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HomeMy WebLinkAboutBLD2021-00545-05- Stormwaterstormwater calc worksheet QR code – REV. 5/31/2019 page 1 of 2 DEPARTMENT OF COMMUNITY DEVELOPMENT 621 Sheridan Street, Port Townsend, WA 98368 Tel: 360.379.4450 | Fax: 360.379.4451 Web: www.co.jefferson.wa.us/communitydevelopment E-mail: dcd@co.jefferson.wa.us STORMWATER CALCULATION WORKSHEET PARCEL # PROJECT/APPLICANT NAME: DETERMINING STORMWATER MANAGEMENT REQUIREMENTS: This stormwater calculation worksheet should be completed first to classify the proposal as “small,” “medium,” or “large.” The size determines whether a Stormwater Site Plan is re quired in conjunction with a stand-alone stormwater management permit application, building permit application, or other land use approval application that involves stormwater review. The basic information will also be helpful for completing a Stormwater Site Plan, if required. Land-disturbing activity is any activity that results in movement of earth, or a change in the existing soil cover (both vegetative and non-vegetative) and/or the existing soil topography. Land disturbing activities include, but are not limited to clearing, grading, filling, excavation, and compaction associated with stabilization of structures and road construction. Native vegetation is vegetation comprised of plant species, other than noxious weeds, which reasonably could have been expected to naturally occur on the site. Examples include species such as Douglas fir, western hemlock, western red cedar, alder, big-leaf maple, and vine maple; shrubs such as willow, elderberry, salmonberry, and salal; herbaceous plants such as sword fern, foam flower, and fireweed. LAND DISTURBING ACTIVITY, CONVERSION OF NATIVE VEGETATION, AND VOLUME OF CUT/FILL Calculate the total area to be cleared, graded, filled, Answer the following two questions related to excavated, and/or compacted for proposed development conversion of native vegetation: project. Include in this calculation the area to be cleared for: Does the project convert ¾ acres or more of Construction site for structures _________________ sq/ft native vegetation to lawn or landscaped areas? Drainfield, septic tank, etc. ____________________ sq/ft Circle: Yes No Well, utilities, etc. ___________________________ sq/ft Does the project convert 2 ½ acres or more of native vegetation to pasture? Driveway, parking, roads, etc. ___________________sq/ft Circle: Yes No Lawn, landscaping, etc. ______________________ sq/ft Other compacted surface, etc. _________________ sq/ft Indicate Total Volumes of Proposed: (Includes BMP T5.13 Fill Volume) Temporary construction area ______________ sq/ft Total Land Disturbance ____________________ sq/ft Cut __________ Fill __________ (cu/yd) PARCEL SIZE (I.E., SITE) Size of parcel _________ acres An acre contains 43,560 square feet. Multiply the acreage by this figure. Size of parcel in square feet _________________ sq/ft Scan the QR code to access the digital form John GriffinChris Gorrell & Sydney Johnson-Gorrell REVISED 10/26/22 995600012 .27+/- 11,761 3,590+/- Existing 150+/- 700+/- 2,000 +/- 500+/- 6,940+/-300 +/-67 +/- stormwater calc worksheet QR code – REV. 5/31/2019 page 2 of 2 ~ Applicants for “small” projects must comply only with Minimum Requirement #2—Construction Stormwater Pollution Prevention. Please submit the Small Project Certification (Worksheet “s). The proponent is responsible for employing the 12 Elements to control erosion and prevent sediment and other pollutants from leaving the site during the construction phase of the project. Pick up the Construction Stormwater Pollution Prevention (SWPPP) Best Management Practices (BMPs) Fact Sheet. ~ Applicants for “medium” projects—those that must meet only Minimum Requirements #1 through #5 must submit Worksheet A1 and B1, a stormwater site plan and a construction stormwater pollution prevention site plan (See Reference A1A and B1A for guidance).). ~ “Large” projects—those that must meet all 9 Minimum Requirements— must submit Worksheet A1 and B1, a stormwater site plan and a construction stormwater pollution prevention site plan (See Reference A1A and B1A for guidance). Large projects also may require engineering. See Worksheet L to determine additional large project requirements. APPLICANT SIGNATURE By signing the Stormwater Calculation Worksheet, I as the applicant/owner attest that the information provided herein is true and correct to the best of my knowledge. I also certify that this application is being made with the full knowledge and consent of all owners of the affected property. ________________________________________ ________________________ (LANDOWNER OR AUTHORIZED REPRESENTATIVE SIGNATURE) (DATE) STORMWATER CALCULATIONS – IMPERVIOUS SURFACE Impervious surface is a hard surface that either prevents or slows the entry of water into the soil as under natural conditions prior to development. A hard surface area which causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development. Common impervious surfaces include, but are not limited to roof tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphalt paving, gravel roads, packed earthen materials, and oiled, macadam or other surfaces which similarly impede the natural infiltration of stormwater. NEW EXISTING Structures (all roof area) _________________sq/ft Structures (all roof area) _________________sq/ft Sidewalks _________________sq/ft Sidewalks _________________sq/ft Patios _________________sq/ft Patios _________________sq/ft Solid Decks _________________sq/ft Solid Decks _________________sq/ft (without infiltration below) (without infiltration below) Driveway, parking, roads, etc _______________sq/ft Driveway, parking, roads, etc _______________sq/ft Other _________________sq/ft Other _________________sq/ft Total New _________________sq/ft Total Existing _________________sq/ft TOTAL NEW + TOTAL EXISTING* _________________sq/ft *This amount will be used to check total lot coverage. DEVELOPMENT v. REDEVELOPMENT Divide the total existing impervious surface above by the size of the parcel and convert to a percentage. ____________% Does the site have > 35% or more existing impervious surface? The proposal is considered new development. Answer questions in Figure 2.4.1 Flow Chart for New Development to determine project size (next page). The proposal is considered redevelopment Answer questions in Figure 2.4.2. Flow Chart for Redevelopment to determine project size (next page). yes no John Ulrigg Verified by PDFFiller 08/25/2021 REVISED 10/26/22 3,400 +/- 200 +/- 600+/- 1,104 +/- 680 +/- 4,880+/- 5,384 +/- 1,700 +/- 1,700 +/- 4,182+/- 5,384 +/- 0 8/27/2021 Start HERE! A guide to using stormwater forms Use the quantities reported in this worksheet to determine which minimum requirements apply to your project and what forms will be required using the “Flow Chart for Determining Minimum Requirements.” Step 1 Yes no All projects must read and complete the Stormwater Calculation Worksheet. Small Projects may submit the Worksheet S Small Project Certification sheet. Applicants who are able to sign the certification may STOP HERE. Submit the Stormwater Calculation Worksheet and Worksheet “S” with your appli- cation. No additional submittal is necessary. Step 2 Step 2.1 Step 2.1 Medium Projects must complete worksheets A1, B1, and C or equivalent. Large Projects refer to Worksheet L to determine applicable worksheets are required or if a state -licensed engineer must prepare the submittal. A Note on Engineered Stormwater Submittal: -Many applicants complete stormwater submittal forms independently without professional expertise. For example, full dispersion, if feasible on the site (See Worksheet C), is typically easiest to implement for many different surface types such as roof, driveway, patio etc. -Applicants may opt to submit an engineered stormwater plan even if it isn’t required. This option may be attractive to those who are unsure how some of the requirements will be achieved on the site.In some instances, engineering will be required. Certain Large projects must be engineered (See Worksheet L). Gathering information on infiltration feasibility may need an engineer ’s expertise. Or, sites with greater than 15% slopes may require applicants hire a geologist to recommend if a drainage method i s appropriate. Discharging directly to a marine water via tightline must be engineered. If you cannot do full dispersion on parcels larger than 5 acres, engineering is required. In other instances, site constraints will require an engineered design. -Jefferson County staff may assist by providing and/or explaining Department of Ecology Stormwater Management Manual The project requires or the applicant elects to submit an engineered stormwater plan. The plan is attached hereto with minimum requirement narrative, drawings, calculation, modeling output, construction pollution prevention plan, and site plan. Circle one: Step 3 If you answered YES above, STOP, no further submittal is required. Otherwise, proceed with the following steps. Complete Worksheet A1 Medium/Large Project Report and Stormwater Site Plan or equivalent. Step 3.1 Complete Worksheet C to determine which BMPs are possible and appropriate for your site. Circle the first BMP that is feasible (i.e. none of the infeasibility criteria is checked) for each surface type. Circle the corresponding BMP on Worksheet A1. Step 4 Complete Worksheet B1 Medium/Large Project Construction Pollution Prevention Plan and Worksheet B2 Construction Site Plan or equivalent. A Note on Commercial Projects: •Jefferson County Public Works (JCPW) reviews commercial projects and charges a review fee. JCPW may charge additional fees for any required inspections. •Any commercial projects proposing infiltration facilities may complete Worksheet E—Infiltration Test. Grain size analysis may be used instead of PIT. Commercial projects may elect to use BMP T5.10A and would not need a PIT, just a soil evaluation. •Any development for cottage industries may require a commercial public works review if full dispersion is infeasible. REVISED 10/26/22 This is a "large" project. Large projects refer to Worksheet L for submittal requirements. At a minimum, all large Project must submit Worksheet A1, B1, and C or equivalent. This is a "medium" project. Submit Worksheet A1,B1 and C or equivalent. Complete "Small" Project Certification Worksheet Project must follow Construction Pollution Prevention Fact Sheet Figure 2.4.1 Flow Chart for New Development REVISED 10/26/22 This is a "large" project. Large projects refer to Worksheet L for submittal requirements. At a minimum, all large Project must submit Worksheet A1, B1, and C or equivalent. Figure 2.4.2 Flow Chart for Redevelopment REVISED 10/26/22 construction Pollution Prevention Page 1 of 3 5/31/2019 DEPARTMENT OF COMMUNITY DEVELOPMENT 621 Sheridan Street, Port Townsend, WA 98368 Tel: 360.379.4450 | Fax: 360.379.4451 Web: www.co.jefferson.wa.us/communitydevelopment E-mail: dcd@co.jefferson.wa.us CONSTRUCTION STORMWATER POLLUTION PREVENTION Best Management Practices (BMPs) Fact Sheet For “small” projects (as determined through the Stormwater Calculation Worksheet), submit Worksheet “S” Small Project Certification. Additionally, the applicant shall consider the twelve Construction Stormwater Pollution Prevention elements and implement applicable BMPs. A set of useful BMPs for typical rural residential construction is attached. There is no additional submittal required as part of the permit application. For “medium” and “large” projects, applicants must submit a Construction Stormwater Pollution Prevention Plan (SWPPP) and a Stormwater Site Plan (applicants may use Worksheet B1 or equivalent). The following twelve elements must be considered for Construction Stormwater Pollution Prevention before and during the construction phase of the project: 1. Mark Clearing Limits 7. Protect Drain Inlets 2. Establish Construction Access 8. Stabilize Channels and Outlets 3. Control Flow Rates 9. Control Pollutants 4. Install Sediment Controls 10. Control De-Watering 5. Stabilize Soils 11. Maintain Best Management Practices 6. Protect Slopes 12. Manage The Project Each of the twelve elements is described in more detail below: 1. Mark Clearing Limits By minimizing the limits of clearing on the site, a builder can minimize stormwater runoff and provide effective control of pollution. 2. Establish Construction Access Much of the sediment that leaves a construction site does so on the wheels of delivery and construction vehicles that drive off a project site. Construction access must be limited to a single location and a properly constructed Stabilized Construction Entrance (BMP C105) should be included on the site. 3. Control Flow Rates Stormwater that leaves a project site unimpeded may exceed the capacity of the existing stormwater control facilities downstream and may contain sediment that may be deposited as the velocity of the runoff decreases. Stormwater protection on a construction site should include measures to control the flow rate of runoff from the site. This can be done by installing a Sediment Trap (BMP C240) or other measure that will impede the flow of water off a construction site. 4. Install Sediment Controls In addition to limiting the rate of stormwater flow off a construction site, measures should be put in place to treat the runoff and remove sediment. Limiting of the cleared area (Element 1) will assist in this effort, but there will be exposed soils that may move with the runoff. Suggested BMPs for controlling sediment include Straw Wattles (BMPC235), Brush Barrier (BMP C231), Gravel Filter Berm (BMP C232), and Silt Fence (BMP C233). Installation of a Sediment Trap (Element 3) is an additional sediment control feature. REVISED 10/26/22 construction Pollution Prevention Page 2 of 3 5/31/2019 5. Stabilize Soils An additional measure that can minimize sediment transport in runoff is to stabilize soils on the site with mulch or some other covering. This will limit the amount of soil that is exposed to rainfall, thus limiting the sediment that could potentially leave the site. BMPs that could be used for this include Mulching (BMP C121), Nets and Blankets (BMP C122), and Plastic Covering (BMP C123). During periods of dry weather dust can become a problem and sediment could be transported from the site in high winds. BMP C140 Dust Control should be followed to limit loss of soils in windy conditions. 6. Protect Slopes If the cleared area includes slopes of 3:1 (Horizontal: Vertical) or steeper, the slopes should be protected to limit runoff. If the slopes are not protected, rills and gullies may form, transporting sediment to the lower elevations and potentially off the construction site. The slopes should be graded to minimize erosion and runoff at the downstream end of the slopes, and runoff should be collected and treated. The following BMPs could be used Surface Roughening (BMP C130), Interceptor Dike and Swale (BMP C200), and Pipe Slope Drains (BMP C204). 7. Protect Drain Inlets Runoff from urban construction sites often discharges into existing stormwater collection systems. Water enters the collection system through drain inlets. If there are drain inlets downstream of a construction site, they should be protected using BMP C220 Storm Drain Inlet Protection. 8. Stabilize Channels and Outlets Any temporary on-site channels or ditches that are used to control runoff should be stabilized to prevent erosion in the channel. BMP C202 Channel Lining and BMP C209 Outlet Protection should be used. 9. Control Pollutants The best way to control pollution is to limit the source of pollution. Construction debris should be maintained in a safe location. Vehicle maintenance on the construction site should be minimized and any spill should be promptly cleaned up. Concrete spillage should be kept to a minimum and cleaning of the concrete trucks after they have unloaded should be done in an area that will not drain off site (see BMP C151 Concrete Handling). 10. Control Dewatering In some cases, excavation for the foundation or below ground structures will encounter ground water. This water must be removed (dewatered) from the excavation. Discharge of this ground water must be treated in a manner that will not cause damage downstream due to flow rates or added pollution. There are no specific BMP identified for this activity, but the water should be handled with care to assure that soils or other pollutants are not added to this flow. 11. Maintain BMPs Installation of the appropriate BMPs is not adequate to completely control stormwater runoff. The BMPs that have been installed on the project must be inspected and maintained during the duration of the construction project. In addition, the temporary controls that were installed for construction should be removed within 30 days of completion of the work. Typically, once construction has been completed, the temporary facilities are not maintained, and by removing the facilities, it will ensure that these won’t f ail and discharge water or sediment that had been previously trapped or contained. 12. Manage the Project Management of a project has four aspects: 1. Phasing construction to prevent transportation of runoff and sediment, 2. Limiting the work during seasons where large amounts of rainfall could be anticipated, 3. Coordination with Utilities and other Contractors, and 4. Inspection and Monitoring. All of these for aspects are important and must be followed to ensure a project that will have minimal impact on the environment. Volume II of the Manual contains additional BMPs that could be used on-site. The applicant is encouraged to review the Manual to see if other BMPs may be applicable to, or more useful on, a particular site. REVISED 10/26/22 construction Pollution Prevention Page 3 of 3 5/31/2019 Best Management Practices from 2014 Ecology Stormwater Management Manual The following BMPs for Construction Stormwater Pollution Prevention are sediment and erosion control measures for the construction phase of typical rural residential development. Some projects may not require implementation of all of these BMPs; others may require additional measures not listed here. Click on the BMP to learn more about each BMP’s purpose and design: II-4.1 Source Control BMPs BMP C101: Preserving Natural Vegetation BMP C102: Buffer Zones BMP C103: High Visibility Fence BMP C105: Stabilized Construction Entrance / Exit BMP C106: Wheel Wash BMP C107: Construction Road/Parking Area Stabilization BMP C120: Temporary and Permanent Seeding BMP C121: Mulching BMP C122: Nets and Blankets BMP C123: Plastic Covering BMP C124: Sodding BMP C125: Topsoiling / Composting BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection BMP C130: Surface Roughening BMP C131: Gradient Terraces BMP C140: Dust Control BMP C150: Materials on Hand BMP C151: Concrete Handling BMP C152: Sawcutting and Surfacing Pollution Prevention BMP C153: Material Delivery, Storage and Containment BMP C154: Concrete Washout Area BMP C160: Certified Erosion and Sediment Control Lead BMP C162: Scheduling II-4.2 Runoff Conveyance and Treatment BMPs BMP C200: Interceptor Dike and Swale BMP C201: Grass-Lined Channels BMP C202: Channel Lining BMP C203: Water Bars BMP C204: Pipe Slope Drains BMP C205: Subsurface Drains BMP C206: Level Spreader BMP C207: Check Dams BMP C208: Triangular Silt Dike (TSD) (Geotextile-Encased Check Dam) BMP C209: Outlet Protection BMP C220: Storm Drain Inlet Protection BMP C231: Brush Barrier BMP C232: Gravel Filter Berm BMP C233: Silt Fence BMP C234: Vegetated Strip BMP C235: Wattles BMP C236: Vegetative Filtration BMP C240: Sediment Trap BMP C241: Temporary Sediment Pond BMP C251: Construction Stormwater Filtration REVISED 10/26/22 Worksheet A1 Medium & Large Project Report Submit a site plan demonstrating the project. Refer to REFERENCE A1A for examples of Best Management Practices (BMP’s) that you can use. Remember that all site plans submitted for the project must be consistent and accurate. page 1 of 6 Minimum Requirement # 1 : Preparation of Stormwater Site Plan Describe both existing and proposed site conditions for the following items as applicable in the space below each bullet point. Attach additional pages if needed. • structures • • roads • • utility locations • • wellhead locations • • septic drainfield locations and type • • stormwater run-on from neighboring properties • • expected excavation depths and volumes • • expected work to be done in Right-of-Way (ROW) Complete the following: Minimum Requirement # 2 : Construction Stormwater Pollution Prevention Plan (SWPPP) A SWPPP is designed to be a stand-alone document that addresses construction stormwater management concerns. This document is required to be kept by the contractor performing the work at the jobsite for reference and update during the life of the project. Construction BMP’s must be indicated on the stormwater site plan. REFERENCE B1A includes diagrams of common BMP’s that may be used on the site plan. My completed SWPPP (WORKSHEET B1 or equivalent) is included in this application packet! Minimum Requirement # 3 : Source Control of Pollution (not construction related) The intent of source control is to prevent stormwater from coming in contact with pollutants. Source control BMPs can be operational or structural in nature. A roof over a material storage area is an example of a structural source control BMP. Washing your vehicle on the lawn rather than in the street is an operational BMP. This requirement is generally not applicable to Single Family Residences (SFRs); however, ways to minimize pollution from moving downstream should be considered during the design phase of every project. Specifications on standard source control BMPs that are applicable to various commercial and industrial-type facilities can be found in Volume IV of the 2014 Stormwater Management Manual for Western Washington (SWMMWW) (continued on page 2). NA Existing conventional, permit # SEP93-0490. Lasted inspected 10/27/2020 MIn if any inpact on subject property. 30" Max in some locations - 102 cu/yds OWS (sewer) REVISED 10/26/22 Single Family Residence, 2,382 SQFT, with attached garage, 768 SQFT New Concert driveway, sidewalk, Approx 1,100 SQFT As shown on site plan road approach - concert Worksheet A1 Medium & Large Project Report page 2 of 6 Check one of the following boxes that best represents your project with regards to MR #3. Minimum Requirement # 3 : Source Control of Pollution (continued from page 1) My project is a Single Family Residence (SFR) and after considering operational and structural measures to prevent stormwater from coming in contact with pollutants, I have: determined this MR to not be applicable. made appropriate adjustments to my project. My project is not a SFR and after reviewing Vol. IV of the SWMMWW, I have determined that this MR is not applicable because of the following reason: My project is not a SFR and after reviewing Vol. IV of the SWMMWW, I have determined that the following source control BMPs are applicable to my project and shall be incorporated into the project design and operation. REVISED 10/26/22 Worksheet A1 Medium & Large Project Report Minimum Requirement # 4 : Preservation of Natural Drainage Systems Creating new drainage patterns results in more site disturbance and more potential for erosion and sedimentation during and after construction. to the maximum extent possible, proponents must 1) maintain the natural on-site drainage pattern and concentrated discharge location at the downstream property boundary, and 2) prevent erosion at and downstream of the discharge location. NOTE: All outfalls require energy dissipation. See Table 4.5.1 in Vol. V of the SWMMWW for minimum design standards for rock protection at outfalls. Choose the option below that best describes your project: page 3 of 6 The project site does not currently have any intermittent, seasonal, or continuous concentrated water moving across any part of the property and the proposed improvements to the site will not create new concentrated flow paths or not discharging to existing drainage systems. The project site has existing concentrated flow drainage systems and outfalls. (NOTE: These items must be graphically shown on the Site Plan or equivalent, to include: type, slope, dimensions, channel lining, direction of flow, buffer, etc.) Select below how it will be addressed. This project will not alter the existing drainage system in any way. If the existing outfall(s) show signs of erosion and scour, energy dissipation measures will be installed or improved upon. Construction activity of any kind will not occur within at least 10 ft. of the edge of the channelized flow. BMP C102: BUFFER ZONES will be implemented during the life of the project to include visible flagging or other demarcation technique. The existing concentrated drainage system traversing the property will be impacted as part of this project, as described in the space below and shown on the site plans. Engineering calculations are required that show the altered drainage design can accommodate the existing flows and the added runoff contributed by the project. REVISED 10/26/22 Worksheet A1 Medium & Large Project Report page 4 of 6 My project is a large project. Refer to Worksheet L. If full dispersion isn’t feasible, use LIST #1 (List #2 and List #1 are the same except raingardens are not permitted in List #2). Minimum Requirement # 5 : On-site Stormwater Management On-site stormwater management techniques shall be implemented where possible to accommodate the permanently added stormwater runoff being generated by development. Some on-site stormwater management techniques provide better stormwater detention and treatment than others; however, they are not always appropriate for use due to varying individual site characteristics. Therefore, techniques are presented to applicants on the next pages in a hierarchical order and shall be considered for use in the order listed. The first technique on the list that is determined to be possible shall be implemented. See WORKSHEET C to determine which techniques are feasible. Runoff from developments occurring in drainage basins that drain directly or indirectly to a creek require a higher level of stormwater management, thus, the techniques are presented in three lists below: All properties will be in one of these three categories: My project is located in a drainage subbasin that drains to directly or indirectly to freshwater. PROCEED to Page 5 to use LIST #1. My Project will discharge to a subasin draining to salt water, Dosewallips River, or Hoh River. PROCEED to Page 6 to use LIST #3. REVISED 10/26/22 Worksheet A1 Medium & Large Project Report My project does not have disturbed soils not covered by impervious surfaces. 1. Post-Construction Soil Quality and Depth Disturbed soils shall be amended (BMP T5.13: ). My project does not have Roof areas. 1. Full Dispersion (BMP T5.30) OR Downspout Full Infiltration (BMP T5.10A) 2. Rain Garden (LARGE PROJECTS CANNOT USE) (BMP T5.14A) 3. Downspout Dispersion System (BMP T5.10B) 4. Perforated Stub-Out Connection (BMP T5.10) 5. Each BMP above is infeasible, see WORKSHEET C. STOP. COMPLETE AND SUBMIT WORKSHEET B1. NO OTHER INFORMATION REQUIRED AT THIS TIME. My project does not have Other Hard Surface areas 1. Full dispersion (BMP T5.30) 2. Permeable Pavement (BMP T5.15) OR Rain Garden (LARGE PROJECTS CANNOT USE) (BMP T5.14A) Minimum Requirement # 5 : On-site Stormwater Management (continued) LIST # 1 : Applicable to projects that directly or indirectly drain to freshwater. INSTRUCTIONS: Check the first option that will work for Each Category Below: For each category below, proceed through the LIST from top down. Use WORKSHEET C to determine if the BMP can be used. If number 1 on the list is not possible, document why on WORKSHEET C and move down to number 2, and so on. Category A: Lawn and Landscape Areas Category B: Roofs Category C: Other Hard Surfaces, e.g. gravel and paved driveways, solid decks and patios without infiltration below 3. Sheet Flow Dispersion (BMP T5.12) OR Concentrated Flow Dispersion (BMP T5.11) 4. Each item above is infeasible, see WORKSHEET C. STOP. COMPLETE AND SUBMIT WORKSHEET B1. NO OTHER INFORMATION REQUIRED AT THIS TIME.REVISED 10/26/22 Worksheet B1 Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan) Submit a site plan demonstrating the construction protective measures or best management practices that will be used for the project during the construction phase. Refer to REFERENCE B1A for examples of Construction Best Management Practices (BMP’s) that you can use. The activities that take place during construction are the highest risk for stormwater problems such as erosion and sediment control (you may need to provide an additional site plan with greater detail for stormwater features. If so, make sure it is consistent with the primary site plan. Remember that all site plans submitted for the project must be consistent and accurate). page 1 of 6 Element 1: Preserve Vegetation / Mark Clearing Limits The goal of this element is to preserve native vegetation and to clearly show the limits of disturbance. Choose any of the following that apply: The site was cleared as part of clearing activity that is subject to an enforcement action and will be re-vegetated. Restoration may be necessary to comply with Critical Area Regulations or stormwater requirements. Buffer Zones- BMP C102 may apply if Critical Areas exist on-site and buffer zones shall be protected. The perimeter of the area to be cleared shall be marked prior to clearing operation with visible flagging, orange plastic barrier fencing and/or orange silt fencing as shown on the SWPPP site plan. Vehicles will only be allowed in the areas to be graded, so no compaction of the undeveloped areas will occur. If this option is selected check the BMPS you will use below: C101 Preserving Natural Vegetation C102 Buffer Zones C103 High Visibility Fence It is necessary to disturb the entire property during this project due to existing site conditions, property constraints, and proposed design. I understand that all disturbed land not covered by hard surface at the end of the project is subject to soil amendment requirements per BMP T5.13 Post-Construction Soil Quality and Depth. Element 2: Construction Access The goal of this element is to provide a stabilized construction entrance/exit to prevent or reduce or sediment track out. Choose one of the following: The driveway to the construction area already exists and will be used for construction access. All equipment and vehicles will be restricted to staying on that existing impervious surface. If sediment is tracked off site, the road- way will be cleaned thoroughly at the end of each day. A stabilized construction entrance will be installed prior to any vehicles entering the site, at the location shown on the SWPPP site plan. If sediment is tracked off site, the roadway will be cleaned thoroughly at the end of each day. If this option is selected check the BMPS you will use below: C105 Stabilized Construction Entrance / Exit C106 Wheel Wa sh C107 Construction Road / Parking Area Stabilization REVISED 10/26/22 Worksheet B1 Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan) Element 3: Control Flow Rates The goal of this element is to construct retention or detention facilities when necessary to protect properties and waterways downstream of development sites from erosion and turbid discharges. This element does not apply to my project because (check any that apply): page 2 of 6 Site is mildly sloped (<5%), There are no individually sloped sections greater than 10%, The bulk of the project is scheduled to occur during dry season (May 1-Sept 30) Sediment control BMPs shall be placed at the locations shown on the SWPPP Site Plan. If this option is selected check the BMPS you will use below: C233 Silt FenceC231 Brush Barrier C234 Vegetated Strip C232 Gravel Filter Berm C235 Wattles Element 4: Sediment Control The goal of this element is to construct sediment control BMPs that minimize sediment discharges from the site. Select one of the two statements applicable to the project. The site has already been stabilized and re-vegetated. Element 5: Stabilize Soils • Soil stockpiles will be located within the disturbed area shown on the SWPPP Site Plan. • Soil excavated for the foundation will be backfilled against the foundation and graded to drain away from the building. • No soils shall remain exposed and unworked for more than 7 days from May 1 to September 30 or more than 2 days from October 1 to April 30. • Once the disturbed landscape areas are graded, the grass areas will be amended. • All stockpiles will be covered with plastic or burlap if left unworked. The goal of this element is to stabilize exposed and unworked soils by implementing erosion control BMPs. Select one of the three statements applicable to the project. My project will ensure the following: This element does not apply to my project because: My project must implement specific BMP’s to ensure compliance. (Check BMP’s you will use on the next page). REVISED 10/26/22 Worksheet B1 Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan) page 3 of 6 C120 Temporary & Permanent Seeding C123 Plastic CoveringC121 Mulching C124 SoddingC122 Nets & Blankets C125 Topsoil / Composting C131 Gradient Terraces C140 Dust Control C235 Wattles Element 6: Protect Slopes The goal of this element is to design and construct cut-and-fill slopes in a manner to minimize erosion. Select one of the two statements applicable to the project. No cut slopes over 4 feet high or slopes steeper than 2 feet horizontal to 1 foot vertical, and no fill slopes over 4 feet high will exceed 3 feet horizontal to 1 foot vertical. Therefore, there is no requirement for additional engineered slope protection. The above checkbox is not checked. My submittal is designed by a licensed geologist to protect slopes. Based on the licensed professionals recommendation (please attach their evaluation), the following BMP’s will be used: C120 Temporary & Permanent Seeding C204 Pipe Slope Drains C205 Subsurface Drains C206 Level Spreader C207 Check Dams C208 Triangular Silt Dike (Geotextile-Encased Check Dam) Catch basins on the site or immediately off site in the right-of-way are shown on the SWPPP Site Plan. Storm drain inlet protection shall be installed. If this option is selected check the BMPS you will use below: C220 Storm Drain Inlet Protection The site has open ditches in the right-of-way or private road right-of-way. There are no catch basins on or near the site. Element 7: Protect Permanent Drain Inlets The goal of this element is to protect storm drain inlets during construction to prevent stormwater runoff from entering the conveyance system without being filtered or treated. Select one of the three statements applicable to the project. REVISED 10/26/22 Worksheet B1 Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan) A wattle shall be placed at the end of the swale to prevent erosion at the outlet of the swale. If this option is selected check the BMPS you will use below: C202 Channel Lining C207 Check Dams C235 WattlesC209 Outlet Protection page 4 of 6 Element 8: Stabilize Channels and Outlets The goal of this element is to design, construct, and stabilize on-site conveyance channels to prevent erosion from entering existing stormwater outfalls and conveyance systems. Select one of the three statements applicable to the project. Construction will occur during the dry weather. No storm drainage channels or ditches shall be constructed either temporary or permanent. There are no existing or proposed stormwater conveyance channels on the project site. C151 Concrete Handling C152 Sawcutting and Surfacing Pollution Prevention C153 Material Delivery, Storage, and Containment C154 Concrete Washout Area If one or more of the checkboxes above are unchecked. Any and all pollutants, chemicals, liquid products and other materials that have the potential to pose a threat to human health or the environment will be covered, contained, and protected from vandalism. All such products shall be kept under cover in a secure location on-site. Concrete handling shall follow BMP C151 C154. If this option is selected check the BMPS you will use below: Element 9: Control Pollutants This element does not apply to my project because (circle any that apply - If any box is unchecked this element applies. The goal of this element is to design, install, implement and maintain BMPs to minimize the discharge of pollutants from material storage areas, fuel handling, equipment cleaning, management of waste materials, etc. There will be no concrete work, There will be no sawcutting work, There will be no hazardous materials on-site, There will be no fertilizer or pesticide application, There will be no heavy equipment associated with this project, There will be no pressure washing, equipment maintenance or dewatering REVISED 10/26/22 Worksheet B1 Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan) C203 Water Bars C236 Vegetated Filtration C206 Level Spreader Element 10: Control De-watering No dewatering of the site is anticipated. Dewatering of the site is anticipated. If this option is selected check the BMPS you will use below: page 5 of 6 Select one of the two statements applicable to the project. The goal of this element is to handle turbid or contaminated water from dewatering (removal of water) separately from stormwater. Describe the steps you will take: Element 12: Manage the Project The SWPPP will be implemented at all times. If applicable to the project, erosion control BMPs will be implemented in the following sequence: 1. Mark clearing limits 2. Install stabilized construction entrance 3. Install protection for existing drainage systems and permanent drain inlets 4. Establish staging areas for storage and handling polluted material and BMPs 5. Install sediment control BMPs 6. Grade and install stabilization measures for disturbed areas 7. Maintain BMPs until site stabilization, at which time they may be removed Element 11: Maintain Best Management Practices Best Management Practices or BMPs shall be inspected and maintained during construction and removed within 30 days after the County Inspector or determines that the site is stabilized, provided that they may be removed when they are no longer needed. The goal of this element is to maintain and repair all temporary and permanent erosion and sediment control BMPs to assure continued performance. The goal of this element is to ensure that the owner and those performing the site work comply with the SWPPP and properly coordinate to ensure that all BMPs are deployed at the proper time to achieve full compliance with county regulations throughout the project. REVISED 10/26/22 Worksheet B1 Construction Protection: Medium and Large Projects(SWPPP: Stormwater Pollution Prevention Plan) C102 Buffer Zone C103 High Visibility Fence C233 Silt Fence C231 Brush Barrier C234 Vegetated Strip Applicant or Representative Signature Element 13: Protect Low Impact Development BMPs page 6 of 6 The goal of this element is to protect permanent stormwater management BMPs from siltation and compaction during construction. The permanent stormwater management BMPs used for runoff from roofs and other hard surfaces include: full dispersion, roof downspout full infiltration or dispersion systems, perforated stubout connections, rain gardens, bioretention systems, permeable pavement, sheetflow dispersion, and concentrated flow dispersion. Methods that will be used to protect permanent stormwater management BMPs include: Sequencing the construction in a fashion to install these permanent BMPs at the latter part of the construction grading operations, Excluding equipment from the BMPs and the associated areas, Using the erosion and sedimentation control BMPs listed below to protect facilities such as drywells, raingardens, permeable pavement, or bioretention from accumulating sediment during construction and before site restoration. If this option is selected check the BMPS you will use below: Other John Ulrigg Verified by PDFFiller 08/25/2021 REVISED 10/26/22 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. A minimum forested or native vegetation flowpath length of 100 feet (25 feet for sheet flow from a non-native pervious 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 lot (mound, sand filter pressure distribution, Glendon, aerobic treatment unit). Therefore, there is not at least 3 feet or more of permeable soil from the proposed final grade to the seasonal high groundwater table or other impermeable layer. There is not at least 1 foot or more of permeable soil from the proposed bottom of the infiltration system to the seasonal high groundwater table or other impermeable layer. Downspout Full Infiltration 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. REVISED 10/26/22 N/A 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 infiltration not be used due to reasonable concerns about erosion, slope failure, or down-gradient flooding. 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 safety or reliability of pre-existing underground utilities, pre- existing underground storage tanks, pre-existing structures, or pre-existing road or parking lot surfaces. Where the only area available for siting does not allow for a safe overflow pathway to stormwater drainage system or private storm sewer system. Where there is a lack of usable space for bioretention areas at re-development sites, or where there is insufficient space within the existing public right-of-way on public road projects. 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 based on an evaluation of site-specific conditions and a written recommendation from an appropriate licensed professional (e.g., engineer, geologist, hydrogeologist): Where infiltrating water would threaten shoreline structures such as bulkheads. Where infiltrating water would threaten existing below grade 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 Infiltration (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. REVISED 10/26/22 3 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 Bioretention or Rain Gardens (cont.) BMP T7.30 or T5.14A SWMMWW Volume V, Section 7.4 Where land for bioretention is within an erosion hazard, or landslide hazard area (as defined by PAMC 15.20). Where the site cannot be reasonably designed to locate bioretention areas on slopes less than 8 percent. Within 50 feet from the top of slopes that are greater than 20 percent and over 10 feet of vertical relief. For properties with known soil or groundwater contamination (typically federal Superfund sites or state cleanup sites under the Model Toxics Control Act [MTCA]): • Within 100 feet of an area known to have deep soil contamination. • Where groundwater modeling indicates infiltration will likely increase or change the direction of the migration of pollutants in the groundwater. • Wherever surface soils have been found to be contaminated unless those soils are removed within 10 horizontal feet from the infiltration area. Within 100 feet of a closed or active landfill. Within 10 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is 1,100 gallons or less. As used in these criteria, an underground storage tank means any tank used to store petroleum products, chemicals, or liquid hazardous wastes of which 10 percent or more of the storage volume (including volume in the connecting piping system) is beneath the ground surface. Within 100 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is greater than 1,100 gallons. The following criteria can be cited as reasons for infeasibility without further justification (though some require professional services to make the observation): Within setback provided for BMP T7.30 (SWMMWW Volume V, Section 7.4) Where they are not compatible with surrounding drainage system as determined by the county (e.g., project drains to an existing stormwater collection system whose elevation or location precludes connection to a properly functioning bioretention area). REVISED 10/26/22 4 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 field testing indicates potential bioretention/rain garden sites have a measured (a.k.a., initial) native soil saturated hydraulic conductivity less than 0.30 inches per hour. A small-scale or large-scale PIT in accordance with SWMMWW Volume III, Section 3.3.6 (or an alternative small scale test specified by the local government) shall be used to demonstrate infeasibility of bioretention areas. If the measured native soil infiltration rate is less than 0.30 in/hour, bioretention/rain garden BMPs are not required to be evaluated as an option in List #1 or List #2. In these slow draining soils, a bioretention area with an underdrain may be used to treat pollution-generating surfaces to help meet Minimum Requirement #6, Runoff Treatment. If the underdrain is elevated within a base course of gravel, it will also provide some modest flow reduction benefit that will help achieve Minimum Requirement #7. Where the minimum vertical separation of 3 feet to the seasonal high groundwater elevation or other impermeable layer would not be achieved below bioretention that would serve a drainage area that exceeds the following thresholds (and cannot reasonably be broken down into amounts smaller than indicated): o 5,000 square feet of pollution-generating impervious surface (PGIS) o 10,000 square feet of impervious area o 0.75 acres of lawn and landscape. Any area where these facilities are prohibited by an approved cleanup plan under the state MTCA or Federal Superfund Law, or an environmental covenant under Chapter 64.70 RCW. Within 100 feet of a drinking water well, or a spring used for drinking water supply. Bioretention or Rain Gardens (cont.) Where the minimum vertical separation of 1 foot to the seasonal high groundwater or other impermeable layer would not be achieved below bioretention that would serve a drainage area less than the above thresholds REVISED 10/26/22 5 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 Perforated Stub-Out Connections BMP T5.10C SWMMWW Volume III, Section 3.1.3 For sites with septic systems, the only location available for the perforated portion of the pipe is located up-gradient of the drainfield primary and reserve areas. This requirement can be waived if site topography will clearly prohibit flows from intersecting the drainfield or where site conditions (soil permeability, distance between systems, etc.) indicate that this is unnecessary. There is a mound, sandfilter, Glenden or aerobic treatment device on this or an adjacent lot. Therefore, there is not at least 1 foot of permeable soil from the proposed bottom (final grade) of the perforated stub-out connection trench to the highest estimated groundwater table or other impermeable layer. The only location available for the perforated stub-out connection is under impervious or heavily compacted soils. The only location available is on or above slopes greater than 20% Siting and design criteria cannot be achieved on site. For splash blocks, a vegetated flowpath at least 50 feet in length from the downspout to the downstream property line, structure, stream, wetland, slope over 15 percent, or other impervious surface is not feasible. For trenches, a vegetated flowpath of at least 25 feet in between the outlet of the trench and any property line, structure, stream, wetland, or impervious surface is not feasible. A vegetated flowpath of at least 50 feet between the outlet of the trench and any slope steeper than 15 percent is not feasible. Siting and design criteria cannot be achieved on site. Downspout Dispersion Systems BMP T5.10B SWMMWW Volume III, Section 3.1.2 List #1, #2 and #3 List #1, #2 and #3 Within 10 feet of small on-site sewage disposal drainfield, including reserve areas, and grey water reuse systems. For setbacks from a “large on-site sewage disposal system,” see Chapter 246-272B WAC. 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. 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. 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. REVISED 10/26/22 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 infiltration not be used due to reasonable concerns about erosion, slope failure, or downgradient flooding. Within an area whose ground water drains into an erosion hazard, or landslide hazard area. Where infiltrating and ponded water below the new permeable pavement area would compromise adjacent impervious pavements. Where infiltrating water below a new permeable pavement area would threaten existing below grade basements. Where infiltrating water would threaten shoreline structures such as bulkheads. Down slope of steep, erosion prone areas that are likely to deliver sediment to the area of pervious pavement. Where fill soils are used that can become unstable when 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 failure, or where surface runoff velocities may preclude adequate infiltration at the pavement surface. Citation of any of the following infeasibility criteria must be based on an evaluation of site-specific conditions and a written 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. A minimum forested or native vegetation flowpath length of 100 feet (25 feet for sheet flow from a non-native pervious 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. REVISED 10/26/22 7 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 Permeable Pavement (cont.) BMP T5.15, SWMMWW Vol- ume V, Section 5.3 Within an area designated as an erosion hazard, or landslide hazard. Within 50 feet from the top of slopes that are greater than 20 percent. For properties with known soil or groundwater contamination (typically federal Superfund sites or state cleanup sites under MTCA): • Within 100 feet of an area known to have deep soil contamination. • Where groundwater modeling indicates infiltration will likely increase or change the direction of the migration of pollutants in the groundwater. • Wherever surface soils have been found to be contaminated unless those soils are removed within 10 horizontal feet from the infiltration area. • Any area where these facilities are prohibited by an approved cleanup plan under the state MTCA or Federal Superfund Law, or an environmental covenant under Chapter 64.70 RCW. Within 100 feet of a closed or active landfill. Within 100 feet of a drinking water well, or a spring used for drinking water supply, if the pavement is a pollution- generating surface. The following criteria can be cited as reasons for infeasibility without further justification (though some require professional services to make the observation): Where permeable pavements cannot provide sufficient strength to support heavy loads at industrial facilities such as ports. Where installation of permeable pavement would threaten the safety or reliability of pre-existing underground utilities, per-existing underground storage tanks, or pre-existing road subgrades. * Note that Raingardens may be used in lieu of permeable pavement if subject to List #1. REVISED 10/26/22 8 Worksheet C What’s the best option for your site? Within 10 feet of a small on-site sewage disposal drainfield, including reserve areas, and grey water reuse systems. For setbacks from a “large on-site sewage disposal system,” see Chapter 246-272B WAC. Within 10 feet of any underground storage tank and connecting underground pipes, regardless of tank size. As used in these criteria, an underground storage tank means any tank used to store petroleum products, chemicals, or liquid hazardous wastes of which 10 percent or more of the storage volume (including volume in the connecting piping system) is beneath the ground surface. At multi-level parking garages, and over culverts and bridges. Where the site design cannot avoid putting pavement in areas likely to have long-term excessive sediment deposition after construction (e.g., construction and landscaping material yards). Where the site cannot reasonably be designed to have a porous asphalt surface at less than 5 percent slope, or a pervious concrete surface at less than 10 percent slope, or a permeable interlocking concrete pavement surface (where appropriate) at less than 12 percent slope. Grid systems upper slope limit can range from 6 to 12 percent; check with manufacturer and local supplier. Where the subgrade soils below a pollution-generating permeable pavement (e.g., road or parking lot) do not meet the soil suitability criteria for providing treatment. See soil suitability criteria for treatment in the SWMMWW Volume III, Section 3.3.7. Note: In these instances, the county may approve installation of a 6 inch sand filter layer meeting county specifications for treatment as a condition of construction. Where underlying soils are unsuitable for supporting traffic loads when saturated. Soils meeting a California Bearing Ratio of 5 percent are considered suitable for residential access roads. Where replacing existing impervious surfaces unless the existing surface is a non-pollution generating surface over an outwash soil with a saturated hydraulic conductivity of 4 inches per hour or greater. Other Hard Surfaces (cont.) BMP and Applicable Lists Reason why the BMP will not work on site.Additional Comments If needed Permeable Pavement (cont.) BMP T5.15, SWMMWW Volume V, Section 5.3 * Note that Raingardens may be used in lieu of permeable pavement if subject to List #1. REVISED 10/26/22 9 Worksheet C What’s the best option for your site? Where appropriate field testing indicates soils have a measured (a.k.a., initial) subgrade soil saturated hydraulic conductivity less than 0.3 inches per hour. Only small- scale PIT or large-scale PIT methods in accordance with SWMMWW Volume III, Section 3.3.6 (or an alternative small scale test specified by the local government) shall be used to evaluate infeasibility of permeable pavement areas. (Note: In these instances, unless other infeasibility restrictions apply, roads and parking lots may be built with an underdrain, preferably elevated within the base course, if flow control benefits are desired.) Roads that receive more than very low traffic volumes, and areas having more than very low truck traffic. Roads with a projected average daily traffic volume of 400 vehicles or less are very low volume roads (AASHTO 2001) (U.S. Department of Transportation, 2013). Areas with very low truck traffic volumes are roads and other areas not subject to through truck traffic but may receive up to weekly use by utility trucks (e.g., garbage, recycling), daily school bus use, and multiple daily use by pick-up trucks, mail/parcel delivery trucks, and maintenance vehicles. Note: This infeasibility criterion does not extend to sidewalks and other non-traffic bearing surfaces associated with the collector or arterial. At sites defined as “high-use sites” (refer to the Glossary in the SWMMWW Volume I). In areas with “industrial activity” as identified in 40 CFR 122.26(b)(14). Where the risk of concentrated pollutant spills is more likely such as gas stations, truck stops, and industrial chemical storage sites. Where routine, heavy applications of sand occur in frequent snow zones to maintain traction during weeks of snow and ice accumulation. Where the seasonal high groundwater or an underlying impermeable/low permeable layer would create saturated conditions within 1 foot of the bottom of the lowest gravel base course. Other Hard Surfaces (cont.) BMP and Applicable Lists Reason why the BMP will not work on site.Additional Comments If needed Permeable Pavement (cont.) BMP T5.15, SWMMWW Volume V, Section 5.3 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. (List #1 may use Raingardens in lieu of Permeable Pavement). 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. REVISED 10/26/22 10 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 Where professional geotechnical evaluation recommends infiltration not be used due to reasonable concerns about erosion, slope failure, or down-gradient flooding. 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 safety or reliability of pre-existing underground utilities, pre- existing underground storage tanks, pre-existing structures, or pre-existing road or parking lot surfaces. Where the only area available for siting does not allow for a safe overflow pathway to stormwater drainage system or private storm sewer system. Where there is a lack of usable space for bioretention areas at re-development sites, or where there is insufficient space within the existing public right-of-way on public road projects. 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 based on an evaluation of site-specific conditions and a written recommendation from an appropriate licensed professional (e.g., engineer, geologist, hydrogeologist): Where infiltrating water would threaten shoreline structures such as bulkheads. Where infiltrating water would threaten existing below grade basements. The following criteria can be cited as reasons for infeasibility without further justification (though some require professional services to make the observation): Within setback provided for BMP T7.30 (SWMMWW Volume V, Section 7.4) Where they are not compatible with surrounding drainage system as determined by the county (e.g., project drains to an existing stormwater collection system whose elevation or location precludes connection to a properly functioning bioretention area). Bioretention or Rain Gardens BMP T7.30, SWMMWW Volume V, Section 7.4 List #1 (both) and List #2 (bioretention only) REVISED 10/26/22 11 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 Bioretention or Rain Gardens (cont.) BMP T7.30, SWMMWW Volume V, Section 7.4 Where land for bioretention is within an erosion hazard, or landslide hazard area (as defined by PAMC 15.20). Where the site cannot be reasonably designed to locate bioretention areas on slopes less than 8 percent. Within 50 feet from the top of slopes that are greater than 20 percent and over 10 feet of vertical relief. For properties with known soil or groundwater contamination (typically federal Superfund sites or state cleanup sites under the Model Toxics Control Act [MTCA]): • Within 100 feet of an area known to have deep soil contamination. • Where groundwater modeling indicates infiltration will likely increase or change the direction of the migration of pollutants in the groundwater. • Wherever surface soils have been found to be contaminated unless those soils are removed within 10 horizontal feet from the infiltration area. Within 100 feet of a closed or active landfill. Within 10 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is 1,100 gallons or less. As used in these criteria, an underground storage tank means any tank used to store petroleum products, chemicals, or liquid hazardous wastes of which 10 percent or more of the storage volume (including volume in the connecting piping system) is beneath the ground surface. Within 100 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is greater than 1,100 gallons. Where the minimum vertical separation of 1 foot to the seasonal high groundwater or other impermeable layer would not be achieved below bioretention that would serve a drainage area less than the above thresholds REVISED 10/26/22 12 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 Where field testing indicates potential bioretention/rain garden sites have a measured (a.k.a., initial) native soil saturated hydraulic conductivity less than 0.30 inches per hour. A small-scale or large-scale PIT in accordance with SWMMWW Volume III, Section 3.3.6 (or an alternative small scale test specified by the local government) shall be used to demonstrate infeasibility of bioretention areas. If the measured native soil infiltration rate is less than 0.30 in/hour, bioretention/rain garden BMPs are not required to be evaluated as an option in List #1 or List #2. In these slow draining soils, a bioretention area with an underdrain may be used to treat pollution-generating surfaces to help meet Minimum Requirement #6, Runoff Treatment. If the underdrain is elevated within a base course of gravel, it will also provide some modest flow reduction benefit that will help achieve Minimum Requirement #7. Where the minimum vertical separation of 3 feet to the seasonal high groundwater elevation or other impermeable layer would not be achieved below bioretention that would serve a drainage area that exceeds the following thresholds (and cannot reasonably be broken down into amounts smaller than indicated): o 5,000 square feet of pollution-generating impervious surface (PGIS) o 10,000 square feet of impervious area o 0.75 acres of lawn and landscape. Any area where these facilities are prohibited by an approved cleanup plan under the state MTCA or Federal Superfund Law, or an environmental covenant under Chapter 64.70 RCW. Within 100 feet of a drinking water well, or a spring used for drinking water supply. Within 10 feet of small on-site sewage disposal drainfield, including reserve areas, and grey water reuse systems. For setbacks from a “large on-site sewage disposal system,” see Chapter 246-272B WAC. Bioretention or Rain Gardens (cont.) BMP T7.30, SWMMWW Volume V, Section 7.4 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. REVISED 10/26/22 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 Positive drainage for sheet flow runoff cannot be achieved. Area to be dispersed (e.g., driveway, patio) cannot be graded to have less than a 15 percent slope. For flat to moderately sloped areas, at least a 10 foot-wide vegetation buffer for dispersion of the adjacent 20 feet of contributing surface cannot be achieved. For variably sloped areas, at least a 25 foot vegetated flowpath between berms cannot be achieved. Siting and design criteria cannot be achieved on site. Concentrated Flow Dispersion BMP T5.11, SWMMWW Volume V, Section 5.3 A minimum 3 foot length of rock pad and 50 foot flowpath OR a dispersion trench and 25 foot flowpath for every 700 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. REVISED 10/26/22