN PIPE PIPE LENGTH ENGTH STREAM STRUCT PLAN TRUCTURE INDEX # TYPE CB ? ELEV EL[M] IE IE (M] IE IE (M] YPE SEP, DIAM. TYPE [M] STRUCT INDEX# FILE 53175312 17,E3-12 1 - - - - - - - S - 12 CC - - 53176311 17,F3-11 - 53175314 17,E3-14 2-48. Y 34.49 10.51 28.95 8.82 25.57 7.79 C N 10 PVC - - 53175309 17,E3-9 S-513 53175316 17,E3-16 2-48, N 35.44 10.80 29.94 9.13 26.3 8.02 C N 12 PVC - - 53175309 17,E3-9 S-513 53175317 17,E3-17 2-48. Y 35.98 10.97 30.48 9.29 29.94 9.13 C N 12 PVC - - 53175316 17,E3-16 S-513 53175318 17,E3-18 1 - 35.74 10.89 31.49 9.6 31.32 9.55 S - 12 PVC - - 53175317 17,E3-17 S-513 53175319 17,E3-19 1 - 35.05 10.68 - - - - S - - - - - 53175320 17,E3-20 S-513 53175320 17,E3-20 1 - 35.09 10.7 - - 27.22 8.3 S - 8 CC - - 53175309 17,E3-9 S-513 53175321 17,E3-21 1 - 34.52 10.52 29.89 9.11 29.71 9.06 S - 10 PVC - - 53173314 17,C3-14 S-513 53175401 17,E4-1 2 Y - - - - - - - N 10 CC - - 53174401 17,D4-1 1-3-18. 53175402 17,E4-2 2 Y - - - - - - - N 8 CC - - 53174403 17,D4-3 1-3-18. 53175403 17,E4-3 2 Y - - - - - - - N 12 CC - 53175501 17,E5-1 53175404 17,E4-4 1 - - - - - - - S - 12 CC - - 53176412 17,F4-12 53175405 17,E4-5 2 Y - - - - - - - N 30 CC - - 53175502 17,E5-2 2-3-53/1-405 D,S. V53175407 17,E4-7 1 - - - - - - - S - 12 CC - - 53175408 17,E4-8 1-1-59. 53175408 17,E4-8 - - - - - - - - S - 12 CC - - 53175409 17,E4-9 1-1-59. 53175409 17,E4-9 1 - - - - - - - S - 12 CC - - 53175410 17,E4-10 1-1-59. 53175410 17,E4-10 1 - - - - - - - S - 12 CC - - 53175411 17,E4-11 1-1-59. 53175411 17,E4-11 1 - - - - - - - S - 12 CC - - 53175310 17,E3-10 - 53175501 17,E5-1 2 Y - - - - - - - N 12 CC - - 53174503 17,D5-3 - 53175502 17,E5-2 2 Y - - - - - - N - - - - OUT OUT 1-405,D,S 5 175701 17,E7-1 2-72. N - - 124.68 38.00 - - - N - - - - OUT OUT D-2271 53175801 17,E8-1 1 - - - - - - - - - 12 CC - - 53175802 17,E8-2 - 53175802 17,E8-2 1 - = 12 CC 53175803 17,E8-3 = 53175803 17,E8-3 1 12 CC 53175804 17,E8-4 53175804 17,E8-4 2 Y 351.3 107.07 346.59 105.64 339.08 103.35 C N 12 CC - - 53175818 17,E8-18 R-2038 53175805 17,E8-5 2 Y 328.2 100.04 323.3 98.54 321.04 97.85 C N 12 CC - - 53175806 17,E8-6 R-2038 53175806 17,E8-6 2-48, N 330.1 100.62 324.86 99.02 120.17 36.63 C N 18/16. HDPE 485 147.83 53175701 17,E7-1 D-2271 175806 17,E8-6 1 - 325.9 99.35 321.04 97.85 - - C - 12 CC - - DITCH DITCH R-2038 53175807 17,E8-7 1 - 376.6 114.78 373.27 113.77 372.98 113.69 S - 12 CPEP 30.3 9.24 53175808 17,E8-8 R-2038 53175808 17,E8-8 1 - 376.7 114.81 372.98 113.69 367.4 111.98 S - 12 CPEP 27.5 8.38 53175809 17,E8-9 R-2038 53175809 17,E8-9 1 - 372.4 113.51 367,2 111.92 366.93 111.84 C - 12 CPEP 27.6 8.41 D.T.POND T.POND R-2038 53175810 17,E8-10 1 - 371.1 113.10 368.56 112.34 368.1 112.20 S - 12 CPEP 30.2 9.21 53175811 17,E8-11 R-2038 Aug , 2001 Page 7 t 5317S�-:'s 5317 STORM DRAINAGE AND OUTLET PIPE INVENTORY - SHEET 17 The inventory information for the storm drainage system was compiled from numerous sources and is the best information available at this time and should be used only for GENERAL guidance . The City of Renton is not responsible for errors or omissions when this information is used for engineering purpose. Designers are to field verify this information. DWN DWN GRATE GRATE UPPER UPPER LOWER LOWER RAT O/W PIPE PIPE LENGTH ENGTH STREAM STRUCT PLAN TRUCTURE INDEX # TYPE CB? ELEV EL(M] IE IE [M] IE IE (M] YPE SEP, DIAM. TYPE [M] STRUCT INDEX# FILE 53175811 17,E8-11 1 371.1 113.11 368 112.17 367.3 111.95 S - 12 CPEP 84 25.60 53175809 17,E8-9 R-2038 53175812 17,E8-12 CUL - - - 366.95 111.85 366.86 111.82 - - 12 CPEP 21.4 6.52 53175813 17,E8-13 R-2038 53175813 17,E8-13 2-72. N 372 113.37 366.96 111.85 366.33 111.66 C Y 12 CPEP 129.9 39.59 DITCH DITCH R-2038 53175814 17,E8-14 CUL - - - 365.79 111.49 365.28 111.34 - - 12 CPEP 21.5 6.55 53175815 17,E8-15 R-2038 53175815 17,E8-15 2 N 369.5 112.62 365.18 111.31 355.53 108.37 C Y 12 CPEP 118.1 36.00 53175816 17,E8-16 R-2038 53175816 17,E8-16 2 N 358.7 109.34 355.33 108.31 341.27 104.02 C N 12 CPEP 319.2 97.29 53175817 17,E8-17 R-2038 53175817 17,E8-17 1 - 345.8 105.39 341.27 104.02 339.08 103.35 S - 12 CPEP 15.3 4,66 53175808 17,E8-8 R-2038 �( (53175818 17,E8-18 1 - 344.3 104.94 339.08 103.35 323.3 98.54 S - 12 - - - 53175805 17,E8-5 R-2038-) 53175901 17,E9-1 1 - - - - - - - - - 8 CC - - 53175902 17,E9-2 - 53175902 17,E9-2 2 Y - - - - - - - N 8 CC - - 53175903 17,E9-3 - (53175903 17,E9-3 2 Y - - - - - - - N 12 CC - - 53175801 17,E8-1 - 53176201 17,F2-1 1 - 38.65 11.78 34.85 10.62 34 10.36 - - 12 CMP 41 12.50 53176202 17,F2-2 16-1-252 53176202 17,F2-2 RAVTO/W 39 11.89 33.5 10.21 33.4 10.18 - Y 12 CMP 15 4.57 53176203 17,F2-3 16-1-252 '53176203 17,F2-3 2 Y 37.6 11.46 32.2 9.81 31.69 9.66 - N 18 CMP 101 30.79 53176205 17,172-5 16-1-252 53176204 17,F2-4 2-54. Y - - 31.3 9.54 31.19 9.51 - N 24 CC 30 9.14 53176205 17,F2-5 16-1-355 53176205 17,F2-5 2-54. Y - - 31.19 9.51 30.07 9.17 - N 24 CC 310 94.49 53176206 17,F2-6 16-1-355 53176206 17,172-6 2-54, Y - - 30.07 9.17 29.8 9.08 - N 24 CC 75 22.86 53176207 17,172-7 16-1-355 53176208 17,F2-8 2-48. Y - - 34.3 10.45 33.4 10,18 - N 18 CC 90 27.43 53176209 17,F2-9 16-1-355 53176209 17,F2-9 2-48. Y - - 33.4 10.18 33.2 10.12 - N 18 CC 20 6.10 53176210 17,F2-10 16-1-355 53176210 17,F2-10 1 - - - 33.2 10.12 32.2 9.81 - - 18 CC 100 30.48 53176203 17,F2-3 16-1-355 53176212 17,F2-12 1 - 32.77 9.99 31.22 9.52 31.15 9.49 S - 6 STEEL - - 53176213 17,F2-13 S-513 53176213 17,F2-13 1 - 34.4 10.49 30.99 9.45 - - S - 8 STEEL - - RAIL ROAD AIL ROAD S-513 53176223 17,F2-23 1 39.83 12.14 37.95 11.57 34.38 10.48 S - 12 CC - - 53176208 17,F2-8 R-2265 53176224 17,F2-24 1 - 48.24 14.70 45.18 13.77 38.16 11.63 S - 12 CC - - 53176223 17,F2-23 R-2265 53176301 17,F3-1 1 - - - 109.97 33.52 - - - - 12 CC - - 53176302 17,F3-2 2-1-52. 53176302 17,F3-2 1 - - - - - - - - - - - - - 53176303 17,F3-3 2-1-52. 53176303 17,F3-3 2 Y - - - - - - - N - - - - 53176306 17,F3-6 2-2-103 53176304 17,F3-4 2 Y - - - - - - - N - - - - 53176305 17,F3-5 2-2-103 53176305 17,F3-5 2 Y - - - - - - N - - - - 53176303 17,F3-3 2-2-103 53176306 17,F3-6 2 Y - - - - - - - N 24 - - - 53176307 17,F3-7 2-2-103 53176307 17,F3-7 2 Y - - - - - - N 24 - - - 53176322 17,F3-22 2-3-53. 53176308 17,F3-8 1 - 38.67 11.79 36.77 11.21 36.15 11.02 - - 12 CMP 82 24.99 53176309 17,F3-9 16-1-252 Aug , 2001 Page 8 i i - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- / � ,E<C. 3s I I 7•A E / I I - S.S.M.H- No- 7- 48" ilp r APB /e // / I I STA. 8+ss:b ; 1j RIM EL.=327.2d 475 s' t I 476 AIUN 5' L E. 8"S=iAI 35 / �� #17 •`�G / / I I /E.�CV4✓t!_3i7.3S �r ,, I 8 ;''^' I.E.LE. 8'(Sw)=ovT r STA 6•83.53,ISiT. WGH A O E ,E S• yY / / / g R�: NOTE-MT. O WTX.S.7TH S7.d a S 0 a d Ati1 I / -- -ISEI -- --- AVE. 5. DATUM: usc�c ' /Nh0 / saw '. � -,- � BENCHMARK: CITY of RENTON B.M. No. zeo / > 0 6 / a,a a.-azevo , �. V CHISELED SQUARE AT BACK OF WALK INTERSECTION. S, 1. ' b Q� �/ Sit• f_.. % / ,E.¢21{ )n X I•+,, „.1 titi0 N W CORNER SOUTH 7th ST g HIGH t ELEVATION = 357.87 I l Z; �-F.rCS•EvcE i I � �O 'ilk � O h'•Y';IV' % . :...,_. / -, .I_.... . O �,'.�»_ I �A _ GRAPHIC SCALE GO // / IIc 71111 » r ro » e r P Z/ -STA.9tG 7 \j I� _- ......-• / 0• G 0 c... it P✓C PLdh it=37S SS (IN FEET) \ S.S.M.H. No. 8- 48; RIM EL.-328.Z�.-'' 7 Iee6= 20 STA. 8+43.04 I.E. 8"(NE)aiv ,%/ it PL "' I 'AS-BUILT CERTIFICATE I.E. 8-{Nw)=our .,/ I III '.35�,.. l 1 MV43Y cwrwv reQ ENE Fouzw"N"m ffm STA:7•48A5,38'RT.-BEAC ON / q - I F1gWN 16�OM y1Y A�C3LLT OF,PBD Nl/IVIr I I V•T�f I ail \ NOTE,LDd7K 0 WTX.S.7TH ST.b"' g O. 2 TO h S�tx•�ACON AVE. 0•00-BEACON A / + I I �� 0'w w s� , NOTE: 20 y olwlwzr awrwnxwa wamsrsla� \ / / 1 I' EXISTING ROADWAY STORM DRAIN LINE MUST BE PROTECTED ` t00A1�1 D'� �� I �Il'1rl / 1 III DURING CONSTRUCTION. 2" A/C PAVEMENT OVERLAY OF HIGH G,I�LAOq�I �~- / �II 'I ' AV. S. WILL BE REQUIRED IF DAMAGE OCCURS DURING CONSTRUCTION. �!I ,� 01 II , S.S.M.H. No. 6- aa' S.S.M.H. No. 5- 4e' �.: OTE- R. STA. 10+98.01 NOTE: �J ONTR-AtTOR TO COORDINA%1E`�•' l RIM EL.=3¢5.09 STA. 14+39.21 = STA. 0+00(ON-SITE $S) I O i� I I OVERLAY FULL WIDTH Of S.6TH ST.WITH TN UTILITY FOR UTILIy(.POLE �' I-E. I(E)=iu jr ewyi,,,.,_f3,3:37 2" A/C REWIRED AFTER LE. 8"(SE)=/✓ BILIZATION DUR ,•'' S' I ...1_... l _ I.E. 8"(N)=oaT _ /E�CA.R✓.tl- 4�88 $TRUCTION. ' y BACKFILL OF UTILITY LINES. (w� 3 I NOTE- O ;,A ,\ S7A83.26.39 IO'LT.-S.6TH ST. STA.4.32. 15t T.-MGH AVE.S. ' OCONTRACTTY TO COORDINAR I� 'Y�•-'' l - -- S>�./2>3s �01 ,d 5e Ttu STABILIZATION UZATIO FOR DURING ROLE \`\\ \,. �111'NIP— � _ A DURING .7 TH "n scoNsuc aa. �'\ \ I I \ N' I ,7 15).Ni R6 aQ O E` /3-�"fA 7 0 IT `l j� \ \ - EQUATI h, SO 6th ST�' � --������� " (� 'T 00 S. -a-T:Fi l `---- — -- - - —M -- _yam' �' ../E,a 3t/6.SS a STA 14+39.35 OFF-51 AN. SEWER = I Iy,,\�I HO7�E•WTX.NOT MO AS.' / "tPE,o /435 *F '�, �� g $TA. 0+00 SAW. SEWER THR LOT 11 V I I '\ ' /I - c� — — -- — — — _ — — N69.11'261M / 124Dd- 341.4' - PVC 04.83%,3+Oo -- �+•.ao._.. / - --- _ _ 0 urT ✓ I.E. 0 CROSSING_= 341.00_ AS-BUILT ;�.. 8%9'�'= TPL�C4.40% ew - �j \R1 �' tt' \R.`.�"i,ro ¢ci2r-•.. ,e' LE. O C Of�S51N� - 4 i RIGHT-OF-WAY-"' i ' Y� SEE SHEET 6 of/7 P -- F OR CONTINUATION p I \�\\ I! 'n \ ^\\ YS5 .h�P'fSr�- �- N N 6 PE�c olv6 -- _`F i I � V } \\ (1)1 V\l �I 'I II Ox+-:sue - ._ ji�.w1._!o'- p!i/L._. .-._. _ �w, R�E-#Z.oq _ __N.. ~ -a'`i2¢ I—� C.B. No. 14- TYPE I ,x�T11 \\ '�I",, I _ , j R 350 �:a A4,/Sr-TYPE I __...rE.'r 1dG•CIS -...__... ST +35, 5••RTR(ON-SITE) y� \ \ �T ,' l?• I sfa/i,+iG.7,4$'R _ I yw l 4 LOCKING LID a-- !^ ." eye !'� _..- RI A. 358.73 /l,ii�s6�=SSS,SS 1I \ I �,_. .P/MEF=35l5 77 _ /F a lwJ-lSSs3 le /L"�F�'•34/.17 I I O — 4 0 f ( A. &71T.•S.BTH ST. 8 I as7 3_ 48 34/.r7 I c O� — \ 1 I 1 C.B. No. 15A-TYPE I CITX OF RENTON -At �]EU I I t — — — — — —.� \ \\ (((I�i \��I �15°u--E_•-,y,.;p--_- STA- tt+of.5,4.3 LT. STA.4-27.88,9.45'LT.-HIGH AVE.S. RECOMMENDED DEPARTMENT OF PUBLIC WORKS NOTE,MON 8 WTX.S.7TM ST.A \I y I I ,r ._ -....,. E7(sF N+� w/SOLID LOCKING LID ,I ,;s,s_„N...s MGH AVE.5.'0•00-MGM AVE S. a��1p f/ FOR APPROVAL `QCI t* 1^ ''I l RIM EL-=3447g (OFF LE. 1fl(S N)=33fv9EX1ST.) �_c_y� S.S. & S.D. OFF—SITE PLAN I.E. 12'(E)�39o8(NEW) �.� �e RIVER RIDGE t' \ ( 1 '� yl �''• CONTRACTOR TO VERIFY LOCATION k I.E. DAM 8 13 91 �n PRIOR TO CONSTRUCTION 1 e;•` oASlct� MD rna xAvc 89041 RECOMMENDED ssn�� �� I ((I I FORAPP VAL rip L G 2 OS-gaitT-�oA!SFA✓ STePM tt� /O 29/91 n 1•-20 I t Il,� \ 1 PER REVIEW 9/27/91 ASP MLD 10/3/91 CHDc10iQ 1dD �aE rm V✓WP- .rN, \�� ��I�\�� Il�I �`l•,.1�1 \ eY`�✓ry �� rro. ac tnm er ArrR DAn Arrlm�alx smcrr 10 o►. 18 r TOP OF \ INSTALL NEW PICKET FENCE SET BACK 5'MINIMUM SLOPE ' FROM EDGE OF SLOPE SEE DETAIL 1 NEW SH 8 1 Qy (TYP. / I I 1 f PIPE ANCHOR (TYP.) ' PERMANENT SLOPE STABILIZATION AREA 525 HIGH AVENUE o APPROXIMATE SOUTH CLEARING LIMITo -�" ��0 1 SEE SPECIFICATIONS X-I{J- X/ ASPHALT! APPROXIMATE AL 1 GNMENT OF NE10 I DRIVEWAYi- _ - J GRAVEL XISTI -4NG \�l ( C r NDSCAPE 20 FT. UTILITY EASEMENT AS RECORDED I HIS AVENUE SOUTH 4-- ARK &PLAN G UNDER KING COUNTY RECORDING N0. 9202269004. _ LA KING COUNTY RECORDING NO. 9202269004. 1\�\ \ `// J \ r SK\o r R4 W - l y 7!� IP I- \ W r x / \J INS�fALL HI�NSIBILITY REINSTALL LANDSCAPE BARK/PLANTING NOTE: �� CO STRUCTI,�`,FENCE/ ALONG EDGE OF SLIDE AREA SEE NOTES 1 ' T INA71ON OF.' W THE EXISTING TOPOGRAPHIC AND PHYSICAL FEATURES SHOWN / _/ ,�\ INSTALL TEMPORA Y p --332-... 'I 1 INSTALL NEW-TYPE 11 CB(CB1p1) ' AS-UILTS AND FIE THESE PLANS LD SURVEY DATA PE BASED ON A ROVIDED BY ENTRANCO. / — I / SILT FEN E 1 (EE C. PLAN BN D BURIED TRENCH SECTION / / / / ' 1 I I I I J _-_- ` ---334- �— SEE CONNECTION DETAIL E SEE DETAIL A THIS WAS THE INFORMATION AVAILABLE AT THE TIME OF PLAN PREPARATION. ACTUAL CONDITIONS MAY BE DIFFERENT. THE CONTRACTOR MAY ENCOUNTER VARIATIONS BETWEEN ACTUAL CONDITIONS AND THOSE SHOWN. THESE VARIATIONS WILL NOT BE THE BASIS FOR A CLAIM OR EXTRA COMPENSATION. / y THE LOCATION OF EXISTING UNDERGROUND UTILITIES ARE SHOWN IN AN APPROXIMATE WAY ONLY AND HAVE NOT BEEN INDEPENDENTLY VERIFIED BY THE OWNER OR ENTRANCO. THE CONTRACTOR SHALL DETERMINE THE EXACT LOCATION OF ALL EXISTING U71U17ES BEFORE OUTLET S TUREI / COMMENCING WORK, AND AGREES 70 BE FULLY RESPONSIBLE FOR ANY SEE DETAIL C AND ALL DAMAGES WHICH MIGHT BE OCCASIONED BY THE CONTRACTOR'S APPROXIMATE FAILURE TO EXACTLY LOCATE AND PRESERVE ANY AND ALL UNDERGROUND / WETLAND BOUNDARY NAD 1983191 HORIZ. DATUM UTILITIES. I NAVD 1988 VERT. DATUM BENCHMARK - CONCRETE MOMUMENT AT INSTALL LANDSCAPE BARK ALONG FENCELINE TO MATCH EXISTING INTERSECTION OF HIGH AVE. SOUTH AND LANDSCAPING. PLANT SHRUBS 10'APART. BEACOM WAY SOUTH 358.33 FT 1 ' 1 NO VEHICLE WCCESS ! REMOVE EXITING CATCH]BASIN I f I 1 i i 1 ; I I 1 ;`3 r.• '�, �{` i1 i j EXISTING GROU4D SURFACE —340RI__--"------ -- jj III EIi 40------ EMSr ;I ti! jfjIi I I W !, y%1 �y _t r 2Q340- — r- 7 EMOVE EXIS�NG CMP/At PIPE5=.076 PE-E 18' H---PI-r- ' 2- 320 7 � 22 03 --- AS 1 LT j , E o i 1 3001 - A D I f i - + I �s• :4 N - I j --- \- —— - --- ——a —�--- -- --- - ----4*+ 300---+------ 200 B - ----- - —200 OP"b7 - 180 Li 280 i s 180 i , 260j W j 11 s0 4. <CL 8�-*'o — j 1 SOR 1 EXISTING G40UND SURFACE I 2401 "_ ! i f i I zs I I - 1 ---__—�-- a 140 v) i _ I 140 - - --' �-. ------ --- -- — �---—------ - --- — — - - - a'QAF -�---- �- -�----- ---�-----------+-------� --;------- - _.r----�- ;---------'+--- ---1 -- j-----{— i-------- 240 � ,� i s i da � - � ��� 1 � . 1 � I i 1 i 1 � •___ ' - I E i 2201 i a o i i I i ` i z` i i i i i e f -- --_1-- i - —- ---- *— -- ! _ _ t _ + 120 ==-- f I 1 1 I I I { ! j j roR IIzav I I ( i c A 1N ro� I j I ! ( j - i BY --— - -------* ----- ------ - — ______ 200 100 i -- -- ------' --- --�------�-- — —�- -- �--- --— nv �� __-- ------' -- - i — —- — —— +0 - j I NEW 18'SORI26 HDPE PIPE NEW 16 SDR 26 HDPE PIPE I i 1 -BY I 20 10 0 20 40 +50 +2 } S+I�d — - I I 1 HORIZ 1*=20' I 1 I I - I 20 10 0 20 40 1801 1 i I 1 I 1 { __ 80 CHE FOR P-Ii E i vERr' 1�`20' CITY OF RENTON --- —;-----—�— +--— —�__ - ——- ----- r - ---- -- -- -- - -- 1 -""i-"-" I I f �I I ���+�� t„`N�j+ -" T DEPARTMENT OF PUBLIC WORKS i j Dare i ,� ` � 1 HIGH AVENUE SOUTH Ej N Tj R A I N C 10 - � � DatB�L�=�' � +50 1 4 00 1 STORMWATER OUTFALL IMPROVEMENTS — -- —— ----I�— — -- ---- I---- i +sej ,73 PLAN & PROFILE LE169 1 EMNEERS SC&nSn "NMS SURVRS 160 60 I W�SHINGTON ARIZONA IyDAHO Des cNED:Bwr DATE. 7/10/96 FILE NAME,HAPPI.DW O+fOQ I �rox.L CHECNEO�JWM + i +So +7s 1+00 { +5o 1 2 00 j ; 2+i00 ; i +'0 j 1 3 SCALE, r = 20' FE.{.00{ .A.b f 1 +2s 1 1 +75 , +2s +75 , l0 3 t+zs NO. REVISION BY APPR. DATE APPROVED: SHEET, 2 OF, 4 rwC MII.I.,.n.fq w 3.1 DOWNSTREAM ANALYSIS BY PETERSON CONSULTING ENGINEERS DATED APRIL 10, 2000 h HERITAGE PHILIP ARNOLD Preliminary Technical Information Report City of Renton April 10, 2000 Prepared for: M Bennett Development Nine Lake Bellevue Dr. Suite 100-A Prepared by: Bellevue, WA 98005 Nicole McWhirter Reviewed by: , Jennifer A. Steig, P.E. �� PETERSON � ONSULTING 4030 LAKE WASH INGTON BLVD.NE,SUITE 20O EXPIRES SEPTETi6ER OB. 2QD0 KIRKLAND,WASHINGTON 98033 PCE Job No. HERM-0025 TABLE OF CONTENTS I. PROJECT OVERVIEW 1 H. CONDITIONS AND REQUIREMENTS SUMMARY 4 M. OFF-SITE ANALYSIS 6 TASK 1:STUDY AREA DEFIATHON&MAPS 6 TASK 2:RESOURCE REVIEW 6 TASK 3:FIELD INSPEC17ON 10 TASK 4:DRAINAGE SYSTEMDESCRIP7YONAND PROBLEMSCREENING 11 IV. FLOW CONTROL AND WATER QUALITY ANALYSIS AND DESIGN 13 Existing Site Hydrology 13 Developed Site Hydrology 13 Facility Design 17 V. CONVEYANCE SYSTEMS ANALYSIS AND DESIGN 22 VI. SPECIAL REPORTS AND STUDIES 22 VII. OTHER PERMITS 22 VIIL ESC ANALYSIS AND DESIGN 22 IX.BOND QUANTITIES,FACILITY SUMMARIES AND DECLARATION OF COVENANT 23 XI.OPERATIONS AND MAINTENANCE MANUAL 23 Peterson Consulting Engineers Page i Pre'"'n'laryTechnical Information Re i t for Heritage Phi11 Arnold A ri110 2000 FIGURES Figure 1: Vicinity Map Figure 2: Site Map 2 Figure 3: USGS Map 5 Figure 4: SCS Soils Map 7 Figure 5: KC Level One Table 9 Figure 6: Existing Conditions Map 12 Figure 7: Developed Conditions Map 14 15 APPENDIX Lower Cedar River Sub-Basin Lower Cedar River Basin Map Reconnaissance Report NO. 13 Sensitive Area Folio Maps(Landslide, Seismic, Erosion, Coalmine, Streams and 100-Year Floodplains and Wetlands) Biofltration Swale Worksheet—199 8 King County Surface Water Design Manual(KCS"A4) POCKET Downstream Map Peterson Consulting Engineers Page ii SEC. 20, TWP. 23 N., RGE. 5 E., W.M. PETERSON . CONSULTING II RIVER RIDvE\\ \ 4030 Lake Washington {' Blvd.N.E.,Suite 200 VOL. 163i 99-70f i I 733000 \\ Kirkland,WA 98033 s7216 J i ' \\ Tel(425) Fax(425)822-5874 x 34 Z " STORMICA7ER 43 42 41 40 39 38 37 36 35 TRACT Q i J 33 Q I ,a 'I ROAD_ sa rc 100' ` 0 100' rT >, 32 Q SCALE: 1" = 100' I I e PAW 44 45 46 47 48 49 50 31 , IIU I W I 25655 54 53 52 51 29 c I > I ( �♦ 3 � Q 28 4 4 - A, ROAD 'B' I I ♦ 5 27 ,\ I I 6 7 8 9 10 11 / I 26 / ♦♦ 25 I rL1;�C7' a37 I 16 15 14 13 12 ¢' > ICITY OF PENTON \ 24 I I I PHVP ARNOLD PARK \ QQQQQQQQQQQ I �♦ I 23 1 --—— DESIGNED 1 smo TRACT CADD R I cIfl=D I - \ 17 22 DATE 4/b/DO IFILE NAME:MHER" ( I ♦ 21 I I \ 18 1 —— I I I \ 20 1 — I I L 7RAC / w I I \ SfANP NOT VALID UNLESS SIGNED AND DATED N°',0E`HERM-0025 FIGURE 2 PAGE 5 Preliminary Technicallnformation Report for Heritage Philip Arnold April 10 2000 III. OFF-SITE ANALYSIS TASK 1:STUDYAREA DEFINITION&MAPS The 10.35-acre site is located on the northwest comer of the intersection of Beacon Way, SE 7'h Court, Jones Avenue South and South 71 Street in the City of Renton, Washington. More generally, the site is located in Section 20, Township 23 North, Range 5 East, W.M. in King County, Washington(see Figure 1: Vicinity Map on Page 2). The site is located in the Cedar River Drainage Basin, lower Cedar River Sub-basin as defined in the King County Basin Reconnaissance Program Summary Volume H. The Lower Cedar River Basin Map and a portion of the Basin Reconnaissance Report NO. 13 have been provided in the Appendix. UPSTREAM DRAINAGE ANALYSIS There is no upstream area tributary to the site see Figure 3: USGS Map on Page 7. TASK 2:RESO URCE REVIEW Community Plan The site is located in the Newcastle Community Planning Area. Adopted Basin Plan/Basin Reconnaissance Summary Report The site is located in the Cedar River Basin,Lower Cedar River Sub-basin Collection Point Area#2. Critical Drainage Area The site is not located in any of the Critical Drainage Areas as identified in the 1990 King County Surface Water Design Manual- Peterson Consulting Engineers Page 6 IN bv UPI MOM +ilia! e�\\\,� •`= ,:...:.: �� � �;/✓ � d..�milb�t 1�8�/�I®®�a'�mtr�\\U a1\-�awi—����a� ����.•m.�� �� �� Ifs. � +�� �� •� �`��`�;���f� ����� .: a' �v.,,��t1� �1 ►�,,ice. ��ry',�\,�h�,� U Tw 01, KA i11WS�_-_J1r.yam, 141 �. HIM .� � R� MI 30 • • • : NO. 1 .0 N G I N E E R S •// Preliminary Technical Information Report for Heritage Philip Arnold April 10 2000 Sensitive Area Folio The King County Sensitive Areas maps did not reveal that the site was located in hazard areas, such as, landslide, erosion and seismic. The site has been designated in a coalmine hazard area. The site does not contain any classified wetlands or streams(See Appendix for maps). SCS Soil Survey The soils on the site, per the SCS Soils mapping, are InC-Indianola Loamy Fine Sand and AgC-Alderwood Gravelly Sandy Loam; see Figure 4: SCS Soils Map on page 9. Wetlands Inventory There are no classified wetlands on-site. Peterson Consulting Engineers Page 8 iiiV 1 % UI " 'd An V aseb'Qif 1�''! ---- yGRAVEL i PIT ! Perk PC BM F�c o? • �; I; an • • �`�—� III. •,�PRh . SC D = \`/ C AkF I EvC I AkF r W AkF C M37 AkF •Rl V —testa AMIL, �1°-- �`- \ AgC - - - . • I �� .\ GAO ^r�6s '� [ \\ AgD ° SubstaiAmC�--- -°- --� ° AgC I '•�l `.,=AkF,=-:--_` PQ d \AgD 20 455 AgC vE. \ ,BeC I 1 p a e D u j AgD AgC D •d . Z D .•. Z � Sk � ,• �`J u _ AmC 0 = IBM 29 ASB 169 t203 AgC0 HERITAGE PHILIP ARNOLD FIGURE 4: SCS SOILS MAP SEC. 20, TWN. 23N, RGE. 5E D WN. B Y. DATE. JOB NO. 4030 Lake Washington ET E RS O N Blvd.NE,Suite 2000 NEM 04110100 HERM—0025 O NS U LT I NG Kirkland,WA 98033 Tel(425)827-5874 CHKD. B Y: SCALE: 2 Fax(425)822-7216 PAGE 9 �G NEM 1"=2000' k4 Preliminary Technical Information Report for Heritage Philip Arnold April 10 2000 TASK 3:FIELD INSPECTION A site visit was made on April 4, 2000, a cold rainy day. The site is currently undeveloped; generally the site is covered with meadow and grass with deciduous and evergreen trees and slopes to the northwest at 6-15 percent. Runoff'from the site and upstream area is tributary to the Cedar River. A request for drainage complaints was made to King County DDES in order to investigate past and/or present characteristics of the downstream path. The only complaint on record with the county was from 1985 (complaint# 85-1102)and has been closed for over 14 years. Peterson Consulting Engineers Page 10 Preliminary Technicallnformation Report for Heritage Philip Arnold April 10 2000 TASK 4.DRAINAGE SYSTEM DESCRIPTION AND PROBLEM SCREENING Please reference Figure 5: KC Level 1 Table on Page 12 and Downstream Map in pocket of report. Drainage from the site sheet flows to the northwest comer of the property (point A). From this point any runoff from the site would enter the existing 12" tightline system on the northwest side of Beacon Way SE (point B) approximately 120' from the property comer. This 12" tightline system continues to the northwest along Beacon Way South for approximately 400' before changing directions (point C), north, at the intersection of High Avenue South. The tightline system changes to the north at point D for approximately 260'. The pipe diameter increases from 12 to 18" at point E. The next catch basin contains the top connection for the HDPE outfall (point F). The HDPE pipe is approximately 485' in length and conveys the runoff aboveground over the steep slopes of Renton Hill to a Type 1I-72" SDMH (point G). The manhole contains a jailhouse opening for overflow. The runoff'from the manhole is conveyed via a natural swale (point H), depth and width varying, to a large pond area. Due to the depth of water an outlet was not visible, from this point it was difficult to determine where the runoff was conveyed. Peterson Consulting Engineers Page 11 `".."' " .a '---- aft r irrr+' dams, 9..r OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLE SURFACE WATER DESIGN MANUAL, CORE REQUIREMENT #2 Basin: Cedar River Subbasin Name: Lower Cedar River Subbasin Number: Symbol Drainage Drainage Slope` Distance Existing Potential Observations of field Component Type, Component frO site Problems - Problems ins ppc er, resource „.,v, Name, and Size Descriptron diecliar a "� revdwer', or resident see map Type:sheet flow,Swale, drainage basjn,:Ve0Btatlon, % Ys ml=1,320 ft. constrictions,under capacity pb�din ,� y tnbcatary a"r,'ea;I(kelihood of problem, stream channel,pipe cover depot type of sensitive overtopping;flooding;habitat or ot� nlsfttt overflow pathways,potential pond;Size:diameter, area;:vol�me " destruction;"scouying;bank slougtti�ng, , Impacts surface area sedimentatlon Inclslon''othe A Sheet Flow 6-30 0 None None No standing water observed on-site B 12" tightline system Within Beacon Way 5 120 None None SE C 12" tightline system To West side of High 5 620 None None Ave. S D 12" tightline system North 5 745 None None E 18" tightline system 5 1005 None None F Top connection for 1115 HDPE pipe G Type II-72" SDMH W/jailhouse opening 1600 None None t/a Mile point within this reach H Drainage Swale Width & depth varies 5-10 None None t N cs \ LOWER CEDAR RIVER BASIN Basin Boundary Subcatchment Boundary " Y7i Collection Point I Stream 0299 Tributary Number w 03115 Proposed Project i OItCO ' ;O Miles JUIY,1987 19 3105 .. , 20 � M tx j .3109 w d� `�e o 3121 i 1 3116 032�� i ti o03 , l 3122 1Wk x , i( ' ;d s ' SrwLIP I ~ n 41F " ii ,i Ow N 9 0. \ k Y w 3115 - 86�1TGE WgT6R O&9("':\ r�ra �L I. 22 - :3L. 12 , 311 • , .._.._.___.....I •' '' :. ...' is u ,,. a, x � .x.. v MipM V7IMy � a RECONNAISSANCE REPORT NO. 13 LOWER CEDAR CREEK BASIN JUNE 1937 Natural Resources and Parks Division and Surface Water Management Division King County, Washington King County Executive Tim Hill King County Council Audrey Gruger, District 1 Cynthia Sullivan, District 2 Bill Reams, District 3 Lois North, District 4 Ron Sims, District 5 Bruce Laing, District 6 Paul Barden, District 7 Bob Grieve, District 8 Gary Grant, District 9 Department of Public Works Parks, Planning and Resources Don LaBelle, Director Joe Nagel, Director Surface Water Management Division Natural Resources and Parks Division Joseph J. Simmler, Division Manager Russ Cahill, Division Manager Jim Kramer. Assistant Division Manager Bill Jolly, Acting Division Manager Dave Clark, Manager, River & Water Derek Poon, Chief, Resources Planning Section Resource Section Bill Eckel. Manager. Basin Planning Program Larry Gibbons. Manager, Project Management and Design Section Contributing Staff Contributing Staff Doug Chin. Sr. Engineer Ray Heller, Project Manager & Team Leader Randall Parsons, Sr. Engineer Matthew Clark. Project Manager Andy Levesque, Sr. Engineer Robert R. Fuerstenberg, Biologist & Team Leader Bruce Barker, Engineer Matthew J. Bruengo, Geologist Arny Stonkus, Engineer Lee Benda, Geologist Ray Steiger, Engineer Derek Booth, Geologist Pete Ringen, Engineer Dvanne Sheldon. Wetlands Biologist Cindy Baker, Earth Scientist Di Johnson, Planning Support Technician Robert Radek, Planning Support Technician Randal Bays, Planning Support Technician Fred Bentler. Planning Support Technician Consulting Staff Mark Hudson, Planning Support Technician Sharon Clausen, Planning Support Technician Don Spencer. Associate Geologist, Earth David Truax, Planning Support Technician Consultants, Inc. Brian Vanderbur& Planning Support Technician John Bethel, Soil Scientist, Earth Carolyn M. Byerly, Technical Writer Consultants, Inc. Susanna Hornig. Technical Writer Virginia Newman, Graphic Artist Marcia McNulty, Typesetter Mildred Miller, Typesetter Jaki Reed, Typesetter Lela Lira, Office Technician Marty Cox Office Technician P:CR TABLE OF CONTENTS I. SUMMARY 1 IL INTRODUCTION 1 III. FINDINGS IN LOWER CEDAR RIVER BASIN 2 A. Overview of Basin 2 B. Effects of Urbanization 4 C. Specific Problems 5 1. Drainage and flooding problems 5 2. Damage to property 6 3. Destruction of habitat 6 IV. RECOMMENDATIONS FOR ACTION 7 A. Reduce landslide hazards 7 B. Reduce erosion and flooding C. Prevent future erosion and flooding with appropriate analysis, g planning, and policy development D. Stop present (and prevent future) damage to habitat g by addressing specific problems in stream systems V. MAP 11 APPENDICES: APPENDIX A: Estimated Costs A-1 APPENDIX B: Capital Improvement Project Ranking B-1 APPEDDIX C: Detailed Findings and Recommendations C_1 I_ SUMMARY The Lower Cedar River Basin, in southwest King County, is unique in its development pat- terns and the associated environmental problems that appear throughout the basin. Except for the city of Renton and areas on the Cedar River Valley floor, most of the development in the basin has occurred on the upland plateaus. Most of this development is recent and primarily residential. In addition, the plateau is the site of numerous sand and gravel mining operations and, in the southern uplands, an abandoned coal mine. Peat is also being mined north of Otter Lake. In some areas livestock are being raised on small farms; there are no major crop-related agricultural activities in the basin. The effects of development are most apparent where storm drainage is routed over the valley walls. Impervious surfaces on the plateau have increased the rate and volume of storm runoff, resulting in substantial erosion, siltation, and flooding below. In addi- tion, erosion and siltation have damaged or destroyed habitat in many tributaries, threatening the survival of fish. Habitat and water quality throughout the basin are also threatened by the filling of wetlands and the presence of large amounts of domestic trash in some streams. The reconnaissance team noted that the Peterson Creek system has so far remained in its natural, nearly pristine condition. Maintaining this quality should be a high priority in future basin planning capital project programs. Recommendations in the Lower Cedar River Basin include 1) designing and constructing appropriately sized RID and other drainage facilities; 2) establishing stricter land use policies regarding floodplains, wetlands. and gravel mining; 3) _conducting more detailed and comprehensive hydraulic/hydrologic analyses of proposed developments; and 4) preventing damage to the natural drainage system. The field team also recommends 5) restoring the habitat of several tributaries (e.g., cleaning gravels, revegetating stream banks, and diversifying streambeds for spawning and rearing) as well as 6) protecting the nearly pristine quality of Peterson Creek- II. INTRODUCTION: History and Goals of the Program In 1985 the King County Council approved funding for the Planning Division (now called the Natural Resources and Parks Division), in coordination with the Surface Water Management Division, to conduct a reconnaissance of 29 major drainage basins located in King County. The effort began with an initial investigation of three basins -- Evans, Soos, and Hylebos Creeks -- in order to determine existing and potential surface water problems and to recommend action to mitigate and prevent these problems. These initial investiga- tions used available data and new field observations to examine geology, hydrology, and habitat conditions in each basin. Findings from these three basins led the King County Council to adopt Resolution 6013 in April 1936, calling for reconnaissance to be completed on the remaining 26 basins. The Basin Reconnaissance Program, which was subsequently established, is now an important ele- ment of surface water management. The goals of the program are to provide useful data with regard to 1) critical problems needing immediate solutions, 2) basin characteristics for use in the preparation of detailed basin management plans, and 3) capital costs associated with the early.resolution of drainage and problems. The reconnaissance reports are intended to provide an evaluation of present drainage con- ditions in the County in order to transmit information to policymakers to aid them in developing more detailed regulatory measures and specific capital improvement plans. They are not intended to ascribe in any conclusive manner the causes of drainage or erosion P:LC I Lower Cedar River Basin (continued) problems; instead, they are to be used as initial surveys from which choices for subsequent detailed engineering and other professional environmental analvses may be made. Due to the limited amount of time available for the field work in each basin, the reports must be viewed as descriptive environmental narratives rather than as final engineering conclusions. Recommendations contained in each report provide a description of potential mitigative measures for each particular basin; these measures might provide maximum environmental protection through capital project construction or development approval conditions. The appropriate extent of such measures will be decided on a case-by-case basis by County offi- cials responsible for reviewing applications for permit approvals and for choosing among competing projects for public construction. Nothing in the reports is intended to substitute for a more thorough environmental and engineering analysis possible on a site-specific basis for any proposal. III- FINDINGS IN LOWER CEDAR RIVER BASIN The field reconnaissance of Lower Cedar River Basin was conducted in January 1987 by Robert R. Fuerstenberg, biologist; Bruce L. Barker, engineer: and Lee Benda, geologist. Their findings and recommendations are presented here. A- Overview of Lower Cedar River Basin The lower Cedar River Basin is located in southwest King County and is 27 square miles in area. It extends southeast from the mouth of the Cedar River on Lake Washington to approximately river mile 14.0. The boundary to the northeast is marked by a ridgetop connecting the city of Renton to Webster and Franklin Lakes: the boundary to the southwest runs along Petrovitskv Road to Lake Youngs. Renton is the only incorporated area in the basin. Other population centers include Fair-wood, Maplewood Heights, and Maple Valley. Except for the city of Renton. most of the residential concentrations are located on the upland plateaus overlooking the Cedar River Valley. These upland developments are recent compared to the smaller established communities on the valley floor. The basin lies within portions of three King Countv planning areas: Newcastle in the northeast (which includes Renton), Tahoma-Raven Heights in the east, and Soos Creek (the largest of the three) in the west. Rural areas exist on the valley floor on both sides of the Lower Cedar River. from approximately river mile 5.50 to 13.00. These are limited to pastureland for horses. cows, and some sheep and several small "u-pick" fruit and vegetable farms. Similar areas are located on the southern uplands above the reach from river mile 5.50 to 7.00 and in the Lake Desire-Otter Lake area. The plateau is also the site of sand and gravel mining operations and, in the southern uplands, of the abandoned Fire King Coal Mine. Peat deposits exist west of Lake Desire and north and south of Otter Lake, and peat mining is being carried out north of Otter Lake. Present zoning allows for urban and suburban densities throughout much of the basin. particularly on the upland plateaus and in the Cedar River Valley from its mouth to appoximately river mile 6.50. Population projections for the vear 2000 in the three planninn areas containing the Lower Cedar Basin are over 311.000; an increase of 47 P:LC Lower Cedar River Basin (continued) percent from the present. Most of this growth will occur in the Soos Creek Planning Area. Dominant geological and geomorphic features. The geology of the Lower Cedar River Basin is diverse. Geological formations exposed along the valley include sedimentary rocks, undifferentiated older glacial drift, extensive ground moraine deposits, recent alluvium along the Cedar River, and landslide deposits along the river and its tribu- taries. The sedimentary rocks, composed of moderately dipping sandstones, con- glomerates, mudstones, and shales, are exposed locally along the cliffs of the Cedar River Valley near the mouth of the Cedar River. In addition, the Renton formation, composed of sandstones, mudstones, and shales with periodic deposits of coal, is also exposed along the lower portion of the Lower Cedar River Valley. Undifferentiated glacial deposits found here are composed of three or more till sheets glacio-fluvial sand and gravel, glacio-lacustrine clay, and sand, and non-glacial sand, clay and thin peat. These lie over the sedimentary rock formations and are best exposed in cross-section along the cliffs of the main valley and major tributaries. The morphology of the Lower Cedar River Basin is dominated by the valley formed by the Cedar River. Valley walls are steep cliffs formed by landslides in glacial sedi- ments. A once extensive and meandering River, which created a wide valley floor as it cut its way westward, the Cedar today is diked for most of its length through the lower valley. A narrow but extensive band of landslide deposits exists along the steep cliffs of the main river and its major tributaries. The landslide deposits consist of deformed blocks of glacial sediments and colluvium derived from slides or mass flowage, such as landslides and debris flows. Recent alluvial deposits fill the valley and major tributaries. Small, composite, alluvial debris fans exist at the mouths of the largest tributaries. Closed depressions, principally in the uplands, have lacustrine and peat deposits. The Lower Cedar River Valley has a high potential for erosion due to steep slopes and the existence of a clay laver that promotes soil failures. In addition, the confined nature of tributary channels between steep hillslopes promotes bank erosion during high flows. Numerous recent landslides are evident along cliffs of many of the steep tributaries and along the main stem of the Cedar River. These have been accelerated by the removal of vegetation and the routing of concentrated storm flows over steep slopes in areas where development has occurred. Hydrologic and hydraulic characteristics. The Cedar River Basin is composed of a complex drainage network consisting of the Cedar River and 17 tributaries. The larger tributaries begin in lakes or wetlands on the bluffs and flow through relatively flat, stable channels to the edge of the Cedar River Valley, then plunge down to the valley floor through steep, erodible ravines. Tributaries of this type such as Tributary 0304 (with headwaters at Wetland 3111) and Tributary 0323 (which begins at Lake Desire), are found on the south side of the Cedar River. Another type of tributary collects surface ninoff from urbanized areas pastureland, and wooded areas. Tributaries 0302, 0307, and 0312 are examples of this type of tributary. They are intermittent (depending on rainfall), shorter in length, flow through shallower channels that are steeper at the bluffs and transport more material during times of P:LC 3 Lower Cedar River Basin (continued) high flows. Some of the worst problems located during ' Appendix C for a full listing) c field investigation (see occur on this type of tributary. Catchments 5, 6, and 12 have very infiltrative soils. Urban developments hvae utilized R/D poinds to effectively infiltrate all urban runoff before it reaches the valley hillslopes. The infiltrated runoff then reappears as springs. Two large lakes (Desire and Otter), together with four smaller ones (Shady, Peterson. Webster, and Francis) lie in the southeast third of the basin. Numerous large wetland areas exist in this section as well. The field team identified 10 potential wetland sites that had not been previously identified in the Sensitive Areas Map Folio (SAMF). The system of lakes and wetlands in this area effectively buffers the high flows draining to these tributaries. Habitat characteristics,. With few exceptions, usable fish habitat exists only in peren- nial streams (i.e., Trib. 0302, 0304, 0305, 0323, and possibly 0303). In other streams (e.g., Trib. 0303 and 0310), steep gradients preclude fish use. Steep gradients also reduce fish use in the perennial systems (except for Trib. 0325). Habitat is in various stages of degradation in these systems; pools are being filled and gravels and debris shift regularly. In Tributary 0328 (Peterson Creek), however. habitat diversity is extensive, and the channel is not seriously degraded. At this location the field team observed at least three species of salmonoids. In general, the most diverse and least disturbed habitat in a tributary system occurs in the large wetland areas in the southeast third of the basin. Usable habitat for anadromous fish is found in the low-gradient portions of streams where channels cross the Cedar River Valley floor. In these reaches, however. only spawninghabitat is likely to be available, as the pools and woody debris necessary for successful rearing either do not exist or are quite limited. Excellent spawning and rearing areas exist where pools and riffles are extensive, instream cover and bank vegetation are intact, and diversity of habitat types is abundant. B. Effects of Urbanization in the Basin Flooding, erosion, and the degradation of habitat associated with development in the Lower Cedar River Basin are most apparent where development has eliminated vege- tation along the edges of the valley and where stormwater has been routed down channels and swales. The removal of vegetation, such as trees. above and below the edges of valley walls, as well as the discharging of stormwater over the valley wall, has resulted in tension cracks and landslides that are endangering some houses. The sedi- ments from these failures are depositing in streams and on valley floors and damaging fish habitat and private property. Discharging stormwater from increased impervious areas into steep tributary channels and swales is seriously destabilizing channels and valley walls; this in turn results in channel downcutting, bank erosion, and landslides. The sediments from these problems often degrade fish habitat and settle out on pri- vate property along the valley floor. Two serious instances of development-related erosion occurred during the November 1936 storm: 1) culverts rerouting the stream were plugged, causing the formation of a new channel that destroyed portions of roads on Tributary 0314; and 2) new, uncom- P:LC 4 Lower Cedar River Basin (continued) pacted fill adjacent to new residences near collection point 5 was washed partly away during the storm, causing landsliding and gullvin g. Future problems will be similar to these, as commercial and residential developments increase flow rates and volumes by decreasing natural storage and infiltration. This is expected to occur if wetlands on the upper plateau are encroached upon or lost (e.(, on Trib. 0304 at RM 2.30 and on Trib. 0304A at Rm 1.60). The preservation of wetlands and streambank vegetation and the attenuation of storm flows are essential in this basin. C- Specific Problems Identified The steep valley sideslopes through which streams pass and the often dense upland development result in a number of similar problems that repeat themselves throughout the Lower Cedar River Basin. The most significant of these are outlined and discussed below. L Drainage and flooding problems are often the result of several conditions: a- Undersized culverts and inadequate entrance structures_ The most notable area is on Tributary 0306 at river mile .30, where a culvert here was blocked by debris carried downstream by the stream and caused erosion and flooding of Fairwood Golf Course. The blockage was compounded by the fact that the culvert was undersized; the problem will worsen as flows increase from upstream development. b. Serious instream erosion and subsequent downstream sedimentation. These have been caused by three main factors: 1) runoff from residential developments on the bluffs above the valley, 2) compacted pastureland due to livestock, and 3) runoff from impervious areas originating at gravel pits. These problems will continue and worsen until mitigative measures are taken. (See Appendix C for specific examples.). c- Undersized rechaanclized stems. Tributaries on the valley floor are too small to carry the increased flows originating in developed residential areas along the top of the bluffs. For example, Tributary 0302 at river mile .25. the channel along Maplewood Golf Course, overtops and floods during storms. d- Construction in wetland and floodplain areas, Many of the wetlands on the south side of the Cedar River are peat bogs, and roads built through them continue to settle each year, increasing the amount of flooding on the road. For example, the road crossing with Tributary 0328B north of Lake Desire will experience more severe flooding as the road settles. e. Discharging of stormwater at the top of steep banks. At river mile 2.20 on the Cedar River, a trailer park (constructed on the edge of the cliff) discharges its drainage down the valley wall. Increased flows erode the steep valley, depositing sediments on the valley floor, blocking channels and causing flooding. These problems will eventually stabilize, but only after a large quantity of soil has been eroded. ]':LC 5 Lower Cedar River Basin (continued) 2. Damage to property is being caused by three factors: ` a. Landslides and potential landslides. Landslides are accelerated by the removal of vegetation on steep slopes in preparation for residential construction and/or by the routing of storm flows over hillslopes. For example, a large landslide has already occurred in the front yard of a resi- dence on the Cedar River at river mile 7.80. b. Sedimentation (from landslides). Sedimentation and channel and bank ero- sion are damaging private property along the valley floor (Trio. 0299 and 0310). C. Flooding during storms. Flooding has been brought on by the effects of development and associated changes to the natural drainage systems in the basin. (See "B" above.) 3. Destruction of habitat is being caused by four conditipns: a. Sedimentation of pools and riffles and cementing of gravels. These problems. the result of severe erosion and the transport of bedload material, have been caused by upland developments in the basin and the presence of associated impervious surfaces, which increase the rate and quantity of surface runoff. Sedimentation and cementing of gravels in streambeds destroy natural spawning and rearing habitat. On Tributary 0307 at river mile .40 and Tributary 0305 at river miles .95, 1.20, and 1.70. 5 recent high flows have eroded the streambed at least one foot, contributing to a serious siltation problem downstream. Heavy bedload transport is evi- dent in all systems of the basin except Tributary 0328. In Tributary 0303 at river mile .25, fine sediments are accumulating in gravels that may be used by resident fish. In Tributary 0304 between river miles .95 and 1.20. pools are being filled by sands and gravels and rearing habitat is being rapidly lost. b_ Channelization of stream beds. Loss of habitat through channelization has occurred in all the major streams of the basin, but most noticeably in those reaches that cross the valley floor. These reaches lack habitat diversity. reducing fish use for spawning and rearing. Channelization has damaged or destroyed. habitat in several reaches that were once heavily used by fish: these include Tributary 0302 between river mile .30 and 40. Tributary 0304 between river miles .05 and .18, Tributary 0305 between river mile .20 and .75. and Tributary 032,4 from river mile 1.10 to 1.40. These systems cannot afford a further reduction of habitat and still remain viable fishery resour- ces. C. The accumulation of trash in stream beds. This problem occurs in close proximity to residential areas. Trash degrades water quality and is visually unpleasant. Tires. appliances, furniture, and other trash have been thrown into Tributary 0302 at river miles 1.00 and 1.10 and in Tributary 0303 at river mile .35. P:LC 6 Lower Cedar River Basin (continued) d. Wetland encroachment_ Encroachment destroys habitat and eliminates natural water filtration and storage for surface runoff. Examples of this problem were observed on Tributary 0304 at river mile 2.30, Tributary 0308 at .80, and Tributary 0304A at river mile 1.80. Many wetlands have already been completely lost through filling, for example on Tributary 0306A at river mile .55. Suspected violations were forwarded to Building and Land Development for enforcement. rv- RECOMMF-NDATIONS FOR ACTION The primary recommendations for action in the Lower Cedar River Basin addresses current severe problems related to erosion, habitat destruction, and flooding. Prevention of these problems will be accomplished by controlling locations and densities of new development and providing adequate R/D facilities for storm water. A. Reduce landslide hazards by: I. Including sensitive areas not previously mapped on the Sensitive Areas Map Folio (SAMF). See Appendix C for a full listing of sensitive areas. 2. Establishing building setbacks along cliffs and native growth protection easements along steep ravines. 3. Discouraging or eliminating the routing of stormwater over cliffs, unless adequate tightline systems can be constructed to convey flows in a &cafe, nonerosive manner to the bottom of cliffs. 4. Decreasing peak flews by constructing larger R/D facilities to lessen the landslide and erosion occurrence along tributary slopes. B. Reduce erosion and flooding in the basin by improving surface water management: 1. Direct the Facilities Management Section of the Surface Water Management Division to evaluate existing stormActention and conveyance facilities to deter- mine whether they are properly sized to meet current standards. Evaluation should begin with all single-orifice R/D facilities. 2. Consider areas other than wetlands as regional stormActention facilities. Tributary 0300 at river mile .42 is the site for a proposed.dam, for example. 3. Utilize existing lower quality wetlands (those rated other than # 1) as regional storm-detention facilities. Wetlands 3102 and 3142 could provide more live storage, for example. 4. Review channel and culvert rapacity for conveying existing and future runoff, and establish floodplain areas in regions of slight gradient for existing and future nnoff conditions. 5. Promote the infiltration of surface water through the use of retention facilities and open channels instead of pipes where the soil and slope conditions permit. Collection points 5. 6, and 12 on plateaus have such soil conditions. P:LC 7 Lower Cedar River Basin (continued) a. On Tributary 0304: Clean streambed gravels, add habitat and bed-control weirs, and plant bank vegetation for shade. b. On Tributary 0305: Construct a new channel and move stream from road- side channel to its new location on adjacent lands. Implement a full restoration project to provide channel meanders, habitat structures, pool/riffle enhancement, streambed gravel replacement, and revegetation. C. On Tributary 0303: Move stream from present channel to a location further north, away from the roadside. If relocation is not possible, these minimum steps should be taken: Add habitat structure to existing channel with root masses, deflectors, boulder clusters, and other features; revegetate channel banks with shrubs and small trees; enhance stream crossings with bottomless pipe arches. d. On Tributary 0328 (Peterson Creek): Add habitat structure by replacing the straight, shortened channel with a more natural, meandering one: place habitat structures (such as root masses, deflectors, cover logs and boulder clusters) throughout the channel: and revegetate banks with shrubs common to adjacent riparian zones (salmonberry, ninebark, or dogwood, for example). 3. Protect the Peterson Creek system (Trib. 0328) in its present, near-pristine state. This will include not only the restoration outlined in section A above. but also the adoption of land use management regulations to prevent future habitat destruction: a. Protect all existing wetlands within the subcatchments of Peterson Creek. Employ wetland buffers at least 100 feet wide without exception. b. Restrict development in the critical headwater area (drainage, habitat, water quality) bounded by Lake Desire, Otter Lake, and Peterson Lake to rural densities C. Designate and protect streamside management zones of at least 100 feet from the ordinary high-water mark (OHWM) along the main stem of the creek. Use 25 feet from the OHWM on tributaries. d- Preserve floodplains and their forests for dynamic retention of sediments and water. e. Restrict vegetation removal in streamside/wetland management zones. f. Size RID facilities to store the 100-year storm at a two-to-five-vear release rate. Use the two-cell type of pond with a forebay, a gravel filter, and a vegetated swale outflow where feasible. g. Regulate more closely all septic tank and drain-Meld installations. as well as maintenance schedules, particularly in the Lake Desire, Otter Lake. and Peterson Lake drainage areas. P:LC 9 Lower Cedar River Basin (continued) h. Work with the State Department of Ecology to establish minimum stream_ flow requirements for Peterson Creek and Lake Desire tributary. 4. Develop and promote public education and involvement programs for basin awareness. Work with schools, environmental groups, and the civic and business communities to conduct educational and restoration programs. 5 P:LC 10 Trib. & Collect. Existing Anticipated Item River Mile Point Category Prop. Pro*. Conditions and Problems Conditions and Problems Recommendations 5 0299 13 Geology Horse farm in uplands has Continued high erosion and Develop R/D at horse farm RM 12.1 created extensive imper. sedimentation, to attenuate peak flows: vious surfaces, resulting See Project 3115. in channel scour, bank erosion, landslides, and sedimentation at mouth of basin. Residence overcome with sediment. 6 -- 13 Geology Landslide terrain for sale Site of future mass erosion. Prohibit development here. by realtozs. High risk for Notify Building and Land landslides, flooding (from Development. Add area to springs). SAMF. 7 -- 7 Geology Large-scale landsides Natural process. None. adjacent to Cedar River due to springs and cutting of toeslopes by streams. Appears to be natural. 4 -- O Geology Gullying in valley wall, Unknown. None. possibly from natural springs. 9 -- 14 Geology Landslide debris flow from Existingtension cracks Revegetate hillslope with residence on SE 147th Pl., indicate future instability. trees and shrubs. Renton. P: LC.APC . C-2 , b nib • ���� Wfi� IYP�fiIFb �� iu IN gi MIN �o.. FF • CIApr �7 A ♦ __ \� �Yp_��l� 11r3���.t�7 1!�, �'Y��17i� ���lf�'�('a►��%� .') �`l, f �� �N/�=1���►J _ M. • Grid�".i"..�� �� • ��' TMA I At �" • .Fps ►�d @ r l� Yie��® E "J RUN �r.Irr��re �oais9P.[l:i f�rttgE / �_ i'�'—� 6i... �® �r.�.�•^^=- ,� s 1 own �a al�i✓'B��ryy � [�. � a. � m .�A?YsY�QW �ef�r ..,«C.y��� nllllll� " "'�„ �f r ��" `r - Wt n ie�_ yGic�7YG M a R.Nei H CAPIRk l�Illyfll� ' �` _ � ., 1r •• , FJ. v Flo, i Cabs 1121 ro �pr.e.r• ��'� - r ar• r�� � OVON EVA .,�r• '� ��/i ' MIN � g� -0101 L��.W4 go eWill gIr 0 S s"ME w m60 s MIN y {NRgi1S�ID 7F4�.+� 1 ��w e SEE, gar, �/" f� - p--yr� I■ �Yy�p A l ��'� ► �� � �®mow �� •i- _. �' ��;,, r� � A����i���"�� �, r- �� f0 ���� a ��Grlrre�! 0 4.0 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN 4.1 Existing Site Hydrology The project site is 10.35 acres in size. The surface topography slopes from southeast to northwest at an average slope of approximately 5 percent. The elevation of the southeast corner of the site, the high point, is approximately elevation 400 and the southwest comer of the site, the low point, is approximately elevation 377. The topography of the site is rolling with small areas having slopes up to 30 percent. The existing site is undeveloped and the majority of the site is covered with a young, second growth of mixed deciduous trees. Only a few scattered evergreen trees exist on the site. The groundcover understory includes ferns, blackberries, and other low growth vegetation. The SCS Soils Maps indicate that the on-site soils are Indianola loamy fine sand(InC),classified as outwash soils by Table 3.2.2.13 in the 1998 King County Surface Water Design Manual(KCSWDM). A site-specific soils analysis has been completed by Geotech Consultants and their reports are included in Section 6.0 of this TIR. The Geotech Consultants investigations revealed a layer of topsoil over gravelly sand across the site. The northwest portion of the site has been filled in the past with a mixture of soil,concrete rubble,construction debris, and household garbage. Drainage crosses the site as overland sheetflow in a southeast to northwest direction. Drainage leaves the site as overland sheetflow and enters the tightline drainage system along Beacon Way S.E. Refer to Section 3.0 of this TIR for the downstream drainage system analysis. 4.2 Developed Site Hydrology The subject property will be developed as single-family subdivision consisting of 50 lots with public streets having curb,gutter,and sidewalk. A standard series of catch basins and underground storm drainage pipes will collect and convey drainage from the developed areas and convey the drainage to Tract A at the northwest corner of the site. Each lot will be provided with a rooftop infiltration system that will be equipped with an emergency overflow connection to the storm drainage system. Each lot will be provided with a roof drain stubout for this overflow connection. The Tract A drainage facility will consist of a basic wet pond for water quality treatment followed by an infiltration pond. The basic wet pond has been sized for the developed areas of the site excluding the rooftops that will be handled by the individual lot roof infiltration systems. The infiltration pond has been conservatively sized without credit for the rooftop infiltration systems. This approach allows infiltration distributed over the site. The infiltration pond is sized for the 100- year developed runoff for the entire site using KCRTS. The basic wet pond, which is sized for 60 percent of the 2-year storm, sizing includes the streets, driveways, and front yards, but not the rooftops because they are going into the rooftop infiltration trenches. The design infiltration rate for the pond has been determined based upon field measured infiltration rates and safety factor requirements contained in the 1998 KCSWDM. A portion of the roadway at the northwest corner of the site is too low to drain into the infiltration pond, and therefore will be served by an infiltration trench preceded by an oil/water separator vault. 4.3 Tract A Infiltration Pond Sizing 7797.006[RJA/jss/ca] �.I� 4.3 TRACT A INFILTRATION POND SIZING 4.3 Tract A Infiltration Pond Sizing The Tract A infiltration pond has been designed according to the 1998 KCSWDM. The total site area tributary to the Tract A pond is 9.82 acres. In order to be conservative,we have assumed the entire lot areas are tributary to the pond for sizing calculations without giving any credit for the rooftop infiltration systems that will be provided for each lot. The impervious coverage of streets, sidewalks,open ponds,and driveway tracts have been measured from the construction plan layout. The impervious coverage of houses and driveways on the lots have been estimated according to the maximum impervious coverage permitted by code. This complies with the 1998 KCSWDM (page 3-27). The City of Renton development code states that the maximum building coverage for the R8 zone is 50 percent. For sizing calculations,we have assumed 70 percent impervious area on lots to account for the driveway and patio in addition to the 50 percent maximum building coverage. The calculations of impervious area tributary to the Tract A pond are as follows: Total Basin Area = 9.821 Acres Impervious Area: Roads, Sidewalks,Pond,and Driveway Tracts = 2.166 Acres 50 Lots: 6.891 Acres x 70% = 4.824 Acres Total Impervious Area = 6.990 Acres Pervious Area = 9.821 Acres - 6.99 Acres = 2.831 Acres The developed site runoff has been calculated using the areas shown above with a 100-year KCRTS model according to the 1998 KCSWDM. The other component of the infiltration pond design is the infiltration rate to used. The 1998 KCSWDM(page 5-54)for measured infiltration rates requires field testing of infiltration rates. This was done by Geotech Consultants with a number of test pits within the pond area that ranged from faster than 1 inch per minute to the slowest test pit having a rate of 0.25 inches per minute. The Geotech Consultants report dated November 17,20002,recommends using a measured infiltration rate of 0.25 inches per minute. The 1998 KCSWDM(pages 5-54 and 5-55)for design infiltration rate uses an equation. We have coordinated with Geotech Consultants on this as follows: Imeasured = 0.25 inches per minute Ftesting = 0.30(EPA method used) Fgeometry = 1.00(no groundwater) Fplugging = 0.90(medium sands) Idesign = 0.25 x 0.30 x 1.0 x 0.9 = 0.0675 inches per minute The 1998 KCSWDM (page 5-55) for 100year overflow conveyance requires an additional correction factor of 0.5 if the downstream overflow route does not have capacity to convey the 100- year developed peak flow. Therefore,the design infiltration rate is adjusted as follows: 7797.006[RJA/jss/ca] Idesign = 0.0675 minutes per inch x 0.5 = 0.0338 inches per minute (this equals 29.63 minutes per inch) Given this design criteria,the pond sizing requirements are met by an infiltration pond having a depth of 5 feet,a bottom area of 9,373 square feet,and 2:1 side slopes. 7797.006[RJA/jss/ca] PVsT= EYE/ TMAL KCRTS Program...File Directory: C:\KC_SWDM\KC_DATA\ [C] CREATE a new Time Series ST 0.00 0.00 0.000000 Till Forest 0.00 0.00 0.000000 Till Pasture 0.00 0.00 0.000000 Till Grass 0.00 0.00 0.000000 Outwash Forest 0.00 0.00 0.000000 Outwash Pasture --�2.83 0.00 0.000000 Outwash Grass -F- 0.00 0.00 0.000000 Wetland -->6.99 0.00 0.000000 Impervious 7797-POST.tsf T 1.00000 T Fes- _ D e1v pEAC4411-1 s Flow Frequency Analysis Time Series File:7797-pos.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- FlowRate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 1.79 6 2/09/01 2:00 3.51 1 100.00 0.990 1.50 8 1/05/02 16:00 2.54 2 25.00 0.960 2.15 3 2/27/03 7:00 2.15 3 10.00 0.900 1.74 7 8/26/04 2:00 2.07 4 5.00 0.800 2.07 4 10/28/04 16:00 1.82 5 3.00 0.667 1.82 5 1/18/06 16:00 1.79 6 2.00 0.500 2.54 2 10/26/06 0:00 1.74 7 1.30 0.231 3.51 1 1/09/08 6:00 1.50 8 1.10 0.091 Computed Peaks 3.18 50.00 0.980 INf�Ll%lGN Retention/Detention Facility Type of Facility: Infiltration Pond Side Slope: 2.00 H:lV Pond Bottom Length: 136.92 ft Pond Bottom Width: 68.46 ft Pond Bottom Area: 9374. sq. ft Top Area at 1 ft. FB: 14879. sq. ft 0.342 acres Effective Storage Depth: 5.00 ft Stage 0 Elevation: 386.00 ft \/pLUj�VI� Storage Volume: 57803. cu. ft 1.327 ac-ft f'C)U_ VOL = 'p31 &6 610 � Vertical Permeability: 30.00 min/in Permeable Surfaces: Bottom & Sides Riser Head: 5.00 ft Riser Diameter: 12.00 inches Top Notch Weir: None Outflow Rating Curve: None Stage Elevation Storage Discharge Percolation Surf Area (ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs) (sq. ft) 0.00 386.00 0. 0.000 0.000 0.00 9374. 0.10 386.10 942. 0.022 0.000 0.44 9456. 0.20 386.20 1891. 0.043 0.000 0.44 9538. 0.30 386.30 2849. 0.065 0.000 0.45 9621. 0.40 386.40 3816. 0. 088 0.000 0.45 9705. 0.50 386.50 4790. 0.110 0.000 0.45 9788. 0.60 386. 60 5773. 0. 133 0.000 0.46 9872. 0.70 386.70 6765. 0.155 0.000 0.46 9956. 0.80 386.80 7765. 0.178 0.000 0.46 10041. 0.90 386.90 8773. 0.201 0.000 0.47 10126. 1.00 387.00 9790. 0.225 0.000 0.47 10211. 1.10 387.10 10815. 0.248 0.000 0.48 10297. 1.20 387.20 11849. 0.272 0.000 0.48 10382. 1.30 387.30 12892. 0.296 0.000 0.48 10469. 1.40 387.40 13943. 0.320 0.000 0.49 10555. 1.50 387.50 15003. 0.344 0.000 0.49 10642. 1.60 387.60 16071. 0.369 0.000 0.50 10729. 1.70 387.70 17148. 0.394 0.000 0.50 10816. 1.80 387. 80 18234. 0.419 0.000 0.50 10904. 1.90 387.90 19329. 0.444 0.000 0.51 10992. 2.00 388.00 20433. 0.469 0.000 0.51 11081. 2.10 388.10 21545. 0.495 0.000 0.52 11169. 2.20 388.20 22667. 0.520 0.000 0.52 11258. 2.30 388.30 23797. 0.546 0.000 0.53 11348. 2.40 388.40 24936. 0.572 0.000 0.53 11437. 2.50 388.50 26084. 0.599 0.000 0.53 11527. 2.60 388.60 27242. 0.625 0.000 0.54 11618. 2.70 388.70 28408. 0.652 0.000 0.54 11708. 2.80 388. 80 29583. 0.679 0.000 0.55 11799. 2.90 388.90 30768. 0.706 0.000 0.55 11891. 3.00 389.00 31961. 0.734 0.000 0.55 11982. 3.10 389.10 33164. 0.761 0.000 0.56 12074. 3.20 389.20 34376. 0.789 0.000 0.56 12166. 3.30 389.30 35598. 0. 817 0.000 0.57 12259. 3.40 389.40 36828. 0. 845 0.000 0.57 12352. 3.50 389.50 38068. 0.874 0.000 0.58 12445. 3.60 389.60 39317. 0.903 0.000 0.58 12538. 3.70 389.70 40576. 0.931 0.000 0.58 12632. 3.80 389.80 41843. 0.961 0.000 0.59 12726. 3. 90 389.90 43121. 0.990 0.000 0.59 12821. 4. 00 390.00 44408. 1.019 0. 000 0.60 12916. 4.10 390.10 45704. 1.049 0.000 0.60 13011. 4.20 390.20 47010. 1.079 0.000 0.61 13106. 4.30 390.30 48325. 1.109 0.000 0.61 13202. 4.40 390.40 49650. 1.140 0.000 0.62 13298. 4.50 390.50 50985. 1.170 0.000 0.62 13394. 4.60 390.60 52329. 1.201 0.000 0.62 13491. 4.70 390.70 53683. 1.232 0.000 0.63 13588. 4.80 390.80 55047. 1.264 0.000 0.63 13685. 4.90 390.90 56420. 1.295 0.000 0.64 13783. 5.00 391.00 57803. 1.327 0.000 0.64 13881. 5.10 391.10 59196. 1.359 0.308 0.65 13979. 5.20 391.20 60599. 1.391 0. 871 0.65 14078. 5.30 391.30 62012. 1.424 1.600 0.66 14177. 5.40 391.40 63435. 1.456 2.390 0.66 14276. 5.50 391.50 64867. 1.489 2.670 0.67 14376. 5.60 391.60 66310. 1.522 2. 930 0.67 14476. 5.70 391.70 67762. 1.556 3.160 0.67 14576. 5.80 391.80 69225. 1.589 3.380 0.68 14677. 5.90 391.90 70698. 1.623 3.590 0.68 14777. 6.00 392.00 72181. 1.657 3.780 0.69 14879. 6.10 392.10 73674. 1.691 3.970 0.69 14980. 6.20 392.20 75177. 1.726 4.140 0.70 15082. 6.30 392.30 76690. 1.761 4.310 0.70 15184. 6.40 392.40 78214. 1.796 4.470 0.71 15287. 6.50 392.50 79747. 1.831 4.630 0.71 15389. 6.60 392.60 81291. 1.866 4.780 0.72 15493. 6.70 392.70 82846. 1.902 4.930 0.72 15596. 6.80 392.80 84411. 1.938 5.070 0.73 15700. 6.90 392.90 85986. 1.974 5.210 0.73 15804. 7.00 393.00 87571. 2.010 5.350 0.74 15908. Hyd Inflow Outflow Peak Storage Target Calc Stage Elev (Cu-Ft) (Ac-Ft) 1 3.51 0.00 0.04 5.01 391.01 58000. 1.332 2 2.54 ******* 0.00 1.94 387.94 19794. 0.454 3 2.15 ******* 0.00 2.81 388.81 29721. 0.682 4 2.07 ******* 0.00 1.96 387. 96 20041. 0.460 5 1.82 ******* 0.00 3.65 389.65 40007. 0.918 6 1.79 ******* 0.00 4.06 390.06 45194. 1.038 7 1.74 ******* 0.00 1.24 387.24 12302. 0.282 8 1.50 ******* 0.00 1.08 387.08 10631. 0.244 ---------------------------------- Route Time Series through Facility Inflow Time Series File:7797-pos.tsf Outflow Time Series File:rdout.tsf Inflow/Outflow Analysis 3.2.2 KCRTS/RUNOFF FILES METHOD—GENERATING TIME SERIES • All onsite,predevelopment forest/shrub cover and all offsite forest/shrub cover is defined as"forest," irrespective of age. Post-development onsite land use is defined as forested only if forested areas are in a sensitive area buffer or are otherwise protected and will have a minimum 80%canopy cover within 5 years. In urban areas,unprotected onsite forest cover should be treated as either pasture or grass in the post-development analysis. In rural areas,unprotected forest cover should be assumed 50%grass,50%pasture. • The HSPF grass parameters were developed by the USGS study of regional hydrology and have generally been interpreted as providing the hydrologic response for"urban"grasslands(lawns,etc.), which have relatively low infiltration rates and are drained effectively. The HSPF"pasture" parameters were developed by King County DNR to provide a hydrologic response intermediate to the USGS forest and grass parameters,as might be typified by ungrazed or lightly grazed pasture with good grass cover. Because it is impossible to adequately control grassland management after development,all post-development grassland should be modeled as"grass"(with the exception of unprotected forest in rural development as noted above). All predevelopment grassland should be modeled as"pasture"except for redevelopment of areas with predevelopment land use densities of 4 DU/GA or greater(which are modeled as grass). L r rAuM �oi Sr 4'j_(.00.Sf CALCULATION OF IMPERVIOUS AREA d^d 0`'` g�'�d; r, GodoroIe. 50 'Pcr �o^``.� Co �2 . Total Impervious Coverage CorSerJw(iJC 0_Ie- 70 /a dr;J@V-f --A Pablo. Table 3.2.2.1)(p.3-28) lists percent impe ious coverage for use in KCRTS analysis of existing residential areas. The tabulated figures e useful in offsite analysis that includes large developed residential areas,making a detailed s ey of impervious coverage impractical. Impervious covers osed sidentia d commercial development must be estimated for each specific pro . Impervious coverage of streets,sidewa s,hard su ace trai s,etc., s a I be taken from layouts of the proposal. Houseldriveway or building coverage shall be as follows: • For urban residential development,the assumed impervious coverage shall not be less than 4,000 square feet per lot or the maximum impervious coverage permitted by code(K.C.C.21A.12,030), whichever is less. • For rural residential development,the assumed impervious coverage shall not be less than 8,000 square feet per lot or the maximum impervious coverage permitted by code, whichever is less. • For commercial or multi-family development,impervious coverage shall be estimated from layouts of the proposal. Effective Impervious Area The net hydrologic response of an impervious area depends on whether that area is effectively connected (usually by pipes or a channel)to a storm drainage system. The impervious area that the user inputs to KCRTS is the"Effective Impervious Area"(EIA),the total impervious area multiplied by the effective impervious fraction (see Table 3.2.2.E, p. 3-28). Non-effective impervious area (i.e.,total impervious area less EIA)is assumed to have the same hydrologic response as the immediately surrounding pervious area. For example, for existing residential areas with rooftops draining to splash pads on lawns or landscaping,the non-effective portion of the roof areas would be treated as pasture for predevelopment conditions(if DU/GA<4.0)and grass for post-development conditions. Note: Credits for inf ltration/dispersion of downspouts on individual lots in proposed single family residential subdivisions are applied separately on a site-specific basis(see Note 3, Table 3.2.2.E). The effective impervious fraction can be selected from Table 3.2.2.E or determined from detailed site surveys. With the exception of figures for compacted gravel and dirt roads and parking lots,the figures in Table 3.2.2.E are average figures cited by the USGS (Dinicola, 1990). 1998 Surface Water Design Manual 9/l/98 3-27 SECTION 5.4 INFILTRATION FACILITIES the infiltration facility, and at least one test hole should reach the water table. If the water table is very deep,the test hole need not extend more than one-fourth the maximum width of the pond below the bottom of a pond,or more than 5 feet below the bottom of a tank. If there is any question-about the actual wet-season water table elevation,measurements shall be made during the period when the water level is expected to be at a maximum. Any requirements related to steep slope, landslide hazard,or other sensitive area impacts should also be addressed in the soil study. The geotechnical engineer shall provide a report stating whether the site is suitable for the proposed infiltration facility,and shall recommend a design infiltration rate(see 'Design Infiltration Rate" below). 8 MEASURED INFILTRATION RATES Infiltration rate tests are used to help estimate the maximum sub-surface vertical infiltration rate of the soil below a proposed infiltration facility (e.g.,pond or tank)or a closed depression. The tests are intended to simulate the physical process that will occur when the facility is in operation;therefore, a saturation period is required to approximate the soil moisture conditions that may exist prior to the onset of a major winter L runoff event. 05< �,ZS it c-kes f&a- r4t/vJf-e &r p Testing Procedure �.po� a&•ek P of. 17) Z000 1. Excavations shall be made to the bottom elevation of the proposed infiltration facility. The measured infiltration rate of the underlying soil shall be determined using either the EPA falling head_ percolation test rp ocedure(Design Manual- Onsite Wastewater Treatment and Disposal Systems, EPA, 1980)or the double ring infiltrometer test(ASTM D3385). 2. The test hole or apparatus shall be filled with water and maintained at depths above the test elevation for the saturation periods specified for the appropriate test. 3. Following the saturation period,the rate shall be determined in accordance with the specified test procedures, with a head of 6 inches of water. 4. The engineer shall perform sufficient tests to determine a representative infiltration rate for the site, but at least three tests shall be performed for each proposed infiltration facility site, and at least 2 tests per acre(minimum of 4 tests)shall be performed for a closed depression. 5. A minimum of two soils logs shall be obtained for each tank and for each 10,000 square feet(plan view area)of proposed pond infiltration surface area. Soils shall be logged for a minimum of 5 feet below the bottom of each proposed infiltration facility. The logs shall describe the SCS series of the. soil, indicate the textural class of the soil horizons throughout the depth of the log, note any evidence of high groundwater level(such as mottling),and estimate the maximum groundwater elevation, if within the limits of the log. 2i/D O A ESIGN INFILTRATION RATE In the past,many infiltration facilities have been built which have not performed as the designer intended. This has resulted in flooding and substantial public expenditures to correct problems. Monitoring of actual facility performance has shown that the full-scale infiltration rate is far lower than the rate determined by small-scale testing. Actual measured facility rates of 10%of the small-scale test rate have been seen. It is clear that great conservatism in the selection of design rates is needed, particularly where conditions are less than ideal. Ideally, the design infiltration rate will be determined using an analytical groundwater model to investigate the effects of the local hydrologic conditions on facility performance, but this may be excessively costly for small projects. A simplified method may be used for determining the design infiltration rate by applying correction factors to the measured infiltration rate. The correction factors account for uncertainties in testing. depth to the water table or impervious strata, infiltration receptor geometry,and long-term reductions in permeability 9/1/98 t 1998 Surface Water Design Manual 5-54 5.4.1 GENERAL REQUIREMENTS FOR INFILTRATION FACILITIES due to biological activity and accumulation of fines. Equation 5-9 has been developed to account for these factors. This equation estimates the maximum design infiltration rate(Idesign)i additional reduction in rate beyond that produced by the equation may be appropriate. Note that the design infiltration rate Ide,ign must not exceed 20 'nches/h ur. Idesign = Imeasured X Ftesting X Fgeomety X Fplugging ^ (5-9) Correction factor Fte,,ing accounts for uncertainties in the testing methods. For the PA method,Ftesting = 30 for the ASTM D3385 method,Ftesting=0.50 Fgeometn• accounts for the influence of facility geometry and depth to the water table or impervious strata on the actual infiltration rate. A shallow water table or impervious layer will reduce the effective infiltration rate of a large pond,but this will not be reflected in a small scale test. Clearly, a large pond built over a thin pervious stratum with a shallow water table will not function as well as the same pond built over a thick pervious stratum with a deep water table. Fgeometry must be between 0.25 and 1.0 as determined by e following equation: Fgeomerry=4 D/W+0.05 (5-10) where D = depth from the bottom of the proposed facility to the maximum wet-season water table or nearest impervious layer, whichever is less W = width of the facility Fpltgging accounts for reductions in infiltration rates over the long term due to plugging of soils. This factor is: • 0.7 for loams and sandy loams • 0.8 for fine sands and loamy sands • 0.9 for medium sand • 1.0 for coarse sands or cobbles,or any soil type in an infiltration facility preceded by a water quality facility. a/100-YEAR OVERFLOW CONVEYANCE An overflow route shall be identified for stormwater flows that overtop the facility when infiltration capacity is exceeded or the facility becomes plugged and fails. The overflow route must be able to safely convey the 100-year developed peak flow to the downstream conveyance system or other acceptable discharge point in accordance with conveyance requirements in Section 1.2.4. The requirement to identify and analyze a 100-year overflow pathway may be waived if(1)an additional correction factor of 0 5 r_s used m ca cu atmg a eszgn m iltration rate, (2)the facility is sized to fully infiltrate the 100-year runoff event,and (3)the facility is not bermed on any side. Intent: to address situations where the infiltration facility may be a highly permeable closed depression, such as a gravel pit, where all stormwater is infiltrated. �A r� ❑ SPILL CONTROL DEVICE (0- L All infiltration facilities must have a spill control device upstream of the facility to capture oil or other floatable contaminants before they enter the infiltration facility(see Section 4.2.1.1). If a tee section is used, the top of the riser should be set above the 100-year overflow elevation to prevent oils from entering the infiltration facility. 1998 Surface Water Design Manual 9/1/98 5-55 A DEVELOPMENT STANDARDS FOR SINGLE FAMILY RESIDENTIAL ZONING DESIGNATIONS ill (Primary and Attached Accessory Structures) o y z. . D BUILDING STANDARDS Maximum Building 2 stories and 30 ft.13 2 stories and 30 ft. 13 2 stories and 30 ft. 13 2 stories and 30 ft. ' Height" and Number of Stories, except for uses having a "Public Suffix" (P) designation14 Maximum Height for See RMC 4-4-140G. See RMC 4-4-140G. See RMC 4-4-140G. See RMC 4-4-140G. Wireless Communication F 'e Maximum Building 2% for lots 5 acres or more. 35%. 35%. G N :accessory erage 1 0 50%— Lots 5,000 50%— Lots 5,000 sq. ft. or less. ncluding primary an 5 acres. less. o buildings) 35%for lots 10,000 sq. ft. or less. On lots greater than 1 acre, an additional 5% of the total area may be used for agri- cultural buildings related to practices. EXCEPTIONS Pre-Existing Legal Lots Nothing herein shall be Nothing here in shall be Nothing herein shall be de- Nothing herein shall be determined determined to prohibit the determined to prohibit the termined to prohibit the con- to prohibit the construction of a single construction of a single fam- construction of a single struction of 1 single family family dwelling and its accessory ily dwelling and its accessory family dwelling and its dwelling and its accessory buildings on a pre-existing legal lot buildings on a pre-existing accessory buildings on a buildings on any substan- provided that all setback, lot cover- legal lot provided that all set- pre-existing legal lot pro- dard pre-existing legal lot, age, height limits and parking backs, lot coverage, height vided that all setbacks, lot provided that all setback, lot requirements for this Zone can be limits and parking require- coverage, height limits and coverage, height limits, satisfied. ments for this Zone can be parking requirements for sewer, and parking require- satisfied. this Zone can be satisfied. ments can be met. Conflicts:See RMC 4-1.080. 4.4 TRACT A WET POND SIZING 4.4 Tract A Wet Pond Sizing As previously discussed,rooftop infiltration systems will be provided on each lot. The wet pond will receive drainage from the roads,curbs,sidewalks,driveway tracts,individual lot driveways, and front yards. The wet pond will receive drainage from 115,695 square feet of impervious surface and 114,563 square feet of lawn(outwash grass). The basic wet pond requires a volume factor f=3.0. The rainfall r for the mean annual storm is 0.039 feet per Figure 6.4.LA of the 1998 KCSWDM. r 7797.006[RJA/jss/ca] Wetpond Sizing Worksheet Summary of the 1998 Surface Water Design Manual Requirements Project Name: Project Number: Step 1) Determine volume factor f. Basic size............................................. f= 3 Large size............................................. f= 4.5 Step 2) Determine rainfall R for mean annual Storm Detemine rainfall R for mean annual storm Rainfall................................................. 0.039 (feet) Step 3)Calculate runoff from mean annual storm V,= (0.9A;+ 0.25A�9+0.10Atf+0.01 kg) X R A;=tributary area of impervious surface 115,695 (sf) A,g=tributary area of till grass 0 (sf) Atf=tributary area of till forest 0 (sf) AOg =tributary area of outwash grass 114,563 (sf) R = rainfall from mean annual storm 0.039 (feet) Vr= Volume of runoff from mean annual storm 4,106 (cf) Step 4)Calculate wetpool Volume Vb =fVr f=Volume Factor 3 Vb=Volume runoff, mean annual atorm 4,106 (cf) Vr=Volume of the wetpool 12,317 (cf) Step 5) Determine wetpool dimensions a) Determine geometry of first cell Volume in first cell 4,671 (cf) Depth h 1st cell (minus sed. Storage) 4 (feet) Determine horizontal xs area at mid-depth using 1,167 (sf) A mid=Vol. 1 st cell/h Mid-width 23 (feet) Mid-length 50 (feet) Determine xs area at surface Z= Side slope length (3HA V) 3:01 3:1 recommended 2(h/2 x Z) = 12 (feet) Dimensions of top of pond adjusted for geometrics Top width 35 (feet) 7797.008.xls[DED/ca] Top length 62 (feet) Area of Top 2194 (feet) b) Determine geometry of second cell Volume in second cell 8,715 (cf) Depth h 2nd cell 5 (feet) Determine xs area at mid-depth using 1,743 (sf) A mid= Vol. 2nd cell/h Mid-width 26 (feet) Mid-length 63 (feet) Determine horizontal xs area at surface Z=Side slope length ( 31HI V) 3:01 3:1 recommended 2(h/2 x Z) = 12 (feet) Dimensions of top of pond adjusted for geometrics Top width 38 (feet) Top length 75 (feet) Area of Top 2850 (feet) Adjustment to cells (If necessary) Geometry check: Overall pond L:W at mid-depth =3:1 Pond width (mid-depth) 26 Cell 1 length (mid-depth) 50 Cell 2 length (mid-depth) 63 Pond Length (mid-depth) = Cell 1 + Cell 2 113 L mid : W mid= 4.36 Total Wetpond Surface area required= 5,044 Total Wetpond Bottom area required= 1,142 7797.008.xls[DED/ca] 6.4.1 WETPONDS—BASIC AND LARGE—METHODS OF ANALYSIS FIGURE 6.4.1.A PRECIPITATION FOR MEAN ANNUAL STORM IN INCHES(FEET) 11 ST 1.0/ LA ST 1.1 , ST 1.0 LA 0.8 LA. 0.9 1.0 LA 1.2 €Se°C i/err/ ` -r•fa r I u � q t.tlb .,btlTT Ir yv e T r 14-1 It ,� Er�• r f/� _ t 1 z '." xb.•. Y r . jam .sue. / v' `,, / n yr V r ri lJ'`a 0 y 0 tc 1 d 0 045' TAACt CYbtliT 0.47" (0.039' ) \ Incorporated Area ; .czo River/Lake 0.47" — Major Road (0.0391) 0.52" (0.043' 0.65" NOTE:Areas east of the easternmost isopluvial should use 0.65 6.56" (0.054' ) inches unless rainfall data is available for the location of interest (0.0471) 24 The mean annual stone is a conceptual stone found . by dividing the annual precipitation by the total number of stone events per year result,generates large amounts of runoff. For this application,till soil types include Buckley and bedrock soils,and alluvial and outwash soils that have a seasonally high water table or are underlain at a shallow depth(less than 5 feet)by glacial till. U.S. Soil Conservation Service(SCS)hydrologic soil groups that are classified as till soils include a few B,most C,and all D soils. See Chapter 3 for classification of specific SCS soil types. 1998 Surface Water Design Manual 9/1/98 6-69� 4.5 TRACT A INFILTRATION TRENCH SIZING 4.5 Tract A Infiltration Trench Sizing The Tract A infiltration trench has been designed according to the 1998 KCSWDM. The total site area tributary to the Tract A trench is 0.5 acres. The impervious coverage of streets and sidewalks has been measured from the construction plan layout. There are not any houses or driveways on the lots tributary to the infiltration trench. This infiltration trench is necessary because the new roadway from Station 1+16 to Station 3+50 is too low to drain into the Tract A pond. It receives drainage from 7,488 square feet of impervious road surface subject to vehicular travel. The calculations of impervious area tributary to the Tract A trench are as follows: Total Basin Area = 0.50 Acres Impervious Area: Roads and Sidewalks = 0.22 Acres Pervious Area = 0.28 Acres The developed site runoff has been calculated using the areas shown above with a 100-year KCRTS model according to the 1998 KCSWDM. The other component of the infiltration trench design is the infiltration rate to used. The 1998 KCSWDM(page 5-54)for measured infiltration rates requires field testing of infiltration rates. This was done by Geotech Consultants with a number of test pits within the trench area that ranged from faster than 1 inch per minute to the slowest test pit having a rate of 0.25 inches per minute. The Geotech Consultants report dated November 17, 20002, recommends using a measured infiltration rate of 0.25 inches per minute. The 1998 KCSWDM(pages 5-54 and 5-55)for design infiltration rate uses an equation. We have coordinated with Geotech Consultants on this as follows: IMEASURED = 0.25 inches per minute FTESCING = 0.30(EPA method used) FGEOMEMY = 1.00(no groundwater) F,,uGGING = 0.90(medium sands) IDESIGN = 0.25 x 0.30 x 1.0 x 0.9 = 0.0675 inches per minute The 1998 KCSWDM(page 5-55)for 100year overflow conveyance requires an additional correction factor of 0.5 if the downstream overflow route does not have capacity to convey the 100-year developed peak flow. The downstream drainage system does have capacity for emergency overflow from this 0.50 acres tributary to the trench. Therefore, the design infiltration rate is not adjusted. Given this design criteria,the trench sizing requirements are met by an infiltration trench having a depth of 5 feet,a width of 10 feet,and a length of 62 feet. 7797.006[RJA/jss/ca] It's-T- by TIME '5FWt-S KCRTS Program...File Directory: C:\KC_SWDM\KC_DATA\ [C] CREATE a new Time Series ST 0.00 0.00 0.000000 Till Forest 0.00 0.00 0.000000 Till Pasture 0.00 0.00 0.000000 Till Grass 0.00 0.00 0.000000 Outwash Forest 0.00 0.00 0.000000 Outwash Pasture --�0.28 0.00 0.000000 Outwash Grass �- 0.00 0.00 0.000000 Wetland --�0.22 0.00 0.000000 Impervious e, — 7797-DEV.tsf T 1.00000 I N Ft L- . Teepsz M -- PbST- DO I tzw Flow Frequency Analysis Time Series File:7797-dev.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- FlowRate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.062 5 2/09/01 2:00 --i0.125 1 100.00de- 0.990 0.047 8 1/05/02 16:00 0.081 2 25.00 0.960 0.077 3 2/27/03 7:00 0.077 3 10.00 0. 900 0.055 7 8/26/04 2:00 0.066 4 5.00 0.800 0.066 4 10/28/04 16:00 0.062 5 3.00 0.667 0.058 6 1/18/06 16:00 0.058 6 2.00 0.500 0.081 2 10/26/06 0:00 0.055 7 1.30 0.231 0.125 1 1/09/08 6:00 0.047 8 1.10 0.091 Computed Peaks 0.110 50.00 0.980 r•� t 1..._ . TIZsz N DES l ANC-'S ' Retention/Detention Facility Type of Facility: Gravel Infiltration Trench Facility Length: 62.00 ft Facility Width: 10.00 ft Facility Area: 620. sq. ft 4Q Effective Storage Depth: 5.00 ft jl AP) - 62-b SF Stage 0 Elevation: 373.00 ft Storage Volume: 930. cu. ft Vertical Permeability: -1-5,40 min/in Permeable Surfaces: Bottom Riser Head: 5.00 ft Riser Diameter: 12.00 inches Top Notch Weir: None Outflow Rating Curve: None Stage Elevation Storage Discharge Percolation (ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs) 0.00 373.00 0. 0.000 0.000 0.00 0.06 373.06 11. 0.000 0.000 0.06 0.16 373.16 30. 0.001 0.000 0.06 0.26 373.26 48. 0.001 0.000 0.06 0.36 373.36 67. 0.002 0.000 0.06 0.46 373.46 86. 0.002 0.000 0.06 0.56 373.56 104. 0.002 0.000 0.06 0.66 373.66 123. 0.003 0.000 0.06 0.76 373.76 141. 0.003 0.000 0.06 0.86 373.86 160. 0.004 0.000 0.06 0.96 373.96 179. 0.004 0.000 0.06 1.06 374.06 197. 0.005 0.000 0.06 1.16 374.16 216. 0.005 0.000 0.06 1.26 374.26 234. 0.005 0.000 0.06 1.36 374.36 253. 0.006 0.000 0.06 1.46 374.46 272. 0.006 0.000 0.06 1.56 374.56 290. 0.007 0.000 0.06 1.66 374.66 309. 0.007 0.000 0.06 1.76 374.76 327. 0.008 0.000 0.06 1.86 374.86 346. 0.008 0.000 0.06 1.96 374.96 365. 0.008 0.000 0.06 2.06 375.06 383. 0.009 0.000 0.06 2.16 375.16 402. 0.009 0. 000 0.06 2.26 375.26 420. 0.010 0.000 0.06 2.36 375.36 439. 0.010 0.000 0.06 2.46 375.46 458. 0.011 0.000 0.06 2.56 375.56 476. 0.011 0.000 0.06 2.66 375.66 495. 0.011 0.000 0.06 2.76 375.76 513. 0.012 0.000 0.06 2. 86 375.86 532. 0.012 0.000 0.06 2.96 375.96 551. 0.013 0.000 0.06 3.06 376.06 569. 0.013 0.000 0.06 3.16 376.16 588. 0.013 0.000 0.06 3.26 376.26 606. 0.014 0.000 0.06 3.36 376.36 625. 0.014 0.000 0.06 3.46 376.46 644. 0.015 0.000 0. 06 3.56 376.56 662. 0.015 0.000 0.06 3.66 376.66 681. 0.016 0.000 0.06 3.76 376.76 699. 0.016 0.000 0.06 3. 86 376. 86 718. 0.016 0.000 0.06 3.96 376.96 737. 0.017 0.000 0.06 4.06 377.06 755. 0.017 0.000 0.06 4.16 377.16 774. 0.018 0.000 0.06 4.26 377.26 792. 0.018 0.000 0.06 4.36 377.36 811. 0.019 0.000 0.06 4.46 377.46 830. 0.019 0. 000 0.06 4.56 377.56 848. 0.019 0.000 0. 06 4.66 377.66 867. 0. 020 0.000 0.06 4.76 377.76 885. 0.020 0.000 0.06 4.86 377.86 904. 0.021 0.000 0.06 4.96 377.96 923. 0.021 0.000 0.06 5.00 378.00 930. 0.021 0.000 0.06 5.10 378.10 930. 0.021 0.308 0.06 5.20 378.20 930. 0.021 0.871 0.06 5.30 378.30 930. 0.021 1.600 0.06 5.40 378.40 930. 0.021 2.390 0.06 5.50 378.50 930. 0.021 2.670 0.06 5. 60 378.60 930. 0.021 2.930 0.06 5.70 378.70 930. 0.021 3.160 0.06 5.80 378.80 930. 0.021 3.380 0.06 5.90 378.90 930. 0.021 3.590 0.06 6.00 379.00 930. 0.021 3.780 0.06 6.10 379.10 930. 0.021 3.970 0.06 6.20 379.20 930. 0. 021 4.140 0.06 6.30 379.30 930. 0.021 4.310 0.06 6.40 379.40 930. 0.021 4.470 0.06 6.50 379.50 930. 0.021 4.630 0.06 6.60 379.60 930. 0.021 4.780 0.06 6.70 379.70 930. 0.021 4.930 0.06 6. 80 379.80 930. 0. 021 5.070 0.06 6. 90 379.90 930. 0.021 5.210 0.06 7.00 380.00 930. 0.021 5.350 0.06 Hyd Inflow Outflow Peak Storage Target Calc Stage Elev (Cu-Ft) (Ac-Ft) 1 0.12 0.00 0.00 4.93 377.93 918. 0.021 2 0.08 ******* 0.00 0.50 373.50 93. 0.002 3 0.08 ******* 0.00 0.43 373.43 81. 0.002 4 0.07 ******* 0.00 0.21 373.21 40. 0.001 5 0.06 ******* 0.00 0.14 373.14 26. 0.001 6 0.06 ******* 0.00 0.06 373.06 11. 0.000 7 0.06 ******* 0.00 0.05 373.05 9. 0.000 8 0.05 ******* 0.00 0.04 373.04 8. 0.000 Route Time Series through Facility J� O D` Inflow Time Series File:7797-dev.tsf Outflow Time Series File:rdout Inflow/Outflow Analysis Peak Inflow Discharge: 0.125 CFS at 6:00 on Jan 9 in Year 8 Peak Outflow Discharge: 0.000 CFS at 10:00 on Jan 9 in Year 8 Peak Reservoir Stage: 4.93 Ft 5.4.1 GENERAL REQUIREMENTS FO INFILTRATION FACILITIES ❑ CONSTRUCTION GUIDELINES Excavation of infiltration facilities should be done with a backhoe working at"arms length"to minimize disturbance and compaction of the completed infiltration surface. If the bottom of the facility will be less than three feet below final grade,the facility area should be cordoned off so that construction traffic does not traverse the area. The exposed soil should be inspected by a soils engineer after excavation to confirm that soil conditions are suitable. Two simple staff gages for measuring sediment depth should be installed at opposite ends of the bottom of ponds. The gages can consist of 1-inch pipe driven at least one foot into the soil in the bottom of the pond,with 12 inches of the pipe protruding above grade. ❑ OFFSITE GROUNDWATER LEVEL IMPACTS Potential impacts to groundwater levels off the project site should be considered. In general,replacing vegetation with impervious cover will increase the total annual volume of runoff generated on a site. Infiltrating this runoff will tend to increase ground water recharge,which may affect groundwater levels offsite. The impacts of infiltration could include increased water to landslide hazard areas,increased groundwater resources available,increased water levels in closed depressions,and higher groundwater levels. Higher groundwater levels offsite could result in increased flooding of basements,or impaired functioning of infiltration systems resulting in surface water flooding. Evidence of offsite groundwater flooding problems should be examined during the offsite analysis required under Core Requirement#2 (see Section 1.2.2). In general,groundwater level impacts will be very difficult to reduce,and there are no specific requirements which apply in many cases. The design engineer is encouraged to consider whether there are any feasible approaches to reduce groundwater flooding impacts,such as moving facilities or changing facility geometry,retaining forest cover,minimizing impervious coverage,or fixing downstream problems. ❑ GROUNDWATER PROTECTION The protection of groundwater quality is recognized as an issue of greater concern than in the past,and groundwater protection standards are changing rapidly. Increased safeguards are often required. The applicant should check groundwater management plans for the area,as well as with local water purveyors to determine if the project lies within a wellhead or groundwater protection zone,or aquifer recharge area. The groundwater protection requirements of this manual set forth in Chapter 1 call for implementing one of the following actions when infiltrating runoff from pollution-generating surfaces: 1. Provide water quality treatment prior to infiltration as specified in Core Requirement Nand Special Requirement#5or 2. Demonstrate that the soil beneath the infiltration facility has properties which reduce the risk of groundwater contamination from typical stormwater runoff. Such properties are defined below depending on whether the project is located outside of or within a sole-source aquifer area. Sole- source aquifers are shown in the King County Comprehensive Plan(1994). Note: The soil properties given below are primarily for groundwater protection and do not necessarily satisfy other protection needs. For example,projects infiltrating runoff within a quarter-mile of a sensitive lake may still be required to provide water quality treatment to meet the resource protection needs of the sensitive lake. See Core Requirement#8(Section 1.2.8)for additional WQ requirements. _�OJJ - - cotJ fA 4ee- 1998 Surface Water Design Manual 9/1/98 5-57 1.2.8 CORE REQUIREMENT#8:WATER QUALITY 1.2.8 CORE REQUIREMENT #8: WATER QUALITY All proposed projects, including redevelopment projects, must provide water quality(WQ)facilities to E treat the runoff from new and/or replaced pollution-generating impervious surfaces and pollution- E a generating pervious surfaces. These facilities shall be selected from one of the area-specific WQ menus M described in Section 1.2.8.1 (p. 1-52) and implemented according to the applicable WQ implementation requirements in Section 1.2.8.2 (p. 1-57). Intent: To require an efficient,cost-effective level of water quality treatment tailored to the sensitivities and resource protection needs of the downstream receiving water to which the project site drains, or,in the case of infiltration,protection of the receiving groundwater system. Quip to.Applying Core Require ment:#8 3 gCore ttegatirement#8 regttues that?WQ treatment facilities be provided to relztove pollutants from runoff 3 It , ttsr � rardith nne of the four-area-specific WQ menus found in asp p4Y of rout �. ,.. � ,�tgnt �p de levels of treatment tar eted es �Caun �� led � ..� � � rty �, W¢ reagnt aTeus here are e ca on lio o ted vw`ih this matttt t}idefh �> e s - P� �!kdCemap:pocirer , �treatruent'aresiasaifet �t aa�see ntias described in WQ imp entaat�tt req uirements are the minimum re%lsztements for anal�yrng,designing, and maintarnrngWQda r es For efficient applrcatr � reZexlutremeiit#8,the following steps are recommend ' 1 Gheck the eXero anguagerpage:l-50 to determine if and/or which portions of your project , must provide,­,-,Q..Wreabxfen actlrtres per Core Requirement#8. 2. If your project is a`redevelpp ment protect,you may apply the Basic WQ menu as described on page 1752,irrespective Qfth'e�WQ,x lications Map,and proceed to Step s below. 3. Use i4 WQ Applications'Iv�ap to determine the "WQ treatment area"where your project is located.:, If this`determination can not be made from the map,a more detailed delineation of WQ treatment_ areas is available on Ki iS!.County's Geographic-lnfarmation System. 4. For the Q, Mien ea clentt>�re 'aI�t vir,determine which a p I n " x e & specific WQ menu applies to your ioeoth slnfozrztatronmecxrgn1�281`�P 12). U �r: t r s S ee � M +detetnatne thettntmi4itY'7egiiirements-for implementing water qurtjr,trea Other Important Information about Core Requirement #8 Core Requirement#8 is the primary component of an overall water quality protection strategy required by this manual. Other requirements include the following: • Core Requirement#4: Conveyance System,Spill Control Provisions, Section 1.2.4 (p. 1-40)—This provision generally applies whenever a project constructs or replaces onsite conveyance system elements that receive runoff from pollution-generating impervious surfaces. The provision requires that runoff from such impervious surfaces be routed through a spill control device prior to discharge from the project site or into a natural onsite drainage feature. • Special Requirement#4: Source Control, Section 1.3.4(p. 1-61)—This requirement applies water quality source controls from the King County Stonnwater Pollution Control Manual to those projects proposing to develop or redevelop a commercial, industrial, or multifamily site. 1998 Surface Water Design Manual 1-49 9/1/98 SECTION 1.2 CORE REQUIREMENTS • Special Requirement#5: Oil Control, Section 1.3.5 (p. 1-62)—This requirement applies special oil controls to those projects proposing to develop or redevelop a high-use site. Key Definitions • Pollution-generating impervious surface(PGIS)Definition:Those impervious surfaces considered to be a significant source of pollutants in stormwater runoff. Such surfaces include those which are subject to vehicular use46 or storage of erodable or leachable materials, wastes, or chemicals,47 and which receive direct rainfall or the run-on or blow-in of rainfall.48 Metal roofs are also considered to be PGIS unless they are treated to prevent leaching. • Pollution-generating pervious surface(PGPS)Definition:Any non-impervious surface with vegetative ground cover subject to use of pesticides and fertilizers. Such surfaces include,but are not limited to,the lawn and landscaped areas of residential or commercial sites,golf courses,parks and sports fields. ❑ EXEMPTIONS FROM CORE REQUIREMENT#8 There are five possible exemptions from the requirement to provide a formal water quality facility per Core Requirement#8: 1- Surface Area Exemption A proposed project or any threshold discharge area within a project is exempt if it meets all of the following criteria:� p( a) Less than 5,000 square feet of�new PGIS49 will he add d ANi� ���f (-7) "Q b Less thano 5,000 square feet of contiguous PGISS will be created through any combination of new and/or replaced impervious surface as part of a redevelopment project,AND c) Less than 1 acre of contiguous PGPS51 will be added and/or modified,52 OR there is a formal agreement with King County to implement a landscape management plan53 for the PGPS areas on the site(or a farm management plan in the case of an agricultural land use). 46 A surface,whether paved or not,shall be considered subject to vehicular use if it is regularly used by motor vehicles. The following are considered regularly-used surfaces roads,unvegetated road shoulders,bike lanes within the traveled lane of a roadway,driveways,parking lots,unfenced firelanes,diesel equipment storage yards;and airport runways. The following are not considered regularly-used surfaces:road shoulders primarily used for emergency parking,paved bicycle pathways,bicycle lanes adjacent to unpaved or paved road shoulders primarily used for emergency parking,fenced firelanes,and infrequently used maintenance access roads. 47 Erodable or leachable materials, wastes,or chemicals are those substances which,when exposed to rainfall,measurably alter the physical or chemical characteristics of the rainfall runoff(examples include erodable soil,uncovered process wastes, manure,fertilizers,oily substances,ashes,kiln dust,garbage dumpster leakage,etc.). as A covered parking area would be considered pollution-generating if runoff from uphill could regularly run through it,or if rainfall could regularly blow in and wet the pavement surface. The same parking area would not be included if it were enclosed by walls or if a low wall and berm prevented stormwater from being blown in or from running onto the covered area. 49 New PGIS means new impervious surface(as defined on page 1-4)that is pollution-generating. so Contiguous PGIS means a discrete patch of PGIS that is all together as opposed to being separated in different locations on the project site. As used in this and other exemptions,the intent is to apply Core Requirement#8 to those redevelopment projects that are replacing and/or adding enough impervious surface in one location to allow for opportune installation of a water quality facility. 51 Contiguous PGPS means a patch of PGPS that is all together as opposed to being separated in different locations on the project site. 52 Modified PGPS means any existing PGPS that is re-graded or re-contoured by the proposed project. 53 Landscape management plan means a King County approved plan for defining the layout and long-term maintenance of landscaping features to minimize the use of pesticides and fertilizers,and to reduce the discharge of suspended solids and other pollutants. Guidelines for preparing landscape management plans can be found in Reference Section 4-A. Submittal requirements are detailed in Section 2.3.1.4. 9/l/98 1998 Surface Water Design Manual 1-50 1.2.8 CORE REQUIREMENT#8:WATER QUALITY 2. Cost Exemption for Redevelopment Projects A redevelopment project or any threshold discharge area within a redevelopment project is exempt if it meets all of the following criteria: a) Less than$500,000 of total site improvements is proposed,AND b) Less than 5,000 square feet of new PGIS will be added,AND c) Less than 1 acre of contiguous PGPS will be added and/or modified, OR there is a formal agreement with King County to implement a landscape management plan for the PGPS areas. 3. Forested Open Space Exemption for Rural Residential Projects Any natural discharge area within a proposed rural residential project(zoned RA-2.5,RA-5,RA-10, or R-20)is exempt if all of the following criteria are met: a) At least 65% of the unsubmerged portion54 of the natural discharge area is set aside as forested open space as specified in Section 5.2.1,AND b) The runoff from roads and driveways is dispersed through at least 100 feet of native vegetation as described in Section 5.2.1,AND c) The runoff from contiguous lawn areas of 1 acre or more is dispersed through at least 25 feet of native vegetation onsite as specified in Section 1.2.8.2 (p. 1-57). 4. Standard Infiltration Exemption A proposed project or any drainage area within a project is exempt if the runoff from pollution- generating pervious and impervious surfaces is infiltrated in soils with a measured infiltration rate55 of less than or equal to 9 inches per hour,except in designated sole-source aquifer areas56 where the measured rate must be less than or equal to 2.4 inches per hour. 5. Soil Treatment Exemption A proposed project or any drainage area within a project is exempt if the runoff from pollution- generating impervious surfaces is infiltrated in soils which meet the "groundwater protection criteria" outlined below,except where the measured infiltration rate is greater than 9 inches per hour in designated sole-source aquifer areas or areas within one-quarter-mile of a sensitive lake.57 Groundwater Protection Criteria:The first 2 feet or more of the soil beneath an infiltration facility must meet one of the following specifications for general protection of groundwater: a) The soil must have a cation exchange capacity58 greater than 5 and an organic content59 greater than 0.5%,OR b) The soil must be composed of less than 25% gravel by weight with at least 75%of the soil passing the#4 sieve,and the portion passing the#4 sieve must meet one of the following gradations: • At least 50%must pass the#40 sieve and at least 2%must pass the#100 sieve, OR • At least 25%must pass the#40 sieve and at least 5%must pass the#200 sieve. 54 Unsubmerged portion means any portion outside the ordinary high water line of streams,lakes,and wetlands. s5 Measured infiltration rate shall be as measured by the EPA method or the Double Ring Infiltrameter Method(ASTM D3385). For some soils,an infiltration rate of less than 9 inches per hour may be assumed based on a soil texture determination rather than a rate measurement. For more details,see the"Groundwater Protection'requirements in Section 5.4.1. ss Sole-source aquifer areas are designated by the EPA and depicted on the Areas Highly Susceptible to Groundwater Contamination Map adopted as part of the King County Comprehensive Plan. 57 Sensitive lake is a designation applied by the County to lakes that are particularly prone to eutrophication from development- induced increases in phosphorus loading. Such lakes are identified on the Water Quality Applications Map adopted with this manual(see map pocket on inside of back cover). 59 Cation exchange capacity shall be tested using EPA Laboratory Method 9081. sOrganic content shall be measured on a dry weight basis using ASTM D2974. 1998 Surface Water Design Manual 9/1/98 1-51 SECTION 1.2 CORE REQUIREMENTS 1.2.8.1 AREA-SPECIFIC WATER QUALITY MENUS Projects subject to Core Requirement#8 must provide a facility selected from one of the four area- specific WQ treatment menus listed below,whichever applies per the threshold information detailed in this section: q EBasi:cWa�terQu�afityen USC4 M T Sensitive Lake Protection menu • Resource Stream Protection menu • Sphagnum Bog Protection menu. Exception:Redevelopment projects subject to Core Requirement#8 need only apply the Basic WQ menu as described below,regardless of where they are located. Note:A higher standard may be imposed by an adopted resource management plan through Special Requirement#1,Section 1.3.1, or the proposed project may apply a higher standard voluntarily. Intent:To apply an appropriate level of water quality treatment based on the sensitivities of receiving waters for the drainage area in which the project lies. These drainage areas are identified as WQ treatment areas on the WQ Applications Map adopted with this manual. In addition to a minimum basic standard which applies broadly to most geographic areas,special menus are provided for sites within the watersheds of sensitive lakes,regionally significant stream reaches,and sphagnum bog wetlands. Redevelopment projects may apply the Basic WQ menu for all WQ treatment areas because application of WQ treatment to these projects incrementally reduces existing pollutant loads and concentrations to all water bodies. This benefits sensitive as well as typical water bodies and Iimits the cost of stormwater treatment in areas that are already developed. 10 I BASIC WQ MENU The Basic WQ menu is primarily applied in areas of King County where a general,cost-effective level of treatment is desired and where more intensive,targeted pollutant removal is not needed to protect 5 receiving bodies. Such areas are designated by King County as Basic WQ Treatment Areas. Most Basic WQ Treatment Areas are delineated on the WQ Applications Map adopted with this manual(see the map pocket inside the back cover). The forest production zone and any other areas of unincorporated King County not shown on this map are also considered to be Basic WQ Treatment Areas. Note: The Basic WQ menu is also applied to all redevelopment projects that are subject to Core Requirement#8 regardless of the WQ treatment area in which they are located Threshold A treatment option from the Basic WQ menu shall be used to treat runoff from any of the following types H of proposed projects: e 1. A project located within a Basic WQ Treatment Area as defined above,OR s 0 2. A project located within another WQ treatment area but which does not meet the threshold for o application of the area-specific requirement for that area,OR 3. A redevelopment project located in any WQ treatment area. Treatment Goal and Options The treatment goal for facility options in the Basic WQ menu is 80%removal of total suspended solids (TSS)for a typical rainfall year,assuming typical pollutant concentrations in urban runoff.60 TSS is the 60 For evaluation purposes,typical concentrations of TSS in Seattle area runoff are between 30 and 100 mg/L(Table 1,'Water Quality Thresholds Decision Paper,'King County Surface Water Management Division,April 1994). 9/1/98 1 ace Water Design ual 1.2.8 REQ 8:WATER QUALITY beneral perfo ance indicator for basic water quality protection because it is the most obvious pollutant of concern. The Basic WQ menu includes facilities such as wetponds,combined detention/wetponds, biofiltration swales,filter strips,and sand filters. See Chapter 6 for specific facility choices and design details. Intent The Basic WQ menu is intended to be applied to both the stormwater discharges that drain to surface waters and those that infiltrate into soils which do not provide adequate groundwater rotection (see Exemptions 4 and 5 from Core Requirement#8). Overall,the 80%TSS removal objective, junction with special requirements for source control and high-use site controls,is expected to result in good stormwater quality for all but the most sensitive water bodies. Additional water quality treatment is indicated only for sensitive lakes,regionally-significant stream reaches, and sphagnum bog wetlands. ❑ SENSITIVE LAKE PROTECTION MENU The Sensitive Lake Protection menu is primarily applied in areas of King County that drain to lakes which have a combination of wa er quality characteristics and watershed development potential that makes them particularly prone to eutrop ication induced by development. Such areas are designated by King County as Sensitive Lake WQ Trea'qnent Areas and are delineated on the WQ:2Applications Map adopted with this manual (see the map pock e inside the back cover). Threshold f' A treatment option from the Sensitive ake Protection menu s 1 be used to treat runoff from any H proposed project(excluding redevelopm t projects)which is cated within a Sensitive Lake WQ s* Treatment Area as indicated on the WQ A lications Map, which discharges runoff in either of the following ways: N 1. Discharges runoff by surface flows' to the I e in qu stion,OR D 2. Infiltrates runoff in soils having high infiltrate r tes62 and located within one-quarter-mile of the lake's mean-high-water level. Notes: • If the proposed project is located within a S tsitive e WQ Treatment Area but does not meet the above threshold criteria, then the Basic W menu shal pply as detailed on page 1-52. • If a lake management plan has been pre red and adopte y King County, additional treatment and/or other water quality measures y be required as spe ' ed in the plan and pursuant to Special Requirement#1,Section 1.3.1 (p. 1- ). A list of adopted lake nagement plans is provided in Reference Section 2-B. • If the project site discharges to re than one special WQ feature(i. a sensitive lake, regionally- significant stream reach, or sph gnum bog), the following order of precedence shall apply: L Sphagnum Bog Protection enu 2. Sensitive Lake Protection menu 3. Resource Stream Protection menu. 61 Surface flow means that which travels over land or in an open or piped conveyance system. 62 High infiltration rates are those in excess of 9 inches per hour as measured by the EPA method or the Double Ring Infiltrameter method(ASTM D3385). These will typically be medium to coarse sand or gravel soil with low silt content. See Section 5.4.1 for information on measuring infiltration rates. 1998 Surface Water Design Manual 9/1/98 1-53 SECTION 1.3 SPECIAL REQUIREMENTS 1.3.5 SPECIAL REQUIREMENT #5: OIL CONTROL Projects proposing to develop or redevelop a hi h- s -si a(dgfned below)must provide oil controls in addition to any other water quality controls required by this manual. Such sites typically generate high concentrations of oil due to high traffic turnover or the frequent transfer of oil. A high-use site is any one of the following: },0&655- — � A k,Gk 0-r� • A commercial or industrial site subject to an expected average daily traffic (ADT)count equal to or greater than 100 vehicles per 1,000 square feet of gross building area,OR • A commercial or industrial site subject to petroleum storage and transfer in excess of 1,500 gallons per year,not including routinely delivered heating oil,OR P ��C' • A commercial or industrial site subject to use,storage,or maintenance of a fleet of 25 or more diesel P vehicles that are over 10 tons gross weight(trucks,buses,trains,heavy equipment,etc.),OR • A road intersection with a measured ADT count of 25,000 vehicles or more on the main roadway and 15,000 vehicles or more on any intersecting roadway,excluding projects proposing primarily pedestrian or bicycle use improvements. The oil control requirement for high-use sites applies to all sites that generate high concentrations of oil, regardless of whether the project creates new impervious surface or makes site improvements to an existing high-use site. The traffic threshold identified focuses on vehicle turnover per square foot of building area(trip generation)rather than ADT alone. This is because oil leakage is greatest when engines are idling or cooling. In general,all-day parking areas are not intended to be captured by these thresholds except for diesel vehicles, which tend to leak oil more than non-diesel vehicles. The petroleum storage and transfer stipulation is intended to address regular transfer operations such as service stations,not occasional filling of heating oil tanks. Threshold Requirement IF a proposed project either. THEN the project must treat runoff from the • develops a site which will have high-use high-use portion of the site using oil control site characteristics (defined above),OR treatment options from the High-Use menu (described below and detailed in Chapter 6). • is a redevelopment project proposing $100,000 or more of improvements to an existing high-use site. . . High-Use Menu High-use oil control options are selected to capture and detain oil and associated pollutants. The goal of treatment is to have no visible sheen for runoff leaving the facility, or to have less than 10 mg/L total petroleum hydrocarbons(TPH),depending on the BMP. Oil control options include facilities that are small,handle only a limited site area,and require frequent maintenance,as well as facilities that treat larger areas and generally have less frequent maintenance needs. Facility choices include catch basin inserts, linear sand filters,and oil/water separators. See Chapter 6 for specific facility choices and design details. Application of this Requirement For high-use sites located within a Iarger commercial center,only the impervious surface associated with the high-use portion of the site is subject to treatment requirements. If common parking for multiple businesses is provided,treatment shall be applied to the number of parking stalls required for the high-use business only. However,if the treatment collection area also receives runoff from other areas,the treatment facility must be sized to treat all water passing through it. 911/98 1998 Surface Water Design Manual 1-62 1.3.5 SPECIAL REQUIREMENT#5:OIL CONTROL High-use roadway intersections shall treat lanes where vehicles accumulate during the signal cycle, including left and right turn lanes and through lanes,from the beginning of the left turn pocket(see Figure 1.3.5.A below). If no left turn pocket exists,the treatable area shall begin at a distance equal to three car-lengths from the stop line. If runoff from the intersection drains to more than two collection areas that do not combine within the intersection, treatment may be limited to any two of the collection areas. Note: For oil control facilities to be located in public road right-of-way and maintained by King County, only coalescing plate or baffle oiUwater separators shall be used unless otherwise approved by a adjustment. Methods of Analysis The traffic threshold for the High-Use menu shall be estimated using information from Trip Generation, published by the Institute of Transportation Engineers,or from a traffic study prepared by a professional engineer or transportation specialist with experience in traffic estimation. FIGURE 1.3.5.A TREATABLE AREAS FOR HIGH-USE ROAD INTERSECTIONS t � t � t � KIN, High use area d intersection " - s ' RM .ems' A`tfi� day "`.^��" j R t 1998 Surface Water Design Manua] 9/1/98 1-63 SECTION 6.1 WATER QUALITY MENUS 6.1.1 BASIC WATER QUALITY MENU 0 �g Where applied:The Basic Water Quality menu is generally applied to areas outside the drainage basin of sensitive lakes,regionally significant stream reaches,or sphagnum bog wetlands. Redevelopment projects,irrespective of location, also apply the basic WQ menu. The Basic WQ menu applies to stormwater conveyed to surface waters as well as to groundwater unless the project is exempt from treatment per Section 1.2.8. For precise details on the application of this and other area-specific water quality menus,refer to Section 1.2.8, "Core Requirement#8:Water Quality." Treatment goal:The Basic Water Quality menu facility choices are designed to remove 80 percent of total suspended solids' (TSS)for flows or volumes up to and including the WQ design flow or volume (defined in Section 6.2.1,p. 6-17). Flows and volumes in excess of the WQ design flow or volume can be routed around the WQ facility or can be passed through untreated. Basis:The goal of 80 percent TSS removal was chosen since it provides good pollutant removal. For higher removals,there are diminishing returns,and relatively less treatment is gained for incremental increases in facility size. There are seven facility options that comprise the Basic WQ menu;any one option may be chosen to satisfy the basic WQ protection requirement. ❑ BASIC WQ OPTION 1 -BIOFILTRATION SWALE A biofiltration Swale is a long,gently sloped,vegetated ditch designed to filter pollutants from stormwater. Grass is the most common vegetation used. Design details are given in Section 6.3.1 (p.6-37). The wet biofiltration swale(see Section 6.3.2,p.6-52)is a variation of the basic biofiltration Swale for use where the longitudinal slope is slight(1 to 2 percent or less),water tables are high,or continuous low base flow is likely to result in saturated soil conditions. Under such conditions,healthy grass growth is not possible; wetland plants are used to provide the biofiltration mechanism in saturated soil conditions. The continuous inflow biofiltration Swale(see Section 6.3.3,p.6-55)may be used in situations such as roadways where water enters the swale continuously rather than at one discrete inflow point. Table 6.1.LA(below)summarizes when the biofiltration swale and its variations are to be applied. ❑ BASIC WQ OPTION 2-FILTER STRIP A filter strip is a grassy area with gentle slopes which treats stormwater runoff from adjacent paved areas before it concentrates into discrete channels;see Section 6.3.4(p.6-56)for design details. The narrow area filter strip may be used along a roadway or parking lot in limited space situations as specified in Section 6.3.5 (p.6-64). ❑ BASIC WQ OPTION 3-WETPOND Wetponds are stormwater ponds that maintain a pool of water for most of the year. Stormwater entering the pond is treated during the relatively long residence time within the pond. The sizing method used in this manual is based on a method developed by the Nationwide Urban Runoff Program(NURP). The basic wetpond has a volume three times larger than the volume of runoff from NURP's mean annual storm? See Section 6.4.1 (p. 6-67)for design details. ❑ BASIC WQ OPTION 4—WETVAULT An underground vault may be used to comply with the Basic Water Quality menu. The treatment volume is the same as for the basic wetpond; see Section 6.4.2(p.6-80)for design details. ' This goal assumes the project generates a typical level of TSS(between 30 and 100 milligrams per liter(mg/L). For projects expected to generate a higher level of TSS,such as a sand and gravel operation,a higher treatment goal may be appropriate. 2 The mean annual storm is derived from dividing the annual rainfall(in inches)by the number of storms per year. 9/1198 1998 Surface Water Design Manual 64 6.1.1 BASIC WATER QUALITY MENU ❑ BASIC WQ OPTION 5—STORMWATER WETLAND A stormwater wetland uses biological processes of plant uptake and bacterial degradation as well as physical and chemical processes and gravity settling to remove pollutants. The footprint of the stormwater wetland is sized based on the wetpond sizing,but the depth of water in the second cell is reduced to encourage plant growth; see Section 6.4.3 (p.6-86)for design details. ❑ BASIC WQ OPTION 6—COMBINED DETENTION AND WETPOOL FACILITIES This option allows the wetpond,wetvault,or stormwater wetland to be placed under the detention pond live storage. Where site conditions permit its use, this option occupies less space than separate siting of detention and water quality facilities. The basic wetpond portion of the combined facility is sized using he same method as the wetpond in Option 3;see Section 6.4.4(p. 6-92)for design details. BASIC WQ OPTION 7—SAND FILTER A sand filter is a depression or pond with the bottom made of a layer of sand. Stormwater is treated as it percolates downward through the sand layer. Sand filters treat to a higher level of TSS removal than do the other water quality facilities. Therefore,slightly less of the annual runoff volume can be treated through the sand filter and still meet the Basic WQ menu goal for TSS removal. Sand filters can be built as open ponds,underground vaults or linear perimeter trenches; see Section 6.5.2 (p.6-100)for basic and large sand filters, Section 6.5.3 (p. 6-120)for sand filter vaults,and Section 6.5.4 (p. 6-126)for linear sand filters. sand la o be installed above an infiltr and or vault to treat stormwater before it infiltrates. Presettling is required prior to sand filtration other W or G detention facility precedes the sand_._fil_ t_ er.TABLE 7:a OlaITE -`TSite Cinces Biofiltration Swale Type Flow enters at head of swale Wet biofiltration swale (Section 6.3.2, p. • Longitudinal slope 1%or less OR 6-52) • Located downstream of a Level 2 or 3 detention facility Flow enters at head of swale EITHER wet biofiltration swale (Section • Longitudinal slope between 1 and 2% 6.32), OR basic biofiltration swale • Soil saturation or base flows likely in wet season (Section 6.3.1, p.6-37), depending on site; may require underdrain or low-flow drain. Flow enters at head of swale Basic biofiltration swale (Section 6.3.1, • Longitudinal slope>_2% p. 6-37); may require low-flow drain, • Base flows may or may not be likely in wet season depending on site • Not downstream of Level 2 or 3 detention. Along a roadway or parking lot with: Continuous inflow biofiltration swale • Continuous inflow into the biofilter, OR (Section 6.3.3, p.6-55) • Numerous discrete inflows with no single inflow contributing more than about 10%of total swale flow. 1998 Surface Water Design Manual 9/l/98 6-5 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL 6.5 MEDIA FILTRATION FACILITY DESIGNS This section presents the methods,criteria,and details for analysis and design of sand filters and generic information for leaf compost filters. Specifically,the following specific facility designs are included in this section: Qand Filters—BaDuld Large,Section 6.5.2 • Sand Filter Vaults, Section 6.5.3 • Linear Sand Filters, Section 6.5.4 • Leaf Compost Filters(LCF),Section 6.5.5 The information presented for each filtration facility is organized into the following categories: 1. Methods of Analysis: Contains a step-by-step procedure for designing and sizing each facility. Information used in the procedure is based on available literature,but clarified or modified where deficiencies were identified.' 2. Design Criteria: Contains the details,specifications,and material requirements for each facility. 6.5.1 GENERAL REQUIREMENTS FOR MEDIA FILTRATION FACILITIES Presettling Requirement Filtration facilities are particularly susceptible to clogging. Presettling must therefore be provided before stormwater enters a filtration facility. This requirement may be met by any of the following: 1. A water quality facility from the Basic WQ Menu(see Section 6.1.1 for facility options). 2. A presettling pond or vault,which can be integrated as the first cell of the filtration facility,with a treatment volume equal to 0.75 times the runoff from the mean annual storm(V,.=0.75). See Section 6.4.1.1 (p.6-68)for information on computing V,. See design requirements below. Note:For the linear sand filter, use the sediment cell sizing given in the design instead of the above sizing. 3. A detention pond sized to meet the Level 2 flow control standard. Other Pretreatment Requirements 1. Sand filters not preceded by a facility that captures floatables,such as a spill control tee,must provide pretreatment to remove floatable trash and debris before flows reach the sand bed. This requirement can be met by providing a catch basin with a riser on the inlet to the sand filter(see Figure 6.5.2.C,p. 6-118). 2. For high-use sites,sand filters must be preceded by an oil control option from the High-Use menu, Section 6.1.5 (p.6-14). Design Criteria For Presettling Cells 1. If water in the presettling cell or upstream WQ facility will be in direct contact with the soil,it must be lined per the liner requirements in Section 6.2.4. Intent:to prevent groundwater contamination from untreated stormwater runoff in areas of excessively drained soils. 33 Such modifications were often based on computer modeling using the King County Runoff Time Series(KCRTS)model. Less frequently,they were based on bench-scale studies. Back-up studies are listed in Reference Section 5. 1998 Surface Water Design Manual 9/1/98 6-99 SECTION 6.5 MEDIA FILTRATION FACILITY DESIGNS 2. The presettling cell shall conform to the following: a) The length-to-width ratio shall be 3:1. Berms or baffles may be used to lengthen the flowpath. - b) The minimum depth shall be 3 feet;the maximum depth shall be 6 feet. 3. Inlets and outlets shall be designed to minimize velocity and reduce turbulence. 6.5.2 SAND FILTERS -BASIC AND LARGE A sand filter operates much like an infiltration pond(see the sand filter detail in Figure 6.5.2.A,p.6-116). However,instead of infiltrating into native soils,stormwater filters through a constructed sand bed with an underdrain system. Runoff enters the pond and spreads over the surface of the filter. As flows increase, water backs up in the pond where it is held until it can percolate through the sand. The treatment pathway "is vertical(downward through the sand)rather than horizontal as it is in biofiltration swales and filter strips. High flows in excess of the WQ treatment goal simply spill out over the top of the pond. Water that percolates through the sand is collected in an underdrain system of drain rock and pipes which directs the treated runoff to the downstream drainage system. A sand filter removes pollutants by filtration. As stormwater passes through the sand,pollutants are trapped in the small spaces between sand grains or adhere to the sand surface. Over time,soil bacteria will also grow in the sand bed,and some biological treatment may occur. To get better performance from a sand filter,the volume of water spilled over the top should be reduced. Increasing the sand thickness will not dependably improve performance. The following design procedures,requirements,and recommendations cover two sand filter sizes: a basic size and a large size. The basic sand filter is designed to meet the Basic WQ menu goal of 80%TSS removal. The large sand filter is expected to meet the Sensitive Lake Protection menu goal of 50%total phosphorus removal. Applications and Limitations A sand filter can be used in most residential,commercial,and industrial developments where site topography and drainage provide adequate hydraulic head to operate the filter. An elevation difference of about 4 feet between the inlet and outlet of the filter is usually needed to,install a sand filter. Sand filters could be easily integrated into landscape plans as areas for summer sports,such as volleyball. Landscape uses may,be somewhat constrained because the vegetation capable of surviving in sand is limited. Trees and shrubs which generate a large leaf fall should be avoided in the immediate vicinity of the filter because leaves and other debris can clog the surface of the filter. Sand filters are designed to prevent water from backing up into the sand layer(the underdrain system must drain freely). Therefore,a sand filter is more difficult to install in areas with high water tables where groundwater could potentially flood the underdrain system. Water standing in the underdrain system will also keep the sand saturated. Under these conditions,oxygen can be depleted,releasing pollutants such as metals and phosphorus that are more mobile under anoxic conditions. Because the surface of the sand filter will clog from sediment and other debris,this facility should not be used in areas where heavy sediment loads are expected. A sand filter should not be used during construction to control sediments unless the sand bed is replaced periodically during construction and after the site is stabilized. Consult the water quality menus in Section 6.1 (p. 6-3)for information on how basic and large sand filters can be used to meet Core Requirement#8. 9/l/98 1998 Surface Water Design Manual 6-100 6.5.2 SAND FILTERS—BASIC AND LARGE—METHODS OFANALYSIS 6.5.2.1 METHODS OF ANALYSIS This section presents the methods of analysis for both basic and Iarge sand filters. A sand filter is designed with two parts: (1)a temporary storage reservoir to store runoff,and(2)a sand filter bed through which the stored runoff must percolate. Usually the storage reservoir is simply placed directly above the filter,and the floor of the reservoir pond is the top of the sand bed. For this case,the storage volume also'determines the hydraulic head over the filter surface,which increases the rate of flow through the sand. Two methods are given here to size sand filters:a simple method and a detailed computer modeling method. The simple method uses standard values to define filter hydraulic characteristics for determining the sand surface area. This method is useful for planning purposes,for a first approximation to begin iterations in the detailed method,or when use of the detailed computer model is not desired or not available. The simple sizing method very often results in a larger filter than the detailed method. The detailed routing method uses the King County Runoff Time Series(KCRTS)computer model to determine sand filter area and pond size based on individual site conditions' Use of the KCRTS design method very often results in smaller filter sizes than the simple method;especially if the facility is downstream of a detention pond. Both methods include parameters for sizing either a basic or a large sand filter. Background There are several variables used in sand filter design which are similar and often confused,even by well- trained individuals. Use of these variables is explained below. The sand filter design is based on Darcy's law: Q = KiA (6-16) where Q = WQ design flow(cfs) K = hydraulic conductivity(fps) A = surface area perpendicular to the direction of flow(sf) i = hydraulic gradient(ft/ft)for a constant head and constant media depth,computed as follows: i = h+1 (6-17) 1 where h = average depth of water above filter(ft),defined for this design as d(2 d = maximum storage depth above filter(ft) l = thickness of sand media(ft) Although it is not seen directly,Darcy's law underlies both the simple and the routing design methods. V, or more correctly,I/V,is the direct input in the sand filter design. The relationship between V and K is revealed by equating Darcy's law and the equation of continuity,Q= VA. Note: When water is flowing into the ground, V is commonly called the filtration rate. It is ordinarily measured in a percolation test. 34 These flows are roughly equivalent to the WO design flows used by the Dept.of Ecology in it's 1992 stormwater management manual. The Ecology design flow is based on the peak flow predicted by the SBUH event model for 64%of the 2-year 24- hour rainfall. 1998 Surface Water Design Manual 9/1/98 6-101 SECTION 6.5 MEDIA FILTRATION FACILITY DESIGNS Specifically: Q = KiA and Q = VA so VA = KiA or V = Ki (6-18) Note that V#K—that is,the filtration rate is not the same as the hydraulic conductivity,but they do have the same units(distance per time). K can be equated to V by dividing V by the hydraulic gradient i,which is defined above in Equation(6-17). The hydraulic conductivity K does not change with head nor is it dependent on the thickness of the media,only on the characteristics of the media and the fluid. The hydraulic conductivity of 1 inch per hour(2.315 x 10-5 fps)used in this design is based on bench-scale tests of conditioned rather than clean sand. This design hydraulic conductivity represents the average sand bed condition as silt is captured and held in the filter bed. Unlike the hydraulic conductivity,the filtration rate V changes with head and media thickness,although the media thickness is constant in the sand filter design. Table 6.5.2.B on page 6-106 shows values of V for different water depths d(remember,d=2h). The KCRTS program uses the inverse of the filtration rate, 1/V,in units of minutes per inch;this is how Darcy's law is expressed in the design. The simple method is also based on IIV,but flows and areas are computed for the user in terms of acre equivalents. Thus both the simple and the KCRTS method are based on Darcy's law. The simple sizing method is different from the KCRTS method because it does not route flows through the filter. It determines the size of the filter based on the simple assumption that inflow is immediately discharged through the filter as if there were no storage volume. An adjustment factor—the 0.7 in Equation (6-19)—is applied to compensate for the greater filter size resulting from this method. Even with this adjustment factor,however,the simple method generally produces larger filter sizes than the detailed routing method. Simple Sizing Method The simple method has been developed to design sand filters that meet the required treatment volume without performing detailed modeling. Steps for the simple sizing procedure are summarized below. Step 1: Determine whether a basic or large sand filter is needed. Consult the water quality menus in Section 6.1 (p. 6-3)to determine the size of filter needed,either basic or large. Step 2:Determine the rainfall region and regional scale factor. Regional scale factors are used to account for differences in rainfall at locations distant from the two gaging locations in King County, Sea-Tac Airport and Landsburg. Refer to the precipitation scaling map in Chapter 3,Figure 3.2.2.A,to determine the scale factor for the project area. Step 3:Determine maximum depth of water above sand filter. Determine the maximum water storage depth above the surface of the filter. This depth is defined as the depth at which water begins to overflow the reservoir pond,and it depends on site topography and hydraulic constraints. The depth is chosen by the designer. 35 King County has tested various sand mixes conditioned with simulated stormwater to establish realistic design standards. Tests were conducted under falling head conditions in columns containing 18 inches of sand underlain with a 2-inch layer of washed drain gravel containing a section of 2-inch perforated PVC pipe to simulate the underdrain system. Details are given in Koon,John,'Determination of infiltration rate and hydraulic conductivity for various sand filter media.' January 1996. 9/1/98 6-102 1998 Surface Water Design Manual 6.5.2 SAND FILTERS—BASIC AND LARGE—METHODS OF ANALYSIS Step 4: Determine site characteristics. Determine the total number of impervious acres and the total number of grass acres draining to the sand filter. Determine whether the site is on till or outwash soils. Refer to Table 3.2.2.B in Chapter 3 to determine which soil types are considered till and which are considered outwash. Step 5. Calculate minimum required surface area for sand filter. Determine the sand filter area by multiplying the values in Table 6.5.2.A by the site acreages from Step 4 using the following equation: A.Sf =0.7CS(TiAi+TtgAtg+ T^f+TogAog) (6-19) where ASf = sand filter area(sf) 0.7 = adjustment factor to account for routing effect on size Cs = regional scale factor(unitless)from Step 2 Ti tg og = tributary area per soil/cover type(acres) Ai,tg og = filter area per soil/cover type(sf/acre)from Table 6.5.2.A For depths between the values given in the table,areas can be interpolated. For depths outside the range presented in the table,the detailed routing method must be used. TABLE 6 5 Z.A SAND An AREA INCREMENTSFOR VARIOUS SOIL AND COYERTYPES SOIL AND COVER TYPES36 [filter area(sf)/tributary area(acre)] Region and Maximum Depth Ai A+8 A09 Treatment Goal above filter(ft) Impervious Till Grass Outwash Grass Sea-Tac 6 760 160 140 ---------- —————————— ---------------------- Basic size 3 1140 240 210 ---------- ---------- ---------- ---------- 1 1711 360 314 Landsburg 6 819 180 160 ------------------------------------------------ Basic size 3 1229 270 235 —————————— ---------------------------------- 1 1844 405 355 Sea-Tac 6 1179 279 250 ---------- ---------------------------------- Large size 3 1769 419 370 ---------- ---------------------------------- 1 2654 629 550 Landsburg 6 1300 300 260 ---------- ---------------------- ----------- Large size 3 1950 449 395 —————————— ------------—————————— ---------- 1 2926 674 590 Note:Forested areas may be ignored. Vegetated areas other than grass may still be represented as grass for the simple sizing method, or the detailed routing method may be employed using actual cover types. 36 The values in Table 6.5.2.A were derived as follows. Flows were estimated using the KCRTS model for one acre of the cover types selected in the table. Darcy's law(Q=Ki A)was then used to determine sand filter area using this flow Q,the hydraulic gradient i for the various ponding depths given,and a hydraulic conductivity k of 2.3 X 10 5 fps(1 inch/hr)_ The hydraulic gradient i was calculated as(h+n//,where h=the average depth of water above the filter,taken to be the ponding depth d/2, and/=the thickness of the sand layer,which is 1.5 feet. The hydraulic conductivity represents a partially plugged sand condition found by bench-scale testing using successive trials with turbid water. 1998 Surface Water Design Manual 9/l/98 6-103 SECTION 6.5 MEDIA FILTRATION FACILITY DESIGNS Step 6: Size the underdrain system. The underdrain system is sized to convey the peak filtered flows to the outlet. The design criteria in "Underdrain Systems" (p.6-1 10)can be used in lieu of analyzing conveyance capacity for feeder pipes. Strip drains must be analyzed for conveyance per manufacturer's specifications. The collector pipe(i.e.,the pipe collecting flows from the rest of the underdrain system) shall be sized to convey the 2-year, 15-minute peak flow with one foot of head above the invert of the upstream end of the collector pipe. Conveyance capacity can be checked using the "BW"computer program. Intent: The underdrain must be We to remove standing water from beneath the sand. If standing water remains,the sand will remain saturated. This could cause oxygen depletion and reducing conditions in the sand,allowing some pollutants to become mobile and be released from the filter to downstream receiving waters. Simple Method Sizing Example For a site near the city of Snoqualmie with 2 acres of impervious area and 2 acres of outwash grass draining to the sand filter,and 3 feet of head above the filter,the required sand area for a basic size sand filter would be found as follows: Table 6.5.2.A values for Landsburg, Site Areas basic size 2 acres x 1229 sf/acre = 2458 sf + 2 acres x 235 sf/acre = 470 sf 2928 sf Multiply 2928 square feet by the CS for the Snoqualmie area,which(from Figure 3.2.2.A)is 1.2 times the increments for the Landsburg area. Also,multiply that result by the 0.7 adjustment factor. 2928 sf x 1.2 x 0.7 = 2460 sf The required sand bed area is therefore 2460 square feet. Note:Find the total facility area by adding 3H:1 V side slopes for the 3 foot ponding depth plus extra vertical height to convey the 100-year flow. If the total pond depth is 3.5 feet, the sand filter will require a total land area of(50 ft+ 1 a5 ft)x(50 ft+ 10.5 ft) =3660 square feet,plus access and setback requirements. Detailed KCRTS Routing Method The KCRTS routing method allows the designer to optimize filter geometry and sizing to meet specific site conditions. For sand filters located downstream of detention ponds,this method will result in significantly smaller facilities than using the simple method described above. The detailed method requires a trial and error solution using KCRTS to route the inflow runoff time series through various sand filter configurations until the amount of runoff that passes through the filter media and is treated meets the treatment objective defined for the facility. Refer to the KCRTS Computer Software Reference Manual for general instructions on using the KCRTS program. Steps for the design process,with specific instructions on how to use KCRTS for sand filter sizing,are described below. Step 1:Determine whether a basic or large sand filter is required. Consult the water quality menus in Section 6.1 (p. 6-3)to determine the size of filter needed. A basic sand filter is sized so that 90%of the runoff volume will pass through the filter, rather than 95%as stated in Section 6.2.1 (p. 6-17)for the WQ 9/1/98 1998 Surface Water Design Manual 6-104 6.5.2 SAND FILTERS—BASIC AND LARGE—METHODS OF ANALYSIS design volume. A large sand filter is sized to permit the full 95%of the runoff volume to pass through the filter.37 Step 2: Determine rainfall region and regional scale factor. Regional scale factors are used to account for differences in rainfall at various locations in King County. Refer to the precipitation scaling map in Chapter 3,Figure 3.2.2.A,to determine the scale factor for the project area. Step 3: Create inflow time series. The developed inflow time series is created using the KCRTS program as described in Chapter 3. If the sand filter is upstream of detention,the time series is that of the developed site. If the sand filter is downstream of detention,the time series is that leaving the detention pond. Note:Sand filters located downstream from detention ponds are significantly smaller than those treating runoff before it is detained. Likewise, sand filters receiving flows from Level 2 detention ponds are smaller than those below Level 1 ponds. Step 4:Determine the design overflow volume(on-line facilities). The percent of total runoff volume required to pass through the filter was determined in Step 1 (either 90 or 95%). To determine the design overflow volume,multiply the total runoff volume by one minus the percentage(either 0.10 or 0.05). The total runoff volume can be found using the"Compute Volume Discharge"routine found in the"Analysis Tools"module after the inflow time series is created. Detailed instructions for creating the time series can be found in the KCRTS Computer Software Reference Manual.38 The start and end dates for the reduced runoff time series are as follows: Start date: 10/1/0 End date: 9/30/8 Note: For most WQ facilities, the designer can chose to design the facility as either on-line(all flow goes through the facility)or off-line(flows above the WQ design flow bypass the facility). An off-line sand filter has a high-flow bypass with an upstream flow spliner designed to bypass flows above 60%of the 2- yr peak discharge using 15-min time steps calibrated to specific site conditions(see Section 6.2.5,p. 6-27, for more information on flow spliner design). The design overflow volume for off-line sand filters is zero, since all flows routed to the filter will be at or below the WQ design flow. Step 5:Define sand filter modeling parameters. Sand filters can be sized with the"Size a Facility" routine using the infiltration pond option. The following parameters are required for the analysis: a) Manual Mode: When specifying the filename for the facility,switch the'Design Technique"to manual which allows the user full control of all facility parameters. b) Side slope:horizontal component of slope(ft/ft)for the pond(above the sand filter) c) Sand filter area A�f: the surface area of the filter(sf). As a first approximation,it is recommended that the area calculated using the simple sizing method be used. KCRTS refers to this area as the bottom area of the infiltration pond. d) Maximum water depth d over filter:depth at which runoff begins to overflow the sand filter(ft), referred to in KCRTS as the effective storage depth of the reservoir. 37 For sand filters,the volume to be treated to meet the Basic menu goal is only 90%(rather than 95%)of the total runoff volume. This is because the sand filter has been documented to provide better than 80%TSS removal,and thus exceeds the treatment goal of the Basic WO menu. Therefore,less runoff volume can be treated and still meet the basic water quality goal. 38 Instructions for creating the time series are summarized as follows:Select'CREATE a new time series'at the main menu. Enter rainfall region and scale factor(see Figure 32.2.A),soil and land cover areas,time step,and data type(reduced record). Select"COMPUTE total area.' Enter a name for the inflow time series. Select'COMPUTE time series.' Press F10 to view information created;press'ENTER'to return to main menu. At the main menu,select*ENTER analysis tools module.' Select'COMPUTE volume discharge,'and enter the inflow time series name. Enter start date and end date for time series. Select'EXTRACT discharge volume.' This is the total runoff volume in the time series. Select"CONTINUE,' and then select'RETURN to main menu.' 1998 Surface Water Design Manual 9/1/98 6-105 SECTION 6.5 MEDIA FILTRATION FACILITY DESIGNS e) Permeable surfaces:bottom only. f) Riser and orifice information: • Elevation at 0 stage: 0 is fine for design. This sets a datum adjustment; which if set,the program will display water levels based on relative stage and absolute elevation. • Riser head: same as the maximum water depth. • Riser diameter: 12-36 inches(must meet the criteria for"Overflow and Bypass Structures," p. 6-108). • Number of orifices: zero. • Top of riser:flat. g) Vertical infiltration:the inverse of the filtration rate V,or 1/V, and is entered in units of minutes per inch. Values for V and 1/V for various ponding depths are summarized in Table 6.5.2.B (below). -651Z �"SA1D) `TERFDESTGI�MARAII�IEZERS¢{ Sand Filter Design Parameters Facility ponding depth d(ft) 1 2 3 4 5 6 Filtration rate V(in/hr)' 1.33 1.67 2.00 2.33 2.67 3.0 1/V(min/in) 45 36 30 26 22.5 20 Note:The filtration rate is not used directly but is provided for information. V equals the hydraulic conductivity K times the hydraulic gradient i. The hydraulic conductivity used is 1 inch/hr. The hydraulic gradient=(h+1)/1,where h=d/2 and 1=the sand depth (1.5 ft). See'Background" (p.6-101)for more information on the definition of terms. Step 6:Size the sand filter. The KCRTS facility sizing routine is used to design the sand filter as follows: a) Select"Size a facility" option from the KCRTS main menu. b) Specify a filename to save the sand filter data. c) Toggle the"Design Technique"to manual mode. d) Select"Create a New Detention Facility." e) Specify an infiltration pond as the facility type,and input the facility specifications determined in Step 5. The primary variable to be adjusted by the designer is the bottom area,which corresponds to the required filter area. f) Once specified,select the "Save Facility" option. Step 7:Specify the filename of the Inflow time series. a) From the main "Facility"menu,select [H] "Edit Inflow Hydrograph List." b) Specify the filename of the inflow time series. c) Select'Return to Main Menu." Since sizing of sand filters in done in manual(rather than automatic) mode, there is no need to complete the setup of the test inflow hydrograph list. 9/l/98 1998 Surface Water Design Manual 6-106 6.5.2 SAND FILTERS—BASIC AND LARGE—METHODS OFANALYSIS Step 8: Route inflow time series through sand filter and compare volumes. Compare the outflow volume passing through the filter with the required treatment volume. KCRTS can perform the time series routing and the volume comparisons. To set up the volume comparison,perform the following steps: a) Select [M] "Modify Auto-Analysis,"and enter facility outflow name. b) Toggle the"Volume Calculation" on. c) Select "Edit Peak/Duration/Volume Information," and specify the same start and end dates specified in Step 4. d) Return to the main facility design menu and select[A] "Route Time Series." e) Select "Perform Auto-Analysis." Press F10 to display routing data;press RETURN twice to continue with volume calculation. Press 1`10 to view the time series outflow volume. This represents the total volume of water which overtopped the facility. Compare the discharge volume with the design discharge volume identified in Step 4. • If the volume of water spilled exceeded the design outflow volume,increase the bottom area of the facility by selecting[E] "Edit Facility." Repeat this step until the desired performance is achieved. • If the volume of water spilled is less than the design outflow volume,decrease the bottom area until the outflow and the design outflow match(approximately). Step 9:Size the underdrain system. The underdrain system is sized to convey the peak filtered flows to the outlet. The design criteria in "Underdrain Systems" (p.6-110)can be used in lieu of analyzing conveyance capacity for feeder pipes. Strip drains must be analyzed for conveyance per manufacturer's specifications. The collector pipe(i.e.,the pipe collecting flows from the rest of the underdrain system)shall be sized to convey the 2-year, 15-minute peak flow with one foot of head above the invert of the upstream end of the collector pipe. Conveyance capacity can be checked with the"KCBW"computer program. Intent:The underdrain must be able to remove standing water from beneath the sand. If standing water remains,the sand will remain saturated. This could cause reducing conditions in the sand,allowing some pollutants to become mobile and be released from the filter to downstream receiving waters. 1998 Surface Water Design Manual 9/l/98 6-107 SECTION 6.5 MEDIA FILTRATION FACILITY DESIGNS 6.5.2.2 DESIGN CRITERIA General design concepts and a typical layout of a sand filter are shown in Figure 6.5.2.13 (p.6-116)and Figure 6.5.2.0(p.6-118). Sand Filter Geometry 1. Any shape sand bed may be used,including circular or free-form designs. Note: The treatment process is governed by vertical flow, so short-circuiting is not a concern as it is in wetponds. 1-6,{'`t�J—2. Sand depth(1)shall be 18 inches(1.5 feet)minimum. (pro�rjle — 3. Depth of storage over the filter media(d)shall be 6 feet maximum. f Pretreatment, Flow Spreading, and Energy Dissipation 1. See general presettling and pretreatment requirements for filtration facilities in Section 6.5.1 (p.6-99). 2. A flow spreader shall be installed at the inlet along one side of the filter to evenly distribute incoming runoff across the filter and prevent erosion of the filter surface. See Section 6.2.6(p. 6-3 1)for details on flow spreaders. a) If the sand filter is curved or an irregular shape,a flow spreader shall be provided for a minimum of 20 percent of the filter perimeter. b) If the length-to-width ratio of the filter is 2:1 or greater,a flow spreader must be located on the longer side and for a minimum length of 20 percent of the facility perimeter. c) In other situations,use good engineering judgment in positioning the spreader. 3. Erosion protection shall be provided along the first foot of the sand bed adjacent to the flow spreader. Geotextile(meeting the specifications in Table 6.5.2.D,page 6-109)weighted with sand bags at 15-foot intervals may be used. Quarry spalls may also be used. Overflow and Bypass Structures 1. On-line filters shall be equipped with overflows(primary, secondary, and emergency)in accordance with the design criteria for detention ponds(see Section 5.3.1.1,criteria for"Overflow" and"Emergency Overflow Spillway"). Note: The primary overflow may be incorporated into the emergency spillway in cases where the spillway discharges into a downstream detention facility, or where overflows can be safely controlled and redirected into the downstream conveyance system. 2. For off-line filters,the outlet structure must be designed to pass the 2-yr peak inflow rate,as determined using KCRTS with 15-minute time steps calibrated to specific site conditions. Intent: Overflow capacity is required for low-flow,high-volume storms which may exceed the storage capacity of the filter. 3. To the extent base flow conditions can be identified,base flow must be bypassed around the filter to keep the sand from remaining saturated for extended periods of time. Filter Composition A sand filter consists of three or four layers: • Top layer(optional): grass seed or sod grown in sand • Second layer: sand 39 Whether a WO facility is designed as on-line(all flow going through the facility)or off-line(high flows bypassing the facility)is a choice made by the designer. Section 6.2.5(p.6-27)contains information on flow splitters for WO facilities. 9/1/98 1998 Surface Water Design Manual 6-108 6.5.2 SAND FILTERS—BASIC AND LARGE—DESIGN CRITERIA • Third layer: geotextile fabric • Fourth layer: underdrain system. Sand Specifications The sand in a filter shall consist of a medium sand with few fines meeting the size gradation (by weight) given in Table 6.5.2.C. The contractor must obtain a grain size analysis from the supplier to certify that the No. 100 and No.200 sieve requirements are met. Note: Many sand mixes supplied locally meet this specification. However, standard backfill for sand drains(as specified in the Washington Standard Specifications 9-03.13)does not meet this specification and should not be used for sand filters. TABLE 6 5 2 C SAND:A DIA SPECIFICATIONS U.S. Sieve Size Percent passing U.S. No.4 95 to 100 percent U.S. No.8 70 to 100 percent U.S. No. 16 40 to 90 percent U.S. No.30 25 to 75 percent U.S. No.50 2 to 25 percent U.S. No. 100 Less than 4 percent U.S. No.200 Less than 2 percent Geotextile Materials Geotextile material requirements are summarized in Table 6.5.2.D. TABLE 65.2 D -GEOTEXTILE SPECIFICATIONS Geotextile Property Value Test Method Grab strength(Ibs) 75 (min) ASTM D4632 Burst strength(psi) 130(min) ASTM D3786 Trapezoid tear(Ibs) 40(min) ASTM D4533 Permeability(cm/sec) 0.2(min) ASTM D4491 0 AOS (sieve size) #60-#70 ASTM D4751 \a Ultraviolet resistance 70 percent or greater ASTM D4355 Notes: • Acceptability of geotextile material shall be based on ASTM D-4759. • Minimum values should be in the weaker principal direction. All numerical values represent minimum average roll value (i.e.,test results from any sampled lot shall meet or exceed the minimum values in the table). Stated values are for noncritical and nonsevere applications. 1998 Surface Water Design Manual 9/1/98 6-109 6.5.2 SAND FILTERS—BASIC AND LARGE—DESIGN CRITERIA F7� FIGURE 6.5.2.B SAND FILTER WITH LEVEL SPREADER(CONTINUED) 3H : 1 V slope erosion recommended protection grass(optional) no topsoil may be added design WS 6'max. 8"min: o. o� o O 24"min. .� trench optional, but 8"crushed SECTION A-A invert of underdrain gravel required over drain pipe NTS above seasonal high ground water level r. 18"min. 8"min. bo'o -N a o0 0 sand 0 ��� geotextile fabric underdrain collector pipe drain rock or gravel backfill (6 min.) TRENCH DETAIL NTS spill control provided by type II catch basin with tee section (not required if filter proceeded by facility with spill control) V WQ design WS inlet grating(optional) b SECTION B-B NTS 1998 Surface Water Design Manual 9/I/98 6-117 ul 5.0 CONVEYANCE SYSTEM ANALYSIS AND DESIGN Enclosed are calculations necessary for sizing the conveyance system for the project. The rational method and Mannings formula were used for sizing each of the pipes. The conveyance pipes have been sized to accommodate the 100-year storm event at full flow condition, pursuant to Section 1.2.4.1 of the 1998 KCWSWDM. The intent of this pipe system within public roadways is to convey stormwater runoff from the houses and roads into the drainage facility located in Tract A. 5.1 25-Year Conveyance A 25-year conveyance analysis has been completed in accordance with the 1998 King County Surface Water Design Manual providing conveyance for the 100-year/24-hour storm. For ease in making these calculations,we have utilized the rational method as defined by the 1998 King County Surface Water Design Manual for this task. Tributary areas have been calculated to each of the catch basins connected to the proposed piping system and precipitation has been derived from the Renton/Seattle IDS curve. An average"C"factor was calculated for each tributary area, that will be utilized for these calculations. 7797.006 WA/jss/cal 7797-10 BARGHAUSEN CONSULTING ENGINEERS-PIPE FLOW CALCULATOR using the Rational Method 8 Manning Formula KING COUNTY DESIGN FOR 100 YEAR STORM JOB NAME: NOTE:ENTER DEFAULTS AND STORM DATA BEFORE BEGINNING JOB#: DEFAULTS C= 0.7 n= 0.012 d- 12 Tc= 6.3 REVISED'. A=Contributing Area(Ac) Qd=Design Flow(cfs) COEFFICIENTS FOR THE RATIONAL METHOD"Ir"-EQUATION C=Runoff Coef&lent Of--Full Capacity Flow(cfs) STORM Ar Sr Tc=Time of Concentration(min) Vd=Velocity at Design Flow(fps) 2YR 1.58 0.58 1=Intensity at Tc(in/hr) Vf=Velocity at Full Flow(fps) 10YR 2.44 0.64 PRECIP= 3.9 d=Diameter of Pipe(In) s=Slope of pipe(�) 25YR 2.66 0.65 2.61 L=Length of Pipe(ft) n=Manning Roughness Coefficient 50YR 2.61 0.65 0.83 D=Water Depth at Qd(in) Tt=Travel Time at Vd(min) t00YR 2.61 0.63 FROM TO A s L d Tc n C SUM A A'C SUM A"C I Qd Qf Qd/Qf D/d D Vf Vd Tt : C821 CB20 0.38 1.57 7 12 6.3 0.012 0.7 0.382 0.27 0.27 3.19 0.85 4.83 0.177 0.281 3.38 6.16 4.63 0.03 CB20 CB19 0.10 1.12 107 12 6.3 0.012 0.7 0.482 0.07 0.34 3.18 1.07 4.08 0.263 0.351 4.21 5.20 4.39 0.41 CB19 CB17 0.68 3.11 195 12 6.7 0.012 0.7 1.162 0.48 0.81 3.06 2.49 6.80 0.366 0.417 5.01 8.67 8.00 0.41 CB17 CB16 0.79 3.11 175 12 7.1 0.012 0.7 1.952 0.55 1.37 2.95 4.03 6.80 0.593 0.553 6.63 8.67 9.01 0.32 C815 CB13 0.63 4.04 122 12 7.5 0.012 0.7 2.582 0.44 1.81 2.87 5.19 7.76 0.669 0.598 7.17 9.88 10.56 0.19 CB13 CB11A 0.26 1.49 201 18 7.7 0.012 0.7 2.842 0.18 1.99 2.82 5.62 13.89 0.408 0.356 6.41 3.3 7..3 0.45 CB11A CB10 0.49 4.27 221 18 8.1 0.012 0.7 3.332 0.34 2.33 2.72 6.35 23.51 0.270 0.356 6.41 13.31 11.32 0.33 CB32 CB31 0.19 4.96 107 12 6.3 0.012 0.7 0.19 0.13 0.13 3.19 0.42 8.59 0.049 0.153 1.83 10.95 5.62 0.32 CB31 CB30 0.56 5.13 39 12 6.6 0.012 0.7 0.75 0.39 0.53 3.10 1.62 8.74 0.186 0.289 3.47 11.14 8.47 0.08 CB30 CB29 0.47 1.86 90 12 6.7 0.012 0.7 1.22 0.33 0.85 3.07 2.62 5.26 0.499 0.499 5.99 6.71 6.74 0.22 50 30 15 6.9 0.012 0.7 1.46 0.17 1.02 3.01 3.08 4.95 0.622 0.581 8.71 4.03 4.28 0.12 20 CB29 C628 0.24 0. CB29 CB26 0.23 4.50 85 15 7.0 0.012 0.7 1.69 0.16 1.18 2.98 3.52 14.34 0.246 0.337 5.05 11.69 9.66 0.15 CB26 CB25 0.19 4.54 112 15 T2 0.012 0.7 1.88 0.13 1.32 2.94 3.87 14.91 0.260 0.348 5.21 12.16 10.21 0.18 CB26 CB23 1.20 2.58 79 15 7.4 0.012 0.7 3.08 0.84 2.16 2.89 6.24 11.24 0.565 0.532 7.97 9.16 9.38 0.14 CB23 CB11 1.20 2.00 40 15 7.5 0.012 0.7 3.47 0.27 2.43 2.86 6.95 9.89 0.702 0.618 9.27 8.07 8.75 0.08 CB11 CB10 0.19 2.00 31 15 7.6 0.012 0.7 3.66 0.13 2.56 2.84 7.28 9.89 0.736 0.638 9.58 8.07 8.83 0.06 CB10 CB7 0.18 1.45 179 18 8.4 0.012 0.7 0.18 0.13 5.02 2.66 13.34 13.70 0.974 0.794 14.29 7.76 8.77 0.34 CB7 CB6 0.88 1.00 18 24 8.8 0.012 0.7 1.06 0.62 6.64 2.59 14.61 24.50 0.596 0.555 13.32 7.80 8.13 0.04 .00 5.64 2.59 14.57 24.50 0.595 0.554 13.30 7.80 8.12 0.06 CB6 POND 0.00 1.00 29 24 8.8 0.012 0.7 1.06 0 C822 CB19 0.52 3.77 71 12 6.3 0.012 0.7 0.52 0.36 0.36 3A9 1.16 7.49 0.155 0.264 3.17 9.55 6.89 0.17 CB18 CB17 0.24 0.50 31 12 6.3 0.012 0.7 0.24 0.17 0.17 3.19 0.54 2.73 0.197 0.297 3.57 3.48 2.68 0.19 CB16 CB15 0.11 0.50 31 12 6.3 0.012 0.7 0.11 0.08 0.08 3.19 0.25 2.73 0.090 0.200 2.40 3.48 2.10 0.25 CB12 CB11A 0.21 0.50 31 12 6.3 0.012 0.7 0.21 0.15 0.15 3.19 0.47 2.73 0.172 0.278 3.33 3.48 2.60 0.20 CB27 CB26 0.11 0.50 31 12 6.3 0.012 0.7 0.11 0.08 0.08 3.19 0.25 2.73 0.090 0.200 2.40 3.48 2.10 0.25 CB24 CB23 0.24 0.50 31 12 6.3 0.012 0.7 0.24 0.17 0.17 3.19 0.54 2.73 0.197 0.297 3.57 3.48 2.68 0.19 5.60 80 12 6.3 0.012 0.7 0.67 0.47 0.47 3.19 1.50 9.13 0.164 0.271 3.26 11.63 8.55 0.16 Cgg CB8 0.67 C88 CB7 0.12 . 0 31 12 6.5 0.012 0.7 0.79 0.08 0.55 3.14 1.74 2.73 0.637 0.586 7.04 3.48 3.70 0.14 CBt CB2 0.27 0.50 34 12 6.3 0.012 0.7 0.27 0.19 0.19 3.19 0.60 2.73 0.221 0.317 3.80 3.48 2.79 0.20 CB2 INFIL. 0.22 0.50 21 12 6.5 0.012 0.7 0.49 0.15 0.34 3.13 1.07 2.73 0.393 0.436 5.23 3.48 3.27 0.11 Page 1 MSC PL ,mot P. _.� PPP—SS—TM CITY OF RENTON QN PIPE SQ BASN AREA MAP ,� DATUM Planning/Bullding/Publlc Works D•pt N0. 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B.C.E.JOB NO. 7797 + 6.0 SPECIAL REPORTS AND STUDIES 6.1 Results of Subsurface Infiltration Testing by Geotech Consultants dated November 17, 2000 6.2 Results of Test Pits for Fill Exploration by Geotech Consultants dated November 9,2000 6.3 Geotechnical Engineering Study by Geotech Consultants dated September 14, 1999 6.4 Phase 1 Environmental Site Assessment by Geotech Consultants dated September 9, 1999 6.5 Abandoned Mine Assessment by Hart Crowser dated August 23, 1999 7797.006[RJA/}ss/ca] 6.1 RESULTS OF SUBSURFACE INFILTRATION TESTING BY GEOTECH CONSULTANTS DATED NOVEMBER 17, 2000 November 17, 2000 JN 99330 Bennett Corporation 9 Lake Bellevue Drive, Suite 204 Bellevue, Washington 98005 Attention: Chris Austin via facsimile: (425) 709-6553 Subject: Results of Subsurface Infiltration Testing Heritage Renton Hill Project Southeast Corner of Beacon Way South and South 7th Court Renton, Washington Dear Mr. Austin: We have previously prepared a geotechnical engineering study for the above-referenced site dated September 14, 1999. An infiltration pond to be located in the northwestern corner of the property has been proposed for the disposal of storm water from the development. This letter summarizes the findings of our most recent explorations and subsurface infiltration testing in the area of the proposed storm water pond. We were provided with a drainage control plan prepared by Peterson Consulting Engineers, dated April 2, 2000. This plan shows the preliminary layout of the 57 lots on the property. Based on this plan, we anticipate that the infiltration pond will have a bottom elevation of 349.5 feet, with a 200- foot-long biofiltration swale bordering the south and east perimeter of the pond. At its present proposed location, cuts to reach the pond bottom range from 12 to 17 feet. The subsurface conditions were explored by excavating eight test pits at the approximate locations shown on the attached copy of the pond layout. The test pits were excavated on October 19 and November 3, 2000, with a track-mounted backhoe. A geotechnical engineer from our staff observed the excavation process, logged the test pits, conducted infiltration tests in the native soils, and obtained representative soil samples. The logs of the test pits are attached to this letter. The test pits generally encountered loose sands that became denser with depth. As illustrated by the grain size analyses contained in Appendix A, the native sands contain a low percentage of fines (particles smaller than the U.S. No. 200 sieve). Test Pits B through H encountered varying depths of loose, silty sand fill containing asphalt and concrete debris, and assorted household garbage. The depth of this fill ranged from 3 feet in Test Pit B to at least 15 feet in Test Pit D, which was excavated where the ground surface is highest in the center of the proposed pond. The soils encountered in our recent subsurface investigation are similar to those found during our geotechnical engineering study in September of 1999. No groundwater seepage or wet soils were observed in the test pits. Test Pits F through H were excavated to an approximate elevation of 344 to 345 feet. The test pits were conducted following the end of a relatively dry summer. GEOTECH CONSULTANTS, INC. Bennett Corporation JN 99330 November 17, 2000 Page 2 INFILTRATION TESTS Falling head infiltration tests were performed in Test Pits E, G, and H with a 6-inch-diameter PVC pipe driven into native soil near, or slightly below, the likely bottom-of-pond elevation. We also conducted infiltration tests in the native sands found below the fill in Test Pit C, although the test was conducted approximately 4 feet above the proposed pond bottom. It was not possible to conduct infiltration tests in the center of the pond area, as the higher existing ground elevation, and the caving conditions in the fill soils made entering such a deep test pit unsafe. The infiltration tests were conducted in general accordance with the King County Surface Water Design Manual. After soaking the underlying soils, each test was performed three times, with an average falling head infiltration rate taken over a 6-inch drop in the water surface. The following table summarizes the average infiltration test rates that resulted from our testing: TESTPIT DEPTH OF INFILTRATION AVERAGE TEST INFILTRATION TEST,feet RATE,inches/minute B 9 0.23 E 12 4.5 G 13 0.26 H 14 8.2 CONCLUSIONS AND RECOMMENDATIONS Based on the results of our subsurface investigation and infiltration tests, we recommend using an average test infiltration rate of 0.25 inches per minute. While this rate is substantially lower than the results for the tests in Test Pits E and H, it should be conservative and more appropriate to account for inherent variability in results of subsurface infiltration tests. The King County Surface Water Design Manual includes additional influence factors to account for the configuration of the infiltration structure and the tendency of soil to clog with silt and debris carried into the system. Over time, the infiltration capability of the soil close to the system will decrease, reducing the effectiveness of the system's infiltration. The effective life of the system can be lengthened by frequent cleaning of the catch basins that collect the runoff. Homeowners should also be notified of the sensitivity of the system so that they can minimize the amount of soil and debris that is flushed into the catch basins. Periodic maintenance, such as scraping the clogged soil from the bottom of the pond should be expected. The fill soils found in the eastern end of the pond area are not suitable for infiltration. However, it appears that the proposed bottom-of-pond elevation will be near the transition from fill to native soils found in our test pits. It is possible, however, that overexcavation will be necessary to remove fill remaining once the pond has been excavated to its planned elevation. GEOTECH CONSULTANTS, INC. Bennett Corporation JN 99330 November 17, 2000 Page 3 We trust that this report meets your immediate needs for the proposed development. Please contact us if we can be of further service. Respectfully submitted, GEOTECH CONSULTANTS, INC. g. Mc4' WAS�f��./�� P 27845 cry 0't' ISTF, �`sSjONAL S' GG V71PO EXPIRES 10/25 i 2,nM Marc R. McGinnis, P.E. Principal Attachments: Test Pit Locations Test Pit Logs Grain Size Analyses cc: Peterson Consulting Engineers—Jennifer Steig 4030 Lake Washington Boulevard Northeast, Suite 200 Kirkland, Washington 98033 Via facsimile: (425) 822-7216 MRM: aft GEOTECH CONSULTANTS, INC. (`� — S� �.` J , / LUR EL. = 353.0 LENGTH = 204 POND BOTTOM EL. = 349.5 I WID TH = 9' I CE AREA 2,000 SF _ SLOPE = 1.5% I IM 46.5— — — — 7 _CT CHWL. 340.1 (NESW / — — _ — — _ S8( CONNECT TO E I TN_ 'Y"i 6 WOOD FENCE( i • ��( TYP /f TOP A 1 1 O'RN/A TER I r \P�4\ TRACT � � 44 OVERFLOW \ \ SYSTEM\ \x1 ` ` ' / / , _� - �•�_.� ••.__ `\� � 14V \ \ \ \ % FLQW\ ■ f PROPOSEQ STORM j DRAINAGE CATCH BASII \ .may\• y V \f (TYP.) In \\\ 1 \SPILL C NTROL' / �� �, - \c 1, s LIS ` \ 17RACT PARK �\ \NWY \ NORTH Test Pit conducted for \1 \ ' ® Sept. 14, 1999 study \\ �\ ; ` 2 i Test Pit conducted for recent infiltration testing i \ \\ �-0 14"M% 4 e � ,`�l, TEST PIT A " G SS" ��°�"o�`'G7 Description Elevation +/- 354' Brown SAND, some gravel, fine-grained, dry to moist, loose - becomes brown/gray, moist, loose to medium-dense 5 SP becomes medium- to coarse-grained, medium-dense to dense - becomes brown, gravelly, very moist 10 * Test Pit was terminated at 10 feet on October 19, 2000. * No groundwater seepage was observed during excavation. * Light caving was observed from 0 to 6 feet during excavation. 15 �0 CON TEST PIT B ��� 0�5 NP c� ti0 CP Description Elevation +/- 360' Dark brown, silty SAND, assorted household garbage, loose (FILL) FILL rown SAND, some gravel, fine-grained, dry to moist, loose 5 becomes brown/gray, gravelly, fine- to medium-grained, medium-dense .SP ; 10 becomes brown, less gravelly, medium- to coarse-grained, dense - becomes very moist * Test Pit was terminated at 13 feet on October 19, 2000. 15F * No groundwater seepage was observed during excavation. * Light to moderate caving was observed from 0 to 7 feet during excavation. TEST PIT LOG GEOTECH Beacon Way South and South 7th Court CONSULTANTS,INC. Renton, Washington Job No: Date: Logged by: Plate: ^� 99330 Oct.2000 1 GDB "' roti� TEST PIT C � �� G5 G o a 5 Description Elevation +/- 364' Dark brown, silty SAND with asphalt, concrete, and assorted household garbage, loose (FILL) 5 FILL 10 Old TOPSOIL Brown, gravelly SAND, fine- to medium-grained, moist, medium-dense 15 SP 18 * Test Pit was terminated at 18 feet on October 19, 2000. * No groundwater seepage was observed during excavation. * Light to moderate caving was observed from 0 to 7 feet during excavation. TEST PIT LOG GEOTECH Beacon Way South and South 7th Court CONSULTANTS,INC. Renton, Washington Job No: Date: Logged by. Plate. ^�— 99330 Oct.2000 GDB 1 {e,�ol� TEST PIT D �• 0 e,' aO' e G5 9e4 G° Description Elevation +/- 366' TOPSOIL Dark brown, silty SAND with concrete, asphalt, and household garbage, loose (FILL) 5 FILL 10 15Brown to gray 6AND, fine- to medium-grained, moist o we , oose o medium- dense FILL? * Test Pit was terminated at 16 feet on November 3, 2000. * No groundwater seepage was observed during excavation. * Light to moderate caving was observed from 0 to 8 feet during excavation. { TEST PIT E 5 Description Elevation +/- 362' FILL Brown, silty SAND with organics, household garbage, and old 45's, loose (FILL) Gray, gravelly, silty SAND with wood chips, fine- to medium-grained, moist, loose 5 FILL to medium-dense (FILL) Gray, gravelly SAND, medium-grained, moist, medium-dense 10 PSP - becomes brown, moist to very moist, medium-dense to dense 15 * Test Pit was terminated at 16 feet on November 3, 2000. * No groundwater seepage was observed during excavation. * Light to moderate caving was observed from 0 to 8 feet during excavation. TEST PIT LOG GEOTECH Beacon Way South and South 7th Court CONSULTANTS,INC. Renton, Washington A Job No: Dale: Logged by: Plate: 99330 Nov.2000 GDB TEST PIT F GS Description Elevation +/- 362' Dark brown, silty SAND with concrete, asphalt, and household garbage, loose (FILL) 5 FILL 10 - becomes gray Brown, gravelly SAND, medium-grained, moist to very moist, medium-dense 15 SP :: " Test Pit was terminated at 19 feet on November 3, 2000. " No groundwater seepage was observed during excavation. " Light to moderate caving was observed from 0 to 10 feet during excavation. TEST PIT LOG GEOTECH Beacon Way South and South 7th Court CONSULTANTS,INC. Renton, Washington Job No: Date 99330 Nov.2000 �pg Pate: ��`ti�` TEST PIT G 9��n "Y SS" V �SG� Description Elevation +/- 363' Brown, silty SAND with roots, fine- to medium-grained, moist, loose (FILL) 5 - becomes gray and gravelly, with household garbage, asphalt, concrete, tires FILL 10 TOPSOIL Gray, gravelly SAND, fine- to medium-grained, moist, medium-dense 15 SP - becomes brown, less gravelly becomes gravelly, medium-grained, medium-dense to dense * Test Pit was terminated at 18 feet on November 3, 2000. " No groundwater seepage was observed during excavation. " Light caving was observed from 0 to 12 feet during excavation. TEST PIT LOG GEOTECH Beacon Way South and South 7th Court CONSULTANTS,INC. Renton, Washington 4 Job No: Date Logged by: Plate. 99330 Nov.2000 GDB {�Jio TEST PIT H Description Elevation +/- 360' Dark gray, silty SAND with roots, asphalt, concrete, household garbage, and beer FILL bottles, loose (FILL) 5 Brown to gray, gravelly SAND, fine- to medium-grained, slightly moist, medium- dense 10 . SP - becomes gray, less gravelly 15 - becomes brown/gray, medium-grained, moist to very moist * Test Pit was terminated at 17 feet on November 3, 2000. " No groundwater seepage was observed during excavation. * Light caving was observed from 0 to 2 feet during excavation. TEST PIT LOG GEOTECH Beacon Way South and South 7th Court CONSUL,TAWS,INC. Renton, Washington A Job No: Date: Logged by: Plate: 99330 Nov. GDB Appendix A — Grain Size Analyses Beacon Way South and South 7th Court Renton, Washington GEOTECH CONSULTANTS,INC. sieve analysis Job Data: Client: Job Number: 99330 Job Name: Date: 11/07/00 Sample Data: Test Pit/Boring: TP- E Tare: 0 Sample: Wet Weight: 512.2 Depth: 12' Dry Weight: 488.1 %Moisture: 4.9 Wash Data: Dry weight(before wash): 488.1 grams Dry Weight(after wash): 479.9 grams Washed Soil weight: 8.2 grams ;Sieve-US;- Sieve SI Weight Retained Percent Inches or Ho., mm. ( rams Percent Retained Priced Each Total Each 'Tofat T-otat I , , , 01 0=0�--- 0_0i 100.0 3/4 ' 19 05 45.9' 45.91 9.41 9.41 90.6 --------&---=-- ----�------4-----_1-------t------ 3/8 9.53 1 79.61 125.51 16.31 25.71 74.3 -------- -----r----- ----- +------r------4------ 4 4.75 1 47.91 173.41 9.81 35.51 64.5 -------- -----t------ ------+-----1------t------ 10 2.00 i 46.11 219.51 9.4 i 45.01 55.0 40 i 0.43 i 195.31 414.81 40.01 85.01 15.0 --------r-----r----- -----7------T------ 100 i 0.15 i 64.01 478.81 13.11 98.1 i 1.9 -------- ---200---1 0.08 i 3.01 481.81 0.61 98.71 1.3 <200 0.00 r 0.11 481.91 0.0,----98.7T----1.3 Tbtat 490.11 1 100.4 44 Sieve Opening(rrm.) 100.00 10.00 1.00 0.10 0.01 100 100.0 90 90.6 80 70 74 3 m 64 5 60 0�0 J550 50 a c 40 ar 30 a 20 15.0 10 1.9 1.3 0 Page 1 sieve analysis Job Data: Client: Job Number: 99330 Job Name: Date: 11/07/00 Sample Data: Test Pit/Boring: TP - E Tare: 0 Sample: Wet Weight: 645.9 Depth: 16' Dry Weight: 619.7 %Moisture: 4.2 Wash Data: Dry Weight(before wash): 619.7 grams Dry Weight(after wash): 613.5 grams Washed Soil Weight: 6.2 grams S eve S- Se eMrened ev Percent tnches'or No. rrm. arms) Percent Retained Passel Each Total EachC Total fiota( __L_38_10- ---0-0�--- -01----0-"0_j---- 0_0i-- 1-00.0 3/4 19.05 1 5631 56.3' 9.1 1 9.1 90.9 3/8 9.53 1 178.01 234.31 28.71 37.81 62.2 --------E------F------+-----4-----A------ 4 1 4.75 1 113.31 347.61 18.31 56.11 43.9 10 1 2.00 1 74.61 422.21 12.01 68.11 31.9 40 i 0.43 i 166.91 589.1 i 26.91 95.11 4.9 100 i 0.15 i 24.91 614.01 4.O i 99.11 0.9 -------- __ 2_0_01 0.08 i 2.01 616.01 0.3i 99.4� 0.6 <200 0.00 0.3 616.3 0.0 99.5 0.5 Total 6225 100,5 4:.5 Sieve Opening(mm.) 100.00 10.00 1.00 0.10 0.01 100 100.0 90.9 90 80 7 v m 60 a 62.2 a 50 .. c - 40 43.9 m 31.9 30 a 20 10 4.9 10 ro!9 0.6 Page 1 sieve analysis Job Data: Client: .Job Number: 99330 Job Name: Date: 11/07/00 Sample Data: Test Pit/Boring: TP- G Tare: 0 Sample: Wet Weight: 304.5 Depth: 14' Dry Weight: 286.3 %Moisture: 6.4 Wash Data: Dry Weight(before wash): 286.3 grams Dry Weight(after wash): 280.8 grams Washed Soil Weight: 5.5 grams Sieve US T=v-e ,WekjM Reta n tncties No: mm. ams Percent Retained Passed Each Tow Each Total Total -- 1 1/2 3810 0 01 0.01 0.01 0.01 100.0 3/4 19.05 1 0.01 0.01 0.01 0.01 100.0 --------1------1-------1-----4-----:..I------a------ 3/8 9.53 4.81 4.81 1.71 1.71 98.3 --------H-----H-----1-----4------I------4------ 4 4.75 6.91 11.71 2.41 4.11 95.9 - -------r----- -----1----- r-----1------t------ 10---1 2.00 7.81 19.51 2.71 6.81 93.2 40 1 0.43 122.91 142.41 42.91 49.71 50.3 100 0.15 1 138.21 280.61 48.31 98.01 2.0 -------- ___200---1 _0.08 _1 __ 1.81 282.41 0.61 98.61 1.4 <200 r 0.00 ' 0.61 283.01 0.2,----98.87----1.2 Toil 288.5 100.8 48 Sieve Opening(nm) 100.00 10.00 1.00 0.10 0.01 100 t 00.0 100.0-96.3 95.9 !931.2 90 80 7 d 6 50 a 50.3 CD 40 d 30 a 20 10 2.0 1.4 0 Page 1 sieve analysis Job Data: Client: Job Number: 99330 Job Name: Date: 11/7/00 Sample Data: Test Pit/Boring: TP- G Tare: 0 Sample: Wet Weight: 612 Depth: 18' Dry Weight: 585.6 %Moisture: 4.5 Wash Data: Dry Weight(before wash): 585.6 grams Dry Weight(after wash): 579.1 grams Washed Soil Weight: 6.5 grams sieve US- Sieve Weight RetainedPercent Inches or No. ' mm. (grams) Percent Retained Passed Each ; Total Each ; Total Total 1 1/2 38.10 0.01 0.01 0.01 0.01 100.0 ----------------F----------�r----------F---------- ------------F------------+----------- ___-__3/4 19.05 111.11 111.11 19.01 19.01 81.0 318 9.53 1 51.91 163.01 8.91 27.81 72.2 ----------------►----------+----------L----------+-----------L------------ 4 4.75 ; 49.7; 212.7; 8.5; 36.3; 63.7 ------- ----------t----------r-----------------------r------------'+------------ ____--1 ------ 2.00 ; 71.8; 284.5; 12.3; 48.61 51.4 r - ---r----------r----------T-----------r------------4------------ 40 1 0.43 1 24 0.11 524.61 41.01 89.61 10.4 ----------------F-----------F----------F-----------i------------F------------i------------ 100 0.15 1 53.71 578.31 9.21 98.81 1.2 200 0.08' ' 2.4580_7 0.41 99.2i 0.8 - <200 0.00 1.21 581.91 0.2; 99.4; 0.6 Total T 1 588.41 1 100.5 :9 5 Sieve Opening(mm.) 100.00 10.00 1.00 0.10 0.01 100 100.0 - 90 80 81.0 70 0 72.2 60 a 63.7 50 a 51.4 = 40 d 3 a 20 10 F10 0 1.2 0.8 Page 1 sieve analysis Job Data: Client: Job Number: 99330 Job Name: Date: 11/07/00 Sample Data: Test PitBoring: TP - H Tare: 0 Sample: Wet Weight: 731.3 Depth: 17' Dry Weight: 700.5 %Moisture: 4.4 Wash Data: Dry Weight(before wash): 700.5 grants Dry Weight(after wash): 691.9 grams Washed Soil Weight: 8.6 grams sieve' - lave.,1 eta�ned rcen lnct►es or Nc% mn. ( rams Percent t2etained Paned Each Total Each Total Total ---1 1/2 ' 38 10 ' 0.0' 0.0' 0.0' 0.0' 100.0 -- ------ -----J-----1------�------1------ 3/4 21.0' 21.0' 79.0 -------- ------------�----- ------j------4------ 3/8 1 9.53 ' 177.0' 324.2' 25.3' 46.31 53.7 - -------F------ ---- -----{-----A------4------ ----4 ---1 4.75 1 117.01 441.21 16.71 63.01 37.0 ------I 1 2.00 1 68.81 510.01 9.81 72.81 27.2 _40 i 0.43 i 131.91 641.91 18.81 91.61 8.4 --r-----r------1-----T------ ------T------ 100 i 0.15 i 48.01 689.91 6.91 98.51 1.5 ---------- 200 1 _0.08 i __ 2.21 692.11 0.31 98.81 1.2 <200 1 0.00 0.5,--692.6, 0.1,----98.9T----1.1 Total 701.z 10fl.1 =' -0:t Sieve Opening(mm.) 100.00 10.00 1.00 0.10 0.01 100 100.0 90 80 79.0 70 d 60 a � a 53.7 40 m 37.0 30 a 27.2 20 10 8.4 0 1.5 1.2 Page 1 sieve analysis Job Data: Client: Job Number: 99330 Job Name: Date: 11/7/00 Sample Data: Test PitBoring: TP- H Tare: 0 Sample: Wet Weight: 382.9 Depth: 14' Dry Weight: 370.2 %Moisture: 3.4 Wash Data: Dry weight(before wash): 370.2 grams Dry Weight(after wash): 357.3 grams Washed sal Weight: 12.9 grams SieveSieveWeight a ai ercen Inches or No. ' mm (grams) Percent<Retained Passed Each I Total Each I Total Total 11/2 38.10 1 0.01 0.01 '0.0� ----------------t---------- ----------F-----------I------------f-----------+-----1 00_0 3/4 1 19.05 1 0.01 0.01 0.01 ___-_-- 0 01, 100_0 3/8 9.53 35.5; 35.5; 9.6, 9.6; 90.4 ---------------------------------------►---------- ------------ ------------41 4.75 23.6; 59.1; 6.4; 16.0; 84.0 ----------------r----------I----------r----------.t-----------r------------r-__---__--- 10 2.00 28.21 87.31 7.61 23.61 76.4 ---------------r-----------r-----------r----------T-----------r------------r----------- 40 1 0.43 1 194.71 282.01 52.61 76.21 23.8 ----------------f---------------------f----------------------F-------------I---- ------100 1 0.15 1 72.01 354.01 19.41 95.61 4.4 200 ----------- ---_____--- <200 0.00 1 0.71 360.01 0.21 97.21 2.8 Total 1 372.91 1 100.7 -0.7 Sieve Opening(mm.) 100.00 10.00 1.00 0.10 0.01 100 100.0 100.0 - 90 90.4 80 84.0 76.4 70 d 60 a 50 a c 40 CD 30 a -M-- 23.8 20 10 4 4 2.9 No Page 1 N 6.2 RESULTS OF TEST PITS FOR FILL EXPLORATION BY GEOTECH CONSULTANTS DATED NOVEMBER 9, 2000 GEOTEC 13256 NE 201h Street, Suite 16 z Bellevue, WA 98005 CONSULTANTS, INC. (425) 747-5618 FAX 747-8561 Memo JN: 99330 To: Chris Austin Ronr Marc R.McGinnis Company. Bennett Development Date: November 9, 2000 Address: 9 Lake Bellevue Drive, Suite 204 FAX: (425)709-6553 Bellevue,WA 98005 Phone: (206) RE- Results of Test Pits for Fill Exploration Heritage—Renton Hill Renton,Washington This memo presents a summary of the depths of existing fill found in the test pits that previously conducted and have recently excavated during the infiltration testing for the proposed pond. The following table summarizes the depths of fill encountered in the test pits. Test Pit Depth of Fill Below Existing Grade 3 Greater than 12 feet 4 13 feet 5 10 feet A 0 feet B 3 feet C 12 feet D At least 15 feet, possibly greater than 16 feet E 8 feet F 13 feet G 12 feet H 5 feet 1 3 feet 1 2 feet K 7.5 feet L Tires to max.3 feet excavated M Tires to max. 3 feet excavated N 3 feet O 5 feet P 0 feet Q 5.5 feet Generally, the fill consisted of a silty sand that contained chunks of concrete and asphalt, and varying amounts of organic and household debris. Strictly on a visual basis, we estimate that concrete and asphalt, and other debris comprised approximately 25 percent of the fill, by volume. Of this, approximately one-half would be the debris. The concrete, asphalt, and debris will need to be screened from the fill, then the silty sand could be used in non-structural applications on the site. The debris will likely need to be hauled to a landfill, and the concrete/asphalt could likely go to a recycler. c Peterson Coruultin, Jennifer Steig (425)822-7216(FAX) b IL J,J4.i (�W) EX. CB TYPE I 2" 31.8 (SE) TOP 343,5 � 1.6 (NW) 12" IE 340.4 (S) OVERFLOW ISTRUCTURE CAS 0 12" IE 340.5 (NE,� \ _ _ _ gpNNOT TO FX/SnNG PRO OSED INFILTRATION POND I PROPOSED WM ` I SL �5� r 1 •� — 1 MWS EL. = 353.0 LENGTH = LU4' FVC�w r _ POND BOTTOM EL. = 349.5 I WIDTH = 9 p ! i SURF6CE AREA - 2,000 SF I SLOPE = 1.59 ACT CHWL. 340.1 WE,SW) r� CONNECT TO E STN _ �� / / 6' 7000 FENCE( / lE 353.0 fir \ "\//1 ■� lJ TYP I TOP I 'q,- 349.5 T P 0�' l WA TER P'T 4\ \ TRACT 44 , PTLUTP J PV OVERFLOW\ x f S �R TP SPUTTER I 1 DRA, LENGTH / \ \�� `I` \i (rYF 58.68' TR�� \ -P_-9- I G I �� \\ �►�' \ \ \SPILZ C N 1ROL / �� (� i T P P7L� LIS -T P T PP=JV�` 4 \ _ r \\ \� ITRACT PARK ,'I _ _ A � , 30, I NORTH ® Test Pit conducted for \ \\ \� \ 12 I ( Sept, 14, 1999 study % Test Pit conducted for 2 I recent infiltration testing Test Pit for fill depth determination\ y N W I �l_ 14"M ' r� I Sc>�Ie - -.5'C� L54n%C 44L5 W 6.3 GEOTECHNICAL ENGINEERING STUDY BY GEOTECH CONSULTANTS DATED SEPTEMBER 14, 1999 G E O FIF E C H September 14, 1999 CONSULTANTS, INC. '256 NE 20th Street,Suite 16 JN 99330 ,ellevue,WA 98005 (425)747-5618 FAX(425)747-8561 The Bennett Corporation 9 Lake Bellevue Drive, Suite 204 Bellevue, Washington 98005 Attention: Ryan Fike Subject: Transmittal Letter— Geotechnica/Engineering Study Proposed Heritage Arnold Project South 7th Street and Beacon Way Southeast Renton, Washington Reference: Hart Crowser, Inc.; Abandoned Mine Assessment, Heritage Arnold Property, Renton, Washington; August 16, 1999. Dear Mr. Fike: We are pleased to present this geotechnical engineering report for the proposed residential subdivision to be constructed at the Heritage Arnold property in Renton. The scope of our work consisted of exploring site surface and subsurface conditions, and then developing this report to provide recommendations for general earthwork, design criteria for foundations, retaining walls, and pavements and mitigation of potential coal mine subsidence hazards. This work was authorized by your acceptance of our proposal, P-5004, dated August 16, 1999. The subsurface conditions of the proposed building site were explored with fourteen test pits that encountered native topsoil and weathered, gravelly sand overlying dense to very dense, gravelly sand. Loose fill with concrete rubble, construction debris, and household garbage was encountered as deep as 13 feet below existing grade on the western portion of the site. It appears that the small rise in this area consists of fill. Single-family residences may be supported on conventional foundations bearing directly on native, medium-dense to dense, gravelly sands. Depending on the final site grades and on the locations of the residences, some overexcavation may be required to expose competent bearing soils. The fill soils are not suitable for supporting the loads associated with the proposed development; foundations in these areas either will need to be overexcavated, or be pile- or pier-supported. The site is underlain by three deep coal seams, which were mined until the early 1920s. Hart Crowser, Inc. developed a report detailing mine activity and potential subsidence issues at the subject site. Applicable recommendations from their study have been incorporated into this report. The Bennett Corporation JN 99330 September 14, 1999 Transmittal Letter— Page 2 The attached report contains a discussion of the study and our recommendations. Please contact us if there are any questions regarding this report, or if we can be of further assistance during the design and construction phases of this project. Respectfully submitted, GEOTECH CONSULTANTS, INC. H� Marc R. McGinnis, P.E. Associate EMT/MRM: alt GEOTECH CONSULTANTS, INC. GEOTECHNICAL ENGINEERING STUDY Proposed Heritage Arnold Project South 7th Street and Beacon Way Southeast Renton, Washington This report presents the findings and recommendations of our geotechnical engineering study for the site of the proposed subdivision in Renton. We were provided with a topographic map. Mead Gilman & Associates developed this plan, which is dated July 28, 1999. Development of the property is in the planning stage, and detailed plans were not made available to us. Based on conversations with Ryan Fike, we understand that the site will be developed with a number of single-family residences. We anticipate that access to the residences will be via paved common streets and private driveways. We were also provided with the Abandoned Mine Assessment, prepared by Hart Crowser, Inc. This report, which is dated August 16, 1999, discusses historical coal mining activity at the subject site and provides recommendations to protect the development from significant hazards presented by potential ground subsidence. SITE CONDITIONS SURFACE CONDITIONS The Vicinity Map, Plate 1, illustrates the general location of the site. The triangular, approximately 10.4-acre site is located near the intersection of South 7th Street and Beacon Way Southeast. The property is bordered on its southern, angled side by the Cedar River Pipeline easement, and on its northern and eastern sides by single-family residences and undeveloped woodlands, respectively. The northeastern property corner is located at the top of a steep, undeveloped slope. This slope has an estimated height of 30 feet and an inclination of 50 to 60 percent. The terrain on the site is generally rolling, with small rises and hollows located throughout the parcel. It appears that some grading has been done on the property, resulting in a steep, U-shaped cut slope located near the center of the site. An abandoned gravel road winds through the southeastern side of the site and ends at the steep cut slope. The flat area at the base of the cut slope may have been a gravel pit at some time during the past. The small rise located on the western side of this flat area consists of fill; some pea gravel is visible on the surface. The westernmost portion of the site is strewn with large amounts of household garbage and construction debris, and appears to have been used as a dump. The eastern portion of the site is densely wooded with tall evergreen and deciduous trees. The ground is covered with ferns, blueberry and blackberry bushes, and other low-growth vegetation. No obvious signs of slope instability were observed during our site visit. Additionally, no visible indications of air shafts, trenches, or ground subsidence were observed on the portions of the site that we traversed. GEOTECH CONSULTANTS, INC. The Bennett Corporation JN 99330 September 14, 1999 Page 2 SUBSURFACE CONDITIONS The subsurface conditions were explored by excavating fourteen test pits at the approximate locations shown on the Site Exploration Plan, Plate 2. The field exploration program was based upon the proposed construction and required design criteria, the site topography and access, the subsurface conditions revealed during excavation, and the scope of work outlined in our proposal. The test pits were excavated on August 26, 1999 with a trackhoe. A geotechnical engineer from our staff observed the excavation process, logged the test pits, and obtained representative samples of the soil encountered. "Grab" samples of selected subsurface soil were collected from the backhoe bucket. The Test Pit Logs are attached to this report as Plates 3 through 9. The test pits encountered native topsoil overlying loose, gravelly sand that became medium-dense to dense with depth. This native sand contained occasional boulders. The test pits on the westernmost corner of the site encountered loose fill that contained construction debris and concrete and asphalt rubble to depths of 10 to 13 feet. Native sand was encountered underlying the fill, except in Test Pit 3, which revealed fill to the maximum 12-foot depth that was possible. The final logs represent our interpretations of the field logs. The stratification lines on the logs represent the approximate boundaries between soil types at the exploration locations. The actual transition between soil types may be gradual, and subsurface conditions can vary between exploration locations. The logs provide specific subsurface information only at the locations tested. The relative densities and moisture descriptions indicated on the test pit logs are interpretive descriptions based on the conditions observed during excavation. The compaction of backfill was not in the scope of our services. Loose soil will therefore be found in the area of the test pits. If this presents a problem, the backfill will need to be removed and replaced with structural fill during construction. Groundwater No groundwater seepage or wet.soil was observed during excavation. It should be noted that groundwater levels vary seasonally with rainfall and other factors; the absence of groundwater in our explorations does not eliminate the possibility that groundwater could be encountered during future excavations. However, due to the granular nature of the site soils, encountering significant near-surface groundwater is unlikely. We anticipate that groundwater could be found between the near-surface weathered soil and the underlying denser soil. CONCLUSIONS AND RECOMMENDATIONS GENERAL Based on our explorations at the subject site, it is our opinion that construction of the proposed single-family residences is feasible from a geotechnical engineering standpoint. The proposed residences may be supported on conventional foundations bearing directly on medium-dense to dense, native soil. Depending on final site grading, some overexcavation may be required to expose competent sand. The loose fill encountered on the western corner of the site is not suitable GEOTECH CONSULTANTS, INC. The Bennett Corporation JN 99330 September 14, 1999 Page 3 to support the loads associated with the proposed development. The fill should be removed from building areas, or deep foundations should extend to the underlying, native, gravelly sand. We can provide recommendations and design criteria for driven piles or drilled piers, if requested. The steep slope near the northeast corner of the property may experience shallow slope movement in the future. To protect against structural damage, houses and other occupied buildings should be set back at least 25 feet from this slope. No clearing or grading should occur within 10 feet of the slope's crest. Water from drains and impervious surfaces should not be directed toward the steep slope. The site is underlain by three deep coal seams which were mined until the early 1920s. Hart Crowser, Inc. completed an assessment of the historical mine use and potential hazards associated with development over abandoned mines. Their study concludes that there is a risk of noticeable differential foundation settlement due to ground subsidence. However, the maximum calculated ground strain would result in a differential settlement of approximately 3 inches in a distance of 50 feet. Because of the approximately 80 years that have elapsed since the last documented mining, it is likely that most subsidence has already occurred. Therefore, the risk of significant area-wide subsidence is low. We highlight the following recommendations as applicable to the proposed development: • All footings should be continuous, with increased steel reinforcement, to span potential isolated subsidence areas and reduce differential settlement. • Post-and-beam construction should be considered to allow for relatively easy releveling in the event of settlement. • Concrete slabs-on-grade should be avoided in favor of floors on joists. • All new construction should include vapor barriers and well-ventilated crawl spaces to mitigate mine gas emissions. • Rigid structural materials, such as concrete and masonry, should be avoided where possible in favor of more flexible materials like steel and timber. • Avoid siding, weather stripping materials, and interior floor and wall coverings that are settlement-sensitive. • Plan regular maintenance for weather stripping, utilities, and mechanical systems which may be affected by building movement. At the time of earthwork, any areas of fill in structural areas should be thoroughly investigated to verify that they are not underlain by old air shafts or mine openings. Ground subsidence could result in distress or damage to pavements and utilities. Periodic maintenance and repair of these elements should be expected. Where the existing fill is not removed, on-grade elements such as pavements and slabs would experience noticeable long-term settlement. Pavements over existing fill should be underlain by at least 18 inches of gravelly structural fill to reduce, but not eliminate, differential settlement. Final slopes in developed portions of the site should be graded to an inclination of no steeper than 2:1 (Horizontal:Vertical). The erosion control measures needed during the site development will depend heavily on the weather conditions that are encountered. We anticipate that a silt fence will be needed around the GEOTECH CONSULTANTS, INC. The Bennett Corporation JN 99330 September 14, 1999 Page 4 downslope side of any cleared areas. Rocked construction access roads should be extended into the site to reduce the amount of mud carried off the property by trucks and equipment. Following rough grading, it may be necessary to mulch or hydroseed bare areas that will not be immediately covered with landscaping or an impervious surface. Geotech Consultants, Inc. should be allowed to review the final development plans to verify that the recommendations presented in this report are adequately addressed in the design. Such a plan review would be additional work beyond the current scope of work for this study, and it may include revisions to our recommendations to accommodate site, development, and geotechnical constraints that become more evident during the review process. CONVENTIONAL FOUNDATIONS The proposed single-family residences can be supported on conventional continuous footings bearing on undisturbed, native, gravelly sand, or on structural fill placed above this competent, native soil. See the later sub-section entitled GENERAL EARTHWORK AND STRUCTURAL FILL for recommendations regarding the placement and compaction of structural fill beneath structures. Adequate compaction of structural fill should be verified with frequent density testing during fill placement. We recommend that continuous footings have minimum widths of 12 and 16 inches, respectively. The foundations should be reinforced to span a minimum distance of 10 feet without soil support, similar to grade beams. They should be bottomed at least 18 inches below the lowest adjacent finish ground surface. Footing subgrades must be cleaned of loose or disturbed soil prior to pouring concrete. Depending upon site and equipment constraints, this may require removing the disturbed soil by hand. Depending on the final site grades, some overexcavation may be required below the footings to expose competent, native soil. Unless lean concrete is used to fill an overexcavated hole, the overexcavation must be at least as wide at the bottom as the sum of the depth of the overexcavation and the footing width. For example, an overexcavation extending 2 feet below the bottom of a 3-foot-wide footing must be at least 5 feet wide at the base of the excavation. If lean concrete is used, the overexcavation need only extend 6 inches beyond the edges of the footing. An allowable bearing pressure of 3,000 pounds per square foot (pso is appropriate for footings supported on medium-dense to dense gravelly sand. For footings supported on structural fill, an allowable bearing pressure of 2,000 psf is appropriate. A one-third increase in these design bearing pressures may be used when considering short-term wind or seismic loads. Lateral loads due to wind or seismic forces may be resisted by friction between the foundation and the bearing soil, or by passive earth pressure acting on the vertical, embedded portions of the foundation. For the latter condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded by level structural fill. We recommend using the following design values for the foundation's resistance to lateral loading: Parameter Design Value Coefficient of Friction 0.45 Passive Earth Pressure 350 pcf GEOTECH CONSULTANTS, INC. The Bennett Corporation JN 99330 September 14, 1999 Page 5 Where:(i)pcf is pounds per cubic foot,and(ii) passive earth pressure is computed using the equivalent fluid density. If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. We recommend a safety factor of at least 1.5 for the foundation's resistance to lateral loading, when using the above design values. SEISMIC CONSIDERATIONS The site is located within Seismic Zone 3, as illustrated on Figure No. 16-2 of the 1997 Uniform Building Code (UBC). In accordance with Table 16-J of the 1997 UBC, the soil within 100 feet of the ground surface is best represented by Soil Profile Type S. (Very Dense Soil). The site soils are not subject to seismic liquefaction because of their dense nature and because of the absence of near-surface groundwater. PERMANENT FOUNDATION AND RETAINING WALLS Retaining walls backfilled on only one side should be designed to resist the lateral earth pressures imposed by the soil they retain. The following recommended design parameters are for walls that restrain level backfill: Parameter Design Value Active Earth Pressure 35 pcf Passive Earth Pressure 350 pcf Coefficient of Friction 0.45 Soil Unit Weight 135 pcf Where:(i)pcf is pounds per cubic foot,and(ii)active and passive earth pressures are computed using the equivalent fluid pressures. For a restrained wall that cannot deflect at least 0.002 times its height,a uniform lateral pressure equal to 10 psf times the height of the wall should be added to the above active equivalent fluid pressure. The values given above are to be used to design permanent foundation and retaining walls only. The passive pressure given is appropriate for the depth of level structural fill placed in front of a retaining or foundation wall only. We recommend a safety factor of at least 1.5 for overturning and sliding, when using the above values to design the walls. Restrained wall soil parameters should be utilized for a distance of 1.5 times the wall height from corners in the walls. The design values given above do not include the effects of any hydrostatic pressures behind the walls and assume that no surcharges, such as those caused by slopes, vehicles, or adjacent foundations will be exerted on the walls. If these conditions exist, those pressures should be added to the above lateral soil pressures. Where sloping backfill is desired behind the walls, we will need GEOTECH CONSULTANTS, INC. The Bennett Corporation JN 99330 September 14, 1999 Page 6 to be given the wall dimensions and the slope of the backfill in order to provide the appropriate design earth pressures. The surcharge due to traffic loads behind a wall can typically be accounted for by adding a uniform pressure equal to 2 feet multiplied by the above active fluid density. Heavy construction equipment should not be operated behind retaining and foundation walls within a distance equal to the height of a wall, unless the walls are designed for the additional lateral pressures resulting from the equipment. The wall design criteria assume that the backfill will be well-compacted in lifts no thicker than 12 inches. The compaction of backfill near the walls should be accomplished with hand-operated equipment to prevent the walls from being overloaded by the higher soil forces that occur during compaction. Retaining Wall Backrill and Waterproofing Backfill placed behind retaining or foundation walls should be coarse, free-draining, structural fill containing no organics. This backfill should contain no more than 5 percent silt or clay particles and have no gravel greater than 4 inches in diameter. The percentage of particles passing the No. 4 sieve should be between 25 and 70 percent. If the native sand is used as backfill, a drainage composite similar to Miradrain 6000 should be placed against the backfilled retaining walls. The drainage composites should be hydraulically connected to the foundation drain system. For increased protection, drainage composites should be placed along cut slope faces, and the walls should be backfilled with pervious soil. The purpose of these backfill requirements is to ensure that the design criteria for a retaining wall are not exceeded because of a build-up of hydrostatic pressure behind the wall. The top 12 to 18 inches of the backfill should consist of a compacted, relatively impermeable soil or topsoil, or the surface should be paved. The ground surface must also slope away from backfilled walls to reduce the potential for surface water to percolate into the backfill. The sub-section entitled GENERAL EARTHWORK AND STRUCTURAL FILL contains recommendations regarding the placement and compaction of structural fill behind retaining and foundation walls. The above recommendations are not intended to waterproof below-grade walls. The performance of any subsurface drainage system will degrade over time. Also, groundwater drainage patterns can change, even if seepage is not evident in the temporary excavation. Therefore, if future moist conditions or seepage through the walls are not acceptable, waterproofing should be provided. This typically includes limiting cold-joints and wall penetrations, and using bentonite panels or membranes on the outside of the walls. Applying a thin coat of asphalt emulsion is not considered waterproofing, but will only help to prevent moisture, generated from water vapor or capillary action, from seeping through the concrete. EXCAVATIONS AND SLOPES Excavation slopes should not exceed the limits specified in local, state, and national government safety regulations. Temporary cuts to a depth of about 4 feet may be attempted vertically in unsaturated soil, away from property fines, utilities, and existing structures, if there are no indications of slope instability. Based upon Washington Administrative Code (WAC) 296, Part N, GEOTECH CONSULTANTS, INC. The Bennett Corporation JN 99330 September 14, 1999 Page 7 the native sand at the subject site would generally be classified as Type B. Therefore, temporary cut slopes greater than 4 feet in height cannot be excavated at an inclination steeper than 1:1 (Horizontal:Vertical), extending continuously between the top and the bottom of a cut. The above-recommended temporary slope inclination is based on what has been successful at other sites with similar soil conditions. Temporary cuts are those that will remain unsupported for a relatively short duration to allow for the construction of foundations, retaining walls, or utilities. Temporary cut slopes should be protected with plastic sheeting during wet weather. The cut slopes should also be backfilled or retained as soon as possible to reduce the potential for instability. Please note that sand can cave suddenly and without warning. Utility contractors should be made especially aware of this potential danger. All permanent cuts into native soil should be inclined no steeper than 2:1 (H:V). Fill slopes should not be constructed with an inclination greater than 2:1 (H:V). To reduce the potential for shallow sloughing, fill must be compacted to the face of these slopes. This could be accomplished by overbuilding the compacted fill and then trimming it back to its final inclination. Water should not be allowed to flow uncontrolled over the top of any temporary or permanent slope. Also, all permanently exposed slopes should be seeded with an appropriate species of vegetation to reduce erosion and improve the stability of the suficial layer of soil. Any disturbance to the existing steep slope beyond the northeastern corner of the site may reduce the stability of the slope. Damage to the existing vegetation and ground should be minimized, and any disturbed areas should be revegetated as soon as possible. Soil from the excavations should not be placed on, or near, the slope. DRAINAGE CONSIDERATIONS Foundation drains are required where crawl spaces or basements will be below a structure, or the outside grade does not slope downward from a building. Drains should also be placed at the base of all earth-retaining walls. These drains should be surrounded by at least 6 inches of 1-inch- minus, washed rock and then wrapped in non-woven, geotextile filter fabric (Mirafi 140N, Supac 4NP, or similar material). At its highest point, a perforated pipe invert should be at least 6 inches below the bottom of a slab floor or the level of a crawl space, and it should be sloped for drainage. Drainage should also be provided inside the footprint of a structure, where a crawl space will slope or be lower than the surrounding ground surface, or an excavation encounters significant seepage. We can provide recommendations for interior drains, should they become necessary, during excavation and foundation construction. All roof and surface water drains must be kept separate from the foundation drain system. A typical drain detail is attached to this report as Plate 10. For the best long-term performance, perforated PVC pipe is recommended for all subsurface drains. No groundwater was observed during our field work. If seepage is encountered in an excavation, it should be drained from the site by directing it through drainage ditches, perforated pipe, or French drains, or by pumping it from sumps interconnected by shallow connector trenches at the bottom of the excavation. GEOTECH CONSULTANTS, INC. The Bennett Corporation A 99330 September 14, 1999 Page 8 The excavations and site should be graded so that surface water is directed away from the tops of slopes. Water should not be allowed to stand in any area where foundations, slabs, or pavements are to be constructed. Final site grading in areas adjacent to the buildings should slope away at least 2 percent, except where the area is paved. Water from roof, storm water, and foundation drains should not be discharged onto slopes; it should be tightlined to a suitable outfall located away from any slopes. PAVEMENT AREAS The pavement sections may be supported on competent, native soil or on structural fill compacted to a 95 percent density. We recommend that the pavement subgrade must be in a stable, non- yielding condition at the time of paving. Granular structural fill or geotextile fabric may be needed to stabilize soft, wet, or unstable areas. To evaluate pavement subgrade strength, we recommend that a proof-roll be completed with a loaded dump truck immediately before paving. In most instances where unstable subgrade conditions are encountered, an additional 12 inches of granular structural fill will stabilize the subgrade, except for very soft areas where additional fill could be required. The subgrade should be evaluated by Geotech Consultants, Inc., after the site is stripped and cut to grade. Recommendations for the compaction of structural fill beneath pavements are given in a later sub-section entitled GENERAL EARTHWORK AND STRUCTURAL FILL. The performance of site pavements is directly related to the strength and stability of the underlying subgrade. The pavement for lightly-loaded traffic and parking areas should consist of 2 inches of asphalt concrete (AC) over 4 inches of crushed rock base (CRB) or 3 inches of asphalt-treated base (ATB). We recommend providing heavily-loaded areas with 3 inches of AC over 6 inches of CRB or 4 inches of ATB. Heavily-loaded areas are typically main driveways, dumpster sites, or areas with truck traffic. The pavement section recommendations and guidelines presented in this report are based on our experience in the area and on what has been successful in similar situations. We can provide recommendations based on expected traffic loads and California Bearing Ratio tests, if requested. As with any pavements, some maintenance and repair of limited areas can be expected as the pavement ages. To provide for a design without the need for any repair would be uneconomical. GENERAL EARTHWORK AND STRUCTURAL FILL All building and pavement areas should be stripped of surface vegetation, topsoil, organic soil, and other deleterious material. The stripped or removed materials should not be mixed with any materials to be used as structural fill, but they could be used in non-structural areas, such as landscape beds. Structural fill is defined as any fill placed under a building, behind permanent retaining or foundation walls, or in other areas where the underlying soil needs to support loads. All structural fill should be placed in horizontal lifts with a moisture content at, or near, the optimum moisture content. The optimum moisture content is that moisture content that results in the greatest compacted dry density. The moisture content of fill is very important and must be closely controlled during the filling and compaction process. GEOTECH CONSULTANTS, INC. The Bennett Corporation JN 99330 September 14, 1999 Page 9 The allowable thickness of the fill lift will depend on the material type selected, the compaction equipment used, and the number of passes made to compact the lift. The loose lift thickness should not exceed 12 inches. We recommend testing the fill as it is placed. If the fill is not compacted to specifications, it can be recompacted before another lift is placed. This eliminates the need to remove the fill to achieve the required compaction. The following table presents recommended relative compactions for structural fill: Location of Minimum Fill Placement Relative Compaction Beneath footings or 95% walkways Behind retaining walls 90% 95%for upper 12 inches of Beneath pavements subgrade; 90% below that level Where:Minimum Relative Compaction is the ratio,expressed in percentages,of the compacted dry density to the maximum dry density, as determined in accordance with ASTM Test Designation D 1557-91 (Modified Proctor). Use of On-Site Soil If grading activities take place during wet weather, or when the site soils are wet, site preparation costs may be higher because of delays due to rain and the potential need to dry the site soils. The moisture content of the on-site soil must be at, or near, the optimum moisture content, as the soil cannot be consistently compacted to the required density when the moisture content is significantly greater than optimum. The on-site, non-organic sand could be used as structural fill, if grading operations are conducted during hot, dry weather, when drying the wetter soil by aeration is possible. During excessively dry weather, however, it may be necessary to add water to achieve the optimum moisture content. LIMITATIONS The analyses, conclusions, and recommendations contained in this report are based on site conditions as they existed at the time of our exploration and assume that the soil and groundwater conditions encountered in the test pits are representative of subsurface conditions on the site. If the subsurface conditions encountered during construction are significantly different from those observed in our explorations, we should be advised at once so that we can review these conditions and reconsider our recommendations where necessary. Unanticipated soil conditions are commonly encountered on construction sites and cannot be fully anticipated by merely taking soil samples in test pits. Subsurface conditions can also vary between exploration locations. Such unexpected conditions frequently require making additional expenditures to attain a properly constructed project. It is recommended that the owner consider providing a contingency fund to accommodate such potential extra costs and risks. This is a standard recommendation for all projects. GEOTECH CONSULTANTS, INC. The Bennett Corporation JN 99330 September 14, 1999 Page 10 This report has been prepared for the exclusive use of the Bennett Corporation, and its representatives, for specific application to this project and site. Our recommendations and conclusions are based on observed site materials, and selective engineering analyses. Our conclusions and recommendations are professional opinions derived in accordance with current standards of practice within the scope of our services and within budget and time constraints. No warranty is expressed or implied. The scope of our services does not include services related to construction safety precautions, and our recommendations are not intended to direct the contractor's methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. This report, and the study by Hart Crowser, should be provided to any future property owners to inform them of our findings and recommendations. Additionally, this report should be provided in the project contract documents for the information of the contractor. ADDITIONAL SERVICES In addition to reviewing the final plans, Geotech Consultants, Inc. should be retained to provide geotechnical consultation, testing, and observation services during construction. This is to confirm that subsurface conditions are consistent with those indicated by our exploration, to evaluate whether earthwork and foundation construction activities comply with the general intent of the recommendations presented in this report, and to provide suggestions for design changes in the event subsurface conditions differ from those anticipated prior to the start of construction. However, our work would not include the supervision or direction of the actual work of the contractor and its employees or agents. Also, job and site safety, and dimensional measurements, will be the responsibility of the contractor. We conducted an environmental assessment for this site which is presented in a separate report. The following plates are attached to complete this report: Plate 1 Vicinity Map Plate 2 Site Exploration Plan Plates 3 - 9 Test Pit Logs Plate 10 Typical Footing Drain GEOTECH CONSULTANTS, INC. The Bennett Corporation JN 99330 September 14, 1999 Page 11 We appreciate the opportunity to be of service on this project. If you have any questions, or if we may be of further service, please do not hesitate to contact us. Respectfully submitted, GEOTECH CONSULTANTS, INC. 167�"d Erin M. Toland Geotechnical Engineer �G OM � WAS I� r 27845 O�cc �FCISTF"TL SS��INA �G EXPIRES Marc R. McGinnis, P.E. Associate EMT/ MRM: alt GEOTECH CONSULTANTS, INC. r R5t _ _ Ln AV y 128 wo S-NECA AV SW SENECA 5 h G l AV SW L ND V AV SW BICCEY P Sue t�k .. NF ECA C lI �1900 N �, N �� 700 PF ,�N i2 SW STEVENS'�IAV LE ---iLIND su L NO AV 400 cn MAPLE PIENw Nil, E LLEY I R —� o '° H! 1E ArI F+ AvHARDIE ,S R NA _ W Y AV sW �L\I ', '''1 O isms '1"�t�n a b� v° cn cn N z • A d �1 I I� n 0051 ■ a 1 W LAKES AV cKE NV v JNM2i� Es�iN .. 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'JOB, � ( ` � ( `V.Jq., .J j(/�.'j�{�• 1` •\� � V'•�,�r ��30�V� . ° •JI: \--fir .`�__l'�� ' \w J\ �\r\\��,��, ° ]i Cl)oAl VV'• Jam_ co 390 ``,, ,1_JI �I �, 777 � ,� •JI Acn fA rV CD ° CD c.1. sv 'QJ CD N I-1` {e, °�� TEST PIT 1 Description FILL Concrete rubble with old building materials, loose (FILL) RlDark brown, silty SAND, moist, loose (Topsoil) over tan, slightly silty SAND, dry to slightly moist, loose 5 * Test Pit was terminated at 4 feet on August 26, 1999. * No groundwater seepage was observed during excavation. * Caving was observed to bottom during excavation. 10 15 "e, �t TEST PIT 2 o� ella� 5 � �aro� �5G Description Topsoil Red-brown SAND, dry to slightly moist, loose (TOPSOIL) Brown, slightly gravelly SAND, medium-grained, dry, loose - becomes more gravelly, slightly moist, medium-dense 5 sP - becomes moist, medium-to coarse-grained, less gravelly, dense 10 * Test Pit was terminated at 11 feet on August 26, 1999. * No groundwater seepage was observed during excavation. 15 * Caving was observed to 8 feet during excavation. TEST PIT LOG GEOTECH South 7th Street & Beacon Way Southeast CONSULTANTS,INC. Renton, Washington 4 Job No: Date: Logged by: Plate: 99330 1 Sept. 1999 1 EMT 3 TEST PIT 3 Description Dark brown, silty SAND, with concrete rubble, moist, loose (FILL) - piece of old carpet 5 FILL - asphalt chunks 8-12" in size - becomes gray-black, silty, gravelly SAND 10 - large tree stump * Test Pit was terminated at 12 feet on August 26, 1999. 15L * No groundwater seepage was observed during excavation. * Caving was observed to 12 feet during excavation. {q�`i 0 { TEST PIT 4 o op Description G5 G° �° ��' Description Red-brown, silty SAND, with roots, concrete rubble, and metal debris, dry to slightly moist, loose (FILL) - large asphalt chunk (6 feet across and 6 inches thick) 5 - some glass, household debris FILL - becomes gray-black, silty, gravelly sand, with asphalt chunks and household debris 10 sP Red-brown, slightly silty, gravelly SAND, medium- to coarse-grained, moist, medium-dense to dense 15 - becomes brown at 13.5 feet, dense * Test Pit was terminated at 14.5 feet on August 26, 1999. No groundwater seepage was observed during excavation. * Caving was observed to 13 feet during excavation. TEST PIT LOG GEOTECH South 7th Street & Beacon Way Southeast CONSULTANTS, INC. Renton, Washington Job No: Date: Logged by: Plate: 99330 1 Sept. 1999 EMT 4 1 {Q °10 TEST PIT 5 d ti� 5 Description Red-brown, silty, gravelly SAND, with cobbles, brick debris, and household garbage, loose (FILL) - large tree stump and root ball 5 FILL - becomes gray, slightly silty, gravelly SAND, moist 10 SP Red-brown,weathered, slightly silty SAND, fine-to medium-grained, moist, medium-dense -becomes brown, dense * Test Pit was terminated at 11.5 feet on August 26, 1999. * No groundwater seepage was observed during excavation. 15L Caving was observed to 10 feet during excavation. 1 {e, °iO TEST PIT 6 IQ G° �a "` Description FILL Red-brown, silty SAND, with abundant roots, dry to slightly moist, loose (FILL) 6 inches of dark brown TOPSOIL over Red-brown, gravelly SAND, fine-to medium-grained, moist, loose 5 sP - becomes medium-dense to dense - becomes less gravelly, dense 10 * Test Pit was terminated at 8.5 feet on August 26, 1999. * No groundwater seepage was observed during excavation. * No caving was observed during excavation. 15 TEST PIT LOG GE O TE C H South 7th Street & Beacon Way Southeast CONSULTANTS,INC. Renton, Washington Job No: Date: I Logged by: I Plate: —�� 99330 Sept. 1999 EMT 5_j TEST PIT 7 o������a��ti� G5 Description Brown, slightly silty SAND, with abundant roots, dry, loose (TOPSOIL) Red-brown SAND, with occasional boulders up to 1 foot diameter, fine-grained, dry to slightly moist, medium-dense gp - becomes brown, with gravel and cobbles, moist, dense 5 10 * Test Pit was terminated at 8.5 feet on August 26, 1999. * No groundwater seepage was observed during excavation. * Some caving in upper 4 feet was observed during excavation. 15 TEST PIT 8 c �`���a� ti� GS Description Dark brown, slightly silty SAND, with occasional gravel, with abundant roots, dry to slightly moist (TOPSOIL) Red-brown, silty, gravelly SAND, fine-to medium-grained, moist, medium-dense gM to dense - becomes brown, very dense 5 * Test Pit was terminated at 6.5 feet on August 26, 1999. * No groundwater seepage was observed during excavation. 10 * No caving was observed during excavation. 15 TEST PIT LOG GEOTECH South 7th Street & Beacon Way Southeast CONSULTANTS,INC. Renton, Washington Job No: Date: Logged by: Plate: 99330 Sept. 1999 1 EMT 1 6 1 {� `i� TEST PIT 9 G°� � ro �`' Description Dark brown, silty SAND, loose (TOPSOIL) Red-brown, silty, gravelly SAND, with abundant roots, fine-grained, moist, SM medium-dense - becomes brown, dense to very dense 5 * Test Pit was terminated at 5.5 feet on August 26, 1999. * No groundwater seepage was observed during excavation. * No caving was observed during excavation. 10 15 �`� TEST PIT 10 Description Topsoil Red-brown TOPSOIL, loose Brown, silty, gravelly SAND, with abundant roots, fine-to medium-grained, moist, medium-dense to dense SM 5 - becomes dense to very dense * Test Pit was terminated at 5.5 feet on August 26, 1999. * No groundwater seepage was observed during excavation. * No caving was observed during excavation. 10 15 TEST PIT LOG GE O TE C H South 7th Street & Beacon Way Southeast CONSULTANT'S,INC. Renton, Washington Job No: Date: Logged by: Plate: 99330 Sept. 1999 EMT 7 l J10 TEST PIT 11 aa�%e, �G5 G 4 Description Dark brown, silty SAND, with abundant roots, moist, loose (TOPSOIL) Red-brown SAND, medium-grained, moist, medium-dense sP - becomes dense, brown 5 * Test Pit was terminated at 7 feet on August 26, 1999. 10 * No groundwater seepage was observed during excavation. * Some caving of upper 4 feet was observed during excavation. 15 {e, �i� TEST PIT 12 ell 9 Go Description Dark brown, slightly silty SAND, with abundant roots, dry to slightly moist (TOPSOIL) sp Reddish-brown SAND, with some gravel and sandstone chunks, medium-grained, moist, medium-dense to dense 5 - becomes brown, very dense * Test Pit was terminated at 6 feet on August 26, 1999. * No groundwater seepage was observed during excavation. * No caving was observed during excavation. 10 15 TEST PIT LOG GEOTECH South 7th Street & Beacon Way Southeast CONSULTANT'S,MC. Renton, Washington Job No: Date: ILoggedby: Plate: 99330 Sept. 1999 EMT 1 8 TEST PIT 13 Go�� a,�tie �G5 Description Dark brown, silty SAND, with abundant roots, dry to slightly moist, loose (TOPSOIL) SP Red-brown SAND with gravel, medium-grained, moist, medium-dense - becomes brown, dense to very dense 5 * Test Pit was terminated at 5.5 feet on August 26, 1999. * No groundwater seepage was observed during excavation. * No caving was observed during excavation. 10 15 TEST PIT 14 r 0������0; %G G5 G° Description Red-brown, slightly silty SAND,with abundant roots, fine-grained, dry to slightly moist, loose - becomes medium-dense sP - becomes moist, dense to very dense 5 * Test Pit was terminated at 5 feet on August 26, 1999. * No groundwater seepage was observed during excavation. * No caving was observed during excavation. 10 15 TEST PIT LOG GEOTECH South 7th Street & Beacon Way Southeast CONSULTANT'S,INC. Renton, Washington A _ Job No: Date: I Logged by: Plate: ��� 99330 1 Sept. 1999 EMT 9 Slope backfill away from foundation. TIGHTLINE ROOF DRAIN Do not connect fo fooling drain. BACKFIL L See text for VAPOR BARRIER requirements. SLAB WASHED ROCK o.° '.° `^; `� �, 4 min. 6 m ° FREE-DRAINING SAND/GRAVEL NONWOVEN GEOTEXTILE FILTER FABRIC 4"PERFORATED HARD PVC PIPE Invert at least as low as fooling and/or crawl space. Slope to drain. Place weepholes downward. TYPICAL FOOTING DRAIN GEOTECH South 7th Street & Beacon Way Southeast CONSULTANTS,nvc. Renton, Washington — Job No: Date: plate. 99330 1 Sept. 1999 :10 :1 6.4 PHASE 1 ENVIRONMENTAL SITE ASSESSMENT BY GEOTECH CONSULTANTS DATED SEPTEMBER 9, 1999 G E O T E C H September 9, 1999 CONSULTANTS, INC. 256 NE 20th street,suite 16 JN 9930A sllevue,WA 98005 (425)747-5618 FAX(425)747-8561 Bennett Corporation 9 Lake Bellevue Drive, Suite 204 Bellevue, Washington 98005 Attention: Ryan Fike Subject: Transmittal Letter Phase 1 Environmental Site Assessment Proposed Heritage Arnold Project Beacon Way Southeast Renton, Washington Dear Mr. Fike: Geotech Consultants, Inc. is pleased to present the results of our recently completed Phase 1 Environmental Site Assessment for the subject property. Our work was completed in accordance with our proposal dated August 18, 1999. Please find the assessment attached.- We appreciate this opportunity to be of service to Bennett Corporation on this project. If you have any questions, or if we may be of additional service, please contact us. Respectfully submitted, GEOTECH CONSULTANTS, INC. David Bair Environmental Engineer DB: alt �i _ PHASE 1 ENVIRONMENTAL SITE ASSESSMENT Proposed Heritage Arnold Project Beacon Way Southeast Renton, Washington Submitted by: GEOTECH CONSULTANTS, INC. David Bair Environmental Engineer FV AS CA �SSj�NAL �G /j0l9 EXPIRES 8/17/o1 James R. Finley, P.E. Principal GEOTECH CONSULTANTS, INC. TABLE OF CONTENTS 1.0 EXECUTIVE SUMMARY.......................................................................................................1 2.0 INTRODUCTION...................................................................................................................1 2.1 Special Terms and Conditions 2.2 Purpose and Scope of Work 3.0 SITE DESCRIPTION AND RECONNAISSANCE...................................................:..............2 3.1 Location and Legal Description 3.2 Site and Vicinity Characteristics 3.3 Hazardous Materials 3.4 Other Conditions of Concern 4.0 HISTORICAL USE INFORMATION ......................................................................................6 4.1 Previous Environmental and Geotechnical Investigations 4.2 Historical Maps 4.3 Tax Assessor Records 4.4 State Archive Records 4.5 Renton Directories 4.6 Aerial Photographs 5.0 ENVIRONMENTAL SETTING...............................................................................................8 5.1 Regional Physiographic Conditions 5.2 Soil and Geologic Conditions 5.3 Hydrogeologic Conditions 6.0 RECORDS REVIEW.............................................................................................................8 6.1 Federal Records Sources 6.2 State Records Sources 6.3 Local Agency Sources 6.4 Assumptions and Opinion of Contaminant Mobility and Site Vulnerability 7.0 RESULTS OF INVESTIGATION.........................................................................................10 7.1 Findings 7.2 Conclusions and Recommendations 7.3 Limitations 8.0 REFERENCES....................................................................................................................11 ATTACHMENTS Plate 1 Vicinity Map Plate 2 Site Plan Plates 3 &4 Site Photographs Appendix V1S's Site Assessment GEOTECH CONSULTANTS, INC. PHASE 1 ENVIRONMENTAL SITE ASSESSMENT Proposed Heritage Arnold Project Beacon Way Southeast Renton, Washington 1.0 EXECUTIVE SUMMARY Presently, the site is undeveloped and covered with trees, brambles, and other native vegetation. The Vicinity Map, Plate 1, illustrates the general location of the site. Land use in the surrounding area is characterized by single-family residences. Two tunnels from abandoned coal mines underlie the site. Historical research revealed that the northern portion of the site was excavated, then filled with imported material that included construction debris. This assessment did not reveal any recognized environmental conditions in connection with the subject property. A discussion of the scope of our work, our site observations, and our conclusions are contained in this report. 2.0 INTRODUCTION This report presents the results of our Phase 1 Environmental Site Assessment of the Heritage Arnold property at Beacon Way Southeast in Renton, Washington. 2.1 Special Terms and Conditions The scope of work for our review of this site did not include the examination, sampling, or analysis of subsurface soil or groundwater on the site for potential environmental contaminants. If new information is developed in future site work, which may include excavations, borings, or studies, Geotech Consultants, Inc. should be given the opportunity to review the findings, re-evaluate the conclusions of this report, and provide amendments as required. 2.2 Purpose and Scope Of Work The purpose of an environmental assessment is to satisfy one of the requirements to qualify for the innocent landowner defense in the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA): that is, to make "all appropriate inquiry into the previous ownership and uses of the property consistent with good commercial or customary practice." Our scope of work and the limitations of our study are consistent with American Society for Testing and Materials (ASTM) Designation E 1527: Standard Practice for Environmental Site Assessments: Phase 1 Environmental Site Assessment Process. The objective of a Phase 1 assessment is to minimize potential future liability for environmental problems by demonstrating that at the time this report was prepared, the owner, holder, or buyer had no knowledge or reason to know that any hazardous substance had been released or disposed on, in, at, or near the property. An additional objective of the Phase 1 assessment is to identify potential contamination sources. The goal of the processes established by the ASTM is to identify recognized environmental conditions. The term "recognized environmental conditions" means the presence, or likely GEOTECH CONSULTANTS, INC. Bennett Corporation JN 9930A September 9, 1999 Page 2 presence, of any hazardous substances or petroleum products on a property under conditions that indicate an existing release, a past release, or the material threat of a release of any hazardous substances or petroleum products into structures on the property or into the ground, groundwater, or surface water of the property. The term includes hazardous substances or petroleum products even under conditions in compliance with laws. The term is not intended to include de minimis conditions that generally do not present a material risk of harm to public health or the environment and that generally would not be the subject of an enforcement action if brought to the attention of the appropriate governmental agencies. Our study included: • A review of the chronology of ownership and site history, using county assessor records, archival property record cards, recent and historical maps, and aerial photography as primary resources. An attempt was made to identify possible former industries or uses presenting some probability of generating waste, which may have included dangerous or hazardous substances, as defined by state and federal laws and regulations. • A reconnaissance of the property to look for evidence of potential contamination in the form of soil stains, odors, vegetation stress, discarded drums, or discolored water. • The acquisition and review of available reports and other documentation pertaining to the subject property or nearby sites. • A review of a search by Vista Information Services, Inc. (VIS) of available state and federal government records. VIS reported those sites and businesses that are located within the minimum search distances specified by American Society for Testing and Materials (ASTM) Designation E 1527. Additionally, through observations made during our site reconnaissance, we attempted to identify local topographic conditions that may influence the potential for regulated facilities to adversely impact the subject property. 3.0 SITE DESCRIPTION AND RECONNAISSANCE 3.1 Location and Legal Description The subject property is an approximately triangular-shaped parcel of land that covers 10.36 acres. It is located on a plateau approximately one-half mile southeast of downtown Renton. The Vicinity Map, Plate 1, illustrates the general location of the site. The property is situated in the northeast quarter of Section 20, Township 23 North, Range 5 East, Willamette Meridian, in King County, Washington. The tax identification number, as recorded by the King County Assessor's Office, is 202305-9110. 3.2 Site and Vicinity Characteristics An environmental engineer from our firm visited the site on September 1, 1999 to observe on-site conditions and land use practices in the surrounding area. Land use in the immediate vicinity is characterized by single-family dwellings and a park. GEOTECH CONSULTANTS, INC. Bennett Corporation JN 9930A September 9, 1999 Page 3 3.2.1 Site Improvements The entire 10.36-acre lot is undeveloped. Potable water is provided by the City of Renton. Storm and sanitary sewer services are provided by the King County Department of Metropolitan Services (METRO). 3.2.2 Building Materials No structures are currently on the property. 3.2.3 Current Uses of Property The subject property is the proposed location for a high-density residential development. At present, the site is undeveloped. The southern portion of the property is covered by trees, brush, and other native vegetation. An unpaved road, now heavily overgrown, leads onto the property from the southeastern border. The northern portion of the property appears to have been excavated (see Section 4.4), then filled. This area contains some trees and is heavily overgrown by brambles. We observed construction debris (wood, plastic piping, pieces of concrete and asphalt, etc.) along with tires, bottles, furniture, yard waste, and other household items. The majority of the casual dumping appears to have taken place on the northern portion of the property. None of the material appears to be hazardous. At the time of our site visit, no major stains, odors, or unusual vegetative conditions that might indicate the potential presence of hazardous contamination were noted on the subject property. 3.2.4 Current Uses of Adjoining Properties Land use in the site vicinity is characterized by residential development. More specifically, the property is bordered as follows: North: To the north of the subject site is the River Ridge subdivision of single- family houses constructed in 1994. East: To the east of the subject site is the Falcon Ridge subdivision of single- family houses constructed in 1989 and a parcel of undeveloped land that slopes steeply down to the northeast. South-: A gated, asphalt-paved maintenance road (Southeast Beacon Way) over- West lying the City of Seattle's Cedar River water supply pipeline runs along the southwestern border of the property. Across this road is Philip Arnold Park, then single-family residences. During our reconnaissance, we did not observe any obvious signs of improper storage or disposal practices of hazardous waste on any of the neighboring sites that would negatively impact the subject property. GEOTECH CONSULTANTS, INC. Bennett Corporation A 9930A September 9, 1999 Page 4 3.3 Hazardous Materials 3.3.1 Storage Tanks and Containers At the time of our site visit, we looked for evidence of underground or above-ground storage tanks on the subject parcel. No signs of underground or above-ground storage tanks were observed during our site reconnaissance. 3.3.2 Asbestos-Containing Materials Asbestos gained widespread use in the 1930s, 1940s, and 1950s for fireproofing, for thermal insulation, and to enhance strength, and has been used in over 3,000 commercial products. In buildings, it is most commonly found in boiler and pipe insulation, in "popcorn" ceiling texture, in vinyl flooring, in plaster and drywall compounds, in mastics and adhesives, in cement board siding, and in roofing. The knowledge that exposure to asbestos fibers can cause harm to humans became widespread between about 1955 and 1975. Diseases linked to asbestos exposure include asbestosis, a scarring of the lung tissue; lung cancer; and mesothelioma, a cancer of the lining of the chest and abdominal cavity. The EPA banned the use of asbestos in some applications in 1973, and by 1989 had announced a gradual ban on most remaining uses. Building materials imported from Canada or other areas outside the United States may still contain asbestos. No structures are on the site. We did not observe signs of asbestos-containing materials on the property. 3.3.3 Lead-Based Paint Until the 1960's, paint containing 30 to 40 percent lead was commonly used on the interior and exterior surfaces of buildings. Exposure to particles of lead-based paint (LBP), either through inhalation or ingestion, has been found to cause a variety of adverse human health effects. Children are particularly sensitive to these effects, and chronic exposure to lead can cause learning difficulties, mental retardation, and delayed neurological and physical development. In 1977, the Consumer Products Safety Commission banned consumer use of paint products that contain lead in excess of 0.06 percent. The current LBP standard, as defined by the Lead-Based Paint Poisoning Prevention Act and the Department of Housing and Community Development Act, Title 10, is any paint or other surface coating that contains lead in excess of 1.0 milligrams per centimeter squared or 0.5 percent by weight (5,000 parts per million). No structures are on the subject property. We did not observe any signs of lead-based paint on the site. 3.3.4 PCBs Prior to 1979, polychlorinated biphenyls (PCBs) were widely used in electrical equipment, such as transformers, capacitors, switches, fluorescent light ballasts, and voltage regulators, owing to their excellent cooling properties. In 1976, the EPA initiated GEOTECH CONSULTANTS, INC. Bennett Corporation JN 9930A September 9, 1999 Page 5 the regulation of PCBs through the Toxic Substances Control Act (TSCA). These regulations generally control the use, manufacture, storage, documentation, and disposal of PCBs. The EPA eventually banned PCB use in 1978, and the adoption of amendments to TSCA under Public Law 94-469 in 1979 prohibited any further manufacturing of PCBs in the United States. No buildings are on the property. We did not observe any transformers on the subject property. 3.3.5 Waste Generation and Disposal No solid or hazardous waste is generated at the subject property. 3.4 Other Conditions of Concern 3.4.1 Radon Radon is a naturally occurring, highly mobile, chemically inert, radioactive gas created through the radioactive decay of uranium and thorium. The potential for the occurrence of radon varies widely and depends on: (1) the concentration of radioactive materials in the underlying bedrock, (2) the relative permeability of soils with respect to gases, and (3) the amount of fracturing or faulting in the surficial materials (EPA, 1987). The EPA has established a concentration for radon of 4 pico-Curies per liter (pC/1) of air as a maximum permissible concentration "action level." According to some studies, the average concentration in homes across the United States is on the order of 1.4 pC/I. Typically, the Puget Sound area of Washington is underlain by a consolidated thickness of glacial drift and rocks that do not contain radon-forming minerals. The Washington Department of Health, Division of Radiation Protection, published a study listing the King County average as 0.7 pC/I. Based on this information, it is our opinion that the potential for elevated levels of radon at this site is low. 3.4.2 Coal Mine Hazards Coal has been mined in several areas of King County since the late nineteenth century. Although current production is entirely from surface mines, nearly all the coal produced prior to about 1970 was from underground workings. Abandoned subsurface mine workings leave large underground voids which are hazardous in several ways. Gradual failure of the roof and sides of these voids may result in subsidence of the ground surface over a large area overlying the mines. Noxious gases and "dead air" (lacking oxygen) may also collect in these voids. In addition, animals or people may fall into surface openings, shafts, or tunnels. Unstable mine spoil piles, frequently covered with vegetation and resembling natural hills, pose hazards as well. We reviewed a mine hazard assessment of the property prepared by HartCrowser, Inc. The report stated that the Heritage Arnold property is underlain by three coal seams, two of which have historic mine workings. The shallowest of the workings lies approximately GEOTECH CONSULTANTS, INC. Bennett Corporation A 9930A September 9, 1999 Page 6 250 to 300 feet beneath the surface, while the deeper workings lie 475 to 765 feet beneath the surface. There was no indication of mining on, or adjacent to, the property after the early 1920s. The HartCrowser report identified three potential mine-related hazards: trough-type settlements, sinkholes, and mine gas emissions. They concluded that sinkholes and mine gas emissions were unlikely to be problems at the property and that, although trough-type subsidence could occur, the magnitude of settlement would be unlikely to cause damage to conventionally-constructed structures. 4.0 HISTORICAL USE INFORMATION Sources reviewed for information on site and area development and land use included historic aerial photography and the resources of the King County Assessor's Office and the Puget Sound branch of the Washington State Archives. 4.1 Previous Environmental and Geotechnical Investigations Geotech Consultants, Inc. has not completed geotechnical or environmental engineering studies for the site. We were provided with a copy of an abandoned mine assessment for the site prepared by HartCrowser, Inc. that is summarized in section 3.4.2. 4.2 Historical Maps Sanborn Fire Insurance maps do not cover the vicinity of the subject property. A U.S. Geological Survey map of the Renton Quadrangle, dated 1949, shows the subject site as a mine in an area that is otherwise undeveloped. Revisions made to the map in 1968 and 1973 show areas of residential development to the west and to the southeast. 4.3 Tax Assessor Records The King County Assessor's Office lists the current taxpayer as the Renton School District 403. According to information from the Assessor's Office, the residential subdivision to the north, River Ridge, was developed in 1994 while the subdivision to the south, Falcon Ridge (or Cedar Ridge) was developed in 1989. 4.4 State Archive Records Information on file at the archives indicates that the subject property was once part of a 32.03-acre site owned by the Puget Sound Power and Light Company. A wooden water tank, located on the present site of Philip Arnold Park, was the structure shown on the property. This large parcel was divided in 1964, and the subject site in its present size and shape was created through a second division in 1966. It was acquired at that time by the Renton School District from Puget Properties. GEOTECH CONSULTANTS, INC. Bennett Corporation A 9930A September 9, 1999 Page 7 4.5 Renton Directories Renton city directories did not cover the area of the subject property. 4.6 Aerial Photographs We reviewed aerial photographs dated 1936, 1946, 1960, 1968, 1974, 1980, 1985, 1990, and 1995. Development on the subject property and in the surrounding area for each of these years is discussed in the paragraphs that follow. 1936: In this photograph, the subject property is covered by low vegetation. An unpaved road, the City of Seattle's Cedar River Pipeline Road, runs northwest-to southeast along the southwestern border of the property. To the north is a smaller, unnamed road that winds to the southeast before splitting into small trails. Farther north is Maple Valley. A residential area covering a few blocks lies to the west. The land to the south and the east is undeveloped and covered by low vegetation. 1946: The subject site remains undeveloped and covered by low vegetation. Residential development to the west is denser. A power line right-of-way running east to west has been cleared approximately one-quarter mile to the south. 1960: A small cleared area can be seen at the southeastern corner of the property. A baseball field appears to the west. Several housing developments can be seen to the south. 1968: The northern portion of the property has been cleared of vegetation, and appears to have been excavated. An electrical substation has been constructed approximately one-quarter mile to the south. 1974: The subject site appears unchanged from the 1968 photograph. At Philip Arnold Park to the west, a building and a parking lot have been constructed. 1980: The northern portion of the property is now covered by low vegetation. The vegetation on the remaining portion is much denser. 1985: Residential development in the area has increased greatly. 1990: The Falcon Ridge housing development now appears to the southeast of the subject site. 1995: The River Ridge housing development now appears to the north of the subject site. The site and the surrounding area appear as described in our 1999 site visit. GEOTECH CONSULTANTS, INC. Bennett Corporation JN 9930A September 9, 1999 Page 8 5.0 ENVIRONMENTAL SETTING 5.1 Regional Physiographic Conditions The site is located on the Covington Drift Upland, a gently rolling, elevated drift plain in the Puget Sound Lowland geomorphic province. The Puget Sound Lowland is a basin lying between the Cascade Mountains to the east and the Olympic Mountains to the west and is covered mainly by glacially-deposited sediments. The plain was formed during the last period of continental glaciation that ended approximately 13,500 years ago. The site lies near the northwestern corner of the upland plain at an approximate elevation of 400 feet above sea level. 5.2 Soil and Geologic Conditions A published geologic map for the site vicinity suggests that much of the material underlying the subject site is glacial till, a dense, heterogeneous mixture of silt, sand, and gravel. Typically, the till exhibits relatively low vertical hydraulic conductivity, which frequently results in formation of a perched water table along its upper contact. The perched water table (if present) is frequently seasonal and derives recharge primarily from infiltration of precipitation through more permeable overlying soils. Geotech Consultants, Inc. is preparing a geotechnical engineering study of the site that will discuss subsurface conditions in greater detail. 5.3 Hydrogeologic Conditions The geologic unit that we assume characterizes the site is of relatively low permeability, although unmapped deposits of higher permeability sand and gravel may occur within this unit. Based upon local drainage patterns and upon our review of a U.S. Geological Survey map of the area, it is likely that the flow of surface, or shallow-seated subsurface, water across the property would be toward the northwest to the Cedar River. According to a U.S. EPA Ground Water Handbook, shallow water tables typically conform to surface topography. 6.0 RECORDS REVIEW Geotech Consultants, Inc. utilized the services of Vista Information Services, Inc. (VIS) to complete a search of available state and federal government records. VIS reported those sites and businesses that are located within the minimum search distances specified by American Society for Testing and Materials (ASTM) Designation E 1527. Additionally, through observations made during our site reconnaissance, we attempted to identify local topographic conditions that may influence the potential for regulated facilities to adversely impact the subject property. The databases searched by VIS, as well as the search areas applied to each, are summarized in the following sections. A copy of the VIS Site Assessment is included with this report as an appendix. GEOTECH CONSULTANTS_ INC