HomeMy WebLinkAbout03710 - Technical Information Report - Drainage .♦ , NE 7th North Short Plat LUA13-001131 013005672 3506 NE 7th StreettlPc\l.I. Renton, Washington 98056 pogevc4 DRAINAGE REPORT Ot(L'4 2 October 29, 2013 (Updated December 18, 2013) (Updated January 14, 2014) Prepared for: KRRV Development, LLC Attn: Kyle Miller P.O. Box 908 Ravensdale, Washington 98051 (425) 432-5932 office Prepared by: / SAa�+ Offe Engineers, PLLC .44., 4,OF � ,'Y' Darrell Offe, P.E. • (64 13932 SE 159th Place ci co ` ,, .. Renton, Washington 98058-7832 ,A - 1141 �, ,. 425 260-3412 office 4' S" w ( ) �: '44'0/27,ASS" ,.. (425) 227-9460 fax -'9`'pQNALEtIG darrelioffe(@comcast.net I 3 7/0 Table of Contents • Technical Information Worksheet • Section 1: Project Overview • Section 2: Conditions and Requirements Summary • Section 3: Offsite Analysis • Section 4: Flow Control and Water Quality Facility Analysis and Design • Section 5: Conveyance System Analysis and Design • Section 6: Special Reports and Studies • Section 7: Other Permits • Section 8: CSWPPP Analysis and Design • Section 9: Bond Quantities, Facility Summaries, and Declaration of Covenant • Section 10: Operations and Maintenance Manual • • • J City of Renton TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND Part 2 PROJECT LOCATION AND PROJECT ENGINEER DESCRIPTION Project Owner: KRRV Development, LLC Project Name: NE 7th North Short Plat Address: P.O. Box 908 Ravensdale,WA 98051 Location Phone: (425) 432-5932 Township: 23 North Project Engineer: Darrell Offe, P.E. Range: 5 East Company: Offe Engineers, PLLC Section: 5 Address/Phone: 13932 SE 159th Place Renton, WA 98058 (425) 260-3412 Part 3 TYPE OF PERMIT Part 4 OTHER REVIEWS AND PERMITS APPLICATION Subdivision — 1 DFW HPA — Shoreline Management X Short Subdivision 1 COE 404 Rockery ❑ Grading ❑ DOE Dam Safety Structural Vaults ❑ Commercial ] FEMA Floodplain C Other C Other ❑ COE Wetlands Part 5 SITE COMMUNITY AND DRAINAGE BASIN Community North Renton Drainage Basin Maplewood Creek/Cedar River/Lake Washington Part 6 SITE CHARACTERISTICS C River ❑ Floodplain Seeps/Springs C Stream _ High Groundwater Table _ Critical Stream Reach Groundwater Recharge ❑ Depressions/Swales C. Other ❑ Lake C Steep Slopes • Part 7 SOILS Soil Type Slopes Erosion Potential Erosive Velocities Qgt 5— 10% minor 1 Additional Sheets Attached Part 8 DEVELOPMENT LIMITATIONS REFERENCE LIMITATION/SITE CONSTRAINT ❑ Ch. 4—Downstream Analysis "Limited Dispersion" C ❑ Additional Sheets Attached Part 9 ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION AFTER CONSTRUCTION ❑ Sedimentation Facilities ❑ Stabilize Exposed Surface ❑ Stabilized Construction Entrance ❑ Remove and Restore Temporary ESC Facilities ❑ Perimeter Runoff Control ❑ Clean and Remove All Silt and Debris ❑ Clearing and Grading Restrictions ❑ Ensure Operation of Permanent Facilities ❑ Cover Practices C Flag Limits of SAO and open space ❑ Construction Sequence preservation areas ❑ Other Cl Other C. r Part 10 SURFACE WATER SYSTEM El Grass Lined Tank Infiltration Method of Analysis Vault Channel _ _ Depression 2009 City of Renton El Pipe System _ Energy Dissipater _ KCRTS Wetland X Flow Dispersal IA Open Channel Compensation/Mitigati ❑ Dry Pond _ Stream L Waiver on of Eliminated Site Storage — Regional Detention Brief Description of System Operation: Catch basins within curb line of street will convey runoff to existing City system downstream, limited dispersion of houses, perforated pipe connection to storm system, and sheet flow dispersion of driveways. Facility Related Site Limitations Reference Facility Limitation Part 11 STRUCTURAL ANALYSIS Part 12 EASEMENTS/TRACTS Cast in Place Vault Drainage Easement Retaining Wall X Access Easement Rockery >4' High ❑ Structural on Steep Slope Tract ❑ Other _ Other Part 13 SIGNATURE OF PROFESSIONAL ENGINEER I or a civil engineer under my supervision my supervision have visited the site. Actual site condi .. s as observed were incorporated into this worksheet and the attachments. To the best of my . edge the information provided here is accurate. Signed/Date • Section 1: Project Overview The proposal is to create four individual single family lots from this 28,699 square foot parcel located in the Renton Highlands near the Renton Vocational College. The property address is: 3506 NE 7th Street; King County Tax parcel #801110-0045. The existing residence, and impervious areas, and out buildings on the property will be removed to create these four new lots. The property is located within the"existing conditions"area of the drainage basin map. There are no sensitive areas on the project site. The property has a gentle slope of approximately 3% towards the southwest corner of the property. The soils on the site have been identified by a Geotechnical Engineers as"glacial consolidated till"(Qgt). These soils are not suitable for Full Infiltration of storm water runoff. The soil logs indicate moist silty sands with no ground water within the holes at 4'. The drainage calculations within this report will show that the developed runoff from the project is less than 0.10 cfs during a 100-year storm event between the existing runoff and the developed (mitigated) runoff. Based upon this review and analysis, the project does not require stormwater treatment. The project does not add 5,000 square feet of new impervious surface and therefore is except from water quality treatment. Section 2: Conditions and Requirements Summary 2009 City of Renton Drainage Manual Preliminary Conditions of Short Plat Approval Section 3: Offsite Analysis The downstream system was walked on April 19th, 2013. The site drainage currently sheet flows across the property to the west and eventually entering the City storm system in NE 7th Place. The proposed development is to convey the drainage form the site into NE 7th Street and then to the west into the City storm system at Newport Court NE and NE 7th Street. This point of inflow is approximately 500 feet above the current sheet flow point. The drainage system is completely tight lined from Newport Court NE/ NE 7th Street through the City storm piping to an apartment site, Hilltop Homes Apartments downstream. The network of pipes runs 810 feet to a storm water pond within the Hilltop Apartments. The storm pipe system was visually inspected in three locations downstream; at CB #113111, CB #113118, and CB #113041. These are City of Renton storm water codes for City catch basins. The system of pipes were 12"concrete entering into Type II catch basins. There appeared to be no overtopping of the basins or capacity issues. The roadway area above these catch basins had no indication of overflow. The storm water enters into a pond within Hilltop Apartments, City node #145531. This pond is heavily over grown with trees and blackberries. A walk of the parameter of the pond shows no signs of overtopping or erosion. The parking lot to the south of the pond is about 4' below the pond berm. There were no signs of overtopping in this area either. The drainage leaves the pond and enters into Monroe Avenue NE about 200 feet north of NE 4th Street. The storm system is within the centerline of the road and was not inspected. The storm system continues to the south in Monroe Ave until it enters the City Shop Area at NE 2th Street. 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L 410' ` 34s 116 52, [ H'*" fl7 \1\ I i r--C--`r' 116953' 4 F4NE - 17 T23N RO5E NE 1/4 - Pg. 72 Structures CtifJert(Private) Facility Pond " Surface Water Utility Renton Maintained Diameter Renton Maintained 4 Sala!l6111Wrinlikil ,: Mal 44 •`. 3431 4 ■ Type 1 Catchbasin or Inlet - - Unknown �6I • Type 2Catehbaain-Manhole T� 8-24 • ` �1 �5' �a � Tank `� _ Asset Inventory 4 Access Riser 25-48 ® Vault 4302 `4301 5306 1�cc �iCeN1�l�� © Vault 49-105 b \ ` -,I■- 1 q a,L7 iia ry Unknown e) Bios.. �■ �►its Pipe(Public) dal c�� r tv/ r l �"�� PrivatelyMaintainedOMMINTSIESplime aIt-omp May 2013 Privately Maintained Diameter■ Catchba sin or Inlet —Oa- Unknown `6�•�+�• i,-a ,O Type2Catchbasin-Manhole �►" 8"-2t' Tank uJl 'W�aiO1�� 53116 illMri ;l8 Access Riser a>_� 25'-48" ® Vault .giMill - a 0 Vault EINEM 49"+ co •323`� .ire ■ Bioswale �. aZ,5320 1 ■ Fel Unknown Pipe(Private) ® �ilv.dl>, �4�a�e7�Ir1 tt � Rain In ai n ��� Unknown Maintenance Diameter 1 `, i '.�0� 1 50 300 600 Unknown Matntainence r 5329 • n Catchbasin or Inlet —4► Unknown ` Pond k i die.X11® �1 :a Feet Catchbasin-Type2MH mar 8'-24' _ Culvert(Public) �. 25 -46" Pumpsutlon tri ,` RIO„41/41/gr932M � Diameter a 49'+ I I li, ! l'RENTON Ml��'+'�� �� MIEN' --° Unknown Other Conveyance I I PAA .1 4201 Y! 11515 � 5202 , Tr 8'-24” ConveyenceType tOeContourfill , � � � Mil 1 TOE :Y4e■ 25'-48" —0.- Pipe(Unknown Maini) ri ■Yrmi■•7memor � � rm � 49'+ ------ Ditch :' 0 9 T23N RO5E S E 1 /4 Disclaimer: This Inventory information is schematic only. It was compiled from numerous sources. It is the best — City of information available at this time and should be used enton for spon ibl guidance or only. The City of Renton is not neNrorl a"�DorT"ecuavE 5 responsible for errors or omissions. When this information Public Works Department is used for planning,design,and/or construction purposes, 5309 • - v users are to field verify this information. E5S E Pg. 48 1. . Section 4: Flow Control and Water Quality Facility Analysis and Design FLOW CONTROL REVIEW Based upon the City Drainage Manual, the following steps are required to determine the mitigation of storm water runoff of the developed project: Full Dispersion — N/G (no good) —the property does not have 100 feet of flow path available on each new lot; Full Infiltration — N/G —the available soils on the property are silty sandy (Alderwood) soils and do not provide adequate depth for full infiltration. Limited Infiltration — acceptable — no ground water was found in the test holes below 6 feet, therefore limited infiltration using gravel filled trenches will be utilized to treat 1,000 square feet of developed impervious runoff. The gravel filled trenches will be installed at a depth to bottom of trench of 3' (36"). The proposal is to mitigate all the Lots using gravel filled trenches located in the rear yards to treat 1,000 square feet of impervious area; to utilize sheet flow of the driveway across the front yards to mitigate the runoff from the impervious area of the driveway; to utilize perforated pipe connection at the connection to the storm conveyance system within the front yards. The frontage along NE 7th Street will be collected and conveyed into an existing public storm system located across NE 7th and west approximately 250 feet. A curb and gutter will be installed along the west side of the private access road (Olympic Avenue NE) to collect the runoff from the road. This runoff together with the connection to each lot will be conveyed into the NE 7th Street system. Based upon the attached analysis the following flows were developed to compare to existing runoff. Pre-Developed Condition (runoff) Mitigated Developed Condition (runoff) 2 Year 0.053 cfs 2 year 0.112 cfs 10 year 0.087 cfs 10 year 0.134 cfs 100 year 0.186 cfs 100 year 0.243 cfs The difference between 100 year"Pre-Developed Condition"and "Mitigated Developed Condition" is 0.243 — 0.186 = 0.057. The"Mitigated Developed Condition" runoff if less than 0.10 cfs during a 100 year storm event than the"Pre-Developed Condition" runoff. Therefore, based upon the City Drainage Manual, no storm water detention is required for this project. The calculations for the above analysis are located within this Section. WATER QUALITY REVIEW The City Manual requires water quality treatment for projects that add 5,000 square feet or more of"new" pollution generating imperious surfaces (PGIS). The proposed developed (PGIS) condition consists of: DEVELOPED (PGIS) EXIS 1'NG (PGIS) Access Road 5,309 Sq. feet Driveway 1,088 sq. feet Each Lot (D/W) 0 Sq. feet (mitigated) Asphalt in Road 1,406 sq. feet Frontage Widening 1,536 Sq. feet Shoulder 240 sq. feet Frontage Access Apron 160 Sq. feet Developed PGIS = 7,005 Square feet Existing PGIS = 2,734 sq. feet The proposed "Developed Condition"generates 4,271 square feet of NEW PGIS. Based upon the City Drainage Manual this is less than 5,000 square feet and therefore water quality treatment is not required. ' NE 7th North (2) (3) Area Breakdown ** Impervious (1) Mitigated Impervious Surface Developed Condition Lot Area Impervious Surfaces Runoff Pervious Area Breakdown (sa. feet) (sq. feet) jsa. feet) (so. feet) (so. feet) (50% *(2)) (50% *(2)) Lots Lot 1 6720 House, walkways, patio 2300 1000 1800 500 Driveway 300 300 150 150 Road (PGIS) 1400 0 1400 Landscaping 0 2720 3350 3370 Lot 2 6240 House, walkways, patio 2300 1000 1800 500 Driveway 300 300 150 150 Road (PGIS) 1460 0 1460 Landscaping 0 2180 3410 2830 Lot 3 7872 House, walkways, patio 1800 1000 1300 500 Driveway 300 300 150 150 Road (PGIS) 2449 0 2449 Landscaping 0 3323 3899 3973 Lot 4 7872 House, walkways, patio 2600 1000 2100 500 Driveway 300 300 150 150 Road 0 0 0 Landscaping 0 4972 2250 5622 Frontage Sidewalk 330 330 Apron (PGIS) 160 0 160 NE 7th Street (PGIS) 1536 0 1536 Landscape strip 0 854 2026 14935 16649 0.34 0.39 Acres Acres **-Lot mitigation includes "limited Infiltraion"of 1,000 square feet of roof area(credit 50%impervious runoff) and "sheet flow"dispersion of driveway(20'x 15) -each lot. Mitigation of 1,300 square feet per lot Existing Condition Impervious Pervious Area Breakdown Total Areas (sq. feet) !sq. feet) Parcel 28699 House 1820 Driveway (PGIS) 1088 Walkways 512 Sheds (outbuildings) 148 Landscaping 25131 Frontage 2880 Aspahlt (PGIS) 1406 Compacted garvel shoulder (PGIS) 240 Lawn 1234 5214 26365 0.12 0.61 Acres Acres NE 7th North Short Plat (Pre Developed — pre-existing conditions) 7 land Use S —UxJ Area Till Forest 0.00 acres Till Pasture 0.00 acres Till Grass 0.61 acres Outwash Forest 0.00 acres; Outwash Pasture 0.00 acres Outwash Grass 0.00 acres Wetland 0.00 acres' s Impervious 0.12 acres! Total ! 1 0.73 acres! Scale Factor : 1.00 Hourly Reduced Time Series: NE 7th North Short Plat (pre-ex) »1 Compute Time Series I Modify User Input File for computed Time Series 1.TSF1 `'4ttetp 1 Fifes - KCR7`; =(oJ xJ Flow Frequency Analysis Time Series File:ne 7th north short plat (pre-ex) . tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Frequency Analysis Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0.084 4 2/09/01 2 :00 0 . 186 1 100. 00 0.990 0.053 6 1/05/02 16:00 0. 104 2 25. 00 0. 960 0. 104 2 2/27/03 7: 00 0.087 3 10. 00 0. 900 0.041 8 8/26/04 2 : 00 0.084 4 5. 00 0.800 0.053 7 10/28/04 16 :00 0.080 5 3. 00 0.667 0.087 3 1/18/06 16: 00 0 .053 6 2. 00 0. 500 0. 080 5 11/24/06 3: 00 0.053 7 1 . 30 0. 231 0. 186 1 1/09/08 6:00 0 . 041 8 1. 10 0. 091 Computed Peaks 0. 158 50. 00 0. 980 d NE 7th North Short Plat (Developed Conditions) Q Land Use S j Area .1 Till Forest 0.00 acres Till Pasture 0.00 acres Till Grassi 0.39 acres Outwash Forest 0.00 acres? Outwash Pasture 0.00 acres Outwash Grass 0.00 acres/ Wetland 0.00 acres Impervious 0.34 acres] Total -, 0.73 acres] Scale Factor : 1.00 Hourly Reduced Time Series: NE 7th North (Developed Conditions) »I Compute Time Series Modify User Input File for computed Time Series [.TSF] 17--Neap!Rtes- KCHT`' OJ J Flow Frequency Analysis Time Series File:ne 7th north (developed conditions) . tsf Project Location:Sea-Tac ---Annual Peak Flow Rates--- Flow Frequency Analysis Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob (CFS) (CFS) Period 0. 117 5 2/09/01 2: 00 0.243 1 100.00 0.990 0.090 8 1/05/02 16:00 0. 142 2 25.00 0.960 0.142 2 2/27/03 7:00 0. 134 3 10.00 0. 900 0.092 7 8/26/04 2:00 0. 124 4 5.00 0.800 0. 112 6 10/28/04 16:00 0. 117 5 3.00 0.667 0.124 4 1/18/06 16:00 0. 112 6 2.00 0.500 0.134 3 10/26/06 0:00 0.092 7 1.30 0.231 0.243 1 1/09/08 6:00 0.090 8 1 . 10 0.091 Computed Peaks 0.209 50.00 0. 980 C.2.3 LIMITED INFILTRATION C.2.3 LIMITED INFILTRATION invited infiltration is the use of infiltration devices from Section C.2.2 in soils that are not as permeable as the medium sands or coarse sands/cobbles targeted for full infiltration in Section C.2.2. These less desirable soils include fine sands,loamy sands,sandy loams,and loams,which tend to be more variable in permeability,more frequently saturated during the wet season,and more prone to plugging over time. While full infiltration may be possible under the best of these soil conditions,in the long run,these conditions will conspire to limit average infiltration capacity to something much less than that of full infiltration. Therefore,using limited infiltration as specified in this section will not be credited the same as using full infiltration as specified in Section C.2.2. Applicable Surfaces Limited infiltration may be applied to any impervious surface(e.g.,roof,driveway,parking area,or road) subject to the minimum requirements and design specifications in this section. Operation and Maintenance See Section C.2.3.5(p.C-50). C.2.3.1 REQUIRED SOILS REPORT In order to properly design limited infiltration devices,a soils report is required to identify the depth to impermeable layers(i.e.,hardpan)and to the maximum wet season groundwater level. See Section C.2.2.1 (p.C-41)for more details on this report. In many cases,this report will have already been prepared as required in Sections C.1.3.1 and C.1.3.2 for lots where full dispersion is not feasible or applicable to target impervious surface per Section C.2.1. C.2.3.2 MINIMUM DESIGN REQUIREMENTS FOR LIMITED INFILTRATION The minimum requirements for limited infiltration are the same as those for full infiltration,except infiltration depressions are excluded and existing soils in the location of the infiltration device may be fine sands,loamy sands,sandy loams,or loams as opposed to only medium sands or better. Note that gravel and medium sand soils used for full infiltration correspond to Soil Types 1A, IB, 2A and 2B in the Soil Textural Classification system used for onsite septic system design;fine sands are Type 3;and loamy sands,sandy loams and loams are Type 4 soils. Silt and clay loams, and cemented till(hardpan)are not suitable for limited infiltration systems. C.2.3.3 USE OF GRAVEL FILLED TRENCHES FOR LIMITED INFILTRATION The specifications for use of gravel filled trenches for limited infiltration are the same as those used for full infiltration,except the 1 im a surface requires different trench lengths as follows a)75 feet if the soil is a fine sand/loamy sand, b) 125 feet if the soil is a sandy loam,or(c) 190 fee. C.2.3.4 USE OF DRYWELLS FOR LIMITED INFILTRATION The specifications for use of drywells for limited infiltration are the same as those used for full infiltration, except that every 1,000 square feet of tributary impervious surface requires different gravel volumes as follows:(a)230 cubic feet if the soil is a fine sand/loamy sand,(b)380 cubic feet if the soil is a sandy loam,or(c)570 cubic feet if the soil is a loam. 2009 Surface Water Design Manual—Appendix C 1/9/2009 C-49 • SECTION C.2 FLOW CONTROL BMPs C.2.3.5 MAINTENANCE INSTRUCTIONS FOR LIMITED INFILTRATION If the limited infiltration flow control BMP is proposed for a project,the following maintenance and operation instructions must be recorded as an attachment to the required declaration of covenant and grant of easement per Requirement 3 of Section C.1.3.3 (p.C-18). The intent of these instructions is to explain to future property owners,the purpose of the BMP and how it must be maintained and operated. These instructions are intended to be a minimum; DDES may require additional instructions based on site- specific conditions. Also,as the County gains more experience with the maintenance and operation of these BMPs, future updates to the instructions will be posted on King County's Surface Water Design Manual website. TEXT OF INSTRUCTIONS Your property contains a stormwater management flow control BMP (best management practice)called "limited infiltration,"which was installed to mitigate the stormwater quantity and quality impacts of some or all of the impervious surfaces on your property. Limited infiltration is a method of soaking runoff from impervious area (such as paved areas and roofs) into the ground. Infiltration devices, such as gravel filled trenches, drywells, and ground surface depressions,facilitate this process by putting runoff in direct contact with the soil and holding the runoff long enough to soak most of it into the ground. To be successful,the soil condition around the infiltration device must be able to soak water into the ground for a reasonable number of years. The infiltration devices used on your property include the following as indicated on the flow control BMP site plan: ❑ gravel filled trenches, ❑ drywells. The size, placement, and composition of these devices as depicted by the flow control BMP site plan and design details must be maintained and may not be changed without written approval either from the King County Water and Land Resources Division or through a future development permit from King County. Infiltration devices must be inspected annually and after major storm events to identify and repair any physical defects. Maintenance and operation of the system should focus on ensuring the system's viability by preventing sediment-laden flows from entering the device. Excessive sedimentation will result in a plugged or non-functioning facility. If the infiltration device has a catch basin, sediment accumulation must be removed on a yearly basis or more frequently if necessary. Prolonged ponding around or atop a device may indicate a plugged facility. If the device becomes plugged, it must be replaced. Keeping the areas that drain to infiltration devices well swept and clean will enhance the longevity of these devices. For roofs, frequent cleaning of gutters will reduce sediment loads to these devices. 1/9/2009 2009 Surface Water Design Manual—Appendix C C-50 C.2.2 FULL INFILTRATION fiAL(11.1. FIGURE C.2.2.A TYPICAL TRENCH INFILTRATION SYSTEM roof • - ,/ drain PLAN VIEW NTS 4"rigid or 6"flexible perforated pipe 3 J • infiltration trench sump w/solid lid PLAN VIEW roof drain NTS II overflow 4"rigid or 6"flexible splash block .1 perforated pipe i :4 ° ' 6 oQ �. l' illiml ' ° 0 washed rock ' ' \° Q o°p C 1'711 5.0'min I 12"j ;• — 1 1/2"3/4„ 'D.'"...° 0°°o 0: / I1' n n Q.4__r� .r' fine mesh CB sump w/solid lid erroen Loo. varies------ -- - - A filter fabric i compacted backfill 6" I1 _ :�• 4"rigid or 6"flexible ° °°' ° °a perforated pipe 24" °9 ° °4 ' i`o o S ,0° o ' :0 4° 78' V * washed rock 12" r o o a � i 4. ,a0 ,,,, ,o oa° p ° 1 washed /2"-3/4" 0. .--• -24" ...I SECTION A NTS 2009 Surface Water Design Manual-Appendix C 1/9/2009 C-45 C.1.3 APPLICATION OF FLOW CONTROL BMPS C.1.3 APPLICATION OF FLOW CONTROL BMPS Flow control BMPs are methods and designs for dispersing,infiltrating,or otherwise reducing or preventing development-related increases in runoff at or near the sources of those increases. Flow control BMPs include,but are not limited to,preservation and use of native vegetated surfaces to fully disperse runoff;use of other pervious surfaces to disperse runoff;roof downspout infiltration;permeable pavements;rainwater harvesting;vegetated roofs;and reduction of development footprint. For projects subject to Small Project Drainage Review,the application of flow control BMPs is mandatory for individual lot projects(i.e.,projects not subdividing land)and is optional for subdivision projects unless otherwise specified by DDES. For individual lot projects,flow control BMPs must be applied as specified by one of the following two sets of BMP requirements,whichever is applicable based on the size of site/lot: • "Small Lot BMP Requirements"(for sites/lots<22,000 square feet),Section C.1.3.1 • "Large Lot BMP Requirements"(for sites/lots 22,000 square feet),Section C.1.3.2 These requirements specify both the order of preference for selection of flow control BMPs and their extent of application to the developed surfaces of an individual lot project. This application of requirements is illustrated by the flow chart in Figure C.1.3.A(p.C-123). In addition,the implementation of flow control BMPs by projects on either size of site/lot must be in accordance with the"BMP Implementation Requirements"detailed in Section C.1.3.3. If the proposed project is a single family residential subdivision(i.e.,plat or short plat project),the application of flow control BMPs for future anticipated improvements on the lots created by the subdivision may be deferred until an individual lot project is proposed for permit approval on each lot. Alternatively,the BMPs required for anticipated improvements on each lot may be installed as part of the subdivision project if the applicant so chooses. In either case,the required application of BMPs,in terms of order of preference and extent of application to developed surfaces,is the same as that for an individual lot project(i.e.,as specified in Sections C.1.3.1 or C.1.3.2,and C.1.3.3). Note:road right-of-way improvements constructed as part of a subdivision project may require implementation offlow control BMPs or other mitigation as determined necessary by DDES. C.1.3.1 SMALL LOT BMP REQUIREMENTS Any proposed project that is on an individual site/lot smaller than 22,000 square feet must comply with the flow control BMP application requirements in this section. A. MITIGATION OF IMPERVIOUS SURFACE For projects subject to small lot BMP requirements,flow control BMPs must be applied to the project's target impervious surface according to the order of preference and extent of application specified in the following requirements: 1. The feasibility and applicability of full dispersion as detailed in Section C.2.1 (p.C-26)must be evaluated for the roof area(or an impervious area of equivalent size)on the site/lot. If feasible and applicable,full dispersion of roof runoff must be implemented as part of the proposed project. Typically,small lot full dispersion will be applicable only in subdivisions where enough forest was preserved by tract,easement,or covenant to meet the minimum requirements for full dispersion in Section C.2.1.1 (p.C-26). If this first requirement is met for the site/lot,no other flow control BMPs are required for mitigation of impervious surface,and the remaining requirements below are optional. 2. Where full dispersion of roof runoff(or equivalent)is not feasible or applicable,or will cause flooding or erosion impacts,the feasibility and applicability of full infiltration as detailed in Section C.2.2(p.C-41)must be evaluated for roof runoff(note, this will require a soils report for the siteulot). 2009 Surface Water Design Manual—Appendix C 1/9/2009 C-13 • SECTION C.1 SMALL PROJECT DRAINAGE REVIEW REQUIREMENTS If feasible and applicable,full infiltration of roof runoff must be implemented as part of the proposed project. If this requirement or the full dispersion requirement above is met for the site/lot, no other flow control BMPs are required,and the remaining requirements below are optional. 3. Where full dispersion or full infiltration of roof runoff as specified in Requirements 1 and 2 above is not feasible or applicable,or will cause flooding or erosion impacts,one or more of the following BMPs must be applied to(or used to mitigate for)an impervious area equal to at least 10%of the site/lot for site/lot sizes up to 11,000 square feet and at least 20%of the site/lot for site/lot sizes between 11,000 and 22,000 square feet. For projects located within a critical aquifer recharge area,1°these impervious area amounts must be doubled. The BMPs listed below may be located anywhere on the site/lot subject to the limitations and design specifications for each BMP. These BMPs must be implemented as part of the proposed project. • Limited Infiltration(see Section C.2.3) • Basic Dispersion(see Section C.2.4), • Rain Garden(see Section C.2.5), • Permeable Pavement(see Section C.2.6), • Rainwater Harvesting(see Section C.2.7), • Vegetated Roof(see Section C.2.8), • Reduced Impervious Surface Credit(see Section C.2.9), • Native Growth Retention Credit(see Section C.2.10). 4. Any proposed pipe connection of roof downspouts to the local drainage system11 must be via a perforated pipe connection as detailed in Section C.2.11. B. MITIGATION OF NEW PERVIOUS SURFACE For projects subject to small lot BMP requirements, no flow control BMPs are required for new pervious surface. Note, however, that KCC 16.82.100(G)requires amendment of the soil to mitigate for lost moisture holding capacity in any area that has been compacted or that has had some or all of the duff layer or underlying topsoil removed. The amendment must be such that the replaced topsoil is a minimum of 8 inches thick, unless the applicant demonstrates that a different thickness will provide conditions equivalent to the soil moisture holding capacity native to the site. The replaced topsoil must have an organic content of 8-13%dry weight and a pH suitable for the proposed surface vegetation(for most soils in King County, 4 inches of well-rotted compost tilled into the top 8 inches of soil is sufficient to achieve the organic content standard). The amendment must take place between May 1 and October 1. C. MITIGATION OF WATER QUALITY IMPACTS For projects subject to small lot BMP requirements,most water quality impacts will be adequately addressed through proper application of flow control BMPs to impervious surface as specified above. However,if the project results in 5,000 square feet or more of new pollution-generating impervious surface from which runoff is not fully dispersed in accordance with Section C.2.1 (p.C-26),then one of the following actions must be taken: 10 Critical aquifer recharge area is the critical area designation,defined and regulated in KCC 21A,that is applied to areas where extra protection of groundwater quantity and quality is needed because of known susceptibility to contamination and importance to drinking water supply. Such areas are delineated on the King County Critical Aquifer Recharge Area Map available at DDES or on the County's Geographic Information System(GIS). See the definition of this term in KCC 21A.06 for more details. 11 Local drainage system means any natural or constructed drainage feature that collects and concentrates runoff from the site and discharges it downstream. 1/9/2009 2009 Surface Water Design Manual—Appendix C C-14 Section 5: Conveyance System Analysis and Design The analysis of the new conveyance system is attached to this Section. The new conveyance system was analyzed using the"Rational Method of Analysis" per section 3.2 King County Drainage Manual. The calculated 25 year storm event was 3.96 cfs from runoff of the existing upstream area and the developed site conditions (NE 7th North Short Plat). Based upon this flow, a backwater analysis was performed on the new system (see attached). The analysis concluded that the storm system is adequate to convey the 25 year event. Rational Method Runoff from Basin 25 year event P(25) 3.40 inches (from attached Isopluvials Map) A(T) 4.20 acres Areas A(1) 3.50 acres single family residential 1.4DU/GA - existing A(2) 0.70 acres single family residential 5.7 DU/GA - development (NE 7th North) A(T) 4.20 acres Description of flow Path k® L1 250 feet s1 0.05 Lawn/landscaping 7.0 L2 220 feet s2 0.10 Nearly bare ground 10.1 L3 170 feet s3 0.08 Asphalt 20.0 Composite Runoff Coefficient A(1); C(1) 0.33 A(2); C(2) 0.54 C© 3.50*0.33 + 0.70*0.54/4.20 0.37 Time of Concentration T(1) 250/60*{(7.0)*(0.05)**0.5)} 3 minutes T(2) 220/60*{(10.1)*(0.10)**0.5)} 2 minutes T(3) 170/60*{(20.0)*(0.08)**0.5)} 1 minute USE 7 minutes Compute i® i®=(aR)*(Tc) i® = 2.66*7**-0.65 0.75 Compute I(25) I(25)=(P25)*(i25) I(25)=3.40*0.75 2.55 Q(25) = C*I(25)*A Q(25) = 0.37*2.55*4.20 3.96 cfs 3.2.1 RATIONAL METHOD TABLE 3.2.1.A RUNOFF COEFFICIENTS- "C"VALUES FOR THE RATIONAL METHOD General Land Covers Single Family Residential Areas* Land Cover C Land Cover Density C Dense forest 0.10 0.20 DU/GA(1 unit per 5 ac.) 0.17 Light forest 0.15 0.40 DU/GA(1 unit per 2.5 ac.) 0.20 Pasture 0.20 0.80 DU/GA(1 unit per 1.25 ac.) 0.27 ACI) Lawns 0.25 1.00 DU/GA 0.30 Playgrounds 0.30 1.50 DU/GA 0.33 - Gravel areas 0.80 2.00 DU/GA 0.36 Pavement and roofs 0.90 2.50 DU/GA 0.39 Open water(pond, lakes, 1.00 3.00 DU/GA 0.42 wetlands) 3.50 DU/GA 0.45 4.00 DU/GA 0.48 4.50 DU/GA 0.51 A(1) 5.00 DU/GA 0.54 • 5.50 DU/GA 0.57 6.00 DU/GA 0.60 •Based on average 2,500 square feet per lot of impervious coverage. For combinations of land covers listed above, an area-weighted"C,:x A,"sum should be computed based on the equation Cc: x A,=(C1 x A1)+(C2 x A2)+ ...+(C"x An),where A,=(A1+A2+ ...+219),the total drainage basin area. TABLE 3.2.1.B COEFFICIENTS FOR THE RATIONAL METHOD"iR" EQUATION Design Storm Return Frequency aR bR 2 years 1.58 0.58 5 years 2.33 0.63 10 years 2.44 0.64 25 years 2.66 0.65 50 years 2.75 0.65 100 years 2.61 0.63 TABLE 3.2.1.0 kR VALUES FOR T,USING THE RATIONAL METHOD Land Cover Category kR Forest with heavy ground litter and meadow 2.5 Fallow or minimum tillage cultivation 4.7 Short grass pasture and lawns 7.0 Nearly bare ground 10.1 Grassed waterway 15.0 Paved area(sheet flow)and shallow gutter flow 20.0 2009 Surface Water Design Manual 1/9/2009 3-13 SECTION 3.2 RUNOFF COMPUTATION AND ANALYSIS METHODS FIGURE 3.2.1.0 25-YEAR 24-HOUR ISOPLUVIALS �S �'— __ _ __ [SHcoYNO COUNTY ...../ 2.8 o i 39 ® ® Dv To 4• C 333 Cli ,,off ') s,� mt a �` .. _.. .. 5.0 => 110 SI 1 6, 0 \ N a7 _ - - 1 t v jii cYj , CO 0 433. oi �- ..,,t, _ --` _KING COUNTY (L. PIERCE COUNTY , WESTERN JIs KING COUNTY \ p 5s N 50 4.5 25-Year 24-Hour , ://., Precipitation N �, ti,��rf 0� �Miles �• n3• - � in Inches io,• 1/9/2009 2009 Surface Water Design Manual 3-16 STORMWATER CONVEYANCE BACKWATER CALCULATION SHEET (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) Barrel Entrance Entrance Pipe 25 year Pipe Outlet Inlet Barrel Barrel Velocity TW Friction HGL Head Segment Q Length Pipe "n" Elev Elev Area Velocity Head Elev Loss Elev Loss CB to CB (cfs) (ft) Size Value (feet) (feet) (sq. feet) (fps) (feet) (feet) (feet) (feet) (feet) #EX - #1 3.96 30 12" 0.011 382.07 382.37 0.7854 5.04 0.39 382.20 0.0054 382.21 0.08 #1 - #2 3.96 230 12" 0.011 382.37 384.67 0.7854 5.04 0.39 383.36 0.0054 383.36 0.08 #2 - #3 3.96 89 12" 0.011 386.30 391.12 0.7854 5.04 0.39 387.50 0.0054 386.11 0.08 #2 - #4 1.45 20 12" 0.011 384.67 385.60 0.7854 1.85 0.05 386.11 0.004 386.11 0.01 (14) (15) (16) (17) (18) (19) (20) (21) Exit Outlet Inlet Approach Bend Junction Head Control Control Velocity Head Head HW RIM ELEV Loss Elev Elev Head Loss Loss Elev UPSTREAM (feet) (feet) (feet) (feet) (feet) (feet) (feet) CB 0.39 382.68 383.75 0.39 0 0 383.36 385.40 OK! 0.39 383.83 386.50 0.39 0 0 386.11 389.30 OK! 0.39 386.58 392.00 0.39 0 0 391.61 394.12 OK! 0.05 386.18 387.50 0.39 1.3 0 388.41 390.50 OK! • 4.2.1 PIPE SYSTEMS—METHODS OF ANALYSIS FIGURE 4.2.1.K BEND HEAD LOSSES IN STRUCTURES I I I I ' — _ c4j�2 — — frOM — — Gia k 1.2 — — r D il,,.... 1.0 — #4), — 4, Y 0.8 4. c °' — Bend at Manhole, — o no Special Shaping — 43 — 0 U — — o — Deflector — 0.6 — — .4 Curved — Bend at Manhole, Curved or Deflector — I \YY - 0.4 — Curved Sewer — r/DI=2 i— 0.2 Sewer r/D>6 - ., 4 0.0 I I I I 0° 200 40° 60° 80° 90° 100° Deflection Angle 7, Degrees 2009 Surface Water Design Manual 1/9/2009 4-27 SECTION 4.3 CULVERTS AND BRIDGES TABLE 4.3.1.B ENTRANCE LOSS COEFFICIENTS Type of Structure and Design Entrance Coefficient,Ke Pipe, Concrete, PVC, Spiral Rib, DI, and LCPE C��) Projecting from fill, socket(bell)end 0.2 .1 Projecting from fill, square cut end 0.5 Headwall, or headwall and wingwalls Socket end of pipe(groove-end) 0.2 Square-edge 0.5 Rounded(radius= 1/12D) 0.2 Mitered to conform to fill slope 0.7 End section conforming to fill slope* 0.5 Beveled edges, 33.7°or 45°bevels 0.2 Side-or slope-tapered inlet 0.2 Pipe, or Pipe-Arch, Corrugated Metal and Other Non-Concrete or D.I. Projecting from fill (no headwall) 0.9 Headwall, or headwall and wingwalls(square-edge) 0.5 Mitered to conform to fill slope(paved or unpaved slope) 0.7 End section conforming to fill slope* 0.5 Beveled edges, 33.7°or 45°bevels 0.2 Side-or slope-tapered inlet 0.2 Box, Reinforced Concrete Headwall parallel to embankment(no wingwalls) Square-edged on 3 edges 0.5 Rounded on 3 edges to radius of 1/12 barrel dimension or beveled 0.2 edges on 3 sides Wingwalls at 30°to 75°to barrel Square-edged at crown 0.4 Crown edge rounded to radius of 1/12 barrel dimension or beveled top 0.2 edge Wingwall at 10°to 25°to barrel Square-edged at crown 0.5 Wingwalls parallel (extension of sides) Square-edged at crown 0.7 Side-or slope-tapered inlet 0.2 * Note: "End section conforming to fill slope"are the sections commonly available from manufacturers. From limited hydraulic tests they are equivalent in operation to a headwall in both inlet and outlet control. 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U 113W7)10-1399----7-1-- c,!0o.• r �sonoa.""1 00 t 2135Ys3O , Sf7¢ 1`351�55' 9 �7y J562- •�_ \ r ,,ii. 'fii -1 • '36252 60 ! �,�1 15851 + t W so0 - 61 °' 3655 nt . 59360,1,..1907 913 3919' if 1 • I : 'soI ' I - 135221 -71 r$»� 410 ..�' 1151 1121+ ��.S � I • 7 0 i45531 ��,i \ J s: -. 150 "0I so0 I , led --. I •. • 249 11 s r 5 - ie _'` " ' 3>---. ` led , ,. i1,45831�"�''t�..� .1wt.l ill 3....i E---47z-Ti--1 •_�y .., • Section 6: Special Reports and Studies Geotechnical Study attached GEOSPECTRUM CONSULTANTS, INC. Geotechnical Engineering and Earth Sciences August 15, 2013 Mr. Mike Lombardo KRRV Development, LLC P. O. Box 908 Ravensdale, WA 98051 SUBJECT: GEOTECHNICAL EVALUATION Proposed 4-Lot 7th Street North Plat 3506 NE 7th Street Renton, Washington Project No. 13-121-01 Dear Mike, This report presents the results of our geotechnical evaluation for the site of your proposed new residential development on the `subject property. The purpose of our work was to provide geotechnical engineering evaluations of the site and geotechnical recommendations for the residential development including design of foundations, site grading, site drainage and erosion control. Our work was performed in accordance with the scope and conditions of our proposal dated July 22, 2013. A site topographic map and development plan (see Figure 2) was provided to us and was used as a reference for our evaluations. Based on our review of the plan provided and discussions with you, we understand that the property will be divided into 4 lots and the development will include a new 2-to 3-story wood-frame residence on each of the new lots. The structures will include ground level garages which will have slab-on- grade floors and the remainder of structures may have raised floors with crawl space or slab-on-grade. We assume that bearing wall loads will be in the range of about 2 to 3 klf and maximum column loads to be in the range of about 10 to 20 kips. If actual structural loads exceed the above values by more than 25%, this office should be notified. Review of the Renton online Sensitive Areas Maps indicates that the property is not indicated to be within a Landslide Hazard, Erosion Hazard, Seismic Hazard or Coal Mine Hazard area. P.O. Box 276, Issaquah, WA 98027-0276 • Phone: (425) 391-4228 Fax: (425) 391-4228 a KRRV Development, LLC August 15, 2013 SCOPE OF WORK Our geotechnical evaluation included review of geologic mapping, site explorations, engineering analyses and evaluations and the preparation of this report. The scope of work included the following specific tasks: o Review of published geologic mapping of the site vicinity and our recent explorations on the adjacent property to the east. o Performed a reconnaissance of the site as well as observations of the adjacent developed lots to the east. o Observed and logged four test pit explorations on the site (see Figure 2) to depths up to 4 feet below existing ground. Logs of the test pits and results of field and laboratory testing are presented in the Test Pit summaries of Appendix A along with log% of adjacent explorations on the adjoining property to the east. o Performed geotechnical engineering evaluations of the proposed site development and developed our geotechnical recommendations for foundation design and site grading. o Prepared this geotechnical report summarizing our findings and recommendations. OBSERVED SITE CONDITIONS The property is bordered on the west, north and east by developed residential lots (we previously performed geotechnical evaluations for new development along the south side of 7tn Street). At the time of our field exploration the property was developed with a residence and some small sheds and a hot tub as shown in Figure 2. The topographic mapping included on the site plan of Figure 2 indicates that the property generally slopes very gently down to the west/southwest at gradients that range from less than 3 percent up to about 6 percent in localized areas and overall average gradients across the property from northeast to southwest are less than 3 percent with a maximum elevation difference across the property of about 8 feet from northeast to southwest. The site was well vegetated primarily with grasses but also included shrubs, ivy, elderberry and numerous evergreen trees to 3+ feet in diameter as shown on Figure 2. We did not observe any seeps or springs or evidence of current or past erosion on the site. Project No. 13-121-01 Page 2 KRRV Development, LLC August 15, 2013 Subsoils Our evaluation of the subsurface conditions was based on our observations of four exploratory test pits within the property. Approximate locations of the onsite test pits and the previous adjoining test pits are shown on Figure 2. Logs of the onsite test pits are presented in Appendix A. Subsoils encountered in our test pits were found to include some minor fill and natural glacially consolidated soils. Fill soils were encountered in TP-4 located at the lower south side of the property as shown on Figure 2. Fill soils at TP-4 were silty crushed gravel and were only about 1.5 feet thick at that location. Natural soils encountered at the test pit locations were generally silty fine or very fine sand with some medium to coarse sand and gravel. The upper soils were typically loose to medium dense soils to depths of about 2 to 3 feet below the natural surface becoming very dense and hard and cemented at greater depths. Ground Water No ground water or seepage was observed in any of the test pits. Typically the shallow soils were classified as slightly moist and the deeper soils were classified as slightly moist to moist. The measured moisture contents of the soils generally ranged from about 5 to 9 percent. Subsurface Variations Based on our experience, it is our opinion that some variation in the continuity and depth of subsoil deposits and ground water levels should be anticipated due to natural deposition variations and previous onsite structures and grading. Due to seasonal moisture changes, ground water conditions should be expected to change with time. Care should be exercised when interpolating or extrapolating subsurface soils and ground water conditions between or beyond our test pits. Project No. 13-121-01 Page 3 • KRRV Development, LLC August 15, 2013 SITE EVALUATIONS General The referenced geologic map of Figure 1 indicates the site vicinity to have surface exposures of glacial till (Qgt) soils. The Qgt glacial till soils are highly consolidated, heterogeneous mixtures of sand, silt, clay and gravel soils deposited during the advance of the Vashon glaciation, the last glacial advance into the Puget Sound area, approximately 13,000 to 16,000 years ago. Based on the soils observed on the site and review of the referenced map, it is our opinion that the natural very dense/hard silty sand with gravel soils underlying the property and are most likely glacially consolidated till deposits (Qgt). Based on the results of our field investigations combined with our own experience and judgment, it is our opinion that the geotechnical site conditions are suitable for the proposed development provided our recommendations are followed. Hazard Assessment Landslide: The Renton Sensitive Areas Maps indicate the site is not within a Landslide Hazard area. In addition, the geologic map of Figure 1 indicates no mapped landslides within the site vicinity and our site observations indicate the site is currently stable. Considering the very gentle slope gradients and the observed glacial till soils, it is our opinion that the potential for future instability on the site is very low to nil. Erosion: The Renton Sensitive Areas Maps indicate the site is not within a Erosion Hazard area. We observed that the site is well vegetated we observed no indication of any seepage or concentrated water flow or current or past erosion on the site. Based on our site observations and explorations it is our opinion that there is no unusual erosion risk at this site and any potential erosion potential resulting from development will be mitigated by our recommended grading procedures and drainage/erosion control measures and by final re-vegetation/landscaping incorporated into the proposed development plans. 3 Coal Mine: The Renton Sensitive Areas Maps indicate the site is not within a Coal Mine Hazard area. Seismic: The Renton Sensitive Areas Maps indicate the site is not within a Seismic Hazard area, however the Puget Sound region is a seismically active area. About 17+ moderate to large earthquakes (M5 to M7+) have occurred in the Puget Sound and northwestern Cascades region since 1872 (141 years) including the 2/28/01 M6.8 Nisqually earthquake and it is our opinion that the proposed structures will very likely experience significant ground shaking during their useful life. Project No. 13-121-01 Page 4 KRRV Development, LLC August 15, 2013 Based on a recently published study the site lies only about 2.5 miles south of the southern mapped location of the Seattle fault and about 18 miles southwest of the estimated trace of the South Whidbey-Lake Alice fault both of which have postulated maximum credible magnitudes of 7.0 to 7.5. Another recent study of the Vashon- Tacoma area presents evidence for the east-west trending Tacoma Fault which is indicated to pass through the south end of Vashon and the middle of Maury Island about 10.5 miles southwest of the site. The study suggests that the Tacoma Fault and the Seattle fault may be linked by a master thrust fault at depth. The Seattle fault has been documented to have moved at its west end (Bainbridge Island) about 1000 to 1100 years ago and evidence of movement at the east end has also recently been documented. Some experts feel that the recurrence interval between large events on the Seattle Fault may be on the order of several thousands of years but our calculations indicate it may be on the order of 1200 to 1400 years. The activity of the documented Tacoma fault is considered to be on the same order as the Seattle fault. The recurrence of a maximum credible event on the South Whidbey fault is not known but some experts have assigned a recurrence of about 3000 years, however smaller events will occur more frequently as evidenced by the 5.3 event on May 2, 1996 which was attributed to that fault. In addition to Puget Sound seismic sources, a great earthquake event (M8 to M9+) has been postulated for the Cascadia Subduction Zone (CSZ) along the northwest Pacific coast of Oregon, Washington and Canada. The current risk of a future CSZ event is not known at this time. Published reports have indicated recurrence intervals for a CSZ event to range from as little as 100-200 years to as long as 1000+ years and the time of the last event is reported to have been about 313 years ago. The 2009 International Building Code (IBC) adopted by the City of Renton requires consideration of a spectral acceleration level with probability of exceedance of 2 percent in 50 years for seismic structural design. This corresponds to about a 2475- year recurrence interval earthquake ground motion. Based on the short period spectral response accelerations presented in Figure 1613.5(1) of the 2009 IBC, adjusted as per equations 16-36, 16-38 and factored as per section 1803.5.12(2), we estimate the IBC peak ground acceleration for soils and foundation design at this site to be about 0.38g. Please note that the 0.38g peak ground acceleration includes the additional reduction factor of section 1803.5.12(2) and is not intended for structural analyses. We recommend the site be considered a Site Class D for structural design. Secondary seismic hazards due to earthquake ground shaking include induced slope failure, liquefaction, lateral spreading and ground settlement. Considering the very dense/hard nature of the soils recommended for bearing at the site, it is our evaluation that the potential for damage to the structures due to liquefaction, lateral spreading and settlement is very low to nil. The potential for seismically induced shallow failures is also considered very low to nil. A Project No. 13-121-01 Page 5 KRRV Development, LLC August 15, 2013 Structure Support Considerations In our opinion the undisturbed very dense/hard natural glacial till soils encountered in our explorations should provide good support for the proposed structure foundations. Bearing soils are expected to be encountered at depths ranging from about 2 to 3 feet below the natural ground surface at the site. Foundations should penetrate through any existing fill, topsoil and loose/medium dense soils to bear on undisturbed very dense/hard natural soils. Conventional spread footings are considered appropriate for support of the proposed structures considering that bearing soils are at shallow depths. However, if any deep fill areas are encountered on the site, lean concrete footing extensions or pipe piles could be used to transfer foundation loads to the deep bearing soils in those areas. We have included recommendations for spread footings and lean concrete support in this report. RECOMMENDATIONS The following subsections present our recommendations for design of foundations, site grading, drainage control and erosion control. Also included are recommendations for plan review and observations and testing during construction. Spread Footing Foundations Conventional spread footings founded on undisturbed very dense/hard natural glacial till soils should provide good support for the proposed structures. Bearing soils are expected to be encountered at depths ranging from about 2 to 3 feet below the natural ground surface of the site. Continuous wall footings should be at least 18 inches wide. Square footings for column support should be at least 24 inches wide. Footings supported on undisturbed very dense/hard natural glacial till soils may be designed based on an allowable bearing pressure of 2000 psf. All footings should be founded at least 18 inches below the lowest adjacent final grade. Where the natural bearing soils slope, the footing excavation should be stepped to maintain a horizontal bearing surface. If deep fill or other unsuitable soils are encountered, foundation loads may be transferred from the recommended minimum foundation depths to the recommended very dense/hard bearing soils by a monolith of lean concrete having a minimum compressive strength of 1000 psi. The width of an un-reinforced lean concrete monolith should be at least as wide as the footing or at least one-third of the monolith height, whichever is greater. Reinforced monoliths should be designed by a structural engineer. A suitable width trench should be excavated with a smooth edged excavator Project No. 13-121-01 Page 6 KRRV Development, LLC August 15, 2013 bucket (no teeth) to expose the dense/very dense bearing soils under observation by our office and backfilled as soon as possible with the lean concrete to the footing elevation. The estimated settlement of a 18-inch wide continuous footing carrying a load of 3 kips per foot is on the order of 1/4 to 1/2 inch. Our settlement estimates assume that foundations are supported on undisturbed very dense/hard natural bearing soils and that all fill and loose/disturbed material is removed from the bearing surface prior to concrete pour. Maximum differential settlement within the proposed structures is expected to be 1/2 inch or less. Settlements are expected to occur primarily during construction. 3 Resistance to lateral loads can be assumed to be provided by friction acting at the base of foundations and by passive earth pressure. A coefficient of friction of 0.45 may be assumed with the dead load forces in contact with on-site soils. An allowable static passive earth pressure of 250 psf per foot of depth may be used for the sides of footings poured against undisturbed medium dense to dense natural soils or properly compacted structural fill. An allowable static passive earth pressure of 150 psf per foot of depth may be used for the sides of footings or grade beams poured against existing loose soils. The vertical and lateral bearing values indicated above are for the total dead load plus frequently applied live loads. For short duration dynamic loading caused by seismic or wind forces, the vertical bearing values may be increased by 50 percent and allowable lateral passive pressures may be increased by 33 percent. Site Grading Site grading is expected to consist primarily of excavation for proposed foundations and subgrade preparation for slab and pavement areas and utility trenches. Onsite granular soils cleaned of debris and organics are considered suitable for use in general compacted fills but in our experience the onsite glacial till soils will be moisture sensitive with regard to grading and compaction characteristics. Grading should be scheduled for the late summer months if possible. Wet weather grading may require the use of imported clean granular fill soils which are more easily compacted at higher moisture levels. Recommendations for site preparation, temporary excavations, structural fill, subgrade preparation, site drainage and trench backfill are presented below. Site Preparation: Existing vegetation, debris, fill soils, and loose or organic natural soils should be stripped from the areas that are to be graded. During rough grading, excess soils may be stockpiled for later use. Stripping in subgrade areas is expected to average about 1 foot. Soils containing more than 1% by weight of organics may be used in planter areas, but should not be used for structural fill. Stumps, debris and trash, plus rocks and rubble over 6 inches in size, should be removed from the site. Project No. 13-121-01 Page 7 KRRV Development, LLC August 15, 2013 Subsoil conditions on the site may vary from those encountered in our test pits. Therefore, our office should observe the prepared areas prior to placement of any new fills. Temporary Excavations: Sloped temporary construction excavations may be used where planned excavation limits will not undermine existing structures or interfere with other construction. Where there is not enough room for sloped excavations, shoring should be provided. Based on the subsurface conditions encountered in the test pits, it is our opinion that sloped temporary excavations may be made vertically to depths of 4 feet or less. Excavations up to 10 feet in depth should be sloped no steeper than 1:1 within loose/medium dense soils and no steeper than.' :1 (horizontal:vertical) within the un- weathered, hard natural glacial till soils. It should be noted that the contractor is responsible for safety and maintenance of construction slopes. We recommend that cuts over 4 feet in depth be covered with visqueen tarp to help control ravelling and sloughing. Surface drainage should be directed away from the top edge of cut slopes. Surcharge loads should not be allowed within 5 feet of the top of the slope or within a 1:1 (horizontal:vertical) plane extending up from the toe of excavation, whichever is greater. Structural Fill: Provided that soil moisture can be reduced and maintained near optimum, excavated onsite soils cleaned of organics and debris may be used for general structural fill but the onsite soils are expected to be moisture sensitive and during the rainy season the soils may become too wet for practical compaction. Therefore imported granular fill soils should be used if moisture conditions cannot be adequately controlled. Loose soils, formwork and debris should be removed prior to placing fill or backfill. Structural fill should be placed in horizontal lifts not exceeding 8 inches in loose thickness and compacted to at least 90 percent of the maximum dry density as determined by the ASTM D1557 test method. Imported granular fill should consist of clean, well-graded sand and gravel materials free of organic debris and other deleterious material. Imported material for wet weather grading should be a sand/gravel mixture with less than 5 percent fines based on the sand fraction. Slab/Pavement Support: Slabs-on-grade and pavement should be supported directly on undisturbed dense natural soils or on properly compacted structural fill over medium dense natural soils. Where unsuitable soils such as existing fill, loose/disturbed soils (from tree stump removal) and organic soils exist at subgrade level, subgrade preparation should include excavation of the unsuitable soils as required to expose medium dense natural soils or to a maximum depth of 2 feet (or deeper as required to remove all loose/disturbed soils from tree stump removal) and placement of structural Project No. 13-121-01 Page 8 KRRV Development, LLC August 15, 2013 fill to final subgrade elevation. Subgrade fill should be placed in accordance with the recommendations for structural fill except that the top 6 inches of the subgrade fill should be compacted to at least 95 percent of the ASTM D1557 maximum dry density in pavement and driveway areas. It should be noted that where the proposed slabs cross a fill/natural contact line, there will be a high risk of cracking. Risk of cracking can be reduced by placing construction joints at the contact and by proper steel reinforcement of the slab. Interior concrete slabs should be underlain by a capillary break consisting of a polyethylene vapor barrier of at least 6 mil thickness. Utility Trenches: Buried utility conduits should be bedded and backfilled around the conduit in accordance with the project specifications. Bedding material should extend from six inches below the pipe to six inches above the pipe. Where conduit underlies pavement or slabs-on-grade, the remaining backfill above the pipe should be placed and compacted in accordance with the recommendations for structural fill. If imported granular fill is used for trench backfill it should be capped with 12 inches of onsite silty soils. Drainage Control Surface drainage from the site and adjoining upslope areas should be controlled and diverted around the development area in a non-erosive manner. Adequate positive drainage should be provided away from the structures and on the site in general to prevent water from ponding and to reduce percolation of water into subsoils. Granular backfill should be capped with paving or 6 inches of onsite silty soils. A desirable slope for surface drainage is 2% in landscaped areas and 1% in paved areas. Roof drains should be tightlined into the storm drain system (no discharge on the ground surface). A permanent perimeter drain, independent of the roof drain system, should be placed adjacent to the base of the continuous exterior foundations. The drain should consist of a four-inch diameter perforated PVC drain pipe placed in at least one cubic foot of washed drain gravel per lineal foot along the base of the foundations. The drain gravel zone around the pipe should be encapsulated with a membrane of Mirafi 140 filter fabric or equivalent between the drainage zone and onsite silty soils. Erosion Control Although we observed no evidence of erosion, onsite soils are expected to be erodible when disturbed and exposed to concentrated water flows. Siltation fences or other detention devices should be provided around the downslope side of the disturbed site area and soil stockpile areas during construction to control the transport of eroded material. The lower edge of the silt fence fabric should have "J" shaped embedment in a trench extending at least 12 inches below the ground surface. Project No. 13-121-01 Page 9 KRRV Development, LLC August 15, 2013 Surface water flow should be collected in area drains and tightlined to the storm water system, no water should be discharged on the site unless via a properly designed and approved infiltration/dispersion system. Exposed final graded soil areas should be planted immediately with grass and deep rooted plants. Plan Review This report has been prepared to aid in the evaluation of this site and to assist the architect, structural and civil engineers in the design and construction of the project. It is recommended that this office be provided the opportunity to review the final design drawings and specifications to determine if the recommendations of this report have been properly implemented and to make any supplemental design recommendations which may be required. Observations and Testing During Construction Recommendations presented in this report are based on the assumption that soil conditions exposed during construction will be observed by our office so that any necessary design changes or supplements may be made. Foundation excavations should be observed to verify that they expose undisturbed very dense/hard bearing soils and that excavations are free of loose and disturbed materials. All structural fill and slab/pavement subgrade areas should be observed by a representative of this office after stripping and prior to placing fill. Drainage control systems should be observed by our office to verify proper construction. Proper fill placement and compaction should be verified with field and laboratory density testing by a qualified testing laboratory. Project No. 13-121-01 Page 10 • KRRV Development, LLC August 15, 2013 CLOSURE This report was prepared for specific application to the subject site and for the exclusive use of KRRV Development, LLC and their representatives. The findings and conclusions of this report were prepared with the skill and care ordinarily exercised by local members of the geotechnical profession practicing under similar conditions in the same locality. We make no other warranty, either express or implied. Variations may exist in site conditions between those described in this report and actual conditions encountered during construction. Unanticipated subsurface conditions commonly occur and cannot be prevented by merely making explorations and performing reconnaissance. Such unexpected conditions frequently require additional expenditures to achieve a properly constructed project. If conditions encountered during construction appear to be different from those indicated in this report, our office should be notified. Respectfully submitted, GEOSPECTRUM CONSULTANTS, INC. Va,tzwerd'ofilirri"kawytii • p,. DOp James A. Doolittl �`'of WAS, ,, �T `..,A0�0��' Principal Engineer C-44, Encl: Figures 1 and 2 Appendix A 3623 oto, Fcrsr�� y 67oNAL G.� Dist: 2/Addressee EXPIRES 3/19/ 20 t r' Project No. 13-121-01 Page 11 1 , :a • ! E 1`% 11 t I1 0 . 11 f f f`-J ...\ .• ,,,-.41. 1 t 1 y� \ •• • ighl'an i. . l ,.s '' 1 . rTE :\..� /i i Q '`'a'- 1t ► ,` , Sch i tF , 1 . r • / L • ' 1\,_ 1 1.c\ N ' ...) s'•- 4' a Icit:4 I I, a i BM Ai 4-/ • \ i I • •:•• l . I. • 1 !It i 1 ) - ••• ..• • •. 1 t1 -• 1 ,Ii I e ( 1 . 4,. • r c) ....`� •• 1 I� ili lel \�_ I, .i a '� • ••• •t. ••--S— JI.I. •.• �'i,, . 10 ' :\.. :‘----, ° \..l \i ; !I,1 J c' x342 Q 1 ♦•.•Ilgell d ♦ 1 1 i 1 c . �,c.� / 1" t a . • 11 ti `�' 11I If AZA=''T r1,1 I ,L___7„.___,/ I I ■ II ,� ,• ` • II r ' �j � .r� ` ii/ II • t! li V \ ��r =� �� 11 1 II \ I i 1/ :1 Greenwoe�ht , II . aI308 � II �1 I .. Jt C �' i %- - II • r \. X / II rl \,. \ \ II ` `�� \ I. II Tank . T�� g Area 11 . rte. ,o0 1 ,3 " ii (Aband ` ed) /�j 1406 • I \ \ ,, / 0 .....••••\:.. y 1 I °t 9 n�.� 3M 4o os /• '"', , �,. I °4 • of t` ti �x j J % ® \` , 1 �'.\ •u Q uo• ° rRf: Geologic Map of the Renton Quadrangle by D. R. Mullineaux, USGS Map GQ-405, 1965 Enlarged Scale: 1"=1000' SITE VICINITY GEOLOGIC MAP GEOSPECTRUM CONSULTANTS, INC.. Proposed 060NE 7thI Str street North Plat Renton, Washington>>::1: ::: k :> Geotechn/cc/Eng/nearing cnd Earth Sconce* Proj. No.13-121 Date 8/13 Figure 1 . • I I'4.3.5'46 5r01 ‘ e. 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NE 7th STREET ', ,,, ref: Site Plan provided by client, undated, scale: lu= 40' SITE DEVELOPMENT & EXPLORATION PLAN Proposed 4-Lot 7th Street North Plat GEOSPECTRUM CONSULTANTS, INC. 3506 NE 7th Street Renton, Washington GEDcateachniccal ErmilneaearIng (=Ind Ecult)Scicancos Proj. No.13-121 Date 8/13 Figure 2 APPENDIX A FIELD EXPLORATION Our field exploration included a site reconnaissance and test pit explorations. During the site reconnaissance, the surface site conditions were noted, and the locations of the test pits were approximately determined. The test pits were approximately located using the existing structures as a guide. The approximate locations of the test pits are shown on Figure 2. Test Pit elevations were estimated based on the topographic mapping shown on Figure 2. Test pits were advanced using a trackhoe excavator. Soils were continuously logged and classified in the field by visual examination, in accordance with the ASTM Soil Classification system. Logs of the on-site test pits are presented on the test pit summary sheets A-1 and A-2. The test pit summaries include descriptions of the soils and pertinent field data. Soil consistency and moisture conditions indicated on the logs are interpretations based on the conditions observed in the field. Boundaries between soil strata indicated on the logs are approximate and actual transitions between strata may be gradual. TEST PIT NO. 1 Logged by JAD Date: 7/24/13 Elevation: 406' Depth Blows Class. Soil Description Consistency Moisture Color W(%) Comments 0 OL Organic duff& ivy loose slightly brown SM gravelly Silty Sand, fine _ 1 w/abundant roots to %" 5.1 o 2 — f rae cturiceme ng medium & brown gray 3 — very cemented hard , gray-brn 4.6 4 _ Maximum depth 3.5 feet. No ground water observed. 5 - 6 - 7 TEST PIT NO. 2 Logged by JAD Date: 7/24/13 Elevation: 403' Depth Blows Class. Soil Description Consistency Moisture Color W(%) Comments 6 OL Organic duff loose mlisah ly brown is 1 _ SM Silty fine Sand w/some m-c sand " to IIi ht n 7.3 moist blgow very cemented hard 7.5 3 — Maximum depth 2.5 ft. No ground water observed. 4 - 5 — 6 — 7 — GEOSPECTRUM CONSULTANTS, INC. Proposed 4-Lot 7th Street North Plat 3506 NE 7th Street Geotechnical Engineering and Earth Sciences Renton, Washington Proj. No. 13-121 Date 8/13 Figure A-1 TEST PIT NO. 3 Logged by JAD Date: 7/24/13 Elevation: 404' Depth Blows Class. Soil Description Consistency Moisture Color W(%) Comments 0 OL Organic duff& decayed wood loose slightly brown 1 — SM Silty Sand, very fine 5.8g/ambcs anndt &ooravtel3" 2 — with some cementation medium light dn 3 — _ very cemented hard gray-brn 5.8 , 4 — Maximum depth 3.5 feet. 5 — No ground water observed. 6 7 — TEST PIT NO. 4 Logged by JAD Date: 7/24/13 Elevation: 400' Depth Blows Class. Soil Description Consistency Moisture Color W(%) Comments 0 OLsod dry FILL GM Silty Gravel, crushed to 3" dense sli�Stly a light 1 — tt 9 Y 2 — SM wigv srya i e Sand w/orq. & roots loose sli�fitly dk brn brown to9.0 3 _ moist 4 — m. dense _ becomes cemented v. dense gray-brn 6 6 5 _ Maximum depth 4.5 ft. No ground water observed. 6 — 7 — GEOSPECTRUM CONSULTANTS, INC. Proposed 4-Lot 7th Street North Plat 3506 NE 7th Street Geotechnical Engineering and Earth Sciences Renton, Washington Froj. No. 13-121 Date 8/13 Figure A-2 Section 7: Other Permits None applicable at this time Section 8: CSWPPP Analysis and Design The proposed development and improvements comprise of 0.73 acres of property. The actual exposed and "worked" area on the project will consist of widening NE 7th Street and installing a private access road along the west side of the property. This"open and worked"construction area will be 0.20 acres. All construction activities will be concentrated on NE 7th Street. The entire property is NOT proposed to be graded and worked. Erosion control for the project will consist of filter fabric fencing along the westerly edge of the new private road. The existing paved driveway will be used for construction entry. The Developer constructing the improvements on NE 7th North Short is also the same developer that is constructing the NE 7th (three) short plats on the south side of NE 7th. The project to the south is under construction and properly protected from erosion. All staging of materials and vehicle parking will be provided off site on the project to the south. Therefore minimizing disturbance to the NE 7th north property can be accomplished. This will provide for more un-disturbed surface areas to filtering and minimize erosion runoff during construction. A temporary pond is not proposed due to allow for minimal disturbance of the property. There is an existing house and crawl space on the property that will be demolished under a separate permit. The crawl space area will provide a localize depression if additional filtration is necessary. This area could be used as a small ponding depression. Section 9: Bond Quantities, Facility Summaries, and Declaration of Covenant A Declaration of Covenant (Operation, maintenance, and restrictions) is attached for the proposed BMP's shown on the civil construction plans. Section 10: Operation and Maintenance Manual The Operation and Maintenance of the proposed BMP's provided will be included within the Declaration of Covenant from Section 9. These documents will be provided for review on as part of the utility permit submittal. • • r APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL,CONVEYANCE,AND WQ FACILITIES NO. 5-CATCH BASINS AND MANHOLES Maintenance Defect or Problem Condition When Maintenance is Needed Results Expected When Component Maintenance is Performed Structure Sediment Sediment exceeds 60%of the depth from the Sump of catch 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 the invert of the lowest pipe into or out of the catch basin. Trash and debris Trash or debris of more than'/: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. 1/3 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 Comer of frame extends more than%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 1/4 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 1/2 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 1/2 inch and longer than 1 foot No cracks more than 1/4 inch wide at at the joint of any inlet/outlet pipe or any evidence the joint of inlet/outlet pipe. of soil particles entering catch basin through cracks. Settlement/ 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'A-inch at the joint of the No cracks more than''h-inch wide at inlet/outlet pipes or any evidence of soil entering the joint of inlet/outlet pipes. the catch basin at the joint of the inlet/outlet 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 oil film. Inlet/Outlet Pipe Sediment Sediment filling 20%or more of the pipe. Inlet/outlet pipes clear of sediment. accumulation Trash and debris Trash and debris accumulated in inlet/outlet No trash or debris in pipes. pipes(includes floatables and non-floatables). Damaged Cracks wider than'',cinch at the joint of the No cracks more than%-inch wide at inlet/outlet pipes or any evidence of soil entering the joint of the inlet/outlet pipe. at the joints of the inlet/outlet pipes. .) 2009 Surface Water Design Manual—Appendix A 1/9/2009 A-9 f APPENDIX A MAINTENANCE REQUIREMENTS FLOW CONTROL,CONVEYANCE,AND WQ FACILITIES 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'/,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 cannot 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. 1/9/2009 2009 Surface Water Design Manual—Appendix A A-I() APPENDIX A MAINTENANCE REQUIREMENTS FOR FLOW CONTROL,CONVEYANCE,AND WQ 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 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 oil film. Damage to protective Protective 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 structural integrity of the pipe. Ditches Trash and debris Trash and debris exceeds 1 cubic foot per 1,000 Trash and debris Geared 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 to 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. 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 1/9/2009 A-I1