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HomeMy WebLinkAboutBLD2021-00599 - 05 Stormwater Plan115 E Railroad Ave., Suite 203, Port Angeles, WA 98362 (360) 912-5191 www.gounitedengineering.com October 28, 2021 STORMWATER, EROSION, AND SEDIMENT CONTROL PLAN FOR PARCEL #965000135, LOT 247, KALA POINT, PORT TOWNSEND, WASHINGTON 98368 United Engineering, Inc. was retained by Anderson Homes, LLC, on behalf of Andrew Reed & Marilyn Meyer, to prepare a Stormwater Management Plan for a single-family residential project located on Jefferson County Tax Parcel #965000135 in the Kala Point area of Port Townsend, WA. A single-family residence is proposed to be constructed. The home will be served by a gravel driveway off Belvedere Drive. This plan will conform to the 2019 Stormwater Management Manual for Western Washington. Existing Conditions The site has an overall slope between 15-20% from the west downward to the east. The parcel is 36,112 sf. It is currently undeveloped, but is part of a larger partially developed subdivision, Kala Point. The lot is currently vegetated with forest like condition. No existing stormwater system is in place for the surrounding subdivision, an on site system will be prescribed. Soil Conditions Per the United States Department of Agriculture Natural Resources Conservation Services (NRCS) Web Soil Survey, site soils for are Hoypus gravelly loamy sand. Septic test pits were dug in August of 2018 by Timothy Thomas. These test pits confirmed medium sands and no water table to a depth of greater than 6 feet. No evidence of mottling or shallow ground water level were found. New Development The proposed project will result in about 5,757 square feet of new impervious surfaces, of which about 4,156 square feet will be non-pollution generating impervious surfaces (new roof, deck, sidewalk), and about 1,601 square feet will be pollution generating impervious surfaces (new gravel driveway/gravel parking area). The project results in more than 5,000 square feet of new impervious surfaces, so all Minimum Requirements, RECEIVED BY DCD 11/1/21 Western Washington (SWMMWW), apply. Minimum Requirement #1 Preparation of Stormwater Site Plans See Stormwater Site Plan. Minimum Requirement #2 Construction Stormwater Pollution Prevention For description of Best Management Practices (BMPs) listed below for Elements #1 through #9, and except where specifically noted otherwise, refer to the 2019 SWMMWW. Element #1 Preserve Vegetation/Mark Clearing Limits Before land disturbing activity begins, the clearing limits must be marked with siltation fence or high visibility fencing. The native topsoil and existing vegetation must be retained in an undisturbed state to the maximum degree practical. Element #2 Establish Construction Access Unless a written variance is granted in advance, a stabilized construction entrance (BMP C105) for this project shall be provided via Belvedere Dr. See the Stormwater Site Plan and referenced detail sheets for specific location and details for the stabilized construction entrance. Any sediment tracked off the site must be cleaned thoroughly at the end of each day, or more frequently if determined necessary, by shoveling, sweeping, transporting to a controlled sediment disposal area, street washing, and/or other necessary and appropriate measures. Element #3 Control Flow Rates Because of the heavily vegetated nature of the site, stormwater flows are not expected to concentrate in any significant volume or flow rate. Runoff Control systems that will serve roofs, pavements, sidewalks, and other impervious areas must be constructed as soon as possible to avoid any flow concentration. Activities such as roof gutter and downspout installation, paving, and similar construction activities, must be promptly completed in the proper sequence to control flows and minimize the potential for erosion and sedimentation. Silt fence (BMP C233), wattles (BMP C235), and/or other appropriate BMPs must be used as necessary for control of flow rates. Element #4 Install Sediment Controls Siltation fence will serve as the sediment control for the project. The location of the siltation fence is shown on the Stormwater Site Plan and must be in place in all areas where sediment could potentially leave the site. Element #5 Stabilize Soils Soils must not remain exposed and unworked for more than the time periods set forth below: May 1 to September 30: 7 days. RECEIVED BY DCD 11/1/21 October 1 - April 30: 2 days. Bare soils, particularly bare slopes, and soil stockpiles must be protected from erosion with sediment trapping measures. To the maximum extent possible, stockpiles must be located away from storm drain inlets, waterways, and drainage channels. Temporary and permanent seeding (BMP C120), mulching (BMP C121), nets and blanketing (BMP C122), plastic covering (BMP C123), top-soiling and/or composting (BMP C125), and/or other appropriate BMPs must be used as necessary for stabilizing of soils. Additionally, post-construction soil quality and depth enhancement (BMP T5.13; refer to Building Soil; Guidelines and Resources for Implementing Soil Quality and Depth BMP T5.13, 2016 Edition) must be implemented to improve infiltration capacity of the newly created and restored lawn areas. Element #6 Protect Slopes Blanketing or other effective temporary measures shall be taken to prevent erosion. Slope construction and slope stabilization should be scheduled during dry weather (usually May 1 to September 30) to minimize potential for erosion. Temporary and permanent seeding (BMP C120), mulching (BMP C121), nets and blanketing (BMP C122), plastic covering (BMP C123), and/or other appropriate BMPs must be used as necessary for protection of slopes. Element #7 Protect Drain Inlets Inlet protection shall also be placed in all existing and new catch basins and inlets that could potentially receive stormwater flows directly from the site. Storm drain inlet protection (BMP C220), use of oil-absorbent-rated catch basin inlet fabric insert bags, and/or other appropriate BMPs must be used as necessary for inlet protection. Inlet protection must not obstruct vehicle traffic on the site. Element #8 Stabilize Channels and Outlets This project does not have any channels or outlets where concentrated flows could leave the site and enter natural or man-made bodies of water or wetlands. Element #9 Control Pollutants All chemicals, liquid products, petroleum products, and other materials that have the potential to pose a threat to human health or the environment must be provided with secondary containment and protection from weather, vandalism, and/or other adverse circumstances. Secondary containment means placing tanks and/or containers within an impervious structure capable of containing 110% of the volume contained in the largest tank or container within the containment structure. RECEIVED BY DCD 11/1/21 Fueling, maintenance, and repair of heavy equipment and vehicles must include use of spill prevention and control measures. Washout of concrete trucks, dumping of excess concrete, and similar activities shall not be performed on-site. Washout of concrete trucks, dumping of excess concrete, and similar activities shall only be performed in off-site locations specifically approved for such activities. Proper concrete handling (BMP C151), saw cutting and surfacing pollution prevention (BMP C152), proper material delivery, storage, and containment (BMP C153), and/or other appropriate BMPs must be used as necessary for control of pollutants. Any and all spills associated with this project, either on site or off site, must be reported to the proper authorities and thoroughly cleaned up to meet applicable City, County, State, and/or Federal standards. Element #10 Control Dewatering In the unlikely event that dewatering is required, water from dewatering operations shall be discharged in such a manner that it does not result in erosion and sedimentation. Special care shall be taken to avoid sedimentation of existing and new stormwater control facilities. Element #11 Maintain BMPs All temporary and permanent erosion and sediment control BMPs must be maintained and repaired as needed to assure continued performance of their intended function in accordance with BMP specifications. All temporary erosion and sediment control BMPs shall be removed within 30 days after achieving final site stabilization or after the temporary BMPs are no longer needed. An adequate supply of appropriate spare materials shall be kept on site for maintenance of BMPs (BMP C150). Element #12 Manage the Project Accurate and timely BMP installation, monitoring, and maintenance, SWPPP preparation and up-dating as necessary, and record-keeping of construction SWPPP activities for the project, shall be under the supervision of a Certified Erosion and Sediment Control Lead (BMP C150 and BMP C160). To the extent possible, work shall be schedule to take advantage of normal seasonal dry weather conditions (BMP C162). Element #13 Protect Low Impact Development BMPs Stormwater control facilities shall be protected from sedimentation and other harmful processes. Silt fence (BMP C233), wattles (BMP C235), oil absorbent RECEIVED BY DCD 11/1/21 fabric catch basin inlet bags, and/or other appropriate BMPs must be used as necessary to protect stormwater facilities. Minimum Requirement #3 Source Control of Pollution All known, available and reasonable source control BMPs must be applied to this project to prevent stormwater from coming into contact with pollutants. Source control BMPs must be selected, designed, and maintained according to the 2019 SWMMWW. Construction-related pollution control is addressed above under Minimum Requirement #2, Element #9 above. Dust control may be achieved by sprinkling dry soils with water, but not to the point that the dust control water creates turbid runoff. Pollutant Source Specific BMP S411 BMPs for Landscaping and Lawn Management shall be implemented per the SWMMWW and appendices in this report. Minimum Requirement #4 Preservation of Natural Drainage Systems and Outfalls There are no natural drainage systems or outfalls on this site. The primary mechanism of runoff is sheet flow through the lot, and native infiltration. Minimum Requirement #5 Onsite Stormwater Management This parcel is in a sub-basin which discharges into a salt water body making it flow control exempt. List #3 will be followed to meet this minimum requirement. For lawn and landscaped areas BMP T5.13, Post-Construction Soil Quality and Depth will be applied to disturbed areas which will not be converted into impervious surface. An SWMMWW will be placed throughout the lawn area and other disturbed areas by amending the existing soil with imported compost material. Roof runoff will be collected in downspouts and routed to the designed infiltration system designed per SWMMWW BMP T5.10. Driveway runoff will be collected in a channel drain and routed to the infiltration system. The site layout does not allow for dispersion of the driveway in the front yard area of the residence. Dispersion in the rear of the residence will potentially flow into the septic system area. The Infiltration system has been sized to handle the added area of the driveway and will limit potentially negative effects of the septic system and neighboring parcels downstream. Minimum Requirement #6 Runoff Treatment This project results in less than 5,000 sf of pollution-generating hard surface, therefore a runoff treatment BMP is not required. RECEIVED BY DCD 11/1/21 Minimum Requirement #7 Flow Control This project results in less than 10,000 sf of effective impervious surface, therefore additional flow control analysis is not required. Minimum Requirement #8 Wetlands Protection No known wetlands exist on the site. Minimum Requirement #9 Operation and Maintenance An operations and maintenance manual for on-site stormwater facilities can be found in Appendix III. 4.0 THE LIMITATIONS OF OUR INVESTIGATION AND FINDINGS The observations and conclusions of this report apply only to the subject property and they are not transferable to nearby or adjoining property. This report was prepared for Andrew Reed & Marilyn Meyer and may be used by others only with permission. United Engineering, Inc. warrants this report was conscientiously prepared in accordance with the practice of professional civil engineering. No other warranty, either express nor implied, is provided. Respectfully, Zachary N Slota, P.E. Principal Engineer RECEIVED BY DCD 11/1/21 RECEIVED BY DCD 11/1/21 RECEIVED BY DCD 11/1/21 - - - - RECEIVED BY DCD 11/1/21 RECEIVED BY DCD 11/1/21 - RECEIVED BY DCD 11/1/21 Worksheet A1 Medium & Large Project Report structures roads Complete the following: RECEIVED BY DCD 11/1/21 Worksheet A1 Medium & Large Project Report RECEIVED BY DCD 11/1/21 Worksheet A1 Medium & Large Project Report Engineering RECEIVED BY DCD 11/1/21 Worksheet A1 Medium & Large Project Report LIST #1 LIST #1 LIST #3 RECEIVED BY DCD 11/1/21 Worksheet A1 Medium & Large Project Report LIST # 3 Roof * Other Hard Surface areas * RECEIVED BY DCD 11/1/21 Worksheet B1 Choose any of the following that apply: Choose one of the following: RECEIVED BY DCD 11/1/21 Worksheet B1 This element does not apply to my project because (check any that apply): Select one of the two statements applicable to the project. Select one of the three statements applicable to the project. This element does not apply to my project because: RECEIVED BY DCD 11/1/21 Worksheet B1 Select one of the two statements applicable to the project. Select one of the three statements applicable to the project. RECEIVED BY DCD 11/1/21 Worksheet B1 Select one of the three statements applicable to the project. This element does not apply to my project because (circle any that apply - RECEIVED BY DCD 11/1/21 Worksheet B1 Select one of the two statements applicable to the project. Describe the steps you will take: RECEIVED BY DCD 11/1/21 Worksheet B1 RECEIVED BY DCD 11/1/21 1 Worksheet C What’s the best option for your site? Roofs BMP and Applicable Lists Reason why the BMP will not work on site.Additional Comments If needed Lawn and Landscaped Areas BMP and Applicable Lists Reason why the BMP will not work on site.Additional Comments If needed Minimum Requirement #5 (On-Site Stormwater Management) The following tables summarize the criteria that can be used to justify why you cannot use various stormwater management best management practices (BMPs) for consideration for Minimum Requirement #5. This information is also included under the detailed descriptions of each BMP in the Department of Ecology’s Stormwater Management Manual for Western Washington (SWMMWW [2014]). Where any inconsistencies or lack of clarity exists, the requirements in the main text of the SWMMWW shall be applied. HOW TO USE: Evaluate the feasibility of the BMPs in priority order based on Worksheet A1 page 5 (List #1) or 6 (List #3) or Worksheet L for Large Projects (List #2). Only one criterion needs to be selected for a BMP before evaluating the next BMP on the list. Full Dispersion BMP T5.30, SWMMWW Volume V, Section 5.3 A 65 to 10 ratio of forested or native vegetation area to impervious area cannot be achieved. surface) and protected by easement cannot be achieved. Siting and design criteria cannot be achieved on site. There is an alternatie septic system on this lot or an adjacent treatment unit). Therefore, there is not at least 3 feet or seasonal high groundwater table or other impermeable layer. There is not at least 1 foot or more of permeable soil from high groundwater table or other impermeable layer. Downspout Full BMP T5.10A, SWMMWW Volume III, Section 3.1.1 Post-construction Soil Quality and Depth (BMP T5.13 SWMMWW Volume V, Section 5.3) Lawn and landscape area is on till slopes greater than 33 percent. Siting and design criteria cannot be achieved on site. List #1, #2 and #3 List #1 and #2 List #1, #2 and #3 None of the above boxes are checked. This is the BMP that must be used for lawn and landscaped areas. On Worksheet A1, indicate that this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the project. If none, STOP. None of the above boxes are checked. This is the BMP that must be used for roofs. On Worksheet A1, indicate that this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the project. If none, STOP. RECEIVED BY DCD 11/1/21 2 Worksheet C What’s the best option for your site? Roofs (cont.) BMP and Applicable Lists Reason why the BMP will not work on site.Additional Comments If needed Where professional geotechnical evaluation recommends Within an area whose ground water drains into an erosion hazard, or landslide hazard area. Where the only area available for siting would threaten the Where the only area available for siting does not allow for private storm sewer system. Where there is a lack of usable space for bioretention areas Note: Criteria with setback distances are as measured from the bottom edge of the bioretention soil mix. Citation of any of the following infeasibility criteria must be recommendation from an appropriate licensed professional (e.g., engineer, geologist, hydrogeologist): such as bulkheads. basements. Bioretention or Rain Gardens BMP T7.30 or T5.14A SWMMWW Volume V, Section 7.4 List #1 (both) and List #2 (bioretention only) Downspout Full (cont.) BMP T5.10A, SWMMWW Volume Slopes steeper than 25% or less than 200’ from slope steeper than 40%. Siting and design criteria cannot be achieved on site. None of the above boxes are checked. This is the BMP that must be used for roofs. On Worksheet A1, indicate that this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the project. If none, STOP. RECEIVED BY DCD 11/1/21 6 Worksheet C What’s the best option for your site? Other Hard Surfaces BMP and Applicable Lists Reason why the BMP will not work on site.Additional Comments If needed Where professional geotechnical evaluation recommends Within an area whose ground water drains into an erosion hazard, or landslide hazard area. pavement area would compromise adjacent impervious pavements. area would threaten existing below grade basements. such as bulkheads. Down slope of steep, erosion prone areas that are likely to deliver sediment to the area of pervious pavement. saturated. Excessively steep slopes where water within the aggregate base layer or at the subgrade surface cannot be controlled by detention structures and may cause erosion and structural Citation of any of the following infeasibility criteria must be recommendation from an appropriate licensed professional (e.g., engineer, geologist, hydrogeologist): Permeable Pavement BMP T5.15, SWMMWW Volume V, Section 5.3 List #1 and #2 Full Dispersion BMP T5.30 SWMMWW Volume V, Section 5.3 A 65 to 10 ratio of forested or native vegetation area to impervious area cannot be achieved. surface) cannot be achieved. Siting and design criteria cannot be achieved on site. List #1 and #2 None of the above boxes are checked. This is the BMP that must be used for hard surfaces. On Worksheet A1, indicate that this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the project. If none, STOP. * Note that Raingardens may be used in lieu of permeable pavement if subject to List #1. RECEIVED BY DCD 11/1/21 13 Worksheet C What’s the best option for your site? Other Hard Surfaces (cont.) BMP and Applicable Lists Reason why the BMP will not work on site.Additional Comments If needed Sheet Flow Dispersion BMP T5.12, SWMMWW Volume V, Section 5.3 Area to be dispersed (e.g., driveway, patio) cannot be graded to have less than a 15 percent slope. contributing surface cannot be achieved. For variably sloped cannot be achieved. Siting and design criteria cannot be achieved on site. Concentrated Flow Dispersion BMP T5.11, SWMMWW Volume V, Section 5.3 sq. ft. of drainage area followed with applicable setbacks cannot be achieved. More than 700 sq. ft. drainage area drains to any dispersion device. Siting and design criteria cannot be achieved on site. List #1, #2 and #3 List #1, #2 and #3 None of the above boxes are checked. This is the BMP that must be used for hard surfaces. On Worksheet A1, indicate that this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the project. If none, STOP. None of the above boxes are checked. This is the BMP that must be used for hard surfaces. On Worksheet A1, indicate that this will be the BMP used. CONTINUE to complete the form for other surface types applicable to the project. If none, STOP. RECEIVED BY DCD 11/1/21 RECEIVED BY DCD 11/1/21