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HomeMy WebLinkAboutMisc 16-000425Project: Prepared For: Prepared By: Reviewed By: Date: A CIVIL ENGINEERING COMPANY 219 First Avenue S., Suite 401 Seattle, WA 98104 106.402.4644 CONDITIONAL USE PERMIT TECHNICAL INFORMATION REPORT Renton Commons 215 Whitworth Ave Renton, WA 98057 Tonkin Architecture 204 1" Ave South Seattle, WA 98104 Ryan Yokum, EIT Marc Errichetti, PE June 7, 2016 Section No. SECTION I SECTION II SECTION Ill SECTION IV TABLE OF CONTENTS Subject Page No. PROJECT OVERVIEW ........................................................................... 1 CONDITIONS AND REQUIREMENTS SUMMARY ................................. 9 OFFSITE ANALYSIS ............................................................................ 11 FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS ........................................................................... 16 SECTION V CONVEYANCE SYSTEM ANALYSIS AND DESIGN ............................... 19 SECTION VI SPECIAL REPORTS AND STUDIES ...................................................... 19 SECTION VII OTHER PERMITS ............................................................................... 19 SECTION VIII CSWPPP ANALYSIS AND DESIGN ...................................................... 19 SECTION IX BOND QUANTITIES AND DECLARATION OF COVENANTS ........................................................ 20 SECTION X OPERATIONS AND MAINTENANCE MANUAL. .................................. 21 LIST OF FIGURES FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 VICINITY MAP ..................................................................................... 2 TIR WORKSHEET ................................................................................. 3 EXISTING SITE SOILS ........................................................................... 6 EXISTING LAND COVER ....................................................................... 7 DEVELOPED LAND COVER .................................................................. 8 OFF-SITE STUDY AREA ...................................................................... 11 DOWNSTREAM STORMWATER SYSTEM .......................................... 15 LIST OF APPENDIXES APPENDIX A CONVEYANCE CALCULATIONS APPENDIX B FLOW CONTROL APPENDIX C GEOTECHNICAL REPORT APPENDIX D OPERATION AND MAINTENANCE MANUAL • SECTION I -PROJECT OVERVIEW General Description: The proposed Renton Commons project is located at 215 Whitworth Avenue in Renton Washington (See Figure 1 for vicinity map). The project consists of the demolition of an existing single family house and associated hardscape, and the construction of a new low income residential building comprising five stories with parking located within the building, on the ground floor. The proposed project also involves the creation of new hardscape walkways and landscaped areas, as well as a small outdoor play area. The proposed redevelopment is designed to meet the requirements of the 2009 King County Surface Water Design Manual {KCSWDM) and the 2010 City of Renton Amendments to the King County Surface Water Design Manual. A summary of the project data is provided in the TIR worksheet (see Figure 2). Predeveloped Conditions: The existing site comprises a 0.32 acre parcel. Approximately .04 acres of the site comprises the existing single family home, while the remaining area is comprised of grass. The underlying soils are silt and silty sand with gravel. {See Figure 3 for soil map). Topography on the majority of the site is characterized by moderately sloping surfaces with slopes ranging from 1-4%. It is surmised that existing roof drainage is collected via roof downspouts and conveyed to the existing PSS in Whitworth Ave S. Runoff from landscaped areas appears to sheet flow off the site; no formal site drainage collection or conveyance system is evident. For a detailed description of the downstream stormwater system see Section Ill of this report. The predeveloped conditions described above are presented graphically in Figure 4. Developed Conditions: The areas of proposed redevelopment account for 0.32 acres of the 0.32 acre parcel. The proposed site will include a new low income housing building, landscaping, walkways, and a small play area. See Figure 5 for proposed developed surfaces. Stormwater runoff from the proposed improvements will be collected via roof drains, catch basins, and area drains. Runoff will be routed to a duplex pump chamber and will be discharged to the existing storm main in the SPU ROW to the north of the project site. Per Core Requirement #4 of KCSWDM, the proposed conveyance system has been designed to convey runoff resulting from the peak rates resulting from the 100-year storm event. Renton Commons Page 1 Project No. 16001 Sitewise Design PLLC c. Renton Commons ..,,, . .,, .. . ·•··~-'. SITE LOCATION~:••, ••••• . .. \ • • : ' : , ...... -•l.•. B ... .-.- • • : .i,s~i\ ... s • • • • • • • • ............. ", -~· . ·~' o..t, , .. , FIGURE 1-VICINITY MAP Pagel •. Project No. 16001 Sitewise Desi1n PLLC FIGURE 2 TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Project Owner: Low Income Housing Institute Address: 2407 First Avenue, Seattle, WA Phone : (206) 957-8050 Project Engineer: Marc Errichetti, PE Company: Sitewise Design, PLLC Address/Phone: 206 402 4644 Part 3 TYPE OF PERMIT APPLICATION C Subdivision n Short Subdivision • Grading • Commercial Part 5 SITE COMMUNITY AND DRAINAGE BASIN Community Renton Drainage Basin Black River I Part 6 SITE CHARACTERISTICS Renton Commons Part 2 PROJECT LOCATION AND DESCRIPTION Project Name : Renton Commons LlC Location: 215 Whitworth Ave, Renton, WA 98057 Quarter: SE Section: 18 Township: 23 Range:5 Part 4 OTHER REVIEWS AND PERMITS _ DFW HPA C Shoreline Management L COE 404 C Rockery _ DOE Dam Safety [ Structural Vaults FEMA Floodplain C Other COE Wetlands Page 3 Project No. 16001 Sitewise Design PLLC River n Stream w Critical Stream Reach [ Depressions/Swales n '-Lake [ Steep Slopes Part 7 SOILS Soil Type Silt and silty sand with Gravel Slopes 0%to40% Additional Sheets Attached Part 8 DEVELOPMENT LIMITATIONS [ C [ i [ [, REFERENCE [ Additiona I Sheets Attached j Part 9 ESC REQUIREMENTS Renton Commons Floodplain ~ Wetlands Seeps/Springs High Groundwater Table ' u Groundwater Recharge LJ Other Erosion Potential Moderate LIMITATION/SITE CONSTRAINT Page4 Erosive Velocities Project No. 16001 Sitewise Design PLLC MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION AFTER CONSTRUCTION [ Sedimentation Facilities • Stabilize Exposed Surface • Stabilized Construction Entrance • Remove and Restore Temporary ESC Facilities • Perimeter Runoff Control • Clean and Remove All Silt and Debris • Clearing and Grading Restrictions • Ensure Operation of Permanent Facilities • Cover Practices Flag limits of SAO and open space preservation • Construction Sequence areas D Other Other Part 10 SURFACE WATER SYSTEM C Grass Lined Channel [] Tank D Infiltration Methorl nf Analysis • Pipe System D Vault D Depression (KcRTS) LJ Open Channel D Energy Dissipater D Flow Dispersal Compensation/Mitigatio n of Eliminated Site LJ Dry Pond " L Wetland D Waiver Storage i Wet Pond D Stream [] Regional Detention N/A Brief Description of System Operation: Piped conveyance to 1211 storm main north of site Facility Related Site limitations Reference Facility Limitation Part 11 STRUCTURAL ANALYSIS ~ L Cast in Place Vault ~ Retaining Wall L Rockery> 4' High D Structural on Steep Slope 1' Other Renton Commons Part 12 EASEMENTS/TRACTS D D D D D Page 5 Drainage Easement Access Easement Native Growth Protection Easement Tract Other Project No. 16001 Sitewise Design PLLC Part 13 SIGNATURE OF PROFESSIONAL ENGINEER ! or a civil engineer under my supervision my supervision have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attachments. To the best of my knowledge the information provided here is accurate. 'fr) ,,-~ I (i(.-[-·-·- r 7 Renton Commons r;,/7/ir,,, Signed/Dote Page6 Project No. 16001 Sitewise Design PLLC FIGURE 3 -EXISTING SITE SOIL CONDITIONS Renton Commons P~ge 7 Project No. 16001 Sitew ise Design PLLC i -----------------------------, I / i / I I i I ~ 8 C, I I I I I I I I I I I I I I I I I ;:::i / g I \/ I I L _____________________ / WHITWORTH AVE S FIGURE 4 -EXISTING CONDITIONS SCA LE 1· -20' • "' 0 Ul () )> ' ~ ~ -. 0 N o. "' 0 ' '' ... . . I • • WHITWORTH AVE S D~DDD ~D .-?f -C) "' -u --u -"' .... :0 -c, ;...,,~ &l ~ . ,.., ',;: ~ . 8 :..;,::, g; C, a> "' 8"" "',:; "' ~.., -< C7> (/) z ~?;; :~ <I) "' o',? 1(,1 ~ <I)"' .., "< <I) ..,8 ~ .., ,.. .., ~~ ,.., ,., C, .., "' -u s:; C ~ CD ~ CD z ,.., ::0 " ~ <I) FIGURE 5 -DEVELOPED CONDITIONS SCALE 1• • 20' r m 0 m z CJ "' 0 "' 0 SECTION Ill -OFFSITE ANALYSIS Task 1-Study Area Definition and Maps The Study Area extends approximately 1 mile downstream from the site and is shown in Figure 6 below. The map below was obtained via King County iMap. .. DOWNSTREAM Renton Commons SITE AREA ~ 0.32 Ac. < _____ ...,, " C ~ ~ "' C ~ Sl 5l~!>t 0 "' g 'l: ! ~ s "' 128 Ac . l "'s 11 5 .c: f 1' j.j,, ., . 1J'i- s i th St J ' •--._' .... {,. ~ 1. "'~<1• ~ l I ,- Laite A.¥@ 5 / )~ Figure 6 -Study Area Page 12 Pr oject No. 16001 Site w ise Design PLLC Task 2 -Resource Review The following resources were reviewed for existing/potential problems in the study area: • Adopted basin plans o King County Watershed: Green/Duwamish River • Floodplain/Floodway (FEMA) Maps o The site is not within a floodplain or floodway per FEMA mapping. • Other Offsite Analysis Reports o No problems identified. • Environmentally Sensitive Areas Map o There are no environmentally sensitive areas mapped within the study area. • DNRP Drainage Complaints o There are no known open drainage complaints within the study area. • Road Drainage Problems o There are no known road drainage problems within the study area. • Soils o A goetech report has been completed; site soils are silt and silty sand with gravel. • Wetlands Inventory Maps o There are no wetlands mapped within the study area. Renton Commons Page 13 Project No. 16001 Sitewise Design PLLC Task 3 -Field Inspection A Level 1 downstream analysis was performed to a point a point located approximately 1/4-mile downstream of the site. The following is a summary of the field inspection: • Investigate any problems reported or observed during the resource review. There were no problems reported or observed during the resource review. • Locate all existing/potential constrictions or lack of capacity in the existing drainage system. There are no known or observed existing/potential constrictions or lack of capacity in the existing drainage system. • Identify all existing/potential downstream drainage problems as defined in Section 1.2.2.1 There are no known or observed existing/potential drainage problems downstream of the site. • Identify existing/potential overtopping, scouring, bank sloughing, or sedimentation. There was no existing/potential overtopping, scouring, bank sloughing, or sedimentation observed downstream of the site. • Identify significant destruction of aquatic habitat or organisms (e.g., severe siltation, bank erosion, or incision in a stream}. There were no observed signs of destruction of aquatic habitat or organisms. • Collect qualitative data on features such as land use, impervious surfaces, topography, and soil types. Qualitative data on features such as land use, impervious surfaces, and topography observed during the field inspection are summarized in Section 1 of this report. • Collect information on pipe sizes, channel characteristics, drainage structures, and relevant critical areas (e.g., wetlands, streams, steep slopes). Information on pipe routes, channel characteristics, drainage structures, and relevant critical areas were obtained from the City of Renton GIS maps and record drawings to establish the downstream conveyance route and potential issues. • Verify tributary basins delineated in Task 1. Basins delineated in Task 1 were confirmed to be consistent with conditions observed during field investigation. • Note the date and weather conditions at the time of the inspection. The Level 1 downstream analysis was performed on the morning of May 25, 2016. Weather conditions consisted of partially cloudy skies and temperatures in the mid- SOs. Renton Commons Page 14 Project No. 16001 Sitewise Design PLLC NORTH Renton Commons ' ;~ 1,•.s "'~'L' pu1 I J· 1/4-MILE DOWNSTREAM 1,,, "~ \jlJ: '-'llll'i' S. Ul ~<'~ )H ··~:-t, 1,.:, • .,.1 .------'-'~----.. •• 1-MILE DOWNSTREAM LANDSLIDE HAZARD AREA OUTFALL: BLACK RIVER/ RIPARIAN FOREST Figure 7 -Downstream Conveyance System Page 15 Project No. 16001 Sitewise Design PLLC Task 4-Drainage System Description and Problem Description . There are no known problems with the downstream system. Task S -Mitigation of Existing or Potential Problems Based on the observations made during the field inspection and the requirements that are being met for the design of the proposed drainage systems, no negative impacts to the systems downstream are anticipated from the proposed project. No existing problems were identified. SECTION IV-FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Flow Control: Flow control is not required as the project will create less than a 0.1 cfs increase in the existing site condition's 100 year peak flow. KCRTS results are provided in Appendix B. Flow Control BMPs: The site to be redeveloped is approximately 13,917 SF. This project must therefore address the small lot BMP requirements listed in section C.1.3.1 of the 2009 KCSWDM. See attached figure C.1.3.A for the flowchart used in determining the application of flow control BMPs (following this section). • Full Dispersion -Not feasible due to flow path limitations. • Full Infiltration -Per the geotechnical report, the site soils are not suitable for concentrated infiltration. As full dispersion and full infiltration are not feasible for this project, one or more of the flow control BMPs listed in part A of section C.1.3.1 of the KCSWDM must be implemented to impervious surfaces equal to or greater than 20% of the site/lot, which results in a targeted surface area of 2,780 SF. Proposed application of selected flow control BMPs for the targeted areas is described below, and equals 2,896 SF: • Selected BMPs: Vegetated Roof: Vegetated roof will be used to mitigate 1,200 SF of targeted impervious surface. Permeable Pavement: Permeable pavement will be used to mitigate 1,696 SF of targeted impervious surface. Surface collection will also be provided for these permeable pavement areas via catch basins and area drains. Water Quality Water treatment is not required as the project will create approximately 1,110 SF of new plus replaced PGIS. Renton Commons Page 16 Project No. 16001 Sitewise Design PLLC C. 1.3 Al'l'LlCATION OF FLOW CONTROL llMl'S FIGURE C.1.3.A JiLOWCIIART FOR DETERMINING Al'l'LICATION OF FLOW CONTROL JIMPS Is the project on a site/lot smaller than 22,000 square feet? Is it feasible and applicable to --Yes implement full -------~ No further BMPs Apply one or more of the following to impervious area dispersion for the required. Note: ~10% of site/lot for site/lot sizes < 11,000 sf and :::. 20% of roof area as per Any proposed site/!ot for site/lot sit.es between 11,000 and 22,000 sf (For Section C.2.1? connection of roof projects located in cri/ical aquifer recharge areas lhese c~;-I --downspouts to impervious area amounts double): ) local drainage 1. Limited Infiltration (Section C.2.3) ~-system must be 2. Basic Dispersion {Section C.2.4) Is it feasible via perforated ~. Rain Garden (Section C.2.5) and applicable pipe connection 4) Permeable Pavement {Section C.2.6) (No) to implement Yes per Section 5. Rainwater Harvesting (SecUon C.2.7) full infiltration . C.2.11 . 6) Vegetated Roof (Section C.2_8) of the roof 7. Reduced 1mpervlous Service Credit (Section C.2.9) runoff as per 8. Natlve Growth Retention Credit (Section C.2.10} Section C.2.2? ~-I Notes: No flow control BMPs are required for new pervious surfaces. '~'Valer ~ J!•.•-~~-~t_s -~-~~ acf!gttetelp eddressecl ,titi=I the eB!)_• e Clen eeAtFel QMPe. Comply with last note box below. ···-------~ The project must be a site/lot Is it feasible greater than or equal to 22,_o~~ _square fee_t? -·- -... and applicable to implement full Yes No further BMPs dispersion on required. Note: all target impervious surface as per Any proposed connection of roof One or more of the following BMPs must be implemented Section C.2.17 downspouts lo for target impervious surface not addressed with full Not local drainage dispersion or with full infiltration of roof runoff: Is it feasible and system must be 1. Full Infiltration {Section C.2.2) No applicable lo implement via perforated 2. Limited Infiltration (Section C.2.3) full infiltration of the plpe connection 3. Basic Dispersion (Section C.2.4} roof runoff as per per Section 4. Rain Garden (Section C.2.5) Section C.2.27 C-2.11. 5. Permeable Pavement (Section C.2.6) 6. Rainwater Harvesting (Section C.2.7) Yes_t •• 7. Vegetated Roof (Section C.2.8} 1s· 'there anY remaining target B. Reduced Impervious Servlce Credit (Section C.2.9) Yes impervious surface not addressed No 9. Native Growth Retention Credit (Section C.2.10) with full dispersion or with full I inffltralion of roof runoff? ' note: Flow conlrol BMPs are required for all new pervious surface when it exceeds 35,000 sf. Flow control BMPs musl be applied in the following order of preference: 1. The feasibility and applicability of full dispersion as detailed in Section C.2.1 must be evaluated for au new pervious surtaces. 2. For those pervious surfaces not addressed in Requirement 1 above, one or more of the following BMPs must be implemented: Basic Dispersion (Section C.2.4) Rain Garden /Section C.2.51 Note: The following extra water quality provisions must be Implemented lf the project results in 5,000 sf or more of addllional pollution generating impervious surface from which runoff is not fully dispersed in accordance with Section C.2.1: 1. Reduce existing or proposed pollution generating impervious surface so that lhe 5,000 sf threshold is not triggered. 2. Provide water quality facilities designed by a licensed clvll engine&r in accordance with Section 1.2.8 of the SWDM. ------······ .. ---- I 2009 Smfoce Water Design Mamml Appendix C 1/9/21109 C-17 SECTION V-CONVEYANCE SYSTEM DESIGN AND ANALYSIS Surface water runoff from the proposed surfaces will be collected via a system of rain leaders, area drains, and catch basins and conveyed by storm drainage pipes to a duplex pump chamber at the northwest corner of the site. Conveyance calculations are provided in Appendix A. SECTION VI -SPECIAL REPORTS AND STUDIES A geotechnical report for the site was completed and is included in Appendix C. SECTION VII -OTHER PERMITS A building permit will be required for construction of the proposed project. SECTION VIII -CSWPPP ANALYSIS AND DESIGN Part A: ESC Measures will be addressed as follows: • Clearing Limits: Clearing limits will be delineated by perimeter silt fencing and chain link fencing. • Cover Measures: Temporary cover will be installed if an area is to remain unworked for more than seven days during the dry season (May 1 to September 30) or for more than two consecutive working days during the wet season (October 1 to April 30). Any area to remain unworked for more than 30 days shall be seeded, sodded, or protected with plastic covering. • Perimeter Protection: Perimeter protection will be implemented by installing silt fencing around the site perimeter where drainage paths require. • Traffic Area Stabilization: A stabilized construction entrance will be provided for construction traffic. • Sediment Retention: Catch basin protection will be provided. • Surface Water Control: Surface water will be collected and conveyed via swales as necessary. Check dams are not warranted as grades are relatively flat. • Dust Control: Dust control, if required, will be provided through the limited use of water trucks. Renton Commons Page 18 Project No. 16001 Sitewise Design PLLC Part B: Anticipated SWPP Activities and the BMPs used to address them are indicated below. The contractor (to be determined later) will be required to provide and maintain a detailed SWPPP on site that will be maintained by the contractor's CESCL. Stormwater Pollution Prevention Plan -Activity Worksheet Summary ~ ,.ctlvity/Category l5lte Specific vilnlmum BMP ~dd'tl 8MB ~ctlvlt'f mplemented Implemented ~-1 Required BMPs for All Commercial Oean storm drainage system; Eliminate Properties Ilic it connections to strom drainage ystem; Stencil storm drains ~-· Storage of Soil, Sand, and Other ~tockpile soil for over stockpiles; Routine maintenance ::atch basin inserts ~rodable Materials backfill ~-9 Storage of Scrap and Recycling Material! Comtruction wasw Designated area for contaminated liquids; fcatch basin inserts; wood, GWB, metal heck incoming equipment for potential fluid lonsite Recycling studs, cardboard, and batteries; Remove old batteries; Scrap plastic, paper} material stored off the ground; Cover stockpiles of material; Routine maintenance A-11 ,.,Jeaning or Washing of Tools and leaning small Holding tank and disposal into sewer Equipment ools "·1 7 Fueling Operations ue!ing lifts ocate fueling to ens.ure leaks don't discharge lspil! control kit nto storm, surface, or ground; Use drip pans or onsite absorbent pads; lighting if fueling at night; outine maintenance A-20 .. oncrete and Asphalt at Temporary Concrete slurry )rip pans where appropriate; Storm drain covers; 1...atch basin inserts ~ites nto backfill pits Contain and collect slurry; No discharge into street, storm, or drainage ditches; Routine maintenance A·26 andscaping Activities Topsoil at No pesticides to suface waters; Manufacturer erosion control andscaping areas recommendations; Dispose of vegetation onsite, properly; Use mulch or erosion control where ncluding silt 150ils are exposed; Avoid noxious weeds; Routine endng maintenance •27 learing, Grading, and Preparation of 3rading site oordinate clearing, grading, and erosion rosion control II.and for Small Construction Projects antral requirements with City of onsite, including silt 5amammish fencing; Catch basin inserts A-28 !Demolition of Buildings pemolition of l5pray water to control dust; Filter fabric at atch basin inserts existing library ~rains; Sweep street gutters, sidewalks, ~rives, and other paved areas "\-31 Jehicle and Equipment Parking and Vehicles parked weep parking lots; Erosion control as Erosion control plan; !Storage ionsite equired Catch basin inserts; Spill control kit onsite SECTION IX -BOND QUANTITIES AND DECLARATION OF COVENANT A bond quantity worksheet may be required for this project. A Declaration of Covenant for inspection and maintenance of the proposed flow control BMPs may be required. A draft of the Declaration of Covenant will be included with the final TIR to be submitted for the building permit. Renton Commons Page 19 Project No. 16001 Sitewise Design PLLC SECTION X -OPERATIONS AND MAINTENANCE MANUAL An operation and maintenance manual which outlines required regular maintenance necessary for the proposed stormwater system is provided in Appendix D. The maintenance of the stormwater facilities will by be performed by the Owner. Renton Commons Page 20 Project No. 16001 Sitewise Design PLLC Appendix A Conveyance Calculations A CIVIL ENGINEERING COMPANY 219 first Ave. S., Suite 401 Seattle WA 98104 206 402 4644 , , 'I ' Designed by: ........ (:.:j(i\t.l ...... .,J,!Y .. !i.i.1!\ .................................. ,, ............................................ Date: Checked by: ................................... . . ......................................................................... Job#: ............ . Project: ........... f<,:'.o:l.t.1,1.1. .... /1;.J.':!i: . .i::;.:: ............................................................... ,, ............... Page ....... .'· ........ of .......... '. .... .. (r) () 1,)1) Vf\/ ' ·, '\ /: ; ·, (7 ff.!' ,,, (· ,-; I i I cl \ i ) Y) r.t:~1;0..: ' ) ': j .\ 'l-1 /1,k ( ( l1~l(l(l, ,) r {) "5 " () ~) . ;; /, Ar A1 Ar n · ,0 1 '.~ A . ~! n .or~ (."J.){l;;'.;) 11'(0:i) I' " f) / {) U' ' ' B \ (. I '.'. •. 1 )0•5 (1, () k I.!. ' •·:. {l A ·,(( .,/· ,. ' ,.<. ~' ) v· ) Appendix B KCRTS Results EXISTING CONDITIONS MODEL (Hourly time step, reduced) Total Site area: 0.32 Ac. Impervious area: 0.04 Ac. Pervious area: 0.28 Ac. till grass Flov Frequency Analys,s -------------------------------------------------------- Time Se1·-1es F1.le ren. t on_prede~J tsf ProJect Loc:ttion Sea-Tac ---Annual Peak Flow Rates--------Flow Frequency Ana.l ys1.s------- Flew Rate Ra.nk Time of Pe,ok --Peaks -- (CFS) ~ 0 035 4 2/09/01 2 00 0.021 6 1·05/02 lb 00 4 0 044 2 2/27/03 7 00 0 036 0 OlS 8 8/26/04 2 00 0 035 0 020 7 10/2$/04 1i, 00 0 033 0 016 3 1/18/06 16 00 0 021 0 .033 s ll/ 24f06 3 .00 0 .020 0 078 1 l/09/08 6 00 0 015 Cc1r1tpu ted Peaks 0 067 DEVELOPED CONDITIONS MODEL (Hourly time step, reduced) Total Site area: 0.32 Ac. Impervious area: 0.26 Ac. Rank Return Prob Penod 1 100 00 0 990 2 25 00 I) %0 3 10 00 0 900 4 5 00 0 800 s J .00 0 667 6 2 00 0 500 7 1 30 0 2H 8 1 10 0 091 50 .00 0 9SO Pervious area: .06 Ac. till grass (.03 grass+ .03 grass for flow control BMP credit) T11,e Series F1le:renton dev tsf - Project location Se.~-Ta.c ---A.nnucl Peak Flow Ra.tes--------Flow Fi·equency Anely:iiS·------- Flow Rate Rank Tune of Peak --Peaks -Rank Return Prob (CFS} ~ Penod 0 067 6 2/09/01 2 00 1 100 00 0 990 0 057 8 VQS/02 16 00 ' 2 2 r; 00 0 %0 0 080 3 12,'08/02 18 00 0 080 3 10 00 0 900 0 063 7 $/26/04 0 00 0 076 4 5 00 0 800 -0. 076 4 10/28/04 16 00 0 . 071 C "' 3. 00 0 667 0 071 5 l/18/06 16 00 0 067 6 ~ .00 0 .500 " 0 092 2 10/26/06 0 00 0 (16 3 7 1 30 0 231 0 133 1 1 .. ·09.•'08 6 00 0 057 8 1 10 0 091 (,::imputed Pee-.ks I) 120 '50 00 0 980 SUMMARY 0.133 cfs (Developed) -0.078 cfs (Existing)= 0.055 cfs < 0.1 cfs --• NO FLOW CONTROL REQUIRED AppendixC Geotechnical Report GEOTECH CONSULTANTS, INC. Low Income Housing Institute for Renton Commons LLC 2407 First Avenue Seattle, Washington 98121 Attention: Robin Amadon Subject: Transmittal Letter -Geotechnical Engineering Study Proposed Apartment Building 215 Whitworth Avenue South Renton, Washington Dear Ms. Amadon: 13256 ;\"orthe;:ts.! 10th Street. Sui~e 16 Bellevue, \Vashington 980()5 (425) 747-5618 I (;EOTECHNW.COM July 31, 2015 JN 15274 via email: ramadon@fihi.org We are pleased to present this geotechnical engineering report for the apartment building to be constructed in Renton, Washington. The scope of our services consisted of exploring site surface and subsurface conditions, and then developing this report to provide recommendations for general earthwork and design criteria for foundations and retaining walls. This work was authorized by your acceptance of our proposal, P-9192, dated May 15. 2015. The attached report contains a discussion of the study and our recommendations. Please contact us if there are any questions regarding this report, or for further assistance during the design and construction phases of this project. TRC/DRW: at Respectfully submitted, GEOTECH CONSULTANTS, INC. Thor Christensen, P.E. Senior Engineer GEOTECH CONSULTANTS, INC. GEOTECHNICAL ENGINEERING STUDY Proposed Apartment Building 215 Whitworth Avenue South Renton, Washington This report presents the findings and recommendations of our geotechnical engineering study for the site of the proposed apartment building to be located in Renton. We were provided with a preliminary site plan prepared by Tonkin Architecture dated July 14, 2015. Based on this plan, we understand that the development will consist of a five-story apartment building, with the lowest floor elevation close to the existing ground surface. No basement is proposed. The building will have setbacks of 1 O to 15 feet from property lines. If the scope of the project changes from what we have described above, we should be provided with revised plans in order to determine if modifications to the recommendations and conclusions of this report are warranted. SITE CONDITIONS SURFACE The Vicinity Map, Plate 1, illustrates the general location of the site in Renton. The site is bordered to the east by Whitworth Avenue South, to the north and south by commercial properties, and to the west by a duplex. Most of the site is flat, but the western side slopes gently down toward the southwest to northwest from a high point near the center of the site. The northwest corner of the site has the lowest elevation. There is a change in elevation on the order of 5 feet across the site. A concrete retaining wall is located along about the western third of the northern property line, and has a height of up to 3 feet. The northeastern portion of the site is developed with a two-story house that includes a basement. The house has a stucco facing and a masonry foundation. We observed numerous diagonal cracks extending outward from the corners of windows and doorways. We also observed a few cracks up to about Y, inch wide in the masonry foundation. A gravel parking area is located north and northeast of the house. We understand that a garage with a shallow basement was located at the west side of that gravel parking area, but has been removed. A low area about 4 feet below surrounding grade remains at that location; thick blackberry vines grow in the low area. The undeveloped part of the site is vegetated with grass, landscaping bushes, and scattered trees. Rows of evergreen trees are located along the western and southern edges of the site. SUBSURFACE The subsurface conditions were explored by drilling three test borings at the approximate locations shown on the Site Exploration Plan, Plate 2. Our exploration program was based on the proposed construction, anticipated subsurface conditions and those encountered during exploration, and the scope of work outlined in our proposal. GEOTECH CONSULTANTS. INC. Low Income Housing Institute for Renton Commons LLC July 31, 2015 JN 15274 Page 2 The test borings were drilled on July 23, 2015 using a track-mounted, hollow-stem auger drill. Samples were taken at approximate 5-foot intervals with a standard penetration sampler. This split-spoon sampler, which has a 2-inch outside diameter, is driven into the soil with a 140-pound hammer falling 30 inches. The number of blows required to advance the sampler a given distance is an indication of the soil density or consistency. A geotechnical engineer from our staff observed the drilling process, logged the test borings, and obtained representative samples of the soil encountered. The Test Boring Logs are attached as Plates 3 through 5. Soil Conditions The test borings encountered very loose to medium-dense silt and silty sand with gravel from the ground surface to depths of approximately 8 to 11 feet. In Test Boring 2, located near the northwest corner of the site, we observed pieces of concrete in the upper few feet of drilling cuttings. We expect that the ground surface in that area has been disturbed or some fill has been placed in that area. Below the silt and silty sand, the test borings revealed sand with varying amounts of gravel that was very loose to loose to depths of 14 to 21 feet before becoming medium-dense. The sand with gravel was dense to very dense below depths of 30 to 40 feet, and this material extended to the full depths of the test borings, 40.5 to 41.5 feet below the ground surface. Groundwater Conditions Groundwater seepage was observed at depths of 12 to 14 feet. The seepage levels on the logs represent the location of transient water seepage and may not indicate the static groundwater level. Groundwater levels encountered during drilling can be deceptive, because seepage into the boring can be blocked or slowed by the auger itself. It should be noted that groundwater levels vary seasonally with rainfall and other factors. However, we expect groundwater in this range below the ground surface most of the year, with possibly more shallow depths in the winter and early spring months. The stratification lines on the logs represent the approximate boundaries between soil types at the exploration locations. The actual transition between soil types may be gradual, and subsurface conditions can vary between exploration locations. The logs provide specific subsurface information only at the locations tested. Where a transition in soil type occurred between samples in the borings, the depth of the transition was interpreted. The relative densities and moisture descriptions indicated on the test boring logs are interpretive descriptions based on the conditions observed during drilling. CONCLUSIONS AND RECOMMENDATIONS GENERAL THIS SECTION CONTAINS A SUMMARY OF OUR STUDY AND FINDINGS FOR THE PURPOSES OF A GENERAL OVERVIEW ONLY. MORE SPECIFIC RECOMMENDATIONS AND CONCLUSIONS ARE CONTAINED IN THE REMAINDER OF THIS REPORT. ANY PARTY REL YING ON THIS REPORT SHOULD READ THE ENTIRE DOCUMENT. The test borings conducted for this study encountered silt and silty sand and then sandy soil that was loose to medium-dense to depths of approximately 30 to 40 feet. Competent, dense to very dense native sand with gravel was revealed below the upper, looser soil. Due to the significant GEOTEC'l CONSULTANTS. INC. Low Income Housing Institute for Renton Commons LLC July 31, 2015 JN 15274 Page 3 depth to the competent soil, the condition of the loose to medium-dense sands, and the shallow. groundwater depth at the site, some significant geotechnical engineering considerations are needed for this project as noted below. The loose to medium-dense, saturated sandy soil is very susceptible to seismic liquefaction during a moderate to large earthquake, which could cause settlement on the order of 6 inches. The upper loose soil is also susceptible to a lesser amount of static settlement, as illustrated by the settlement-related distress of the existing house. Due to the potential for settlement if a conventional footing foundation were used for the proposed building, we recommend that the building be founded on a deep foundation system. We believe that driven pipe piles would be a suitable deep foundation system for this project. Recommendations for design and installation of pipe piles are provided in a later section of this report. It is possible that some settlement of the ground surrounding pile-supported buildings could occur over time. In order to reduce the potential problems associated with this, we recommend the following: • Fill to the desired site grades several months prior to constructing on-grade slabs, walkways, and pavements around the buildings. This allows the underlying soils to undergo some consolidation under the new soil loads before final grading is accomplished. • Connect all in-ground utilities beneath the floor slabs to the pile-supported floors or grade beams. This is intended to prevent utilities, such as sewers, from being pulled out of the floor as the underlying soils settle away from the slab. Hangers or straps can be poured into the floors and grade beams to carry the piping. The spacing of these supporting elements will depend on the distance that the pipe material can span unsupported. • Construct all entrance walkways as reinforced slabs that are doweled into the grade beam at the door thresholds. This will allow the walkways to ramp down and away from the building as they settle, without causing a downset at the threshold. • Isolate on-grade elements, such as walkways or pavements, from pile-supported foundations and columns to allow differential movement. The erosion control measures needed during the site development will depend heavily on the weather conditions that are encountered. We anticipate that a silt fence will be needed around the downslope sides of any cleared areas. Existing pavements, ground cover, and landscaping should be left in place wherever possible to minimize the amount of exposed soil. Rocked staging areas and construction access roads should be provided to reduce the amount of soil or mud carried off the property by trucks and equipment. Wherever possible, the access roads should follow the alignment of planned pavements. Trucks should not be allowed to drive off of the rock-covered areas. Cut slopes and soil stockpiles should be covered with plastic during wet weather. Following clearing or rough grading, it may be necessary to mulch or hydroseed bare areas that will not be immediately covered with landscaping or an impervious surface. On most construction projects, it is necessary to periodically maintain or modify temporary erosion control measures to address specific site and weather conditions. The drainage and/or waterproofing recommendations presented in this report are intended only to prevent active seepage from flowing through concrete walls or slabs. Even in the absence of active GEOTECH CONSULTANTS, INC. Low Income Housing Institute for Renton Commons LLC July 31, 2015 JN 15274 Page 4 seepage into and beneath structures, water vapor can migrate through walls, slabs, and floors from the surrounding soil, and can even be transmitted from slabs and foundation walls due to the concrete curing process. Water vapor also results from occupant uses, such as cooking and bathing. Excessive water vapor trapped within structures can result in a variety of undesirable conditions, including, but not limited to, moisture problems with flooring systems, excessively moist air within occupied areas, and the growth of molds, fungi, and other biological organisms that may be harmful to the health of the occupants. The designer or architect must consider the potential vapor sources and likely occupant uses, and provide sufficient ventilation, either passive or mechanical, to prevent a build up of excessive water vapor within the planned structure. Geotech Consultants, Inc. should be allowed to review the final development plans to verify that the recommendations presented in this report are adequately addressed in the design. Such a plan review would be additional work beyond the current scope of work for this study, and it may include revisions to our recommendations to accommodate site, development, and geotechnical constraints that become more evident during the review process. We recommend including this report, in its entirety, in the project contract documents. This report should also be provided to any future property owners so they will be aware of our findings and recommendations. SEISMIC CONSIDERATIONS In accordance with the International Building Code (!BC), the site soil profile within 100 feet of the ground surface is best represented by Site Class Type E (Soft Site Class). This accounts for the loose, liquefiable nature of the soils, and the fact that the fundamental period of the building will be less than 0.5 seconds. As noted in the USGS website, the mapped spectral acceleration value for a 0.2 second (S,) and 1.0 second period (S 1 ) equals 1.44g and 0.54g, respectively. The IBC states that a site-specific seismic study need not be performed provided that the peak ground acceleration be equal to S05/2.5, where Sos is determined in ASCE 7. It is noted that Sos is equal to 2/3SMs-SMs equals F, times Ss, where Fa is determined in Table 11.4-1. For our site, Fa= 1.0. The calculated peak ground acceleration that we utilized for the seismic-related parameters (earth pressures and seismic surcharges) of this report equals 0.54g. The loose to medium-dense sand soils that are saturated are susceptible to seismic liquefaction during a moderate to large earthquake event. This statement regarding liquefaction includes the knowledge of the peak ground acceleration that is anticipated for a Maximum Considered Earthquake (MCE) under a 1-in-2,500-year seismic event of 0.54g. The underlying dense to very dense soil is not susceptible due its competent condition. The proposed pipe pile foundation system will extend into these competent soils and will maintain support of the structure in the event of liquefaction of the looser, overlying soils. Lateral spreading due to seismic liquefaction is not a concern for the site because of the flat conditions in the surrounding area. PIPE PILES Four, 6-or 8-inch-diameter pipe piles driven with an 850, 1,100-or 2,700-or 3,000-pound hydraulic jackhammer to the following final penetration rates may be assigned the following compressive capacities. GEOTECH CONSULTANTS, INC. Low Income Housing Institute for Renton Commons LLC July 31, 2015 INSIDE PILE DIAMETER 6 inches 8 inches 'FINAL DRIVING RATE (850-pound hammer) "I/A :\I/A ,_----~- FINAL FINAL DRIVING DRIVING RATE RATE (1,100-pound (2, 700-pound hammer) hammer) FINAL DRIVING RATE 3,000-pound hammer) I • JN 15274 Page 5 ALLOWABLE COMPRESSIVE CAPACITY J",ote: The refusal criteria indicated in the above table are valid only for pipe piles that are installed using a hydraulic impact hmmncr carried on leads that allow the hammer to sit on the top of the pile dming driving. If the piles arc iHstallcd by alternative methods. such as a ,ibrntory hammer or a hammer that is hard-mounted lo the installation nwchine, numerous load Wsls to 260 percent of the design capacity would be necessary to substantiate the allowable pile load. The appropriate number of load tests would need to be determined at the time the contractor and installation method arc chosen. As a minimum, Schedule 40 pipe should be used. The site soils should not be highly corrosive. Considering this, it is our opinion that standard "black" pipe can be used, and corrosion protection, such as galvanizing, is not necessary for the pipe piles. We recommend a minimum pile length of 35 feet to achieve embedment into dense to very dense, native soils. This is simply a minimum length needed to develop sufficient capacity. Our experience with installation of small-diameter pipe piles indicates that ii is likely that they will be longer than this minimum length to reach refusal. Pile caps and grade beams should be used to transmit loads to the piles. Isolated pile caps should include a minimum of two piles to reduce the potential for eccentric loads being applied to the piles. Subsequent sections of pipe can be connected with slip or threaded couplers, or they can be welded together. If slip couplers are used, they should fit snugly into the pipe sections. This may require that shims be used or that beads of welding flux be applied to the outside of the coupler. Lateral loads due to wind or seismic forces may be resisted by passive earth pressure acting on the vertical, embedded portions of the foundation. For this condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded by level compacted fill. We recommend using a passive earth pressure of 250 pounds per cubic foot (pcf} for this resistance. If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. We recommend a safety factor of at least 1.5 for the foundation's resistance to lateral loading, when using the above ultimate passive value. As discussed above in the General section, if lateral resistance from fill placed against the foundations is required for this project, the structural engineer should indicate this requirement on the plans for the general and earthwork contractor's information. Compacted fill placed against the foundations should consist of granular soil that is tamped into place using the backhoe or is compacted using a jumping jack compactor. II is necessary for the fill to be compacted to a firm condition, but ii does not need to reach even 90 percent relative compaction to develop the passive resistance recommended above. GEOTECH CONSULTANTS. INC. Low Income Housing Institute for Renton Commons LLC July 31, 2015 FOUNDATION AND RETAINING WALLS JN 15274 Page 6 Retaining walls backfilled on only one side should be designed to resist the lateral earth pressures imposed by the soil they retain. The following recommended parameters are for walls that restrain level backfill: 250 pcf Soil Unit Weight 120 pcf Where: pcf is Pounds per Cubic foot, and Active ·and Passive Earth Pressures are computed using the Equivalent Fluid Pressures. * For a restrained wall that cannot deflect at least 0.002 times its height, a uniform lateral pressure equal to 10 psf times the height of the wall should be added to the above active equivalent fluid pressure. The design values given above do not include the effects of any hydrostatic pressures behind the walls and assume that no surcharges. such as those caused by slopes, vehicles, or adjacent foundations will be exerted on the walls. If these conditions exist, those pressures should be added to the above lateral soil pressures. Where sloping backfill is desired behind the walls, we will need to be given the wall dimensions and the slope of the backfill in order to provide the appropriate design earth pressures. Heavy construction equipment should not be operated behind retaining and foundation walls within a distance equal to the height of a wall, unless the walls are designed for the additional lateral pressures resulting from the equipment. The values given above are to be used to design only permanent foundation and retaining walls that are to be backfilled, such as conventional walls constructed of reinforced concrete or masonry. It is not appropriate to use the above earth pressures and soil unit weight to back-calculate soil strength parameters for design of other types of retaining walls, such as soldier pile, reinforced earth, modular or soil nail walls. We can assist with design of these types of walls, if desired. The passive pressure given is appropriate only for a shear key poured directly against undisturbed native soil, or for the depth of level, well-compacted fill placed in front of a retaining or foundation wall. The values for friction and passive resistance are ultimate values and do not include a safety factor. Restrained wall soil parameters should be utilized for a distance of 1.5 times the wall height from corners or bends in the walls. This is intended to reduce the amount of cracking that can occur where a wall is restrained by a corner. Wa/1 Pressures Due to Seismic Forces The surcharge wall loads that could be imposed by the design earthquake can be modeled by adding a uniform lateral pressure to the above-recommended active pressure. The recommended surcharge pressure is 8H pounds per square foot (psf), where H is the design retention height of the wall. Using this increased pressure, the safety factor against sliding and overturning can be reduced to 1.2 for the seismic analysis. GEOTECH CONSULTANTS. INC. Low Income Housing Institute for Renton Commons LLC July 31, 2015 Retaining Wall Backfill and Waterproofing JN 15274 Page 7 Backfill placed behind retaining or foundation walls should be coarse, free-draining structural fill containing no organics. This backfill should contain no more than 5 percent silt or clay particles and have no gravel greater than 4 inches in diameter. The percentage of particles passing the No. 4 sieve should be between 25 and 70 percent The purpose of these backfill requirements is to ensure that the design criteria for a retaining wall are not exceeded because of a build-up of hydrostatic pressure behind the wall. Also, subsurface drainage systems are not intended to handle large volumes of water from surface runoff. The top 12 to 18 inches of the backfill should consist of a compacted, relatively impermeable soil or topsoil, or the surface should be paved. The ground surface must also slope away from backfilled walls to reduce the potential for surface water to percolate into the backfill. Water percolating through pervious surfaces (pavers, gravel, permeable pavement, etc.) must also be prevented from flowing toward walls or into the backfill zone. The compacted subgrade below pervious surfaces and any associated drainage layer should therefore be sloped away. Alternatively, a membrane and subsurface collection system could be provided below a pervious surface. It is critical that the wall backfill be placed in lifts and be properly compacted, in order for the above-recommended design earth pressures to be appropriate. The wall design criteria assume that the backfill will be well-compacted in lifts no thicker than 12 inches. The compaction of backfill near the walls should be accomplished with hand-operated equipment to prevent the walls from being overloaded by the higher soil forces that occur during compaction. The section entitled General Earthwork and Structural Fill contains additional recommendations regarding the placement and compaction of structural fill behind retaining and foundation walls. The above recommendations are not intended to waterproof below-grade walls, or to prevent the formation of mold, mildew or fungi in interior spaces. Over time, the performance of subsurface drainage systems can degrade, subsurface groundwater flow patterns can change, and utilities can break or develop leaks. Therefore, waterproofing should be provided where future seepage through the walls is not acceptable. This typically includes limiting cold-joints and wall penetrations, and using bentonite panels or membranes on the outside of the walls. There are a variety of different waterproofing materials and systems, which should be installed by an experienced contractor familiar with the anticipated construction and subsurface conditions. Applying a thin coat of asphalt emulsion to the outside face of a wall is not considered waterproofing, and will only help to reduce moisture generated from water vapor or capillary action from seeping through the concrete. As with any project, adequate ventilation of basement and crawl space areas is important to prevent a build up of water vapor that is commonly transmitted through concrete walls from the surrounding soil, even when seepage is not present. This is appropriate even when waterproofing is applied to the outside of foundation and retaining walls. We recommend that you contact an experienced envelope consultant if detailed recommendations or specifications related to waterproofing design, or minimizing the potential for infestations of mold and mildew are desired. The General, Slabs-On-Grade, and Drainage Considerations sections should be reviewed for additional recommendations related to the control of groundwater and excess water vapor for the anticipated construction. GEOTECH CONSULTANTS. <NC. Low Income Housing Institute for Renton Commons LLC July 31, 2015 · SLABS-ON-GRADE JN 15274 Page 8 The building floors can be constructed as slabs-on-grade on at least 12 inches of structural fill. The subgrade soil must be in a firm, non-yielding condition at the time of slab construction or underslab fill placement. Any soft areas encountered should be excavated and replaced with select, imported structural fill. We recommend that extra steel be placed in the slab to the loose nature of the underlying site soil. Even where the exposed soils appear dry, water vapor will tend to naturally migrate upward through the soil to the new constructed space above it. This can affect moisture-sensitive flooring, cause imperfections or damage to the slab, or simply allow excessive water vapor into the space above the slab. All interior slabs-on-grade should be underlain by a capillary break drainage layer consisting of a minimum 4-inch thickness of clean gravel or crushed rock that has a fines content (percent passing the No. 200 sieve) of less than 3 percent and a sand content (percent passing the No. 4 sieve) of no more than 10 percent. Pea gravel or crushed rock are typically used for this layer. As noted by the American Concrete Institute (ACI) in the Guides for Concrete Floor and Slab Structures, proper moisture protection is desirable immediately below any on-grade slab that will be covered by tile, wood, carpet, impermeable floor coverings, or any moisture-sensitive equipment or products. AC! also notes that vapor retarders such as 6-mil plastic sheeting have been used in the past, but are now recommending a minimum 10-mil thickness for better durability and long term performance. A vapor retarder is defined as a material with a permeance of less than 0.3 perms, as determined by ASTM E 96. It is possible that concrete admixtures may meet this specification, although the manufacturers of the admix!t.1res should be consulted. Where vapor retarders are used under slabs, their edges should overlap by at least 6 inches and be sealed with adhesive tape. The sheeting should extend to the foundation walls for maximum vapor protection. If no potential for vapor passage through the slab is desired, a vapor barrier should be used. A vapor barrier, as defined by ACI, is a product with a water transmission rate of 0.01 perms when tested in accordance with ASTM E 96. Reinforced membranes having sealed overlaps can meet this requirement. The General, Permanent Foundation and Retaining Walls, and Drainage Considerations sections should be reviewed for additional recommendations related to the control of groundwater and excess water vapor for the anticipated construction. EXCAVA T/ONS AND SLOPES No excavated slopes are anticipated other than for utility trenches. Excavation slopes should not exceed the limits specified in local, state, and national government safety regulations. Temporary cuts to a depth of about 4 feet may be attempted vertically in unsaturated soil, if there are no indications of slope instability. However, vertical cuts should not be made near property boundaries, or existing utilities and structures. Based upon Washington Administrative Code (WAC) 296, Part N, the soil at the subject site would generally be classified as Type B if it is not saturated. Therefore, temporary cut slopes greater than 4 feet in height should not be excavated at an inclination steeper than 1: 1 (Horizontal:Vertical}, extending continuously between the top and the bottom of a cut. If the soil were saturated, the temporary excavations should be made flatter. The above-recommended temporary slope inclination is based on the conditions exposed in our explorations, and on what has been successful at other sites with similar soil conditions. It is GEOTECH CONSULTANTS, iNC. Low Income Housing Institute for Renton Commons LLC July 31, 2015 · · JN15274 Page 9 possible that variations in soil and groundwater conditions will require modifications to the inclination at which temporary slopes can stand. Temporary cuts are those that will remain unsupported for a relatively short duration to allow for the construction of foundations, retaining walls, or utilities. Temporary cut slopes should be protected with plastic sheeting during wet weather. It is also important that surface runoff be directed away from the top of temporary slope cuts. Cut slopes should also be backfilled or retained as soon as possible to reduce the potential for instability. Please note that sand or loose soil can cave suddenly and without warning. Excavation. foundation, and utility contractors should be made especially aware of this potential danger. These recommendations may need to be modified if the area near the potential cuts has been disturbed in the past by utility installation, or if settlement-sensitive utilities are located nearby. All permanent cuts into native soil should be inclined no sleeper than 2: 1 (H:V). Water should not be allowed to flow uncontrolled over the top of any temporary or permanent slope. All permanently exposed slopes should be seeded with an appropriate species of vegetation to reduce erosion and improve the stability of the surficial layer of soil. DRAINAGE CONSIDERATIONS Footing drains should be used where: (1) crawl spaces or basements will be below a structure; (2) a slab is below the outside grade; or, (3) the outside grade does not slope downward from a building. Drains should also be placed at the base of all earth-retaining walls. These drains should be surrounded by at least 6 inches of 1-inch-minus, washed rock that is encircled with non-woven, geotextile filter fabric (Mirafi 140N, Supac 4NP, or similar material). At its highest point, a perforated pipe invert should be at least 6 inches below the bottom of a slab floor or the level of a crawl space. The discharge pipe for subsurface drains should be sloped for flow to the outlet point. Roof and surface water drains must not discharge into the foundation drain system. A typical drain detail is attached to this report as Plate 6. For the best long-term performance, perforated PVC pipe is recommended for all subsurface drains. II may be necessary to provide special drainage or waterproofing measures for the elevator pit. If no seepage into the elevator pit is acceptable, it will be necessary to provide a footing drain and free-draining wall backfill, and the walls should be waterproofed. If the footing drain will be too low to connect to the storm drainage system, then it will likely be necessary to install a pumped sump to discharge the collected water. Alternatively, the elevator pit could be designed to be entirely waterproof; this would include designing the pit structure to resist hydrostatic uplift pressures. As a minimum, a vapor retarder, as defined in the Slabs-On-Grade section, should be provided in any crawl space area to limit the transmission of water vapor from the underlying soils. Crawl space grades are sometimes left near the elevation of the bottom of the footings. As a result, an outlet drain is recommended for all crawl spaces to prevent an accumulation of any water that may bypass the footing drains. Providing even a few inches of free draining gravel underneath the vapor retarder limits the potential for seepage to build up on top of the vapor retarder. Groundwater was observed during our field work. If seepage is encountered in an excavation, it should be drained from the site by directing it through drainage ditches, perforated pipe, or French drains, or by pumping it from sumps interconnected by shallow connector trenches at the bottom of the excavation. The excavation and site should be graded so that surface water is directed off the site and away from the tops of slopes. Water should not be allowed to stand in any area where foundations, GEOTECH CONSULTANTS, INC. . Low Income Housing Institute for Renton Commons LLC July 31, 2015 JN15274 Page 10 slabs, or pavements are to be constructed. Final site grading in areas adjacent to a building should slope away at least 2 percent, except where the area is paved. Surface drains should be provided where necessary to prevent ponding of water behind foundation or retaining walls. A discussion of grading and drainage related to pervious surfaces near walls and structures is contained in the Foundation and Retaining Waifs section. GENERAL EARTHWORK AND STRUCTURAL FILL All building and pavement areas should be stripped of surface vegetation, topsoil, organic soil, and other deleterious material. It is important that existing foundations be removed before site development. The stripped or removed materials should not be mixed with any materials to be . used as structural fill, but they could be used in non-structural areas, such as landscape beds. Structural fill is defined as any fill, including utility backfill, placed under, or close to, a building, behind permanent retaining or foundation walls, or in other areas where the underlying soil needs to support loads. All structural fill should be placed in horizontal lifts with a moisture content at, or near, the optimum moisture content. The optimum moisture content is that moisture content that results in the greatest compacted dry density. The moisture content of fill is very important and must be closely controlled during the filling and compaction process. The allowable thickness of the fill lift will depend on the material type selected, the compaction equipment used, and the number of passes made to compact the lift. The loose lift thickness should not exceed 12 inches. We recommend testing the fill as it is placed. If the fill is not sufficiently compacted, it can be recompacted before another lift is placed. This eliminates the need to remove the fill to achieve the required compaction. The following table presents recommended relative compactions for structural fill: LOCAT!O'< OF FILL I\ll'<BffM RELA TIYE Pl,ACEMENT COMPACU0:-1 Beneath slabs or walkways 95% Filled slopes and behind :i retainina walls 90% i' !I Beneath pavements 95% for upper 12 inches of subgrade; 90% below that level Where: Minimum Relative Compaction is the ratio, expressed in percentages, of the compacted dry density to the maximum dry density, as determined in accordance with ASTM Test Designation D 1557-91 (Modified Proctor). Structural fill that will be placed in wet weather should consist of a coarse, granular soil with a silt or clay content of no more than 5 percent. The percentage of particles passing the No. 200 sieve should be measured from that portion of soil passing the three-quarter-inch sieve. GEOTECH CONSULTANTS, INC. Low Income Housing Institute for Renton Commons LLC July 31, 2015 LIMITATIONS JN15274 Page 11 The conclusions and recommendations contained in this report are based on site conditions as they existed at the time of our exploration and assume that the soil and groundwater conditions encountered in the test borings are representative of subsurface conditions on the site. If the subsurface conditions encountered during construction are significantly different from those observed in our explorations, we should be advised at once so that we can review these conditions and reconsider our recommendations where necessary. Unanticipated conditions are commonly encountered on construction sites and cannot be fully anticipated by merely taking samples in test borings. Subsurface conditions can also vary between exploration locations. Such unexpected conditions frequently require making additional expenditures to attain a properly constructed project It is recommended that the owner consider providing a contingency fund to accommodate such potential extra costs and risks. This is a standard recommendation for all projects. This report has been prepared for the exclusive use of Low Income Housing Institute for Renton Commons LLC, and its representatives for specific application to this project and site. Our conclusions and recommendations are professional opinions derived in accordance with our understanding of current local standards of practice, and within the scope of our services. No warranty is expressed or implied. The scope of our services does not include services related to construction safety precautions, and our recommendations are not intended to direct the contractor's methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. Our services also do not include assessing or minimizing the potential for biological hazards, such as mold, bacteria, mildew and fungi in either the existing or proposed site development ADDITIONAL SERVICES Geotech Consultants, Inc. should be retained to provide geotechnical consultation, testing, and observation services during construction. This is to confinm that subsurface conditions are consistent with those indicated by our exploration, to evaluate whether earthwork and foundation construction activities comply with the general intent of the recommendations presented in this report, and to provide suggestions for design changes in the event subsurface conditions differ from those anticipated prior to the start of construction. However, our work would not include the supervision or direction of the actual work of the contractor and its employees or agents. Also, job and site safety, and dimensional measurements, will be the responsibility of the contractor. During the construction phase, we will provide geotechnical observation and testing services when requested by you or your representatives. Please be aware that we can only document site work we actually observe. It is still the responsibility of your contractor or on-site construction team to verify that our recommendations are being followed, whether we are present at the site or not. The following plates are attached to complete this report: Plate 1 Plate 2 Plates 3 -5 Plate 6 Vicinity Map Site Exploration Plan Test Boring Logs Typical Footing Drain Detail GEOTECH CONSULTANTS, INC, Low Income Housing Institute for Renton Commons LLC July 31, 2015 JN 15274 Page 12 We appreciate the opportunity to be of service on this project. Please contact us if you have any questions, or if we can be of further assistance. TRC/DRW:at Respectfully submitted, GEOTECH CONSULTANTS, INC. D. Robert Ward, P.E. Principal GEOTECH CONSULTANTS. INC. J ' I ,_y,,. ., .. ,, J. ± i {, GEOTECH CONSULTANTS, I'.'IC. NORTH :, ' 'i ~ ... '.J r """'!,ii 'c' ,I i ' f r )-?·.r:i; >,"'!ti w:: (Source: Microsoft MapP;;mt, 2013) VICINITY MAP 215 Whitworth Avenue South Renton, Washington I Job No: 15274 I Date: July 2015 I _8-1 " - legend : ~ T e st Bori ng Loca t ion . ~.4, GEOTECH i 1 a={.;=_,-" 8-3 ~ NORTH '\ ~ :::r ~ ~ 0 ::i :::r )> < CD :, C: CD CJ) 0 C: -:::r SITE EXPLORATION PLAN 215 Whitworth Avenue South Renton , Wash ington ., !I I; l' ., :1 I Job No: Date: Plate: 15274 Jul 2015 No Sca le 2 I- I--- 5 -.... 4 .... I-... 10 -I-6 ... --'Y 15 --6 I-... - 20 --7 ---38 25 --19 ... I-... 30 -I-17 ... I- I- 35 --20 ... I- I- 40-50/6" BORING 1 Description Grass and topsoil over: I ' • II I~~ I Brown SILT with sand, non-plastic, fine to medium-grained, moist, loose 'Ii I i I I 1 I \II i I 2 1 1 I 1, I I -becomes gray, reduced medium sand content I.:.~~.". ll~"".:: J SW 1~ Brown SAND, fine to coarse-grained, moist, loose ,,,,.,. :,'",;·a ... ~\}~;!~~ 3 ; ·r.~:,.0 ,' -becomes wet and gray, with a 3-inch layer of silty fine sand ~. '.'..., ""' 'ii'~;;~ S, ~, ,)"00 ::., .1" -_.-C~tc.", ~Ce }:) ,> C "- 4 i :,;'~:{;:~; -becomes gray-brown :;l~J ~~ ~; ; ; :,.~: ~ ~;- 5 I /_,;·{.: -becomes dense, with gravel 6 ii·,~'~':,(:,; -becomes medium-dense, reduced gravel content ,.. 't ~-~ ii p ,C-(c,.;~;;; }{~.,~ 2~ -i[.u t-;, S)~ ·"' t/'C: ~';,, 71 J>}~: ' t=, ~.c~~ '",~.!) ~,: ~ I> ~ ". ,:, 'o,.~, ~ ·"" -'c, "' ,,<·~~ '?, ec<; (.' -:"f·C: ~;,~ .. 8 II \ 0 ;:::; R -becomes gray Ii _,,.,,·,,r J):iii; \c. ;'-0 ""' ~o " Po"'" ,. ~~, D ~ . .', _'.,:; -becomes very dense 9; .......... ;;;&..~.;.;....;.;..;.;...._;;.;..;;.;.;.. ________________ _ • Test boring was terminated at 40.5 feet on July 23, 2015. • Groundwater seepage was encountered at 14 feet during drilling. GEOTECH CO/liSUJ;rANTS, INC. BORING LOG 215 Whitworth Avenue South Renton, Washington Job Date: Logged by: Plate; 15274 July2015 TRC 3 BORING 2 - Description FILL Grass and topsoil over: Brown silty SAND with gravel and pieces of concrete, fine to coarse-grained. moist, loose (Fill/ Disturbed Ground) ---------- 5 14 Brown silty SAND with gravel, fine to coarse-grained, moist, medium-dense Brown SILT, non-plastic, moist, loose 10 5 Brown SAND, fine to coarse-grained. wet, loose 15 15 -with gravel, becomes medium-dense and gray-brown 20 23 -increased gravel content, becomes gray 25 21 -reduced gravel content, becomes brown 30 23 35 57 7 -becomes very dense and gray-brown 40 43 • est oring was terminated at 41.5 eel on July 23, 5 . ..-----------* ...... G::.:r.:::.o.:::.u.:an.:::.d.:aw.:::.a.;;.;te_r..:s;.;::e.:::.e.i.;-age was encountered at 12 feet durin BORING LOG GEOTECH CONSULTAl'ff.S, INC. .. ,-.. ££ Z!Z Job 215 Whitworth Avenue South Renton, Washington Logged by: Plate: TRC 4 Date: 15274 July 2015 5 10 15 20 25 30 35 40 2 2 2 19 26 32 41 52 BORING 3 Description Grass and topsoil over: Brown SILT to silty SAND, non-plastic, fine to medium-grained, moist, very loose Brown SAND, fine to coarse-grained, moist, very loose -wet below 11 feet -becomes wet and gray, with a 3-inch layer of silt, non-plastic -becomes medium-dense and brown, with gravel and a 2-inch layer of silt, non-plastic .-----------·--"'G""ro;::.u;::.n:.:;d::.;w:.:.a..,t"'e""r""s""ee""'t.age was encountered at 14 feet durin BORING LOG ~-', GEOTECH CONSULTA!VfS, L'1C. 1~~.t;;,,,,s,=,,;o""". ~r~=-- 215 Whitworth Avenue South Renton, Washington Job Date: Logged by: Plate: 15274 July 2015 TRC 5 Slope backfill away from foundation. Provide surface drains where necessary. Backfill (See text for requirements) Washed Rock (7/8" min. size) Nonwoven Geotextile Filter Fabric ' Ill '~ .:·::re: 0 ,-:;: ; . 11! "Cl . C :::, Tightline Roof Drain (Do not connect to footing drain) . 0 · l----------------:;E1,I. '. Possible Slab Vapor Retarder/Barrier and Capillary Break/Drainage Layer (Refer to Report text) '---4" Perforated Hard PVC Pipe (Invert at least 6 inches below slab or crawl space. Slope to drain to appropriate outfall. Place holes downward.) NOTES: (1) In crawl spaces, provide an outlet drain to prevent buildup of water that bypasses the perimeter footing drains. (2) Refer to report text for additional drainage, waterproofing, and slab considerations. ___ ,, GEOTECH CONSULTANTS, INC. 11',..~~=-~=·=':>-~==,,,... FOOTING DRAIN DETAIL 215 Whitworth Avenue South Renton, Washington ' Job No: I Date: I . 15274 July 2015 • Appendix D Operation and Maintenance Manual ' ' . APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE, ANO WQ FACILITIES NO. 5 -CATCH BASINS AND MANHOLES Maintenance Defect or Problem Condltlon When Maintenance is Needed Results Expected When Component Maintenance Is Performed -· Structure Sediment Sediment exceeds 60% of the depth from the Sump of calch basin contains no bottom of the catch basin to the invert of the sediment. lowest pipe into or out of the catch basin or is within 6 inches of lhe invert of the lowest pipe into or out of the catch basin. Trash and debris Trash or debris of more than Y:z cubic foot which No Trash or debris blocking or is located immediately in front of the catch basin potentially blocking entrance to opening or is blocking capacity of the catch basin catch basin, by more than 10%. Trash or debris in the catch basin that exceeds No trash or debris in the catch basin. 1 /:1 the depth from the bottom of basin to invert the lowest pipe into or out of the basin. Dead animals or vegetation that could generate No dead animals or vegetation odors that could cause complaints or dangerous present within catch basin. gases (e.g., methane). Deposits of garbage exceeding 1 cubic foot in No condition present which would volume. attract or support the breeding of insects or rodents. Damage to frame Corner of frame extends more than o/,. inch past Frame is even with curb. and/or top slab curb face into the street (If applicable). Top slab has holes larger than 2 square Inches or Top slab is free of holes and cracks. cracks wider than Y. inch. Frame not sitting flush on top slab, I.e., Frame is sitting flush on top slab. separation of more than~ inch of the frame from the top slab. Cracks in walls or Cracks wider than 1h inch and longer than 3 feet, Catch basin is sealed and bottom any evidence of soil particles entering catch structurally sound. basin through cracks, or maintenance person judges that catch basin is unsound. Cracks wider than Y2 inch and longer than 1 foot No cracks more than 1 /. inch wide at at the joint of any inleUoutlet pipe or any evidence the joint or in1eVoutlet pipe. of soil particles entering catch basin through cracks. SeUlemenU Catch basin has settled more than 1 inch or has Basin replaced or repaired to design misalignment rotated more than 2 inches out of alignment standards. Damaged pipe joints Cracks wider than 1h-inch at the joint or the No cracks more than 1h-inch wide at inleVoutlet pipes or any evidence of soil entering the joint of inleUoutlet pipes. the catch basin at the joint of the lnleUoutlet pipes. Contaminants and Any evidence of contaminants or pollution such Materials removed and disposed of pollution as oil, gasoline, concrete slurries or paint. according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface o!I film. lnleVOutlet Pipe Sediment Sediment filling 20% or more of the pipe. lnletJouUet pipes clear of sediment. accumulation Trash and debris Trash and debris accumulated In inlet/outlet No trash or debris in pipes. pipes (includes floalables and non-floatables). Damaged Cracks wider than Yrinch at the joint of the inleUoutlet pipes or any evidence of soil entering No cracks more than %-inch wide at the joint of the inleVoutlet ptpe. at the jolnls of the lnleUoutlet pipes. 2009 Surface Wutcr Design Manual -Appendix A A-9 1/9/2009 .. APPENDIX A MAINTENANCE REQUIRFMENTS FLOW CONTROi., CONVEYANCE, AND WQ FAUL!TIES NO. 5-CATCH BASINS AND MANHOLES Maintenance Defect or Problem Condition When Maintenance is Needed Results Expected When Component Maintenance Is Performed -- Metal Grates Unsafe grate opening Grate with opening wider than 7/6 inch. Grate opening meets design (Catch Basins) standards. Trash and debris Trash and debris that is blocking more than 20% Grate free of trash and debris. of grate surface. footnote to guidelines for disposal Damaged or missing Grate missing or broken member(s) of the grate. Grate is in place and meets design Any open structure requires urgent standards. maintenance. Manhole Cover/Lid Cover/lid not in place Cover/lid is missing or only partially in place. Cover/lid protects opening to Any open structure requires urgent structure. maintenance. Locking mechanism Mechanism carmot be opened by one Mechanism opens with proper tools. Not Working maintenance person with proper tools. Bolts cannot be seated. Self~locking cover/lid does not work. Cover/lid difficult to One maintenance person cannot remove Cover/lid can be removed and Remove cover/lid after applying 80 lbs. of lift. reinstalled by one maintenance person. _, ........ , __ ,,_ 1/9/20119 2009 Surface Water Design Manuell-Appendix A A-10 . ' .. APPENDIX A MAJNTJ'NANCE REQUIREMENTS FOR FLOW CONTROL, CONVEYANCE. A ND W() FACILITIES NO. 6-CONVEYANCE PIPES AND DITCHES - Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed Pipes Sediment & debris Accumulated sediment or debris that exceeds Water flows freely through pipes. accumulation 20% of the diameter of the pipe. Vegetation/roots Vegetation/roots that reduce free movement of Water flows freely through pipes. water through pfpes. Contaminants and Any evidence of contaminants or pollution such Materials removed and disposed of pollution as oil, gasoline, concrete slurries or paint. according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface oil film. Damage to protective Protectlve coating is damaged; rust or corrosion Pipe repaired or replaced. coating or corrosion is weakening the structural integrity of any part of pipe. Damaged Any dent that decreases the cross section area of Pipe repaired or replaced. pipe by more than 20% or is determined to have weakened stnictural integrity or the pipe. Ditches Trash and debris Trash and debris exceeds 1 cubic foot per 1,000 Trash and debris cleared from square feet of ditch and slopes. ditches. Sediment Accumulated sediment that exceeds 20% of the Ditch cleaned/flushed of all sediment accumulation design depth. and debris so that it matches design. Noxious weeds Any noxious or nuisance vegetation which may Noxious and nuisance vegetation constitute a hazard to County personnel or the removed according lo applicable public. regulations. No danger of noxious vegetation where County personnel or the public might normally be. Contaminants and Any evidence of contaminants or pollution such Materials removed and disposed of pollution as oil, gasoline, concrete slurries or paint. according to applicable regulations. Source control BMPs implemented if appropriate. No contaminants present other than a surface all film. Vegetation Vegetation that reduces free movement of water Water flows freely through ditches. through ditches. Erosion damage to Any erosion observed on a ditch slope. Slopes are not eroding. slopes Rock lining out of One layer or less of rock exists above native soil Replace rocks to design standards. place or missing (If area 5 square feet or more, any exposed native Applicable) soil. 2009 Surface Water Design Manual -Appendix A 119/2009 A-I I I .. APPENDIX A MAINTPNANCE REQUIRFMFNTS FLOW CONTROL, CONVEYANCI' .. AND WQ FACILITIES NO. 11 -GROUNDS (LANDSCAPING) Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance ls Performed ~ .-' ---- Site Trash or litter Any trash and debris which exceed 1 cubic foot Trash and debris cleared from site. per 1,000 square feet (lhis is about equal 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. Noxious weeds Any noxious or nuisance vegetation which may Noxious and nuisance vegetation constitute a hazard to County personnel or the removed according lo applicable public. regulations. No danger of noxious vegetation where County personnel or the public might normally be. Contaminants and Any evidence of contaminants or pollution such Materials removed and disposed of pollution as oil, gasoline, concrete slurries or paint. according to applicable regulations. Source control BMPs implemented.if appropriate. No contaminants present other than a surface oil film. Grass/groundcover Grass or groundcover exceeds 18 inches in Grass or groundcover mowed to a height. height no greater than 6 inches. Trees and Shrubs Hazard Any tree or limb of a tree identified as having a No hazard trees in facility. potential to fall and cause property damage or threaten human life. A hazard tree identified by a qua lifled arborist must be removed as soon as possible. Damaged Limbs or parts or trees or shrubs that are split or Trees and shrubs with less than 5% broken which affect more than 25% of the total of total foliage with split or broken foliage of the tree or shrub. limbs. Treas or shrubs that have been blown down or No blown down vegetation or knocked over. knocked over vegetation. Trees or shrubs free of injury. Trees or shrubs which are not adequately Tree or shrub in place and supported or are leaning over, causing exposure adequately supported; dead or of the roots. diseased trees removed. 119/2009 2009 Surface Water Design Manual -Apprn<lix A A-lo