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HomeMy WebLinkAboutSWP272964 (2) DEBAR PLAT City of Renton, Washington Technical Information Report & Level I Downstream Analysis Prepared by: Scott R. Borgeson, P.E. Reviewed by: Clay A. Loomis, P.E. MM TRIAD ASSOCIATES January 30 , 2002 TRIAD JOB #00 - 220 • DEBAR PLAT City of Renton, Washington CITY OF RENTON RPOEIV® FEB r ' 2002 Technical Information Report & Level I Downstream Analysis Prepared by: P� A-L0� Scott R. Borgeson, P.E. of Reviewed by: a Clay A. Loomis, P.E. 891 9 �IA7w �GI STEg� C>� s`sI ONAL EXPIRES: 10/22/02 //3%2 AWM TRIAD ASSOCIATES January 30 , 2002 TRIAD JOB # 00 - 220 Table of Contents 1 PROJECT OVERVIEW...................................................................................................................1-1 2 CONDITIONS AND REQUIREMENTS SUMMARY..................................................................2-2 3 OFFSITE ANALYSIS.......................................................................................................................3-5 4 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN...........4-6 4.1 DRAINAGE CONCEPT....................................................................................................................4-6 4.2 KCRTS METHODOLOGY..............................................................................................................4-6 4.3 INFILTRATION VAULT DESIGN......................................................................................................4-6 4.3.1 Tributary Developed Basin Modeling..................................................................................4-7 4.3.2 Infiltration Rate...................................................................................................................4-8 4.3.3 Vault Infiltration Modeling..................................................................................................4-8 4.3.4 Vault Water Quality Design...............................................................................................4-10 4.3.S Design Vault......................................................................................................................4-10 4.4 INDIVIDUAL SPLASH BLOCKS.....................................................................................................4-1 1 5 CONVEYANCE SYSTEM ANALYSIS AND DESIGN..............................................................5-12 6 SPECIAL REPORTS AND STUDIES..........................................................................................6-16 7 OTHER PERMITS..........................................................................................................................7-17 8 ESC ANALYSIS AND DESIGN....................................................................................................8-18 9 BOND QUANTITIES,FACILITY SUMMARIES,AND DECLARATION OF COVENANT9-22 10 OPERATIONS AND MAINTENANCE MANUAL...............................................................10-23 APPENDIX Developed Conditions Exhibit Tributary Area Exhibit • Triad Associates DeBar Plat Page i Technical Information Report / SECTION I PROJECT OVERVIEW • • • 1 Project Overview The DeBar plat proposes to create 14 new single-family lots on 4 existing tax parcels. The total area of the tracts is approximately 3.09 acres. The project site is bordered on the north by a bluff(property extends down the bluff face approximately to the toe)and on the south by N.E.28`h Street(existing street addresses of 2132, 2200, 2216 and 2224 NE 281h Street). The site is in SE Section 32, Township 24 N, Range 5 E, W.M. in the City of Renton, King County, Washington. Please refer to the Vicinity Map below. Four single-family residences (and their associated outbuildings) are present on the existing tax parcels. In addition to the 14 proposed lots,two of the existing homes will be retained(the easternmost);the other two (westernmost)will be demolished for the proposed development. A boundary line adjustment will provide for the exclusion of the two existing houses(the existing lot for each will be reduced in size). y� I� o :N , ,� z \'y o- g 1�4 S£ 89TH 34 tH S7 ST n S£ 90TH ST 3 SE '91sr , sr o 40. City of Renton a r 37 7 sr I 1 1 Y I • _ ��. Z 9T`... x 71E 'RL NE 28TH S z r --- -- — c� NE. 27TH ST NE - `I- 2 27TH iL J n cr 2 Y >. .• 'DALE ,. O W z a a NE 25TH W y Q. W Q Si� 2s. .''PARK Q ST.- h Q Q 2 Q Q Qi 23epp. PL O �NE23RD S7 Q o NE 23RD 51 NE 22NO i m W W NE 22ND ST ma � Z Q of NE 20 TH ST VICINITY MAP NOT TO SCALE • Triad Associates DeBar Plat Page 1-1 Technical Information Report - OWN" SECTION II 10 CONDITIONS & REQUIREMENTS SUMMARY 2 Conditions and Requirements Summary In the Preliminary Report to the Hearing Examiner for the public hearing date July 24, 2001, it is recommended by City staff that this project comply with the mitigation measures imposed by the City's Environmental Review Committee. The specific measures imposed by the committee, which apply to the storm drainage aspects of this project have been summarized and responded to below. 1. The recommendations included in the report, "Geotechnical Engineering Report Debar Site," by Cornerstone Geotechnical, Inc., dated April 5, 2001, shall be followed by the developer during project design,construction,and following construction. The recommendations of the project geotechnical engineer contained in the referenced report have been followed during the preparation of this report and the Road, Storm Drainage and Utility Plans that accompany it. 2. A"foundation setback line" shall be established thirty-five feet(35')back from the face of native slope soils. This setback shall be defined as the horizontal distance measured from the outside edge of the building footing facing the slope to the face of native soils, as identified by the geotechnical engineer of record. This foundation setback line shall be recorded on the final plat. This setback line has been considered during the preparation of these plans and will be identified • on the final plat. 3. Buildings shall be no closer than 25 feet from the top of the slope. This building setback requirement shall be recorded on the final plat. This building setback has been considered during the preparation of these plans and will be identified on the final plat. 4. The proposed project shall be required to be designed to the standards of the 1998 King County Surface Water Design Manual. This project has been designed per the standards of the 1998 King County Surface Water Design Manual(KCSWDM)as documented in several locations in this report. 5. The applicant shall limit site disturbance including clearing, grading, utility and roadwork activities to occur during the relatively dry months of April through October. This seasonal limitation has been noted on the plans. Triad Associates DeBar Plat Page 2-2 Technical Information Report 6. 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 1998 King County Surface • Water Design Manual (KCSWDM). This will be required during the construction of both off-site and on-site improvements as well as building construction. This erosion control measure is included in the design as shown on the plans that accompany this report. 7. 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. This erosion control measure is included in the design as shown on the plans that accompany this report. 8. 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 1998 KCSWDM. Temporary pipe systems can also be used to convey stormwater across the site. This will be required during the construction of both off-site and on-site improvements as well as building construction. • These erosion control measures are included in this design as shown on the plans that accompany this report. 9. 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. This construction requirement has been noted on the plans. 10. 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. This construction requirement has been noted on the plans and acknowledge by the project engineer of record. Triad Associates DeBar Plat Page 2-3 Technical Information Report 11. Rocked construction access roads shall be extended into the site to reduce the amount of soil carried off the property by trucks and equipment. • A rocked construction entrance has been included in the erosion control design, as shown on the plans. 12. Following rough grading, bare areas that will not be immediately covered with impervious surfaces shall be mulched. This construction and erosion control requirement has been noted on the plans. • Triad Associates DeBar Plat Page 2-4 Technical Information Report SECTION III OFFSITE ANALYSIS 3 Offsite Analysis Per the Geotechnical Report for the site (Cornerstone Geotechnical Inc. April 5, 2001, included in Section 6, Special Reports and Studies), the majority of the site and the surrounding neighborhood infiltrates and generates little or no runoff for most storm events. Also included here is the Level 1 Downstream Analysis. The downstream analysis identifies the likely downstream route for the existing site runoff (likely only during the more extreme storm events). • • Triad Associates DeBar Plat Page 3-5 Technical Information Report • DEBAR PLAT City of Renton, Washington Level One Downstream Analysis Prepared by: Schwin Chaosilapakul Reviewed by: William J. Goggin, P.E. TRIAD ASSOCIATES March 22 2001 TRIAD JOB # 00 - 220 TABLE OF CONTENTS Page TABLEOF CONTENTS....................................................................................................... I INTRODUCTION..................................................................................................................1 VICINITYMAP.....................................................................................................................2 ANALYSIS OF DRAINAGE BASINS.................................................................................2 UPSTREAM DRAINAGE ANALYSIS ..................................................3 DOWNSTREAM DRAINAGE ANALYSIS........................................... 3 DOWNSTREAM DRAINAGE PROBLEMS.......................................... 3 RESOURCES USED FOR ANALYSIS...............................................................................4 APPENDIX Off-Site Tributary Area Map Off-Site Drainage Maps Off-Site Analysis Drainage System Table • Basin Map SCS Soils Map USGS Map FEMA Map Sensitive Areas Maps City of Renton PBPW— Storm Drainage Complaints Catalog • LEVEL ONE DRAINAGE ANALYSIS FOR SPECIALIZED HOMES—Page i INTRODUCTION The proposed project is a four Parcel residential development. There will be 14 lots on approximately 3.09 acres. The project site is bordered on the north by a bluff and on the south by N.E. 28tl' St. More generally, the site is located in Section 32, Township 24 N, Range 5 E, W.M. in the City of Renton, King County, Washington. Please refer to the Vicinity Map located on the following page. The site is located in Cedar River drainage basin as defined in the King County Basin Reconnaissance Program Summary Volume I (please refer to the Basin Map in the Appendix). Site visits were made on February 20th (warm and sunny) and 21St (cool and rainy), 2001. Vegetation on the site is varied, with the areas proposed to be developed being primarily pasture with some trees and underbrush. The topography of the site creates a single basin sloping west and northwest bordered by a ridge on the east side of the site (please refer to the Sub-Basins Map in the Appendix). Runoff from the site is tributary to May Creek (please refer to the Basin Reconnaissance Map in the Appendix), which eventually flows into Lake Washington. The soils on the site consist of Indianola type `A' soils. Please refer to the SCS Soils Map located in the Appendix. LEVEL ONE DRAINAGE ANALYSIS FOR SPECIALIZED HOMES—Page 1 0 200m, � 6 sooft NY hJth St a ° i �Q p — O t` s 16 Fi erJriydale l N9325th St IA" L1nn'05'-'P-'ark ._._ V I 6 I N q 24th St Ne • 02001 Mapquest.com, Inc.; 02001 N.3v'raatbn Technobgis*ynd St VICINITY MAP Not to Scale ANALYSIS OF DRAINAGE BASIN The following paragraphs provide in depth information about the location and characteristics of the developed sub-basins on the project site. Please refer to the King County Off-Site Drainage System Table and the Off-Site Drainage Map for each sub-basin located in the Appendix. • LEVEL ONE DRAINAGE ANALYSIS FOR SPECIALIZED HOMES—Page 2 UPSTREAM DRAINAGE ANALYSIS The site does not have any upstream tributary area because it is situated on the southeast corner of the basin. The basin is defined by two ridges, one along the eastern border and one at the southern border of the site (N.E. 28`h St.). DOWNSTREAM DRAINAGE ANALYSIS Stormwater generally infiltrates into the ground throughout the site. Under severe storm conditions, some runoff may sheet flow over pasture towards the northwest. If runoff occurs, it will sheet flow over a slope of approximately 74% (Path A). This flow from the site would collect along a beaten path (Former Pacific Rail Road Right of Way) into a moderately defined channel that runs parallel to the bottom edge of the bluff. The runoff would then discharge between a gap in a ridge located at a low point in the old railroad bed almost directly north of the center of the site. Some of the flow from the site could discharge in a similar manner at a location 70ft west of the primary discharge point. The flow would continue north-northwest down a steep slope approximately 47% (Path B), initially in the form of channel flow but turning to sheet flow as it travels for about 240 ft over various vegetation. At this point the steep slope gradually levels to approximately 7% where runoff can again regroup into channel flow (Path Q. The runoff would continue to flow in this state for approximately 520 ft curving from a north-northwest direction to more of a westward direction running almost parallel to NE 3 1" St. The flow would eventually enter May Creek near a bridge that marks the intersection of May Creek and NE 3 1" St. The analysis ends at this point approximately 680ft from the site. The downstream was not investigated further (to a quarter mile downstream) since it had joined a major drainage course. The site is an insignificant portion of the entire upstream basin. Please refer to the Basin Reconnaissance Map in the Appendix for the off-site area that is tributary to this point DOWNSTREAM DRAINAGE PROBLEMS Signs of erosion that were observed were fallen trees and loose soil (seen in partly uprooted trees). These problems occurr along the bottom of the bluff and around the old railroad bed. LEVEL ONE DRAINAGE ANALYSIS FOR SPECIALIZED HOMES—Page 3 • RESOURCES USED FOR ANALYSIS ADOPTED BASIN PLAN The site is located in the Cedar River Basin, May Creek Subbasin. A Basin Reconnasaince map of May Creek is not available at this time. See Appendix for appropriate maps. CRITICAL DRAINAGE AREAS MAP The site is not located in any of the critical drainage areas discussed in the reference section of the 1998 King County Surface Water Design Manual. FLOOD PLAIN/FLOODWAY MAP The site is not located on or near any flood plain as shown on the FEMA Flood Insurance Rate Map (please refer to the FEMA Maps in the Appendix). KING COUNTY SOIL SURVEY The soils on the site consist of Indianola type `A'. It is a form of outwash soil and are formed from highly permeable sands and gravels. Please refer to the S.C.S. Soils Map in the Appendix. LEVEL ONE DRAINAGE ANALYSIS FOR SPECIALIZED HOMES—Page 4 SENSITIVE AREAS FOLIO The King County Sensitive Areas Map did not reveal the site to be in a landslide, seismic, erosion, or wetland hazard area(please refer to the Appendix for the appropriate maps). CITY OF RENTON PBPW (Planning/Building/Public Works Record of Complaints) A review of the storm water related complaints that King County has on file showed that no upstream or downstream problems have been reported that were relevant to this project (please refer to the facsimile from City of Renton PBPW in the Appendix). i LEVEL ONE DRAINAGE ANALYSIS FOR SPECIALIZED HOMES—Page 5 APPENDIX s • LEVEL ONE DRAINAGE ANALYSIS FOR SPECIALIZED HOMES N„ 0'OZ IL£o VO N„ 0'0 V.L£o VO N. O'O L£o b0 N„ 0'09 6 it A 5j i����y111 , t bk � a 4.i4j 0 a` ° co .. LL LL »,� �' ads" m�F Pill CC} ' T a �. Wig" .- i i -�ll V k '41 ON kIto 40 Jo J, Ir Ail' GCD e` y MA All, LLAM . r P1 „ w v m nire, I " . Sys) t 0'. ' �� <� P,�• �M >�T 1 � m _ s 0 O _-77 (6 wn+ 3 A LLJ z C) V) 7-7 N., O'07..LP'_/V0 1 1 1 1 1 1 N„ 0'0L ,L£..LVO N„00'0I,LE o VO N, O OS 0£< VO 10 C . D . H I L L MAN; S 74 75 � , I L90 ; N. E. 33RD ST. ... 64L20TV zau LAKE VGA S H I N GT O N _ o M 6 A R D E N OF E D E I i GA ■■��wv�q■- J L f 2 77 76 41 364 367 371 t< \` Sll I f D I V 1510 N ® I � 1/4 MILE PAINT DIVISION N - 6 • 1�3` f✓ C T ✓ P E N ;v 4 • i(7j 'arc i d-,o c S MA3i 6,9 57 ZUo 'T 20 N 50.? 3`SY - tSo 44 O i F 0 6567 S ! � C � K P A R 1 55 54 363 368 T Y F A R K `! ;, •: E •y � R C C R E A T 7 ;N 0 E ? T — .! 1 a` - _ram �;�� __�:� • �` 1 i' - ' - 1 A 15E0� 1517 � 387 sJ erz A j \. \X s 3'u55e 7 clac =cnirt.- 278? klilc .7 m B la 9b a9ss sgss.oz I ; �654 G7 I 12 SITE � 40o 3t i • l 5 '+; ; �a A s—Icim loo N. r 28TH P r r• /FIJI , ' 1... 4 93 ` N 60 34.6/ Cam} F: •� - 9 .,f.V N - m t _ '. n � 3 2 n I y Z`' .. I �/ �'• q f ISC.04."—v s4.49 Go so.lz ^ 32 .dm .� ;� • w ....... • -... ... ..mow • • t.�-...� � � ' m-.® — .,_- -_--. .-. • e • . e • • . �V .q+ .®„ , LEG E ND OFF-SITE DRAINAGE MAP 1 =200 - - 13L;iLc N,s +- 1 I ... .REPRODUC(,)N rN I HOLE _3G9E -- OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLE Surface Water Design Manual, Core Requirement #2 Basin: Cedar River Subbasin Name: May Creek Subbasin Number: NA Symbol Drainage Drainage Component Slope Distance Existing Potential Observations of field inspector Component Type Description from site Problems Problems or resource reviewer Name, Size discharge Type: sheet, Swale, constrictions, under capacity, ponding see map stream, channel, pipe, drainage basin, vegetation, % 1/4 mi= 1320 ft overtopping,flooding,habitat or organism tributary area, likelihood of problem, pond; Size:diameter, cover, depth, type of sensitive destruction, scouring, erosion, other overflow pathways, potential impacts. surface area area,volume A sheet cover/vegetation 74.0% 80ft fallen trees, landslide moderately defined channel, erosion flow discharge at gap in ridge B sheet/channel vegetation 47.0% 320ft none erosion various vegetation to help dissipate flow C channel vegetation 7.0% 840ft none sedimentation high groundwater condition Triad Associates 6 -—-—-—-—-—- S. Chely Ceek 0—i ? Z71 vbe� AJL*. pw" T4 SN N7 -. ^\ wa lm Oeek.. o 'ILI 31 1 SITE Mere Island ........... PUPET. Jmie Fi— J; J Rayi r Rwei, C4"* (jay{ • �� I ! tl­ p _'Low 6 1 v DRAINAGE BASINS RAINAG King County 1987 IZ Major Basin Boundary COMA Sub-Basin Boundary Source: King County Basin Reconnaissance Program BASIN MAP • 0 1 2 3 4 5 6 7 8 Miles 1- 300,000 t AgD KPB• Pin ra ors LV eVS�7lk Ur .. • InA i 4.L .AgC` • ` n, t 1 r ' • o r AmC KPD,iF £ Ur Y Nevi 3 L ' _ M • I EvC BeD ••eC PD 8 AmC I AgC Bh a ,i Bh' .•� f Q 4 !! AgC '\ C-7 y K C Y Ma e p .EvC• .S f OvD • O N (n _ B \ AgD _----- --•�------ — ---BMA�gM 1�1 690 692 vo rn I AgC No X AgC ; BMD n q _� 605 oo , • • a Sm BeC AgC 1 AgC ` AgD �c 1 = n S 1 T EAgD qgD 11 34 • 'U� D AgC l.. /• -o\ �L� -I. •\•, 11 \ Kennydale • al "' �= ,I �` ' a InC I Ak I AkF AkF J I qgC E.B I 1 BeG EvC U, • GRAVEL •` y eman Poin Q P/T CO t. AkF 306 ai 'InA 1 I PP �•'• AgC B KAgC qgD D N — --- _ n BMl l m n BM',903 « n • n Z it Q •1� I' � pp E� Ag D I Evc/11 l nV. ^1• �� �• - i=� 1111 - - qgC 6M• •i AkF 1 aril AmC - Sm 0 l /� Inc 1 . l ::• i AgC• AkF n� •II Ur .i• ; I Sm �u * •; : I AMC dC Ur BDY -- — _._y NJ - BM� / /• i ( (—I _, a EvC. PlantiII- R �TON �' ♦• �\® J I ., AgC Rd ON 7.9 mi. 12130/1 (Joins sheet 1 1) RdC 10' PENTON 1.7 M1. " -Scale 7 24 G00 1 9 000' N� v C. t F11e5 2COC2 - i; C --- -- _ pr, !CGQr Fe.. • SCS SOILS MAP 04 "30 50.0 "N 04 °311 0.0 'N 047°31 10.0 "N 047°31' 0.0 "N Cn 0 Z ° D u �. oN m � ..• " _ N m a ..° - W.. CD 0 o m Alzz m9 `• ;ire ` " ' vim'« ,. MAL 3 m N y� u v 7 y fl tl . N ta "JAW wi a f _ '' ",.rW"., ,n N p a7 w o m co ' o ds" y V a x., x 7==Ml Em- a h e 04 °30 50.0 "N I I I I 1 1 04 °31 0.0 'N 04 °31' 10.0 "N 04 °31' 0.0 'N LEGEND _ NOTES _ZONE X _ This map is for use in administering the National Flood Insurance Program. N .1-TH Rtv121v s - it does not necessarily identify all areas subject to iloodin TREE _ Y I g particulars from SPECIAL FLOOD HAZARD AREAS INUNDATED 0 z z local drainage sources of small size. or all planimetric features outside BY 100-YEAR FLOOD Special Flood Hazard Areas. ZONE A No bate flood clevatiuns determined j T cc 0 Coastal base flood elevations apply only landward of 0.0 NGVD.and include ZONE AE Rase flood elevations determined J j the effects of wave action; these elevations may also differ significantly Z \\ from those developed by the National VWeatner Service for hurricane v CO i evacuation planning. ZONE AH Rood depths of I to 3 tcct iusualiv area, z 1 . of pondingg base flood elevations ME4GGPi _ \ > Areas of Special Flood Hazard(100-year flood) include Zones A.AE.AH.AO. determined E niORTH '� U I A99.V,and VE. 32 ZONE AO Flood depth, of 1 s 3 feet w>ually sheer ? w 4- \ I Certain areas not in Special Flood Hazard Areas may be protected by SL = flood control structures. flow on sloping terrain): amrrage depth, -TH STREET Z Z � ! determined.For areas of alluvial fan flooding. w a \ I Boundaries of the interpolated between crossy sections.r computed The floodways cross were eCbased and velocities also determined. w Z SE 86TH STREET hydraulic considerations with regard to requirements of the Federal ZONE A99 To be protected from ll10-vcar flood in• w g Federal flood protection system under NORTH 37TH STREET > Emergency Management Agency. Q construction: no base elevations determined 52 Z i SE 87TH STREET Floodway widths in some areas may be too narrow to show to scale. ZON Floodway widths are provided in the Flood Insurance Study Report. ZONE V Coastal Fluud with velocity hazard wwave � �. I actions: no base flood elevations determined I STREET C z ! This map may incorporate approximate boundaries of Coastal Barrier w 1� j Resource System Units and/or Otherwise Protected Areas established ZONE VE Coastal flood with velocity hazard (wave w I under the Coastal Barrier Improvement Act of 1990 (PL 101-59U action): base flood elevations determined. w Z j 88TH SIRE Corporate limits shown are current as of the date of this map. The user NORTH 36TH STREET NE 36TH STREET r should contact appropriate community officials to determine if corporate FLOODVVAY AREAS IN ZONE AE 32 �J� limits have changed subsequent to the issuance of this map. EET '� ,� I �� OTHER FLOOD AREAS z 1 P ccm For community map revision history prior to countywide mapping, see ZONE X Areas of 500-vear flood; areas of 100-year KING COUNTY �'�b� SE 89TH Section 6.0 of the Flood Insurance Study Report. flood with average depths of less than _Z AREAS n PLACE SE 89TH I font or with drainage areas less than IEET > UNINCORPORATED AREAS '�'✓ MapFadjoining map panels and base map source see separately panted 1 square mile: and areas protected by Q 62 = ar levees from 1(Xf-year flood. 3 = _ 530071 j a OTHER AREAS 6� ;� MAP REPOSITORY � :.� ��// Bj = ZONE X Areas determined to be outside SW-year EET Refer to Repository Listing on Map Index floudplain. Z EDMON a ZONE D Areas in which flood hazards are ili � .Y (/'i AVENUE EFFECTIVE DATE OF undetermined. ACE ? Creek F COUNTYWIDE FLOOD INSURANCE RATE MAP: 72 ZONE X SEPTEMBER 29.1989 UNDEVELOPED COASTAL BARRIERS 3 CITY OF RENTON LU EFFECTIVE DATES)OF REVISION(S)TO THIS PANEL: ZONE X 1 ](�l�pp � SJtJV00 �< Revised May 16.1995 to update map format. L � W M M O Identified Identified Otherwise NORTH 32ND STREET �l �" tZ 1983 1990 Protected Areas 77 cc OZONE X ZONE X O laslal barrier areas are normally located within or adjacent to Spec,al i ZONE X U god Hazard Areas. >� v 117TH� To determine if flood insurance is available.contact an insurance agent or Flood Boundary ` AVENUE SE call the National Flood Insurance Program at(800)638-6620. 9� Floodway Boundary RM211 RM212 SjPcGl ZONE AEco Zone D Boundary � to O x �� SE g3R0 LONE AE �3 Boundary Dividing Special Flood I 118TH Hazard Zones, and Boundary NORTHEAST 30TH STREET PLACE X 92/ Or J \ t ^J` 1 \PLACE SE f g a Dividing Areas of Different I SOUTHEAST \� Coastal Base Flood Elevations T ;� Z � Q MAY VALLEY La Within Special Flood Hazard �y Np ROAD h Zones. E �'� Base Flood Elevation Line; -` �-+ ^ ZON X eel ZONE X ^ 513 Elevation in Feet. See Map Index 1 �P� p SITE �R0 / for Elevation Datum. N � .-t THEAST D D Cross Section Line S 8TH e FEET �'3 v \ Base Flood Elevation in Fee[ u 1324 \ (EL 987) Where Uniform Within Zone. �+Cr NE 28TH ST OF NORTHEAST 28TH SIRE ZONE XREET RM7 See Map Index for Elevation Datum Z� T23N T23N X Elevation Reference Mark 2 F O I SE 96TH ?O ¢O NORTHER LIMIT OF PLACE • M2 River Mile Z JOORTHEASTUE Sr 27T.4 ZONE X H DETAILED STUDY STREET NORTHEAST 0 o Horizontal Coordinates Based on North � NE 27TH t v 7 07'30'".32 22'30" American Datum of 1927 (NAD 21) y S COURT Projection. v 2/TH w Q CAMAS PARK � AVENUE NE Q KING COUNTY Lu> FERNDALE CITY OF RENTOt Q I AVENUE NE r� 500' • \ 26Tfi STREET I 1 w + Z < \x w to \ t 1 w > � j = 0 Q w I 0 �NE 25TH FEMA MAP _ C w = Z STREET otr r` O I D i \ - 0 Z 1 NE 24TH STREET Q w,p 1 u 1'p• �- �.. 1 fJ�r�-` ' ..,.J.r�/ ( �� a+ (/j'� ,� _ _�. l r�� ,.,� '1.�V1�+°. `r / tln I-- LU1,.': '.4 �t' ;f( .''11• r.i'� �i Tf- h� 1,1 •r f �JJ F V' �`t 1 C � -/ j' ' � ~��, � ^fit /'� ,ry ,r R +i a�`,r; ll�'i/ •, I a - �., � r s �v r , - r; .... .,�yd, �•, � ,.';�. 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YJ.c lo$ �" i� :a ,�..i/.' v -. -. ..=;i ..::: v:•.<.,.�s':,b,:.c..'tyG�s '....ti�' x�h°` � r �(.1;i1!8/r ^6/��.i i PS-66 1400 BLK PARK PL N EAST 12 POTENTIAL TO CAUSE LAKE LANDSUDE X ELW-4-S WASH PS-57 HOUSER WAY NORTH EAST 14 STANDING WATER DUE TO X (N 8TH TO LK WA LAKE FAILING STORM SYSTEM ELW-5-S BLVD.) WASH (WS00T& CITY) MAY BE CAUSING ROAD TO PS-58 NE 6TH AND EDMONDS EAST 14 LDOCALI ED FEGRADE LOODING OF AVE NE LAKE THE CITY STREET AND X ELW-6-S WASH PRIVATE PROPER TO LACK OF -- �, o c 00INNSTREA m a w PS-69 NE 28TH ST SYSTEM CAPACITY. _ e EAST 12 CITY SYSTEM LAKE DISCHARGES TO PRIVATE X WASH PROPERTY a PS-60 NE 43Rp PLACE / EAST 11 OVERFLOW OF EXISTING X w WASH CULVERT AND °a DOWNSTREAM SYSTEM ` v CAPACITY RESULT IN PONDING OF RUNOFF o 0 0 ACROSS STREET DURING x m 3 O FREQUENT STORM EVENTS. vi N PS-61 DOWNSTREAM RIPLEY EAST 11 EXISTING STORM SYSTEM x I LANE TO LAKE LAKE IS UNDERSIZED AND o WASHINGTON WASH LACKS SUFFICIENT G p r CD CAPACITY TO CONVEY + fCD n FLOWS WHICH RESULT IN UPSTREAM PONDING (PS- I 50) ON PRIVATE N Z PROPERTY AND PUBLIC RIGHT OF WAY. • CITY OF RENTON PLANNINGBUILDINGIPUBLIC WORKS MEMORANDUM DATE: June 5, 1996 TO: Gregg Zimmerman FROM: Ron Olsen Staff Contact: Mike Dotson SUBJECT: Referral#22-96 Mr.David Sager,North 28th Street/Park Avenue North Private Road Drainage Complaint ISSUE: • Mr. David Sager, 1025 N 28th Place, called us on May 17, 1996, concerning a drainage issue. He sent a letter to the Mayor on May 24, 1996. As stated in his correspondence, Mr. Sager is concerned that the outfall discharging runoff collected at the intersection of North 28th Street and Park Ave North is causing erosion to a private access road_ In addition he states that he would like a solid lid installed on a manhole located in another location. He also requests that a"No Dumping" sign be place at the ourfall location. RECOMMENDATION: It is our opinion that the problem(s) Mr_ Sager has raised are minor. There are no immediate public safety issues. The access road is private. According to our records, and Mr. Sager, the current stormwater conveyance system has existed for many years. It is difficult to determine how much, if any, erosion is occurring as a result of the subject outfall. The Maintenance Section has offered to repave the existing berm (improving the conveyance features) and to clean the outfall area. The property owners will have the future responsibility to maintain the conveyance system through the property. The Maintenance Section will also replace the grated manhole with a solid lid. The request for a "No Dumping"sign has been referred to the Code Enforcement Officer. We recommend that the above actions are sufficient to address Mr. Sager's concerns. As requested by the Mayor's office (Referral #22-96), we have drafted a letter to Mr. Sager (see attached). The letter explains the actions, as described above, in response to his requests. BACKGROUND: • Surface water runoff at the intersection of North 28th Street and Park Avenue North collects in a catchbasin at the northeast corner and is discharged via a 6" CMP pipe at the southwest edge of the right-of-way (see attached map). After it outfalls, it is conveyed by an asphalt berm to the south edge of the private road. From that point it runs onto private property, eventually finding its way to . -. ,- m in I I fin i k 1�11 �n i i T- +-7•C T T PP;:7-77-Q -1 Gregg Zimmerman June 4, 1996 Page 2 • Kennydale Creek. Mr. Sager is concerned that some of the flow is eroding the private road. He and his neighbors use the private road for access to their back yards. The runoff normally runs over the land and Mr. Sager stated that the asphalt berm usually works quite well_ It is only when debris and sediments block the berm that overflows occur, damaging the private road. He has requested that a pipe system be installed to alleviate the overflow problems_ He believes the City is responsible for the installation. We have not recommended that the new pipe system be installed for the following reasons: 1) The improvements would be required to be installed on private property. Installation of improvements on private property may set a dangerous precedence. 2) The current system works adequately when properly maintained. It has been adequate for many years. In addition, 3) we are not sure that the pipe system would accomplish the effects that Mr. Sager believes it would. There is a large area, below the subject outfall, that will continue to drain onto the private road, possibly causing more erosion. Mr. Sager had previously contacted us in December of 1993. We responded to his requests at that time by cleaning and repairing the existing asphalt berm. Mr. Sager now states that the previous action was insufficient. SITE MEETING SUMMARY: John Thompson and Mike Dotson met Mr. Sager at the site at 3:00 PM on May 22, 1996_ He described the problem and stated his concerns, as summarized above. John and Mike stated that the • outfall is on private property and that the City crews cannot install improvements on private property. Mr. Sager stated that he believes that it is our responsibility to convey water from our right-of-way in such a manner that it does not damage his property. In response, Mr. Thompson stated that he would have the City crews clean the existing asphalt berm. He would also install additional asphalt to help direct flows away from the private road. Mr. Sager stated that he did not think that this action was sufficient. He stated that the asphalt berm requires a great deal of maintenance and he is not able to complete it. He $fated that he would continue to peruse the issue and asked for the names of our Mayor and supervisors. They departed the site at approximately 3:45 PM. H:D005:96-36LMDD'ps CC: Ron Straka • r'r .rn I T-I -,I In I I T"1 or SECTION IV vowlso FLOW CONTROL & WATER QUALITY FACILITY ANALYSIS & DESIGN 4 Flow Control and Water Quality Facility Analysis and Design 4.1 Drainage Concept The site has porous soils with a high rate of infiltration(measured rates by EPA methodology in excess of 60 inches per hour) and deep groundwater (see Geotechnical Report in Section 6) so onsite infiltration is proposed for flow control. A central infiltration vault is proposed for the collected site drainage. The infiltration vault facility will be preceded by a wet vault cell to improve water quality and remove fines. Because there is no suitable downstream conveyance feasible for the site, the vault is sized assuming no overflow system is present(additional safety factors used, as detailed in the following sections). The site's storm drainage facilities are designed to per the 1998 King County Surface Water Design Manual (KCSWDM),as adopted by the City of Renton. 4.2 KCRTS Methodology The 1998 KCSWDM requires the King County Runoff Time Series (KCRTS) model for design of retention/detention systems. The KCRTS program was developed as a hydrologic modeling tool for western King County based on the U.S.Environmental Protection Agency's Hydrologic Simulation Period- FORTRAN(HSPF) 10 model, which is a continuous hydrologic model (in contrast to event-based models such as SBUH or SCS). The runoff files have been pre-simulated for a range of land cover conditions and soil types for different regions of King County using the HSPF10 model. The HSPF10 modeling was calibrated with regional parameters developed by the U.S. Geologic Survey and King County Basin Planning. The KCRTS program simulates the project hydrology through the scaling, summing, lagging, and level-pool routing of these runoff files. The KCRTS program includes a group of analytical tools to provide statistical data on the generated Time Series Files(TSF). The KCRTS modeling is summarized in the following sections. 4.3 Infiltration Vault Design The proposed infiltration vault will be located under the proposed Tract A, which is to be designated for open space uses. The vault is designed per Section 5.4 Infiltration Facilities of the KCSWDM. The onsite tightline conveyances will be tributary to the infiltration vault. The vault has been designed to completely infiltrate site discharges for up to the 100-year return period (i.e. the 100-year storm). The design infiltration rate has been reduced by safety factors to account for various non-ideal conditions. Additionally, the design infiltration rate has been halved to account for no regular overflow conveyance(as per KCSWDM Section 5.4.1 General Requirements for Infiltration Facilities subheading 100-Year • Overflow Conveyance). Triad Associates DeBar Plat Page 4-6 Technical Information Report 4.3.1 Tributary Developed Basin Modeling The onsite tightline conveyance system will collect stormwater runoff from the proposed road and frontage • improvements. The roof downspouts of all of the proposed lots will be connected to the tightline conveyance system. The driveways for all the lots are assumed to sheet-flow to the street. The onsite soils are fine to medium sands and are modeled as outwash. See the Developed Conditions Exhibit in the Appendix for delineation of the tributary areas. Developed Basin Areas(see Developed Conditions Exhibit) Total Tributary Area: AT=2.11 acres(includes frontage improvements and roof/driveway area for all lots) The estimated(modeled)tributary impervious area is: Ai=Ai-ROW+Ai-d.+Ai-roof 5 � 5 Where: Ai-Row O. acres,onsite road and frontage ' provements to the crown. Ai-d,,= .1 acres,driveway area,assumed 0 sf/lot for 14 lots. Ai_roor= .61 acres,roof area, assumed 1,90 sf/lot for 14 lots Therefore,Ai= =1.42 acres. The remaining area was assumed to be grass coverage on outwash soils,Ag=2.11 — 1.42=0.69 acres KCRTS Modeling • The scale factor for the site is Sea-Tac 1.0 (see KCSWDM Figure 2.2.2.A Rainfall Regions and Regional Scale Factors, included at the end of this section). Below is the peak analysis for the TSF modeled tributary to the infiltration vault. Flow Frequency Analysis Time Series File:devell.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis------- FlowRate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.366 6 2/09/01 2:00 0.721 1 100.00 0.990 0.304 8 1/05/02 16:00 0.515 2 25.00 0.960 0.442 3 2/27/03 7:00 0.442 3 10.00 0.900 0.354 7 8/26/04 2:00 0.420 4 5.00 0.800 0.420 4 10/28/04 16:00 0.370 5 3 .00 0.667 0.370 5 1/18/06 16:00 0.366 6 2.00 0.500 0.515 2 10/26/06 0:00 0.354 7 1.30 0.231 0.721 1 1/09/08 6:00 0.304 8 1.10 0.091 Computed Peaks 0.652 50.00 0.980 Triad Associates DeBar Plat Page 4-7 Technical Information Report 4.3.2 Infiltration Rate The design infiltration rate (Ide51g„) is calculated per KCSWDM Section 5.4.1 General Requirements for • Infiltration Facilities subheading Design Infiltration Rate. The measured infiltration rate (In easured) is 60 inches per hour(Cornerstone Geotechnical Inc.April 5,2001,included in Section 6). Idesign—Imeasured x Fiesting x Fgeome,ry x Fplugging (KCSWDM Equation 5-9) Where: ✓ F,es,ing is 0.30 for the EPA testing method and 0.50 for the ASTM D3385. The infiltration rates were measured using the EPA method,so F,,,,;„g=0.30 V Fgeametry=4DI W+0.05 Accounts for the influence of facility geometry and depth to the water table or impervious strata (i.e.attempts to account for groundwater mounding). 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. The geotechnical investigation revealed no groundwater or impervious strata in proximity to the proposed vault location,so Fgeame,ry m 1.0 Fp,„ggi„g accounts for reductions in infiltration rates over the long term due to plugging of soils. The site generally has fine to medium sands,so FP,„gg,„g#0.8 Therefore,Idesig„=(60 inches/hour)x 0.30 x 1.0 x 0.8= 14.4 inches/hour • Further,the design infiltration rate is halved to account for no downstream overflow route,therefore, Idesign=72 inches/hour For the KCRTS model,this is converted to minutes/inch,Id,,ig„=8.3 nunutes/inch 4.3.3 Vault Infiltration Modeling The infiltration vault has been designed with minimum internal dimensions of 66.50 feet by 17.75 feet. The permeable area at the bottom of the vault is reduced from these dimensions by the concrete footings required to satisfy structural requirements. For purposes of these calculations, the footings are assumed to extend 1.50 feet into the vault on all four walls,thus resulting in a permeable surface at the base of the vault of 63.50 feet by 14.75 feet. The KCRTS program uses the input values of the design infiltration rate and the vault's internal dimensions for modeling the proposed vault. However, since the area of permeable surface is less than the area between the vault's walls, an adjustment to the input values has to be made in order to achieve accurate results. The infiltration rate to be input into the KCRTS program was determined by calculating the ratio of the total internal vault area to the permeable surface area and then multiplying the result by the design infiltration rate derived above. This calculation is summarized as follows: Triad Associates DeBar Plat Page 4-8 Technical Information Report Total Infiltration Vault Area =66.50'x 17.75' 3 Permeable Surface Area=63.50'x 14.75' S Ratio: (66.50 x 17.75)/(63.50 x 14.75)= 1.26 r I u s KCRTS Infiltration Rate= 1.26 x Id,,ig„ Ides;gn=8.3 minutes/inch KCRTS Infiltration Rate=10.5 minutes/inch The KCRTS Infiltration Rate calculated above is a larger number than the design infiltration rate,however, it actually represents a lower infiltration rate than the design rate,due to the units that the KCRTS program requires. The KCRTS Infiltration Rate and the vault's actual dimensions were input into the KCRTS program to model the vault and determine the design water surface elevation for the 100-year design storm event. These calculations are summarized below with the actual program output. Retention/Detention Facility Type of Facility: Infiltration Pond Side Slope: 0.00 H:1V Pond Bottom Length: 66.50 ft Pond Bottom Width: 17.75 ft Pond Bottom Area: 1180. sq. ft Top Area at 1 ft. FB: 1180. sq. ft 0.027 acres Effective Storage Depth: 15.00 ft • Stage 0 Elevation: 100.00 ft Storage Volume: 17706. cu. ft 0.406 ac-ft Vertical Permeability: 10.50 min/in Permeable Surfaces: Bottom Riser Head: 15.00 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) 0.00 100.00 0. 0.000 0.000 0.00 1180. 0.20 100.20 236. 0.005 0.000 0.16 1180. 8.40 108.40 9915. 0.228 0.000 0.16 1180. 8.60 108.60 10151. 0.233 0.000 0.16 1180. 8.80 108.80 10387. 0.238 0.000 0.16 1180. 9.00 109.00 10623. 0.244 0.000 0.16 1180. Hyd Inflow Outflow Peak Storage Target Calc Stage Elev (Cu-Ft) (Ac-Ft) 1 0.72 0.00 0.00 8.45 108.45 9971. 0.229 2 0.37 ******* 0.00 4.60 104.60 5434. 0.125 3 0.37 ******* 0.00 4.40 104.40 5193. 0.119 4 0.37 ******* 0.00 3.67 103.67 4336. 0.100 5 0.44 ******* 0.00 3.35 103.35 3953. 0.091 6 0.42 ******* 0.00 2.32 102.32 2737. 0.063 7 0.35 ******* 0.00 0.87 100.87 1025. 0.024 8 0.30 ******* 0.00 0.74 100.74 868. 0.020 Triad Associates DeBar Plat Page 4-9 Technical Information Report 4.3.4 Vault Water Quality Design A wetpool facility is required per City of Renton guidelines in order to settle-out fines that could plug the infiltrative surface and to enhance water quality prior to infiltration. The first cell of the proposed vault has been designed to satisfy the wetvault requirements of Section 6.4.2 of the KCSWDM and the basic wetpond requirements of Section 6.4.1.1. The required cell volume is 3.O V„ where V, is the volume of runoff estimated for the Mean Annual Storm(MAS). The mean annual storm precipitation is obtained by locating the project site on KCSWDM Figure 6.4.LA, Precipitation for Mean Annual Storm, (included at the end of this section) and interpolating between the isopluvials. For this site,the mean annual storm precipitation is 0.47 inches(R). The runoff from the mean annual storm is then calculated using KCSWDM Equation(6-13): Vr=(0.9Ai+0.25Atg+0.1 OA,f+0.0IA,)x(RI12) Where, V,=volume of runoff from mean annual storm(ft) A;=area of impervious surface(ft) Atg=area of till soil covered with grass(ft2) A,f=area of till soil covered with forest(ft) A,,=area of outwash soil covered with grass or forest(ft2) RI12=rainfall from mean annual storm(feet) Therefore, Vr=[0.9(43,560 sf/Ac)(1.42 Ac)+0.01(43,560 sf/Ac)(0.69)]x(0.47/12) • Vr=2,192 ft3 Therefore the required volume of the wetvault cell is V„,y=3.0(2,192)=6,576 ft3. 4.3.5 Design Vault The stormwater vault has been designed to satisfy the minimum volumetric requirements calculated above and to provide additional volume as a factor of safety to account for potential construction imperfections. The infiltration vault is required to be 66.50' x 17.75' x 8.45' deep, thus providing a retention volume of 9,974 ft3. The infiltration vault has actually been designed with a depth of 9.00' from the 294.50 elevation of the infiltrative surface to the 100-yr storm event design water surface of 303.50. It therefore provides a retention volume of 10,623 ft3 and a 6.5%elective construction factor of safety. The wetvault is required to provide 6,576 ft3 of dead storage volume. The wetvault cell has actually been designed to provide 6,783 ft3 of volume from the 295.50 elevation at the top of the sediment storage to the 303.50 elevation of the outlet to the infiltration vault, thus providing a 3% elective construction factor of safety. It is proposed to have internal dimensions of 66.50' x 12.75' x 8.00' deep. The detailed design of the stormwater vault can be found in the Debar Plat-Road, Storm Drainage and Utility Plans submitted concurrently with this report. Triad Associates DeBar Plat Page 4-10 Technical Information Report 4.4 Individual Splash Blocks In accordance with the recommendations of Cornerstone Geotechnical, Inc., as contained in their April 5, 2001 report, splash blocks are proposed for dispersion of the stormwater runoff from the roof downspouts of the six lots not adjacent to the steep slope (lots 1-4, 13 and 14). The splash blocks are proposed as a means to help distribute the runoff generated by these roofs over a larger area and avoid concentration of the flow. The splash blocks are not being used as an alternate to providing volume in the infiltration vault for these impervious surfaces, as the roof areas of all of these lots are included in the vault sizing calculations as if they were tight-lined to the vault. The splash blocks will be orientated to distribute the roof runoff across the lawns,promoting infiltration. Private lot storm drainage lines will still be stubbed to all of the lots so that the footing drains can be tight-lined to the central stormwater vault. • Triad Associates DeBar Plat Page 4-11 Technical Information Report SECTION 3.2 RUNOFF COMPUTATION AND ANALYSIS METHODS FIGURE 3.2.2.A RAINFALL REGIONS AND REGIONAL SCALE FACTORS ST 1.0/ ST 1.1 ST 1.0 LA 0.8 LA 0.9 LA 1.0 LA 1.2 SN ONONISN COUNTY F ` �T `OTNEL4\ \ NMNVRIS N K1N0 COUNiv 5 T-IJ.' REDYOND Q � f ROE ONO _.� i 4` f1GBB � ELLEVl1EBq F rr �YERCER I /t seATTLE l { , Ni[atty �'•NowauRr y ENTO BUREY: 1'TUIdYRI� O i !� O -' .. Ic[aunrzw N A TA'r- Si TAC ; �•.,`_ ; ,� LANDSBURG 1 Arra / �I' � ,1 .aY� tNloeirUl6 r` �__•_—�i- �;• 1 � DBURY.- / x n` y� V, K[ • ST 1.1 ,.EDERAL W [ , [f� / _ •\r _. I FiC ~IK1NG COUNTY� \ 0 PIERCE COUNTY \ / ST 1.0ST \ Rainfall Regions and LA 0.8/ Regional (3oale Factors LA 0.9 -_ Incorporated Area LA 1.0 LA 1.2 --a= River/Lake 0 — Major Road 9/1/98 1998 Surface Water Design Manual 3-22 6.4.1 WETPONDS—BASIC AND LARGE—METHODS OF ANALYSIS FIGURE 6.4.1.A PRECIPITATION FOR MEAN ANNUAL STORM IN INCHES(FEET) ST 1.0/ LA 1 2 ST 1.0 LA 0 8 LA. 0.9 LA 1 0 ST 1.1 N . . \ _ _ q .. . . q ells tt Bxy ...I Puget • 4 e Sated � I V i 0.54" 0.47" (0.039') i___ Incorporated Area - -c=D River/Lake 0.47" Major Road (0.039' ) 0.52" " 0.65" NOTE:Areas east of the easternmost isopluvial should use 0.65 (0.043 ' 561, (0.0541 ) inches unless rainfall data is available for the location of interest (0.04 7' ) 24 The mean annual storm is a conceptual storm 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 SECTION V \ CONVEYANCE SYSTEM ANALYSIS & DESIGN 5 Conveyance System Analysis and Design The tightlined portions of the drainage system were designed to convey the 100-year flows without overtopping. The King County Backwater(KCBW) Program Pipe Routine (BWpipe) was used to check the onsite conveyance designs for the 25- and 100-year flows. The BWpipe program output is included at the end of this section. As per the requirements of KCSWDM Table 3.2, "Acceptable Uses of Runoff Computation Methods," conveyance flows were calculated based on the Rational Method, with a weighted C-value calculated for the site. Each CB was assigned a Q-ratio based on its net tributary area. The rational flow rates were based on an assumed 6.3-minute minimum time-of-concentration. Spreadsheets showing Q-ratio calculations for the KCBW program are included at the end of this section. The design overflow water surface in the wetvault was used as the tailwater elevation for the tributary conveyance system. Rational Method Calculations The rainfall intensities were calculated assuming a 6.3-minute minimum time-of-concentration(T,), which reflects the developed nature of the collected basin. The rainfall intensity equation is per KCSWDM Equation(3-4). 100-year Peak Rainfall Intensity: • I.=P,.(a,.)(T,)-b,, =3.7(2.61)(6.3)-0.63 =3.19 in/hr Where, Iron = 100-year rainfall intensity(for a given site and T,)(inches/hour) P100= 100-year 24-hour total rainfall depth(inches)=3.90 inches aloo=Coefficient from KCSWDM Table 3.2.1.13=2.61 bloo=Coefficient from KCSWDM Table 3.2.LB=0.63 25-year Peak Rainfall Intensity: Izs =Pzs(azs)(T�)-b=` =3.2(2.66)(6.3)-065 =2.77 in/hr Where, 125 =25-year rainfall intensity(for a given site and T,)(inches/hour) P25=25-year 24-hour total rainfall depth(inches)=3.45 inches a,s=Coefficient from KCSWDM Table 3.2.LB=2.66 b,5=Coefficient from KCSWDM Table 3.2.1.13=0.65 C„ Calculation The weighted runoff coefficient for use in the rational method is estimated from the overall developed areas: Total Tributary Area= 1.42+0.69=2.11 Acres Total Impervious Area=0.05+0.28+0.70+0.16+0.17+0.06= 1.42 Acres Total Landscape Area=0.10+0.29+0.14+0.16=0.69 Acres C,y= Impervious Area x 0.9+Landscape Area x 0.25 • Total Collected Area C,,. =0.69 Q Calculation Triad Associates DeBar Plat Page 5-12 Technical Information Report The developed site conveyance system consists of seven catch basins, one of which has a solid cover, and thus the site has six catchment areas. The catchment areas are delineated on the Tributary Area Exhibit . located in the Appendix. The Rational Method flows were calculated for each catchment area, as summarized below. i QR - C,,IAT Where, QR =peak flow(cfs)for a storm of return frequency R C. =weighted runoff coefficient I =peak rainfall intensity(in/hr)for a storm of return frequency R AT =catchment area(acres) AREAS acres RATIONAL METHOD FLOWS cfs CATCHMENT IMPERVIOUS PERVIOUS TOTAL Q25 Q100 1 0.05 0.10 0.15 0.29 0.33 ----------------------------- -------------------------------------------------------------------------------------------------------------------------------------- 57 -------------------------- 0.28 0.29 -------0----------- - 1.09 ---------- 1=25---- - --------------------------------- -------- 3 0.70------------------0_00---------------0.70--------------------1-34----- ----- 1.54 ----------------------------- ---------------- - -------------------------------- 4 0.16 0.14 0.30 0.57 0.66 ---------------------------- -------------------------------------------------------------------------------------------------------------------------------------- 5 0.17 0.16 0.33 0.63 0.73 ----------- 6 0.00 0.00 0.00--------------------0.00-----------------------------�=------------------- v ------------- ----------------------------------------------------------0.0- - 7 0.06 0.00 0.06 0.11 0.13 TOTALS 1.42 0.69 2.11 4.03 4.64 • Backwater Analysis The annotated backwater program documentation files are included at the end of this section. Each of the proposed conveyance pipes that convey developed condition flows to the water quality/ infiltration vault were modeled. As shown below, at least 0.5 feet of freeboard will be provided in each catch basin for the 100-year storm event, which satisfies the requirements of the KCSWDM for both the 100-year and 25-year storm events. Triad Associates DeBar Plat Page 5-13 Technical Information Report BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:0220bwl.bwp Surcharge condition at intermediate junctions Tailwater Elevation:303.5 feet Discharge Range:4.03 to 4.64 Step of 0.61 [cfs] Overflow Elevation:308.84 feet Weir:NONE Upstream Velocity:5. feet/sec PIPE NO. 1: 14 LF - 1211CP @ 15.00% OUTLET: 301.42 INLET: 303.52 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 308.47 BEND: 90 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.72 Q( FS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI *** *************************************************************************** 4.03 1.75 305.27 * 0.012 0.86 0.36 2.08 2.08 0.86 ***** 1.75 4.64 2.12 305.64 * 0.012 0.90 0.39 2.08 2.08 0.90 ***** 2.12 The Qloo headwater elevation in C.B. #1(305.64)is below the rim elevation(308.47)by 2.83 feet. PIPE NO. 2: 41 LF - 1211CP @ 0.90% OUTLET: 303.52 INLET: 303.89 INTYP: 5 JUNC NO. 2: OVERFLOW-EL: 308.75 BEND: 25 DEG DIA/WIDTH: 2.0 Q-RATIO:10.69 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 2.34 1.74 305.63 * 0.012 0.66 0.59 1.75 1.75 1.53 1.74 1.03 2.70 2.23 306.12 * 0.012 0.71 0.64 2.12 2.12 1.95 2.23 1.14 The Q100 headwater elevation in C.B. #4(306.12)is below the rim elevation (308.75)by 2.63 feet. PIPE NO. 3: 90 LF - 1211CP @ 0.34% OUTLET: 304.39 INLET: 304.70 INTYP: 5 JUNC NO. 3: OVERFLOW-EL: 309.33 BEND: 90 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.00 • Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.20 0.94 305.64 * 0.012 0.19 0.21 1.24 1.24 0.94 0.94 0.25 0.23 1.43 306.13 * 0.012 0.20 0.22 1.73 1.73 1.43 1.43 0.27 The Q100 headwater elevation in C.B. #6(306.13)is below the rim elevation(309.33)by 3.20 feet. PIPE NO. 4: 121 LF - 12"CP @ 0.90% OUTLET: 304.70 INLET: 305.79 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.20 0.19 305.98 * 0.012 0.19 0.16 0.94 0.94 0.19 ***** 0.16 0.23 0.37 306.16 * 0.012 0.20 0.18 1.43 1.43 0.37 0.00 0.18 The Qioo headwater elevation in C.B. #7(306.16)is below the rim elevation(308.84)by 2.68 feet. • Triad Associates DeBar Plat Page 5-14 Technical Information Report BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:0220bw2.bwp Surcharge condition at intermediate junctions • Tailwater Elevation:306.12 feet Discharge Range:0.63 to 0.73 Step of 0.1 [cfs] Overflow Elevation:308.75 feet Weir:NONE Upstream Velocity:5. feet/sec PIPE NO. 1: 31 LF - 1211CP @ 1.03% OUTLET: 303.89 INLET: 304.21 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 0.63 1.92 306.13 * 0.012 0.34 0.28 2.23 2.23 1.92 1.55 0.28 0.73 1.92 306.13 * 0.012 0.36 0.30 2.23 2.23 1.92 1.55 0.30 J The Qioo headwater elevation in C.B. #5(306.13)is below the rim elevation(308.75)by 2.62 feet. BACKWATER COMPUTER PROGRAM FOR PIPES Pipe data from file:0220bw3.bwp Surcharge condition at intermediate junctions Tailwater Elevation:305.64 feet Discharge Range:2.43 to 2.79 Step of 0.36 [cfs] Overflow Elevation:308.17 feet Weir:NONE Upstream Velocity:5. feet/sec PIPE NO. 1: 61 LF - 1211CP @ 0.51% OUTLET: 303.52 INLET: 303.83 INTYP: 5 JUNC NO. 1: OVERFLOW-EL: 308.17 BEND: 90 DEG DIA/WIDTH: 2.0 Q-RATIO: 0.81 • Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* 2.43 2.32 306.15 * 0.012 0.67 0.74 2.12 2.12 2.06 2.32 1.09 2.79 2.47 306.30 * 0.012 0.72 0.84 2.12 2.12 2.13 2.47 1.22 The Q1o0 headwater elevation in C.B. #2(306.30)is below the rim elevation(308.17)by 1.87 feet. PIPE NO. 2: 31 LF - 1211CP @ 0.52% OUTLET: 303.83 INLET: 303.99 INTYP: 5 Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI ******************************************************************************* J1.34 2.20 306.19 * 0.012 0.49 0.50 2.32 2.32 2.20 1.88 0.32 1.54 2.36 306.35 * 0.012 0.53 0.54 2.47 2.47 2.36 2.06 0.38 The Qloo headwater elevation in C.B. #3(306.35)is below the rim elevation(308.17)by 1.82 feet. • Triad Associates DeBar Plat Page 5-15 Technical Information Report / SECTION VI SPECIAL REPORTS & STUDIES 6 Special Reports and Studies Included here is the Geotechnical Report prepared by Cornerstone Geotechnical, Inc, April 5, 2001. This • report addresses the steep slopes onsite and the site's suitability for infiltration. • Triad Associates DeBar Plat Page 6-16 Technical Information Report • Geotechnical Engineering Report Debar Site Renton, Washington For Specialized Homes • Cornerstone PO Box 1750 Woodinville, WA 98072 Phone: 425-844-1977 Geotechnical , Inc. Fax: 425-844-1987 • April 5, 2001 Mr. Bob Niemann Specialized Homes 600 First Avenue, Suite 500 Seattle, Washington 98104 Geotechnical Engineering Report Debar Site Renton,Washington CG File No. 1085 • Dear Mr. Niemann: INTRODUCTION This report presents the results of our geotechnical engineering investigation at your proposed residential subdivision known as the Debar Site. The site is located at 2132, 2200, 2216, and 2224 NE 28th Street in Renton, Washington, as shown on the Vicinity Map in Figure 1. For our use in preparing this report we have been provided with a site plan prepared by Triad Associates, dated March 26, 2001. The project site consists of four residential properties with houses located on each lot. The eastern two residences are planned to remain on the site, and the western two residences will be removed. A steep slope is located along the northern property boundary. The site is planned to be developed into 14 new residential lots, which will be accessed by a cul-de-sac that extends onto the site from NE 281h Street. Minimal cuts and fills are expected for the site. Lots 5 through 12 are located on the north side of planned roadway along the top of the slope. Geotechnical Engineering Report Debar Site April 5, 2001 • CG File No. 1085 Page 2 A critical aspect of site development is infiltration of the on-site storm water runoff. The proposed infiltration facility is a vault with a bottom elevation approximately 14 feet below current grade. Storm water runoff from roadways and driveways is planned to be routed to the vault. SCOPE The purpose of this study is to explore and characterize the subsurface conditions and present recommendations for site development. Specifically, our scope of services consisted of Phases I, II, and III as outlined in our Proposal for Services, dated February 14, 2001, and our Memorandum, dated March 2, 2001, which included slope mapping, subsurface explorations, field infiltration testing, and the following: I. Recommend structure setbacks from the top of slope. 2. Provide foundation design recommendations. 3. Provide recommendations for site preparation and grading. 4. Provide recommendations for slab-on-grade. 5. Provide temporary and permanent cut slope recommendations. 6. Recommend infiltration rates for use in design, based on field-measured infiltration tests. 7. Provide lateral pressures for the design of the infiltration pond walls. 8. Provide roadway pavement design recommendations. SITE CONDITIONS Surface Conditions The project site consists of four rectangular-shaped lots located on the north side of NE 28`h Street. The ground surface is generally flat lying with a gentle downward gradient to the northwest, toward the top of slope. The north margin of the site slopes steeply. Part way down the slope, an abandoned railroad grade has been cut into the slope. The railroad cut has been incised into the hillside, which has created a 10-foot tall ridge on the north side of the railroad grade below the western lot and the two eastern lots. This area is working as a catchment area for the trash debris that has been thrown down the hillside. The ground surface further north and below the railroad grade slopes down steeply to the May Creek Valley floor. May Creek is currently located away from the toe of the site slope,and flows on the north side of the valley. Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5,2001 CG File No. 1085 Page 3 Abundant debris consisting of yard clippings,branches, wood and metal debris, and other garbage has been dumped over the top of slope. Scattered mature evergreens exist within the gently sloping upland portion of the site. The upper portion of the slope (defined as the part above the railroad grade) is vegetated with ferns and scattered small- to medium-sized trees. The lower portion of the slope (below the railroad grade) is mostly vegetated with scattered medium-sized trees, ferns, and salmonberry bushes. The lower portion of the western end of the slope is vegetated largely by devil's club. A residence and outbuildings are currently located on each of the lots. It appears that storm water runoff from the roadway for the neighborhood is currently infiltrated in shallow ditches along the side of the road. We did not observe any continuous storm water ditches. All of the water throughout the neighborhood appears to infiltrate. Geology The geologic and topographic conditions at this site are largely the result of the area's glacial • history. The last episode of glaciation, the Vashon Stade of the Fraser Glaciation, ended approximately 11,000 years ago. During the Vashon Stade, this part of the Puget Sound region was overridden by roughly 3,000 feet of ice_ Soil units deposited during previous glacial and nonglacial intervals, and sediment deposited in front of the advancing glacier, were compacted beneath the ice. Other sediments were deposited during ice retreat, some of which were partly consolidated by minor re-advances during the general period of ice retreat. A typical glacial sequence in the Puget Sound region includes recessional outwash sand and gravel underlain by glacial till, advance outwash, and older, glacial and nonglacial sediments. Many of the topographic features visible in the Puget Sound lowland today are a result of scouring by the glacial ice or deposition by recessional meltwater streams. The Preliminary Geologic Map of Seattle and Vicinity, Washington by Howard H. Waldron, Bruce A. Liesch, Donal R. Mullineaux, and Dwight R. Crandell (USGS 1962), was reviewed for information regarding geologic and soil conditions within the project area. The project site is mapped as Qys (Younger Sand), which we interpret to be recessional outwash. The recessional outwash consists of a well-sorted sand deposited by glacial meltwater streams as the glacier retreated. The lower portion of the slope below the site is mapped as Qc (Older clay, till, and tgravel). These are older soils,deposited before the most recent glacial advance. Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 • CG File No. 1085 Page 4 Our explorations at the site (from youngest to oldest) encountered recessional outwash, glacial till, and advance outwash. The glacial till consists of a very dense, nonstratified mixture of silt, sand, and gravel deposited directly by melting ice beneath the glacier. The advance outwash consists of sand and gravel deposited in front of glacial meltwater streams from the advancing glaciers. Both the till and advance outwash were overridden by the glacier and are, therefore, very dense. Explorations Subsurface conditions were explored at the site on February 27, 2001, by excavating four test pits with an extendahoe backhoe. The test pits were excavated to depths of 14 to 16 feet below the ground surface. The explorations were located in the field by a geologist from this firm who also examined the soils and geologic conditions encountered, and maintained logs of the test pits. The approximate locations of the test pits are shown on the Site Plan in Figure 2. The soils were visually classified in general accordance with the Unified Soil Classification System, a copy of which is presented as Figure 5. The logs of the test pits are presented in Figures 6 and 7. In the . following paragraphs, we present a brief description of the subsurface conditions encountered in our explorations. A more detailed description of the subsurface conditions can be found in the test pit logs. The explorations were extended to the maximum depth attainable with the extendahoe,but deeper explorations were needed to identify the bottom of the recessional outwash sand. Therefore, deeper subsurface conditions were explored at the site on March 13, 2001, by drilling Borings 1 through 4 with a truck-mounted, hollow-stem auger, Mobile B-61 drill rig. The borings were advanced to depths ranging from 24 to 59 feet below the ground surface. The logs of the borings are shown on Figures 8 through 13. The boring samples were obtained at 5-foot intervals beginning 2.5 feet below the ground surface, except Boring 4, which was drilled to a depth of 17.5 feet before beginning sampling because of the close proximity to Test Pit 1. The samples were obtained using the Standard Penetration Test (SPT) method in general accordance with ASTM D 1586. The SPT consists of driving a 2-inch- outside-diameter sampler using a 140-pound hammer falling 30 inches. The standard method is • to drive the sampler 18 inches and record the blows for each 6 inches of penetration. The total number of blows for the last 12 inches of penetration (unless otherwise noted) is termed the Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 . CG File No. 1085 Page 5 Standard Penetration Resistance blow count, or ''N-value" (units: blows per foot). These values are shown on the boring logs. Subsurface Conditions Our site explorations encountered recessional outwash sands overlying glacial till. The contact of the outwash with the underlying till was generally a gradational contact. The till appears to be thin and locally may pinch out. The till would be a low permeable layer but if was not encountered in Boring 4. Our deeper explorations extended through the till and recessional outwash, and encountered the underlying advance outwash. The advance outwash consisted of sand and gravel, including some fine sand. Our explorations encountered a surficial layer of topsoil, about 0.3 to 1.3 feet in thickness. The topsoil consisted of loose, silty fine sand with organic matter. The topsoil was underlain by a weathered soil horizon, 0.7 to 2.5 feet in thickness. These soils consisted of loose, fine to medium sand with silt, to a silty fine to medium sand with gravel. We have interpreted these soils . as weathered recessional outwash. The weathered outwash was underlain by loose to medium dense, fine to medium sand. We have interpreted these soils as recessional outwash. The recessional outwash was encountered to the full depths explored with the backhoe-excavated test pits. In Test Pits 3 and 4, which are located in the easternmost lot, silty fine sand lenses were encountered in the sand deposit below a depth of about 6 feet. A grain size analysis was completed on a sample of soil 3.5 feet deep collected from Test Pit 2. This sample is representative of the soils encountered within the planned infiltration area. The results of that grain size are presented on Figure 14. The soil has been classified as fine to medium sand, with 51 percent of the soil being medium-grained. Boring 1 encountered recessional outwash sand to a depth of about 22 feet. From 22 feet to the bottom of the boring at 34 feet, dense to very dense, silty fine to medium sand with gravel was encountered; we have interpreted these soils as glacial till. Boring 2 encountered recessional sand to a depth of about 16 feet. Glacial till consisting of medium dense to very dense, silty fine sand with gravel was encountered to the depth explored,24 feet. • Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 6 Boring 3 encountered recessional outwash sand to a depth of 34 feet. The deposit graded into a very fine sand and then into a silty fine sand with gravel, interpreted to be glacial till. The sample obtained below the till, at a depth of 42.5 to 44.0 feet consisted of a very dense, fine sand and is interpreted to be advance outwash. Boring 4 encountered recessional outwash deposits to a depth of about 39 feet. The outwash generally consisted of fine to medium sand, except, for 2- to 3- inch, silty, very fine sand seams that were encountered in the 27.5 and 37.5 feet samples. Dense sand and gravels were encountered from 39 to 47 feet and are interpreted to be advance outwash deposits. Below 47 feet, very dense, fine to medium sand with silty fine sand seams was encountered. These soils are also interpreted to be advance outwash deposits. Site Slopes General: Cross-Sections A-A' and B-B' were surveyed by Triad Associates. We also extended the cross sections down the slope using a hand-held clinometer and 100-foot measuring tape. The results of these measurements are included as Figures 3 and 4. • Cross-Section A-A' (West end of site): Cross-Section A-A' was measured at the west end of the site through a swale-like feature, interpreted to have resulted from shallow slope failures. The railroad has been constructed across this feature, indicating that the feature is older than the railroad grade. The upper portion of the slope is inclined at 42 to 46 degrees down to the railroad grade. The contact of the recessional outwash sand with the underlying glacial till is interpreted to be about halfway down the upper portion of the slope. The railroad grade is about 10 feet in width. The portion of the slope immediately below the railroad grade is inclined at about 35 degrees and the lowest portion of the slope adjacent to the valley floor has an inclination of about 24 degrees. Indications of seepage were not observed along the upper portion of the slope. Wet and saturated surface soils were observed along the lowest portion of the slope. The vegetation also indicated wet soils. We suspect pre-Vashon deposits with a low permeability are located on the lower portion of this slope, although these soils were not observed during our reconnaissance. Cross-Section B-B' (East end of Site): Cross-Secton B-B' was measured at the east end of the site. Generally, the upper 20 feet of the upper slope is inclined at about 34 degrees, and the ground surface from there to the railroad grade slopes more steeply at 34 to 48 degrees. The • break in slope is interpreted to be a contact where the recessional outwash sand overlies the Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 . CG File No. 1085 Page 7 glacial till,but it may also be related to the railroad excavation. The railroad grade is incised into the slope at this location, and is about 10 feet wide. North of the railroad grade, the ground surface slopes up at about 41 degrees as part of a narrow ridge that parallels the railroad grade. Based on observations of the surface geometry, it appears that some fill was placed on the ridge area during construction of the railroad. The ground surface slopes downward to the valley floor at about 30 to 40 degrees below the narrow ridge area. Indications of ground water seepage were not observed anywhere along this cross section. Hydrologic Conditions Ground water seepage was encountered during drilling in Boring 1 at a depth of about 22.0 feet. The ground water was perched within the recessional sand overlying the glacial till. Wet, silty fine sand seams were encountered in the samples at 27.5 and 37.5 feet in Boring 4. Piezometers were installed in all of the borings and the ground water levels were measured during and after the field infiltration test. Ground water was detected only in Boring 1 during our monitoring period. The ground water level in this boring was 24.28 feet deep on the last date measured, March 17,2001. We did not observe indications of ground water seepage along Cross-Section B-B', or along the upper portion of the slope above the railroad grade. Saturated surface soils were observed along the lower portion of the slope below the western end of the site along Cross-Section A-A'. We interpret the occurrence of ground water to be perched water. Perched water occurs when surface water infiltrates through the more permeable soils and accumulates on top of the underlying, less permeable soils. The more permeable soils consist of the topsoil, weathered soil horizon, and the recessional outwash sand. The less permeable soils consist of the glacial till and the silty sand seams within the recessional and advance outwash. The observed perched water does not constitute a coherent ground water table. It should be noted that the local amount of perched ground water probably varies depending upon the time of year and the recharge conditions. Typically, we would expect to encounter ground water along the contact between the more permeable outwash and the less permeable glacial till. The ground water was encountered only in • Boring 1, and the ground water level was measured to drop during our monitoring period, which Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 8 was shortly after a rainfall event. We observed no indications of ground water seepage along the upper portions of the steep slope,even though the till is exposed there. Therefore, we believe that the perched ground water on the till flows away from the slope. Based on the subsurface explorations we believe that ground water recharge within the site moves downward and westward,along the upper contact of the glacial till. Slope Stability The May Creek valley wall originated as a result of downcutting by the creek during deglacial and post-glacial time. However, the upper portion of the slope is interpreted to be, at least in part, a cut slope created during construction of the railroad grade. Some of the lower portion of the slope adjacent to the railroad grade is interpreted to be a fill slope. Debris consisting of yard waste, garbage, etc. has been dumped over the top of slope, and some of this debris has slid and rolled down the slope over the years. These failures are interpreted to be shallow surface failures. The slope inclinations are steep and the slope has been performing very well at these steep inclinations. This good performance is at least partly due to the lack of ground water seepage on the upper slope. The direction of ground water perched on the glacial till beneath the site appears to be largely westward, or southwestward,rather than northward toward the steep slope. There is no indication that the site has experienced, or might experience, deep-seated failures. However, due to the steep slope angles and the existing loose debris along the slope, we consider the slope to be at risk for shallow failures. We observed some indications of shallow failures along the slope. The biggest such feature is the one at the west end of the site, along the alignment of Cross-Section A-A'. This feature is interpreted to be old, as it predates the railroad grade. Recommendations to mitigate against these types of failures are provided in this report. Seismic Hazard Seismic considerations include liquefaction potential, amplification of ground motions by soft soil deposits, and a reduction of slope stability. The liquefaction potential is highest for loose sand or silty sands with a high ground water table. The site is not considered to have a high potential for liquefaction, due to the lack of a high ground water table. The granular, loose to very dense site soils are not considered to be at risk for a significant amplification of ground • motion during a seismic event. However,due to the steep site slope angles, and the loose surface Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 9 soils and debris along the slope, we consider the slopes to be at risk for some shallow slope failures during a seismic event due to shaking. This risk is taken into consideration with the effective setback and foundation embedment recommended in the report. Infiltration Test A large-scale field infiltration test was completed at the site on March 15, 2001. A large test was performed to evaluate infiltration rates and also effects of migrating ground water. Piezometers were installed to evaluate if water was migrating toward the slope. The location of the infiltration test is shown on the Site Plan, Figure 2. A test pit was excavated to a depth of 13.3 feet below the ground surface. The log of the infiltration test pit is shown on the Test Pit Logs, Figure 7. The recessional outwash sand was encountered at the test elevation, which consisted of a fine to medium sand. Boring 3 was located about 60 feet south of our infiltration test location. This boring encountered permeable soils until a depth of 34 feet, where the soils graded into glacial till. Therefore, we do not expect impermeable soil horizons or ground water for at least 20 feet below the infiltration test location. A 3-foot-diameter, 13-foot-long pipe was placed in the infiltration test pit. Soil was backfilled around the pipe and water was added to the pipe to run the infiltration test. The soil at the bottom of the pipe was about 12.5 feet below the top of pipe elevation. Approximately 7,500 gallons of water obtained from a fire hydrant was used for our test. Water was kept continuously in the pipe for at least 6 hours. The pipe was filled to the top with water four times, and then the depth of water and time were recorded for the water to infiltrate. Our results of these measurements are shown on the plot, which is included as Figure 15. This figure shows the drawdown of the water with respect to time. Three tests were also completed with about 1.0 foot of head in the pipe, which showed similar results to the curves plotted on Figure 15. We also walked the slope and measured the piezometers for two days following the test. We did not detect any water in the nearby borings or on the slope face. Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 10 CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the site is well-suited with the planned development. The underlying medium dense to very dense native granular soils will provide good support for the planned structures and pavements. The soils expected to be encountered during construction consist of clean, granular, recessional outwash sands. Due to the clean, granular soils at the site, project planning can include wintertime construction. The slopes along the northeastern site margin are very steep and have been performing well at the steep slope inclinations for many years. However, the steep slopes are considered at risk to shallow failures. Protection to the structures from these shallow failures can be provided by adequate setback and embedment of the foundations. This can be achieved with an effective setback from the slope face. We recommend an effective setback of 35 feet from the face of the native soils on the slope face. This is discussed further in the Structure Setback and Embedment subsection of this report. The site soils are clean, granular, and well-suited for infiltration. Our investigation indicates that the ground water perched on the till slopes away from the top of slope. A critical aspect of the site development is to not concentrate water and direct it towards the slope. Therefore, we recommend that Lots 5 through 12 be connected with the storm drain system. The storm drain system could include a perforated tightline connection similar to Kings County Surface Water Manual, Appendix C, Figure C.2.1. The remaining lots could utilize splash blocks. We also recommend that runoff from the roadway and driveway be directed to the infiltration vault. Erosion Control Measures The erosion hazard for the soils in the upland, flat-lying areas is considered slight when stripped of vegetation. The steep portions of the site are extremely sensitive and the native soils and vegetation should not be disturbed. Best management practices (BMPs) may be used to reduce the erosion potential during construction. This includes routing surface water away from the top of slopes, using straw bales and silt fences to reduce water velocity and covering disturbed areas or cut slopes with straw or plastic sheeting. Silt fences should be erected on the downslope side of construction areas to reduce the potential for fines to leave the site. All sloping areas where Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 11 the soil is exposed either by construction or natural processes should be revegetated to reduce erosion. The vegetation should be maintained and repaired until established. When slope failures occur, the slopes should be immediately covered with plastic to reduce erosion. Adequate design and landscaping should then be implemented until established. To reduce the potential of collecting all the water from impervious surfaces and concentrating the flow at one location, it is our opinion the impervious surfaces such as sidewalks and roof downspouts be allowed to naturally infiltrate throughout the site. The roof downspouts should have splash blocks and direct water to very shallow swales of the landscaping. The sidewalks and patios should have a slight slope to allow infiltration in the adjacent grass or landscaping. This approach will reduce water concentration and allow water infiltration to be as is. Drainage rock trenches are not expected to be needed based on our testing and the neighborhood's existing infiltration. Site Preparations and Grading The first step of site preparation should be to strip the vegetation, topsoil, any fill or disturbed soils to expose the native soils in pavement and building areas. This material should be removed from the site, or stockpiled for later use as landscaping fill. After site stripping, our borings indicate that the exposed soils will be loose, therefore, the resulting subgrade should be compacted to a firm, non-yielding condition. Areas observed to pump or weave should be repaired prior to placing hard surfaces. Project planning can include this site for consideration during wintertime construction. If earthwork is conducted during the drier summer months, we expect that moisture will need to be added to the site soils to be near optimum moisture content. If earthwork is attempted during the wetter times of the year, we expect some delays may occur while waiting for the soils to drain following heavy rainfall events. Depending upon the site conditions, a blanket of rock spalls or imported sand and gravel in traffic and roadway areas may need to be placed to minimize disturbance to the prepared subgrade. This can be evaluated at the time of construction. Structural Fill General: All fill placed beneath buildings, pavements or other settlement sensitive features, isshould be placed as structural fill. Structural fill, by definition, is placed in accordance with Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 12 prescribed methods and standards, and is monitored by an experienced geotechnical professional or soils technician. Field monitoring procedures would include the performance of a representative number of in-place density tests to document the attainment of the desired degree of relative compaction. Structural fill should not be added in the setback area of the site without specific review by the geotechnical engineer. It is best to leave the setback area in its natural state. Materials: Imported structural fill should consist of a good quality, free-draining granular soil, free of organics and other deleterious material, and be well graded to a maximum size of about 3 inches. Imported, all-weather structural fill should contain no more than 5 percent fines (soil finer than a Standard U.S. No. 200 sieve), based on that fraction passing the U.S. 3/4-inch sieve. The recessional outwash sands expected to be encountered during construction are predominately a medium-grained, uniform sand. Compaction of uniform sands can be difficult, particularly if !� the soils are dry. Therefore we expect that moisture will likely need to be added to the soils to achieve compaction depending upon the moisture conditions at the time of earthwork. We expect that if the soils become saturated during a heavy rainfall event that they will drain to a compactable state following a period of dry weather. Fill Placement: Following subgrade preparation, placement of the structural fill may proceed. Fill should be placed in 8- to 10-inch-thick uniform lifts, and each lift should be spread evenly and be thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying building areas, and the upper 2 feet of fill below pavement and sidewalk subgrade, should be compacted to at least 95 percent of its maximum dry' density. Maximum dry density, in this report,refers to that density as determined by the ASTM D 1557 compaction test procedure. Fill more than 2 feet beneath sidewalks and pavement subgrades should be compacted to at least 90 percent of the maximum dry density. The moisture content of the soil to be compacted should be within about 2 percent of optimum so that a readily compactable condition exists. All compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree of compaction. Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 13 Temporary and Permanent Slopes Temporary cut slope stability is a function of many factors, such as the type and consistency of soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open, and the presence of surface or ground water. It is exceedingly difficult under these variable conditions to estimate a stable temporary cut slope geometry. Therefore, it should be the responsibility of the contractor to maintain safe slope configurations, since the contractor is continuously at the job site, able to observe the nature and condition of the cut slopes, and able to monitor the subsurface materials and ground water conditions encountered. We anticipate temporary cuts for installation of utilities and the infiltration vault. We note that significant caving of the vertical test pit sidewalls was encountered during our explorations. For planning purposes, we recommend that temporary cuts in the recessional outwash sand be no greater than 1.5 Horizontal to 1.0 Vertical (1.51-1:LOV). If ground water seepage is encountered, we would expect that flatter inclinations would be necessary. We recommend that cut slopes be protected from erosion. Measures taken may include covering cut slopes with plastic sheeting and diverting surface runoff away from the top of cut slopes. We do not recommend vertical slopes for cuts deeper than 4 feet, if worker access is necessary. We recommend that cut slope heights and inclinations conform to local and WISHA/OSHA standards. We recommend that permanent slope inclinations for structural fill and the cuts in the native soils be no steeper than 2H:1V. Lightly compacted fills or common fills should be no steeper than 3H:IV. Common fills are defined as fill material with some organics that are "trackrolled" into place. They would not meet the compaction specification of structural fill. Final slopes should be vegetated and covered with straw or jute netting. The vegetation should be maintained until it is established. Structure Setback and Embedment Uncertainties related to building along the top of steep slopes are typically addressed by the use of building setbacks. The purpose of the setback is to establish a "buffer zone" between the structure and the top of the slope, so that ample room is allowed for normal slope recession Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 14 during a reasonable life span of the structure (usually taken to be 100 years). In a general sense, the greater the setback, the lower the risk. From a geological standpoint, the setback dimension is based on the slope's physical characteristics, such as slope height, surface angle, material composition and hydrology. Other factors such as historical slope activity,rate of regression, and the type and desired life span of the structures are important considerations as well. Based on our observations of the slope activity, we expect that shallow failures will continue to occur on the slope. Therefore, we recommend the footings have adequate setback and embedment. This can be achieved by establishing an "effective setback" of at least 35 feet from the face of slope. The "effective setback" is the horizontal distance measured from the nearest edge of the footing to the slope face. This measurement should be taken to the face of the native soils, and not to the face of the debris resting on the slope. This setback detail is shown on Figure 17. The deeper the bottom of footing extends, the closer to the top of slope the structure can be built. However, the structure should be no closer than 25 feet from the top of slope. It is our opinion that the recommended effective setback and embedment criteria will provide adequate • setback from the slope for the design life of the structure and if proper care of the slope is maintained. We recommend that no excavation or stockpiling of soils occur within 15 feet of the top of slope during construction, unless reviewed and approved by the geotechnical engineer. The closer to the top of slope, the deeper the footings will need to extend to achieve the effective setback and embedment criteria. This can be achieved by supporting the structures on deep foundations, such as piles, or casting the footings on Controlled Density Fill (CDF)trenches. The base of the CDF trenches should be excavated to the depth to achieve the effective setback, and then the excavation can be filled with CDF to typical footing subgrade elevations. Significant caving of the soils was encountered during our test pit explorations. Therefore, it is likely that significant caving of the CDF trench sidewalls will be encountered, making excavation very challenging. We also expect that open-hole drilled piers will likely not work due to expected caving sand conditions. The loose, outer surface soils, trash, and debris located along the slope are considered at risk of failure. If it is feasible to remove the loose trash and debris with minimal disturbance to the underlying native soils, it is a good idea. This should be done with small equipment, or by hand Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 • CG File No. 1085 Page 15 to limit disturbance as much as possible. Any resulting area of bare soil should be immediately revegetated and the vegetation should be maintained until established. If the loose trash and debris is left in place, it should be considered at risk for shallow failures. Under no circumstances should any additional fill or debris be placed over or on the top of slope. Foundations General: The density of the soils expected to be encountered at typical foundation depths is loose. Therefore, we recommend that the exposed footing subgrade be thoroughly compacted with a walk-behind, double-drum roller, or other suitable piece of compaction equipment. Conventional shallow spread foundations should be founded on the compacted native soils, or be supported on structural fill extending to those soils. Footings should extend at least 18 inches below the lowest adjacent finished ground surface for frost protection and bearing capacity considerations. Minimum foundation widths of 14 and 20 inches should be used for continuous and isolated spread footings, respectively. Standing water should not be allowed to accumulate in footing trenches. All loose or disturbed soil should be removed from the foundation excavation prior to placing concrete. Design Values: For foundations constructed as outlined above, we recommend an allowable design bearing pressure of 2,000 pounds per square foot (psf) be used for the footing design. Uniform Building Code (UBC) guidelines should be followed when considering short-term transitory wind or seismic loads. Potential foundation settlement using the recommended allowable bearing pressure is estimated to be less than 1-inch total and '/z-inch differential between footings or across a distance of about 20 feet. Higher soil bearing values may be appropriate for footings founded on the unweathered very dense soils, and with wider footings. These higher values can be determined after a review of a specific design. Lateral loads can be resisted by friction between the foundation and subgrade soil, and by passive soil resistance acting on the below-grade portion of the foundation. For the latter, the foundation must be poured"neat" against undisturbed soil or backfilled with clean, free-draining, compacted structural fill. Passive resistance may be calculated as a triangular equivalent fluid pressure distribution. We recommend that an equivalent fluid density of 250 pounds per cubic foot (pcf) be used to calculate the allowable lateral passive resistance for the case of a level ground surface Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 16 adjacent to the footing. An allowable coefficient of friction between footings and soil of 0.45 may be used, and should be applied to the vertical dead load only. Seismic Design: The site is located within Zone 3 of the Seismic Zone Map shown as Figure 16- 2 of the 1997 Uniform Building Code (UBC). This corresponds to a Seismic Zone Factor, Z, of 0.30. This, in turn, corresponds to an effective peak horizontal acceleration of 0.3 g. Site conditions best fit the UBC description for Soil Profile Type SD("Stiff Soil Profile"). Slabs-on-Grade Slab-on-grade areas should be prepared as recommended in the Site Preparation and Grading subsection. Slabs should be supported on the compacted, firm, native soils, or on structural fill extending to these soils. Where moisture control is a concern, we recommend that slabs be underlain by 6 inches of free-draining sand or gravel for use as a capillary break. A suitable vapor barrier, such as heavy plastic sheeting, should be placed over the capillary break. If desired, a sand blanket could be placed over the vapor barrier to aid in curing of the concrete and to protect the vapor barrier. Pavement Areas Pavement subgrade should be prepared as outlined in the Site Preparation and Grading subsection. It will be important to proof roll the roadway areas prior to paving. The proof roll should be completed with a heavy, rubber-tired piece of equipment, such as a loaded 10-yard dump truck. Areas that yield under proof rolling equipment should be repaired. We should be retained to observe the proof roll prior to placement of the asphalt or hard surfaces. Over the prepared subgrade, we recommend that a pavement section consisting of 4 inches of crushed rock be overlain by 2 inches of Class B Asphalt can be placed. An alternative pavement section would be 3 inches of Asphalt-Treated-Base (ATB) overlain by 2 inches of Class B Asphalt. Drainage We recommend that runoff from roadways and driveways be routed to the infiltration system. We also recommend that the roof downspouts on Lots 5 through 12, which are located along the top of slope, be routed to the infiltration system. The tightline pipe for Lots 5 through 12 could Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 17 be perforated as shown in the Kings County Surface Water Manual, Appendix C, Figure C.2.1. Splash blocks could be used on the other lots. The use of these methods will help distribute the runoff across a larger area, and avoid concentrating the flow. Final site grades should allow for drainage away from buildings. We suggest that the finished ground surface be sloped at a gradient of 3 percent minimum for a distance of at least 10 feet away from buildings. Due to the granular, free-draining nature of the native soils and the expected shallow crawl spaces, footing drains are optional. It would be best to leave the crawl space elevation as high as possible if the footing drains are omitted. If low permeable soils are encountered at a relatively shallow depth below the footing subgrade, footing drains or positive drain from the crawlspace should be installed. Infiltration Vault General: Based on our findings it is our opinion that the site is well suited for infiltration. We have not been provided with specific details of the infiltration vault, although we understand that • at this time, the vault is planned to be located within the tot lot area, with a bottom elevation of about 14 feet below current grades. Our exploration near the infiltration area did not indicate a ground water table or impermeable zone for at least 20 feet below the planned vault bottom elevation. It is important for long-term performance of the infiltration system that the storm water be clean and free of clay or silt particles to prevent plugging of the subsurface soil layer. At this time, the vault is planned to be located 130 feet or greater from the top of slope. It is our opinion that this location is a sufficient distance from the slope face to not impact slope stability. We recommend that we be retained to review plans once the final location and design details of the vault are determined. Infiltration Rates: The site soils consist of a medium-grained sand that is well suited for infiltration. We present a plot of the field measured infiltration rate versus head of water in Figure 16. We recommend that a design infiltration value of 60 inches per hour be used for 6 inches of head. We consider this value conservative since the system will have more head, which will provide higher rates. Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 18 Vault Footings: Medium dense bearing soils are expected to be encountered at the planned footing subgrade elevation. Footings should be placed on the medium dense or better native soils, or structural fill extending to these soils. We recommend that an allowable design bearing pressure of 2,000 pounds per square foot (psf) be used for footings at least 16 inches wide. Higher bearing pressures may be appropriate based on review of a specific design. We are available to review specific design and loading conditions at your request. Vault Lateral Pressures: Walls that are free to yield at least one-thousandth of the height of the wall are in an "active" condition. Walls restrained from movement by stiffness or bracing are in an "at-rest" condition. Earth pressure can be calculated based on equivalent fluid density. Equivalent fluid densities for active and at-rest earth pressure of 35 pounds per cubic foot (pcf) and 55 pcf, respectively, may be used for design for a level backslope. These values assume that the on-site soils or granular import soils are used for backfill are compacted to at least 90 percent of maximum dry density from ASTM D 1557. If the walls are not drained, the equivalent fluid densities should be increased to 80 pcf and 90 pcf for active and at-rest earth pressure conditions, respectively. If the on-site clean sands are used as wall backfill, we do not expect wall drains will be needed. The preceding values do not include the effects of surcharges, such as foundation loads, traffic or other surface loads. Surcharge effects should be considered where appropriate. The above lateral pressures may be resisted by friction at the base of the structure and passive resistance against subsurface walls and the foundation. A coefficient of friction of 0.45 may be used to determine the base friction in the recessional outwash. An equivalent fluid density of 250 pcf should be used for passive resistance design. To achieve this value of passive resistance, the foundations should be poured "neat" against the native dense soils, or compacted fill should be used as backfill against the front of the footing, and the soil in front of the wall should extend a horizontal distance at least equal to three times the foundation depth. We recommend that the upper 1 foot of soil be neglected when determining the passive resistance. Vault Wall Backfill: All wall backfill should be well compacted. Care should be taken to prevent the buildup of excess lateral soil pressures due to overcompaction of the wall backfill. This can be accomplished by placing wall backfill in 8-inch loose lifts and compacting with • small,hand-operated compactors. Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 Page 19 USE OF THIS REPORT We have prepared this report for Specialized Homes, LLC and their agents, for use in planning and design of this project. The data and report should be provided to prospective contractors for their bidding and estimating purposes, but our report, conclusions, and interpretations should not be construed as a warranty of subsurface conditions. Final site development plans were not available at the issue of this report. We recommend that we be retained to provide a plan review when the plans are available. This could include specific recommendations for use in design of the infiltration vault. The scope of our work does not include services related to construction safety precautions, and our recommendations are not intended to direct the contractors' methods, techniques, sequences or procedures, except as specifically described in our report, for consideration in design. There are possible variations in subsurface conditions. We recommend that project planning include contingencies in budget and schedule, should areas be found with conditions that vary from those described in this report. We should be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, and to provide recommendations for design changes, should the conditions revealed during the work differ from those anticipated. As part of our services, we would also evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. Within the limitations of scope, schedule and budget for our work, we have strived to take care that our work has been completed in accordance with generally accepted practices followed in this area at the time this report was prepared. No other conditions, expressed or implied, should be understood. 000 Cornerstone Geotechnical, Inc. Geotechnical Engineering Report Debar Site April 5, 2001 CG File No. 1085 • Page 20 We appreciate the opportunity to be of service to you. If there are any questions concerning this report or if we can provide additional services, please call. Sincerely, Cornerstone Geotechnical, Inc. Jxal?.lQ, �9� Andrea Ernst Project Geologist Principal Geologist Donald W.Tubbs • Sp- :105 Rick B. Powell, PE Senior Engineer ALE:RBP:nt Three Copies Submitted Seventeen Figures cc: Mick Matheson, PE—Triad Associates(Three Copies) • Cornerstone Geotechnical, Inc. Vicinity Map N C D E F 183RD �frY Q0 B5TH r T 87TH 3 f M; J li: a ¢ 1 _ 90TH 91ST - 9 s 1 3oTN P 4 27TH Site H , 99Ui T}i ?61 H - f �a 100TH , F� 3 4 :24TH 104"(H 5 . ,. 3 x i , 6 >� ©1995 Thomas Bros. Maps Cornerstone Phone:425-844-1977 Kennydale Site Geotechnical, Inc. Fax:425-844-1987 File Number Figure P.O. Box 1750• Woodinville, WA • 98072 1085 1 A Site Plan V ' - �P� 5 6422 W \Q74J O.1{7hc Le end 0.Il33oc ' - TP 5204 Number andApproximate Location of Test Pit / 4845 SF.- \ 'i TP-4 B-1 B-1 \ a Number and Approximate /- Location of Soil Boring f` -F-- !T-1 + Number and Approximate L_ Location of Infiltration Test 12 -- aism- I 3 -15229 Sr + IT-1 6715 sr w ua ialml- + a,-s2 i A Name and Location of cross section 4593 SF I:...- alOSloc B-3 + --- 14 a'f6 + l + + + l4W SF - , 0 60 120 -- -- -- -- ___ -- -- -- -- Scale 1 = 60 NE 28TH STREET" Cornerstone Phone:425-844-1977 Kennydale Site Geotechnical Inc. Fax-425-844-1987 File Number Figure Reference: Site Plan created from a drawing titled "Specialized Homes Kennydale Site" , ; s prepared by Triad Associates and dated March 26, 2001. P.O. Box 1750- Woodinville, WA- 98072 1 1085 2 Cross-Section A-A' 340 340 B-3 B-4 300 FReuXceional Recessional 300ash Outwash Till ? Advance Advance Till Old Railroad 260 260 Outwash Outwash Grade 220 220 Wet Below *-"'this Elevation 180 180 Ponded Surface Water 40 140 100 100 Scale: 1 inch = 40 feet (Horizontal & Vertical) Cornerstone Phone-425-844-1977 Kennydale Site Note: Cross sections measured in the filed using a hand-held clinometer and a 100-foot measuring tape. Geotechnical, Inc. Fax:425-844-1987 File Number Figure Elevations referenced to a field surveyed stakes provided by Triad Associates. P.O. Box 1750• Woodinville, WA • 98072 1085 3 Cross-Section B-B' 340 340 TP-4 B-1 B-2 TP-3 Recessional Recessional 300 Outwash I Outwash 300 -� -------� ---,- ---- ---------------2-----------2----- Till---- Till Till Old Railroad Grade 260 260 Fill 220 220 180 18 140 140 100 100 Scale: 1 inch = 40 feet (Horizontal & Vertical) Cornerstone Phone-425-844-1977 Kennydale Site Note: Cross sections measured in the filed using a hand-held clinometer and a 100-foot measuring tape. /�+ Fax Elevations referenced to a field surveyed stakes provided by Triad Associates. 2OteChCllCal, Inl,. File Number Figure P.O. Box 1750• Woodinville, WA• 98072 1085 4 Unified Soil Classification System MAJOR DIVISIONS GROUP GROUP NAME SYMBOL • COARSE- GRAVEL CLEAN GRAVEL GW WELL-GRADED GRAVEL,FINE TO COARSE GRAVEL GRAINED MORE THAN 50%OF GP POORLY-GRADED GRAVEL COARSE FRACTION SOILS RETAINED ON NO.4 GRAVEL SILTY GRAVEL SIEVE WITH FINES GM GC CLAYEY GRAVEL MORE THAN 50%a RETAINED ON SAND CLEAN SAND NO.200 SIEVE SW WELL-GRADED SAND,FINE TO COARSE SAND SP POORLY-GRADED SAND MORE THAN 50%OF COARSE FRACTION SAND PASSES NO.4 SIEVE WITH FINES SM SILTY SAND Sc CLAYEY SAND FINE- SILT AND CLAY INORGANIC ML SILT GRAINED LIQUID LIMIT CL CLAY LESS THAN 50% SOILS ORGANIC OL ORGANIC SILT,ORGANIC CLAY MORE THAN SIEVE SILT AND CLAY PASSES NO.200 INORGANIC MH SILT OF HIGH PLASTICITY,ELASTIC SILT SI LIQUID LIMIT CH CLAY OF HIGH PLASTICITY, FAT CLAY 50%OR MORE ORGANIC OH ORGANIC CLAY,ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT NOTES: SOIL MOISTURE MODIFIERS 1) Field classification is based on Dry-Absence of moisture, dusty, dry visual examination of soil in general to the touch accordance with ASTM D 2488-83. 2) Soil classification using laboratory Moist- Damp, but no visible water tests is based on ASTM D 2487-83. Wet-Visible free water or saturated, 3) Descriptions of soil density or usually soil is obtained from consistency are based on below water table interpretation of blowcount data, visual appearance of soils, and/or test data. Cornerstone Phone:425-844-1977 Unified Soil Classification System wg_-F y Geotechnical Inc. Fax:425-844-1987 P.O. Box 1750• Woodinville, WA• 98072 Figure 5 LOG OF EXPLORATION DEPTH USC SOIL DESCRIPTION • TEST PIT ONE 0.0—0.3 SM DARK BROWN SILTY FINE TO MEDIUM SAND WITH ORGANICS (LOOSE, MOIST) (TOPSOIL) 0.3— 1.0 SP-SM RUST BROWN FINE TO MEDIUM SAND WITH SILT (LOOSE, MOIST) (WEATHERED RECESSIONAL OUTWASH) 1.0-14.0 SP TAN-GRAY FINE TO MEDIUM SAND (LOOSE TO MEDIUM DENSE, MOIST) (RECESSIONAL OUTWASH) SAMPLES WERE COLLECTED AT 3.0 FEET GROUND WATER SEEPAGE WAS NOT ENCOUNTERED SEVERE TEST PIT CAVING WAS ENCOUNTERED FROM 0 TO 14 FEET TEST PIT WAS COMPLETED AT 14.0 FEET ON 2/27/01 TEST PIT TWO 0.0— 1.0 SM DARK BROWN SILTY FINE TO MEDIUM SAND WITH ROOTS AND ORGANICS(LOOSE, MOIST)(TOPSOIL) 1.0—2.5 SP-SM RUST-TAN GRAY FINE TO MEDIUM SAND WITH SILT (LOOSE, MOIST)(WEATHERED RECESSIONAL OUTWASH) 2.5 —14-0 SP TAN-GRAY FINE TO MEDIUM SAND (LOOSE TO MEDIUM DENSE, MOIST) (RECESSIONAL OUTWASH) -SOIL GRADATION FIGURE 14 51%MEDIUM SAND 38%FINE SAND 9%GRAVEL 2%SILT/CLAY • SAMPLES WERE COLLECTED AT 3.5 FEET GROUND WATER SEEPAGE WAS NOT ENCOUNTERED SEVERE TEST PIT CAVING WAS ENCOUNTERED FROM 0 TO 14 FEET TEST PIT WAS COMPLETED AT 14.0 FEET ON 2/27/01 TEST PIT THREE 0.0—1.3 SM DARK BROWN SILTY FINE TO MEDIUM SAND WITH ORGANICS (LOOSE, MOIST) (TOPSOIL) 1.3—2.0 SP-SM RUST BROWN FINE TO MEDIUM SAND WITH SILT (LOOSE, MOIST) (WEATHERED RECESSIONAL OUTWASH) 2.0—6.5 SP TAN-GRAY FINE TO MEDIUM SAND (LOOSE TO MEDIUM DENSE, MOIST) (RECESSIONAL OUTWASH) 6.5— 15.0 SP TAN-GRAY FINE SAND WITH TRACE SILTY FINE SAND LENSES (LOOSE TO MEDIUM DENSE,DRY TO MOIST)(RECESSIONAL OUTWASH) SAMPLES WERE COLLECTED AT 3.0,6.5,AND 14.0 FEET GROUND WATER SEEPAGE WAS NOT ENCOUNTERED MINOR TEST PIT CAVING WAS ENCOUNTERED FROM 0 TO 6 FEET TEST PIT WAS COMPLETED AT 15.0 FEET ON 2/27/01 • Cornerstone Geotechnical, Inc. File No. 1085 Figure 6 LOG OF EXPLORATION DEPTH USC SOIL DESCRIPTION TEST PIT FOUR 0.0-0.5 SM DARK BROWN SILTY FINE SAND WITH ROOTS AND ORGANICS (LOOSE, MOIST) (TOPSOIL) 0.5-3.0 SM TAN-GRAY SILTY FINE TO MEDIUM SAND WITH TRACE GRAVEL (LOOSE, MOIST) (WEATHERED RECESSIONAL OUTWASH) 3.0-16.0 SP GRAY FINE TO MEDIUM SAND WITH TRACE SILTY FINE SAND LENSES BELOW 6 FEET(LOOSE TO MEDIUM DENSE,MOIST)(RECESSIONAL OUTWASH) SAMPLES WERE COLLECTED AT 2.0,3.0,AND 10.0 FEET GROUND WATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 16.0 FEET ON 2/27/01 • INFILTRATION TEST ONE 0.0-0.8 SM DARK BROWN SILTY FINE SAND WITH ROOTS(LOOSE,MOIST)(TOPSOIL) 0.8-1.5 SP-SM RUST BROWN FINE TO MEDIUM SAND WITH SILT(LOOSE, MOIST) (WEATHERED RECESSIONAL OUTWASH) 1.5-13.3 SP TAN-GRAY FINE TO MEDIUM SAND (LOOSE TO MEDIUM DENSE, MOIST) (RECESSIONAL OUTWASH) SAMPLES WERE COLLECTED AT 13.0 FEET GROUND WATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS ENCOUNTERED FROM 0 TO 13 FEET TEST PIT WAS COMPLETED AT 13.3 FEET ON 3/15/01 Cornerstone Geotechnical, Inc. File No. 1085 Figure 7 SOIL DESCRIPTION w o Standard Penetration Resistance a_ U F__ (140 lb. weight, 30" drop) B Q W • Blows per foot U) c� o ace Elevation: 10 20 30 40 50 Rust-brown medium sand with trace silt and T SP gravel (loose, moist) 1 (Weathered Recessional Outwash) 5 Tan-gray fine sand (medium dense, moist) T (Recessional Outwash) 1 10 Tan-gray fine to medium sand (medium dense, I moist)(Recessional Outwash) 1 1 5 .. . . . . . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . Gray fine to medium sand (medium dense, moist to wet) (Recessional Outwash) ust-mottled and gray silty fine sand with SM gravel (dense, moist) (Till) 25 _ N=50(5") 30 . . :. . . . . . . . . . . . . . ... . . . . . . : . . . . . . . . . . . . . . Rust-mottled and gray silty fine to medium sand with trace gravel (very dense, moist to wet)(Till) N=2G-35-50 Boring completed at 34.0 feet on 3/13/01 Ground water encountered at 22.0 feet LEGEND * Liquid limit Native backfill P Sample pushed Z Depth 2"O.D.split spoon sample ■ Moisture content Water level TV Torvane reading, driven. tons/ft2 + Plastic limit Piezometer tip PP Pocket penetrometer 3"O.D.thin-wall sample reading,tons/ft2 OOTtE; The stratification lines represent the approximate boundaries between soil types and the transition may be gradual. rnerstone Phone-.425-844-1977 Kennydale Site rs Geotechnical, Inc. Fax:425-844-1987 File Number 1085 Figure 8 P.O. Box 1750• Woodinville, WA• 98072 SOIL DESCRIPTION w o Q Standard Penetration Resistance b a_ BID (140 lb. weight, 30" drop) cri Q � 3: W • Blows per foot ace Elevation: 10 20 30 40 50 Rust-brown fine to medium sand with silt SP- (very loose, moist) SM (Weathered Recessional Outwash) -r Gray fine to medium sand (very loose, moist) Sp 1 (Recessional Outwash) 5 Tan-gray fine sand (loose, moist) I (Recessional Outwash) 1 10 . . . . Tan-gray fine to medium sand T (medium dense, moist) 1 (Recessional Outwash) - 15 . . . . . —'------�------'- -----?-- —' Gray silty fine sand with trace gravel SM T (medium dense, moist) (Till) 1 20 Illust-mottled gray silty fine sand with gravel (very dense, moist) (Till) I Boring completed at 24.0 feet on 3/13/01 1 N=12-20-34 Ground water not encountered 25 30—— - - - - - --- - - - - - --- - - - - - - - - - - - - LEGEND Z Depth 2"O.D.split spoon sample * Liquid limit native backfill P Sample pushed driven. ■ Moisture content Water level TV Torvane reading, 3"O.D.thin-wall sample tons/ft2+ Plastic limit Piezometer tip PP Pocket penetrometer reading,tons/ft NOTE: The stratification lines represent the approximate boundaries between soil types and the transition may be gradual. Cornerstone Phone:425-844-1977 Kennydale Site IWO. Geotechnical, Inc. Fax:425-844-1987 File Number Figure P.O. Box 1750• Woodinville, WA• 98072 1085 9 SOIL DESCRIPTION w o Standard Penetration Resistance B-3 v a- � F- � (140 lb. weight, 30" drop) v) Q of � W • Blows per foot 7D cn C3 0 ace Elevation: 10 20 30 40 50 Rust-brown fine to medium sand with silt SP- (loose, moist) SM (Weathered Recessional Outwash) I Tan-gray fine to medium sand (loose, moist) SP (Recessional Outwash) 5 Tan-gray fine to medium sand (medium dense, moist) I (Recessional Outwash) 10__ . .. . . . . . .:. . . . . . . : . . . . . . .:. . . . . . . :. . . . . I 15 ;. . . . I 20 I I 25 :. . I 30 . . . . . ... . . . . . . . . . . . . . . . . . . . . . Tan gray fine sand grades to very fine sand (medium dense, moist) (Recessional Outwash) I ----- 2-----a-----?------- —-?i LEGEND I Depth 2"O.D.split spoon sample * Liquid limit Native backfill P Sample pushed driven. ■ Moisture content Water level TV Torvane reading, Y O.D.thin-wall sample tons/ftz + Plastic limit Piezometer tip PP Pocket penetrometer reading,tons/ft NOTE: The stratification lines represent the approximate boundaries between soil types and the transition may be gradual. tCornerstone Phone:425-844-1977 Kennydale Site i— Geotech n ICal, Inc. Fax:425-844-1987 File Number Figure °`' £ P.O. Box 1750• Woodinville, WA• 98072 1085 10 SOIL DESCRIPTION w o Standard Penetration Resistance w = (140 lb. weight, 30" drop) B-3 (Cont d) vi Q � w • Blows per foot iftace Elevation: 10 20 30 40 50 Slightly rust-mottled gray silty fine sand with SM gravel (very dense, moist)(Till) T 1 N=12-21 35 40 :. Gray fine sand (very dense, moist) SP (Advance Outwash) Boring completed at 44.0 feet on 3/13/01 45 N=16-29-38 Ground water not encountered : 5 . . . . . 5 60 :. . . . . . .:. . . . . . . ... . . . . . ... . . . . . . ... . . . . . . 65 : LEGEND I Depth 2"O.D.split spoon sample * Liquid limit Native backfill P Sample pushed driven. ■ Moisture content Water level TV Torvane reading, TT 3"O.D.thin-wall sample tons/ft2 + Plastic limit Piezometer tip PP Pocket penetrometer reading,tons/fe NOTE: The stratification lines represent the approximate boundaries between soil types and the transition may be gradual. Cornerstone Phone:425-844-1977 Kennydale Site 4 Geotechnical, Inc. Fax:425-844-1987 File Number 1085 Figure 11 P.O. Box 1750• Woodinville,WA• 98072 SOIL DESCRIPTION w o Standard Penetration Resistance v _ W 2: (140 lb. weight, 30" drop) B 4 vi Q 0 w • Blows per foot � cn C� o Aka- Elevation: 10 20 30 40 50 Fu st-brown medium sand with trace silt and SP/ gravel (loose, moist) SM Weathered Recessional Outwash Tan-gray fine sand (medium dense, moist) SP (Recessional Outwash) = 5 10 - - - - - - - .:. . . . . . . . . . . ... . . . . . . :. . . . . . 15 Tan-gray fine to medium sand (medium dense, I moist to wet) (Recessional Outwash) _ I 25 - - - - - . . . Tan-gray fine sand with 3-inch wet silty very fine sand seam (medium dense, moist) I (Recessional Outwash) -L 30 :. . . . . . ... . . . . . ... . . . . . . . . . . . . . . . . . . . . . Tan-gray fine sand grades to silty fine sand SS I (medium dense, moist) SM (Recessional Outwash) = 35— . . . . . . . . . LEGEND * Liquid limit Native backfill P Sample pushed I Depth 2"O.D.split spoon sample ■ Moisture content Water level TV Torvane reading, driven. tons/ft' 3"O.D.thin-wall sample + Plastic limit Piezometer tip PP Pocket penetrometer reading,tons/ft' TE: The stratification lines represent the approximate boundaries between soil types and the transition may be gradual. Cornerstone Phone:425-844-1977 Kennydale Site Geotechnical, Inc. Fax:425-844-1987 File Number 1085 Figure 12 P.O. Box 1750• Woodinville, WA• 98072 SOIL DESCRIPTION w o Standard Penetration Resistance ii LU T_ (140 lb. weight, 30" drop) B-4 (Cont d } C6 Q w 40 Blows per foot U) U o ce Elevation: 10 20 30 40 50 Tan-gray fine sand grades to silty fine sand SP/ (medium dense, moist) SM (Recessional Outwash) T 1 35 :. . . . . . . . . . . . . . . . . . . Tan-gray fine sand with 2-inch wet silty fine sand seam (medium dense, moist) (Recessional Outwash) Tan-gray fine to coarse sand with gravel Sw 40 . . . . . .. . . . . . . (medium dense, moist)(Advance Outwash) Tan-gray fine sand with gravel and trace silt I SP with gravel (dense, moist)(Advance Outwash) N=50(6'7) 45 . ... . . . . . . . Gray fine to medium sand with a silty fine seam (very dense, moist)(Advance Outwash I N=52 41 50 . . . ... . . . . . . : - - - - - - - ray fine to medium sand with 6-inch silty fine r(GI medium sand with trace gravelery dense, moist) (Advance Outwash) N-64 55 :. . Gray silty fine sand with trace silt lenses SM (dense, moist) (Advance Outwash) Boring completed at 59.0 feet on 3/13/01 60 Ground water was not encountered - - 65 . . . . . . . LEGEND * Liquid limit Native backfill P Sample pushed I Depth 2"O.D.split spoon sample ■ Moisture content Water level TV Torvane reading, driven. tons/ft2 + Plastic limit Piezometer tip PP Pocket penetrometer 1[Y O.D.thin-wall sample reading,tons/ft ITtEThe stratification lines represent the approximate boundaries between soil types and the transition may be gradual. ornerstone Phone-425-844-1977 Kennydale Site x Geotechnical, Inc. Fax:425-844-1987 File Number Figure 1085 13 P.O. Box 1750• Woodinville, WA• 98072 Imp 0 U.S. STANDARD SIEVE SIZE sc O G7 100 lop, \p \p 1p \p \° (D O (D N 90 o C 80 7 /p OC W O � gp Q 50 G z D TI o CD ID N OO 00 U 0 -� -A LLJ 20 co 10 T m 1000 100 10 1.0 0.1 0.01 0.001 o GRAIN SIZE IN MILLIMETERS 0 GRAVEL SAND CI1 (D COBBLES I a SILT OR CLAY COARSE I FINE COARSE MEDIUM FINE `G Q. EXPLORATION SAMPLE SYMBOL NUMBER DEPTH SOIL DESCRIPTION T_ r-� C) m • Test Pit #2 3.5 feet Gray fine to medium sand Water Head Results of 3-foot diameter Pipe 14.000 - . I 12.000 i i i i f 10.000 I —+- 10:24am 8.000 - 11:13am 12:17pm j 6.000 1:10Pm I i 4.000 i I j I 2.000 I ti i 0.000 0:00 0:07 0:14 0:21 0:28 0:36 0:43 0:50 Time Cornerstone Phone:425-844-1977 Kennydale Site Geotechnical, Inc, Fax:425-844-1987 File Number Figure P.O. Box 1750- Woodinville, WA• 98072 1085 15 Infiltration Rate vs. Head of Water 500 I 450 _ i 400 — — t 350 ZZ 300 - __ _ Actual Infiltration Rate(in/hr) cc: 250 °a 11:13am o — ' 12:17pm m 200 110pm i 150 — — Design Infiltration of 60 inlhr with 6 inches of Head 100 _I i 50 i 0.000 2.000 4.000 6.000 8.000 10.000 12.000 Head of water(ft) Cornerstone Phone:425-844-1977 Kennydale Site Geotechnical, Inc. Fax:425-844-1987 File Number Figure P.O. Box 1750- Woodinville, WA- 98072 1085 16 Effective Setback Detail (Not to Scale) FT� M Top of Slope 1--------------------------------L 35-Foot Horizontal Effective Setb\top Bottom of Footing Residential building structure should not be within 25 fof the slope without a specific geotechnical review and Cornerstone Phone:425-844-1977 Kennydale Site Geotechnical, Inc. Fax:425-844-1987 File Number Figure P.O. Box 1750• Woodinville, WA • 98072 1085 17 SECTION VII OTHER PERMITS 7 Other Permits This Technical Information Report and the related Road, Storm Drainage and Utility Plans, both prepared by Triad Associates, are being submitted to the City in order to obtain approval to perform on-site grading and to construct the necessary public and private road and utility improvements. Plans will be prepared separately by a licensed structural engineer for the proposed stormwater vault, in order to obtain approval to construct this facility. Additionally, architectural plans will be prepared by others, and submitted separately,for the City to review the building improvements proposed for this site. • Triad Associates DeBar Plat Page 7-17 Technical Information Report loolow SECTION VIII V� ESC ANALYSIS & DESIGN 8 ESC Analysis and Design The onsite soils have minimal runoff and erosion potential during construction. However,the Grading and • Temporary Erosion and Sediment Control (TESC) Plan has been designed per the 1998 KCSWDM (Appendix D: Erosion and Sediment Control Standards) to meet Core Requirement #5: Erosion and Sediment Control, as adopted by the City of Renton. The TESC plan is intended to prevent the transport of sediment from the site to significant drainage features and adjacent properties. The plan includes recommended Best Management Practices (BMPs) for all seven measures recognized by the KCSWDM: Clearing Limits, Cover Measures, Perimeter Protection, Traffic Area Stabilization, Sediment Retention, Surface Water Controls,and Dust Control. The clearing limits will be clearly flagged. The downhill perimeters of clearing will be protected with filter fabric fencing, and other perimeter protection methods as required. Cleared areas will be stabilized with various cover measures as required (e.g. temporary/permanent seeding, mulching, and placement of road subgrade). A stabilized construction entrances will be provided at the construction access to the site. Interceptor dikes/swales will be installed to collect and route runoff from the disturbed areas to sediment retention facilities. Particular care will be taken to prevent discharges over the bluff. The temporary sediment retention facilities (sediment infiltration ponds) will not be located near the proposed infiltration vault. Site runoff will not be allowed to drain to the proposed permanent infiltration vault until the site is stabilized. These measures will prevent plugging of the infiltrative soils below the vault with construction- related sediment. Dust control measures will be implemented if there is a need onsite (i.e., if there is a • particularly dry period during construction). Generally,the sediment retention facility(sediment pond and subsequent infiltration pond)was designed to settle out the design particle(medium silt, 0.02 mm). The required surface area of the sediment pond was computed using an inflow rate equal to the developed 2-year KCRTS peak runoff. Stormwater will flow from the sediment pond to the proposed temporary infiltration pond, where the stormwater will be discharged into the ground. The sediment pond riser, overflow spillway and temporary infiltration pond were each sized for the 100-year design storm event. A summary of the erosion control calculations for this facility is included below. Triad Associates DeBar Plat Page 8-18 Technical Information Report The following is the peak analysis for the TSF modeled for the proposed road and sidewalk impervious areas tributary to the sediment retention facility. Flow Frequency Analysis Time Series File:0220tesc.tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- -----Flow Frequency Analysis-- Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.150 7 2/09/01 2 :00 0.293 1 100.00 0.990 0.132 8 1/05/02 16:00 0.225 2 25.00 0.960 0. 183 3 12/08/02 18:00 0.183 3 10.00 0.900 0.155 6 8/26/04 2 :00 0.183 4 5.00 0.800 0.183 4 10/28/04 16:00 0.161 5 3 .00 0.667 0.161 5 1/18/06 16:00 0.155 6 2.00 0.500 0.225 2 10/26/06 0:00 0.150 7 1.30 0.231 0.293 1 1/09/08 6:00 0.132 8 1.10 0.091 Computed Peaks 0.270 50.00 0.980 Required Surface Area Required Surface Area(Pond)=2 x(Q2yr/0.00096) Required Surface Area(Pond)=2080 x Q2yr Required Surface Area(Pond)=2080 x 0.155=322 sf • Provided Surface Area(Pond)=441 sf Overflow Riser The overflow riser is designed to convey the 100-year peak flows from the sediment pond to the temporary infiltration pond and is 12-inch diameter(D). The riser will allow overflow at a water surface elevation of 308.50 feet. Using the 100-year peak KCRTS flow rate(Q)of 0.29 cfs modeled for the proposed road and sidewalk impervious areas tributary to the sediment retention facility, the riser diameter was checked to determine the overflow depth (f) per the 1998 KCSWDM Figure 5.3.4.1-1, Riser Inflow Curves, and the accompanying equations. Q,t,eu=9.739DH3 2,QweU=0.29 cfs,D= 12 in= 1 ft(acting as a weir) .'.H=[(QWeir)/(9.739D)]23=0.10 The 12-inch riser can convey 0.29 cfs with 0.10 feet of head above the top of the riser. Triad Associates DeBar Plat Page 8-19 Technical Information Report Dewatering Orifice The discharge orifice was designed,according to chapter 5 of the KCSWDM,as follows: AO _ A Y2 _ s(2h) 0.6(3600)(T)g12 T=24 hours;g=32.2 ft/sec2 AS=441 ft2 h=3.5ft AO=0.004 ft2 D=24 x(Ao/,g)0.5=0.86" A 1-inch diameter orifice will be specifted for this project since this is the minimum orifice diameter allowed per the requirements of the KCSWDM. Overflow Spillway An overflow spillway will convey flows from the sediment pond to the infiltration pond. The overflow spillway is designed to the 6-foot wide minimum design width. A 6-foot wide spillway with 0.5 feet of overflow depth can pass 8.17 cfs, which exceeds the 100-year peak flow for this project site. Q100 =C(2g)05(2/3LHY +8/15TAN(9)H512) Where: C=0.6(discharge coefficient) TAN(0)=3 for 3:1 slopes on spillway g= 32.2 ft/s2(acceleration of gravity) L=spillway length H=head on spillway Temporary Infiltration Pond The temporary infiltration pond was designed using the KCRTS program's infiltration pond modeling feature using the design infiltration rate calculated in Section 4.3.2 above. The pond is proposed to provide storage from a bottom elevation of 304.5 to the design water surface elevation of 308.50. The dimensions of the pond were determined as shown in the actual program output below. The pond is proposed to have bottom dimensions of 12.5' on all sides and 3:1 internal sideslopes. Triad Associates DeBar Plat Page 8-20 Technical Information Report Retention/Detention Facility Type of Facility: Infiltration Pond Side Slope: 3.00 H:1V • Pond Bottom Length: 12.50 ft Pond Bottom Width: 12.50 ft Pond Bottom Area: 156. sq. ft Top Area at 1 ft. FB: 1806. sq. ft 0.041 acres Effective Storage Depth: 4.00 ft Stage 0 Elevation: 304.50 ft Storage Volume: 2593. cu. ft 0.060 ac-ft Vertical Permeability: 10.50 min/in Permeable Surfaces: Bottom & Sides Riser Head: 4.00 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) 0.00 304.50 0. 0.000 0.000 0.00 156. 0.06 304.56 10. 0.000 0.000 0.02 165. 3.96 308.46 2540. 0.058 0.000 0.17 1315. 4.00 308.50 2593. 0.060 0.000 0.18 1332. Hyd Inflow Outflow Peak Storage Target Calc Stage Elev (Cu-Ft) (Ac-Ft) 1 0.29 0.00 0.00 4.00 308.50 2591. 0.059 2 0.16 ******* 0.00 2.95 307.45 1424. 0.033 3 0.16 ******* 0.00 2.87 307.37 1347. 0.031 4 0.18 ******* 0.00 2.78 307.28 1271. 0.029 . 5 0.15 ******* 0.00 2.61 307.11 1129. 0.026 6 0.18 ******* 0.00 2.60 307.10 1124. 0.026 7 0.13 ******* 0.00 1.89 306.39 644. 0.015 8 0.15 ******* 0.00 1.83 306.33 614. 0.014 Triad Associates DeBar Plat Page 8-21 Technical Information Report --IV SECTION IX BOND QUANTITIES, FACILITY SUMMARIES, & DECLARATION OF COVENANT 9 Bond Quantities, Facility Summaries, and Declaration • of Covenant A bond quantities worksheet will be prepared after approval of the engineering plans,and submitted with the final version of this report. • • Triad Associates DeBar Plat Page 9-22 Technical Information Report SECTION X \ OPERATIONS & MAINTENANCE MANUAL • 10 Operations and Maintenance Manual Included here is the standard operations and maintenance manual appendix from the KCSWDM. None of the proposed stormwater facilities will require special maintenance standards. Triad Associates DeBar Plat Page 10-23 Technical Information Report KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL KING COUNTY,WASHINGTON SURFACE WATER DESIGN MANUAL APPENDIX A MAINTENANCE REQUIREMENTS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES Section No. Subiect 1 61ee+ ieRoR4c,-- 2 Infiltration 3 Closed Detention Systems 5 Catch Basins i Fe„GiRg • -�--�.at;es 10 Conveyance Systems 111 6rednds 12 Access Roads/Easements 13 Water Quality Facilities A) Biofiltration Swale B) Filterstrips C) Wetponds D) Wetvaults E) Sand Filters F) Leaf Compost Filters G) Infiltration Ponds ;14 Oil-�,-Fao:r:ties A) Oil/Water Separators B) Catch Basin Inserts 9/1/98 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 2-INFILTRATION Maintenance Defect Conditions When Maintenance Results Expected When Component Is Needed Maintenance Is Performed General Trash&Debris See`Ponds'Standard No.1 See'Ponds'Standard No.1 Poisonous Vegetation See'Ponds'Standard No.1 See'Ponds'Standard No.1 Pollution See'Ponds'Standard No. 1 See'Ponds'Standard No.1 Unmowed Grass/ See'Ponds'Standard No.1 See'Ponds'Standard No.1 Ground Cover Rodent Holes See'Ponds'Standard No.1 See'Ponds'Standard No.1 Insects See"Ponds'Standard No.1 See'Ponds'Standard No.1 Storage Area Sediment A percolation test pit or test of facility indicates Sediment is removed and/or facility facility is only working at 90%of its designed is cleaned so that infiltration system capabilities. If two inches or more sediment is works according to design. present,remove. Sheet Cover(If Sheet cover is visible and has more that three Sheet cover repaired or replaced. Applicable) 1/4-inch holes in it. Sump Filled with Any sediment and debris filling vault to 10%of Clean out sump to design depth. Sediment and Debris depth from sump bottom to bottom of outlet pipe (if Applicable) or obstructing flow into the connector pipe. Filter Bags Filled with Sediment Sediment and debris fill bag more than 1/2 full. Replace filter bag or redesign and Debris system. Rock Filters Sediment and Debris By visual inspection,little or no water flows Replace gravel in rock filter. through filter during heavy rain storms. Side Slopes of Pond Erosion See'Ponds'Standard No. 1 See'Ponds'Standard No.1 Emergency Rock Missing See'Ponds'Standard No. 1 Overflow Spillway Settling Ponds and Sediment Remove when 6'or more. • Vaults Note: Sediment accumulation of more than.25 inches per year may indicate excessive erosion is occurring upstream of the facility or that conveyance systems are not being properly maintained_ The contributing drainage area should be checked for erosion problems or inadequate maintenance of conveyance systems if excessive sedimentation is noted in an infiltration facility. Check twice a year during first 2 years of operation;once a year thereafter. Clean manholes/catch basins,repair damaged inlets/outlets, clean trash racks. 9/1/98 1998 Surface Water Design Manual A-2 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 3-CLOSED DETENTION SYSTEMS(PIPES/TANKS) Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed • Storage Area Plugged Air Vents One-half of the cross section of a vent is blocked at Vents free of debris and any point with debris and sediment sediment Debris and Accumulated sediment depth exceeds 10%of the All sediment and debris Sediment diameter of the storage area for'h length of storage removed from storage area. vault or any point depth exceeds 15%of diameter. Example:72-inch storage tank would require cleaning when sediment reaches depth of 7 inches for more than 1h length of tank. Joints Between Any crack allowing material to be transported into All joint between tank/pipe Tank/Pipe Section facility sections are sealed Tank Pipe Bent Any part of tank/pipe is bent out of shape more than Tank/pipe repaired or replaced Out of Shape 10%of ifs design shape to design. Manhole Cover Not in Place Cover is missing or only partially in place.Any open Manhole is closed. manhole requires maintenance. Locking Mechanism cannot be opened by one maintenance Mechanism opens with proper Mechanism Not person with proper tools.Bolts into frame have less tools. Working than 1/z inch of thread(may not apply to self-locking lids.) Cover Difficult to One maintenance person cannot remove lid after Cover can be removed and Remove applying 80lbs of lift. Intent is to keep cover from reinstalled by one maintenance sealing off access to maintenance. person. Ladder Rungs King County Safety Office and/or maintenance person Ladder meets design standards Unsafe judges that ladder is unsafe due to missing rungs, allows maintenance person safe misalignment,rust,or cracks. access. • Catch Basins See"Catch Basins"Standards No.5 See"Catch Basins"Standards No.5 • 1998 Surface Water Design Manual 9/l/98 A-3 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 5-CATCH BASINS Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed General Trash&Debris Trash or debris of more than 1/2 cubic foot which is No Trash or debris located (Includes Sediment) located immediately in front of the catch basin immediately in front of catch opening or is blocking capacity of the basin by basin opening. more than 10% Trash or debris(in the basin)that exceeds 1/3 the No trash or debris in the catch depth from the bottom of basin to invert the lowest basin. pipe into or out of the basin. Trash or debris in any inlet or outlet pipe blocking Inlet and outlet pipes free of more than 1/3 of its height, trash or debris. Dead animals or vegetation that could generate No dead animals or vegetation odors that could cause complaints or dangerous present within the catch basin. gases(e.g.,methane). Deposits of garbage exceeding 1 cubic foot in No condition present which volume would attract or support the breeding of insects or rodents. Structure Damage to Comer of frame extends more than 3/4 inch past Frame is even with curb. Frame and/or Top Slab curb face into the street(If applicable). Top slab has holes larger than 2 square inches or Top slab is free of holes and cracks wider than 1/4 inch(intent is to make sure cracks. all material is running into basin). • Frame not sitting flush on top slab,i.e.,separation Frame is sitting flush on top of more than 3/4 inch of the frame from the top slab. slab. Cracks in Basin Walls/ Cracks wider than 1/2 inch and longer than 3 feet, Basin replaced or repaired to Bottom any evidence of soil particles entering catch basin design standards. through cracks,or maintenance person judges that structure is unsound. Cracks wider than 1/2 inch and longer than 1 foot No cracks more than 1/4 inch at the joint of any inlet/outlet pipe or any evidence wide at the joint of inlet/outlet of soil particles entering catch basin through pipe. cracks. Sediment/ Basin has settled more than 1 inch or has rotated Basin replaced or repaired to Misalignment more than 2 inches out of alignment. design standards. • 1998 Surface Water Design Manual 9/1/98 A-5 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 5-CATCH BASINS(CONTINUED) Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed • Fire Hazard Presence of chemicals such as natural gas,oil and No flammable chemicals gasoline. present. Vegetation Vegetation growing across and blocking more than No vegetation blocking opening 10%of the basin opening. to basin. Vegetation growing in inlet/outlet pipe joints that is No vegetation or root growth more than six inches tall and less than six inches present. apart. Pollution Nonflammable chemicals of more than 1/2 cubic foot No pollution present other than per three feet of basin length. surface film. Catch Basin Cover Cover Not in Place Cover is missing or only partially in place.Any open Catch basin cover is closed catch basin requires maintenance. Locking Mechanism Mechanism cannot be opened by on maintenance Mechanism opens with proper Not Working person with proper tools.Bolts into frame have less tools. than 1/2 inch of thread. Cover Difficult to One maintenance person cannot remove lid after Cover can be removed by one Remove applying 80 lbs.of lift;intent is keep cover from maintenance person. sealing off access to maintenance. Ladder Ladder Rungs Ladder is unsafe due to missing rungs,misalignment, Ladder meets design standards Unsafe rust,cracks,or sharp edges. and allows maintenance person safe access_ Metal Grates Grate with opening wider than 7/8 inch. Grate opening meets design (If Applicable) standards. Trash and Debris Trash and debris that is blocking more than 20%of Grate free of trash and debris. • grate surface. Damaged or Grate missing or broken member(s)of the grate. Grate is in place and meets Missing. design standards. NE). 6 DEBRIS BARRIERS •, Maintenance Defect Condition When Maintenance is Needed Results Expected When Components Maintenance is Performed. General Trash and Debris Trash or debris that is plugging more than 20%of Barrier clear to receive capacity the openings in the barrier. flow. Metal Damaged/Missing Bars are bent out of shape more than 3 inches. Bars in place with no bends more Bars. than 3/4 inch. Bars are missing or entire barrier missing. Bars in place according to design. Bars are loose and rust is causing 50%deterioration Repair or replace barrier to to any part of barrier. design standards. 9/I/98 1998 Surface Water Design Manual A-6 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 10-CONVEYANCE SYSTEMS(PIPES & DITCHES) Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed 10 Pipes Sediment&Debris Accumulated sediment that exceeds 20%of the Pipe cleaned of all sediment diameter of the pipe. and debris. Vegetation Vegetation that reduces free movement of water All vegetation removed so water through pipes. flows freely through pipes. Damaged Protective coating is damaged;rust is causing Pipe repaired or replaced. more than 50%deterioration to any part of pipe. Any dent that decreases the cross section area of Pipe repaired or replaced. pipe by more than 20%. Open Ditches Trash&Debris Trash and debris exceeds 1 cubic foot per 1,000 Trash and debris cleared from square feet of ditch and slopes. ditches. Sediment Accumulated sediment that exceeds 20%of the Ditch cleaned/flushed of all design depth. sediment and debris so that it matches design. Vegetation Vegetation that reduces free movement of water Water flows freely through through ditches. ditches. Erosion Damage to See"Ponds"Standard No. 1 See"Ponds"Standard No.1 Slopes Rock Lining Out of Maintenance person can see native soil beneath Replace rocks to design Place or Missing(If the rock lining. standards. Applicable). Catch Basins See"Catch Basins:Standard No.5 See"Catch Basins"Standard No.5 Debris Barriers See"Debris Barriers"Standard No.6 See"Debris Barriers"Standard (e.g.,Trash Rack) No.6 Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed General Weeds Weeds growing in more than 20%of the landscaped Weeds present in less than 5% (Nonpoisonous) area(trees and shrubs only). of the landscaped area. Safety Hazard Any presence of poison ivy or other poisonous No poisonous vegetation vegetation. present in landscaped area. Trash or Litter Paper,cans,bottles,totaling more than 1 cubic foot Area clear of litter. within a landscaped area(trees and shrubs only)of 1,000 square feet. Trees and Shrubs Damaged Limbs or parts of trees or shrubs that are split or Trees and shrubs with less than broken which affect more than 25%of the total 5%of total foliage with split or foliage of the tree or shrub. broken limbs. Trees or shrubs that have been blown down or Tree or shrub in place free of knocked over. injury. Trees or shrubs which are not adequately supported Tree or shrub in place and or are leaning over,causing exposure of the roots. adequately supported;remove any dead or diseased trees. 1998 Surface Water Design Manual 9/1/98 A-9 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 12-ACCESS ROADS/EASEMENTS Maintenance Defect Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed General Trash and Debris Trash and debris exceeds 1 cubic foot per 1,000 Roadway free of debris which square feet i.e.,trash and debris would fill up could damage tires. one standards size garbage can. Blocked Roadway Debris which could damage vehicle tires(glass Roadway free of debris which or metal). could damage tires. Any obstruction which reduces clearance above Roadway overhead clear to 14 feet road surface to less than 14 feet high. Any obstruction restricting the access to a 10 to Obstruction removed to allow at 12 foot width for a distance of more than 12 feet least a 12 foot access. or any point restricting access to less than a 10 foot width. Road Surface Settlement, Potholes, When any surface defect exceeds 6 inches in Road surface uniformly smooth Mush Spots,Ruts depth and 6 square feet in area.In general,any with no evidence of settlement, surface defect which hinders or prevents potholes,mush spots,or ruts. maintenance access. Vegetation in Road Weeds growing in the road surface that are Road surface free of weeds taller Surface more than 6 inches tall and less than 6 inches than 2 inches. tall and less than 6 inches apart within a 400- square foot area. Modular Grid Build-up of sediment mildly contaminated with Removal of sediment and disposal Pavement petroleum hydrocarbons. in keeping with Health Department recommendations for mildly contaminated soils or catch basin sediments. Shoulders and Erosion Damage Erosion within 1 foot of the roadway more than 8 Shoulder free of erosion and • Ditches inches wide and 6 inches deep. matching the surrounding road. Weeds and Brush Weeds and brush exceed 18 inches in height or Weeds and brush cut to 2 inches hinder maintenance access. in height or cleared in such a way as to allow maintenance access. 9/l/98 1998 Surface Water Design Manual A-10 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 13-WATER QUALITY FACILITIES A.) Biofiltration Swale Maintenance Defect Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed Biofiltration Swale Sediment Accumulation Sediment depth exceeds 2-inches No sediment deposits on grass on Grass Layer layer of the bio-swale,which would impede filtration of runoff. Vegetation When the grass becomes excessively tall Vegetation is mowed or nuisance (greater than 10-inches);when nuisance weeds vegetation is eradicated,such that and other vegetation starts to take over. flow not impeded. Grass should be mowed to a height between 4 inches and 9 inches. Inlet Outlet Pipe Inlet/outlet pipe clogged with sediment and/or No clogging or blockage in the inlet debris. and outlet piping. Trash and Debris Trash and debris accumulated in the bio-swale. Trash and debris removed from Accumulation bioswale. Erosion/Scouring Where the bio-swale has eroded or scoured Bioswale should be re-graded and the bottom due to flow channelization,or higher re-seeded to specification,to flow& eliminated channeled flow. Overseeded when bare spots are evident. NO. 13-WATER QUALITY FACILITIES (CONTINUE[) B. Grasslined Filter Strips Maintenance Defect Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed • Filter Strip Sediment Accumulation Sediment depth exceeds 2 inches. No sediment deposits on grass on Grass Layer layer of the filter strip,which would impede filtration runoff. Vegetation When the grass becomes excessively tall Vegetation is mowed or nuisance (greater than 10-inches);when nuisance weeds vegetation is eradicated,such that and other vegetation starts to take over. flow not impeded.Grass should be mowed to a height between 4 inches and 9 inches. Trash and Debris Trash and debris accumulated on the filter Trash and Debris removed from Accumulation strip. filter. Erosion/Scouring Where the filter strip has eroded or scoured Strip should be re-graded and re- due to flow channelizabon,or higher flows. seeded specification,to eliminate channeled flow.Overseeded when bare spots are evident. V-Notch Pipe Weir When the V-Notch pipe becomes damaged or Cleaned and properly functioning clogged with sediment/debris. weir,such that flows uniformly spread. 1998 Surface Water Design Manual 9/l/98 A-11 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES C.) Wetponds Maintenance Defect Condition When Maintenance is Needed Results Expected When . Component Maintenance is Performed Wetpond Vegetation Vegetation such as grass and weeds need to be Vegetation should be mowed to mowed when it starts to impede aesthetics of pond. 4 to 5 inches in height. Trees Mowing is generally required when height exceeds and bushes should be removed 18-inches.Mowed vegetation should be removed where they are interfering with from areas where it could enter the pond,either pond maintenance activities. when the pond level rises,or by rainfall runoff. Trash and Debris Accumulation that exceeds 1 CF per 1000-SF of Trash and debris removed from pond area. pond. Inlet/Outlet Pipe Inlet/Outlet pipe clogged with sediment and/or No clogging or blockage in the debris material. inlet and outlet piping. Sediment Sediment accumulations in pond bottom that Removal of sediment from pond Accumulation in Pond exceeds the depth of sediment zone plus 6-inches, bottom. Bottom usually the first cell. Oil Sheen on Water Prevalent and visible oil sheen. Removal of sediment from pond bottom. Erosion Erosion of the pond's side slopes and/or scouring of Slopes should be stabilized by the pond bottom,that exceeds 6-inches,or where using proper erosion control continued erosion is prevalent. measures,and repair methods. Settlement of Pond Any part of these components that has settled 4- Dike/berm is repaired to Dike/Berm inches or lower than the design elevation,or specifications. inspector determines dike/berm is unsound. Rock Window Rock window is clogged with sediment. Window is free of sediment and debris. Overflow Spillway Rock is missing and soil is exposed at top of Replace rocks to specifications. • spillway or outside slope. 9/l/98 1998 Surface Water Design Manual A-12 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 13-WATER QUALITY FACILITIES(CONTINUED) D.)Wetvaults Maintenance Defect Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed Wetvault Trash/Debris Trash and debris accumulated in vault,pipe or Trash and debris removed from Accumulation inlet/outlet,(includes floatables and non- vault. floatables). Sediment Accumulation Sediment accumulation in vault bottom that Removal of sediment from vault. in Vault exceeds the depth of the sediment zone plus 6- inches. Damaged Pipes Inlet/outlet piping damaged or broken and in Pipe repaired and/or replaced. need of repair. Access Cover Cover cannot be opened or removed,especially Pipe repaired or replaced to Damaged/Not Working by one person. proper working specifications. Vault Structure Vault:Cracks wider than 1/2-inch and any No cracks wider than 1/4-inch at Damaged evidence of soil particles entering the structure the joint of the inlet/outlet pipe. through the cracks,or maintenance/inspection Vault is determined to be personnel determines that the vault is not structurally sound. structurally sound. Baffles Baffles corroding,cracking,warping and/or Repair or replace baffles to showing signs of failure as determined by specifications. maintenance/inspection staff. Access Ladder Damage Ladder is corroded or deteriorated,not functioning Ladder replaced or repaired to properly,missing rungs,has cracks and/or specifications,and is safe to misaligned. use as determined by inspection personnel. 1998 Surface Water Design Manual 9/1/98 A-13 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 13-WATER QUALITY FACILITIES (CONTINUED) E.) Sand Filters Maintenance Defect Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed Above Ground Sediment Sediment depth exceeds 1/2-inch. No sediment deposit on grass Accumulation on Grass layer of sand filter which would Layer impede permeability of the filter section. Trash and Debris Trash and debris accumulated on sand filter bed. Trash and debris removed from Accumulations sand filter bed. Sediment/Debris in When the yard drain CB's and clean-out become Sediment,material from the Yard Drains/Clean- full or partially plugged with sediment and/or CB's and clean-outs removed. Outs] debris. Vegetation When the grass becomes excessively tall(greater Vegetation is mowed or than 6-inches);when nuisance weeds and other nuisance vegetation is vegetation starts to take over. eradicated,such that flow is not impeded. Sand Filter Media Drawdown of water through the sand filter media, Usually requires replacement of takes longer than 24-hours,and/or flow through top 6 to 12-inches of media. the overflow pipes occurs frequently. May require replacement of entire sand filter section, depending on section. Prolonged flows Sand is saturated for prolonged periods of time Limit the low,continuous flows (several weeks)and does not dry out between to a small portion of the facility storms due to continuous base flow or prolonged by using a low wooden divider or flows from detention facilities. slightly depressed sand surface. Short Circuiting When flows become concentrated over the sand Flow and percolation of water filter rather than dispersed. through the sand filter is uniform and dispersed across the filter section. Erosion Damage to Erosion over 2-inches deep where cause of Slopes should be stabilized by Slopes damage is prevalent or potential for continued using proper erosion control erosion is evident. measures. Rock Pad Missing or Soil beneath the rock is visible. Replace or rebuild the rock pad Out of Place to design specifications. V-Notch Pipe Weir When the V-Notch pipe becomes damaged or Clean and properly functioning clogged with sediment/debris. weir,such that flows uniformly spread. Damaged Pipes Any part of the piping that is crushed or deformed Pipe repaired or replaced_ more than 20%or any other failure to the piping. Below Ground Sediment Sediment depth exceeds 1/2-inch. No sediment deposits on sand Vault. Accumulation on Sand filter section,which would Media Section impede permeability of the filter section. Sediment Sediment depth exceeds 6-inches in vault bottom. No sediment deposit in the first Accumulation in Vault chamber of the vault. Trash/Debris Trash and debris accumulated in vault,or pipe Trash and debris removed from Accumulation inlet/outlet,floatables and non-floatables vault,and inlet/outlet piping. Sediment in Drain When drain pipes,ceanouts,and yard drains Remove the material from the Pipes/Yard Drains/ become full with sediment and/or debris. facilities. Cleanouts 9/l/98 1998 Surface Water Design Manual A-14 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 13-WATER QUALITY FACILITIES(CONTINUED) E.)Sand Filters (Continued) Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed Below Ground Short Circuiting When seepage/flow occurs along the vault walls Sand filter media section re-laid Vault(Continued) and corners. and compacted along perimeter of vault to form a semi-seal. Vertical Riser Pipes Plugged,failure due to cracking deformation_Flows Clean out the riser pipe;replace tend to back-up in first chamber of the vault. pipe as needed. Damaged Pipes Inlet or outlet piping damaged or broken and in Pipe repaired and/or replaced. need of repair. Access Cover Cover cannot be opened,one person cannot open Cover repaired to proper Damaged/Not the cover,corrosion/deformation of cover. working specifications or Working replaced_ Vault Structure Cracks wider than 1/2-inch and any evidence of soil Vault replaced or repaired to Damaged;Includes particles entering the structure through the cracks, design specifications. Cracks in Walls, or maintenance/inspection personnel determines Bottom,Damage to that the vault is not structurally sound. Frame and/or Top Slab. Cracks wider than 1/2-inch at the joints of any inlet/ No cracks more than 1/4-inch outlet pipe or any evidence of soil particles entering wide at the joint of the inlet/ the vault through the walls. outlet pipe. Baffles Baffles corroding,cracking,warping and/or showing Repair or replace baffles to signs of failure as determined by maintenance/ specifications. inspection person. Access Ladder Ladder is corroded or deteriorated,not functioning Ladder replaced or repaired to Damaged properly,missing rungs,cracks,and misaligned. specifications,and is safe to use as determined by inspection personnel. 1998 Surface Water Design Manual 9/1/98 A-15 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 13-WATER QUALITY FACILITIES(CONTINUED) F.) Leaf Compost Filters Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed Above Ground Sediment Sediment depth exceeds 0.25-inches. No sediment deposits on fabric Open Swale accumulation on Geo- layer which would impede Textile/media permeability of the fabric. Trash and debris Trash and debris accumulated on compost filter Trash and debris removed from accumulations bed. compost filter bed. Sediment/debris in When the yard drain CB's and clean-outs become Remove the accumulated drain/yard drains/ full of sediment and/or debris. material from the facility. clean-outs. Vegetation Vegetation impending flow through section,or Vegetation is mowed or encroaching into compost media. eradicated such that flow is no longer impeded. Leaf Compost Media Drawdown of water through the leaf compost, Replace media with new to takes longer than 12-hours,and/or flow through design specifications,in addition the overflow pipes occurs frequently. to replacing fabric. Short-Circuiting When Channeled flow occurs over the leaf media; Flow is uniform over the entire and where flow perks through the media at the width of the media section,and baffles. concentrated percolation does not occur at the baffle walls. Media needs to be graded and re-set at the baffles to form a seal.Weir plate may need to be adjusted in addition. Erosion Damage to Eroded damage over 2-inches deep where cause Slopes should be stabilized by Slopes of damage is prevalent or potential for continued using proper erosion control erosion is prevalent. measures. • Damaged Geo-Textile When fabric is tom,deteriorated,raveled,etc. Fabric replaced as necessary. Fabric. Rock Pad Missing or Soil beneath the pad is visible. Replace or rebuild the rock pad out of place to design standards. Damaged Pipes Any part of the pipe system that is crushed, Pipe repaired or replaced. damage due to corrosion,and/or settlement. V-Notch Weir Flow is not being uniformly spread over filter Clean,repair or replace the weir Assemblies media. systems. Below Ground Sediment Sediment depth exceeds 0.25-inches. No sediment deposits on fabric Vault Accumulation on Geo- layer which would impede Textile/Media. permeability of the fabric and compost media. Sediment Sediment depth exceeds 6-inches in first chamber. No sediment deposits in vault Accumulation in Vault bottom of first chamber. Trash/Debris Trash and debris accumulated on compost filter Trash and debris removed from Accumulation bed. the compost filter bed. Sediment in Drain When drain pipes,clean-outs,yard drains become Remove the accumulated Pipes/Yard Drains/ full with sediment and/or debris. material from the facilities. Clean-Outs 9/I/98 1998 Surface Water Design Manual A-16 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 13-WATER QUALITY FACILITIES (CONTINUED) Leaf Compost Filter(Continued) Maintenance Defect Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed Below Ground Leaf Compost Media Drawdown of water through the leaf compost,takes Replace media with new longer than 12-hours,and/or overflow occurs compost to specifications,in frequently. addition to replacing fabric. Short Circuiting When seepage occurs along the vault wall and Percolation of water occurs comers occur. along the walls and corners and not through the media section. Media needs to be re-set along the vault wall and corners to form a semi-seal. Plugged/Damaged Flow tends to backup unusually high in the first Clean out the elbow fittings and/ Elbows chamber of the vault, or replace if damaged. Damaged Geo-Textile Fabric is tom,deteriorated,raveled,etc. Fabric replaced as necessary. Fabric Rock Pad Missing or Soil beneath the pad is visible. Replace or rebuild the rock pad Out of Place to design standards. Damaged Pipes Any part of the pipes that are crushed,damaged Pipe repaired and/or replaced. due to corrosion and/or settlement. Access Cover Cover cannot be opened,one person cannot open Cover repaired to proper Damaged/Not the cover,corrosion/deformation of cover. working specifications or Working replaced. V-Notch Weir Flow does not spread uniformly over filter media by Clean,repair and/or replace the Assemblies weir section. weir plate section,or adjust height. • Vault Structure Cracks wider than 1/2-inch and any evidence of soil Vault replaced or repaired to Includes Cracks in particles entering the structure through the cracks, design specifications. Wall,Bottom, or maintenance/inspection personnel determines Damage to Frame that the vault is not structurally sound. and/or Top Slab Baffles Baffles corroding,cracking warping,and/or showing Repair or replace baffles to signs of failure as determined by maintenance/ specification. inspection person. Access Ladder Ladder is corroded or deteriorated,not functioning Ladder replaced or repaired and Damaged properly,missing rungs,cracks,and misaligned. meets specifications,and is safe to use as determined by inspection personnel. Cracks wider than 1/2-inch at the joint of any No cracks more than 1/4-inch inlet/outlet pipe or any evidence of soil particles wide at the joint of the inlet/ entering the vault through the walls. outlet pipe. 1999 Surface Water Design Manual 9/1/98 A-17 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 13-WATER QUALITY FACILITIES(CONTINUED) G.) Infiltration Ponds Maintenance Defect Condition When Maintenance is Needed Results Expected When rComponent Maintenance is Performed Infiltration Pond Vegetation Vegetation such as grass and weeds needs to be Vegetation should be mowed to mowed when it starts to impede infiltration function. 2-inches in height.Trees and Mowing is generally required when height exceeds bushes should be removed 12 inches. where they impact the infiltrating area of the pond. Sand Filter Layer Sand filter layer has sediment deposits that exceeds Remove sediment and top layer 1/2-inch or the infiltration rate of the sand layer is of sand,and replace in kind per less than 2 in/hr. specification. Sediment Sediment accumulations in pond bottom that Removal of sediment from pond Accumulation in exceeds 1/2-inch in depth or percolation test of the bottom. Pond Bottom pond indicates facility is only working at 90%of it's design percolation rate. Trash and Debris Accumulation that exceeds 1-CF per 1,000-SF of Trash and Debris removed from pond area. pond. Inlet/Outlet Pipe Inlet/outlet pipe clogged with sediment and/or No clogging or blockage in the debris material. inlet and outlet piping. Erosion Erosion of the pond's side slope and/or scouring of Slopes should be stabilized by the pond bottom,that exceeds 2-inches,or where using proper erosion control potential for continued erosion is prevalent. measures and repair methods. Sediment of Pond Any part of these components that has settled 4- Slopes should be stabilized by Dike/Berm inches or lower than the design elevation,or where using proper erosion control potential for continued erosion is prevalent. measures and repair methods. Rock Window Rock window is clogged with sediment. Window is free of sediment and debris. • Overflow Spillway Rock is missing and soil is exposed Replace rocks to specifications. Infiltration Vault/ Sediment Tanks:Sediment depth exceeds 6-inches in depth. No sediment deposits in tank Tank Accumulation in bottom. Vault Trash and Debris Trash and debris accumulated in tank,vault or Trash and debris removed from Accumulation connecting pipe.Includes floatables and non- each facility. floatables. Access Cover Cover cannot be opened or removed,especially by Cover repaired or replaced to Damaged/Not one person. proper working specifications or Working replaced. Tank or Vault Tank:Joints between tank sections failing,such that Tank replaced or repaired to Structure Damaged leakage occurs and.or material being washed design specifications. through into facility;or maintenance/inspection person determines the tank is not structurally sound. 9/1/98 1998 Surface Water Design Manual A-18 APPENDIX A MAINTENANCE STANDARDS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 13-WATER QUALITY FACILITIES (CONTINUED) G.) Infiltration Ponds (Continued) Maintenance Defect Conditions When Maintenance is Needed Results Expected When • Component Maintenance is Performed Infiltration Vault/ Tank or Vault Structural Vault:Cracks wider than 1/2-inch and any Tank replaced or repaired to Tank Damage evidence of soil particles entering the structure design specifications. through the cracks,or maintenance inspection personnel determines that the vault is not structurally sound. Access Ladder Damaged Ladder is corroded or deteriorated,not Ladder replaced or repaired to functioning properly,missing rungs,has cracks specifications,and is safe to and/or misaligned. use as determined by inspection personnel. • 1998 Surface Water Design Manual 9/1/98 A-19 0 Appendix Triad Associates DeBar Plat Technical Information Report SE 1/4 SEC 32, TV➢1P 24N RGE 5E ¢' ' RQpO8' T R� e s- fax s" TRIAD ASSOCIATES t. f.. ✓ .✓ /. 2 Rajed Waagsmeot fE P�`• �:r/i X M O�r f BY y co i 1IDLi ..n r ,�gD:F r ram :::;:•' as B� C• r 11e14 I Ism A><.NE Ki.Ll.w.TA 9M-BC28 Tel 425.821.8448 F.425,821.us[ \`OQ�Xf F✓ r f ff ` :"''Jr''.•. :::56'T •S`r'•2iYF' ••-��� S Tall Pros BM488.rM mr.lneEanoc.mm - Q�e 0 ru, r c7 O �•�f fi '4i'�LLf%! f r__• fir..•` 16Y ' 20"F ; r ' '�'.:.;::�•'.. ::� �. r�1— i 2 LG"r 3 W F+� - - j $,[ fb ,/ d Y ?/ _ ..••••„ EA Of EX SHFD V1 ' IL 66 711.f EXISTING TREE ,,,.. :;2.� ,, f •.f f -� j r'l /i�Y.. TO BE REMOVED LU ETa ) lz G (j(/�, 2,° A, 3DY a SOLE: 1 " = 60' o LU �� .. ::..: Q rr•`w ZylX:QY^.. ....f' /•O.r ,;,Y, {:•.� '_. j "4O PRO 0 30 60 1 120 r / O U M STORbf ORA r r 1 i W W P1 .,:. .. .... .. ... SHED 1 � X t Q LU COLLECTEDI BASIN cc EXISTING TREE - OBE SAVED �..� ... 3 ,-', 1 .. \ 1 — 1` - o AREA OFJIMPERWOU� U- r 12 .' p£x S4ED 1 I m SURFACE$ ON LOTS 5-12, f € frr •, •w , - Iv 1'1 k'~' W WHICH A E TO BE /GHT—LINED '- 3 £XIS ITNG TREE 1 1 J I r , 1 I r.'• I k ---,� L_ U t { TO BE SAVED 1 I Ex GARAGE I s s�` arlro`' ` :; TO THE -1TORMWAT VAULT, if DEVELOPMENT r�1a ; 1 .";% 2 r w i 3 4 ° WERE AL 0 INCLUD D IN V ,EX CONC '' REQUIREMENTS .. 4 { r 12.75X66.5 ` —r— m VAULT /BUTARY EA DR,4£ ,, �...o« . ALlow(1YP) T WETVAULT YY 1 7 I w < 1 w 17.75X66.5'INfTLTRAJION fx. c {: VAULT CONNECT TO EX 8' ANl A Y SEKER A! a s'c �✓ 1 m i .-..t rr 3 __t{____•_`••i__ 3• ^•CK''YsRXSEL `'1- 76'B I PARKLNG•- 1 I Ex.co vcRE7E 'awe`,`:"•.\ W ' 11 / 3� —:.L I 1 '-- 1 '(•� z W Ex irowl �x 1 / E� � o i -j �; . + f .:: L REPLACE EX 2'6ATER `'. wALL ' I 1 I r T:' 'I PAI I 1 I x ' DEcx I 1 1 li 11'91 S ¢ MAIN WITH 8 W TER MAIN. # pFP A. va 1 r EX Buff DING I o 1'r l L---- ——l I.n•1 } r o RECONNECT ALL X. WATER a4 d cove: r I I fx BULaNc 11 I I I Ex.CNAI' ' n I 1 / I o i y METERS TO MAI LINK FENc i [_ h 0 I I ke 1 � I -� ^ #:� r` # PROVIDE INDENT T ION ( &I I t ' I PN F, I PRONDE INDENTATION zp < t. Ux IN PAVEMENT TO SAVE /N PAVEMENT T SAVE I I m. 1' 3 f TREE. TREES Lx R=3 ' { I I f 30 .: of i W i. He `I I 1 i 1 4 ( o YONti L WAESOK PE x {f ; r qIN(INK FENCE EX GRAVEL�' :' -� FEN I t 3O�LI I IBEX PICKET fENCf•11 1 ' RQ�1Pi EE 1ULM pt3 cu[x. ....1 x•. I _ - 1 1 PItOIHCI SURMON . :��.-5- Ex alAm� XI t ii i S �W IYAI , OR1lE — - X. C .. 1I I EX GRAVEL PARKR/G � + — ., ' S. • CHAIN INK FENCE • i LBd4 PE In ro,..,...,,....,.w eb ...��.,. --- -------- �-- PItOlHC1 ENGIN�R _______mug __ 1 �� ��®EX GRA 14T / ' _ �, 'i7 8 PROJRc1 LAEtDSCAPR ARCRIITxi' o _ �- ram' Wiz• '- — -- '+--- ----- -----'�_—_ DATE: of/ao/oz i — _ +xy .._"%- .rv....,•� •` '.f n'' .-ram:+ — VRRT.N/A •>28 TA _ M JDY — o PIT EX.caAVEy C \ DRI I I I Ir 1 UIP w/sL z 1 f — ——— m ----- fr v. Rcu� eows:l-= t I 1 £X CHAIN LINK ffNCf••�U7P IEK GRAS£U— X -A I£ a MN L v Elx.DRIVE IvIec I I F L DR 4£ I +£ DR/lf IVE 2 I I I PROPOSED 8"SAN'TSEWER =--J E 1_ORnf E..I — L- _ja __ _meµ PROPOSED 8' WA MAIN 3 NECT TO EX. Q. a CONNECT TO EX END ROADWAY IMPROV£MEN75 WATER MAIN i o I B WATER MAIN [ AT PROPERTY UNE � F # W ) I { NOTE.' � € W l n LOTS 1-4 ANO 13-14 SHALL HAVE S ¢ ' SPLASH BLOCKS LOTS 5-12 SHALL � EXDRv�r. F --- -B 1 Q I I I BE TIGHT—UNd TO STORM Dl?1/N N jZ I ...................................... ... .......... o 1 W I `I sue a _I 11 i2} S E f STAW NOT VALID EX. C I UNLESS SIGNED AND DATED .N 1 11 I`_ rEX.COMC i 5 OI I. �- nE-.a..• ..,..,..r..... ....,,N..,.,...,...N...,..,..<..... .'.e.....,,,..•..r..,,.,K.<. f y - i JOB NUMBER 00-220 uj Gj 8 co j I y .'• r{ 3 7, '2 1 I Q V I :# f ,,,.,.,,,,ry,.,.•,., .. .:.,.,..r.,•„v,..,v.•.v.....+.<.......:. L E OE I '� i € I ... w .. ..: g ©2002 TRIAD SBHE7 NUNBFR AASSOCIATES b SE 1/4 SEC 32, T1141P 24N RUE 5E TRIBUTARY AREAS (IN ACRES) TRI �0,, r f �"� AD ASSOCIATES CB IMPERVIOUS PERVIOUS TOTAL P`�Rp ' �: t .•! o � E as .� 1 0.05 0.10 0.15 SR' �4j �;:: . � + L,s «g 2 0.28 0.29 0.57 ,� . 3 0.70 0.00 0.70 flm_w.tm Td 4 G(� / Melt 11su I.n.r>8 G.tlw,n ueoel-ern 4 0.16 0.14 0.30 `00� 25 aZ1-04M /2 a21.S E1 To P Pa 34^S i ' SS re: �.Uvdaoc.rom 4 � 5 0.17 0.16 0.33 p0 6 0.00 0.00 0.00 OF f �b% $ g 2 7 0.06 0.00 0.06 f` ��s 207 TOTALS 0.69 2.11 � �, , r- /s r `�Z�4• I -' ;¢ •1(i F fiG'P � EAVE OF EX 'WED ! 3 o v ❑ µ „v -- .x .mw,,,,,,.,.:...,,w ,,,...N,.,-...•.,..v.. ..K.. ,:w..,...,,,,,.�.,», - r r 12 CUl ;' 60 i r` r tft7t f / f uj SOLE: 1 = 60 Q Ncc ww� ° R�' 0 37 60 a 120 Q V MQ } zca ii 91E0 r^ : ..... ..,. Q. . ...•_ tit• X { ex I — LL swo j I I EX GARAGE 1 :,:� t .: ,., j +• .! `` +' U ,310' Z i w ID I EX.CQNc r J 7 y 1 ORIV£ ; �.-•�•�..•.�, •s -� o I WETVAULT —— �. INnol?ATJON VAULT b'%• F r f G VC � I• Oki --- .,} BASIN LIKES ;..... :� !•c 13 1 m t / � ;:::; :. . INDICATE AREA 7RIBU TAR Y TO Ex coNcrrETE I j 2 ; _ I EACH CATCH BASIN. f OOF AND ------ ' �"' DRIVEWAY AREAS ON 107S 5-12 s 12-H i 1 _ Y , r Z I 1 (- "` .I } !'• WALL _ '• ARE ALSO INCLUDED SINCE THEY A # 4 Z I ! ' :I PN l�,', I x _ °EO ! I j�• ,81 f ARE T1GHT4-L1NED TO€1HE STORM 1 m # EX L71A1' t• 5-1_• "#�,I}• 1 / I EX. BUAO/NG I 2 f I �'I ..� —1 •.'�t'•l I ! �) �a 3 LINK EEN I [- 'r' I> I / CB t ' I I QI I EX BU&MC I 1;4�It 1 WATER VA(jLT # I' �. I ' 1 7 121P ( 5�+ 7 VW I II II 1 I--P-'-H6=�T 1 ' 1 —II 1 '; ►1$t1 1 # Fh i -ei. -/ "" c:; .. I I I?'( I I :l I I l 1 unlAn L NA e[ca•L PE A/f�•^� EX CIIAM kI I 1 , I :1 e� 1 PROIICI MANAGER FENCE EX GRAVEL I: j -. I y'.I Nel _( y CIM(FENCEW y I _ - _I_�- :I , RO�RT L MILLS AS I. v ItLI / CHAIN K NCE `,•„/ I i) _ EX P/GfET FEN 1 PROJECT SURVEYOR A;$ .•..,..... ........ :: , ,.. ; .,... .. r L-. . 1 [X.GRAVEL PARKING v ,I CLAY A LDCAA PE u.., Ex DRIVE F _ . uss i,:,:±—S,s,r..;.—-.<.'.. —i ;— -----,,,,,—. --.�c;..-y;�— NB- _ _ —————— ———-------——--—-—_ ----=s•• _Itt--��.—...-.._,.,.w.w..M —.._.., r—w...w--.,.—,�wrw i�,✓I :E<�en�.<w—,.-v...vrr a =M — it s PROJECT ENGINEER BO 12 - .......... PROJECT LANDSCAPE AR CD7ECi O 39V————— = DATE: 01130102 WV �-_ — — —— -- SCAM- BOIZ:1'=6� VW-N IA — —_— _ ——— —————— _——— ——— \—— R xn - Q) E °'B cx. GRALEIII I...,0� ,.t.. ..:.......... y ..MB�� —— — ————— F ; a r Il iC.,t, UTP IP,SL `i A } .yr,...<_u ———1 .... ..,o-.,:. I —"G ------- - 1�-- j.:.,,....1MA _v+.'•FPS•..w,,,..�,.w.....+ to L'QVC .LB 6 3 I \EID EX CHAIN CM'K FEND`;UT➢ iSt Y SEX -+s� 'IX GRAI P — il i ---oqlvr I_OPoYE ,—aW # ROADWAY IMPROVEMENTSv m } I # k $ AT PROPERTY LINE NOTE.• o EX cLxlE� W I t # LOTS 1-4 AND 13-14 SHALL :AVE ?o DRIVE: SPLASH BLOCKS. LOTS 5-12 MALL BE 77GHT-LINED TO STORM DR IN O # SYSTEM. 1 � I I � i I 3 NAB -, I W IW .. V U EX. NCI I 1 # $ 3 } # STAMP NOT YAM O i i���4�y,,,..., Ex.cow $ UNLESS SIGNBD AND DATED VIE ,DD NDMDt7t 00-220 $ W i Q I� # SIIEBt NUMBER 1ae 1 s. ©2002 TRIAD ASSOCIATES