Public Works Department 104 W. Magnolia Street, Suite 109 Bellingham, WA 98225 (360) 778-7900 STORMWATER PERMIT SUBMITTAL REQUIREMENTS Most development within the City of Bellingham that involves disruption of soils, or construction of buildings, streets, parking lots, etc. requires the issuance of a Stormwater Permit. This packet contains material that will aid you in providing a complete application for this permit. Stormwater Permit requirements are based on either the amount of soil to be disrupted (grading, vegetation removal), or the amount of impervious surface that is created or replaced on a site (building footprint, concrete, asphalt or gravel parking, sidewalk, etc.). A Stormwater Site Plan consists of plan sheets showing all proposed Stormwater systems and facilities, Stormwater Pollution Prevention Plan (SWPPP), and if applicable, a Stormwater report by a licensed civil engineer. Please follow the steps on the worksheets to determine the level of stormwater management required for your project. Many applications will not need to use all information provided in this packet. If you need assistance in your determination, contact the Development section of the Public Works Dept. located at 104 W. Magnolia St., Suite 109 or call (360) 778-7900. STORMWATER MANAGEMENT REQUIREMENT CHECKLIST Provide the following information as part of your submittal: Impervious surface calculation (see next page) Stormwater management requirement determination Stormwater site plan and/or erosion control plan as stated on the applicable Requirements List I, II, or III Attach a copy of a General Construction Stormwater Pollution Prevention Plan (SWPPP) to Site Plan (see Page 7 of this packet) and erosion control details (see Page 8)
IMPERVIOUS SURFACE CALCULATION Per Bellingham Municipal Code 15.42 Stormwater Management (http://www.codepublishing.com/wa/bellingham/?bellingham15/bellingham1542.html), Impervious surface means a hard surface area that either prevents or retards the entry of water into the soil mantle 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, packed gravel surfaces, packed earthen materials, or other surfaces which similarly impede the natural infiltration of stormwater. The total square footage of impervious surface on your project site will determine the storm water management requirements and the storm water utility fees. Impervious surface calculations must include all of the impervious areas on your project site. "New impervious surface means impervious surfaces that replace or supplant existing pervious surfaces. For example, resurfacing by upgrading from dirt to gravel, asphalt, or concrete. "Replaced impervious surface" means, for structures, the removal and replacement of any exterior impervious surfaces or foundation. For other impervious surfaces, the removal down to bare soil or base course and replacement is considered "replaced". Provide detailed information about your project in the following table. Enter 0 in the sections that are not applicable to your project. Impervious Surface Area (square feet) Existing Removed Proposed New Proposed Replaced Totals LAND DISTURBANCE Land Disturbance* (square feet) *Greater than 500 square feet of land disturbance requires a Stormwater Permit. 2 P age
STORMWATER MANAGEMENT REQUIREMENT DETERMINATION Follow the diagram using information from your impervious surface calculation. Your answers will determine the stormwater management requirements list you will use. Is your project less than 120 S.F. new, replaced or new plus replaced imperious surface AND less than 500 S.F. land disturbance? YES NO STORMWATER PERMIT REQUIRED NO Is the total new or replaced impervious surface greater than 5,000 S.F.? OR Does the project disturb more than 1 acre of land? YES Address the requirements of STORMWATER MANAGEMENT REQUIREMENTS LIST III NO Is your project inside the Lake Whatcom watershed? YES NO Is your project a new single family residence or duplex? NO YES Address the requirements of STORMWATER MANAGEMENT REQUIREMENTS LIST II Does the project contain more than 2,000 S.F. of new, replaced or new plus replaced impervious area? YES NO Address the requirements of STORMWATER MANAGEMENT REQUIREMENTS LIST I 3 P age
STORMWATER MANAGEMENT REQUIREMENTS LIST I If the project includes less than 2,000 square feet of new, replaced or new plus replaced impervious surface (and is not a new single family residence or duplex) or land disturbance greater than 500 square feet, provide a simplified site plan which shows: Clearing limits and indicate how limits will be marked on property. Construction entrance location and silt fence location (show location on site plan and attach standard plan sheet, see page 8). Attach General Construction Stormwater Pollution Prevention Plan (SWPPP) to site plan (see page 8). If project is a new single family residence or duplex residence see Stormwater Management Requirements List II on page 5 In addition, consider the following elements for your project: Stormwater management (tight lined to City storm system or On-Site Stormwater Management, see Appendix B). Stabilize soils Protect slopes Protect drain inlets Stabilize channels and outlets Control pollutants Control de-watering Maintain "Best Management Practices" (BMPs) Manage the project 4 P age
STORMWATER MANAGEMENT REQUIREMENTS LIST II If your project is a new single family home or duplex or between 2,000 and 5,000 square feet of new, replaced or new plus replaced impervious surface or 5,000 square feet or more of land disturbance, the project requires compliance with the following listed minimum requirements. For specific information, please refer to the current edition of the Washington State Department of Ecology's Stormwater Management Manual for Western Washington (click on link: https://fortress.wa.gov/ecy/publications/summarypages/1410055.html). 1. Preparation of Site Plans The following elements must be considered during the development of the site plan: Existing public and private development, including utility infrastructure on and adjacent to the site. Minor hydrologic features, including seeps, springs, closed depression areas, drainage swales. Major hydrologic features such as streams, wetlands and waterbodies. Flood hazard areas on or adjacent to the site, if present. Geologic Hazard areas as defined by the local jurisdiction. Topographic features that may act as natural stormwater storage, infiltration or conveyance. Underlying soils on the site utilizing soil surveys, soil test pits, soil borings, or soil grain analyses (see http://websoilsurvey.nrcs.usda.gov/app/homepage.htm for soil survey information). Plat conditions or other restrictions on the allowed impervious surface coverage. Easements and/or other restrictions associated with the project area. 2. Construction Stormwater Pollution Prevention Plan (SWPPP) See the attached requirements for "General Construction Stormwater Pollution Prevention Plan" on page 8 3. Source Control of Pollutants See Appendix A for information about available source control BMPs 4. Preservation of Natural Drainage Systems and Outfalls Natural drainage patterns shall be maintained, and discharges for the project site shall occur at the natural location, to the maximum extent practicable. The manner by which runoff is discharged from the project site must not cause a significant adverse impact to downstream receiving waters and downgradient properties. All outfalls require energy dissipation. Where no conveyance system exists at the adjacent downgradient property line and the discharge was previously unconcentrated flow or significantly lower concentrated flow, you may need to obtain an easement or consider an engineered storm system to prevent impacts to downstream property. 5 P age
5. On-Site Stormwater Management Projects shall employ on-site stormwater management BMPs to infiltrate, disperse, and retain stormwater runoff on-site to the maximum extent feasible without causing flooding or erosion impacts. Roof downspout control BMPs (see Appendix B), and Dispersion and Soil Quality BMPs shall be required to reduce the hydrologic disruption of developed sites. 6 P age
STORMWATER MANAGEMENT REQUIREMENTS LIST III If your project is greater than 5,000 square feet of new, replaced or new plus replaced impervious surface. The project requires compliance with the following minimum requirements. The plan must be designed by a licensed civil engineer. For specific information, please refer to the most current edition of the Washington State Department of Ecology Stormwater Management Manual for Western Washington (https://fortress.wa.gov/ecy/publications/summarypages/1410055.html). 1. Preparation of Stormwater Site Plans 2. Construction Stormwater Pollution Prevention Plan (SWPPP) 3. Source Control of Pollution 4. Preservation of Natural Drainage Systems and Outfalls 5. On-site Stormwater Management 6. Runoff Treatment 7. Flow Control 8. Wetland Protection 9. Basin/Watershed Planning 10. Operation and Maintenance 7 P age
GENERAL CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN SWPPP Purpose To prevent the discharge of sediment and other pollutants to the maximum extent practicable from small construction projects. Design and Installation Plan and implement proper clearing and grading of the site. It is most important only to clear the areas needed, keeping exposed areas to a minimum. Phase clearing so that only those areas that are actively being worked are uncovered. Note: Clearing limits shall be flagged on the lot or project area prior to initiating clearing. From October 1 through April 30, no soils shall remain exposed and unworked for more than two days. From May 1 to September 30, no soils shall remain exposed and unworked for more than seven days. Soil shall be managed in a manner that does not permanently compact or deteriorate the final soil and landscape system. If disturbance and/or compaction occur the impact must be corrected at the end of the construction activity. This shall include restoration of soil depth, soil quality, permeability, and percent organic matter. Construction practices must not cause damage to or compromise the depth of permanent landscape or infiltration areas. Locate any soil piles away from drainage systems. Soil piles should be tarped or mulched until the soil is either used or removed. Piles should be situated so that sediment does not run into the street or adjoining yards. Backfill foundation walls as soon as possible after backfilling. This will eliminate any sediment loss from surplus fill. The construction entrance shall be stabilized where traffic will be leaving the construction site and traveling on paved roads or other paved surfaces. Provide for periodic street cleaning to remove any sediment that may have been tracked out. Sediment should be removed by shoveling or sweeping and carefully removed to a suitable disposal area where it will not be re eroded. Street washing is prohibited without special permission from the SSW utility, call (360) 778-7900. 8 P age
SEDIMENT BARRIER (STRAW WATTLE) 9 P age
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FEES What are the fees? Part One Permit Fees: Charged when a permit is needed for construction activity. The fee amount is based on either the amount of impervious surface added and/or replaced or the amount of land disturbance. Stormwater Permit Fees Effective 08/01/05 per ordinance 2005-06-051 Permit Type Amount of Amount of Clearing Fee Impervious & Grading Level One Permit (fee per site) 300 to 1000 SF 500 to 5000 SF $113.00 Level Two Permit (fee per site) 1000 to 5000 SF 5,000 to 30,000 SF $316.00 Level Three Permit (fee per site) 5000 SF to 1 acre More than 30,000 SF $633.00 Level Four Permit (fee per site) More than 1 acre N/A $844.00 Part Two Development Charges: Charged on each parcel of property that is developed or redeveloped within the City of Bellingham. Stormwater Type of Use Single Family Residence (SFR) & Duplexes All other types of new impervious surface greater than or equal to 3,000 square feet Amount $678.00 per SFR $0.226 per square foot of impervious What are the standards for stormwater design? Stormwater designs must be done in accordance with Bellingham Municipal Code 15.42, the most current Stormwater Management Manual for Western Washington, and the Low Impact Technical Guidance Manual for Western Washington. These documents are subject to change. 11 P age
APPENDIX A SOURCE CONTROL BMPS. There are two categories of Source Control BMPs: operational and structural. Here is a link to Volume IV - Source Control of the Department of Ecology's Stormwater Management Manual: https://fortress.wa.gov/ecy/publications/parts/1410055part6.pdf. Operational Source Control BMPs are non-structural practices that prevent or reduce pollutants from entering stormwater. Examples include formation of a pollution prevention team, good housekeeping practices, preventive maintenance procedures, spill prevention and cleanup, employee training, inspections of pollutant sources, and record keeping. They can also include process changes, raw material/product changes, and recycling wastes. Operational Source Control BMPs are considered the most cost-effective pollutant minimization practices. The following operational source control BMPs must be implemented at the commercial and industrial establishments listed in Appendix IV-A, where required by Ecology's Industrial General Permit or by local government ordinances. Assign one or more individuals to be responsible for stormwater pollution control. Hold regular meetings to review the overall operation of the BMPs. Establish responsibilities for inspections, operation and maintenance, and availability for emergency situations. Train all team members in the operation, maintenance and inspections of BMPs, and reporting procedures. Promptly contain and clean up solid and liquid pollutant leaks and spills including oils, solvents, fuels, and dust from manufacturing operations on any exposed soil, vegetation, or paved area. Sweep paved material handling and storage areas regularly as needed, for the collection and disposal of dust and debris that could contaminate stormwater. Do not hose down pollutants from any area to the ground, storm drain, conveyance ditch, or receiving water unless necessary for dust control purposes to meet air quality regulations and unless the pollutants are conveyed to a treatment system approved by the local jurisdiction. Clean oils, debris, sludge, etc. from all BMP systems regularly, including catch basins, settling/detention basins, oil/water separators, boomed areas, and conveyance systems, to prevent the contamination of stormwater. Refer to Appendix IV-D R.3 for references to assist in determining if a waste must be handled as hazardous waste. Promptly repair or replace all substantially cracked or otherwise damaged paved secondary containment, high-intensity parking and any other drainage areas, which are subjected to pollutant material leaks or spills. Promptly repair or replace all leaking connections, pipes, hoses, valves, etc. which can contaminate stormwater. Operational and structural BMPs that are designed to address specific types of pollutant sources are presented in Stormwater Management Manual for Western Washington (DOE Stormwater Manual), Volume IV, Chapter 2, section 2 12 P age
APPENDIX B ON-SITE WATER MANAGEMENT Roof Downspout Controls Roof downspout controls are simple pre-engineered designs for infiltrating and/or dispersing runoff from roof areas for the purposes of limiting development impacts. Here is a link to Volume V - Runoff Treatment BMPs, Department of Ecology Stormwater Management Manual for Western Washington https://fortress.wa.gov/ecy/publications/parts/1410055part7.pdf. Selection of Roof Downspout Controls Where roof downspout controls are planned, the following three types must be considered in the order of preference show below. 1. Downspout infiltration systems 2. Downspout dispersion systems 3. Downspout perforated stub-out connections 1. Downspout Infiltration Systems Downspout infiltration systems are trench or drywell designs intended only for use in infiltrating runoff from roof downspout drains. They are not designed to directly infiltrate runoff from pollutant-generating impervious surfaces. Please check the soils map (Potential Infiltration Areas). If your project site is in a shaded area, you may be able to use infiltration. Contact the Public Works Development Section at (360) 778-7900 to confirm applicability. Infiltration System Setbacks All infiltration systems should be at least 10 feet from any structure, property line, or sensitive area (except slopes over 40%). All infiltration systems must be at least 50 feet from the top of any slope over 40%. The setback may be reduced based on a geotechnical evaluation, but in no instances may it be less than the buffer width. Infiltration Trench should be designed according to the following specifications: The minimum lengths (linear feet) per 1,000 square feet of roof area based on soil type may be use for sizing downspout infiltration trenches. Coarse sands Medium sand Fine or Loamy sand Sandy Loam cobbles loam 20 LF 30 LF 75 LF 125 LF 190 LF Maximum length of trench must not exceed 100 feet from the inlet sump. Minimum spacing between trench centerlines must be 6 feet. Filter fabric must be placed over the drain rock as shown on Figure 1. Infiltration trenches may be located in fill material if the fill is placed and compacted under the direct supervision of a geotechnical engineer of professional civil engineer with geotechnical expertise, and if the measured infiltration rate is at least 8 inches per hour. Trench length in fill must be 60 L.F. per 1000 S.F. of roof area. Infiltration trench should not be built on slopes steeper than 25%. Infiltration Drywell should be designed according to the following specifications: Drywell bottoms must be a minimum of 1 foot above seasonal high groundwater level or impermeable soil layers. If using drywells, each drywell may serve up to 1000 S.F. of imperious surface for either medium sand or coarse sands. Typically drywells are 48 inches in diameter (mini.) and have a depth of 5 feet (4 feet of gravel and 1 foot of suitable cover material). 13 P age
Filter fabric (geotextile) must be placed on the top of the drain rock and on trench or drywell sides prior to backfilling. Spacing between drywells must be a minimum of 4 feet. Downspout infiltration drywells must not built on slopes greater than 25 %(4:1). Drywells may not be placed on or above a landslide hazard area or slopes greater than 15% with evaluation by a professional engineer with geotechnical expertise or qualified geologist and jurisdiction approval. Figure 1 - Typical Downspout Infiltration Trench 14 P age
l Figure 2 Alternative Downspout Infiltration Trench System for Course Sand and Gravel Figure 3 Typical Downspout Infiltration Drywell 15 P age
2. Downspout Dispersion Systems Downspout dispersion systems are splash blocks or gravel-filled trenches, which serve to spread roof runoff over vegetated pervious areas. Dispersion attenuates peak flows by slowing entry of the runoff into the conveyance system, allows for some infiltration, and provides some water quality benefits. Dispersion Trenches should be designed according to the following specifications: 1. A vegetated flowpath of at least 25 feet in length must be maintained between the outlet of the dispersion trench and any property line, structure, stream, wetland, lake or impervious surface. A vegetated flowpath of at least 50 feet in length must be maintained between the outlet of the trench and any steep slope. Sensitive area buffers may count towards flowpath lengths. 2. Maintain a setback of at least 5 feet between trench and structures or property line. 3. Splashblocks require a vegetated flow path of at least 50 feet in length between any property line, structure, stream, wetland, lake or impervious surface. 4. A maximum of 700 square feet of roof area may drain to each splashblock or standard dispersion trench. 5. A trench with a notched grade board may be used for larger areas. 6. No erosion or flooding of downstream properties may result. 7. Runoff discharged towards landslide hazard areas must be evaluated by a professional engineer with geotechnical expertise or a qualified geologist. Downspout dispersion systems may not be placed on or above slopes greater than 20% or above erosion hazard areas without evaluation by a professional engineer with geotechnical expertise or a qualified geologist and jurisdiction approval. Figure 4. Typical Downspout Dispersion Trench 16 P age
Figure 5 Standard Dispersion Trench with Notched Grade Board 17 P age
Figure 6 Typical Downspout Splashblock Dispersion house Roof downspout serves up to 700 sf. Of roof 50 min. Vegetated flow path Splash block Downspout extension Splash block 18 P age
3. Perforated Stub-Out Connections A perforated stub-out connection is a length of perforated pipe within a gravel-filled trench that is placed between roof downspouts and a stub-out to the local drainage system. Figure 7 below illustrates a perforated stub-out connection. These systems are intended to provide some infiltration during drier months. During the wet winter months, they may provide little or no flow control. Perforated stub-outs are not appropriate when the seasonal water table is < 1 foot below trench bottom. In single-family subdivision projects subject to Minimum Requirement #7 for flow control (see Volume I), perforated stub-out connections may be used only when downspout infiltration or dispersion is not feasible. Location of the connection should be selected to allow a maximum amount of runoff to infiltrate into the ground (ideally a dry location on the site that is relatively well drained). To facilitate maintenance, the perforated pipe portion of the system should not be located under impervious or heavily compacted (e.g., driveways and parking areas) surfaces. Perforated stub-out connections should consist of at least 10 feet of perforated pipe per 5,000 square feet of roof area laid in a level, 2-foot wide trench backfilled with washed drain rock. The drain rock should extend to a depth of at least 8 inches below the bottom of the pipe and should cover the pipe. The pipe should be laid level and the rock trench covered with filter fabric and 6 inches of fill (see Figure 7). Setbacks are the same as for infiltration trenches; at least 10 feet from any structure, property line, or sensitive area. Potential runoff discharge towards a landslide hazard area must be evaluated by a professional engineer with geotechnical expertise or a qualified geologist. The perforated portion of the pipe may not be placed on or above slopes greater than 20% or above erosion hazard areas without evaluation by a professional engineer with geotechnical expertise or qualified geologist and jurisdiction approval. For sites with septic systems, the perforated portion of the pipe must be downgradient of the drain field primary and reserve areas. This requirement can be waived if site topography will clearly prohibit flows from intersecting the drain field or where site conditions (soil permeability, distance between systems, etc.) indicate that this is unnecessary. 19 P age
Figure 7 Perforated Stub-Out Connection 20 P age
Purpose and Definition BMP T5.13: Post Construction Soil Quality and Depth Naturally occurring (undisturbed) soil and vegetation provide important stormwater functions including: water infiltration; nutrient, sediment, and pollutant adsorption; sediment and pollutant biofiltration; water interflow storage and transmission; and pollutant decomposition. These functions are largely lost when development strips away native soil and vegetation and replaces it with minimal topsoil and sod. Applications and Limitations Establishing a minimum soil quality and depth is not the same as preservation of naturally occurring soil and vegetation. However, establishing a minimum soil quality and depth will provide improved on-site management of stormwater flow and water quality. Soil organic matter can be attained through numerous materials such as compost, composted woody material, biosolids, and forest product residuals. It is important that the materials used to meet the soil quality and depth BMP be appropriate and beneficial to the plant cover to be established. Likewise, it is important that imported topsoils improve soil conditions and do not have an excessive percent of clay fines. This BMP can be considered infeasible on till soil slopes greater than 33 percent. Design Guidelines Soil retention. Retain, in an undisturbed state, the duff layer and native topsoil to the maximum extent practicable. In any areas requiring grading remove and stockpile the duff layer and topsoil on site in a designated, controlled area, not adjacent to public resources and critical areas, to be reapplied to other portions of the site where feasible. Soil quality. All areas subject to clearing and grading that have not been covered by impervious surface, incorporated into a drainage facility or engineered as structural fill or slope shall, at project completion, demonstrate the following: 1. A topsoil layer with a minimum organic matter content of 10% dry weight in planting beds, and 5% organic matter content in turf areas, and a ph from 6.0 to 8.0 or matching the ph of the undisturbed soil. The topsoil layer shall have a minimum depth of eight inches except where tree roots limit the depth of incorporation of amendments needed to meet the criteria. Subsoils below the topsoil layer should be scarified at least 4 inches with some incorporation of the upper material to avoid stratified layers, where feasible. 2. Mulch planting beds with 2 inches of organic material 3. Use compost and other materials that meet these organic content requirements: a. The organic content for pre-approved amendment rates can be met only using compost meeting the compost specification for Bioretention (BMP T7.30), with the exception that the compost may have up to 35% biosolids or manure. 21 P age
The compost must also have an organic matter content of 40% to 65%, and a carbon to nitrogen ratio below 25:1. The carbon to nitrogen ratio may be as high as 35:1 for plantings composed entirely of plants native to the Puget Sound Lowlands region. b. Calculated amendment rates may be met through use of composted material meeting (a.) above; or other organic materials amended to meet the carbon to nitrogen ratio requirements, and not exceeding the contaminant limits identified in Table 220-B, Testing Parameters, in WAC 173-350-220. The resulting soil should be conducive to the type of vegetation to be established. Implementation Options: The soil quality design guidelines listed above can be met by using one of the methods listed below: 1. Leave undisturbed native vegetation and soil, and protect from compaction during construction. 2. Amend existing site topsoil or subsoil either at default pre-approved rates, or at custom calculated rates based on tests of the soil and amendment. 3. Stockpile existing topsoil during grading, and replace it prior to planting. Stockpiled topsoil must also be amended if needed to meet the organic matter or depth requirements, either at a default pre-approved rate or at a custom calculated rate. 4. Import topsoil mix of sufficient organic content and depth to meet the requirements. More than one method may be used on different portions of the same site. Soil that already meets the depth and organic matter quality standards, and is not compacted, does not need to be amended. Maintenance Establish soil quality and depth toward the end of construction and once established, protect from compaction, such as from large machinery use, and from erosion. Plant vegetation and mulch the amended soil area after installation. Leave plant debris or its equivalent on the soil surface to replenish organic matter. Reduce and adjust, where possible, the use of irrigation, fertilizers, herbicides and pesticides, rather than continuing to implement formerly established practices. 22 P age