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HomeMy WebLinkAboutRS_TIR_210323_v2 Western Washington Division Eastern Washington Division 165 NE Juniper St., Ste 201, Issaquah, WA 98027 108 East 2nd Street, Cle Elum, WA 98922 Phone: (425) 392-0250 Fax: (425) 391-3055 Phone: (509) 674-7433 Fax: (509) 674-7419 www.EncompassES.net TECHNICAL INFORMATION REPORT For Sierra Homes Lots 34-36 1112, 1108, and 1106 N 34th Street Renton, WA 98056 January 25, 2021 Rev. 1: March 10, 2021 3/10/2021 Prepared by: Briana Bennington Encompass Engineering Job No. 20625 Prepared For: Sierra Homes Inc. PO Box 3069 Issaquah, WA 98027 DEVELOPMENT ENGINEERING Nathan Janders 04/07/2021 Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | i Table of Contents List of Figures ................................................................................................................................... i I. PROJECT OVERVIEW ................................................................................................................ 1 II. CONDITIONS AND REQUIREMENTS SUMMARY ...................................................................... 6 III. DOWNSTREAM ANALYSIS ........................................................................................................ 9 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ........................... 14 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ..................................................................... 16 VI. SPECIAL REPORTS AND STUDIES ............................................................................................ 16 VII. OTHER PERMITS ..................................................................................................................... 16 VIII. CONSTRUCTION STORMWATER GENERAL PERMIT............................................................... 16 IX. BOND QUANTITIES and DECLARATION of COVENANT .......................................................... 16 X. OPERATION AND MAINTENANCE MANUAL .......................................................................... 16 List of Figures Figure 1 – TIR Worksheet Figure 2 – Vicinity Map Figure 3 – Soils Map and Legend Figure 4 – Existing Conditions Map Figure 5 – Developed Conditions Map Figure 6 – Drainage Review Flow Chart Figure 7 – Downstream Map Appendix A Soil Assessment by the Riley Group dated December 11, 2020. Appendix B WWHM Output Appendix C Operation and Maintenance Manual Appendix D Lot 34 Single-Family Drainage Narrative Appendix E Lot 35 Single-Family Drainage Narrative Appendix F Lot 36 Single-Family Drainage Narrative Sierra Homes (425) 471-3472 PO Box 3069 Issaquah, WA 98027 Nicole Mecum Encompass Engineering & Surveying (425)392-0250 TBD 24 5 4 4 01/25/2021 4 01/25/2021 03/10/2021 03/10/2021 SW - 32 Sierra Homes Lots 34-36 1106, 1108, & 1112 N 34th Street 4 4 None No Kennydale N/A East Lake Washington Aquifer Protection Zone 24 Peak Rate Flow Control Standard Indianola loamy sand 5-15%Low East Lake Washington 1 1 11/4/2020 Peak Rate Flow Control Standard 2 Limited Infiltration Trenches N/A T.B.D. Aquifer Protection Zone 2X Private Yes Yes Basic 1 None None None N/A No 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 Limited Infiltration 3/10/2021Nicole Mecum Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 1 I. PROJECT OVERVIEW Project: Sierra Homes Lots 34-36 Site Address: 1112, 1108, and 1106 N 34th Street Renton, WA 98056 (See Vicinity Map) Tax Parcel #: 334210-2675, 334210-2680, and 334210-2685 Zoning District: R-8, Single Family Residential Total Site Area: 16,200 SF (0.37 Acres) Site Location: The site is in the City of Renton within the SW quarter of Section 32, Township 24 North, Range 5 East, W.M, King County, Washington. The site is located on the north side of N 34th St, west of the intersection of Park Ave N and N 34th St. Figure 2: Vicinity Map Pre-developed Site Conditions The project is located in the City of Renton on three (3) separate tax parcels that are zoned R-8 (single- family residential). These three (3) parcels recently underwent a Lot Segregation, restoring lots 34, 35 & 36 of the original Hillmans Lake Washington Garden of Eden platting. All on-site structures within the existing parcels were be removed including the residence, driveway, garage and landscaping features as part of the lot segregation process. SITE Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 2 The site is located within a single drainage basin that slopes to the west and southwest at grades between 5 and 15%. Runoff from the existing site generally sheet flows toward the N 34th Street stormwater system, which ultimately discharges to Lake Washington at Kennydale Beach Park. See the full downstream analysis in Chapter III of this Technical Information Report (TIR). An Existing Conditions Map is included as Figure 4 at the end of this Chapter. Critical Areas The City of Renton Mapping system identifies three (3) small areas designated as regulated steep slopes; however, these steep slope conditions were not identified in the field during Encompass Engineering and Surveying’s site visit on November 4, 2020. No other critical areas were identified on or near the site. Soils Per the US Department of Agriculture (USDA), Natural Resources Conservation Service (NCRS) Web Soil Survey (WSS) information, the entire project site is underlain with Indianola loamy sand with 5-15% slopes (See Figure 3 below). The Soils Assessment by the Riley Group (Appendix A) generally confirms this classification. They observed a layer of brown silty sand and sand with silt underlain by a gray sandy silt. No groundwater was encountered. Figure 3: Soil Map and Legend SITE Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 3 Developed Site Conditions The project is located in the City of Renton on three (3) separate tax parcels that are zoned R-8 (single- family residential). These three (3) parcels recently underwent a Lot Segregation, restoring lots 34, 35 & 36 of the original Hillmans Lake Washington Garden of Eden platting. Lot 34 is 5,324 SF and is addressed 1112 N 34th Street; Lot 35 is 5,322 SF and is addressed 1108 N 34th Street; and Lot 36 is 5,319 SF and is addressed 1106 N 34th Street. In addition, a 1.5-FT right-of-way (ROW) dedication will be made along the N 34th Street frontage of the parent parcel to allow for the construction of frontage improvements. N 34th Street is classified as a Residential Access Street; therefore, half-street frontage improvements will include 13 FT of pavement, 0.5 FT curb, 8 FT planter strip, and 5 FT concrete sidewalk. The offsite improvements will result in approximately 915 SF of new driveway, 689 SF of new pavement, and 508 SF of new sidewalk within the existing ROW and future 1.5 FT dedication area. The parent parcel is zoned R-8, which allows for a maximum building coverage of 50% and a maximum impervious surface coverage of 65%. The proposed building/impervious surface coverage for each lot is discussed below: • Lot 34: The Lot 34 project proposes the construction of a 323 SF uncovered asphalt driveway, 2,625 SF house (roof area), and 196 SF of uncovered concrete walkways. The total proposed new on-site impervious area coverage is 3,144 SF, of which 323 SF is pollution generating. The total building coverage is 2,431 SF. The proposed construction results in a building coverage of 2,431 SF/5,324 SF * 100 = 45.7%, which is less than the maximum allowable coverage of 50%. The resulting on-site impervious surface coverage is 3,144 SF/5,324 SF*100 = 59.1%, which is less than the maximum allowable coverage of 65%. • Lot 35: The Lot 35 project proposes the construction of a 343 SF uncovered asphalt driveway, 2,862 SF house (roof area), and 31 SF of uncovered concrete walkways. The total proposed new on-site impervious area coverage is 3,236 SF, of which 343 SF is pollution generating. The total building coverage is 2,481 SF. The proposed construction results in a building coverage of 2,481 SF/5,322 SF * 100 = 46.6%, which is less than the maximum allowable coverage of 50%. The resulting on-site impervious surface coverage is 3,236 SF/5,322 SF*100 = 60.8%, which is less than the maximum allowable coverage of 65%. • Lot 36: The Lot 36 project proposes the construction of a 263 SF uncovered asphalt driveway, 2,619 SF house (roof area), and 28 SF of uncovered concrete walkways. The total proposed new on-site impervious area coverage is 2,910 SF, of which 263 SF is pollution generating. The total building coverage is 2,222 SF. The proposed construction results in a building coverage of 2,222 SF/5,319 SF * 100 = 41.8%, which is less than the maximum allowable coverage of 50%. The resulting on-site impervious surface coverage is 2,910 SF/5,319 SF*100 = 54.7%, which is less than the maximum allowable coverage of 65%. A 9 FTx5 FT limited infiltration trench with a capacity to mitigate up to 625 SF of new impervious surface is proposed for each of the lots. All remaining stormwater from the on-site development will be tightlined to a 10 FT perforated pipe connection prior to leaving the site and entering the N 34th Street stormwater system. Please refer to Core Requirement # 9 in Chapter II and Chapter IV of this TIR for additional discussion on stormwater BMPs. A Developed Conditions Map is provided as Figure 5 at this end of this Chapter. Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 6 II. CONDITIONS AND REQUIREMENTS SUMMARY The 2017 City of Renton Surface Water Design Manual (RSWDM) was utilized to determine and address all core and special requirements. Based on the criteria specified in Figure 1.1.2.A of the RSWDM, the project falls under Full Drainage Review. Per Section 1.1.2.4 of the RSWDM, the project must meet all nine (9) core and all six (6) special requirements. See Figure 6 below for more information on how the type of drainage review was determined. Figure 6: Drainage Review Flow Chart Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 7 Core Requirements Core Requirement #1: Discharge at the Natural Location The proposed development runoff will follow existing drainage patterns, which flow southwest toward the N 34th Street storm system. Refer to the Level 1 Downstream Analysis in Chapter III of this TIR for a complete description of the existing drainage path. Core Requirement #2: Downstream Analysis A Level 1 Downstream analysis has been completed for the site and no existing or potential problems have been identified. This analysis is included in Chapter III of this TIR. Core Requirement #3: Flow Control Facilities Based on the City of Renton’s flow control map, the project site is located within the Peak Rate Flow Control Area (existing site conditions). Projects within the Peak Rate Flow Control Area are required to match the developed peak discharge rates to existing site conditions peak discharge rates for the 2-year, 10-year, and 100-year return periods. The proposed stormwater BMPs result in a 0.0175 CFS decrease in the 100-year flow using 15- minutes time steps. This is well below the allowable threshold of a 0.15 CFS maximum increase per Section 1.2.3.1.B of the RSWDM; therefore, the project meets flow control exemption 2. No formal flow control facilities are proposed at this time; however, flow control BMPs will be implemented as described in Core Requirement #9. Please refer to Chapter IV of this TIR for additional discussion. Core Requirement #4: Conveyance System Conveyance system analysis will be provided if required by the City of Renton. Core Requirement #5: Construction Stormwater Pollution Prevention The limits of construction for the project are less than 1 acre. Temporary erosion and sediment control (TESC) plans providing details on best management practices (BMPs) to be implemented during construction are included with the individual building permit plans for each lot (See Appendices D, E, and F). Core Requirement #6: Maintenance and Operations An Operation and Maintenance Manual has been prepared for the project. Please refer to Chapter X of this TIR for additional discussion. Core Requirement #7: Financial Guarantees and Liability The owner will arrange for any financial guarantees and liabilities required by the permit. Bond Quantities have been prepared for the project and have been submitted under separate cover. Core Requirement #8: Water Quality Facilities Per Exemption 1 in Section 1.2.8 of the RSWDM, projects that result in less than 5,000 SF of new/replaced pollution generating impervious surface (PGIS) and less than ¾ acre of new/replaced pollution generating pervious surface (PGPS) are exempt from Core Requirement #8. The proposed development only results in 2,533 SF of new/replaced PGIS and no new PGPS; Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 8 therefore, the project is exempt. In addition, Leachable Metal Covenants have been provided for each of the lots under separate cover. Core Requirement #9: Flow Control BMPs Flow Control BMPs were evaluated for each lot under the individual lot Residential Building Permit Drainage Narratives. A 9 FTx5 FT limited infiltration trench with a capacity to mitigate up to 625 SF of new impervious surface is proposed for each of the lots. All remaining stormwater from the on-site development will be tightlined to a 10 FT perforated pipe connection prior to leaving the site and entering the N 34th Street stormwater system. Copies of the Residential Building Permit Drainage Narratives for Lots 34, 35, and 36 are provided in Appendices D, E, and F, respectively. Please refer to the Drainage Narratives for a detailed analysis of the selected BMPs for each lot. Special Requirements Special Requirement #1: Other Adopted Area-Specific Requirements Critical Drainage Area – N/A Master Drainage Plan – N/A Basin Plan – N/A Lake management Plan – N/A Shared Facility Drainage Plan – N/A Special Requirement #2: Flood Hazard Area Delineation The limits of this project do not lie within a delineated FEMA 100-year floodplain. Special Requirement #3: Flood Protection Facilities This project does not rely on or propose to modify/construct a new flood protection facility. Special Requirement #4: Source controls The project is a single-family residential development; therefore, this requirement is not applicable. Special Requirement #5: Oil Control This project is not considered high-use in need of oil control. Special Requirement #6: Aquifer Protection Area The site is partially located within an aquifer protection area (Zone 2). The RSWDM requires liners for open flow control and water quality ponds as well as open conveyance ditches; however, the project does not propose any such facilities. Therefore, the liner requirement does not apply. Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 9 III. DOWNSTREAM ANALYSIS A Level 1 Downstream analysis has been conducted per the requirements in Section 1.2.2.1 of the RSWDM. Please see Tasks 1 through 4 below for a summary of the results. Task 1: Define and Map the Study Area The area of analysis extends from the site discharge points along N 34th St to approximately a quarter- mile downstream where the City of Renton storm system discharges into Lake Washington. A Downstream Map is provided in Figure 7 below. Figure 7: Downstream Map Task 2: Review All Available Information on the Study Area Per King county resources, there have been no significant drainage complaints within a quarter-mile downstream of the site. Task 3: Field Inspect the Study Area A field inspection was performed by Encompass Engineering & Surveying on November 4, 2020. The weather on-site was 55 degrees and rainy. Please refer to Task 4 for a detailed description of the downstream drainage system and analysis. Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 10 Task 4: Describe the Drainage System Runoff from the site sheet flows to the west and southwest onto N 34th St from site lawn, driveway and roof areas. Sheet flow off of the eastern portion of the site enters a Type 1 CB (A) on the north side of N 34th St. It is conveyed west downhill via a 12” concrete pipe to another Type 1 CB (C). Stormwater from the west side of the project site sheet flows (B) along the edge of asphalt into this catch basin as well. In addition, a 4” PVC pipe enters this catch basin, fed from area drains present in concrete walkways around the residence. From here, stormwater is conveyed west down N 34th St through a string of Type 1 CBs and 12” concrete storm pipes before it enters a Type 1 CB (D) on the corner of N 34th St and Burnett Ave N and is directed north down Burnett Ave N. Stormwater continues to be conveyed through Type 1 CBs and 12” concrete pipes to a Type 1 CB (E) on the corner of N 35th St and Burnett Ave N. It is redirected to the northwest though a 12” concrete pipe and dives at a steep angle below a parking area and block wall to a series of two Type 1 CBs (F) that were found to be completely covered by ivy but functioning properly. From here, a 12” concrete pipe conveys the stormwater under Lake Washington Blvd N and deposits into a grassy stormwater ditch (G) which flows to the northeast. Here it enters a 12” concrete culvert which heads west before transferring into another 12” concrete culvert (H) and ultimately discharging into Lake Washington at Kennydale Beach Park (I) at approximately ¼ mile from the project site. If conveyance system nuisance, severe erosion, severe flooding, or wetland hydrology problems are identified downstream of the site under Core Requirement #2, additional impact analysis and/or mitigation may be required. As discussed in Task 2, there have been no recent significant drainage complaints within a quarter-mile downstream of the site. As no existing drainage or conveyance issues have been recently identified, further impact analysis and mitigation of the downstream stormwater system is not required. Please refer to the conveyance analysis in Section V of this TIR for additional discussion and evaluation of the on-site conveyance system capacity. Photographs from the site visit are included below. Element A- Type 1 CB on N 34th St collecting Sheet flow from east portion of the site Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 11 Element B & C- Type 1 CB with raised asphalt bump to direct stormwater Element E- Type 1 CB on corner of N 35th St & Burnett Ave N Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 12 Element F- Type 1 on Lake Washington Blvd N shoulder covered by Ivy Element G- Open stormwater ditch Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 13 Element I- 12” Concrete culvert discharges into Lake Washington Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 14 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Part A: Existing Site Hydrology The project is located in the City of Renton on three (3) separate tax parcels that are zoned R-8 (single- family residential). These three (3) parcels recently underwent a Lot Segregation, restoring lots 34, 35 & 36 of the original Hillmans Lake Washington Garden of Eden platting. All on-site structures within the existing parcels were be removed including the residence, driveway, garage and landscaping features as part of the lot segregation process. The property is located within a single drainage basin that slopes to the west and southwest at grades between 5 and 15%. Based on the City of Renton’s flow control map, the project site is located within the Peak Rate Flow Control Area (existing site conditions). Projects within the Peak Rate Flow Control Area are required to match the developed peak discharge rates to existing site conditions peak discharge rates for the 2-year, 10-year, and 100-year return periods. WWHM 2012 was used to model the existing site conditions prior to the recent lot segregation within the 18,603 SF (0.427 AC) limits of disturbance. A summary of the existing conditions analyses is provided in the table in Part B, below. Part B: Developed Site Hydrology Half-street frontage improvements will be constructed along the N 34th Street frontage, which include 13 FT of pavement, 0.5 FT curb, 8 FT planter strip, and 5 FT concrete sidewalk. The offsite improvements will result in approximately 915 SF of new driveway, 689 SF of new pavement, and 508 SF of new sidewalk within the existing ROW and future 1.5 FT ROW dedication area. All proposed frontage improvements are tributary to the existing N 34th Street stormwater system. The Lot 34 project proposes the construction of a 323 SF uncovered asphalt driveway, 2,625 SF house (roof area), and 196 SF of uncovered concrete walkways. The total proposed new on-site impervious area coverage is 3,144 SF, of which 323 SF is pollution generating. The Lot 35 project proposes the construction of a 343 SF uncovered asphalt driveway, 2,862 SF house (roof area), and 31 SF of uncovered concrete walkways. The total proposed new on-site impervious area coverage is 3,236 SF, of which 343 SF is pollution generating. The Lot 36 project proposes the construction of a 263 SF uncovered asphalt driveway, 2,619 SF house (roof area), and 28 SF of uncovered concrete walkways. The total proposed new on-site impervious area coverage is 2,910 SF, of which 263 SF is pollution generating. This results in 8,106 SF of new rooftop, 255 SF of new sidewalk, and 929 SF of new driveway across the three (3) lots. Therefore, the total proposed impervious surface across all three (3) lots is 9,290 SF. A 9 FTx5 FT limited infiltration trench with a capacity to mitigate up to 625 SF of new impervious surface is proposed for each of the lots. This 625 SFx3 = 1,875 SF of rooftop area has been modeled as 90% impervious and 10% lawn in the proposed conditions model. All remaining stormwater from the on-site development will be tightlined to 10 FT perforated pipe connections prior to leaving the site and entering the N 34th Street stormwater system. No flow control credits are available for the use of a perforated pipe connection. All new pervious surface (on- and off-site) will meet the soil amendment requirements as detailed in Section C.2.13 of the RSWDM; therefore, it has been modeled as 100% pasture in the proposed conditions model. Please refer to Core Requirement # 9 in Chapter II and Chapter IV of this TIR for additional discussion on stormwater BMPs. A Developed Conditions Map is provided as Figure 5 at this end of this Chapter. A summary of the existing and proposed analyses is provided in the table on the following page. Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 15 On-site + Off-Site Existing Proposed Condition Measured Modeled Measured Modeled Lawn, Mod: 10,920 SF (0.251 AC) 10,920 SF (0.251 AC) 167 SF (0.004 AC) Pasture, Mod: 7,201 SF (0.165 AC) 7,201 SF (0.165 AC) Roof, Flat: 2,575 SF (0.059 AC) 2,575 SF (0.059 AC) 8,106 SF (0.186 AC) 7,939 SF (0.182 AC) Driveway, Flat: 4,141 SF (0.095 AC) 4,141 SF (0.095 AC) 1,844 SF (0.042 AC) 1,844 SF (0.042 AC) Sidewalk, Flat: 763 SF (0.018 AC) 763 SF (0.018 AC) Road, Flat: 967 SF (0.022 AC) 967 SF (0.022 AC) 689 SF (0.016 AC) 689 SF (0.016 AC) Total Area: 18,603 SF (0.427 AC) 18,603 SF (0.427 AC) 18,603 SF (0.427 AC) 18,603 SF (0.427 AC) Part C: Performance Standards Based on the City of Renton’s flow control map, the project site is located within the Peak Rate Flow Control Area (existing site conditions). Projects within the Peak Rate Flow Control Area are required to match the developed peak discharge rates to existing site conditions peak discharge rates for the 2-year, 10-year, and 100-year return periods. In addition, the site is located within the UGA and is smaller than 22,000 SF. Therefore, the site is subject to the Small Lot BMP Requirements per Appendix C.1.3.1 of the RSWDM. In accordance with Section 1.2.8.1.A of the RSWDM, Basic Water Quality Treatment is required for this project. Part D: Flow Control System As shown in the table below, the proposed stormwater BMPs and soil amendment requirements result in a 0.0175 CFS decrease in the 100-year flow using 15-minutes time steps. This is well below the allowable threshold of a 0.15 CFS maximum increase per Section 1.2.3.1.B of the RSWDM; therefore, the project meets flow control exemption 2. No formal flow control facilities are proposed at this time; however, flow control BMPs will be implemented as described in Core Requirement #9 in Chapter II of this TIR. Please refer to Appendix B for a copy of the full WWHM data output. Sierra Homes Lots 34-36 Technical Information Report 3/10/2021 P a g e | 16 Part E: Water Quality System Per Exemption 1 in Section 1.2.8 of the RSWDM, projects that result in less than 5,000 SF of new/replaced PGIS and less than ¾ acre of new/replaced PGPS are exempt from Core Requirement #8. The proposed development only results in 2,533 SF of new/replaced PGIS and no new PGPS; therefore, the project is exempt. V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN Conveyance system analysis will be provided if required by the City of Renton. VI. SPECIAL REPORTS AND STUDIES • Soil Assessment by the Riley Group dated December 11, 2020. VII. OTHER PERMITS • Clearing and Grading Permit • Right-of-Way Use Permit • Single-Family Building Permits VIII. CONSTRUCTION STORMWATER GENERAL PERMIT The limits of construction for the project are less than 1 acre. Temporary erosion and sediment control (TESC) plans providing details on best management practices (BMPs) to be implemented during construction are included with the individual building permit plans for each lot (See Appendices D, E, and F). The construction limits for the project are less than 1 acre; therefore, a Construction Stormwater General Permit is not required. IX. BOND QUANTITIES and DECLARATION of COVENANT Bond Quantities and Declarations of Covenant have been provided for the project and have been submitted under separate cover. X. OPERATION AND MAINTENANCE MANUAL An Operation and Maintenance Manual is provided in Appendix C of this TIR. Appendix A Soil Assessment by the Riley Group dated December 11, 2020 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone 425.415.0551 ♦ Fax 425.415.0311 www.riley-group.com December 11, 2020 Dan Finkbeiner Sierra Homes Subject: Soil Assessment Sierra Homes Renton Site 1110 North 34th Street Renton, Washington RGI Project No. 2020-504-1 As requested, The Riley Group, Inc. (RGI) is pleased to provide the results of our recent soil assessment at the above-referenced Site (Figure 1). The site is comprised of one King County tax parcel (3342102675) and is approximately 0.37 acres in size. RGI oversaw the completion test pits at the Site to evaluate soil conditions. RGI understands three single family homes will be built at the Site. Subsurface Conditions Review of the Geologic Map of Surficial Deposits in the Seattle 30’ x 60’ Quadrangle, Washington by James C. Yount, et al (1993) indicates that the soil in the project vicinity is mapped as Pre-Fraser deposits undifferentiated (Qpf) which is described as interbedded, oxidized brown, red-brown, and gray gravel, sand, silt, and clay. Moderately to well bedded. Generally non-glacial with abundant peat and woody debris. These descriptions are generally similar to the findings in our field explorations. On December 3, 2020, RGI excavated four test pits (TP-1, TP-2, TP-3, and TP-4) and one hand auger boring (HA-1) at the Site as shown on Figure 2. Subsurface conditions included a layer of brown silty sand and sand with silt of varying thickness underlain by a gray sandy silt at the TP-1 and TP-2 test pit locations. Test pits TP-1 and TP-2 are located on the southwest portion of the Site. The silt is present at 4 feet below grade in TP-1 and 5 feet below grade in TP-2. No groundwater was encountered, mottling was observed at approximately three feet below grade. Mottling can indicate seasonal groundwater inundation. Infiltration Feasibility The site subsurface conditions were evaluated for stormwater infiltration potential per the KCSWDM Appendix C.2. Appendix C.2.2.2 “Minimum Design Requirements for Full Infiltration” outlines requirements for full infiltration. C.2.2.2 (a) Existing soils must be coarse sand or cobbles, or medium sands and cannot be comprised of fill materials. Subsurface soil conditions observed in the test pits at the site are silty sands which do not meet the soil type requirements for full infiltration. Section C.2.3 outlines soil conditions for limited infiltration. Soils that fall under a limited infiltration include fine sands, loamy sands, sandy loams, and loams. The silty sand soils in the shallow subsurface at the site meet the soil classification for limited infiltration. Based on the presence of the silt unit on the southwest portion of the Site, any trenches or drywells should be no deeper than three feet below grade to maintain separation above the silt unit. USGS, 2020, Mercer Island, Washington 7.5-Minute Quadrangle Approximate Scale: 1"=1000' 0 500 1000 2000 N Site Vicinity Map Figure 1 12/2020 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Sierra Homes Renton RGI Project Number: 2020-504-1 Date Drawn: Address: 1110 North 34th Street, Renton, Washington 98056 SITE HA-1TP-1TP-2TP-3TP-412/2020Corporate Office17522 Bothell Way NortheastBothell, Washington 98011Phone: 425.415.0551Fax: 425.415.0311Sierra Homes RentonRGI Project Number:2020-504-1Date Drawn:Address: 1110 North 34th Street, Renton, Washington 98056Figure 2Approximate Scale: 1"=30'0153060N= Test pit by RGI, 12/03/20= Boring by RGI, 12/03/20= Site boundaryGeotechnical Exploration Plan Project Name:Sierra Homes Renton Project Number:2020-504-1 Client:Sierra Homes Test Pit: TP-1 Date(s) Excavated:12/3/2020 Excavation Method:Track hoe Excavator Type:Track hoe Groundwater Level:Not encountered Test Pit Backfill:Cuttings Logged By CM Bucket Size:3' Excavating Contractor:Kelly's Excavating Sampling Method(s)Grab Location 1110 North 34th Street Renton, Washington 98056 Surface Conditions:Grass Total Depth of Excavation:7 feet Approximate Surface Elevation Not surveyed Compaction Method Bucket tamp USCS SymbolTspl SM SP-SM ML REMARKS AND OTHER TESTS 18% Moisture 28% MoistureGraphic LogMATERIAL DESCRIPTION 9" Topsoil Brown silty SAND with trace gravel, moist, dense Gray/red SAND with some silt, moist, dense, moderate mottling Gray SILT with some sand, moist, dense, moderate mottling Test pit terminated at 7 feet bgs.Depth (feet)0 5 10 15 Sample NumberTP1-3 TP1-6Sample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Sierra Homes Renton Project Number:2020-504-1 Client:Sierra Homes Test Pit: TP-2 Date(s) Excavated:12/3/2020 Excavation Method:Track hoe Excavator Type:Track hoe Groundwater Level:Not encountered Test Pit Backfill:Cuttings Logged By CM Bucket Size:3' Excavating Contractor:Kelly's Excavating Sampling Method(s)Grab Location 1110 North 34th Street Renton, Washington 98056 Surface Conditions:Grass Total Depth of Excavation:7 feet Approximate Surface Elevation Not surveyed Compaction Method Bucket tamp USCS SymbolTspl SM SP-SM ML REMARKS AND OTHER TESTS 22% Moisture 24% Moisture 23% MoistureGraphic LogMATERIAL DESCRIPTION 6" Topsoil Brown to red brown silty SAND, moist, medium dense Red SAND with some silt, moist, medium dense Gray SILT with some sand, moist, dense, moderate mottling Test pit terminated at 7 feet bgs.Depth (feet)0 5 10 15 Sample NumberTP2-2 TP2-4 TP2-5Sample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Sierra Homes Renton Project Number:2020-504-1 Client:Sierra Homes Test Pit: TP-3 Date(s) Excavated:12/3/2020 Excavation Method:Track hoe Excavator Type:Track hoe Groundwater Level:Not encountered Test Pit Backfill:Cuttings Logged By CM Bucket Size:3' Excavating Contractor:Kelly's Excavating Sampling Method(s)Grab Location 1110 North 34th Street Renton, Washington 98056 Surface Conditions:Grass Total Depth of Excavation:8 feet Approximate Surface Elevation Not surveyed Compaction Method Bucket tamp USCS SymbolTpsl SM SM REMARKS AND OTHER TESTS 28% Moisture 24% Moisture 27% MoistureGraphic LogMATERIAL DESCRIPTION 7" Topsoil Brown to red silty SAND, moist, medium dense Gray/tan silty SAND with trace gravel, moist, dense, moderate mottling Test pit terminated at 8 feet bgs.Depth (feet)0 5 10 15 Sample NumberTP3-2 TP3-4 TP3-7Sample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Sierra Homes Renton Project Number:2020-504-1 Client:Sierra Homes Test Pit: TP-4 Date(s) Excavated:12/3/2020 Excavation Method:Track hoe Excavator Type:Track hoe Groundwater Level:Not encountered Test Pit Backfill:Cuttings Logged By CM Bucket Size:3' Excavating Contractor:Kelly's Excavating Sampling Method(s)Grab Location 1110 North 34th Street Renton, Washington 98056 Surface Conditions:Grass Total Depth of Excavation:6 feet Approximate Surface Elevation Not surveyed Compaction Method Bucket tamp USCS SymbolTpsl SM SP-SM REMARKS AND OTHER TESTS 14% Moisture 23% MoistureGraphic LogMATERIAL DESCRIPTION 6" Topsoil Light brown silty SAND, moist, medium dense Brown SAND with some silt, moist, medium dense, moderate mottling Test pit terminated at 6 feet bgs.Depth (feet)0 5 10 15 Sample NumberTP4-3 TP4-5Sample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Sierra Homes Renton Project Number:2020-504-1 Client:Sierra Homes Test Pit: HA-1 Date(s) Excavated:12/3/2020 Excavation Method:Track hoe Excavator Type:Track hoe Groundwater Level:Not encountered Test Pit Backfill:Cuttings Logged By CM Bucket Size:3' Excavating Contractor:Kelly's Excavating Sampling Method(s)Grab Location 1110 North 34th Street Renton, Washington 98056 Surface Conditions:Grass Total Depth of Excavation:6 feet Approximate Surface Elevation Not surveyed Compaction Method Bucket tamp USCS SymbolTpsl ML SP-SM REMARKS AND OTHER TESTS 24% Moisture 26% MoistureGraphic LogMATERIAL DESCRIPTION 3" Topsoil Tan SILT with some sand, moist, medium stiff Tan SAND with some silt, moist, medium dense, moderate to severe mottling Hand auger terminated at 3 feet bgs.Depth (feet)0 5 10 15 Sample NumberHA1-1 HA1-2Sample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Sierra Homes Renton Project Number:2020-504-1 Client:Sierra Homes Key to Logs USCS SymbolREMARKS AND OTHER TESTSGraphic LogMATERIAL DESCRIPTIONDepth (feet)Sample NumberSample TypeElevation (feet)1 2 3 4 5 6 7 8 COLUMN DESCRIPTIONS 1 Elevation (feet): Elevation (MSL, feet). 2 Depth (feet): Depth in feet below the ground surface. 3 Sample Type: Type of soil sample collected at the depth interval shown. 4 Sample Number: Sample identification number. 5 USCS Symbol: USCS symbol of the subsurface material. 6 Graphic Log: Graphic depiction of the subsurface material encountered. 7 MATERIAL DESCRIPTION: Description of material encountered. May include consistency, moisture, color, and other descriptive text. 8 REMARKS AND OTHER TESTS: Comments and observations regarding drilling or sampling made by driller or field personnel. FIELD AND LABORATORY TEST ABBREVIATIONS CHEM: Chemical tests to assess corrosivity COMP: Compaction test CONS: One-dimensional consolidation test LL: Liquid Limit, percent PI: Plasticity Index, percent SA: Sieve analysis (percent passing No. 200 Sieve) UC: Unconfined compressive strength test, Qu, in ksf WA: Wash sieve (percent passing No. 200 Sieve) MATERIAL GRAPHIC SYMBOLS SILT, SILT w/SAND, SANDY SILT (ML)Silty SAND (SM) Poorly graded SAND with Silt (SP-SM) TYPICAL SAMPLER GRAPHIC SYMBOLS Auger sampler Bulk Sample 3-inch-OD California w/ brass rings CME Sampler Grab Sample 2.5-inch-OD Modified California w/ brass liners Pitcher Sample 2-inch-OD unlined split spoon (SPT) Shelby Tube (Thin-walled, fixed head) OTHER GRAPHIC SYMBOLS Water level (at time of drilling, ATD) Water level (after waiting) Minor change in material properties within a stratum Inferred/gradational contact between strata ?Queried contact between strata GENERAL NOTES 1: Soil classifications are based on the Unified Soil Classification System. Descriptions and stratum lines are interpretive, and actual lithologic changes may be gradual. Field descriptions may have been modified to reflect results of lab tests. 2: Descriptions on these logs apply only at the specific boring locations and at the time the borings were advanced. They are not warranted to be representative of subsurface conditions at other locations or times. Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415-0551 FAX: (425) 415-0311 GRAIN SIZE ANALYSIS ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Sierra Homes Renton SAMPLE ID/TYPE HA-1 PROJECT NO.2020-504 SAMPLE DEPTH 2 feet TECH/TEST DATE RT 12/3/2020 DATE RECEIVED 12/3/2020 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)308.8 Weight Of Sample (gm)410.9 Wt Dry Soil & Tare (gm)(w2)410.9 Tare Weight (gm) 133.9 Weight of Tare (gm)(w3)133.9 (W6) Total Dry Weight (gm)277.0 Weight of Water (gm)(w4=w1-w2)-102.1 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2-w3)277.0 Cumulative Moisture Content (%) (w4/w5)*100 -37 Wt Ret (Wt-Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100-%ret) % COBBLES 0.0 12.0"133.9 0.00 0.00 100.00 cobbles % C GRAVEL 0.0 3.0"133.9 0.00 0.00 100.00 coarse gravel % F GRAVEL 0.3 2.5" coarse gravel % C SAND 0.1 2.0" coarse gravel % M SAND 1.8 1.5"133.9 0.00 0.00 100.00 coarse gravel % F SAND 6.0 1.0" coarse gravel % FINES 91.9 0.75"133.9 0.00 0.00 100.00 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"133.9 0.00 0.00 100.00 fine gravel D10 (mm)#4 134.6 0.70 0.25 99.75 coarse sand D30 (mm)#10 134.9 1.00 0.36 99.64 medium sand D60 (mm)#20 medium sand Cu #40 139.8 5.90 2.13 97.87 fine sand Cc #60 fine sand #100 147.4 13.50 4.87 95.13 fine sand #200 156.3 22.40 8.09 91.91 fines PAN 410.9 277.00 100.00 0.00 silt/clay DESCRIPTION SILT with trace sand USCS ML Prepared For:Reviewed By:DB Sierra Homes 0102030405060708090100 0.0010.010.11101001000 % P A S S I N G Grain size in millimeters 12"3"2"1".75".375"#4 #10 #20 #40 #60 #100 #200 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415-0551 FAX: (425) 415-0311 GRAIN SIZE ANALYSIS ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Sierra Homes Renton SAMPLE ID/TYPE TP1-6 PROJECT NO.2020-504 SAMPLE DEPTH 6 feet TECH/TEST DATE RT 12/3/2020 DATE RECEIVED 12/3/2020 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)730.5 Weight Of Sample (gm)601.5 Wt Dry Soil & Tare (gm)(w2)601.5 Tare Weight (gm) 133.1 Weight of Tare (gm)(w3)133.1 (W6) Total Dry Weight (gm)468.4 Weight of Water (gm)(w4=w1-w2)129.0 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2-w3)468.4 Cumulative Moisture Content (%) (w4/w5)*100 28 Wt Ret (Wt-Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100-%ret) % COBBLES 0.0 12.0"133.1 0.00 0.00 100.00 cobbles % C GRAVEL 0.0 3.0"133.1 0.00 0.00 100.00 coarse gravel % F GRAVEL 0.1 2.5" coarse gravel % C SAND 1.2 2.0" coarse gravel % M SAND 6.0 1.5"133.1 0.00 0.00 100.00 coarse gravel % F SAND 19.6 1.0" coarse gravel % FINES 73.1 0.75"133.1 0.00 0.00 100.00 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"133.1 0.00 0.00 100.00 fine gravel D10 (mm)#4 133.6 0.50 0.11 99.89 coarse sand D30 (mm)#10 139.2 6.10 1.30 98.70 medium sand D60 (mm)#20 medium sand Cu #40 167.2 34.10 7.28 92.72 fine sand Cc #60 fine sand #100 209.4 76.30 16.29 83.71 fine sand #200 259.2 126.10 26.92 73.08 fines PAN 601.5 468.40 100.00 0.00 silt/clay DESCRIPTION SILT with some sand USCS ML Prepared For:Reviewed By:DB Sierra Homes 0102030405060708090100 0.0010.010.11101001000 % P A S S I N G Grain size in millimeters 12"3"2"1".75".375"#4 #10 #20 #40 #60 #100 #200 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415-0551 FAX: (425) 415-0311 GRAIN SIZE ANALYSIS ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Sierra Homes Renton SAMPLE ID/TYPE TP2-4 PROJECT NO.2020-504 SAMPLE DEPTH 4 feet TECH/TEST DATE RT 12/3/2020 DATE RECEIVED 12/3/2020 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)561.4 Weight Of Sample (gm)479.9 Wt Dry Soil & Tare (gm)(w2)479.9 Tare Weight (gm) 133.4 Weight of Tare (gm)(w3)133.4 (W6) Total Dry Weight (gm)346.5 Weight of Water (gm)(w4=w1-w2)81.5 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2-w3)346.5 Cumulative Moisture Content (%) (w4/w5)*100 24 Wt Ret (Wt-Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100-%ret) % COBBLES 0.0 12.0"133.4 0.00 0.00 100.00 cobbles % C GRAVEL 0.0 3.0"133.4 0.00 0.00 100.00 coarse gravel % F GRAVEL 0.0 2.5" coarse gravel % C SAND 0.0 2.0" coarse gravel % M SAND 3.9 1.5"133.4 0.00 0.00 100.00 coarse gravel % F SAND 84.6 1.0" coarse gravel % FINES 11.5 0.75"133.4 0.00 0.00 100.00 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"133.4 0.00 0.00 100.00 fine gravel D10 (mm)#4 133.4 0.00 0.00 100.00 coarse sand D30 (mm)#10 133.4 0.00 0.00 100.00 medium sand D60 (mm)#20 medium sand Cu #40 146.9 13.50 3.90 96.10 fine sand Cc #60 fine sand #100 367.8 234.40 67.65 32.35 fine sand #200 440.0 306.60 88.48 11.52 fines PAN 479.9 346.50 100.00 0.00 silt/clay DESCRIPTION SAND with some silt USCS SP-SM Prepared For:Reviewed By: Sierra Homes DB 0102030405060708090100 0.0010.010.11101001000 % P A S S I N G Grain size in millimeters 12"3"2"1".75".375"#4 #10 #20 #40 #60 #100 #200 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415-0551 FAX: (425) 415-0311 GRAIN SIZE ANALYSIS ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Sierra Homes Renton SAMPLE ID/TYPE TP3-2 PROJECT NO.2020-504 SAMPLE DEPTH 2 feet TECH/TEST DATE RT 12/3/2020 DATE RECEIVED 12/3/2020 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)672.0 Weight Of Sample (gm)553.1 Wt Dry Soil & Tare (gm)(w2)553.1 Tare Weight (gm) 132.6 Weight of Tare (gm)(w3)132.6 (W6) Total Dry Weight (gm)420.5 Weight of Water (gm)(w4=w1-w2)118.9 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2-w3)420.5 Cumulative Moisture Content (%) (w4/w5)*100 28 Wt Ret (Wt-Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100-%ret) % COBBLES 0.0 12.0"132.6 0.00 0.00 100.00 cobbles % C GRAVEL 0.0 3.0"132.6 0.00 0.00 100.00 coarse gravel % F GRAVEL 1.0 2.5" coarse gravel % C SAND 0.8 2.0" coarse gravel % M SAND 12.4 1.5"132.6 0.00 0.00 100.00 coarse gravel % F SAND 56.1 1.0" coarse gravel % FINES 29.7 0.75"132.6 0.00 0.00 100.00 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"135.3 2.70 0.64 99.36 fine gravel D10 (mm)#4 136.7 4.10 0.98 99.02 coarse sand D30 (mm)#10 139.9 7.30 1.74 98.26 medium sand D60 (mm)#20 medium sand Cu #40 192.2 59.60 14.17 85.83 fine sand Cc #60 fine sand #100 380.6 248.00 58.98 41.02 fine sand #200 428.2 295.60 70.30 29.70 fines PAN 553.1 420.50 100.00 0.00 silt/clay DESCRIPTION Silty SAND USCS SM Prepared For:Reviewed By:DB Sierra Home 0102030405060708090100 0.0010.010.11101001000 % P A S S I N G Grain size in millimeters 12"3"2"1".75".375"#4 #10 #20 #40 #60 #100 #200 Appendix B WWHM Output WWHM2012 PROJECT REPORT WWHM Model 1/22/2021 12:50:16 PM Page 2 General Model Information Project Name:WWHM Model Site Name: Site Address: City: Report Date:1/22/2021 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2019/09/13 Version:4.2.17 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year WWHM Model 1/22/2021 12:50:16 PM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Mod 0.251 Pervious Total 0.251 Impervious Land Use acre ROADS FLAT 0.022 ROOF TOPS FLAT 0.059 DRIVEWAYS FLAT 0.095 Impervious Total 0.176 Basin Total 0.427 Element Flows To: Surface Interflow Groundwater WWHM Model 1/22/2021 12:50:16 PM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Mod 0.004 C, Pasture, Mod 0.165 Pervious Total 0.169 Impervious Land Use acre ROADS FLAT 0.016 ROOF TOPS FLAT 0.182 DRIVEWAYS FLAT 0.042 SIDEWALKS FLAT 0.018 Impervious Total 0.258 Basin Total 0.427 Element Flows To: Surface Interflow Groundwater WWHM Model 1/22/2021 12:50:16 PM Page 7 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.251 Total Impervious Area:0.176 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.169 Total Impervious Area:0.258 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.087593 5 year 0.120496 10 year 0.144364 25 year 0.176964 50 year 0.20307 100 year 0.230775 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.102368 5 year 0.130349 10 year 0.149479 25 year 0.174414 50 year 0.193581 100 year 0.213279 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.133 0.138 1950 0.124 0.138 1951 0.080 0.087 1952 0.053 0.071 1953 0.056 0.077 1954 0.071 0.084 1955 0.077 0.093 1956 0.075 0.092 1957 0.098 0.108 1958 0.067 0.084 WWHM Model 1/22/2021 12:50:47 PM Page 8 1959 0.057 0.083 1960 0.083 0.092 1961 0.079 0.091 1962 0.058 0.076 1963 0.079 0.088 1964 0.069 0.083 1965 0.103 0.110 1966 0.058 0.073 1967 0.123 0.122 1968 0.122 0.137 1969 0.093 0.098 1970 0.082 0.096 1971 0.099 0.113 1972 0.122 0.121 1973 0.050 0.068 1974 0.097 0.104 1975 0.101 0.115 1976 0.073 0.083 1977 0.068 0.084 1978 0.083 0.102 1979 0.102 0.140 1980 0.144 0.140 1981 0.088 0.107 1982 0.145 0.150 1983 0.092 0.118 1984 0.064 0.077 1985 0.088 0.103 1986 0.080 0.091 1987 0.103 0.137 1988 0.057 0.083 1989 0.071 0.104 1990 0.224 0.210 1991 0.163 0.155 1992 0.064 0.077 1993 0.050 0.065 1994 0.047 0.069 1995 0.077 0.094 1996 0.108 0.109 1997 0.093 0.102 1998 0.075 0.096 1999 0.197 0.197 2000 0.090 0.102 2001 0.079 0.107 2002 0.127 0.132 2003 0.104 0.109 2004 0.179 0.189 2005 0.080 0.090 2006 0.075 0.080 2007 0.203 0.184 2008 0.159 0.152 2009 0.099 0.127 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.2235 0.2098 2 0.2028 0.1970 3 0.1974 0.1891 WWHM Model 1/22/2021 12:50:47 PM Page 9 4 0.1793 0.1841 5 0.1634 0.1547 6 0.1586 0.1517 7 0.1451 0.1503 8 0.1439 0.1403 9 0.1333 0.1402 10 0.1271 0.1382 11 0.1244 0.1378 12 0.1234 0.1374 13 0.1221 0.1373 14 0.1216 0.1315 15 0.1076 0.1272 16 0.1040 0.1219 17 0.1032 0.1213 18 0.1026 0.1183 19 0.1016 0.1149 20 0.1008 0.1134 21 0.0993 0.1096 22 0.0991 0.1088 23 0.0981 0.1088 24 0.0972 0.1079 25 0.0933 0.1070 26 0.0927 0.1066 27 0.0916 0.1041 28 0.0896 0.1040 29 0.0882 0.1034 30 0.0878 0.1024 31 0.0833 0.1022 32 0.0826 0.1018 33 0.0821 0.0984 34 0.0799 0.0964 35 0.0799 0.0962 36 0.0796 0.0938 37 0.0792 0.0933 38 0.0786 0.0919 39 0.0785 0.0919 40 0.0772 0.0912 41 0.0765 0.0905 42 0.0754 0.0901 43 0.0751 0.0885 44 0.0748 0.0875 45 0.0734 0.0842 46 0.0715 0.0842 47 0.0711 0.0837 48 0.0687 0.0834 49 0.0684 0.0832 50 0.0669 0.0831 51 0.0642 0.0825 52 0.0639 0.0804 53 0.0578 0.0770 54 0.0576 0.0767 55 0.0570 0.0765 56 0.0568 0.0762 57 0.0558 0.0732 58 0.0528 0.0709 59 0.0503 0.0695 60 0.0500 0.0684 61 0.0474 0.0648 WWHM Model 1/22/2021 12:51:28 PM Page 29 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2021; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com Appendix C Operation and Maintenance Manual X MAINTENANCE INSTRUCTIONS FOR SOIL AMENDMENT Your property contains an on-site BMP (best management practice) called “soil amendment,” which was installed to mitigate the stormwater quantity and quality impacts of some or all of the pervious surfaces on your property. Soil amendment is a method of regaining greater stormwater functions in the post development landscape by increasing treatment of pollutants and sediments, and minimizing the need for some landscaping chemicals. To be successful, the soil condition must be able to soak water into the ground for a reasonable number of years. This on-site BMP shall be maintained per Appendix A of the City of Renton’s Surface Water Design Manual. MAINTENANCE RESTRICTIONS The size, placement, and composition of these devices as depicted by the site plan and design details must be maintained and may not be changed without written approval from the City of Renton or through a future development permit from the City of Renton. INSPECTION FREQUENCY AND MAINTENANCE GUIDELINES To be successful, the soil must be able to soak water into the ground for a reasonable number of years. Return leaf fall and shredded woody materials from the landscape to the site when possible in order to replenish soil nutrients and structure. On turf areas, “grasscycle” (mulch-mow or leave the clippings) to build turf health. Maintain 2 to 3 inches of mulch over bare areas in landscape beds. Re-seed bare turf areas until the vegetation fully covers the ground surface. Avoid using pesticides (bug and weed killers) which damage the soil. Where fertilization is needed (mainly turf and annual flower beds), a moderate fertilization program should be used which relies on compost, natural fertilizers, or slow-release synthetic balanced fertilizers. RECORDING REQUIREMENT These on-site BMP 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.1.3.4 of the City of Renton Surface Water Design Manual. 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; the City of Renton may require additional instructions based on site-specific conditions. See the City of Renton’s Surface Water Design Manual website for additional information and updates. Appendix D Lot 34 Single-Family Drainage Narrative Western Washington Division Eastern Washington Division 165 NE Juniper St., Ste 201, Issaquah, WA 98027 407 Swiftwater Blvd, Cle Elum, WA 98922 Phone: (425) 392-0250 Fax: (425) 391-3055 Phone: (509) 674-7433 Fax: (509) 674-7419 www.EncompassES.net RESIDENTIAL BUILDING PERMIT DRAINAGE ASSESSMENT March 10, 2021 Drainage Narrative: Sierra Homes Lot 34 Site Address: 1112 N 34th St, Renton, WA 98056 Tax Parcel No.: 334210-2675 Abbreviated Legal: Lot 34 of Hillmans Lake WN Garden of Eden #1 Parcel Area: 5,324 SF (0.12 acres) Zoning: R-8 Encompass Job #: 20625 Project Overview: The Sierra Homes Lot 34 project is located in the City of Renton within the SW quarter of Section 32, Township 24 North, Range 5 East, W.M, King County, Washington. The site is located on the north side of N 34th St, west of the intersection of Park Ave N and N 34th St. Lot 34 is 5,324 SF (0.12 AC) and is bound on the east, west and north by single-family residential lots, and to the south by the N 34th St right-of way (ROW). Lot 34 slopes gently from east to west toward the adjacent lot 35 in which a single-family residence is proposed to be built under a separate permit application. The project proposes the construction of a 323 SF uncovered asphalt driveway, 2,625 SF house (roof area), and 196 SF of uncovered concrete walkways. The total proposed new on-site impervious area coverage is 3,144 SF, of which 323 SF is pollution generating. The total building coverage is 2,431 SF. Lot 34 is zoned R-8, which allows for a maximum building coverage of 50% and a maximum impervious coverage of 65%. The proposed construction results in a building coverage of 2,431 SF/5,324 SF * 100 = 45.7%, which is less than the maximum allowable coverage of 50%. The resulting on-site impervious surface coverage is 3,144 SF/5,324 SF*100 = 59.1%, which is less than the maximum allowable coverage of 65%. The development of Lot 34 is subject to Targeted Drainage Review and is required to evaluate the applicable Small Lot BMP Requirements per Appendix C.1.3.1 of the Renton Stormwater Design Manual (RSWDM). In addition, the project must be evaluated for Core Requirement #5 (Erosion and Sediment Control). City of Renton Sierra Homes – Lot 34 03/10/2021 Page | 2 FLOW CONTROL BMPs: The Flow Control BMPs have been evaluated below in order of the listed preference: Impervious Surface BMPs • Full Dispersion: Infeasible. The required flowpath of 100 feet is not available. • Full infiltration: Infeasible. Soils observed on site do not meet the soil classification for full infiltration per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Limited Infiltration: Feasible. Soils observed on-site meet the requirements for limited infiltration per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). Per section C.2.3.3 of the RSWDM, 36 liner feet of 2-FT wide trench per 1,000 SF of tributary impervious surface can be used to design limited infiltration trenches in sandy loam soils. A 36 FTx2 FT trench has an infiltration area of 72 SF; therefore, 72 SF of infiltration area is required per 1,000 SF of tributary impervious surface. Due to structure and property line setbacks as well as the topography of the site, limited infiltration is only feasible in the southwest corner of the lot. The site constraints allow for a maximum trench size of 5 FTx9 FT, which provides an infiltration area of 45 SF. A 5 FTx9 FT trench has the ability to mitigate up to (45 SF/72 SF)x1,000 SF= 625 SF of tributary impervious surface. • Rain Gardens: Infeasible. Due to structure and property line setbacks as well as the topography of the site, a rain garden is only feasible in the southwest corner of the lot. With the limited infiltration trench occupying this location, there is no practical location for a rain garden. In addition, rain gardens rely on the ability of underlying soils to infiltrate stormwater, and soils observed on site do not meet this soil classification per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Bioretention: Infeasible. Due to structure and property line setbacks as well as the topography of the site, a bioretention facility is only feasible in the southwest corner of the lot. With the limited infiltration trench occupying this location, there is no practical location for a bioretention facility. In addition, bioretention relies on the ability of underlying soils to infiltrate stormwater, and soils observed on site do not meet this soil classification per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Permeable Pavement: Infeasible. Permeable pavement relies on the ability of underlying soils to infiltrate stormwater, and soils observed on site do not meet this soil classification per the Soil Assessment by Riley Group dated December 11, 2020 City of Renton Sierra Homes – Lot 34 03/10/2021 Page | 3 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Basic Dispersion: Infeasible. This site does have the required 25 & 50-foot vegetated flowpaths available for basic dispersion facilities downstream of the proposed residence. Per section C.1.3.1 of the RSWDM, BMPs must be implemented, at a minimum, for an impervious area equal to at least 10% of the site for lot areas up to 11,000 SF. Lot 34 is 5,324 SF; therefore, a minimum of 5,324 SF x 0.1= 532 SF of proposed impervious surface is required to be mitigated by the proposed flow control BMPs. As shown on the Architectural Plans, an approximately 561 SF rooftop area is proposed to be directed to the limited infiltration trench, which has a capacity to infiltrate up to 625 SF of rooftop area. This results in 561/5,324= 10.5% of the lot area to be mitigated utilizing flow control BMPs. Pervious Surface BMPs • Full Dispersion: Infeasible. The required flowpath of 100 feet is not available. • Soil Amendment: Feasible; All disturbed, pervious areas of the project will meet soil amendment requirements as detailed in Section C.2.13 of the RSWDM. EROSION AND SEDIMENT CONTROL MEASURES: In order to prevent erosion and trap sediments within the project site, the following BMPs will be used approximately as shown on the ESC plan: • Clearing limits will be marked by fencing at the site limits. • The proposed driveway from N 34th St will be utilized as a Stabilized Construction Entrance to reduce sediment transported off-site. • Catch basins on N 34th St will be equipped with catch basin inserts to prevent sediment accumulation. • Silt fencing will be placed along the site boundary on the west and north limits of the site. • Mulch will be spread over all cleared areas of the site when they are not being worked. Mulch will consist of air-dried straw and chipped site vegetation. Appendix E Lot 35 Single-Family Drainage Narrative Western Washington Division Eastern Washington Division 165 NE Juniper St., Ste 201, Issaquah, WA 98027 407 Swiftwater Blvd, Cle Elum, WA 98922 Phone: (425) 392-0250 Fax: (425) 391-3055 Phone: (509) 674-7433 Fax: (509) 674-7419 www.EncompassES.net RESIDENTIAL BUILDING PERMIT DRAINAGE ASSESSMENT March 10, 2021 Drainage Narrative: Sierra Homes Lot 35 Site Address: 1108 N 34th St, Renton, WA 98056 Tax Parcel No.: 334210-2680 Abbreviated Legal: Lot 35 of Hillmans Lake WN Garden of Eden #1 Parcel Area: 5,322 SF (0.12 acres) Zoning: R-8 Encompass Job #: 20625 Project Overview: The Sierra Homes Lot 35 project is located in the City of Renton within the SW quarter of Section 32, Township 24 North, Range 5 East, W.M, King County, Washington. The site is located on the north side of N 34th St, west of the intersection of Park Ave N and N 34th St. Lot 35 is 5,322 SF (0.12 acres) and is bound on the east, west and north by single-family residential lots, and to the south by the N 34th Street right-of way (ROW). Lot 35 slopes gently from east to west toward the adjacent lot 36 in which a single-family residence is proposed to be built under a separate permit application. The project proposes the construction of a 343 SF uncovered asphalt driveway, 2,862 SF house (roof area), and 31 SF of uncovered concrete walkways. The total proposed new on-site impervious area coverage is 3,236 SF, of which 343 SF is pollution generating. The total building coverage is 2,481 SF. Lot 35 is zoned R-8, which allows for a maximum building coverage of 50% and a maximum impervious coverage of 65%. The proposed construction results in a building coverage of 2,481 SF/5,322 SF * 100 = 46.6%, which is less than the maximum allowable coverage of 50%. The resulting on-site impervious surface coverage is 3,236 SF/5,322 SF*100 = 60.8%, which is less than the maximum allowable coverage of 65%. The development of Lot 35 is subject to Targeted Drainage Review and is required to evaluate the applicable Small Lot BMP Requirements per Appendix C.1.3.1 of the Renton Stormwater Design Manual (RSWDM). In addition, the project must be evaluated for Core Requirement #5 (Erosion and Sediment Control). City of Renton Sierra Homes – Lot 35 03/10/2021 Page | 2 FLOW CONTROL BMPs: The Flow Control BMPs have been evaluated below in order of the listed preference: Impervious Surface BMPs • Full Dispersion: Infeasible. The required flowpath of 100 feet is not available. • Full infiltration: Infeasible. Soils observed on site do not meet the soil classification for full infiltration per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Limited Infiltration: Feasible. Soils observed on-site meet the requirements for limited infiltration per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with Civil Engineering Plans). Per section C.2.3.3 of the RSWDM, 36 liner feet of 2-FT wide trench per 1,000 SF of tributary impervious surface can be used to design limited infiltration trenches in sandy loam soils. A 36 FTx2 FT trench has an infiltration area of 72 SF; therefore, 72 SF of infiltration area is required per 1,000 SF of tributary impervious surface. Due to structure and property line setbacks as well as the topography of the site, limited infiltration is only feasible in the southwest corner of the lot. The site constraints allow for a maximum trench size of 5 FTx9 FT, which provides an infiltration area of 45 SF. A 5 FTx9 FT trench has the ability to mitigate up to (45 SF/72 SF)x1,000 SF= 625 SF of tributary impervious surface. • Rain Gardens: Infeasible. Due to structure and property line setbacks as well as the topography of the site, a rain garden is only feasible in the southwest corner of the lot. With the limited infiltration trench occupying this location, there is no practical location for a rain garden. In addition, rain gardens rely on the ability of underlying soils to infiltrate stormwater, and soils observed on site do not meet this soil classification per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Bioretention: Infeasible. Due to structure and property line setbacks as well as the topography of the site, a bioretention facility is only feasible in the southwest corner of the lot. With the limited infiltration trench occupying this location, there is no practical location for a bioretention facility. In addition, bioretention relies on the ability of underlying soils to infiltrate stormwater, and soils observed on site do not meet this soil classification per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Permeable Pavement: Infeasible. Permeable pavement relies on the ability of underlying soils to infiltrate stormwater, and soils observed on site do not meet this soil classification per the Soil Assessment by Riley Group dated December 11, 2020 City of Renton Sierra Homes – Lot 35 03/10/2021 Page | 3 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Basic Dispersion: Infeasible. This site does have the required 25 & 50-foot vegetated flowpaths available for basic dispersion facilities downstream of the proposed residence. Per section C.1.3.1 of the RSWDM, BMPs must be implemented, at a minimum, for an impervious area equal to at least 10% of the site for lot areas up to 11,000 SF. Lot 35 is 5,322 SF; therefore, a minimum of 5,322 SF x 0.1= 532 SF of proposed impervious surface is required to be mitigated by the proposed flow control BMPs. As shown on the Architectural Plans, an approximately 536 SF rooftop area is proposed to be directed to the limited infiltration trench, which has a capacity to infiltrate up to 625 SF of rooftop area. This results in 536/5,322= 10.1% of the lot area to be mitigated utilizing flow control BMPs. Pervious Surface BMPs • Full Dispersion: Infeasible. The required flowpath of 100 feet is not available. • Soil Amendment: Feasible; All disturbed, pervious areas of the project will meet soil amendment requirements as detailed in Section C.2.13 of the RSWDM. EROSION AND SEDIMENT CONTROL MEASURES: In order to prevent erosion and trap sediments within the project site, the following BMPs will be used approximately as shown on the ESC plan: • Clearing limits will be marked by fencing at the site limits. • The proposed driveway from N 34th St will be utilized as a Stabilized Construction Entrance to reduce sediment transported off-site. • Catch basins on N 34th St will be equipped with catch basin inserts to prevent sediment accumulation. • Silt fencing will be placed along the site boundary on the west and north limits of the site. • Mulch will be spread over all cleared areas of the site when they are not being worked. Mulch will consist of air-dried straw and chipped site vegetation. Appendix F Lot 36 Single-Family Drainage Narrative Western Washington Division Eastern Washington Division 165 NE Juniper St., Ste 201, Issaquah, WA 98027 407 Swiftwater Blvd, Cle Elum, WA 98922 Phone: (425) 392-0250 Fax: (425) 391-3055 Phone: (509) 674-7433 Fax: (509) 674-7419 www.EncompassES.net RESIDENTIAL BUILDING PERMIT DRAINAGE ASSESSMENT March 10, 2021 Drainage Narrative: Sierra Homes Lot 36 Site Address: 1106 N 34th St, Renton, WA 98056 Tax Parcel No.: 334210-2685 Abbreviated Legal: Lot 36 of Hillmans Lake WN Garden of Eden #1 Parcel Area: 5,319 SF (0.12 acres) Zoning: R-8 Encompass Job #: 20625 Project Overview The Sierra Homes Lot 36 project is located in the City of Renton within the SW quarter of Section 32, Township 24 North, Range 5 East, W.M, King County, Washington. The site is located on the north side of N 34th St, west of the intersection of Park Ave N and N 34th St. Lot 36 is 5,319 SF (0.12 AC) and is bound on the east, west and north by single-family residential lots, and to the south by the N 34th Street right-of way (ROW). Lot 36 slopes gently from east to west toward the adjacent single-family residence. The project proposes the construction of a 263 SF uncovered asphalt driveway, 2,619 SF house (roof area), and 28 SF of uncovered concrete walkways. The total proposed new on-site impervious area coverage is 2,910 SF, of which 263 SF is pollution generating. The total building coverage is 2,222 SF. Lot 36 is zoned R-8, which allows for a maximum building coverage of 50% and a maximum impervious coverage of 65%. The proposed construction results in a building coverage of 2,222 SF/5,319 SF * 100 = 41.8%, which is less than the maximum allowable coverage of 50%. The resulting on-site impervious surface coverage is 2,910 SF/5,319 SF*100 = 54.7%, which is less than the maximum allowable coverage of 65%. The development of Lot 36 is subject to Targeted Drainage Review and is required to evaluate the applicable Small Lot BMP Requirements per Appendix C.1.3.1 of the Renton Stormwater Design Manual (RSWDM). In addition, the project must be evaluated for Core Requirement #5 (Erosion and Sediment Control). City of Renton Sierra Homes – Lot 36 03/10/2021 Page | 2 FLOW CONTROL BMPs: The Flow Control BMPs have been evaluated below in order of the listed preference: Impervious Surface BMPs • Full Dispersion: Infeasible. The required flowpath of 100 feet is not available. • Full infiltration: Infeasible. Soils observed on site do not meet the soil classification for full infiltration per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Limited Infiltration: Feasible. Soils observed on-site meet the requirements for limited infiltration per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with Civil Engineering Plans). Per section C.2.3.3 of the RSWDM, 36 liner feet of 2-FT wide trench per 1,000 SF of tributary impervious surface can be used to design limited infiltration trenches in sandy loam soils. A 36 FTx2 FT trench has an infiltration area of 72 SF; therefore, 72 SF of infiltration area is required per 1,000 SF of tributary impervious surface. Due to structure and property line setbacks as well as the topography of the site, limited infiltration is only feasible in the southwest corner of the lot. The site constraints allow for a maximum trench size of 5 FTx9 FT, which provides an infiltration area of 45 SF. A 5 FTx9 FT trench has the ability to mitigate up to (45 SF/72 SF)x1,000 SF= 625 SF of tributary impervious surface. • Rain Gardens: Infeasible. Due to structure and property line setbacks as well as the topography of the site, a rain garden is only feasible in the southwest corner of the lot. With the limited infiltration trench occupying this location, there is no practical location for a rain garden. In addition, rain gardens rely on the ability of underlying soils to infiltrate stormwater, and soils observed on site do not meet this soil classification per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Bioretention: Infeasible. Due to structure and property line setbacks as well as the topography of the site, a bioretention facility is only feasible in the southwest corner of the lot. With the limited infiltration trench occupying this location, there is no practical location for a bioretention facility. In addition, bioretention relies on the ability of underlying soils to infiltrate stormwater, and soils observed on site do not meet this soil classification per the Soil Assessment by Riley Group dated December 11, 2020 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Permeable Pavement: Infeasible. Permeable pavement relies on the ability of underlying soils to infiltrate stormwater, and soils observed on site do not meet this soil classification per the Soil Assessment by Riley Group dated December 11, 2020 City of Renton Sierra Homes – Lot 36 03/10/2021 Page | 3 (Provided as an appendix to the Technical Information Report included with the Civil Engineering Plans). • Basic Dispersion: Infeasible. This site does have the required 25 & 50-foot vegetated flowpaths available for basic dispersion facilities downstream of the proposed residence. Per section C.1.3.1 of the RSWDM, BMPs must be implemented, at a minimum, for an impervious area equal to at least 10% of the site for lot areas up to 11,000 SF. Lot 36 is 5,319 SF; therefore, a minimum of 5,319 SF x 0.1= 532 SF of proposed impervious surface is required to be mitigated by the proposed flow control BMPs. As shown on the Architectural Plans, an approximately 557 SF rooftop area is proposed to be directed to the limited infiltration trench, which has a capacity to infiltrate up to 625 SF of rooftop area. This results in 557/5,319= 10.5% of the lot area to be mitigated utilizing flow control BMPs. Pervious Surface BMPs • Full Dispersion: Infeasible. The required flowpath of 100 feet is not available. • Soil Amendment: Feasible; All disturbed, pervious areas of the project will meet soil amendment requirements as detailed in Section C.2.13 of the RSWDM. EROSION AND SEDIMENT CONTROL MEASURES: In order to prevent erosion and trap sediments within the project site, the following BMPs will be used approximately as shown on the ESC plan: • Clearing limits will be marked by fencing at the site limits. • The proposed driveway from N 34th St will be utilized as a Stabilized Construction Entrance to reduce sediment transported off-site. • Catch basins on N 34th St will be equipped with catch basin inserts to prevent sediment accumulation. • Silt fencing will be placed along the site boundary on the west and north limits of the site. • Mulch will be spread over all cleared areas of the site when they are not being worked. Mulch will consist of air-dried straw and chipped site vegetation.