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HomeMy WebLinkAboutr_TIR_210722_V21 AE2021-13 STORM DRAINAGE TECHNICAL INFORMATION REPORT Proposed Single-Family Residence Located at 16028 SE 144th ST, Renton, WA 98059 For: SINGH MANJIT Parcel # 101600-0020 Prepared by: Anstey Engineering CIVIL ENGINEERING/CONSULTING 8627 NE 180th Street Bothell, Washington98011 Phone: (206) 303-7639 Fax: (425) 658-0923 E-mail: benanstey@ansteyengineering.com 7/20/2021 PR21000228 B21002641 V2 REVISION Received: 07/22/2021 / aalexander BUILDING DIVISION APPROVEDBUILDING DIVISION THIS SET OF APPROVED PLANS MUST BE ON THE JOB AT ALLTIMES DURING CONSTRUCTION. THIS BUILDING IS NOT TO BEOCCUPIED UNTIL AFTER FINAL INSPECTION BY THE RENTONBUILDING DIVISION AND RECEIPT OF CERTIFICATE OFOCCUPANCY. APPROVAL SHALL NOT BE CONSTRUED AS THE AUTHORITY TOVIOLATE OR CANCEL ANY PROVISIONS OF CODES, ORDINANCES,OR OTHER REGULATIONS ENFORCED BY THIS CITY.DATE: 08/23/2021 2 AE2021-13 Table of Contents Project Overview 3 Conditions and Requirements Summary 10 1. Discharge at the natural location 11 2. Offsite Analysis 11 3. Flow Control Facilities 12 4. Conveyance System 14 5. Construction Stormwater Pollution Prevention 14 6. Maintenance and Operations 15 7. Financial Guarantees and Liability 15 8. Water Quality Design 15 9. Flow Control BMPs 15 10. Special Reports and Studies 16 11. Other Permits 16 12. Bond Quantities, Facility Summaries and Declaration of Covenant 16 Appendix Soil information – MacVeign Soil Investigation of 2-2-2018 Drywell figure C.2.2.C Maintenance Instructions for catch basins Silt Fence Detail Construction Entrance Detail General CSWPP Requirements 3 AE2021-13 PROJECT OVERVIEW This storm drainage technical information report has been prepared for the proposed single family residence located at 16028 SE 144th ST, Renton, WA 98059 with parcel 101600-0020. It will be designed to comply with the requirements of the 2017 City of Renton Surface Water Design Manual (CORSWDM). The Legal Description is: BOYDSTONS 1ST ADD LOT 2 LESS E 6 FT TGW LOT 4 OF KC SHORT PLAT NO 677116 RECORDING NO 7905170582 SD SHORT PLAT DAF - BEG SW COR OF TRACT 8 BLK 3 CEDAR PARK FIVE ACRE TRACTS TH S 89-34-39 E 123.43 FT TO TPOB TH N 0-31-37 W PLT W LN SD TRACT 299.65 FT TO N LN SD TRACT TH S 89- 29- 48 E 105.40 FT TO NW COR BOYDSTONS 1ST ADD TH S 0-33-23 W 299.50 FT TO S LN TRACT 8 TH N 89-34-39 W 105.55 FT TO TPOB - AKA LOT B OF KC LOT LN ADJ NO 785013 APPROVED SEPTEMBER 17, 1985 PREDEVELOPED SITE CONDITIONS The 10,240sf site (0.24 acres) is located near intersection of SE 144th St and 160th AVE SE at 16028 SE 144th St, Renton, WA 98059. The site was developed with an existing756sf house, 660sf carport, and 1,345sf concrete pavement. Total existing impervious is 2,761sf or 27%. All these 2,761sf existing impervious area will be demolished. The site is fairly flat. The site is bordered by SE 144th St on the South, and single family houses on the North, East, West and Northwest. There is a ditch and 12” culvert on the SE 144th St in front of the house. This ditch flows down west to other 12”culverts and ditches on the SE 144th St to a 12” concrete pipe to an existing catch basin near southwest corner of the house 14326 160th AVE NE, and continue as it does in city drainage system. Please see the city storm map below. Existing hard surface to be replaced Existing house 28'X27' to be removed (Sf) 756 Existing carport 22'X30' to be removed (Sf) 660 Existing driveway (Sf) to be replaced (Sf) 1,345 Total Ex. Impervious area (SF) 2,761 Total Ex. Impervious area coverage (%) 27% Per Renton Imap, the site is not located in coal mine, landslide, wetland, erosion hazard areas, or other environmentally sensitive areas. There is a drainage complaint upstream (green dot) in King County, but it was closed in 1997. See the Renton critical Imap below. 4 AE2021-13 Per King County Imap, this lot is in the Urban Growth Area and there are drainage complaints in this area, but all were close before March 2009. Drainage Basin= Lower Cedar River; Watershed = Cedar River / Lake Washington ; WRIA=Cedar-Sammamish (8) Quarter-Section-Township-Range = SE-14-23-5 5 AE2021-13 The current stormwater runoff of the site flows into the ditch on the south of the site to the city storm drainage system on the SE 144th St as the dash blue path line is shown in the city storm map below. DEVELOPED SITE CONDITIONS The project is a redevelopment project. All existing impervious will be demolished; a proposed project will involve construction of a new 3,845sf roof house, a new 1,275sf concrete driveway, porch and back step. The total replaced and new impervious surface area will be: 5,120sf or 50% of the site. See the plan for detail. The proposed house will use existing utilities system. Impervious Surfaces: Proposed hard surface New house (roof) (Sf) with overhangs 3,845 New Concrete driveway portch and step 1,275 6 AE2021-13 Total Proposed Impervious area (SF) 5,120 Total Proposed Impervious area coverage (%) 50% Clearing limit area is 7,465sf+/-. 7 AE2021-13 King County Water District 90 8 AE2021-13 Per the Natural Resources Conservation Service soil survey, the soils are as EvB- Everett very gravelly sandy loam, 0 to 8 percent slopes. Typical profile: 9 AE2021-13 Oi - 0 to 1 inches: slightly decomposed plant material A - 1 to 3 inches: very gravelly sandy loam Bw - 3 to 24 inches: very gravelly sandy loam C1 - 24 to 35 inches: very gravelly loamy sand C2 - 35 to 60 inches: extremely cobbly coarse sand Properties and qualities Slope: 0 to 8 percent Depth to restrictive feature: More than 80 inches Drainage class: Somewhat excessively drained Capacity of the most limiting layer to transmit water (Ksat): High (1.98 to 5.95 in/hr) Depth to water table: More than 80 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: Low (about 3.2 inches) 10 AE2021-13 Per Renton soil map, the soils are EvB- Everett very gravelly sandy loam, 0 to 8 percent slopes. 11 AE2021-13 Per Bruce S MacVeigh, P.E- Geotechnical soil letter in Appendix, the soils are deep and very good for infiltration. The soils were investigated by Anstey Engineering on February 3, 2021 Cloudy: Soil Log 0" - 6" Topsoil 6" -34" Gravelly Sandy Loam 34" -36" Medium Sand 12 AE2021-13 We will use two new drywells for 3,228sf new house (roof) and 1,800sf concrete driveway with 86sf walkway/stairs. See on site BMP’s for details. TIR worksheet will be provided separately. CONDITIONS AND REQUIREMENTS SUMMARY Per the 2017 City of Renton Surface Water Design Manual (CORSWDM) section 1.1.2, this lot meets DIRECTED DRAINGE REVIEW STANDARDS in Appendix C as more than 5,000 square feet of new plus replaced impervious surface are created and less than ¾ acre of land disturbing activity. 13 AE2021-13 The project must comply with all nine core requirements in Section 1.2 and five special requirements in Section 1.3. 1. Discharge at the natural location CORE REQUIREMENT #1: DISCHARGE AT THE NATURAL LOCATION (Per 1.2.1) We are proposing connecting the house drainage and driveway to a new catch basin and connecting to two new drywells on the north and south of the house which will infiltrate onto the ground. All rainfall currently infiltrates or sheet flows to south down to roadside ditches of SE 144th St in front of the house, flows to a CB-Type 1 at Rim Elevation 372.39’, and then go through in city storm water system and will continue as it does (see the city storm map above). 2. Offsite Analysis CORE REQUIREMENT #2: OFFSITE ANALYSIS (Per 1.2.2) Level One Downstream Analysis Task 1: Define and map the study area The site is in the urban growth area. The south of the site is SE 144th St Street. The north, east and west of this site are small single family residences. There are no significant on or off site flows onto this property. No downstream drainage problems were observed. There are roadside ditches on SE 144th St adjacent to the site and in front of the house. The existing paved surfaces on this site drain to the ditches and city drainage system in SE 144th St (see the city storm map above). Task 2: Review all available information on the study area Using the King County iMap and Renton COR Maps, it was found that there are no immediate critical areas upstream or downstream of the property. Per King County iMap, the site is in a Class 1 Critical Aquifer Recharge Area, but per Renton COR Maps, there does not refer to Class 1 Critical Aquifer Recharge Area (see the city critical map above). Task 3: Field inspect the study area There are no reported problems to be investigated. The amount of space and soil types present on the property clearly support the flow control BMPs being implemented. There will not be any destruction of aquatic habitat on-site or downstream. The Site was visited on February 3, 2021 and a 1/4 mile downstream investigation was made. As there are no signs of surface flow no problems were identified. The drainage system of SE 144th St flows west through 12” culverts and roadside ditches (about 240lf) to a catch basin type 1 at Rim Elevation 372.39’ at the end of SE 144th St Street and 160th AVE SE, continues sheet flowing northwest 25lf of 12” concrete pipe to another CB-type 1 at Rim Elevation 371.63, flows south through 54lf of 12” corrugated metal pipe (at upper elevation 369.1’ and lower elevation 368.11’) down to a manhole at Rim 14 AE2021-13 elevation 371.56’, and continues flowing to west as the drainage systems do. See the City of Renton storm system map above. Task 4: Drainage System Description and Problem Descriptions For an overall impervious surface of this size, two drywells will be used for the new house and driveway. There are no other significant on or off-site flows. The existing house, carport and driveway drain to roadside ditch of the SE 144th St Street Drainage System or infiltrates on site. Task 5: Mitigation of Existing or Potential Problems There are no known existing or potential drainage problems and / or water quality problems. Upstream Analysis The properties adjacent to the site are fairly flat. Upstream of the site are single-family houses in Northeast of the site. Per King County Imap and Renton COR Maps, there is no critical areas upstream and downstream problem for the houses in upstream of the site. There are no significant flows on this site. No upstream drainage problems were found. 3. Flow Control Facilities CORE REQUIREMENT #3: FLOW CONTROL FACILITIES (Per 1.2.3) Per Renton Flow Control map below, the site is Unincorporated King County Flow Control Standard. Drywells for roof and driveway runoff infiltration will be installed. As full infiltration will be used a an on-site BMP therefore in accordance with rswdm Sections 1.2.3.B.3 and Table 1.2.9.A the impervious areas routed to this can be subtracted from the flow control calculations for the 100 year 15 min Peak Flow. The Mitigated Peak Per WWHM (attached ) is 0.042617cfs – Pre Developed peak = 0.000759= increase of flow is only 0.041858cfs which is less than 0.15cfs. 15 AE2021-13 Existing Site Hydrology: The site is fairly flat. The site will be redeveloped with a new house and driveway. There does not appear to be any significant surface flow. Any runoff from the site will drain to existing roadside ditches on the SE 144th St Street Drainage System. The site does not receive any 16 AE2021-13 significant off-site flows from the adjacent properties. The soils were investigated by Anstey Engineering on February 3, 2021 and found to be sandy (see Anstey Engineering soil log above). This conforms to the MacVeigh Soil Report. See attached. The soils on the site are identified as Everett very gravelly sandy loam soils (EvB), 0 to 8 percent slopes per the natural Resources Conservation Service soil survey. See Soil log in typical profile part of developed site condition above. Developed Site Hydrology When the new house and driveway are constructed, the drainage will be connected to two new Type 40 catch basins on the north and south of the house which drain to two drywells. Performance Standards Flow control BMPs were investigated for their feasibility. Full or Basic dispersion cannot be used as there is not an adequate flow path. Please see details in On-site BMP’s part below. The roof and driveway stormwater runoff will be collected and routed to new type 40 catch basins on the north and south of the house which drain into two drywells. Therefore no additional BMPs are required as all new impervious surface is fully infiltrated. See WWHM Report Attached. The 100 year peak flow increase is less than 0.15cfs so the site meet the Flow Control standard with the 464 cf of drywells. The Mitigated Peak Per WWHM (attached ) is 0.042617cfs – Pre Developed peak = 0.000759= increase of flow is only 0.041858cfs which is less than 0.15cfs This is a single family residence and as such does not pose any significant threat for pollution. No pollution generating activities are planned. This is not a ‘High Use Site’. Part D: Flow Control System The Erosion and Sediment Control Plans along with the Site Plans include the locations of the flow control systems. The roof and driveway stormwater runoff will be collected and routed to new type 40 catch basins on the north and south of the house which drain into two drywells with 464cf of gravel. Per the WWHM Report attached the 100 year peak flow is less than 0.15cfs therefore the site meets the flow control standard Part E: Water Quality System The site will have less than 5,000sf of pollution generating surface (1800sf). Therefore, water quality treatment is not required. This is not a high use site. No additional facilities will be necessary. 4. Conveyance System CORE REQUIREMENT #4 CONVEYANCE SYSTEM (Per 1.2.4) 17 AE2021-13 As the flows on this small site are small, the 6” PVC outlet pipe is adequate. There will be no special conveyance system for this development. The 6” PVC pipe at a 2% slope can easily pass all runoff from the driveway and roof to the catch basin in front of the garage. 5. Construction Stormwater Pollution Prevention CORE REQUIREMENT #5 CONSTRUCTION STORMWATER POLLUTION PREVENTION (Per 1.2.5) Temporary ESC measures will be required as there will be disturbance of the soil to construct the walkway, driveway, and house. A silt fence and a rock construction entrance should be provided at a minimum. No special requirements are needed. See in the Appendix of this report. 6. Maintenance and Operations CORE REQUIREMENT #6 MAINTENANCE AND OPERATION (Per 1.2.6) The stormwater BMPs proposed for this project will be maintained privately by the property owner. The operations and maintenance details for this private facility are provided in the Operations and Maintenance Manual found in Appendix A of 2017 CORSWDM. See the attachment below. 7. Financial Guarantees and Liability CORE REQUIREMENT #7 FINANCIAL GUARANTEES AND LIABILITY (Per 1.2.7) The owner will provide any necessary financial guarantees. The property owner will be responsible to insure that the project is constructed to the approved plans and that the drainage does not cause any problems. 8. Water Quality Facilities CORE REQUIREMENT #8 WATER QUALITY FACILITIES (Per 1.2.8) As this site has less than 5,000sf of pollution generating surface, no special water quality design is required. No additional facilities will be necessary. 9. On-site BMPs CORE REQUIREMENT #9 ON-SITE BMP’S (Per 1.2.9) Section C.1.3.1 of the City of Renton Surface Water Design Manual applies to projects on lots smaller than 22,000 square feet. Section C.1.3.1 states that, if the proposed project is on a site/lot smaller than 22,000 square feet, then flow control BMPs must be applied as specified in Appendix C, Section C.1.3.1 or the project must comply with the LID performance standard. This project proposes to apply small lot BMPs where they are feasible. 18 AE2021-13 Full Dispersion: Full dispersion is not feasible because there is not adequate space for the required 100 foot flow path. Full infiltration: it is feasible for Roof and driveway runoff. Per C.2.2.4 of the CORSWDM, the proposed roof and driveway area of 5,120 square feet will be handled by full infiltration using two drywells a 19’x4’x4’ in the south of the lot and a 10’x4’x4’ on the north of the lot. Per Section C.2.2.4, the medium sand soil on the property would require 90 cubic feet of gravel for each 1,000 square feet of impervious area being directed to the drywells. Impervious area (sf) Drywell required (cf) 90cf/1000sf Drywell designed (cf) % Migitate 5,120 460.8 29’x4’x4’= 464cf 100% Limited Infiltration: limited infiltration is not used as full infiltration will be used. Bioretention and Rain Gardens: For the reason discussed in the above section regarding full infiltration, rain gardens are an unacceptable BMP for this project. Permeable Pavement: it is infeasible as proposed driveway is constructed on the existing driveway location. Basic Dispersion is not feasible as there is not enough space for 25’ from ROW. We use full infiltration for the proposed house and driveway. Rainwater Harvesting: it is not used on this single family residence Special Requirements: Special Requirement #1: Other Adopted Area-Specific Requirements, section 1.3.1 None known. Special Requirement #2: Flood Hazard Area Delineation, section 1.3.2 The site is not in a flood hazard area, so flood hazard area delineation is not required. Special Requirement #3: Flood Protection Facilities, section 1.3.3 The site is not in a flood plain, so no flood protection facilities are required. Special Requirement #4: Source Control, section 1.3.4 (not need) The site is a single family residence; it is not high use and less than 5000sf of PGS is created, so no source control is required. Special Requirement #5: Oil Control, section 1.3.5 This is not a high use site, so oil control is not required. 10. SPECIAL REPORTS AND STUDIES No additional special reports or studies are required for this proposed project. 11. OTHER PERMITS 19 AE2021-13 A building permit for the proposed home will be required for this project. 12. Bond Quantities, Facility Summaries and Declaration of Covenant A bond quantities worksheet is not expected to be required by the City of Renton. Declaration of Covenant will be provided separately. APPENDIX: Soil Report WWHM Report 20 AE2021-13 21 AE2021-13 22 AE2021-13 23 AE2021-13 24 AE2021-13 Maintenance Requirements 25 AE2021-13 26 AE2021-13 27 AE2021-13 28 AE2021-13 29 AE2021-13 30 AE2021-13 31 AE2021-13 32 AE2021-13 33 AE2021-13