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HomeMy WebLinkAboutSWP272823(1) STORM DRAINAGE REPORT for UNITED STATES POST OFFICE HIGHLANDS RENTON, WASHINGTON MAY 1999 Prepared For: Sienna Architecture Company 411 Southwest 6th Avenue Portland, Oregon 97204-1602 Prepared By: Dennis M. Galinato Senior Design Engineer Reviewed By: Doreen S. Gavin P.E., Principal 98027.10 ' STORM DRAINAGE REPORT ' for UNITED STATES POST OFFICE HIGHLANDS RENTON, WASHINGTON ir ■ MAY 1999 ' Prepared For: ' Sienna Architecture Company 411 Southwest 61h Avenue Portland, Oregon 97204-1602 d 23467 Prepared By: ..''��„ �L•'c1sr�R� ki �SS1oNAL i3jgj Dennis M. Galinato EXPIRES 7 Senior Design Engineer ' Reviewed By: I hereby state that this Storm Drainage Report for United States Post Office--Highlands has Doreen S. Gavin, P.E., Principal been prepared by me or under my supervision and meets the standard of care and expertise that is usual and customary in this community for professional engineers. I understand that 98027.10 King County does not and will not assume liability for the sufficiency, suitability,or performances of drainage facilities prepared by me, ' TABLE OF CONTENTS ' SECTION PAGE ' 1. Project Overview------ -------------------------------------------------------------------------------------------------------------------1 1.1 Purpose and Scope-------- --------------------------------------------------------------------------------------------- 1 1.2 Predevelopment Conditions----------------------------------------------------------------------------------------1 1.3 Post-Development Conditions--------------------------------------------------------------------------------- 2 2. Conditions and Requirements Summary---------------------------------------------__-.-----_----------------------2 2.1 Drainage Basins--- ----------------- ----- -------- -------- -------- -------- ------- -------- --- ----_2 3. Off-Site Analysis--------------------------------------------------------------------------------------------------------------------------3 4. Flow Control and Water Quality Facility Analysis and Design--------------------------------------------3 4.1 Existing Site Hydrology---- --------------------------------------------------------------------------------------------3 4.2 Developed Site Hydrology-------------------------------------------------------------------------------------------3 4.3 Flow Control System----------------------------------------------------------------------------------------------------- 4.4 Water Quality System--------------------- -----------------------------------------------------------------------------5 5. Conveyance System Analysis and Design-----------------------------------------------------------------------------5 5.1 Analysis Data------------------------------------------------------- ----------------------------------------------------------5 5.2 Analysis Results------------------------------------------------------------------------------------------------------------- 6. Special Reports And Studies----------- 6 ----------------------------------------------------------------------------------------- 7. TESC Analysis and Design-------------------------------------------------------------------------------------------------------6 8. Operations and Maintenance Plan ------------------------------------------------------------------------------------------ 9. Conclusion ------------------------------------------------------------------------------------------------------------------------------------ ' Appendices ' Appendix A Exhibits Figure 1 Site Vicinity Map Figure 2 Drainage Basin Map ' Figure 3 Sub-Basin Map - Conveyance Calculations Figure 4 Sub-Basin Map - Water Quality Calculations for Bio-swales Figure 5 Sub-Basin Map - 100-Year Storm Conveyance Calculations for Bioswales Figure 6 Reach Map - Conveyance Calculations ' Figure 7 Reach Map — Backwater/Hydraulic Grade Calculations Figure 8 Upstream Contributary Area Figure 9 SCS Map ' Appendix B Hydrologic Analysis Exhibit 1 - Detention Facility Calculations Exhibit 2 - Conveyance Calculations Exhibit 3 - Backwater Calculations ' Exhibit 4 - Water Quality Calculations Exhibit 5 - Off-Site Runoff, Conveyance Calculations iAppendix C Geotechnical Engineering Report Geotechnical Report 1 Supplement No. 1: Stormwater Infiltration Appendix D Sediment Trap Calculations Appendix E Maintenance and Operations Sample Plan 1. PROJECT OVERVIEW 1.1 Purpose and Scope This report accompanies the on-site civil plans for development of the proposed United States Post Office located in the City of Renton on Northeast 4th Street near the intersection of Northeast 41h Street and Union Avenue Northeast. See Appendix A, Figure 1 for Site Location. ' The 1994 King County Surface Water Design Manual_(KCSWDlkI)-a►ad _1.332—.__ Department of Ecology Stormwater Management Manual for the Puget Sound Basin (DOE Manual) were used as guidelines for the design of this project. ' 1.2 Predevelopment Conditions The project site consists of 3.31 acres of land located east of the intersection of ' Northeast 4th Street and Union Ave Northeast. The site is bound to the north by Northeast 4th Street, and to the south, east, and west by residential development. The site is currently undeveloped except for a residence located on the northwest ' portion of the site. The area south and east of the house is overgrown with blackberry bushes and has scattered fruit trees. Forest with brush covers the rest of the site. The site slopes from east to west with approximately 9 feet of fall across the site. Low points exist in the northwest and southwest corners of the site. The topsoil on the site is '/2 to 1 foot deep. Test pits indicate recessional outwash or weathered till and glacial till with mixtures of sand, silt, clay, gravel. Perched groundwater was found 7 to 8 feet below existing grades. Refer the Geotechnical Engineering Report dated October 6, 1998, by AGRA Earth and Environmental ' and Appendix C for the Infiltration Test Report-Supplement 1: Stormwater Infiltration. Refer to Figure 9 for the SCS Map of the area. There is a wetland located in the adjacent property to the west. This wetland will not be affected by the Highlands Post Office development, as runoff from all storm events up to and including the 100-year, 24-hour storm will be conveyed to 1 a ditch/stream located in the same property and the site does not seem to provide significant runoff to the wetland in the pre-developed condition. 1.3 Post-Development Conditions ' Major features to be constructed include: a building pad for the Post Office (t23,200 square feet), parking lots, a concrete snorkel lane at the northeast ' portion of the site, a concrete plaza adjacent to the northwest portion of the building, concrete truck docks, a retaining wall along the west property line, a 115-foot long bioswale located on the south property line, and a 60-foot long ' bioswale located on the west property line. The site will be split into two post-developed sub-basins, identified as BA1 and ' BA2 (see Figure 5, Appendix A). BA1 is comprised of the western 1.05 ' impervious acres of the site; BA2 is comprised of the eastern 2.26 impervious acres of the site. Water quality treatment will be provided by two separate ' biofiltration swales. BA1 runoff is treated by a bioswale located on the western side of the site, and runoff from BA2 is treated by a bioswale located on the ' southern side of the site. See Figure 4, Appendix A for the sub-basins used for bioswale designs. Detention pipes located in the southwest corner of the site provide stormwater retention for runoff from both sub-basins. Outflow from the detention facility is conveyed off-site to a ditch/stream located in the adjacent property to the west. ' 2. CONDITIONS AND REQUIREMENTS SUMMARY 2.1 Drainage Basins ' The project is located in the Maplewood Sub-Basin, which is part of the proposed Lower Cedar River Drainage Basin. The runoff from these basins is routed to the Cedar River, and the Cedar River outlets into Lake Washington (see Figure 2, ' Appendix A). 2 ' 3. OFF-SITE ANALYSIS ' Figure 8, Appendix A, shows that off-site runoff flows to a stream/ditch located in the adjacent lot to the west. This stream/ditch conveys runoff to a large pond in a ' residential area south of the site. No evidence of flooding was found during a field inspection of this pond. ' A ditch and extruded curb convey flow from 136m Avenue and Northeast 4" Street ' to the ditch described above. Approximately 1.29 acres contributes to this flow, including 0.28 acres of residential area. See Figure 8 for the upstream contributary area. 4. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ' 4.1 Existing Site Hydrology The site is currently undeveloped except for a residence located on the northwest portion of the site. The area south and east of the house is overgrown with blackberry bushes and has scattered fruit trees. Forest with brush covers the rest of the site. The site slopes from east to west with approximately 9 feet of fall across the site. Low points exist in the northwest and southwest corners of the site. Runoff flows onto properties to the west, southwest and south. ' 4.2 Developed Site Hydrology In the developed condition, runoff is collected by catch basins and routed to water ' quality facilities, and from there it is routed to detention tanks and conveyed at a controlled rate to the ditch/stream located in the adjacent property to the west. ' Roof runoff from the western half of the building, runoff from the snorkel lane, and runoff form the area west of the building is routed to a bioswale which is located along the west side of the site. The treated water is then routed to detention pipes that are located in the southwest corner of the site. Runoff from the eastern ' half of the building, and runoff from areas south and east of the building are routed to a bioswale located along the southern property line. The treated water is routed from the bioswale to the detention pipes. Roof runoff is collected from the 3 ' building post office and tight-lined to the conveyance system. See Figure 3, Appendix A, for the sub-basin map used in the conveyance calculations. The detention facility is designed to match the pre-developed 2-year, 24-hour and 10-year, 24-hour release rates. The system is designed to bypass the 100-year, 24-hour storm. On-site runoff is routed to an existing 36-inch concrete pipe outfall ' located in Northeast 4th Street 185 feet west of the site. Capacity calculations for ' the bypass/overflow system are presented in Exhibits 1 and 5, Appendix A. ' Contributing runoff from 136' Avenue Southeast and Northeast 4th Street will be received by a curb inlet at the northeast corner of the site. From there, it will be ' conveyed to a curb inlet at the northwest corner of the site and conveyed to the ditch described above. Capacity calculations for the off-site bypass system are ' presented in Exhibits 1 and 5. 4.3 Flow Control System In accordance with the 1994 KCSWDM, on site flows will be detained in two 189 ' foot long, 6-foot diameter detention tanks. The detention facility is designed to match the pre-developed runoff rates from the 2 year, 24-hour and 10-year, 24- ' hour storms. It is also designed to safely bypass runoff from events up to the ' 100-year, 24-hour storm. Runoff is conveyed from both bioswales to 2 catch basins. From there, the water is conveyed to the detention pipes through a manifold system constructed of 15- inch and 36-inch pipes. Water is released through a two-orifice control structure ' with a 12-inch overflow riser. The released runoff is routed off-site to the bypass system described in section 4.2. Refer to Exhibit 1, Appendix A for detention facility calculations. ' 4 ' 4.4 Water Quality System ' In accordance with the 1994 KCSWDM, treatment of stormwater generated from this development shall take place on-site prior to introduction into the detention ' facility. There are two biofiltration swales located on the west and south property lines. Both bioswales are designed to treat runoff from the 6-month, 24-hour ' storm event, and they are sized to convey runoff from the 100-year, 24-hour storm. Bioswale design was done in accordance to the DOE Manual. The ' facilities were first sized for biofiltration, and then they were analyzed to ensure that they had the capacity to convey the 100-year, 24-hour storm. Water velocity ' during this event is less than 5 fps which ensures slope stability. Refer to Exhibit 4, Appendix B for bioswale sizing calculations and illustrations, and refer to Figures 4 and 5, Appendix A for the sub-basin maps used to design the bioswales. 5. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ' The stormwater network was sized to adequately convey the 25- ear, 24-hour storm event, as stipulated by the 1994 KCSWDM. The system was further checked to predict the capacity and backwater effects of the 100-year, 24-hour ' storm event using the Waterworks computer modeling program with the Santa Barbara Unit Hydrograph Method and King County 24-hour storm rainfall Type ' 1 A. ' 5.1 Analysis Data Rainfall data for the conveyance analysis included depths of 3.40 inches for the 25-year, 24 hour storm and 3.90 inches for the 100-year, 24-hour storm event. In order to find runoff from the sub-basins the site was analyzed as 100 percent ' impervious, using a curve number of 98 (Appendix B). During the conveyance analysis, a Manning's "n" of .014 was used, and during the backwater analysis a ' Manning's "n" of .012 was used. 5 ' 5.2 Analysis Results ' Analysis of the conveyance system shows that there is adequate capacity to convey the 25-year, 24-hour storm event. During this event, no pipes in the ' system flow more than 60 percent full. The minimum pipe slope in the system is 0.50 percent, which conforms to the 1994 KCSWDM standards. ' The backwater analysis was performed under the assumption that the 100-year ' storm event would fill the detention tanks to maximum capacity, providing a tail- water elevation of 389 feet. At this elevation, the water would back up into the ' bioswale causing a submerged outlet situation in both bioswales. Backwater analysis of Reach R1 (Exhibit 3, Appendix B) shows that the HGL elevation will not exceed rim elevations of the catch basins during the 100-year, 24-hour event. Exhibit 2, Appendix B contains the conveyance calculations, and Exhibit 3, Appendix B contains the calculations. Figure 6 has the reach map used for the ' conveyance calculations. Figure 7, Appendix A, shows the reach map used for the backwater calculations. 6. SPECIAL REPORTS AND STUDIES A geotechnical engineering report, dated October 6, 1998, was done for the site by AGRA Earth and Environmental. An additional report done by AGRA, ' Supplement No. 1: Stormwater Infiltration dated April 15, 1999, contains information on additional test pits. This additional information was used to design ' the proposed infiltration system. These reports are presented in Appendix C. TESC ANALYSIS AND DESIGN ' The proposed development complies with guidelines set in the KCSWDM. The plan includes erosion/sedimentation control features designed to prevent ' sediment-laden runoff from leaving the site or adversely affecting critical water resources during construction. Specific physical features of the on-site erosion ' and sedimentation control plan are shown on the site development plans. ' 6 The erosion potential of the site is influenced by four major factors: soil characteristics, vegetative cover, topography, and climate. Erosion/sedimentation ' control is achieved by a combination of structural measures, cover measures, and ' construction practices that are tailored to fit the specific site. The following measures will be used to control sedimentation/erosion processes: • Stabilized construction entrances ' • Filter fabric fences for ditch and site runoff protection • Sediment traps ' • Catch basin inlet protection • Rock protection at interceptor ditch outfalls ' The runoff from the site flows from east to west. Runoff is routed to two sediment ' traps via interceptor ditches with rock check dams. Rip-rap pads are located at the interceptor ditch outfalls to prevent erosion of the sediment traps. ' A sediment trap is located in the landscape area in along the west property line, and a second sediment trap is located in the landscape area along the south property line. Because of the considerable cut and fill on-site, the elevation of these traps will be lowered, as the site is developed in order to ensure that ' sediment-laden runoff will flow into them. The calculations for the volume sizing ' of these traps are contained in Appendix D. OPERATIONS AND MAINTENANCE PLAN Operations and maintenance will be the responsibility of the owner. A sample ' Operations and Maintenance Plan from the 1994 KCSWDM is given in Appendix E. ' 7 9. CONCLUSION This site has been designed to meet 1992 DOE Manual and 1994 KCSWDM guidelines for stormwater management. The site incorporates a self-contained infiltration facility for disposal of all site generated stormwater flows, and bioswale for stormwater runoff treatment from paved surfaces. Flow calculations/modeling ' utilized the King County standards for sizing stormwater conveyance networks and infiltration facilities. Department of Ecology standards were used to design treatment facilities. ' It was determined utilizing this criteria that: • The treatment facility will adequately treat the 6 month storm event Pipe networks will be of adequate size to effectively convey the 25-year, 24- ' hour storm event Pipe networks can convey runoff from storms greater than the 100-year, 24- hour storm to the overflow structure at the northwest portion of the site ' without the HGL elevation exceeding any of the on-site rim elevations ' • The detention facility will match the pre-developed release rates from the 2- year, 24- hour and 10-year, 24-hour storms. It will safely bypass the 100- year, 24-hour storm. 1 8 ' This analysis is based on data and records either supplied to, or obtained by, AHBL. These documents are referenced within the text of the analysis. The analysis has been fprepared utilizing procedures and practices within the standard accepted practices of the industry. We conclude that this project, as proposed, will not create any new problems within the downstream drainage system. This project will not noticeably aggravate any existing downstream problems either due to water quality or quantity. AHBL, Inc. ' Dennis M. Galinato Senior Design Engineer DMG/jlg ' May 1999 9802710.rep i 1 9 ' APPENDIX A ' Exhibits ' Figure 1 - Site Vicinity Map Figure 2 — Drainage Basin Map Figure 3 - Sub-Basin Map - Conveyance ' Calculations Figure 4 - Sub-Basin Map - Water Quality ' Calculations for Bio-Swales Figure 5 - Sub-Basin Map - 100-Year Storm ' Conveyance Calculations for Bio-Swales Figure 6 - Reach Map Conveyance Calculations ' Figure 7 - Reach Map Backwater/Hydraulic Grade Calculations ' Figure 8 - Upstream Contributary Area Figure 9 - SCS Map 1 61N N 6TH i PL i i = + NE __ 6TH <' T _ V1 iT / j y, ., WIND"S _ St _ w 2F,� OLYMP[A :� TI PL n 9 '<5 z o 4 > 57H ST z >z NE AV NE ¢ s a _ y „E r < SE NE L� I ST F RENT N p a' WtHO50P ¢ TECHN CAL +c 00 •E t ST WINDSDR¢ F[anDALE NE ■ COLL E 4TH m — ST MILS N Lr 4TH z ST o At A 2500 T I 4300 ' 1300 z uat sr 2 z Cl o I GRE NWDOD > o >a N �0 4 m• ti CD S� I t NE 3RD CT ST m 1 0 —� = CEM RY ---h co PAW(Sl�d ' 8 u sr J�'y j�� %_NE_ $ 2N0 5T SE --- W STC ' NE 3400 2ND 1100TER" "' C711 NT- 1ST`_^j.�.._..... 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' N .�-i - « N T ti i H _ b `h P tih ^'^ SE S 27TH ST SE 1 4TH ST SE 164TH ST p '< ^ °< ?-���Sf L <sF N 10900 W 11100 ,,ire 11100 166TH gi< c SF 165r4 SE ti 164TH T ST I 28 > SE 165TH �S 4 S .� S $f< sr _ a > w f �. ♦5 sE �� 'Ss:c sE 166TH ST Fq j - H h sT o W � s� a � 5 1 ,N sip ,` 166TH < i pv Sr sE 167TH Sr ' ST E t 67TN Si > SE, E 1667H PL i R!IJ = ..<' n- o r CHARLES A >a 5� Sr Sry TTN SF ■L fNDBERfI HS m /o t TW PL /�H B L HIGHLAND POST OFFICE ' 98027.10 FIGURE I CIVIL&STRUCTURAL ENGINEERS,PLANNERS 2215 North 30th Suite 300•TACOMA,WA 98403 SITE VICINITY MAP ' (253)383-2422•FAX:(253)383-2572 Er��_ FIGURE ' ii�f� Lam. _ ,Jrr _ + j(� 9 k$' 43 p.7Yi q, y�r�° � j CITY OF RENTON SURFACE WA TER L� ! DRAINAGE BASINS 4A/ES>aY A* LAKE WASHINGTON AG SOUTHI �`�r�r�r > NNYDA- � J y BASS NAMES SOOS CREW( =Ji ` .F tl [f � ' r I( \ 1,\�1, '''_._. BLACK RIVER 'r EDAR m� ' � Q WEST LAKE WASHINGTON EAST LAKE WASHINGTON {_ • El MAY CREEK ` 1RENTON q (f7 S LOWER CEDAR RIVER DUWAMISH MT. OLIVETS?fe i tt EE PEE G w ■ LAKE ITFANY BASINS Sub—Basin Names yCD . Sub—Basin Boundry M y _ --------- Municipal Boundries � Urban Growth Boundary I I VALLEYLAM ' 1 "`•� 0 4000 8000 t � .., , .e K■ . • i ii� i tv i � r �� I � o �H wl � L� •ice" •� CC1 ��L.JI-1� � � � � •� x,n d x r it �' d J � 3 ��\, if PA THER .Dotson �' ,.�`1 �" r J — aTI '"l � 1 +• P NG bl_ iF�— R.MacOnie, D.Visne'ski Irj' --� �` �- !!f � _ •- r"= :I F_ w � ,i� _ '� ��� �h� - bIkY 25,1995 ' ° I�—il� Kr T". ;+ { 1 '�i• L 5 �I $ 4DY LIKE I\\ -- L p DD BAl Al DO Lf J V ` _ BA2 h v v D --- — — l� �1 _ L Ila BA3 - BA6 I o J I •�,�n�trc:�1 �1�7r. .. I .. •I BA4 ; BA5 ---- -- -- - - - -- BA8 -- - BA9 OF I - - I i . . . I I � D �4y I I I I H LJ ijFN BAl Area = 1.05 Acres t t _ FM i i w I ' i BA2 Area = 2.26 Acres L---------- q q 1 BA1 Area = 1.05 Acres FH r� 1 i i i i i ' BA2 Area = 2.26 Acres L____________J LLL—L 1 c�Z L ld 1 f c� 3 � Z3 �Z 1 c3S � O 1 LS 1 �f3 l; ' c3 c�3 9 60) 1 �HBL HIGHLAND POST OFFICE 9 CIVIL&STRUCTURAL 8027.10 FIGURE 6 ENGINEERS,PLANNERS 2215 North 301h Suite 300•TACOMA,WA 98403 REACH MAP CONVEYANCE CALCULATIONS (253)383-2422•FAX:(253)383-2572 i—j /U>3G+ c�liz13� cgd-3 1'� 3(sU �D�M3 /�HBL HIGHLAND POST OFFICE 98027.10 FIGURE 7 CIVIL&STRUCTURAL ENGINEERS,PLANNERS 2215 North 30th Suite 300•TACOMA,WA 98403 REACH MAP BACKWATER CALCULATIONS ' (253)383-2422•FAX.(253)383-2572 E6 - 10 T23N R5E W 1/2 ir 9,12 1j, -N�) r-r ------------ C 2 Ank ary 1W mr 6nrl-�t SE co SE VO.te 1RJ 1, t JE Is t 41 �19.14 4 ] �a 4 D L t ?.c - v ip. 19 c: 1 3 F .1 35th!�1�t 19 -.v VA L) 19.5510 cc, 55-1 LSE 19.85-4 9.15-14 r 1 O -c CL > /�H BL HIGHLAND POST OFFICE CIVIL&STRUCTURAL 98027.10 FIGURE 8 ENGINEERS,PLANNERS 2215 North 30th Suite 300-TACOMA,WA 98403 (253)383-2422-FAX:(253)383-2572 (AP-57'gfoAM Coli—, ilij—.4,--,Y Ifl"51/*' d 1 f • Cila :f� Rainier y of e �tX , 6 � ,Beach (a I . 5• Eh c e `✓fir' °- —------ is E Pd a Pic 2 ,;� '� .� ate_ •'c;,. 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"Ad ' gravelly sandy loam, Everett fine Sandy loam, " I.v Ma hilly gravelly sandy loam, rolling (15 25 percent slope) rolling (6-15 percent slope) (6.15 percent slope) ' ED EO Ek. .• �HBL HIGHLAND POST OFFICE 98027.10 FIGURE 9 CIVIL&STRUCTURAL ENGINEERS,PLANNERS 2215 North 30th Suite 300-TACOMA,WA 98403 M ' (253)383-2422•FAX:(253)383-2572 / fCfr ' APPENDIX B Hydrologic Analysis ' Exhibit 1 - Detention Facility Calculations Exhibit 2 - Conveyance Calculations ' Exhibit 3 - Backwater Calculations Exhibit 4 - Water Quality Calculations Exhibit 5 - Off-site Runoff Conveyance Calculations INA. u A � it 1������ ►• ' � ���` .� i..jam( -� ► S �i �•.�wu�w III � .; � � 1 11011, Iry WIMIr long q to olls" w�! � •��� : Via► �:k, �� �, ���, SAW �� .,INS ,♦:�/���� �� ut � �, �� �• .. • �� ��''�ter.>�� • e �r� 'r�r�w Ard• tr ` y ` � �,� I NA — in' a��a��r f•w�, ,,r4 , \1 as X FOR wit 'dmill ► .rr WMAN 2111 met 'REPIRA OR \c:=� ►� son- MA wula FA I I FA ma p4m; i � � ii►I�IA��� �I• .. �,�'\. . ` -mar Ma LwRIM ITAI all win i►�, �` Will NJ Mill aim �'' `tom\ ���►� � �rlr �_ ir ��► - No- Lit lVIM i o •at'.3;7�IR MI ar • ��-.. Lis oil IMP vp vow Loa P, ` `. HIS Nkl-; IN 4 L��► �► .�wil WIN OR YAMSRIP �. --_---- ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TABLE 3.5.26 SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS ' SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (Published by SCS in 1982) Runoff curve numbers for selected agricultural, suburban and urban land use for Type 1A rainfall distribution, 24-hour storm duration. CURVE NUMBERS BY HYDROLOGIC SOIL GROUP ' LAND USE DESCRIPTION A B C D Cultivated land(1): winter condition 86 91 94 95 ' Mountain open areas: low growing brush and grasslands 74 82 89 92 Meadow or pasture: 65 78 85 89 Wood or forest land: undisturbed or older second growth 42 64 76 81 Wood or forest land: young second growth or brush 55 72 81 86 Orchard: with cover crop 81 88 92 94 ' Open spaces, lawns, parks, golf courses, cemeteries, landscaping. good condition: grass cover on 75% or more of the area 68 80 86 90 ' fair condition: grass cover on 50% to 75% of the area 77 85 90 92 Gravel roads and parking lots 76 85 89 91 72 82 87 89 Dirt roads and parking lots Impervious surfaces, pavement, roofs, etc. 98 98 98 98 Open water bodies: lakes, wetlands, ponds, etc. 100 100 100 t00 ' Single Family Residential (2) Dwelling Unit/Gross Acre % Impervious (3) ' 1.0 DU/GA 15 Separate curve number 1.5 DU/GA 20 shall be selected 2.0 DU/GA 25 for pervious and 2.5 DU/GA 30 impervious portion 3.0 DU/GA 34 of the site or basin 3.5 DU/GA 38 4.0 DU/GA 42 4.5 DU/GA 46 ' 5.0 DU/GA 48 5.5 DU/GA 50 6.0 DU/GA 52 6.5 DU/GA o4 ' 7.0 DU/GA 56 Planned unit developments, % impervious condominiums, apartments, must be computed commercial business and industrial areas. (1) For a more detailed description of agricultural land use curve numbers refer to National Engineering Handbook, Section 4, Hydrology, Chapter 9, August 1972. (2) Assumes roof and driveway runoff is directed into street/storm system. (3) The remaining pervious areas (lawn) are considered to be in good condition for these curve numbers. ' 3.5.2-3 11/92 1 1 1 i 1 1 Exhibit 1 - Detention Facility Calculations 1 A. 1 1 1 1 1 i 1 1 i 1 HBL 1 Project rds i J/j� No. �� ❑ P ge of rAAHE)L Subject ��� 1 �� f` "'i Phone Calculations ❑ Fax With[To Fax# ❑ Memorandum Address # Faxed Pages ❑ Meeting Minutes ❑Telephone Memo ' Date: rSG C,,, r2„ S-D By A� r _ _ o #S„cMP r / Copies to: r � 1 _ TIArr Cr-ao% r 4 z'✓�r�„ .- 1 22111,3011 Street - ' Suite 300 Tacoma,WA 98403 ---- --- Old Town Historical District 253/383-2422 253/383-2572 FAX _ 1 _ If this does not meet with your understanding,please contact us in writing within seven days.THANK YOU. Project /11CAWE c} ,�1" ' '�C� No. / �T�G ❑ P ge of 1 HBL Subject —`� °� ^ �` J a'� Phone Calculations A ❑ Fax With/To Fax# ❑ Memorandum ' Address #Faxed Pages ❑ Meeting Minutes ❑Telephone Memo ' Date: S/` w7� t By: OGc4'1L t�cucf�t,__ — C/evatJGhF 3csgsa R 'Jr'r tce= Copies to: 71 r 1 2215 N.30th Street ' Suite 300 Tacoma,WA 98403 Old Town Historical District 253/383-2422 253/383-2572 FAX If this does not meet with your understanding,please contact us in writing within seven days.THANK YOU. Project --"��i�(�c� fa� �/t J, No. 3y2 ❑ P e of 1AAHBL Subject !���''�'Or' ��` Phone Calculations ❑ Fax - _ Withrro Fax# ❑ Memorandum 1 Address #Faxed Pages ❑ Meeting Minutes ❑Telephone Memo ' Date: i By Copies to: 2215 N.30th Street Suite 300 Tacoma,WA 98403 Old Town Historical District 253/383-2422 253/383-2572 FAX If this does not meet with your understanding,please contact us in writing within seven days.THANK YOU. 5/7/99 9 : 6 : 26 am AHBL page 1 USPO Highlands, Renton, Wa. 98027 . 10 DETENTION PIPE SIZING K: \CIVIL\YR_1998\98027\DETENTIO ' BASIN SUMMARY=====_______________________ ' BASIN ID: POST100Y NAME : POSTDEVELOPED SITE, 100-YR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 30 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : TYPEIA PERV IMP PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0 . 00 Acres 3 . 30 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 TC. . . . : 0 . 00 min 5 . 00 min ABSTRACTION COEFF: 0 . 20 PEAK RATE : 2 . 69 cfs VOL: 1 . 01 Ac-ft TIME : 480 min ' BASIN ID: POST10YR NAME : POSTDEVELOPED SITE, 10-YR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 30 Acres BASEFLOWS : 0 . 00 cfs ' RAINFALL TYPE. . . . : TYPEIA PERV IMP PRECIPITATION. . . . : 2 . 90 inches AREA. . : 0 . 00 Acres 3 . 30 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 TC. . . . . 0 . 00 min 5 . 00 min ABSTRACTION COEFF : 0 . 20 PEAK RATE : 1 . 98 cfs VOL: 0 . 73 Ac-ft TIME : 480 min BASIN ID: POST2YR NAME : POSTDEVELOPED SITE, 2-YR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 30 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : TYPEIA PERV IMP PRECIPITATION. . . . : 2 . 00 inches AREA. . : 0 . 00 Acres 3 . 30 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 ' TC. . . . . 0 . 00 min 5 . 00 min ABSTRACTION COEFF: 0 . 20 PEAK RATE : 1 . 34 cfs VOL: 0 . 49 Ac-ft TIME : 480 min BASIN ID: PRE-100Y NAME : UNDEVELOPED SITE, 100-YR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 30 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : TYPEIA PERV IMP PRECIPITATION. . . . : 3 . 90 inches AREA. . : 3 . 30 Acres 0 . 00 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 86 . 00 0 . 00 TC. . . . : 32 . 06 min 0 . 00 min ABSTRACTION COEFF : 0 . 20 TcReach - Sheet L: 300 . 00 ns : 0 . 2400 p2yr: 2 . 00 s : 0 . 0560 TcReach - Shallow L: 240 . 00 ks : 5 . 00 s : 0 . 0600 PEAK RATE : 1 . 31 cfs VOL: 0 . 68 Ac-ft TIME: 490 min ' 5/7/99 9 : 6 : 26 am AHBL page 2 USPO Highlands, Renton, Wa. 98027 . 10 DETENTION PIPE SIZING K: \CIVIL\YR-1998\98027\DETENTIO-------------------------------------- BASIN SUMMARY BASIN ID: PRE-10Y NAME : UNDEVELOPED SITE, 10-YR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 30 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : TYPEIA PERV IMP PRECIPITATION. . . . : 2 . 90 inches AREA. . : 3 . 30 Acres 0 . 00 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 86 . 00 0 . 00 TC. . . . : 32 . 06 min 0 . 00 min ABSTRACTION COEFF: 0 . 20 TcReach - Sheet L: 300 . 00 ns : 0 . 2400 p2yr: 2 . 00 s : 0 . 0560 TcReach - Shallow L: 240 . 00 ks : 5 . 00 s : 0 . 0600 PEAK RATE : 0 . 80 cfs VOL: 0 . 43 Ac-ft TIME : 490 min BASIN ID : PRE-2Y NAME : UNDEVELOPED SITE, 2-YR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 3 . 30 Acres BASEFLOWS : 0 . 00 cfs ' RAINFALL TYPE . . . . : TYPEIA PERV IMP PRECIPITATION. . . . : 2 . 00 inches AREA. . : 3 . 30 Acres 0 . 00 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 86 . 00 0 . 00 ' TC. . . . 32 . 06 min 0 . 00 min ABSTRACTION COEFF : 0 . 20 TcReach - Sheet L: 300 . 00 ns : 0 . 2400 p2yr. 2 . 00 s . 0 . 0560 TcReach - Shallow L: 240 . 00 ks : 5 . 00 s : 0 . 0600 ' PEAK RATE : 0 . 38 cfs VOL: 0 . 23 Ac-ft TIME : 490 min r ' 5/7/99 2 : 9 : 11 pm AHBL page 1 USPO Highlands, Renton, Wa . 98027 . 10 DETENTION PIPE SIZING K: \CIVIL\YR_1998\98027\DETENTIO STAGE STORAGE TABLE ' UNDERGROUND PIPE ID No. DETENl Description: DETENTION PIPE Diameter: 6 . 00 ft . Length: 290 . 00 ft . Slope . . . : 0 . 0000 ft/ft upstr: dnstr: STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> STAGE <----STORAGE----> (ft) ---cf--- --Ac-Ft- (ft) ---cf--- --AC-Ft- (ft) ---cf--- --AC-Ft- (ft) ---cf--- --Ac-Ft- ' 383 00 0.0000 0.0000 384.60 1755 0.0403 386.20 4448 0.1021 387.80 7032 0.1614 383.10 29.801 0.0007 384.70 1911 0.0439 386.30 4621 0.1061 387.90 7169 0.1646 383.20 83.862 0.0019 314.80 2069 0.0475 386.40 4714 0.1100 388.00 7301 0.1676 383.30 153.27 0.0035 384.90 2230 0.0512 386.50 4966 0.1140 388.10 7428 0.1705 383.40 234.76 0.0054 385.00 2393 0.0549 386.60 5137 0.1179 388.20 7550 0.1733 383.50 326.36 0.0075 385.10 2558 0.0587 386.70 5307 0.1218 388.30 7665 0.1760 ' 383.60 426.74 0.0098 385.20 2724 0.0625 386.80 5475 0.1257 388.40 7773 0.1784 383.70 534.86 0.0123 385.30 2893 0.0664 386.90 5642 0.1295 388.50 7873 0.1807� 383.80 649.93 0.0149 385.40 3063 0.0703 387.00 5807 0.1333 388.60 7965 0.1828 383.90 771.25 0.0177 385.50 3234 0.0742 387.10 5970 0.1371 388.70 8046 0.1847 384.00 898.27 0.0206 385.60 3406 0.0782 387.20 6131 0.1407 388.80 8116 0.1863 384.10 1030 0.0237 385.70 3579 0.0822 387.30 6289 0.1444 388.90 8170 0.1876 384.20 1167 0.0268 385.80 3752 0.0861 387.40 6444 0.1479 389.00 8200 0.1882 1 384.30 1309 0.0300 385.90 3926 0.0901 387.50 6597 0.1514 384.40 1454 0.0334 386.00 4100 0.0941 387.60 6745 0.1549 384.50 1603 0.0368 386.10 4274 0.0981 387.70 6891 0.1582 5/7/99 2 : 9 : 11 pm AHBL page 2 USPO Highlands, Renton, Wa . 98027 . 10 DETENTION PIPE SIZING ' K_\CIVIL\YR-1998\98027\DETENTIO______________________________________ STAGE DISCHARGE TABLE ' COMBINATION DISCHARGE ID No. COMB1 ' Description: ORIFICE AND RISER Structure : ORIF Structure : Structure : riserl Structure : Structure : ' STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> STAGE <--DISCHARGE---> (ft) ---cfs-- ------- (ft) ---cfs-- ------- (ft) ---cfs-- ------- (ft) ---cfs-- ------- 113.50 0.0000 385.20 0.2125 386.90 0.4131 388.60 2.8969 383.60 0.0709 385.30 0.3009 387.00 0.5103 388.70 3.4331 383.70 0.1003 385.40 0.3092 387.10 0.5538 388.80 3.7163 383.80 0.1229 385.50 0.3172 387.20 0.5885 388.90 3.9757 383.90 0.1419 385.60 0.3250 387.30 0.6185 389.00 4.2167 384.00 0.1586 385.70 0.3327 387.40 0.6456 389.10 4.4428 384.10 0.1737 385.80 0.3402 387.50 0.6706 389.20 4.6565 384.20 0.1877 385.90 0.3475 387.60 0.6940 389.30 4.8596 384.30 0.2006 386.00 0.3547 387.70 0.7161 389.40 5.0538 384.40 0.2128 386.10 0.3617 387.80 0.7371 389.50 5.2400 314.50 0.2243 386.20 0.3686 387.91 0.7171 389.60 5.4193 ' 384.60 0.2353 386.30 0.3753 388.00 0.7764 389.70 5.5923 384.70 0.2457 386.40 0.3820 388.10 0.7951 389.80 5.7597 384.80 0.2557 386.50 0.3885 388.20 0.8131 389.90 5.9220 384.90 0.2654 386.60 0.3949 388.30 0.9395 390.00 6.0797 385.00 0.2747 386.70 0.4012 388.40 1.4134 385.10 0.2837 386.80 0.4075 L388.50 2.0815 1 ' 5/7/99 2 : 9 : 13 pm AHBL page 3 USPO Highlands, Renton, Wa . 98027 . 10 DETENTION PIPE SIZING K_\CIVIL\YR-1998\98027\DETENTIO-------------------------------------- LEVEL POOL TABLE SUMMARY MATCH INFLOW -STO- -DIS- <-PEAK-> OUTFLOW STORAGE ' <___=====DESCRIPTION==-===__=>--(cfs)--(cfs)-==id=-==id=-<=STAGE>-id---(cfs)-VOL-(cf) DETENTION 2YR RELEAS ......... 0.38 1.34 DETENI COMB1 386.55 1 0.39 5054.31 cf DETENTION 10Y RELEAS ......... 0.80 1.98 DETENI COMB1 388.07 2 0.79 7390,35 cf ' DETENTION 100Y OVERF ......... 0.00 2.69 DETENI COMB1 388.49 3 2.69 7863.76 cf 1 HIGHLANDS POST OFFICE ' 98342.10 ON-SITE OVERFLOW CAPACITY ' Manning Pipe Calculator Given Input Data: Shape ........................... Circular Solving for ..................... Depth of Flow Diameter ........................ 12.0000 in ' Flowrate ........................ 2.6900 cfs �� c Slope ........................... 0.0050 ,-- Manning's n ..................... 0014 Computed Results: Depth .•„•.•......•........................... 2.7477 in Area . 0.7854 ft2 Wetted Area ..................... 0.1356 ft2 ' Wetted Perimeter ................ 11.9750 in Perimeter ....................... 37.6991 in Velocity ........................ 19.8376 fps Hydraulic Radius ..... 1.6306 in Percent Full .................... 22.8 7 i 1 C(-5 Full flow Flowrate .......... 2 393 �j k� Full flow velocity .............. 53 fps 117 �� o till r,, 1 1 ' Exhibit - Comeyance Calculations 1 1 1 1 1 1 1 1 1 1 ' A HBL 4/28/99 1 : 49 : 58 pm AHBL page 1 ' CONVEYANCE CALCULATIONS HIGHLAND POST OFFICE K: \CIVIL\YR 1998\98027\CONVEY ' ----------------------- BASIN SUMMARY tBASIN ID : BAl NAME : SNORKEL LANE-25YEAR\24HR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 . 20 Acres BASEFLOWS : 0 . 00 cfs ' RAINFALL TYPE . . . . : TYPElA PERV IMP PRECIPITATION. . . . : 3 . 40 inches AREA. . : 0 . 00 Acres 0 . 20 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 ' TC. . . . . 0 . 00 min 5 . 00 , min ABSTRACTION COEFF: 0 . 20 PEAK RATE : 0 . 14 cfs VOL: 0 . 05 Ac-ft TIME : 480 min ' BASIN ID : BA2 NAME : WEST ENTRANCE-25YEAR\24HR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 . 24 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : TYPElA PERV IMP PRECIPITATION. . . . : 3 .40 inches AREA. . : 0 . 00 Acres 0 . 24 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 ' TC. . . . . 0 . 00 min 5 . 00 min ABSTRACTION COEFF : 0 . 20 PEAK RATE: 0 . 17 cfs VOL: 0 . 06 Ac-ft TIME : 480 min ' BASIN ID : BA3 NAME : WEST OF BUILDING-25YEAR\24HR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 . 51 Acres BASEFLOWS : 0 . 00 cfs ' RAINFALL TYPE. . . . : TYPElA PERV IMP PRECIPITATION. . . . : 3 . 40 inches AREA. . : 0 . 00 Acres 0 . 51 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 ' TC. . . . . 0 . 00 min 5 . 00 min ABSTRACTION COEFF : 0 . 20 PEAK RATE : 0 . 36 cfs VOL: 0 . 13 Ac-ft TIME . 480 min ' BASIN ID: BA4 NAME : EAST OF INFIL-25YEAR\24HR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 . 56 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : TYPElA PERV IMP PRECIPITATION. . . . : 3 .40 inches AREA. . : 0 . 00 Acres 0 . 56 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 TC. . . . : 0 . 00 min 5 . 00 min ' ABSTRACTION COEFF: 0 . 20 PEAK RATE : 0 .40 cfs VOL: 0 . 15 Ac-ft TIME: 480 min 4/28/99 1 :49 : 58 pm AHBL page 2 HIGHLAND POST OFFICE CONVEYANCE CALCULATIONS ' K_\CIVIL\YR-1998\98027\CONVEY________________________________________ BASIN SUMMARY BASIN ID : BA5 NAME : SOUTH OF DOCK-25YEAR\24HR SBUH METHODOLOGY TOTAL AREA. . . . . . 0 . 16 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : TYPElA PERV IMP PRECIPITATION. . . . : 3 . 40 inches AREA. . : 0 . 00 Acres 0 . 16 Acres ' TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 TC. . . . : 0 . 00 min 5 . 00 min ABSTRACTION COEFF: 0 . 20 ' PEAK RATE : 0 . 11 cfs VOL: 0 . 04 Ac-ft TIME : 480 min BASIN ID: BA6 NAME : EAST ENTRANCE-25YEAR\24HR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 . 56 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : TYPElA PERV IMP PRECIPITATION. . . . : 3 .40 inches AREA. . : 0 . 00 Acres 0 . 56 Acres ' TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 TC. . . . . 0 . 00 min 5 . 00 min ABSTRACTION COEFF : 0 . 20 ' PEAK RATE : 0 . 40 cfs VOL: 0 . 15 Ac-ft TIME : 480 min BASIN ID: BA7 NAME : SOUTH OF BA5-25YEAR\24HR ' SBUH METHODOLOGY TOTAL AREA. . . . . 0 . 02 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : TYPElA PERV IMP PRECIPITATION. . . . : 3 . 40 inches AREA. . : 0 . 00 Acres 0 . 02 Acres ' TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 TC. . . . : 0 . 00 min 5 . 00 min ABSTRACTION COEFF: 0 . 20 ' PEAK RATE : 0 . 01 cfs VOL: 0 . 01 Ac-ft TIME : 480 min BASIN ID: BA8 NAME . EAST OF DOCKS-25YEAR\24HR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 . 25 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : TYPElA PERV IMP PRECIPITATION. . . . : 3 .40 inches AREA. . : 0 . 00 Acres 0 . 25 Acres ' TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 TC. . . . . 0 . 00 min 5 . 00 min ABSTRACTION COEFF : 0 . 20 PEAK RATE : 0 . 18 cfs VOL: 0 . 07 Ac-ft TIME : 480 min 1 4/28/99 1 : 49 : 58 pm AHBL page 3 HIGHLAND POST OFFICE CONVEYANCE CALCULATIONS ' K: \CIVIL\YR-1998\98027\CONVEY________________________________________ BASIN SUMMARY BASIN ID : BA9 NAME : SOUTHEAST PARKING-25YEAR\24HR ' SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 . 56 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : TYPElA PERV IMP PRECIPITATION. . . . : 3 . 40 inches AREA. . : 0 . 00 Acres 0 . 56 Acres 1 TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 TC. . . . . 0 . 00 min 5 . 00 min ABSTRACTION COEFF: 0 . 20 1 PEAK RATE : 0 .40 cfs VOL: 0 . 15 Ac-ft TIME : 480 min i i 1 1 i 1 1 1 1 1 5/10/99 3 : 36 :49 pm AHBL page 1 ' CONVEYANCE CALCULATIONS HIGHLAND POST OFFICE K: \CIVIL\YR 1998\98027\CONVEY ' REACH SUMMARY ' Network Reach R1 REACH <-AREA> <-DIA> LENGTH SLOPE < n > DSGN Q % PIPE Ndepth %Depth Vact Vfull C_Area ' ID (Ac) (ft) (ft) ft/ft ------ (cfs) ------ (ft) ------ (fps) (fps) L1 0.20 1.00 85.86 0.0437 0.0140 0.14 1.90 0.10 9.89 3.52 9.74 BA1 Confluence with Network R4 L2 0.44 1.00 137.80 0.0049 0.0140 0.31 12.41 0.25 24.68 2.06 3.28 L3 0.95 1.00 77.00 0.0050 0.0140 0.67 26.63 0.37 36.63 2.58 3.30 BA3 ' Network Reach R2 REACH <-AREA> <-DIA> LENGTH SLOPE < n > DSGN Q % PIPE Ndepth %Depth Vact Vfull C_Area ' ID (Ac) (ft) (ft) ft/ft ------ (cfs) ------ (ft) ------ (fps) (fps) L5 0.16 1.00 152.83 0.0050 0.0140 0.11 4.50 0.15 14.96 1.54 3.29 BA5 Network Reach R3 REACH <-AREA> <-DIA> LENGTH SLOPE < n > DSGN Q % PIPE Ndepth %Depth Vact Vfull C_Area ------ID----(Ac)---(ft)=====(ft)--ft/ft =========(cfs) (ft) (fps)===(fps)====___ ----------------------- L6 0.56 1.00 241.33 0.0059 0.0140 0.40 14.42 0.27 26.63 2.36 3.59 BA6 Network Reach R4 ' REACH <-AREA> <-DIA> LENGTH SLOPE < n > DSGN Q % PIPE Ndepth %Depth Vact Vfull C_Area ID (Ac) (ft) (ft) ft/ft ------ (cfs) ------ (ft) ------ (fps) (fps) L10 0.24 1.00 48.11 0.0052 0.0140 0.17 6.60 0.18 18.04 1.76 3.36 BA2 Network Reach R5 ' REACH <-AREA> <-DIA> LENGTH SLOPE < n > DSGN Q % PIPE Ndepth %Depth Vact Vfull C_Area ID (Ac) (ft) (ft) ft/ft - (cfs) (ft) (fps) (fps) L4 0.56 1.00 85.26 0.0177 0.0140 0.40 8.34 0.20 20.24 3.48 6.21 BA4 Confluence with Network R2 L7 0.74 1.00 64.87 0.0051 0.0140 0.52 20.56 0.32 31.96 2.42 3.33 BA7 L8 0.99 1.00 91.29 0.0048 0.0140 0.70 28.26 0.38 37.83 2.57 3.24 BA8 ' Confluence with Network R3 L9 2.11 1.00 60.00 0.0050 0.0140 1.49 59.14 0.58 57.92 3.16 3.30 BA9 ' 5/10/99 3 : 36 : 49 pm AHBL page 2 HIGHLAND POST OFFICE CONVEYANCE CALCULATIONS K_\CIVIL\YR-1998\98027\CONVEY________________________________________ STRUCTURE REPORT PROPOSED STRUCTURE REACH ID No . CB1 ' Location SNORKEL LANE North 18096:2 . 3802 Str Type TYPE 1 East 1312221 . 1138 Str Cat Catch Basin Rim Elev 394 . 5000 ' Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 390 . 0000 Cont Area : BA1 Hgrade El : 0 . 0000 ft Bend. . . . . : No special shape ' Ent type . : Area/sump : Ent Loss : 0 . 000 Exit : 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 ' Reach <Invert> <Diam> < n > <End> Ll 391 . 500 12 . 00 0 . 014 Upper PROPOSED STRUCTURE REACH ID No. CB12 Location WEST DRIVEWAY North 180975 . 6399 ' Str Type TYPE 1 East 1312136 . 2818 Str Cat Catch Basin Rim Elev 393 . 4400 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El . 386 . 2500 Cont Area: Hgrade El : 0 . 0000 ft ' Bend. . . . . : No special shape Ent type . : Area/sump : Ent Loss : 0 . 000 Exit : 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 ' Reach <Invert> <Diam> < n > <End> Ll 387 . 750 12 . 00 0 . 014 Lower ' L10 387 . 750 12 . 00 0 . 014 Lower L2 387 . 750 12 . 00 0 . 014 Upper ' PROPOSED STRUCTURE REACH ID No. CB23W Location : WEST ENTRANCE-BACKWATER North 180997 . 7091 ' Str Type : TYPE 1 East 1312093 . 5369 Str Cat : Catch Basin Rim Elev 391 . 3100 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El . 385 . 5000 Cont Area: BA2BW Hgrade El : 388 . 0398 ft ' Bend. . . . . : No special shape Ent type . : Area/sump: Ent Loss : 0 . 001 Exit : 0 . 003 App Vel : 0 . 001 Junct : 0 . 000 Bend: 0 . 001 Reach <Invert> <Diam> < n > <End> L1BW 387 . 000 12 . 00 0 . 012 Lower ' L2BW 387 . 000 12 . 00 0 . 012 Upper 5/10/99 3 : 36 :49 pm AHBL page 3 HIGHLAND POST OFFICE CONVEYANCE CALCULATIONS K: \CIVIL\YR_1998\98027\CONVEY STRUCTURE REPORT PROPOSED STRUCTURE REACH ID No. CB3 ILocation WEST OF BUILDING North 180841 . 9598 Str Type TYPE 1 East 1312102 . 8427 Str Cat Catch Basin Rim Elev 393 . 7900 ' Area/sump: 0 . 00 sf/1 . 50 ft Bottom El : 385 . 5700 Cont Area: BA3 Hgrade El : 0 . 0000 ft Bend. . . . . : No special shape ' Ent type . : Area/sump : Ent Loss : 0 . 000 Exit : 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 ' Reach <Invert> <Diam> < n > <End> L3 387 . 070 12 . 00 0 . 014 Upper L2 387 . 070 12 . 00 0 . 014 Lower PROPOSED STRUCTURE REACH ID No. CB4 Location EAST OF INFILTRATION North 180655 . 3192 Str Type TYPE 1 East 1312126 . 8835 Str Cat Catch Basin Rim Elev 392 . 4000 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 387 . 9000 ' Cont Area : BA4 Hgrade El : 0 . 0000 ft Bend. . . . . : No special shape Ent type. : . Area/sump: Ent Loss : 0 . 000 Exit : 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 Reach <Invert> <Diam> < n > <End> ' L4 389 . 400 12 . 00 0 . 014 Upper PROPOSED STRUCTURE REACH ID No . CB5 Location TRENCH DRAIN AT TRUCK DOCK North 180754 . 1045 Str Type TYPE 1 East 1312194 . 9515 ' Str Cat Catch Basin Rim Elev 391 . 6500 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 387 . 1500 Cont Area : BA5 Hgrade El : 0 . 0000 ft ' Bend. . . . . : No special shape Ent type . : Area/sump : Ent Loss . 0 . 000 Exit . 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 Reach <Invert> <Diam> < n > <End> L5- 388 . 650 12 . 00 0 . 014 Upper 5/10/99 3 : 36 :49 pm AHBL page 4 HIGHLAND POST OFFICE CONVEYANCE CALCULATIONS ' K_\CIVIL\YR-1998\98027\CONVEY________________________________________ STRUCTURE REPORT PROPOSED STRUCTURE REACH ID No. CB6 Location EAST OF BUILDGING North 180840 . 4457 Str Type TYPE 1 East 1312352 . 1768 Str Cat Catch Basin Rim Elev 393 . 5500 ' Area/sump: 0 . 00 sf/1 . 50 ft Bottom El : 387 . 0500 Cont Area: BA6 Hgrade El : 0 . 0000 ft Bend. . . . . : No special shape Ent type . : Area/sump : Ent Loss : 0 . 000 Exit : 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 Reach <Invert> <Diam> < n > <End> L6 388 . 550 12 . 00 0 . 014 Upper PROPOSED STRUCTURE REACH ID No. CB7 Location SOUTH SIDE OF TRUCK DOCK North 180601 . 2919 Str Type TYPE 1 East 1312192 . 8398 ' Str Cat Catch Basin Rim Elev 392 . 1900 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 386 . 3900 Cont Area: BA7 Hgrade El : 0 . 0000 ft Bend. . . . . : No special shape Ent type . : Area/sump : Ent Loss : 0 . 000 Exit : 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 ' Reach <Invert> <Diam> < n > <End> L7 387 . 890 12 . 00 0 . 014 Upper L4 387 . 890 12 . 00 0 . 014 Lower L5 387 . 890 12 . 00 0 . 014 Lower PROPOSED STRUCTURE REACH ID No . CB8 Location SOUTH PARKING LOT North 180600 .3955 Str Type TYPE 1 East 1312257 . 7055 Str Cat Catch Basin Rim Elev 392 . 5600 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 386 . 0600 Cont Area: BA8 Hgrade El : 0 . 0000 ft ' Bend. . . . . : No special shape Ent type . : Area/sump: Ent Loss : 0 . 000 Exit : 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 1 Reach <Invert> <Diam> < n > <End> L7 387 . 560 12 . 00 0 . 014 Lower L8 387 , 560 12 . 00 0 . 014 Upper 5/10/99 3 : 36 :49 pm AHBL page 5 HIGHLAND POST OFFICE CONVEYANCE CALCULATIONS K_\CIVIL\YR-1998\98027\CONVEY________________________________________ STRUCTURE REPORT PROPOSED STRUCTURE REACH ID No. CB9 Location OUTLET TO SOUTHERN BIOSWALE North 180599 . 1361 Str Type TYPE 1 East 1312348 . 9842 Str Cat Catch Basin Rim Elev 392 . 5500 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 385 . 6200 Cont Area: BA9 Hgrade El : 0 . 0000 ft Bend. . . . . : No special shape ' Ent type . : Area/sump : Ent Loss : 0 . 000 Exit : 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 Reach <Invert> <Diam> < n > <End> L9 387 . 120 12 . 00 0 . 014 Upper L8 387 . 120 12 . 00 0 . 014 Lower L6 387 . 120 12 . 00 0 . 014 Lower ' Exhibit 3 - Backwater Calculations 1 1 1 1 1 1 1 1 � Ar+eL ' 5/10/99 4 : 7 : 19 pm AHBL page 1 HIGHLAND POST OFFICE BACKWATER/HYDRAULIC GRADE CALCULATIONS K: \CIVIL\YR 1998\98027\CONVEY REACH SUMMARY Network Reach RDUM1 ' REACH <-AREA> <-DIA> LENGTH SLOPE < n > DSGN Q t PIPE Ndepth gDepth Vact Vfull C_Area ID (Ac) (ft) (ft) -ft/ft ------ -(cfs) ------ -(ft) ------ -(fps) (fps) L1BW 0.20 1.00 85.86 0.0437 0.0120 0.16 1.87 0.10 9.83 4.08 11.37 BA1BW Confluence with Network RDUM4 L2BW 0.44 1.00 137.80 0.0049 0.0120 0.36 12.25 0.25 24.52 2.40 3.82 L3BW 0.95 1.00 57.00 0.0050 0.0120 0.77 26.28 0.36 36.38 3.00 3.85 BA3BW Network Reach RDUM2 REACH <-AREA> <-DIA> LENGTH SLOPE < n > DSGN Q t PIPE Ndepth %Depth Vact Vfull C_Area ' ID (Ac) (ft) (ft) ft/ft ------ (cfs) ------ (ft) ------ (fps) (fps) L5BW 0.16 1.00 152.83 0.0050 0.0120 0.13 4.44 0.15 14.87 1.79 3.84 BASBW Network Reach RDUM3 REACH <-AREA> <-DIA> LENGTH SLOPE < n > DSGN Q % PIPE Ndepth gDepth Vact Vfull C Area ID (Ac) (ft) (ft) ft/ft ------ (cfs) ------ (ft) ------ (fps) (fps) L6BW 0.56 1.00 241.33 0.0059 0.0120 0.46 14.23 0.26 26.45 2.74 4.19 BA6BW Network Reach RDUM4 REACH <-AREA> <-DIA> LENGTH SLOPE < n > DSGN Q % PIPE Ndepth %Depth Vact Vfull C Area ID (Ac) (ft) (ft) ft/ft ------ (cfs) ------ (ft) ------ (fps) (fps) ' L10BW 0.24 1.00 48.11 0.0052 0.0120 0.20 6.51 0.18 17.93 2.05 3.92 BA2BW Network Reach RDUMS ' REACH <-AREA> <-DIA> LENGTH SLOPE < n > DSGN Q t PIPE Ndepth $Depth Vact Vfull C_Area ID (Ac) (ft) (ft) ft/ft ------ (cfs) ------ (ft) ------ (fps) (fps) ' L4BW 0.56 1.00 85.26 0.0177 0.0120 0.46 8.23 0.20 20.11 4.05 7.24 BA4BW Confluence with Network RDUM2 L7BW 0.74 1.00 64.87 0.0051 0.0120 0.60 20.30 0.32 31.74 2.81 3.88 BA7BW LBBW 0.99 1.00 91.29 0.0048 0.0120 0.81 27.90 0.38 37.56 2.99 3.78 BABBW Confluence with Network RDUM3 L9BW 2.11 1.00 70.00 0.0050 0.0120 1.72 58.38 0.57 57.45 3.68 3.85 BASBW r r 5/10/99 4 : 7 : 19 pm AHBL page 2 HIGHLAND POST OFFICE BACKWATER/HYDRAULIC GRADE CALCULATIONS rK_\CIVIL\YR-1998\98027\CONVEY________________________________________ STRUCTURE REPORT r PROPOSED STRUCTURE REACH ID No . CB12BW r Location WEST DRIVEWAY-BACKWATER North 180975 . 6399 Str Type TYPE 1 East 1312136 . 2818 Str Cat Catch Basin Rim Elev 393 . 4400 r Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 386 . 2500 Cont Area : Hgrade El : 389 . 0400 ft Bend. . . . . : No special shape r Ent type . : Area/sump: Ent Loss : 0 . 001 Exit : 0 . 003 App Vel : 0 . 001 Junct : 0 . 000 Bend: 0 . 001 Reach <Invert> <Diam> < n > <End> r L1BW 387 . 750 12 . 00 0 . 012 Lower L10BW 387 . 750 12 . 00 0 . 012 Lower L2BW 387 . 750 12 . 00 0 . 012 Upper i PROPOSED STRUCTURE REACH ID No. C1312W Location SNORKEL LANE-BACKWATER North 180962 . 3802 Str Type TYPE 1 East 1312221 . 1138 Str Cat Catch Basin Rim Elev 394 . 5000 ' Area/sump: 0 . 00 sf/1 . 50 ft Bottom El : 390 . 0000 Cont Area : BA1BW Hgrade El : 391 . 5498 ft Bend. . . . . : No special shape ' Ent type . : Area/sump : Ent Loss : 0 . 000 Exit : 0 . 001 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 Reach <Invert> <Diam> < n > <End> L1BW 391 . 500 12 . 00 0 . 012 Upper PROPOSED STRUCTURE REACH ID No. C32SW Location WEST ENTRANCE-BACKWATER North 180997 . 7091 ' Str Type TYPE 1 East 1312093 . 5369 Str Cat Catch Basin Rim Elev 391 . 3100 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 386 . 5000 Cont Area : BA2BW Hgrade El : 389 . 0412 ft r Bend. . . . . : No special shape Ent type . : Area/sump : Ent Loss : 0 . 000 Exit : 0 . 001 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 ' Reach <Invert> <Diam> < n > <End> L103W 388 . 000 12 . 00 0 . 012 Upper r r 5/10/99 4 : 7 : 19 pm AHBL page 3 HIGHLAND POST OFFICE BACKWATER/HYDRAULIC GRADE CALCULATIONS ' K: \CIVIL\YR_1998\98027\CONVEY STRUCTURE REPORT PROPOSED STRUCTURE REACH ID No. CB3BW Location WEST OF BUILDING-BACKWATER North 180841 . 9598 Str Type TYPE 1 East 1312102 . 8427 Str Cat Catch Basin Rim Elev 393 . 7900 ' Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 385 . 5700 Cont Area: BA3BW Hgrade El : 389 . 0258 ft Bend. . . . . : No special shape ' Ent type . : Area/sump: Ent Loss : 0 . 003 Exit : 0 . 015 App Vel : 0 . 003 Junct : 0 . 002 Bend: 0 . 004 Reach <Invert> <Diam> < n > <End> L3BW 387 . 070 12 . 00 0 . 012 Upper L2BW 387 . 070 12 . 00 0 . 012 Lower PROPOSED STRUCTURE REACH ID No. C34BW Location EAST OF INFILTRATION-BACKWATER North 180655 . 3192 Str Type TYPE 1 East 1312126 . 8835 Str Cat Catch Basin Rim Elev 392 .4000 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 387 . 9000 ' Cont Area : BA42W Hgrade El : 389 . 5465 ft Bend. . . . . : No special shape Ent type . : Area/sump : Ent Loss : 0 . 001 Exit : 0 . 005 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 Reach <Invert> <Diam> < n > <End> L4BW 389 ,400 12 . 00 0 . 012 Upper PROPOSED STRUCTURE REACH ID No. CB5BW Location : TRENCH DRAIN AT TRUCK DOCK-BW North 180754 . 1045 Str Type : TYPE 1 East 1312194 . 9515 ' Str Cat : Catch Basin Rim Elev 391 . 6500 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 387 . 1500 Cont Area: BA5BW Hgrade El : 389 . 2017 ft Bend. . . . . : No special shape Ent type . : Area/sump : Ent Loss : 0 . 000 Exit : 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 ' Reach <Invert> <Diam> < n > <End> L5BW 388 . 650 12 . 00 0 . 012 Upper ' 5/10/99 4 : 7 : 19 pm AHBL page 4 HIGHLAND POST OFFICE BACKWATER/HYDRAULIC GRADE CALCULATIONS ' K: \CIVIL\YR_1998\98027\CONVEY STRUCTURE REPORT PROPOSED STRUCTURE REACH ID No. C363W ' Location EAST OF BUILDGING-BACKWATER North 180840 . 4457 Str Type TYPE 1 East 1312352 . 1768 Str Cat Catch Basin Rim Elev 393 . 5500 ' Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 387 . 0500 Cont Area: BA6BW Hgrade El : 389 . 1835 ft Bend. . . . . : No special shape ' Ent type . : Area/sump: Ent Loss : 0 . 001 Exit : 0 . 005 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 Reach <Invert> <Diam> < n > <End> ' L6BW 388 . 550 12 . 00 0 . 012 Upper PROPOSED STRUCTURE REACH ID No. CB7BW Location : SOUTH SIDE OF TRUCK DOCK-BW North 180601 . 2919 ' Str Type : TYPE 1 East 1312192 . 8398 Str Cat : Catch Basin Rim Elev 392 . 1900 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El . 386 . 3900 Cont Area : BA7BW Hgrade El : 389 . 2000 ft 1 Bend. . . . . : No special shape Ent type . : Area/sump: Ent Loss : 0 . 002 Exit : 0 . 009 App Vel : 0 . 005 Junct : 0 . 001 Bend: 0 . 002 Reach <Invert> <Diam> < n > <End> L7BW 387 . 890 12 . 00 0 . 012 Upper ' L4BW 387 * 190 12 . 00 0 . 012 Lower L53W 387 . 890 12 . 00 0 . 012 Lower ' PROPOSED STRUCTURE REACH ID No. CBBBW Location SOUTH PARKING LOT-BACKWATER North 180600 . 3955 ' Str Type TYPE 1 East 1312257 . 7055 Str Cat Catch Basin Rim Elev 392 . 5600 Area/sump : 0 . 00 sf/1 . 50 ft Bottom El . 386 . 0600 Cont Area: BABBW Hgrade El : 389 . 1859 ft ' Bend. . . . . : No special shape Ent type . : Area/sump: Ent Loss : 0 . 003 Exit : 0 . 016 App Vel : 0 . 009 Junct : 0 . 002 Bend: 0 . 000 ' Reach <Invert> <Diam> < n > <End> L7BW 387 . 560 12 . 00 0 . 012 Lower ' LBBW 387 . 560 12 . 00 0 . 012 Upper ' 5/10/99 4 : 7 : 19 pm AHBL page 5 HIGHLAND POST OFFICE BACKWATER/HYDRAULIC GRADE CALCULATIONS ' K: \CIVIL\YR_1998\98027\CONVEY STRUCTURE REPORT ' PROPOSED STRUCTURE REACH ID No. CB9BW ' Location OUTLET TO SOUTHERN BIOSWALE North 180599 . 1361 Str Type TYPE 1 East 131234-8 . 9842 Str Cat Catch Basin Rim Elev 392 . 5500 ' Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 385 . 6200 Cont Area : BA9BW Hgrade El : 389 . 1500 ft Bend. . . . . : No special shape Ent type . : Area/sump : ' Ent Loss : 0 . 015 Exit : 0 . 074 App Vel : 0 . 016 Junct : 0 . 010 Bend: 0 . 022 Reach <Invert> <Diam> < n > <End> ' L9BW 387 . 120 12 . 00 0 . 012 Upper L83W 387 . 120 12 . 00 0 . 012 Lower L613W 387 . 120 12 . 00 0 . 012 Lower Exhibit 4 - Water Quality Calculations 1 1 j�HBL Project /r/1dS /(ups -��lfe No. VP of iAHBL Subject?, S'Wc%/e �C `�"�S Phone ulations ❑ Fax Withlfo Fax# ❑ Memorandum 1 Address #Faxed Pages ❑ Meeting Minutes ❑Telephone Memo 1 Date: BY i 2 �n -Z (Je;n�f J ! / t� +cov\ 3 3 1 .n • 1 Copies to: Ll 1 1 1 y4r c5 1 - 1 1/cSICe'1 3�� Z I vim^f'!at 2215 N.30th Street Z 6 a Suite 300 1 Tacoma,WA 98403 Old Town Historical District 253/383-2422 253/383-2572 FAX If this does not meet with your understanding,please contact us in writing within seven days.THANK YOU. 4/30/99 4 : 50 : 9 pm AHBL page 1 USPO Highlands, Renton, Wa . 98027 . 10 Infiltration Trench K: \CIVIL\YR 1998\98027\BIOSWALE ' BASIN SUMMARY=====_______________________ BASIN ID: BA1 NAME : BASIN AREA-BIOSWALE WEST SIDE SBUH METHODOLOGY TOTAL AREA. . . . . . . : 1 . 05 Acres BASEFLOWS : 0 . 00 cfs ' RAINFALL TYPE. . . . : TYPEIA PERV IMP PRECIPITATION. . . . : 2 . 00 inches AREA. . : 0 . 00 Acres 1 . 05 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 ' TC. . . . : 0 . 00 min 5 . 00 min ABSTRACTION COEFF : 0 . 20 impTcReach - Sheet L: 120 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0200 ' impTcReach - Channel L: 200 . 00 kc :42 . 00 s : 0 . 0050 PEAK RATE : 0 . 43 cfs VOL: 0 . 16 Ac-ft TIME : 480 min BASIN ID: BAl-100 NAME : BIOSWALE WEST SIDE-conveyance ' SBUH METHODOLOGY TOTAL AREA. . . . . . . : 1 . 05 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : TYPEIA PERV IMP ' PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0 . 00 Acres 1 . 05 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 TC. . . . . 0 . 00 min 5 . 00 min ' ABSTRACTION COEFF : 0 . 20 impTcReach - Sheet L: 120 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0200 impTcReach - Channel L: 200 . 00 kc :42 . 00 s : 0 . 0050 PEAK RATE : 0 . 86 cfs VOL: 0 . 32 Ac-ft TIME : 480 min ' BASIN ID: BA2 NAME: BASIN AREA-BIOSWALE SOUTH SIDE SBUH METHODOLOGY ' TOTAL AREA. . . . . . . : 2 . 26 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : TYPEIA PERV IMP PRECIPITATION. . . . : 2 . 00 inches AREA. . : 0 . 00 Acres 2 . 26 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 ' TC. . . . : 0 . 00 min 5 . 00 min ABSTRACTION COEFF: 0 . 20 impTcReach - Sheet L: 120 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0200 ' impTcReach - Channel L: 200 . 00 kc :42 . 00 s : 0 . 0050 PEAK RATE : 0 . 91 cfs VOL: 0 . 33 Ac-ft TIME : 480 min ' 4/30/99 4 : 50 : 9 pm AHBL page 2 USPO Highlands, Renton, Wa . 98027 . 10 Infiltration Trench K_\CIVIL\YR-1998\98027\BIOSWALE-------------------------------------- BASIN SUMMARY ' BASIN ID: BA2-100 NAME : BIOSWALE SOUTH SIDE-conveyance SBUH METHODOLOGY ' TOTAL AREA. . . . . . . : 2 . 26 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : TYPEIA PERV IMP PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0 . 00 Acres 2 . 26 Acres TIME INTERVAL. . . . . 10 . 00 min CN. . . . : 0 . 00 98 . 00 TC. . . . : 0 . 00 min 5 . 00 min ABSTRACTION COEFF : 0 . 20 impTcReach - Sheet L: 120 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0200 ' impTcReach - Channel L: 200 . 00 kc : 42 . 00 s : 0 . 0050 PEAK RATE : 1 . 84 cfs VOL: 0 . 69 Ac-ft TIME : 480 min Highland Post Office-98027. 10 South Bioswale ' Size Biofiltration Swale-Biofiltration Calculation t Flow 0.58 cfs (6 month \ 24 hr storm) slope (s) 1.00% (bottom slope for for biofiltration design) depth (y) 0.33 ft. Mannings n 0.07 Sides (z) 3 (3 to 1 side slope preferred) Actual Length 115 ft. (desired length is 200 ft.) Required bottom width (b) calculation 2 3x� (mannings equation) Q = (1.49/ n) x A x R ' A = (b+ zy)y R = A /(b+ 2y 1+ z ) "b" is solved for using a computer spreadsheet function to obtain a trail and error solution of b = 1.24 feet, for a desired length of 200 feet. ' check Q = 0.580 cfs, OK same as given Velocity = 0.787 fps <1.5 OK Residence Time = 4.2 mins. 0.737 Find bottom width required if actual length is 115 ft. (Minimum length is 50 feet.) For equal residence time: Trial and error solution, required b = 2.90 feet Velocity = 0.45 fps <1.5 OK Residence Time = 4.2 mins. OK For equal Surface Areas: ' Required water Surface area= (2zy+b) x 200 feet 645 SF Actual bottom width required = (Des. Surf. Area)/(length (actual)) - 2zy b = 3.63ft. ' NOTE: EQUAL SURFACE AREA REQUIREMENT NOT USED BY DOE Filename BIOSWALE-SOUTH rls Tab BIOSW,ALE 05107199 11:04 AM Highland Post Office-98027. 10 West Bioswale Size Biofiltration Swale-Biofiltration Calculation Flow 0.28 cfs (6 month \ 25 hr storm) slope (s) 1.00% (bottom slope for for biofiltration design) depth (y) 0.33 ft. Mannings n 0.07 Sides (z) 3 (3 to 1 side slope preferred) Actual Length 65 ft. (desired length is 200 ft.) ' Required bottom width (b) calculation Q = (1.49/ n) x A x R2/3x"JS (mannings equation) A -- (b+ zY)Y R = A/(b+ 2y l+7) "b" is solved for using a computer spreadsheet function to obtain a trail and error solution of b = 0.26 feet, for a desired length of 200 feet. check Q = 0.280 cfs, OK same as given ' Velocity = 0.676 fps <1.5 OK Residence Time = 4.9 mins. 0.414 Find bottom width required if actual length is 65 ft. (Minimum length is 50 feet.) For equal residence time: Trial and error solution, required b = 1.96 feet Velocity = 0.29 fps <1.5 OK Residence Time = 3.8 mins. OK ' For equal Surface Areas: Required water Surface area = (2zy+b) x 200 feet = 449 SF Actual bottom width required = (Des. Surf. Area)/(length (actual)) - 2zy b = 4.93 ft. NOTE: EQUAL SURFACE CRITERIA NOT USED BY DOE ' Filename B10SWALE-WEST.xIs Tab B10SWALE 0510 7199 1 1:16 AM ' HIGHLAND POST OFFICE 98027.10 CONVEYANCE STABILITY CHECK WEST BIOSWALE Channel Calculator ' Given Input Data: Shape ........................... Trapezoidal ' Solving for ..................... Depth of Flow Flowrate ........................ 0.8600 cfs Slope ........................... 0.0100 ft/ft ' Manning's n ..................... 0.0300 Height .......................... 15.0000 in Bottom width .................... 24.0000 in ' Left slope ...................... 0.3300 ft/ft Right slope ..................... 0.3300 ft/ft Computed Results Depth ......... ................. 2.9163 in OK Velocity ........................ 1.7011 fps LESS THAN 5 FPS, OK Flow area ....................... 0.5055 ft2 Flow perimeter .................. 30.1420 in ' Hydraulic radius ................ 2.4152 in Top width ....................... 25.9248 in Area ............................ 3.0156 ft2 ' Perimeter ... 55.5913 in ....................Percent full 19.4421 % 1 1 HIGHLAND POST OFFICE ' 98027.10 CONVEYANCE STABILITY CHECK SOUTH BIO-SWALE Channel Calculator ' Given Input Data: Shape ........................... Trapezoidal Solving for ............... ...... Depth of Flow Flowrate ........................ 1.8400 cfs Slope ........................... 0.0100 ft/ft Manning's n ..................... 0.0300 ' Height .......................... 15.0000 in Bottom width .................... 36.0000 in ' Left slope ....:.::::::.:::::.:: 0.3300 ft/ft Right slope . 0.3300 ft/ft ' Computed Results: Depth........................... 3.5799 in OK Velocity ........................ 1.9906 fps LESS THAN 5 FPS, OK ' Flow area ....................... 0.9243 ft2 Flow perimeter .................. 43.5396 in Hydraulic radius 3.0571 in ' Top width ....................... 38.3627 in Area ............................ 4.2656 ft2 Perimeter ....................... 67.5913 in ' Percent full .................... 23.8660 % ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TABLE 4.3.7E VALUES OF THE ROUGHNESS COEFFICIENT, "n" Type of Channel Manning's Type of Channel Manning's and Description `n" and Description "n" (Normal) (Normal) ' A. Constructed Channels 6. Sluggish reaches, weedy 0.070 a. Earth, straight and uniform deep pools 1. Clean, recently completed 0.018 7. Very weedy reaches, deep 0.100 ' 2. Gravel, uniform section,. 0.025 pools, or floodways with clean heavy stand of timber and 3. With short grass, few 0.027 underbrush weeds b. Mountain streams, no vegetation b. Earth, winding and sluggish 0.025 in channel, banks usually steep, 1. No vegetation 0.025 trees and brush along banks 2. Grass, some weeds 0.030 submerged at high stages 3. Dense weeds or aquatic 1. Bottom: gravel, cobbles, and 0.040 plants In deep channels 0.035 few boulders 4. Earth bottom and rubble 2. Bottom: cobbles with large 0.050 sides 0.030 boulders ' S. Stony bottom and weedy B-2 Flood plains banks 0.035 a. Pasture, no brush 6. Cobble bottom and clean 1. Short grass 0.030 ' sides 0.040 2. High grass 0.035 c. Rock lined b. Cultivated areas 1. Smooth and uniform 0.035 1. No crop 0.030 2. Jagged and irregular 0.040 2. Mature row crops 0.035 ' d. Channels not maintained, 3. Mature field crops 0.040 weeds and brush uncut c. Brush 1. Dense weeds, high as flow 1. Scattered brush, heavy 0.050 depth 0.080 weeds 2. Clean bottom, brush on 2. Light brush and trees 0.060 sides 0.050 3. Medium to dense brush 0.070 3. Same, highest stage of 4. Heavy, dense brush 0.100 flow 0.070 d. Trees ' 4. Dense brush, high stage 1. Dense willows, straight 0.150 B. Natural Streams 0.100 2. Cleared land with tree 0.040 13-1 Minor streams (top width at stumps, no sprouts ' flood stage < 100 ft.) 3. Same as above, but with 0.060 a. Streams on plain heavy growth of sprouts 1. Clean, straight, full stage 4. Heavy stand of timber, a few 0.100 no rifts or deep pools 0.030 down trees, little ' 2. Same as above, but more undergrowth, flood stage stones and weeds 0.035 below branches 3. Clean, winding, some 5. Same as above, but with 0.120 pools and shoals 0.040 flood stage reaching ' 4. Same as above, but some branches weeds 0.040 5. Same as 4, but more stones 0.050 Note, these "n" values are "normal" values for use in analysis of channels. For conservative design for ' channel capacity the "maximum" values listed in other references should be considered. For channel bank stability the minimum values should be considered. 4.3.7-7 1/90 r r i r r rExhibit 5 - Off-site Runoff - Conveyance Calculations r r r r r r r r r r r r r HIGHLAND POST OFFICE 98027.10 OFF-SITE CONVEYANCE CAPACITY ' Manning Pipe Calculator ' Given Input Data: Shape ........................... Circular ' Solving for ..................... Depth of Flow Diameter . 12.0000 in Flowrate 3.4300 cfs. —�T�L•� �r�,•� L � ......................... t. ' Slope ........................ .. 0.0 4;� ;' �c�rr n� Manning's n ............. 0014 , Computed Results: Depth 3.1049 in P Area ............................ 0.7854 ft2 Gj ' Wetted Area ..................... 0.1612 ft2 \` e Wetted Perimeter ................ 12.8073 in Perimeter ....................... 37.6991 in ' Velocity ........................ 21.2830 fps Hydraulic Radius ................ 1.8120 in Percent Full' 25.8743 % 2� S crS ' Full flow Flowrate .............. 23.3933 cf ,j, r�N Full flow velocit 29.7853 f s r i n y .............. p 2 C) 1 ' 5/3/99 4 : 28 :44 pm AHBL page 1 HIGHLAND POST OFFICE OFF-SITE BYPASS CONVEYANCE CALCULATIONS ' K: \CIVIL\YR_1998\98027\CONVEY________________________________________ BASIN SUMMARY BASIN ID: BAOS1 NAME : UPSTREAM CONTRIB-100YEAR\24HR SBUH METHODOLOGY ' TOTAL AREA. . . . . . . : 0 . 99 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE. . . . : TYPEIA PERV IMP PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0 . 79 Acres 0 . 20 Acres TIME INTERVAL- . : 10 . 00 min CN. . . . : 85 . 00 98 . 00 ' TC. . . . : 5 . 00 min 5 . 00 ` min ABSTRACTION COEFF: 0 . 20 impTcReach - Sheet L: 40 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0200 ' impTcReach - Channel L: 600 . 00 kc : 17 . 00 s : 0 . 0200 PEAK RATE : 0 . 59 cfs VOL: 0 . 22 Ac-ft TIME : 480 min ' BASIN ID: BAOS2 NAME : UPSTREAM CONTRIB-4()^ YEAR\24HR SBUH METHODOLOGY TOTAL AREA. . . . . . . : 0 . 28 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE- . : TYPEIA PERV IMP ' PRECIPITATION. . . . : 3 . 90 inches AREA. . : 0 . 28 Acres 0 . 00 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 85 . 00 0 . 00 TC. . . . . 5 . 00 min 0 . 00 min ' ABSTRACTION COEFF : 0 . 20 impTcReach - Sheet L: 40 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0200 impTcReach - Channel L: 600 . 00 kc : 17 . 00 s : 0 . 0200 ' PEAK RATE : 0 . 15 cfs VOL: 0 . 06 Ac-ft TIME : 480 min 1 ' 5/10/99 4 : 36 : 38 pm AHBL page 1 HIGHLAND POST OFFICE BACKWATER/HYDRAULIC GRADE CALCULATIONS K: \CIVIL\YR 1998\98027\CONVEY REACH SUMMARY Network Reach RBP1 ' REACH <-AREA> <-DIA> LENGTH SLOPE < n > DSGN Q % PIPE Ndepth %Depth Vact Vfull C_Area ID (Ac) (ft) (ft) ft/ft - (cfs) (ft) (fps) (fps) LBP1 0.99 1.00 262.94 0.0475 0.0140 0.59 7.56 0.19 19.28 5.54 10.16 BAOS1 LBP2 1.27 1.00 12.00 0.3000 0.0140 0.74 3.78 0.14 13.75 11.34 25.54 BAOS2 ' 5/10/99 4 : 36 : 38 pm AHBL page 2 HIGHLAND POST OFFICE BACKWATER/HYDRAULIC GRADE CALCULATIONS ' K: \CIVIL\YR_1998\98027\CONVEY STRUCTURE REPORT PROPOSED STRUCTURE REACH ID No. CB10 ' Location OFF-SITE BY PASS-EAST ENTRANCE North 180990 . 3566 Str Type TYPE 1 East 1312357 . 1270 Str Cat Catch Basin Rim Elev 399 . 4300 ' Area/sump : 0 . 00 sf/1 . 50 ft Bottom El : 393 . 3500 , Cont Area: BAOS1 Hgrade El : 0 . 0000 ft Bend. . . . . : No special shape ' Ent type . : Area/sump : Ent Loss : 0 . 000 Exit : 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 Reach <Invert> <Diam> < n > <End> ' LBP1 394 . 850 12 . 00 0 . 014 Upper ' PROPOSED STRUCTURE REACH ID No . C311 Location OFF-SITE BY PASS-WEST ENTRANCE North 180998 . 8484 Str Type TYPE 1 East 1312094 . 3262 Str Cat Catch Basin Rim Elev 391 . 3600 Area/sump: 0 . 00 sf/1 . 50 ft Bottom El : 380 . 8700 Cont Area : BAOS2 Hgrade El : 0 . 0000 ft ' Bend. . . . . : No special shape Ent type . : Area/sump: Ent Loss : 0 . 000 Exit : 0 . 000 App Vel : 0 . 000 Junct : 0 . 000 Bend: 0 . 000 ' Reach <Invert> <Diam> < n > <End> LBP1 382 . 370 12 . 00 0 . 014 Lower LBP2 382 . 370 12 . 00 0 . 014 Upper i tKING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ' TABLE 3.5.2B SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS ' SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (Published by SCS in 1982) Runoff curve numbers for selected agricultural, suburban and urban land use for Type 1A ' rainfall distribution, 24-hour storm duration. CURVE NUMBERS BY HYDROLOGIC SOIL GROUP LAND USE DESCRIPTION A B C D Cultivated land(1). winter condition 91 94 95 ' Mountain open areas: low growing brush and grasslands 74 82 89 92 Meadow or pasture: 65 78 85 89 ' Wood or forest land: undisturbed or older second growth 42 64 76 81 Wood or forest land: young second growth or brush 55 72 81 86 Orchard: with cover crop 81 88 92 94 ' Open spaces, lawns, parks, golf courses, cemeteries, landscaping. good condition: grass cover on 75% or more of the area 68 80 86 90 ' fair condition: grass cover on 50% to 75% of the area 77 85r-- 90 92 Gravel roads and parking lots 76 85 89 91 Dirt roads and parking lots 72 82 87 89 ' Impervious surfaces, pavement, roofs, etc. 98 98 98 98 Open water bodies: lakes, wetlands, ponds, etc. 100 100 100 100 Single Family Residential (2) Dwelling Unit/Gross Acre % Impervious (3) 1.0 DU/GA 15 Separate curve number ' 1.5 DU/GA 20 shall be selected 2.0 DU/GA 25 for pervious and 2.5 DU/GA 30 impervious portion 3.0 DU/GA 34 of the site or basin ' 3.5 DU/GA 38 4.0 DU/GA 42 4.5 DU/GA 46 ' 5.0 DU/GA 48 5.5 DU/GA 50 6.0 DU/GA 52 6.5 DU/GA 54 ' 7.0 DU/GA 56 Planned unit developments, % impervious condominiums, apartments, must be computed commercial business and industrial areas. (1) For a more detailed description of agricultural land use curve numbers refer to National Engineering ' Handbook, Section 4, Hydrology, Chapter 9, August 1972. (2) Assumes roof and driveway runoff is directed into street/storm system. (3) The remaining pervious areas (lawn) are considered to be in good condition for these curve numbers. 1 3.5.2-3 11/92 ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL (2) CN values can be area weighted when they apply to pervious areas of similar CN's (within 20 CN points). However, high CN areas should not be combined with low CN areas (unless the low CN areas are less than 15% of the subbasin). In this case, separate hydrographs should be generated and summed to form one hydrograph. FIGURE 3.5.2A HYDROLOGIC SOIL GROUP OF THE SOILS IN KING COUNTY HYDROLOGIC HYDROLOGIC ' SOIL GROUP GROUP' SOIL GROUP GROUP' Alderwood C Orr-as Peat D Arents, Alderwood Material C Oridia D ' Arents, Everett Material B Ovall C Beausite C Pilchuck C Bellingham D Puget D Briscot D Puyallup B ' Buckley D Ragnar B Coastal Beaches Variable Renton D Earlmont Silt Loam D Riverwash Variable Edgewick C Salal C Everett A/B 'Sammamish D Indianola A Seattle D Kitsap C Shacar D Klaus C Si Silt C ' Mixed Alluvial Land Variable Snohomish D Neilton A Sultan C Newberg B Tukwila D Nooksack C Urban Variable Normal Sandy Loam D Woodinville D ' HYDROLOGIC SOIL GROUP CLASSIFICATIONS A. (Low runoff potential). Soils having high infiltration rates, even when thoroughly wetted, and consisting chiefly of deep, well-to-excessively drained sands or gravels. These soils have a high rate of water transmission. B. (Moderately low runoff potential). Soils having moderate infiltration rates when thoroughly wetted, and consisting chiefly of moderately fine to moderately coarse textures. These soils have a moderate rate of water transmission. C. (Moderately high runoff potentiai). Soils having slow Infiltration rates when thoroughly wetted, and consisting chiefly of soils with a layer that impedes downward movement of water, or soils with moderately fine to fine textures. These soils have a slow rate of water transmission. D. (High runoff potential). Soils having very slow infiltration rates when thoroughly wetted and consisting chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a ' hardpan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils have a very slow rate of water transmission. t From SCS, TR-55, Second Edition, June 1986, Exhibit A-1. Revisions made from SCS, Soil Interpretation Record, Form #5, September 1988. ' 3.5.2-2 11/92 bd' t APPENDIX C Geotechnical Engineering Report 1 1 ' AHBL u ' GEOTECHNICAL ENGINEERING REPORT RENTON HIGHLANDS POST OFFICE 43XX S.E. 128T" STREET ' RENTON, WASHINGTON 17 �� � .�� Submitted to: Sienna Architecture Company 411 S.W. Sixth Avenue Portland, Oregon 97204 Submitted by: AGRA Earth & Environmental, Inc. 11335 N.E. 122"1 Way, Suite 100 Kirkland, Washington 98034-6918 October 6, 1998 8-91 M-12442-0 3� r; o AGRA Earth & Environmental ` Lr,GI NE h RING GLOBAL SOI UT IONS AGRA Earth & Environmental AGRA Earth& ' ENGINEERING GLOBAL SOLUTIONS Environmental, Inc. 11335 NE 122nd Way Suite 100 Kirkland,Washington ' USA 98034-6918 October 6, 1998 Tel (425)820-4669 8-91 M-12442-0 Fax (425)821-3914 Sienna Architecture Company 411 S.W. Sixth Avenue Portland, Oregon 97204 Attention: Mr. Erik Goodfriend Subject: Geotechnical Engineering Report Renton Highlands Post Office 43XX S.E. 128`h Street Renton, Washington Dear Erik: AGRA Earth & Environmental, Inc. (AEE) is pleased to submit this report describing our geotechnical engineering evaluation for the above-referenced project. The purpose of our evaluation was to derive design conclusions and recommendations concerning site preparation, excavations, foundations, floors, drainage, retaining walls, pavement sections, stormwater infiltration, and structural fill. As outlined in our proposal letter dated June 30 1998, our scope of work comprised a field exploration, laboratory testing, geotechnical research, geotechnical analyses, and report preparation. We received your written authorization for our evaluation on July 31 1998. This report has been prepared for the exclusive use of Sienna Architecture Company and their consultants,for specific application to this project, in accordance with generally accepted geotechnical engineering practice. We appreciate the opportunity to be of service on this project and would be happy to answer any questions you may have. Sincerely, J1 es M. Bris ine, P. y� / Ssociate Distribution: Sienna Architecture Company (5) Attn: Mr. Erik Goodfriend AHBL Engineers (1) Attn: Ms. Doreen Gavin S\WORDPROC\98\Seattle\12000sU2442\12442 807.wPd TABLE OF CONTENTS 8-91 M-1 2442-0 Paqe 1.0 SITE AND PROJECT DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - -'- 1 2.0 EXPLORATORY METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2.1 Test Pit Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 Infiltration Test Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.0 SITE CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1 Surface Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.2 Soil Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.3 Groundwater Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.4 Infiltration Conditions . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.5 Seismic Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.0 CONCLUSIONS AND RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.1 Site Preparation . . . . . . . . . . . . . . . . . . . . . . . . : I * I I I * I * I , I I * * * I I * . . . . . . 7 4.2 Spread Footings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.3 Slab-On-Grade Floors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Drainage Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.5 Backfilled Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 F, 4.6 Stormwater Ponds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.7 Asphaltic Pavements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.8 Structural Fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5.0 RECOMMENDED ADDITIONAL SERVICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.0 CLOSURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 1 — Location Map Figure 2 — Site & Exploration Plan Figure 3 — Surcharge Pressure Diagrams Test Pit Logs TP-1 through TP-1 2 Grain Size Distribution Graphs (2) a' SAW0RDPR0C\98\Seatt1e\1 2000s\1 2442\1 2442,807.wpd ' GEOTECHNICAL ENGINEERING REPORT 8-91M-12442-0 RENTON HIGHLANDS POST OFFICE 43XX S.E. 128T" STREET ' RENTON, WASHINGTON ' 1.0 SITE AND PROJECT DESCRIPTION The project site consists of residential property, including an existing house and undeveloped land located at 4301 S.E. 128`h Street in Renton, Washington, as shown on the enclosed Location Map ' (Figure 1). This site consists of a roughly rectangular parcel that measures about 310 by 410 feet overall and encompasses approximately 2.9 acres. Site boundaries are generally delineated by residential properties on the east and west, by S.E. 1281h Street on the north, and by undeveloped ' property on the south. The enclosed Site & Exploration Plan (Figure 2) illustrates these site boundaries and adjacent existing features. Development plans call for constructing a new post office facility at the project site. According to conceptual site layout drawings prepared by Sienna Architecture Company, this facility will ' comprise a building located in the northeast portion of the site, with a loading dock at the southwestern corner of the building, an access driveway west of the building, and asphalt-paved parking lots south and west of the building. According to drawings prepared by Sienna Architecture ' Company, the building will cover an area of roughly 23,260 square feet. We anticipate that the building will be one story high and that the walls and columns will impose relatively low foundation loads. Figure 2 illustrates the proposed site features. iThe conclusions and recommendations contained in this report are based on our understanding of the currently proposed utilization of the project site,as derived from conceptual site layout drawings, ' written information, and verbal information supplied to us. Consequently, if any changes are made in the currently proposed project, we may need to modify our conclusions and recommendations contained herein to reflect those changes. ' 2.0 EXPLORATORY METHODS We explored surface and subsurface conditions at the project site during August 1998. Our ' exploration and testing program comprised the following elements: • A visual surface reconnaissance of the site; ' • Twelve test pits (designated TP-1 through TP-12), advanced at strategic locations across the site; ' • Two infiltration tests (designated IT-1 and IT-2), performed in strategically loc ated test pits; ' • Two grain size analyses, performed on selected soil Y � P o samples obtained from strategic locations beneath the site; • A review of published geologic and seismologic maps and literature. S:\W O RD PROC\98\Seattle\12000s\12442\12442.807.wpd ' Sienna Architecture Company 8-91M-12442-0 October 6, 1998 Page 2 Table 1 summarizes the approximate functional locations, surface elevations, and termination ' depths of all pertinent subsurface explorations, and Figure 2 depicts their approximate relative locations. The following text sections describe our procedures used for test pits and infiltration ' tests. TABLE 1 ' APPROXIMATE LOCATIONS, ELEVATIONS, AND DEPTHS OF EXPLORATIONS Exploration Functional Location Surface Termination Elevation Depth ' (feet) (feet) TP-1* East side of proposed infiltration area 392 8 ' TP-2* West side of proposed infiltration area 392 10 TP-3 Platform maneuvering area 397 7 TP-4 Southeast parking area 398 5 TP-5 Southwest parking area 387 8 TP-6 Near northeast corner of building area 400 5 ' TP-7 Near center of building area 396 5%2 TP-8 Near southeast corner of building area 402 5 TP-9 Near southwest corner of building area 394 6 TP-10 South end of access driveway area 390 5 TP-11 North end of access driveway area 389 6 TP-12 Near northwest corner of building area 392 4 ' Elevation datum: 1998 survey map * Includes infiltration test ' The specific number, locations, and depths of our explorations were selected in relation to the existing and proposed site features, under the constraints of surface access, underground utility conflicts, and budget considerations. We estimated the relative location of each exploration by Measuring from existing features and scaling these measurements onto a layout plan supplied to us, then we estimated their elevations by interpolating between contour lines shown on this same ' plan. Consequently, the data listed in Table 1 and the locations depicted on Figure 2 should be considered accurate only to the degree permitted by our data sources and implied by our measuring methods. It should be realized that the explorations performed for this evaluation reveal subsurface conditions only at discrete locations across the project site and that actual conditions in other areas could vary. Furthermore,the nature and extent of any such variations would not become evident until additional explorations are performed or until construction activities have begun. If significant variations are ' S1WORDPROMMSeathe\12000s\12442\12442.807.wpd ' Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 3 ' observed at that time, we may need to modify our conclusions and recommendations contained in this report to reflect the actual site conditions. ' 2.1 Test Pit Procedures Our exploratory test pits were excavated with a track-mounted hoe operated by an independent firm working under subcontract to AEE. A geotechnical specialist from our firm continuously observed ' the test pit excavations, logged the subsurface conditions, and obtained representative soil samples. All samples were stored in watertight containers and later transported to our laboratory for further visual examination and testing. After we logged each test pit,the hoe operator backfilled ' it with excavated soils and tamped the surface. The enclosed Test Pit Logs indicate the vertical sequence of soils and materials encountered in each test pit, based primarily on our field classifications and supported by our subsequent laboratory examination and testing. Where a soil contact was observed to be gradational or undulating, our logs indicate the average contact depth. We estimated the relative density and consistency of the in-situ soils by means of the excavation characteristics and the stability of the test pit sidewalls. Our logs also indicate the approximate depths of any sidewall caving or groundwater seepage observed in the test pits, as well as all sample numbers and sampling locations. 2.2 Infiltration Test Procedures Our infiltration tests were performed in general accordance with the procedures prescribed in the EPA manual entitled On-Site Wastewater Treatment and Disposal Systems, except as modified by King County. Specifically,a test pit was excavated to 1 foot above the desired infiltration test depth, and a 6-inch-diameter test hole was excavated approximately 12 inches into the soil to the desired infiltration test depth at the bottom. The test hole was then filled twice with 12 inches of water, and it was confirmed that the water seeped away completely through the sandy soils in less than 10 minutes. Following this initial testing, the test hole was filled with 12 inches of water, and the time ' required for every 1-inch drop in water level was recorded through a total drop of 6 inches. We repeated this procedure three times at each test location and subsequently calculated the percolation rate using the last water level drop. After completion of all tests, the test pits were completely backfilled. 3.0 SITE CONDITIONS The following sections of text present our observations,measurements,findings,and interpretations regarding surface, soil, groundwater, infiltration, and seismic conditions at the project site. ' 3_1 Surface Conditions Currently, the site is undeveloped except for a small house and yard in the northwestern portion of ' the site. A previously cleared area south and east of the house has scattered fruit trees and is presently overgrown with blackberry bushes. The remainder of the site is covered by dense forest growth with a moderate to dense brush understory. Topography slopes gently to the west, with about 19 feet of relief across the site. tS:\WORDPROC\98\Seattle\12000s\12442\12442.807.wpd ' Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 4 ' 3_2 Soil Conditions According to published geologic maps,soil conditions in the site vicinity are characterized by glacial till, composed of unsorted mixtures of sand, silt, clay, gravel and cobbles. In some areas, the till is mantled by a thin layer of sand and gravel. Our on-site explorations revealed somewhat variable near-surface soil conditions but confirmed the mapped stratigraphy. Specifically, our test pits disclosed about 1 to 2 feet of topsoil and root-laden soil mantling from 0 to 1 foot of loose sand over 0 to 2Y2 feet of medium-dense to dense sand. Very dense glacial till soil was encountered at depths of 2 to 4 feet in our test pits near the east and north-central portions of the site, and at depths of 6 to 7 feet near the central portion of the site. No glacial till was encountered in test pits along the ' west side of the site. Medium-dense to dense recessional outwash sands and gravels were encountered below a depth of about 2 feet in test pits near the west and central portions of the site. The enclosed exploration logs provide a detailed description of the soil strata encountered in our subsurface explorations. Table 2 summarizes the approximate thicknesses and depths of selected soil layers. TABL E2 APPROXIMATE THICKNESSES AND DEPTHS OF SOIL LAYERS ENCOUNTERED IN EXPLORATIONS Exploration Thickness Thickness Thickness Depth of Depth of of Topsoil of Loose of Medium Medium Dense to (feet) Sand Dense Soils Dense Soils Very Dense (feet) (feet) (feet) Soils (feet) TP-1 1'/2 2 2 3'/2 5'/2 ' TP-2 1'Y2 '/2 '/2 2 2'/2 TP 3 1'/2 0 0 N/E 1'/2 TP-4 1'Y2 0 0 N/E 1 Y2 ' TP-5 1'/2 0 1 1'/2 2Y2 TP-6 1'/2 0 2'/2 1'/2 4 ' TP-7 2 0 2'/2 2 4'/2 TP-8 1'/2 0 1 1'/2 2'/2 ' TP-9 1 '/2 2'/2 1'/2 4 TP-10 1 0 1 1 2 TP-11 1 '/2 0 N/E 1 Y2 TP-12 1 0 1 1 2 N/E = not encountered within exploration ' S:\WORDPROC\98\Seattle\12000s\12442\12442.807.wpd ' Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 5 Our geotechnical laboratory tests revealed that the soils have a fines (silt and clay)content on the ' order of 6 to 10 percent, and a moisture content on the order of 2 to 4 percent. We interpret these soils to be currently below their optimum moisture contents, and to be moderately sensitive to moisture content variations. The enclosed laboratory testing sheets graphically present our test results. ' 3_3 Groundwater Conditions At the time of digging(August 1998), none of our explorations encountered groundwater within their - termination depths of 4 to 10 feet. Because our explorations were performed during an extended ' period of generally dry weather,these observed groundwater conditions may closely represent the yearly low levels;somewhat higher levels probably occur during the winter and early spring months. - Perched groundwater probably forms atop the glacial till horizon during periods of heavy rainfall. Throughout the year,groundwater levels would likely fluctuate in response to changing precipitation patterns, off-site construction activities, and site utilization. 3_4 Infiltration Conditions Our field infiltration tests disclosed fairly uniform infiltration conditions within the gravelly sand soils at depth. Specifically, infiltration test IT-1,which was performed on the eastern side of the proposed infiltration pond area, yielded an infiltration rate of 2.3 inches per minute, and infiltration test IT-2, which was performed on the western side of the proposed infiltration pond area, yielded an infiltration rate of 1.6 inches per minute. Table 3 summarizes the results of our infiltration testing. TABLE 3 INFILTRATION TEST RESULTS FOR IN-SITU SOILS Infiltration Exploration Test Soil Type Average Test Depth Infiltration Rate ' (feet) (inches/minute) IT-1 TP-1 5 Gravelly SAND 2.3 ' IT-2 TP-2 5 Gravelly SAND 1.6 3_5 Seismic Conditions Based on our analysis of subsurface exploration logs and our review of published geologic maps, we interpret the on-site soil conditions to correspond to seismic soil profile types S-2 and S-C as ' defined by Table 16-J of the 1994 and 1997 Uniform Building Code, respectively. Current (1996) National Seismic Hazard Maps prepared by the U.S. Geological Survey indicate that a peak bedrock site acceleration coefficient of about 0.30 is appropriate for an earthquake having a ' 10-percent probability of exceedance in 50 years (corresponding to a return interval of 475 years). According to Figure 16-2 of the 1994 and 1997 Uniform Building Code, the site lies within seismic risk zone 3. S:\WORDPROC\98\Seattle\12000s\12442\12442.807.wpd ' Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 6 4.0 CONCLUSIONS AND RECOMMENDATIONS Development plans call for construction of a 23,000-square-foot, single-story post office building with an access driveway, a loading dock, an infiltration pond, and adjoining parking lots. We offer the following general geotechnical conclusions and recommendations concerning this project. • Feasibility: Based on our field explorations, research, and analyses, the proposed project appears feasible from a geotechnical standpoint,contingent on proper design and construction procedures. • Foundation Options: In our opinion, the proposed structure can be supported by conventional spread footings, contingent on appropriate subgrade preparation. • Floor Options: Soil conditions are amenable to the use of a soil-supported slab-on-grade floor, contingent on proper subgrade preparation. • Retaining Wall Options: In our opinion, conventional backfilled, cast-in-place concrete walls will adequately support the anticipated changes in site grade. These walls should be designed to withstand appropriate lateral pressures. • Infiltration Conditions: In our opinion,soil and groundwater conditions are amenable to percolation of stormwater in the proposed stormwater detention pond area to be located near the west-central portion of the site. • Liquefaction Considerations: "Liquefaction" is a sudden increase in porewater " pressure and sudden loss of soil shear strength caused by shear strains, as could result from an earthquake. Research has shown that saturated, loose sands with a silt content less than about 25 percent are most susceptible to liquefaction, whereas other soil types are generally considered to have a low susceptibility. Because our explorations did not reveal any liquefaction-prone soils below the site, ' we interpret the risk of liquefaction to be negligible. • Seismic Considerations: Based on our literature review and subsurface interpretations,we recommend that the project structural engineer use the following seismic parameters for design of buildings, retaining walls,and other site structures, as appropriate. The selection of a soil profile type will depend on which code year governs the project. Design Parameter Value ' Acceleration Coefficient (WSDOT) 0.3 Risk Zone (UBC) 3 Soil Profile Type (1994 UBC) S-2 Soil Profile Type (1997 UBC) S-C ' S:\WORDPROC\98\Seattle\12000s\12442\12442.807.wpd ' Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 7 • On-Site Soil Reuse: Our visual soil classifications and laboratory testing indicate ' most of the on-site soils are moderately to highly moisture-sensitive and susceptible >f to disturbance when wet. In order to maximize the potential for reusing on-site soils as structural fill, earthwork should be scheduled for periods of dry weather, such as usually occur during the summer and early fall months. 0 Subgrade Protection: Due to the moisture-sensitive nature of the on-site soils, the ' contractor should install appropriate temporary drainage systems to keep water out -- of the construction areas, and should minimize traffic over any subgrades prepared within these soils. The following text sections of this report present our specific geotechnical conclusions and recommendations concerning site preparation, spread footings, backfilled walls, slab-on-grade floors, drainage systems, asphaltic pavements, stormwater detention systems and structural fill. WSDOT Standard Specifications and Standard Plans cited herein refer to WSDOT publications M41-10, 1996 Standard Specifications for Road, Bridge, and Municipal Construction, and M21-01, Standard Plans for Road, Bridge, and Municipal Construction, respectively. 4.1 Site Preparation Preparation of the project site should involve demolition, temporary drainage, clearing, stripping, cutting, filling, excavations, and subgrade compaction. The paragraphs below discuss our geotechnical comments and recommendations concerning site preparation. Demolition: The first step in site preparation will likely consist of demolishing the existing house. Any associated underground structural elements or utilities, such as old footings, stemwalls, and drainpipes, should be exhumed as part of this demolition operation. Temporary Drainage: We recommend intercepting and diverting any potential sources of surface or near-surface water within the construction zones before stripping begins. Because the selection of an appropriate drainage system will depend on the water quantity, season, weather conditions, construction sequence, and contractor's methods, final decisions regarding drainage systems are best made in the field at the time of construction. Nonetheless, we anticipate that curbs, berms, or fditches placed around the work areas will adequately intercept surface water runoff. Clearing and Stripping: After surface and near-surface water sources have been controlled, the construction areas should be cleared and stripped of all trees, bushes, sod, topsoil, root balls, root-laden soil, debris, asphalt, and concrete. Our explorations indicate that an average thickness of about 18 inches of sod, duff, topsoil and root-laden soil will be encountered across the site, but ' significant variations could exist. Furthermore, it should be realized that if the stripping operation proceeds during wet weather, a generally greater stripping depth might be necessary to remove disturbed moisture-sensitive soils; therefore, stripping is best performed during a period of dry weather. S:\WORDPROC\98\Seattle\12000s\12442\12442.807.wpd t� Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 8 Excavations: Site excavations ranging up to about 4 feet deep will be required to accommodate the proposed loading dock on the south side of the building, as well as to accommodate underground utilities. Furthermore, an excavation will be needed for the infiltration system to a depth of about 5 feet. Based on our explorations, we anticipate that the excavations in the building area will encounter loose to medium-dense,silty sand over medium-dense to dense,gravelly,silty sand over very dense glacial till soils at a depth of 2 to 6 feet. Excavations in the area of proposed infiltration system will encounter loose to medium-dense sand to a depth of 2%2 to 5 feet and dense sand below this depth. The upper soils can be readily excavated with conventional earthworking equipment, in our estimation, but extra effort will be needed to loosen the underlying glacial till. Although our explorations did not reveal rubble within the fill soils or boulders within the native soils, such obstacles could be present at random locations within these deposits. Temporary Cut Slopes: All temporary soil cuts associated with site regrading or excavations should be adequately sloped back to prevent sloughing and collapse. For the various soil layers that will likely be exposed in on-site cuts, we tentatively recommend the following maximum cut-slope inclinations. However, appropriate inclinations will ultimately depend on the actual soil conditions exposed in the cuts. Maximum Soil Type Inclination Loose, Silty SAND 1'/2HAV Medium-Dense to Dense Gravelly SAND 1HAV Glacial Till '/2HAV subgrade Compaction: Exposed subgrades for footings, floors, pavements, and other structures should be compacted to a firm, unyielding state. Any localized zones of loose granular soils observed within a subgrade should be compacted to a density commensurate with the surrounding soils. In contrast, any organic, soft, or pumping soils observed within a subgrade should be overexcavated and replaced with a suitable structural fill material. On-Site Soils: Because onlyminor cuts are planned for the project, we expect that only small quantities of on-site soils will be generated during earthwork activities. Nonetheless, we offer the following evaluation of these on-site soils in relation to potential use as structural fill. • Surficial Organic Soils: The sod, duff, topsoil, and organic-rich soils mantling most of the site are not suitable for use as structural fill under any circumstances, due to their high organic content. Consequently, these materials can be used only for non-structural purposes, such as in landscaping areas. • Upper Silty Sands and Sandy Silts: The silty sands underlying the surficial organic soils appear marginally suitable for reuse as structural fill at their present moisture contents. However, these soils will be difficult or impossible to reuse during wet weather, due to their moderately high silt contents. R� S:\WORDPROC\98\Seattle\12000s\12442\12442.807 wpd ' Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 9 ' • Recessional Outwash: The gravelly sands and sandy gravels underlying the western part of the site will provide a favorable source of fill soils that can be used in a broad range of weather conditions, although aeration or sprinkling might be needed to achieve an optimum moisture content during especially wet or dry conditions, respectively. • Glacial Till: The weathered and unweathered glacial till soils underlying the upper sands in the eastern and central parts of the site appear suitable for reuse as structural fill at their present moisture contents. However, these soils will be difficult ' or impossible to reuse during wet weather, due to their high silt contents. Permanent Slopes: All permanent cut slopes and fill slopes should be adequately inclined to minimize long-term ravelling, sloughing, and erosion. We generally recommend that no slopes be steeper than 2H:1 V, but cut slopes in glacial till and similarly coherent soils can be inclined as steep as 1 H:1 V if appearance is not a concern. For all soil types, the use of flatter slopes (such as 21/2H:1 V) would further reduce long-term erosion and facilitate revegetation. Slope Protection: We recommend that a permanent berm, swale, or curb be constructed along the top edge of all permanent slopes to intercept surface flow. Also, a hardy vegetative groundcover o• should be established as soon as feasible, to further protect the slopes from runoff water erosion. Alternatively, permanent slopes could be armored with quarry spalls or a geosynthetic erosion mat. 4_2 Spread Footings In our opinion,conventional spread footings will provide adequate support for the proposed building if the subgrades are properly prepared as described in the Site Preparation section. We offer the following comments and recommendations for purposes of footing design and construction. Footing Depths and Widths: For frost and erosion protection, exterior footings should penetrate at ' least 18 inches below adjacent outside grade,whereas interior footings need extend only 12 inches below the surrounding slab surface level. In both cases, however, greater footing depths might be required to achieve adequate bearing capacities, as indicated in Table 3, below. To minimize post-construction settlements, continuous (wall) and isolated (column)footings should be at least 18 and 24 inches wide, respectively. Bearing Soils: We recommend that all footings bear either on the near-surface, medium-dense to dense sands, or on the underlying very dense glacial till soils. Based on our explorations, we expect that the medium-dense to dense sand will be encountered at or near the conventual footing ' depth at 11/2 to 2 feet below existing grades, whereas the glacial till will likely be encountered at depths ranging from 2 to over 6 feet, as summarized in Table 3. In the latter case, the footings would need to be extended downward an additional 21/2 to 3%2 feet, or the overburden soils would need to be overexcavated and replaced with a bearing pad of suitable structural fill. S 1W O RDPROC\98\Seattle\12000s\12442\1244 2.807 mpd 's� i i Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 10 i Bearing Pad Materials: We recommend that bearing pads for low-pressure (3,000 psf or less) footings be composed of well-graded sands and gravels, such as "Ballast' per WSDOT Standard Specification 9-03.9(1), or uniformly graded crushed rock, such as "Crushed Surfacing Base Course" per WSDOT standard Specification 9-03.9(3). Non-Organic on-site soils could be used as bearing pad fill if they are placed at a moisture content near optimum. All bearing pad soil should be compacted to at least 90 percent of the Modified Proctor maximum dry density (based on ASTM:D-1557). Controlled density-fill (CDF) or lean-mix concrete (LMC) should be used for high-pressure (greater than 3,000 psf) footings in order to maintain adequate bearing capacities. -' Bearing Pad Dimensions: We anticipate that the bearing pads will need to range from about %to 3'/z feet thick, depending on the required overexcavation depth. Because foundation stresses are transferred outward as well as downward into the bearing soils, all bearing pads composed of structural fill soil should extend horizontally outward from the edge of each footing a distance equal to the bearing pad thickness. Forbearing pads composed of CDF or LMC,this horizontal distance should be at least half of the overexcavation depth. Therefore, an overexcavation that extends 24 inches below the footing base should also extend 24 inches outward from the footing edges in the case of soil bearing pads, and 12 inches outward in the case of CDF or LMC bearing pads. Subgrade Verification: All footing subgrades should consist of firm, unyielding, non-organic native soils or compacted structural fill materials. Under no circumstances should footings be cast atop loose, soft, or frozen soil, slough, debris, or surfaces covered by standing water. We recommend that the condition of all subgrades be verified by an AEE representative before any concrete is placed. Footing Backfill: We recommend that all footing excavations be backfilled on each side of the footings and stem walls after the concrete has cured. Either imported structural fill or non-organic on-site soils can be used for this purpose, in our opinion. All footing backfill soil should be compacted to a density of at least 90 percent (based on ASTM:D-1557). i Bearing Pressures: In our opinion, footings that bear on properly prepared subgrades can be designed according to the maximum allowable soil bearing pressures presented in Table 3 forstatic loadings and transient (short-term wind or seismic) loadings. 1 iS:\WORDPROC\981Seattle\12000s\12442\12"2.807.wpd i ' Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 11 ' TABLE 3 SUBGRADE BEARING DEPTHS AND RECOMMENDED BEARING PRESSURES " FOR FOOTING DESIGN - Subgrade Allowable Bearing Pressure Subgrade Type Depth s (feet) Static Transient Medium-dense to dense Weathered Till 1%to 2 2,500 3,300 Very dense Glacial Till 2 to 6+ 5,000 6,500 LMC or CDF bearing pad over very 2 to 6+ 5,000 6,500 dense Glacial Till Footing Settlements: We estimate that the total post-construction settlements of properly sized o gS p P P Y footings bearing on properly prepared subgrades will not exceed 3/4 inch. Differential settlements may approach one-half of the actual total settlement between adjacent foundation elements. 4.3 Slab-On-Grade Floors In our opinion, soil-supported slab-on-grade floors can be used in the proposed post office building if the subgrades are properly prepared. Alternatively, a structurally supported (post-tensioned) slab-on-grade floor can be used,without the need for rigorous subgrade preparation. We offer the following comments and recommendations concerning these two types of slab-on-grade floors. E Capillary Break: To retard the upward wicking of groundwater beneath the floor slab, we recommend that a capillary break be placed over the subgrade. Ideally, this capillary break would consist of a 4-inch-thick layer of pea gravel or other clean, uniform, well-rounded gravel, such as "Gravel Backfill for Drains"per WSDOT Standard Specification 9-03.12(4), but clean angular gravel ' can be used if it adequately prevents capillary wicking. Vapor Barrier: We recommend that a layer of plastic sheeting (such as Crosstuff, Visqueen or Moistop) be placed directly between the capillary break and the floor slab to prevent ground moisture vapors from migrating upward through the slab. During subsequent casting of the concrete slab, the contractor should exercise care to avoid puncturing this vapor barrier. Vertical Deflections: Soil-supported slab-on-grade floors can deflect downward when vertical loads ' are applied, due to elastic compression of the subgrade. In our opinion, a subgrade reaction modulus of 250 pounds per cubic inch can be used to estimate such deflections. For structurally supported slab-on-grade floors, this subgrade reaction modulus should be neglected, due to the ' potential for the subgrade to gradually settle away from the floor. S:\WORDPROC\98\Seattle\12000s\12442\12442.807 wpd Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 12 ' 4_4 Drainage Systems In our opinion, the new building should be provided with permanent drainage systems to minimize the risk of future moisture problems. We offer the following recommendations and comments for ' drainage design and construction purposes. Perimeter Drains: We recommend that the building be encircled with a perimeter drain system to collect seepage water. This drain should consist of a perforated pipe within an envelope of pea gravel or washed rock, extending at least 6 inches on all sides of the pipe, and the gravel envelope should be wrapped with filter fabric to reduce the migration of fines from the surrounding soils. The ' drain invert should be installed no more than 8 inches above the base of the perimeter footings. Runoff Water: Roof-runoff and surface-runoff water should not discharge into the perimeter drain ' system. Instead,these sources should discharge into separate tightline pipes and be routed away from the building to a storm drain, infiltration pond or other appropriate location. Grading and Capping: Final site grades should slope downward away from the building so that runoff water will flow by gravity to suitable collection points, rather than ponding near the building. Ideally, the area surrounding the building would be capped with concrete or asphalt to preclude surface-water infiltration. 4.5 Backfilled Walls ' In our opinion, backfilled concrete retaining walls can be used to support grade changes along the building perimeterorsite margins. Ourwall design recommendations and comments are discussed ' below. Footing Depths: For frost and erosion protection, all retaining wall footings should bear at least 18 inches below the adjacent ground surface. However,greater depths might be necessary to develop ' adequate passive resistance in certain cases. ' Curtain Drains: To preclude hydrostatic pressure development behind the retaining wall, we recommend that a 4-inch-diameter perforated drain pipe be installed behind the heel of the wall and that a curtain drain be placed behind the entire wall. This curtain drain should consist of pea gravel, ' washed rock, or some other clean, uniform, well-rounded soils, extending outward a minimum of 2 feet from the wall and extending from the footing drain upward to within about 12 inches of the ground surface. ' Applied Loads: Overturning and sliding loads applied to retaining walls can be classified as static pressures, surcharge pressures, seismic pressures, and hydrostatic pressures. We offer the ' following specific values for design purposes. • Static Pressures: Yielding (cantilever) retaining walls should be designed to ' withstand an appropriate active lateral earth pressure, whereas non-yielding (restrained) walls should be designed to withstand an appropriate at-rest lateral earth pressure. These pressures act over the entire back of the wall and vary with S.\WORDPROC\98\Seattle\12000s\12442\12442 807.wpd ' Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 13 ' the backslope inclination. For various backslope angles, we recommend using the following active and at-rest pressures (given as equivalent fluid unit weights); Active At-Rest ' Backslope Angle Pressure Pressure Level 33 pcf 53 pcf ' 3.0H:1 V 40 pcf 62 pcf 2.0H:1 V 46 pcf 70 pcf ' • Surcharge Pressures: Static lateral earth pressures acting on a retaining wall should be increased to account for any surcharge loadings from traffic, construction equipment, material stockpiles, or structures. The enclosed Surcharge Pressure ' Diagrams(Figure 3)illustrate methods of calculating surcharge loads. Forsimplicity, a traffic surcharge can be modeled as a uniform pressure of 75 psf acting against the wall. ' • Seismic Pressures: Static lateral earth pressures acting on a retaining wall should be increased to account for seismic loadings. These pressures act over the entire back of the wall and vary with the backslope inclination, the seismic acceleration, and the wall height. For a design acceleration coefficient of 0.30 and a wall height of "H" feet, we recommend that these seismic loadings be modeled as a uniform ' horizontal pressure of 4H psf and 12H psf on yielding walls and unyielding walls, respectively, with a horizontal backslope. Resisting Forces: Static pressures, surcharge pressures, seismic pressures, and hydrostatic pressures are resisted by a combination of passive lateral earth pressure, base friction, and subgrade bearing capacity. Passive pressure acts over the embedded front of the wall (neglecting the upper 1 foot) and varies with the foreslope inclination, whereas base friction and bearing capacity act along the bottom of the footings. Assuming a level foreslope at the wall location, we ' recommend the following design values, which incorporate a static safety factor of at least 1.5: Allowable Design Parameter Value Static Passive Pressure 380 pcf Transient Passive Pressure 500 pcf ' Base Friction Coefficient 0.4 Static Bearing Capacity 2500 psf Transient Bearing Capacity 3300 psf Backfill Soil and Compaction: Ideally,all retaining wall backfill placed behind the curtain drain would consist of clean, free-draining, granular material, such as "Gravel Backfill for Walls" per WSDOT Standard Specification 9-03.12(2). However, on-site granular soils can be used as backfill if desired. Because soil compactors place significant lateral pressures on retaining walls, we recommend that only small, hand-operated compaction equipment be used within 3 feet of a S:\WORDPROC\98\Seattle\12000s\12442\12442.807.wpd ' Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 14 ' completed wall. Also,all backfill should be compacted to approximately 90 percent of the maximum dry density(based on ASTM:D-1557);a greater degree of compaction closely behind the wall would increase the lateral earth pressure,whereas a lesser degree of compaction might lead to excessive ' post-construction settlements. Grading and Capping: To retard the infiltration of surface water into the backfill soils, the backfill ' surface of exterior walls should be adequately sloped to drain away from the wall. We also recommend that the backfill surface directly behind the wall be capped with asphalt, concrete, or 12 inches of low-permeability (silty) soils. 4_6 Stormwater Ponds We understand that plans call for stormwater runoff from the developed areas to be discharged into a detention pond on the western side of the site: Our conclusions and recommendations concerning stormwater detention ponds are presented below. ' Field Preparation: The proposed pond area is mantled by topsoil and root-laden soil, and is underlain by sand and gravelly sand soils. In our opinion,the detention pond should extend through this surficial topsoil layer. ' Groundwater Levels: Based on the lack of groundwater seepage or other evidence of groundwater in our test pits, we estimate that the groundwater table lies significantly below the anticipated shallow depth of the ponds. However, we infer that perched groundwater could form atop the glacial till horizon on the eastern side of the proposed pond area, where it lies at a depth of about r 7 feet below existing grades. This perched water would likely be a thin layer (perhaps several s , inches thick). Glacial till was not encountered within the upper 10 feet on the western side of the proposed pond area, and we do not anticipate that perched groundwater conditions would form in this area. Bottom Depths: Soils encountered and infiltration tests performed at a depth of 5 feet indicate that ' infiltration is feasible at this depth. Therefore, a depth of roughly 5 feet could be used for the infiltration ponds. A greater pond depth, such as 7 feet, would not be appropriate on the east side of the proposed pond area,due to the proximity of the glacial till horizon and potential perched water ' zone. If additional pond volume is needed to increase capacity, this volumetric increase should be achieved by extending the infiltration system upward and/or to a depth of about 7 feet on the western side of the proposed infiltration area, thereby taking advantage of the rapid percolation ' rates associated with the thicker recessional outwash deposit overlying the glacial till in this area. Infiltration Rates: Based on the soil conditions observed in our explorations and on the results of our infiltration tests, we recommend using an ultimate infiltration rate of 1.6 inches per minute for the medium-dense to dense recessional outwash sand. However, a safety factor of 2 or more should be applied to this value in order to account for lateral and vertical variabilities in the soil deposit. Therefore, an allowable rate of 0.8 inches per minute would be appropriate, in our opinion. S:\WORDPROC\98\Seattle\12000s\12442\12442 807.wpd . 1 ' Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 15 Berms: If additional pond volume is needed to provide adequate storage capacity,a soil berm could ' be constructed around the perimeter. We generally recommend that such berms consist of well-graded, silty sands or sandy silts compacted to at least 95 percent of the maximum dry density ' (based on ASTM:D-1557). This berm should be keyed at least 2 feet into native soils for stability purposes. Interior and exterior faces of the berm should be no steeper than 3H:1V and 2H:1V (Horizontal:Vertical), respectively. ' 4.7 Asphaltic Pavements We understand that asphaltic pavements will be used for the new car-parking areas, platform maneuvering area, and car/truck driveways. The following comments and recommendations are given for pavement design and construction purposes. f Subgrade Preparation: All soil subgrades should be proof-rolled with a loaded dump truck or heavy compactor to verify the density. Any areas where organic soils are present at or closely beneath the pavement subgrade, as well as any localized zones of yielding subgrade disclosed during this proof-rolling operation, should be overexcavated to a maximum depth of 18 inches and replaced with a suitable structural fill material. All structural fill should be compacted according to our recommendations given in the Structural Fill section. Specifically, the upper 2 feet of soils ' underlying pavement section should be compacted to at least 95 percent(based on ASTM:D-1557), and all soils below 2 feet should be compacted to at least 90 percent. ' Soil Design Values: Soil conditions can be defined by a California Bearing Ratio (CBR), which quantitatively predicts the effects of wheel loads imposed on a saturated subgrade. Based on our classifications of on-site soils and our previous laboratory testing performed on similar soils, we ' estimate that the near-surface soils will provide a CBR value of about 10 percent. Traffic Design Values: Traffic conditions can be defined by a Traffic Index(TI),which quantifies the combined effects of projected car, truck, and bus traffic. Although no specific traffic data was available at the time of our analysis,we estimate that a TI of 4.0 is appropriate for car-parking areas and that a TI of 5.5 is appropriate for driveways subjected to frequent passes by small freight ' trucks. Conventional Sections: A conventional pavement section typically comprises an asphalt concrete ' pavement over a crushed rock base course over a granular subbase course. Using the estimated design values stated above, we recommend using the following conventional pavement sections: f Minimum Thickness Pavement Course Car Areas Driveways Asphalt Concrete Pavement 2'/2 inches 4 inches Crushed Rock Base 3 inches 4 inches Granular Subbase 6 inches 6 inches S:\W0RDPROc\98\Seattle\12000s\12442\12442.807,wPd ti' t Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 16 ' Pavement Materials: For the base course, we recommend using imported crushed rock, such as "Crushed Surfacing Top Course" per WSDOT Standard Specification 9-03.9(3). For the subbase course, we recommend using imported, clean, well-graded sand and gravel, such as "Ballast' or ' "Gravel Borrow" per WSDOT Standard Specifications 9-03.9(1) and 9-03.14, respectively. Compaction and Verification: All subbase and base course material should be compacted to at ' least 95 percent of the Modified Proctor maximum dry density (ASTM:D-1557), and all asphalt concrete should be compacted to at least 92 percent of the Rice value (ASTM:D-2041). We recommend that an AEE representative be retained to verify the compaction of each course before ' any overlying layer is placed. For the subbase and pavement course, compaction is best verified by means of frequent density testing; for the base course, methodology observations and hand-probing are more appropriate than density testing. Pavement Life and Maintenance: It should be realized that no asphaltic pavement is maintenance- free. The above described pavement sections represent our minimum recommendations for an average level of performance during a 20-year design life; therefore, an average level of maintenance will likely be required. Furthermore, a 20-year pavement life typically assumes that an overlay will be placed after about 10 years. Thicker asphalt, base, and subbase courses would ' offer better long-term performance, but would cost more initially; thinner courses would be more susceptible to "alligator" cracking and other failure modes. As such, pavement design can be considered a compromise between a high initial cost and low maintenance costs versus a low initial ' cost and higher maintenance costs. 4.8 Structural Fill tThe term "structural fill" refers to any materials used for building pads, and detention pond berms or placed under foundations, retaining walls,slab-on-grade floors,sidewalks,pavements,and other ' such features. Our comments, conclusions, and recommendations concerning structural fill are presented in the following paragraphs. ' Materials: Typical structural fill materials include clean sand,granulithic gravel,pea gravel,washed rock, crushed rock, quarry spalls, controlled-density fill (CDF), lean-mix concrete, well-graded mixtures of sand and gravel (commonly called "gravel borrow" or "pit-run"), and miscellaneous ' mixtures of silt, sand, and gravel. Recycled asphalt, concrete, and glass, which are derived from pulverizing the parent materials, are also potentially useful as structural fill in certain applications. Soils used for structural fill should not contain any organic matter or debris, nor any individual ' particles greater than about 6 inches in diameter. Fill Placement: Generally, pea gravel, washed rock, quarry spalls, CDF, and lean-mix concrete do ' not require special placement and compaction procedures. In contrast, clean sand, granulithic gravel, crushed rock, soil mixtures, and recycled materials should be placed in horizontal lifts not exceeding 8 inches in loose thickness, and each lift should be thoroughly compacted with a ' mechanical compactor. ' SAW0RDPR0C\98\Seatt1e\12000s\12442\12442.807.wpd Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 17 Compaction Criteria: Using the Modified Proctor test (ASTM:D-1557) as a standard, we recommend that structural fill used for various on-site applications be compacted to the following minimum densities: ' Minimum Fill Application Compaction Footing subgrade or bearing pad 90 percent Footing and stemwall backfill 90 percent Slab-on-grade floor subgrade and subbase 90 percent Retaining wall subgrade 95 percent Retaining wall backfill 90 percent Concrete sidewalk subgrade 90 percent Asphaltic pavement base and subbase 95 percent Asphaltic pavement subgrade (upper 2 feet) 95 percent Asphaltic pavement subgrade (below 2 feet) 90 percent Detention pond berm 95 percent ' Subgrade Verification and Compaction Testing: Regardless of material or location, all structural fill should be placed overfirm, unyielding subgrades prepared in accordance with the Site Preparation section of this report. The condition of all subgrades should be verified by an AEE representative ' before filling or construction begins. Also, fill soil compaction should be verified by means of in-place density tests performed during fill placement so that adequacy of soil compaction efforts may be evaluated as earthwork progresses. Soil Moisture Considerations: The suitability of soils used for structural fill depends primarily on their grain-size distribution and moisture content when they are placed. As the "fines" content (that soil fraction passing the U.S. No. 200 Sieve) increases, soils become more sensitive to small changes in moisture content. Soils containing more than about 5 percent fines (by weight) cannot be consistently compacted to a firm, unyielding condition when the moisture content is more than 2 percentage points above or below optimum. For fill placement during wet-weather site work, we recommend using "clean"fill, which refers to soils that have a fines content of 5 percent or less(by weight) based on the soil fraction passing the U.S. No. 4 Sieve. CDF Strength Considerations: CDF is normally specified in terms of its compressive strength, a Y P which typically ranges from 50 to 200 psi. CDF having a strength of 50 psi (7200 psf) provides r' adequate support for most structural applications and can be readily excavated with hand shovels. A strength of 100 psi (14,400 psf) provides additional support for special applications but greatly ' increases the difficulty of hand-excavation. In general, CDF having a strength greater than about 100 psi requires power equipment to excavate and, as such, should not be used where future {{ hand-excavation might be needed. 1� +' S'.\WORDPROC\98\Seattle\12000s\12442\12442.807.wpd Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 18 5.0 RECOMMENDED ADDITIONAL SERVICES Because the future performance and integrity of the structural elements will depend largely on proper site preparation, drainage, fill placement, and construction procedures, monitoring and testing by experienced geotechnical personnel should be considered an integral part of the i construction process. Consequently,we recommend that AEE be retained to provide the following post-report services: • Review all construction plans and specifications to verify that our design criteria presented in this report have been properly integrated into the design; i • Prepare a letter summarizing all review comments(if required by the City of Renton); • Attend a pre-construction conference with the design team and contractor to discuss important geotechnically related construction issues; ' • Observe all exposed subgrades after completion of stripping and overexcavation to confirm that suitable soil conditions have been reached and to determine appropriate subgrade compaction methods; ' • Monitor the placement of all structural fill and test the compaction of structural fill soils to verify their conformance with the construction specifications; ' • Check all completed subgrades for footings and slab-on-grade floors before concrete is poured, in order to verify their bearing capacity; • Observe the installation of all perimeter drains, wall drains, and capillary break layers to verify their conformance with the construction plans; ' • Prepare a post-construction letter summarizing all field observations, inspections, and test results (if required by the City of Renton). 1 In addition to the aforementioned services AEE can provide inspection and testing of concrete, P P 9 steel, masonry, and other structural materials. Upon request, we could submit a proposal for providing some or all of these construction monitoring, inspection, and testing services. Such a proposal is best prepared after the project plans and specifications have been approved for {� construction. 6.0 CLOSURE ' The conclusions and recommendations presented in this report are based, in part, on the explorations that we performed for this study;therefore, if variations in the subgrade conditions are observed at a later time,we may need to modify this report to reflect those changes. Also, because the future performance and integrity of the project elements depend largely on proper initial site preparation, drainage, and construction procedures, monitoring and testing by experienced geotechnical personnel should be considered an integral part of the construction process. AEE is S:\WORDPROC\98\Seattle\12000s\12442\12442.807.wpd k f Sienna Architecture Company 8-91 M-12442-0 October 6, 1998 Page 19 available to provide geotechnical monitoring, soils and concrete testing, steel and masonry 1 inspection, and other services throughout construction. We appreciate the opportunity to be of service on this project. If you have any questions regarding this report or any aspects of the project, please feel free to contact our office. Sincerely, N. WIC of WAA;.fG�LO A. gyp , 33266 V EXPIRES J mes M. B 'shine, P.E. Mark A. Wicklund, P.E. Associate Project Engineer MAW/JMB/lad S:\W 0 R D P R OC\98\S eattle\12000s\12442\12442.807.wpd J08 NO.: 8-91M-12442-0 DWG DATE: 08-24-98 SCALE: N.T.S. 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L7ETxAt Win` tr - xn+,w {• f. ° �� _N Lr T.t)Rl M n n - ISE138TH AY SE „► T iK ,Iw sr �"k 7L lbr r :. lnsl zt 4 - _ ___ ig S[ rr -- �•_� 'OI u "°9 k '�• V ii p Y A \� Kl r AY ~Tim _ AV _m _9 +� :At �^ 'Y i,# _ .•_�}eTY -AY ._�-_ x pytq C � 'w u l�y a� 1 AY T +� '^ � r■ 6 X f I'a -v r A m ' 2OPERTY LINE s TP-11 � 2y J I TP-12 I � i W I- 1 a w 1 w Z , W _J 3 -� m LEGEND DING , Z TP-12 TEST PIT NUMBER AND n� APPROXIMATE LOCATION 0 IT-2 INFILTRATION TEST NUMBER J AND APPROXIMATE LOCATION U IN TP-6 N O W a � O 1� '-- N ' SITE & EXPLORATION PLAN FIGURE cn 0 40 80 o NTON HIGHLANDS POST OFFICE ^ ' Z SCALE IN FEET L o RENTON, WASHINGTON GROUND SURFACE STRIP FOOTING Q PARALLEL TO EXCAVATION 0 Q/2 ah = 0.64Q(Q—sinQcos2c) D BASE OF EXCAVATION GROUND SURFACE LINE LOAD Q x = mD PARALLEL TO EXCAVATION LINE LOAD PRESSURE (FOR m>0.4) 0 c a 1.28Q m2 n II h= D (m2+ n2)2 ah N D (FOR m< 0.4) oah= Q 0.2 n w D (0.16 + n2)2 D Ln w a w BASE OF EXCAVATION a z w GROUND SURFACE POINT LOAD Q x = mD (FOR m> 0.4) Z o ah= 1.77Q m2 n2 vim- D2 (m2+ n2)3 o II N D (FOR m< 0.4) ah ah= 0.28Q n2 z D2 (0.16 + n2)3 w J a U N BASE OF EXCAVATION �Q Na' a'h=ahcos2(1.16) 0 6 ah h PLAN VIEW OF WALL 3 0 o i N N SURCHARGE PRESSURE DIAGRAMS FIGURE A G R A co Earth & Environmental RENTON HIGHLANDS POST OFFICE 11335 N.E. 122ND WAY, SUITE 100 o KIRKLAND, WA, U.S.A. 98034-6918 RENTON, WASHINGTON ' TEST PIT LOGS 8-91 M-12442-0 ' Depth (feet) Material Description Sample No. Test Pit TP-1 _ Location: Wooded area, approximately 100 feet east of dirt drive ' Approximate ground surface elevation: 392 feet 0.0- 1.5 Forest duff over topsoil with prevalent roots 1.5 -2.5 Loose, damp, tan-brown, silty,fine SAND with scattered roots S-1 2.5 -5.0 Loose to medium-dense, damp, tan, fine SAND with some silt and S-2 scattered roots (Recessional Outwash) 5.0 - 6.0 Medium-dense to dense, moist, tan-gray gravelly SAND with some S-3 cobbles (Recessional Outwash) 6.0 - 7.0 Dense, moist, tan, gravelly, silty SAND with some cobbles (Weathered Till) 7.0 - 8.0 Very dense, moist, tan-gray, gravelly, silty SAND (Glacial Till) S-4 Test pit terminated at approximately 8 feet No caving observed No seepage observed Infiltration test IT-1 at 5 feet: 2.3 inches per minute Test Pit TP-2 Location: Wooded area approximately 60 feet east of dirt drive Approximate ground surface elevation: 392 feet 0.0 - 1.5 Forest duff over topsoil with prevalent roots ' 1.5 - 2.5 Loose to medium-dense, damp, brown, silty, fine SAND with S-1 scattered roots 2.5-- 5.0 Dense, damp, tan-gray SAND with some silt and gravel S-2 (Recessional Outwash) 5.0 - 10.0 Dense, damp, gray, gravelly SAND with trace to some silt S-3 (Recessional Outwash) Test pit terminated at approximately 10 feet �9r� No caving observed 7CL No seepage observed Infiltration test IT-2 at 5 feet: 1.6 inches per minute ' S:\WORDPROC\98\Seattle\12000s\12442\Test Pit Logs.wpd ' 8-91 M-12442-0 Test Pit Logs, Page 2 Depth (feet) Material Description Sample No. Test Pit TP-3 T Location: Wooded south-central site area Approximate ground surface elevation: 397 feet 0.0 - 1.5 Forest duff over topsoil with prevalent roots 1.5 - 6.0 Dense, damp, tan to gray, gravelly SAND with some silt and cobbles S-1 (Recessional Outwash) 6.0- 7.0 Very dense, moist, gray, gravelly, silty SAND (Glacial Till) Test pit terminated at approximately 7 feet No caving observed No seepage observed Test Pit TP-4 Location: Wooded area near southeast corner of site Approximate ground surface elevation: 398 feet 0.0 - 1.5 Forest duff over topsoil with prevalent roots 1.5 - 3.0 Dense, damp, tan, silty, gravelly, cobbly SAND (Weathered Till) 3.0 - 5.0 Very dense, moist, gray, gravelly, silty SAND (Glacial Till) Test pit terminated at approximately 5 feet No caving observed No seepage observed ' S:\WORDPROC\98\Seattle\12000s\12442\Test Pit Logs.wpd s ' 8-91 M-12442-0 Test Pit Logs, Page 3 ' Depth (feet) Material Description Sample No. Test Pit TP-5 Location: Wooded, southwest site area, approximately 50 feet east of dirt drive Approximate ground surface elevation: 387 feet 0.0 - 1.5 Forest duff over topsoil with prevalent roots 1.5 - 2.5 Medium-dense, damp, tan-brown, silty, fine SAND with some gravel S-1 2.5 - 8.0 Dense, damp, tan-gray, gravelly SAND to sandy GRAVEL with S-2, S-3 some silt(Recessional Outwash) Test pit terminated at approximately 8 feet No caving observed No seepage observed Test Pit TP-6 Location: Wooded area near northeast corner of site Approximate ground surface elevation: 400 feet 0.0 - 1.5 Forest duff over topsoil with prevalent roots 1.5 -4.0 Medium-dense, damp, brown, silty, fine SAND with some gravel and scattered roots (Weathered Till) 4.0 - 5.0 Very dense, moist, gray, gravelly, silty SAND (Glacial Till) S-1 Test pit terminated at approximately 5 feet No caving observed No seepage observed S.\WORDPROC\98\Seattle\12000s\12442\Test Pit Logs.wpd 8-91 M-12442-0 Test Pit Logs, Page 4 ' Depth (feet) Material Description Sample No. Test Pit TP-7 _P Location: Northeastern part of site, area of blackberry bushes Approximate ground surface elevation: 396 feet 0.0 - 2.0 Weeds over topsoil with prevalent roots S-1 2.0 -4.5 Medium-dense, damp, tan, gravelly SAND to sandy GRAVEL with S-2 some silt(Recessional Outwash) 4.5 - 5.5 Very dense, tan-gray, silty SAND with some gravel (Glacial Till) Test pit terminated at approximately 5.5 feet No caving observed No seepage observed Test Pit TP-8 Location: Area of blackberry bushes, east side of site Approximate ground surface elevation: 402 feet 0.0 - 1.5 Forest duff and weeds over topsoil with prevalent roots 1.5 -2.5 Medium-dense, damp, tan-brown, silty, fine SAND with some gravel (Weathered Till) 2.5 - 5.0 Very dense, moist, gray, gravelly, silty SAND (Glacial Till) Test pit terminated at approximately 5.0 feet No caving observed No seepage observed S:\WORDPROC\98\Seattle\12000s\12442\Test Pit Logs.wpd ' 8-91 M-12442-0 Test Pit Logs, Page 5 Depth (feet) Material Description Sample No. Test Pit TP-9 Location: By apple tree, southeast of red house Approximate ground surface elevation: 394 feet _ 0.0 - 1.0 Forest duff over topsoil with prevalent roots 1.0 -2.0 Loose to medium-dense, damp, tan-brown, silty, fine SAND with some gravel and cobbles 2.0- 6.0 Medium-dense to dense, damp, tan, gravelly, silty, fine SAND with scattered roots Test pit terminated at approximately 6.0 feet No caving observed No seepage observed Test Pit TP-10 Location: West of red house, approximately 20 feet east of gravel driveway Approximate ground surface elevation: 390 feet 0.0 - 1.0 Weeds and sod over topsoil with prevalent roots 1.0 - 2.0 Medium-dense, damp, tan-brown, silty, fine SAND with some gravel 2.0 -4.0 Dense, damp, tan-gray SAND with some silt, gravel and cobbles (Recessional Outwash) 4.0 - 5.0 Dense, damp, tan, sandy GRAVEL with some silt (Recessional Outwash) Test pit terminated at approximately 5.0 feet No caving observed No seepage observed S:\WORDPROC\98\Seattle\12000s\12442\Test Pit Logs.wpd ' 8-91 M-12442-0 Test Pit Logs, Page 6 Depth (feet) Material Description Sample No. Test Pit TP-11 -� Location: Brushy area near northwest corner of site Approximate ground surface elevation: 389 feet 0.0 - 1.0 Weeds and soil over topsoil with prevalent roots 1.0 - 1.5 Loose to medium-dense, damp, tan-brown, silty, fine SAND with some gravel 1.5- 5.0 Dense, damp, sandy GRAVEL with some cobbles and silt S-1, S-2 (Recessional Outwash) 5.0 - 6.0 Dense, damp, gravelly SAND with trace silt(Recessional Outwash) Test pit terminated at approximately 6.0 feet No caving observed No seepage observed Test Pit TP-12 Location: Brushy area approximately 30 feet south of S.E. 128th Street Approximate ground surface elevation: 392 feet ' 0.0 - 1.0 Brush over topsoil with prevalent roots 1.0 - 2.0 Medium-dense, damp, tan-brown, gravelly, silty SAND (Weathered Till) ' 2.0 -4.0 Very dense, damp, tan-gray, gravelly, silty SAND (Glacial Till) Test pit terminated at approximately 4.0 feet ' No caving observed No seepage observed Date excavated: August 13, 1998 Logged by: MAW 1 S:\WORDPROC\98\Seattle\12000s\12442\Te3t Pit Logs.wpd 1 Grain Size Analysis Report 100 i III I 90 - - - I , i 80 I ii 70 I i W 60 I W ' Z 50 ' LLI U a 40 I 30 i 20 i 10 I � 0 500 100 10 1 0.1 0.01 0.001 GRAIN SIZE -mm %COBBLES %GRAVEL %SAND I %SILT %CLAY 0.0 1 3.9 86.6 9.5 SIEVE PERCENT SPEC." PASS? Soil Description SIZE FINER PERCENT (X=NO) Sand some silt trace gravel 75 in. 100.0 375 in. 96.1 k #10 93.2 Atterber Limits #30 877.2 PL= na LL= na Pl= na 440 450 5 . Coefficients #100 25.0 D85= 0.543 60= 0.310 D50= 0.262 #200 9.5 D30= 0.173 D1 5= 0.101 D1 0= 0.0772 Cu= 4.02 Cc= 1.25 Classification USCS= SP-SM AAbHTU= A-3 Remarks Tested by:KH,FB ' Reviewed by: ML (no specification provided) Sample No.: #2196.1 Source of Sample: TP-1 Date: 8-20-98 Location: S-2 Elev./Depth: 4.0' Client: *AGRA Earth & Environmental Project: RENTON HIGHLANDS P.O. ENGMELRING GLOBAL SOLUTIONS Project No: 12442-0 Plate Anal Report Grain Size Analysis � c 100 90 i I l 80 - ; I , 70 t I I W 60 i i i t ZLL I I ' Z 50 W I � U a ao 30 ! I 20 10 I I ' i I ,i o 500 100 10 1 0.1 0.01 0.001 GRAIN SIZE- mm %COBBLES %GRAVEL %SAND %SILT %CLAY7-1 0.0 83.6 10.6 1 5.8 SIEVE PERCENT SPEC! PASS? Soil Description SIZE FINER PERCENT (X=NO) Gravel some sand trace silt 3.0 in. 100.0 2.0 in. 48.0 1.00 in. 42.9 .375 in. 22.0 AAtter�bergLimits ' ##4 14.4 PL= na LL= na Pl= na #20 1 .8 Coefficients #100 1 077.6 D85= 69.1 g6 0=57.5 D50= 52.1 #200 5.8 D30= 15.8 D15= 3.28 Dip= 0.325 Cu= 176.80 Cc= 13.39 Classification USCS= GP-GM AASHTO= A-1-a Remarks Tested by: KH,FB Reviewed by: ML (no specification provided) ' Sample No.: #2196.2 Source of Sample: TP-7 Date: 8-20-98 Location: S-2 Elev./Depth: 3.0' Client: *AGRA Earth & Environmental Project: RENTON HIGHLANDS P.O. INGINELRING GLOBAL SOLUTIONS Project No: 12442-0 Plate ' April 15, 1999 9-91 M-12442-A ' Sienna Architecture Company 411 S.W. Sixth Avenue Portland, Oregon 97204 ' Attention: Mr. Andy Jacobson ' Subject: Infiltration Test Report Supplement No. 1: Stormwater Infiltration Renton Highlands Post Office 4301 S.E. 1281h Street Renton, Washington ' Dear Andy: ' AGRA Earth &, Environmental, Inc. (AGRA) is pleased to submit this report describing the results of our supplementary infiltration tests for the above-referenced project. The purpose of our testing was to derive appropriate design infiltration capacities for the proposed stormwater infiltration ' system at the site. AGRA previously completed a geotechnical evaluation of the project site and submitted a Geotechnical Engineering Report (8-91 M-12442-0) dated October 6, 1998. ' As outlined in our proposal memorandum dated January 22, 1999, our scope of work was limited to field testing, data interpretation, and report preparation. We received your written authorization for our testing on March 9, 1999. This report has been prepared for the exclusive use of Sienna ' Architecture Company, and their consultants, for specific application to this project, in accordance with generally accepted geotechnical engineering practice. ' SITE AND PROJECT DESCRIPTION The project site consists of residentlal property, including an existing house and undeveloped land, located at 4301 S.E. 128"Street in Renton,Washington. This site comprises a roughly rectangular parcel that measures about 310 by 410 feet overall and encompasses approximately 2.9 acres. Site boundaries are generally delineated by residential properties on the east and west, by S.E. 128' Street on the north, and by undeveloped property on the south. The enclosed Site & ' Exploration Plan (Figure 2) illustrates these site boundaries and adjacent existing features. Development plans call for constructing a new post office facility at the project site. As part of this development, stormwater will be routed through a biofiltration Swale, discharged into underground detention pipes, and subsequently infiltrated into the subsurface soils. The proposed pipes will SaWOROPR0M99 ProjectslSeettle1120WS%12442V 2442A.wM 04/22/99 THU 08: 40 ITX/RX NO 68291 Z 002 \i DI ' Sionne Architecture Company 9-91 M-12442-A April 15, 1999 Page 2 extend about 10 feet below existing grades and will be located in the eastern and southern portions ' of the site. The locations and depths of these currently proposed infiltration pipes do not correlate with the previously proposed infiltration pipes. Consequently, the project civil engineer is requesting additional infiltration tests for design purposes. ' EXPLORATORY METHODS During our previous geotechnical exploration of the project site, we advanced twelve test pits (designated TP-1 through TP-12) and conducted two infiltration tests (designated IT-1 and IT-2) at the locations of the originally proposed infiltration pipes. For this supplemental phase of work, we explored subsurface conditions at the site during March 1999. Our exploration and testing program comprised four test pits(designated TP-13 through TP-16)advanced at strategic locations ' across the site, and four infiltration tests (designated IT-3 through IT-6) performed at strategic depths in our test pits. Table 1 summarizes the approximate functional locations, surface elevations,and termination depths of our pertinent subsurface explorations, and Figure 2 illustrates their approximate relative locations. ' TABLE 1 APPROXIMATE LOCATIONS, ELEVATIONS, AND DEPTHS OF EXPLORATIONS Surface Termination ' Exploration Functional Location Elevation Depth (feet) (feet) TP-1* Previously proposed infiltration pipe; western 392 8 ' side of site TP-2* Previously proposed infiltration pipe; western 392 10 side of site ' TP-13* Proposed stormwater bioswale; northwestern 390 10 corner of site TP-14- Proposed stormwater bioswale and infiltration 392 7 pipe; western side of site TP-15* Proposed infiltration pipe; southwestern corner 389 9 of site TP-16* Proposed infiltration pipe; southeastern corner 396 6 of site Elevation datum: 1999 site plan by AHBL Engineers *Includes infiltration test Our recent infiltration tests were performed in general accordance with the procedures prescribed in the EPA manual entitled On-Site Wastewater Treatment and Disposal Systems, except as modified by King County. Specifically,a test pit was excavated to the desired infiltration test depth, ' a 6-inch-diameter PVC pipe was tamped approximately 6 inches into the soil at the bottom, and ' SAW0RDPROC\9S ProjoclsZoaltle11 2000 511 244211 2 44 2A.wpd 04/22/99 THU 08: 40 tTX/RX NO 68291 Z 003 1`. Sienna Architecture Company 9-91 M-12442-A April 15, 1999 Pane 3 the test pit was fully backfilled with soil. The pipe was then filled with water, and the water level was maintained for at least 4 hours to saturate the test soils. Following this saturation period, the pipe was filled with 12 inches of water, and the time required for every 1-inch drop in water level was recorded through a total drop of 6 inches. We repeated this procedure three times at each test ' location and subsequently calculated the average rate of the three trials. SITE CONDITIONS All of our on-site test pits encountered %to 1'/z feet of topsoil consisting of loose, organic-rich, silty sands, mantling native soils consisting of medium-dense to dense, gravelly sands to silty sands (recessional outwash or weathered till). At depths of 5 to 10 feet, all test pits encountered a very dense, silty sand, which we interpret to be glacial till. In the specific locations of the proposed infiltration systems, we observed the recessional outwash or weathered till horizon at elevations ranging from about 388 to 395 feet, and the glacial till horizon at elevations ranging from 382 to 391 feet. The enclosed Test Pit Logs provide a detailed description of the soil strata encountered in jour subsurface explorations. During our recent exploration (March 1999), two of ourfour explorations encountered groundwater, at depths ranging from 7 to 8 feet below existing grades and at elevations ranging from 382'/2 to 385 feet. We interpret this groundwater to be perched atop or within the glacial till horizon. Because our explorations were performed during an extended period of alternately wet and dry weather, these observed groundwater conditions may closely represent the yearly average levels; somewhat lower levels probably occur during the summer and fall months, whereas higher levels , probably occur during the winter and early spring months. Throughout the year, groundwater levels would likely fluctuate in response to changing precipitation patterns, off-site construction activities, and site utilization. INFILTRATION TEST RESULTS Our field infiltration tests disclosed somewhat variable infiltration rates across the site, reflecting variations in site conditions. Table 2 summarizes the results of our infiltration testing and indicates ' that infiltration rates generally decrease with depth. All four tests performed in the recessional outwash or weathered till soils yielded an average ultimate infiltration rate of 1.73 inches per minute, whereas the underlying glacial till soils yielded an average ultimate infiltration rate of 0.36 inches per minute. However, a safety factor of at least 3.0 should be applied to these rates, to account for variations within each soil deposit. Therefore, our recommended maximum infiltration rates for design purposes would be 0.57 and 0.12 inches per minute for the upper native recessional/weathered soils and the underlying glacial till soils, respectively. For the proposed infiltration pipe elevations supplied to us by AHBL, the glacial till soils and the perched groundwater are expected to have the dominant influence on the proposed system. If greater infiltration rates are desirable, it would be advantageous to raise the system such that infiltration occurs in the overlying recessional/weathered deposit,above the observed groundwater ' levels. Invert elevations would need to be above 391 feet to consistently overlie the glacial till sAwoRIDPROM99 PryieetsAseaivakunoD6\l2442\1244 2A.Wpd 04/22/99 T11LI 08: 40 [TX/RX NO 68291 Z 004 9-91 M-12442-A Sienna Architecture Company Page 4 April 16, 1999 horizon, but invert elevations as low as 382 feet would be feasible for localized areas. Table 3 ' summarizes our recommended criteria for design of the infiltration systems. TABLE 2 INFILTRATION TEST RESULTS FOR IN-SITU SOILS Test Average ' Infiltration Exploration Depth Soil Type Infiltration Rate Test (feet) (inches/min) IT-1 TP-1 5 Gravelly SAND 2.30 IT-2 TP-2 5 Gravelly SAND 1.60 IT-3 TP-13 10 Glacial Till 0.24 IT-4 TP-14 61/2 Glacial Till 0,77 iIT-5 TP-15 81/2 Glacial Till 0.06 IT-6 TP-1l 1 4 1 Gravelly, silty SAND 1.30 TABLE 3 RECOMMENDED ALLOWABLE INFILTRATION RATES Elevation Range of Ultimate Maximum Allowable Soil Type Sall Horizon Infiltration Rate Infiltration Rate (feet) (inches/min) (inches/min) Recess ional/Weathered 388 to 395 1.73 0.57 Glacial Till 382 to 391 0.36 0.12 ' SAWOR0PPZ=99Pr0j8C15\Se811W1ZO 0s\12442\12442A.wpd 04/22/99 THU 08: 40 [TX/RX NO 68291 U 005 ' Sicnna Architecture Company 9-91M-12442-APage 5 April 15, 1999 CLOSURE We appreciate the opportunity to be of service on this project. If you have any questions regarding this report or any aspects of the project, please feel free to contact our office. ' Sincerely, r 1 Grace J. Barrera, E.I.T. James M. Brisbine, P.E. Staff Engineer Associate GJB/JMB/jdp Enclosure: Test Pit Logs TP-13 through TP-16 Distribution: Sienna Architecture (2) Attn: Mr. Andy Jacobson AHBL Engineers (1) Attn: Ms. Connie Linden ' SAWD Df ROC\99 projectylseattle\t:000s\1 2 44 211 2442A,WPI 04/22/99 THU 08: 40 [TX/RX NO 68291 Z006 TP-1Ot9 1 TP-11 I .,I •( fTT-4 \1U s 5 ,7p 2 C r� IIT-2 IT-9 TP-15 I I I O TP-1 rr-1 �. Kul ftii � 1 ON P- Ld I Lo ' � N H CA L�ADIN� a DOG( = ro a � - I :L w L- p9 �7 I Z y I l( FIT LEGEND TP'� PROI OSEO BUILDING I 7L r- R'6 a TP-12 IL51 FIl NUMBER AND APPROXIMATE ` Q0 t9 LDCAnD11 (IV" SR10'n TP-4 C b tsi IT'4 INiILIRAIION TEST NUMBER AND Cyy t9 APflRQXIMAIF LOCATION (1990 STUDY) 1 4 TP-16 TcST P.T NUMBER AND j-J-lC 1MATE I ? Q- l-) LCCATIDN (CURREVT STUDY; TP-6 TP-6 R-6 INf1LTRAAOH TEST NUMBER AND O' APPROXIMATE LOCATION (G=a"iR-NT STUDY) cc �3 N - I l SITE 8i EXPLORATION PLAN FlGU RE c ' - -�- O A G R A U' C 46 80 Earth A Enviroalmental RENTON HIGHLANOS POST OFFICE /� ` L 71335 N.E. 127N0 WAY, gJIJE IDO SCALE IN FEET KIRKLAND, WA. U.E.A 99D34-69:l1 r RLNIIXJ, M'A9tlNCI DN l (t C ' APPENDIX D ' Sediment Trap Calculations 1 1 r i 1 ,�HBL Project ��—// A la rGJ f('�r-f i c No. �� c 2 �� nVCalculations ge of ' AHOL Subject —cd 'C-+ ��lJ �'�//!4 Phone ❑ Fax With/To Fax# _ ❑ Memorandum ' Address #Faxed Pages ❑ Meeting Minutes ❑Telephone Memo Date: /tea s �Vcsy'Sa fca f, Tp o+G' 1 3 _ — 13y. 7" Copies to: ,o'C7(Zun T. a"f .,, �c r K lJat�r- Sri c e f 2215 N.30th Street Suite 300 ' Tacoma,WA 98403 Old Town Historical District ' 253/383-2422 253/383-2572 FAX If this does not meet with your understanding,please contact us in writing within seven days.THANK YOU. Project /�i� U; �S r�� ��*T�"c No. ❑ P4e of ' Subject_ �o/Mc. 7�f� Jr, PhoneL—�/Calculations AHBL ❑ Fax WithlTo Fax# ❑ Memorandum Address #Faxed Pages ❑ Meeting Minutes ❑Telephone Memo ' Date: ' By io '-Fs Copies to: 1 2215 N.30th Street ' Suite 300 Tacoma,WA 98403 Old Town Historical District 253/383-2422 253/383-2572 FAX 1 If this does not meet with your understanding,please contact us in writing within seven days.THANK YOU. ' 5/11/99 8 : 5 : 36 am AHBL page 1 USPO Highlands, Renton, Wa . 98027 . 10 TESCP-SEDIMENT TRAP SIZING K: \CIVIL\YR 1998\98027\027WWK01 BASIN SUMMARY ' BASIN ID: SOUTHSED NAME : SOUTH SED TRAP-10YEAR DEVEL S . SBUH METHODOLOGY TOTAL AREA. . . . . . . : 1 . 39 Acres BASEFLOWS : 0 . 00 cfs ' RAINFALL TYPE. . . . : TYPElA PERV IMP PRECIPITATION. . . . : 2 . 90 inches AREA. . : 0 . 00 Acres 1 . 39 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . . . : 0 . 00 98 . 00 TC. . . . : 0 . 00 min 3 . 75 , min ABSTRACTION COEFF: 0 . 20 impTcReach - Sheet L: 45 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0200 ' impTcReach - Channel L: 524 . 00 kc :42 . 00 s : 0 . 0050 PEAK RATE : 0 . 85 cfs VOL: 0 . 31 Ac-ft TIME : 470 min BASIN ID: WESTSED NAME : WEST SED POND-10YEAR DEVEL S . ' SBUH METHODOLOGY TOTAL AREA. . . . . . . : 1 . 78 Acres BASEFLOWS : 0 . 00 cfs RAINFALL TYPE . . . . : TYPEIA PERV IMP ' PRECIPITATION. . . . : 2 . 90 inches AREA. . : 0 . 00 Acres 1 . 78 Acres TIME INTERVAL. . . . : 10 . 00 min CN. . 0 . 00 98 . 00 TC. . . . . 0 . 00 min 3 . 75 min ' ABSTRACTIONCOEFF : 0 . 20 impTcReach - Sheet L: 45 . 00 ns : 0 . 0110 p2yr: 2 . 00 s : 0 . 0200- impTcReach Channel L: 524 . 00 kc :42 . 00 s : 0 . 0050 PEAK RATE : 1 . 09 cfs VOL: 0 .40 Ac-ft TIME : 470 min r KING COUNTY, WAS HINGTON, SURFACE W ATER DESIGN MANUAL (2) CN values can be area weighted when they apply to pervious areas of similar CN's (within 20 CN points). However, high CN areas should not be combined with low CN areas (unless the low CN areas are less than 1 5% of the subbasin). In this case, separate hydrographs should be generated and summed to form one hydrograph. FIGURE 3.5.2A HYDROLOGIC SOIL GROUP OF THE SOILS IN KING COUNTY HYDROLOGIC HYDROLOGIC ' SOIL GROUP GROUP' SOIL GROUP GROUP` C Orcas Peat D Alderwood C Oridia D Arents, Alderwood Material B Cvall C ' Arents, Everett Material C Pilchuck C Beausite D Puget D Bellingham D Puyallup B Briscot' D B Ragnar Buckley Renton D Coastal Beaches Variable p Riverwash Variable Earlmont Silt Loam Safal C Edgewick C' A/B `Sammamish p Everett Seattle D Indianola A Shacar D Kitsap C C Klaus C Si Silt Mixed Alluvial Land Variable Snohomish D ' A Sultan C Neilton Tukwila D Newberg C L'rban Variable Nooksack p ' Normal Sandy Loam D Woodinville HYDROLOGIC SOIL GROUP CLASSIFICATIONS A. (Low runoff potential). Soils having high infiltration rates, even when thoroughly wetted, and consisting chiefly of deep, well-to-excessively drained sands or gravels. These soils have a high rate of water ' transmission. B. (Moderately low runoff potential). Soils having moderate infiltration rates when thoroughly wetted, and consisting chiefly of moderately fine to moderately coarse textures. These soils have a moderate rate of ' water transmission. C. (Moderately high runoff potential). Soils having slow infiltration rates when thoroughly wetted, and consisting chiefly of soils with a layer that impedes downward movement of water, or soils with moderately fine to fine textures. These soils have a slow rate of water transmission. D. (High runoff potential). Soils having very slow infiltration rates when thoroughly wetted and consisting chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a ' hardpan or clay layer at or near the surface, and shallow soils over nearly impervious material. These soils have a very slow rate of water transmission. ' From SCS, TR-55, Second Edition, June 1986, Exhibit A-1. Revisions made from SOS, Soil Interpretation Record, Form #S, September 1988. 11/92 ' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ' TABLE 3.5.2I3 SCS WESTERN WASHINGTON RUNOFF CURVE NL'NIBERS f ' SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (Published by SCS in 1982) Runoff curve numbers for selected agricultural, suburban and urban land use for Type 1 A ' rainfall distribution, 24-hour storm duration. CURVE NUMBERS BY HYDROLOGIC SOIL GROUP ' LAND USE DESCRIPTION A B C D Cultivated land(1): winter condition I 86 91 94 95 Mountain open areas: low growing brush and grasslands 74 82 89 92 Meadow or pasture: I 65 78 85 89 ' Wood or forest land: undisturbed or older second growth I 42 64 76 81 Wood or forest land: young second growth or brush 55 72 81 86 Orchard: with cover crop 81 88 92 94 ' Open spaces, lawns, parks, golf courses, cemeteries, 7- landscaping. good condition: grass cover on 75% 68 80 86 90 or more of the area ' fair condition: grass cover on 50% to 75% of the area 77 85 90 92 Gravel roads and parking lots I 76 85 89 91 Dirt roads and parking lots I 72 82 87 89 ' Impervious surfaces, pavement, roofs, etc. 98 98 98 98 Open water bodies: lakes, wetlands, ponds, etc. 100 100 100 100 ' Single Family Residential (2) Dwelling Unit/Gross Acre % Impervious (3) 1.0 DU/GA 15 Separate curve number ' 1.5 DU/GA shall be selected 2. 25 for pervious and 2.5 DU/GA 30 impervious portion 3.0 DU/GA DU/GA 34 of the site or basin 3.5 DU/GA 38 4.0 DU/GA 42 4.5 DU/GA 46 ' 5.0 DU/GA 48 5.5 DU/GA 50 6.0 DU/GA 52 6.5 DU/GA 54 ' 7.0 DU/GA 56 Planned unit developments, % impervious condominiums, apartments, must be computed ' commercial business and industrial areas. (1) For a more detailed description of agricultural land use curve numbers refer to National Engineering Handbook, Section 4, Hydrology, Chapter 9, August 1972. (2) Assumes roof and driveway runoff is directed into street/storm system. (3) The remaining pervious areas (lawn) are considered to be in good condition for these curve numbers. 11/92 3.5.'-3 ' APPENDIX E Maintenance and Operations Sample Plan 1 1 1 1 r AHBL KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL MAINTENANCE REQUIREMENTS FOR PRIVATELY MAINTAINED DRAINAGE FACILITIES NO. 1 - PONDS ' MaiMMat►w Conditions When Maintenance Results Expected When Component Defect is Needed Maintenance Is Performed o General Trash & Debris Any trash and debris which exceed 1 cubic Trash and debris cleared from foot per 1,000 square feet (this is about equal site. to the amount of trash it would take to fill up ' one standard size office garbage can). In general, there should be no visual evidence of dumping. Poisonous Any poisonous vegetation which may No danger of poisonous Vegetation constitute a hazard to County personnel or the vegetation where County public. Exampies of poisonous vegetation personnel or the public might include: tansy ragwort, poison oak, stinging normally be. (Coordination with nettles, devils club. Seattle/King County Health Department) Pollution Oil, gasoline, or other contaminants of one No contaminants present other gallon or more or any amount found that than a surface film. (Coordination could: 1) cause damage to plant, animal, or with Seattle/King County Health ' marine life; 2) constitute a fire hazard; or Department) 3) be flushed downstream during rain storms. Unmowed Grass/ If facility is located in private residential area, When mowing is needed, Ground Cover mowing is needed when grass exceeds 18 grass/ground cover should be ' inches in height. In other areas,the general mowed to 2 inches in height. policy is to make the pond site match adjacent ground cover and terrain as long as there is no interference with the function of the facility. Rodent Holes Any evidence of rodent Was if facility is Rodents destroyed and dam or acting as a dam or berm, or any evidence of berm repaired. (Coordination with water piping through dam or berm via rodent Seattle/King County Health holes. Department) Insects When insects such as wasps and hornets Insects destroyed or removed interfere with maintenance activities. from site. Tree Growth Tree growth does not allow maintenance Trees do not hinder maintenance ' access or interferes with maintenance activity activities. Selectively cultivate (i.e., slope mowing, silt removal, vectoring, or trees such as alders for firewood. equipment movements). If trees are not interfering with access, leave trees alone. ' Side Slopes of Erosion Eroded damage over 2 inches deep where Slopes should be stabilized by Pond cause of damage is still present or where using appropriate erosion control there is potential for continued erosion. measure(s); e.g., rock reinforcement, planting of grass, compaction. Storage Area Sediment Accumulated sediment that exceeds 10% of Sediment cleaned out to designed the designed pond depth. pond shape and depth; pond reseeded if necessary to control ' erosion. Pond Dikes Settlements Any part of dike which has settled 4 inches Dike should be built back to the lower than the design elevation. design elevation. Emergency Rock Missing Only one layer of rock exists above native soil Replace rocks to design Overflow/Spillway in are five square feet or larger, or any standards. exposure of native soil. A-1 11194 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ' NO. 3 - CLOSED DETENTION SYSTEMS (PIPES/TANKS) ' Conditions When Maintenance Resutts Expected Maintenance When Maintenance Is Performed Component Defect is Needed ' Storage Area Plugged Air Vents One-haft of the cross section of a vent is Vents free of debris and sediment. blocked at any point with debris and sediment. Debris and Accumulated sediment depth exceeds All sediment and debris removed from Sediment 10%of the diameter of the storage area storage area. for 1/2 length of storage vault or any point depth exceeds 15% of diameter. Example: 72-nch storage tank would require cleaning when sediment reaches depth of 7 inches for more than 1/2 length of tank. Joints Between Any crack allowing material to be All loeidnts between tank/pipe sections are Tank/Pipe Section transported into facility. Tank/Pipe Bent Any part of tank/pipe is bent out of shape Tank/pipe repaired or replaced to design. Out of Shape more than 10%of its design shape. t Manhole Cover not in Place C o is missing or only ma intenance. tn place. Manhole is closed. Any Locking Mechanism cannot be opened by one Mechanism opens with proper tools. Mechanism Not maintenance person with proper tools. Working Bolts into frame have less than 1/2 inch of thread (may not apply to self-locking lids). ' Cover Difficult to One maintenance person cannot remove Cover can be removed and reinstalled by Remove lid after applying 80 pounds of lift. Intent one maintenance person. is to keep cover from sealing off access to maintenance. ' Ladder Rungs King County Safety Office and/or Ladder meets design standards and Unsafe maintenance person judges that ladder is allows maintenance persons safe access. unsafe due to missing rungs, misalignment, rust, or cracks. ' Catch Basins See "Catch Basins" Standard No. 5 See "Catch Basins' Standard No. 5 ' A-3 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL NO. 5 - CATCH BASINS ' Conditions When Maintenance Results Expected Maintenance When Maintenance is Performed Component Defect Is Needed ' General Trash & Debris Trash or debris of more than 1/2 cubic No trash or debris located immediately in (Includes foot which is located Immediately in front front of catch basin opening. Sediment) of the catch basin opening or is blocking capacity of basin by more than 10%. Trash or debris on the basin)that No trash or debris in the catch basin. exceeds 1/3 the depth from the bottom of basin to invert of the lowest pipe into or out of the basin. Trash or debris in any inlet or outlet pipe Inlet and outlet pipes free of trash or blocking more than 1/3 of its height. debris. ' Dead animals or vegetation that could No dead animals or the catch basin.vegetation present generate odors that would cause within complaints or dangerous gases (e.g., methane). ' Deposits of garbage exceeding 1 cubic No condition present which would attract foot in volume. or support the breeding of insects or rodents. Structural Damage Corner of frame extends more than 3/4 Frame is even with curb. to Frame and/or inch past curb face into the street (if Top Slab applicable). Top slab has holes larger than 2 square Top slab is free of holes and cracks. ' inches or cracks wider than 1/4 inch (intent is to make sure all material is running into the basin). Frame not sitting flush on top slab, i.e., Frame is sitting flush on top slab. ' separation of more than 3/4 inch of the frame from the top slab. Cracks in Basin Cracks wider than 1/2 inch and longer Basin replaced or repaired to design Walls/Bottom than 3 feet, any evidence of soil particles standards. entering catch basin through cracks, or maintenance person judges that structure is unsound. Cracks wider than 1/2 inch and longer No cracks more than 1/4 inch wide at the than 1 foot at the joint of any inlet/outlet joint of inlet/outlet pipe. pipe or any evidence of soil particles entering catch basin through cracks. Settlement/ Basin has settled more than 1 inch or has Basin replaced or repaired to design Misalignment rotated more than 2 inches out of standards. alignment. Fire Hazard Presence of chemicals such as natural No flammable chemicals present. gas,oil, and gasoline. Vegetation Vegetation growing across and blocking No vegetation blocking opening to basin. ' more than 10%of the basin opening. Vegetation growing in inlet/outlet pipe No vegetation or root growth present. joints that is more than six inches tall and less than six inches apart. Pollution Nonflammable chemicals of more than No pollution present other than surface 1/2 cubic foot per three feet of basin film. length. A-5 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL NO. 6 - DEBRIS BARRIERS (e.g. Trash Racks) ' Conditfons When Maintenance Results Expected Maintenance is Needed When Maintenance is Performed component Defect ' General Trash and Debris Trash or debris that is plugging more Barrier Gear to receive capacity flow. than 20% of the openings in the barrier. Metal Damaged/ Missing Bars are bent out of shape more than 3' 3Barsi nch in place with no bends more than Bars inches. Bars are missing or entire barrier is Bars in place according to design. missing. Bars are loose and rust is causing 50% Repair or replace barrier to design deterioration to any part of barrier. standards. 1 ' A-7 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ' NO. 8 - FENCING Maintenance Conditions when Maintenance Results Expected Component Defect is Needed When Maintenance Is Performed ' General Missing or Broken Any defect in the fence that permits easy Parts in place to provide adequate Parts entry to a facility. security. Parts broken or missing. Broken or missing parts replaced. ' Erosion Erosion more than 4 inches high and 12- No opening under the fence that exceeds 18 inches wide permitting an opening 4 inches in height. under a fence. ' Wire Fences Damaged Parts Posts out of plumb more than 6 inches. Posts plumb to within 1-1/2 inches. Top rails bent more than 6 inches. Top rail free of bends greater than 1 inch. Any part of fence (including posts,top Fence is aligned and meets design ' rails, and fabric) more than 1 foot out of standards. design alignment. Missing or loose tension wire. Tension wire in place and holding fabric. ' Missing or loose barbed wire that is Barbed wire in place with less than 3/4- sagging more than 2-1/2 inches between inch sag between posts. Posts. ' Extension arm missing, broken, or bent Extension arm in place with no bends out of shape more than 1-1/2 inches. larger than 3/4 inch. Deteriorated Paint Part or parts that have a rusting or scaling Structurally adequate posts or parts with or Protective condition that has affected structural a uniform protective coating. Coating adequacy. Openings in Fabric Openings in fabric are such that an 8- No openings in fabric. inch-diameter ball could fit through. ' A-9 I/'90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL NO. 10 - CONV EYANCE SYSTEMS (Pipes & Ditches) ' Conditions When Maintenance Resufts Expected Maintenance is Needed When Maintenance is Performed Component Defect ' Pipes Sediment&Debris Accumulated sediment that exceeds 20% Pipe cleaned of all sediment and debris. of the diameter of the pipe. Vegetation Vegetation that reduces free movement of All vegetation removed so water flows ' water through pipes. Y 9h pipes. Damaged Protective coating is damaged; rust is Pipe repaired or replaced. causing more than 50%deterioration to any part of pipe. Any dent that decreases the cross section Pipe repaired or replaced. area of pipe by more than 20%. Open Ditches Trash &Debris rash 000 debris exceefeet ds 1dit cubic scopes. Trash and debris cleared from ditches. per Accumulated sediment that exceeds 20% Ditch cleaned/flushed of all sediment and Sediment of the design depth. debris so that It matches design. ' Vegetation Vegetation that reduces free movement of Water flows freely through ditches. water through ditches. Erosion Damage to See 'Ponds' Standard No. 1 See 'Ponds' Standard No. t Slopes Rock Lining Out of Maintenance person can see native soil Replace rocks to design standard. Place or Missing (tf beneath the rock lining. ' 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 No.6 ' (e.g., Trash Rack) A-11 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ' NO. 12 - ACCESS ROADS/EASEMENTS ' C Maintenance ondttions When Maintenance ResuftWhen Maintenance Expected xp enaer ce Is Performed Component Defect Is Nesded y ' General Trash and Debris Trash and debris exceeds 1 cubic foot Trash and debris cleared from site. per 1,000 square feet, i.e.,trash and debris would fill up one standard size garbage can. ' Blocked Roadway Debris which could damage vehicle tires Roadway ti e free of debris which could (glass or metal). damage Any obstructions which reduce clearance Roadway overhead clear to 14 feet high. ' above road surface to less than 14 feet. Any obstructions restricting the access to Obstruction removed to allow at least a a 10-to 12-foot width for a distance of 12-foot access. ' more than 12 feet or any point restricting access to less than a 10-foot width. Road Surface Settlement, When any surface defect exceeds 6 Road surface uniformly smooth with no Potholes, Mush inches in depth and 6 square feet in area. evidence of settlement, potholes, mush ' Spots, Ruts In general, any surface defect which spots,or ruts. hinders or prevents maintenance access. Vegetation in Road Weeds growing in the road surface that Road surface free of weeds taller than 2 Surface are more than 6 inches tall and less than inches. ' 6 inches apart within a 400-square-foot area. Shoulders and Erosion Damage' Erosiothan onrwithhisn 1 foot of wide and the In hes deep oadway ore theShoulderfree of surrounding oadion and matching Ditches Weeds and Brush Weeds and brush exceed 18 inches in Weeds and brush cut to 2 inches in height or hinder maintenance access. height or cleared in such a way as to allow maintenance access. A-13 1/90 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL ' ICING COUNTY, WASHINGTON SURFACE WATER DESIGN MANUAL ' APPENDIX B MASTER DRAINAGE PLAN ' OBJECTIVE, CRITERIA COMPONENTS AND REVIEW ' PROCESS 11/92 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL APPENDIX B MASTER DRAINAGE PLAN OBJECTIVE, CRITERIA AND COMPONENTS, AND REVIEW PROCESS ' Objective The objective of the Master Drainage Plan (MDP) is to propose specific drainage control systems that will prevent significant adverse impacts to the site's natural hydrologic system and to existing and planned off-site drainage systems. Significant adverse impacts are defined as follows: ' (1) Any increase in flow rates and/or volumes that would result in flooding along the natural and/or constructed drainage system, or that would aggravate existing flooding problems, either on-site ' or downstream. (2) An increase of flow rates and/or volumes, both on- and off-site that would de-stabilize the existing geomorphic balance of the natural drainage systems. Examples would include an ' increase in the rate or frequency of streambank erosion resulting in bank/slope failures along stream corridors, and downstream sedimentation reducing channel capacity. (3) Alteration of natural topography and/or native vegetation that would result in unstable soil conditions, slopes, or embankments. (4) Alteration of the natural hydrologic features that would reduce their functional ability to preserve water quality and quantity and/or in-stream and other aquatic habitat values. ' (5) Alteration of ground water/interflow that would adversely change downstream base flows and/or impair existing water rights. ' Criteria The proposed drainage control system and impacts shall be supported by a detailed technical ' analysis and report as a part of the MDP. The report shall include appropriate geotechnical investigations, water quality and aquatic habitat analysis, and hydrologic computer modeling (see Section 3.2 in Chapter 3). The report shall also include maintenance and operation provisions for the existing natural drainage system and any on-site drainage facilities. Specific maintenance plans ' and agreements, identifying maintenance responsibilities, must be provided for any facility privately maintained. The hydrologic and hydraulic analysis of the site, basin, and downstream system shall be done ' using the methods described in this Manual. Exceptions are for plans required to prepare hydrologic models using rainfall and stream gage data. Any upstream contributing systems or sub- basins shall be analyzed for both existing and future development conditions (as shown in the latest adopted Community Plan, the King County Comprehensive Plan, or other land use maps). Components of Master Drainage Plans ' The MDP shall consist of two major components: a technical report; and plans and mapping. (1) Technical Report ' The report shall provide a comprehensive analysis of existing and proposed surface and subsurface water quantity and quality conditions for both on- and off-site systems. Off-site systems may include upstream and downstream hydrology. Upstream analysis shall include the total drainage area contributing to the site. Downstream analysis shall extend to an acceptable receiving body of water. ' � B-1 11/92 KING COUNTY, WASHINGTON, SU RFACE WATER DESIGN MANUAL (a) Delineation of sub-basins of appropriate size/land use for computer model characterization and hydraulic analysis of all tributary flows. ' (b) Location and size of all existing and proposed hydrologic features and facilities in the basins. This includes lakes, ponds, wetlands, swales, streams, pipes, and culverts. ' (c) Overall plan/profile and cross-sections of conveyance systems and identification of the floodplain and floodway and frequency of flooding for existing and developed conditions. (d) Identify areas of in-stream erosion, sedimentation and/or unstable slopes. (e) Identify general required building setbacks, clearing limits and Native Growth Protection Easements in areas of steep slopes and drainage features. (f) Site soils identification and preliminary analysis for controlling erosion during construction and for use in hydrologic modeling. ' (g) Identify upstream and downstream habitat condition, i.e., spawning, rearing, and transport areas; pools, riffles, and other in-stream habitat features; and species and populations observed. Locations shall be keyed to the map produced in Item (2)(b), above. Review Process Master Drainage Plans are submitted directly to the SWM Division for review. They must, however, be a part of a permit application that has been filed with the BALD Division (see Section 1 .1 .1 in Chapter 1). The MDP process should commence coincidentally with the SEPA process. Prior to commencing preparation of the MDP, the applicant and design engineer (often a team ' that includes other design professionals such as geotechnical engineers and/or biologists, etc.) should request a MDP "scoping" meeting with the SWM Division in order to coordinate the requirements for the hydrologic modeling and other special analysis which may be required. At ' this meeting the applicant should present a proposed outline for the proposed MDP that includes a description of the proposed project, a schedule for preparation of the MDP, and a description of any known environmental or regulatory issues related to the proposal. The SWM Division will review the components of the MDP as submitted, in a timely manner. The fees for review of the MDP will be determined from resources (consultant, staff, equipment) required and will be billed to the applicant by King County. Review fees shall be paid by the applicant to King County prior to receiving MDP plan approval. Following approval in concept of all of the MDP components, the applicant will submit four complete final MDP packages to the SWM Division for approval. Two copies will be kept by the SWM Division, one copy will be transmitted to the BALD Division and one copy will be ' returned to the applicant for their records. Any additional questions regarding the MDP review process should be directed to the reviewer tin the SWM Division. B-3 11/92 L t I L 1 I L_ i I 1 k t i i I ri V HBL 'At _i 2215 NORTH 30TH STREET SUITE 300 TACOMA, WA 98403 PH:(206) 383-2422 FAX:(206) 383-2572 ahbl_inc@ix.netcom.com