Mendocino County Municipal Code Ch. 20.717 Water Quality Protection

(A) The purpose of this Chapter is to protect and enhance coastal waters and groundwater recharge within the Town of Mendocino in accordance with the policies of the County's Local Coastal Plan. This Chapter includes application submittal requirements, development standards, and other measures that are intended to help ensure that permitted development will be sited, designed, and managed to conserve natural drainage features and vegetation, minimize the introduction of pollutants into coastal waters to the maximum extent practicable, minimize post-development changes in stormwater runoff flows, and protect the overall quality of coastal waters and groundwater resources.

(B) This Chapter is intended to be used in conjunction with Chapter 20.492, Grading, Erosion and Runoff, of Mendocino County Coastal Zoning Code Division II. Where the standards or provisions overlap or conflict, the resolution that is on balance most protective of coastal resources shall apply.

(Ord. No. 4395, § 2, 11-17-2017)

(A) The provisions of this Chapter shall apply to all development in the Town of Mendocino that is subject to discretionary planning approval. Discretionary planning approvals include, but are not limited to, a coastal development permit or a Mendocino Historical Review Board permit (for new construction or addition).

(B) Development that requires a coastal development permit and has the potential for adverse water quality or hydrologic (i.e., due to changes in runoff flows) impacts to coastal waters shall in most cases require both a construction-phase plan and one (1) of two (2) types of post-development plans for water quality protection.

(1) Construction Pollution Prevention Plan (CPPP). All permit applications for development that entails construction shall include a site-specific Construction Pollution Prevention Plan that describes the temporary BMPs the development will implement to minimize erosion and sedimentation during construction, and to minimize pollution of runoff and coastal waters by construction chemicals and materials. The CPPP's development requirements are described in Section 20.717.020(B), and the application submittal requirements in Section 20.717.025(B).

(2) Post-Development Runoff Plan (PDRP). All permit applications for development that has the potential for adverse post-development water quality or hydrologic impacts to coastal waters shall include a Post-Development Runoff Plan that describes the Site Design strategies, pollutant Source Control BMPs, and other measures the development will implement to minimize stormwater pollution and changes in runoff flows from the site after development is completed. If the development entails activities or changes in land use other than construction as defined in 20.717.015(B), including subdivision or re-division of land, the scope of the plan may be reduced accordingly. The PDRP's development requirements are described in Section 20.717.020(B), and the application submittal requirements in section 20.717.025(C).

(3) Water Quality Mitigation Plan (WQMP). A Water Quality Mitigation Plan shall be required for Developments of Water Quality Concern (see 20.717.010(B).3.a—m, below), which are specified categories of development that have a greater potential for adverse water quality and hydrologic impacts due to the development size, type of land use, and/or proximity to coastal waters. The WQMP shall be prepared by a qualified licensed professional, and shall describe the long-term post-development measures the development will implement, in addition to the requirements of the Post-Development Runoff Plan, to protect coastal resources after the development is completed. The WQMP shall include a polluted runoff and hydrologic site characterization, a design storm standard for sizing BMPs, use of a Low Impact Development (LID) approach to retain the design storm runoff on-site, and documentation of the expected effectiveness of proposed BMPs. Additional plan components that may be required include an alternatives analysis, and a description of the Treatment Control and/or Runoff Control BMPs the development will implement to minimize post-development changes in the stormwater runoff flow regime and post-construction polluted runoff from the development project site. The WQMP's development requirements are described in section 20.717.020(C), and the application submittal requirements in 20.717.025(D).

Developments of Water Quality Concern shall include the following categories:

(a) Residential. Residential development that creates and/or replaces five (5) or more dwelling units.

(b) Hillside. Hillside development on a slope greater than fifteen (15) percent, on a site with erodible soil.

(c) Seventy-five (75) percent or more of site will be impervious surface area. Development where seventy-five (75) percent or more of the site's surface area will be impervious surfaces.

(d) Create and/or replace ten thousand (10,000) square feet or more impervious surface area. Development that creates and/or replaces a cumulative site total of ten thousand (10,000) square feet or more of impervious surface area.

(e) Parking lot. Development of a parking lot that creates and/or replaces a cumulative site total of five thousand (5,000) square feet or more of impervious surface area that may potentially contribute to stormwater runoff.

(f) Vehicle service facility. Development of a vehicle service facility, including a retail gasoline outlet, commercial car wash, or vehicle repair facility.

(g) Street, road, or highway facility. Development of a street, road, or highway facility that creates and/or replaces a cumulative site total of five thousand (5,000) square feet or more of impervious surface area.

(h) Restaurant. Development of a restaurant that creates and/or replaces a cumulative site total of five thousand (5,000) square feet or more of impervious surface area.

(i) Outdoor storage area. Development of a commercial or industrial outdoor storage area that creates and/or replaces a cumulative site total of five thousand (5,000) square feet or more of impervious surface area, or as determined by the County based on the use of the storage area, where used for storage of materials that may potentially contribute pollutants to coastal waters or the storm drain system.

(j) Commercial or industrial development generating a high pollutant load. Commercial or industrial development with a potential for generating a high pollutant load that may potentially enter coastal waters or the storm drain system.

(k) Contaminated soil. Development on land where the soil has been contaminated by a previous land use, and where the contaminated soil has the potential to be eroded or to release the contaminants into runoff.

(l) Near or discharges directly to coastal waters. Development that creates and/or replaces a cumulative site total of two thousand five hundred (2,500) square feet or more of impervious surface area, if the development is located within one hundred (100) feet of coastal waters (including the ocean, estuaries, wetlands, rivers, streams, and lakes) or discharges directly to coastal waters (i.e., does not discharge to a public storm drain system).

(m) Other. Any other development determined by the Planning Director to be a Development of Water Quality Concern.

(Ord. No. 4395, § 2, 11-17-2017)

(A) "Best Management Practices" (BMPs) means stormwater management practices, including structural devices and systems, siting criteria, operational practices, and procedural practices to preventor reduce nonpoint source pollution and/or adverse changes in stormwater runoff flows resulting from development.

(B) "Construction" means clearing, grading, or other activities that involve ground disturbance, building, reconstructing, or demolishing a structure; and creation or replacement of impervious surfaces.

(C) "Design Storm" means the runoff produced by the 85 th percentile twenty-four (24) hour storm event at the Town (i.e., 0.88 inches) for volume-based BMPs, or the 85 th percentile 1-hour storm event (with an appropriate safety factor of two (2) or greater) for flow-based BMPs (i.e., 0.20 inches).

(D) "Discretionary permit" means any coastal development permit, or any action on a development application by the Mendocino Historical Review Board in Historic Zone A or Historic Zone B as depicted on Town Plan Figure 4.13-2.

(E) "Hydromodification" means adverse changes in waterbodies associated with modification of the hydrologic balance (i.e., precipitation, surface runoff, infiltration, surface-water storage, groundwater storage, evaporation, and transpiration) resulting from development.

(F) "Impervious Surface" means a structure, surface covering, or pavement of a developed parcel or lot that prevents the land's natural ability to absorb and infiltrate rainfall or stormwater runoff. Impervious surfaces include, but are not limited to, roof-tops, walkways, patios, driveways, parking lots, paved storage areas, impervious concrete and asphalt, and any other continuous watertight pavement or covering. Pavements that are designed and maintained to be permeable, including pavers with pervious openings or joints, so that runoff infiltrates into a subsurface recharge bed and the underlying soil, if feasible, do not constitute impervious surfaces.

(G) "Low Impact Development" (LID) means a sustainable approach to stormwater management that benefits water supply and contributes to water quality protection. LID emphasizes preventive site design strategies, integrated with small-scale, distributed stormwater management practices to preserve or replicate the natural hydrologic balance through infiltration, evapotranspiration, harvesting for later on-site use, detention, or retention of runoff close to its source. By reducing runoff, LID also reduces the transport of pollutants from the site.

(H) "Runoff Control BMP" means a structural system designed to minimize post-development changes in runoff flow characteristics by processes such as infiltration, evapotranspiration, harvesting for later on-site use, detention, or retention of runoff. Examples include retention structures such as basins, ponds, topographic depressions, and stormwater vaults.

(I) "Self-retaining Area" (also called a "zero discharge area") means an area that is capable of retaining the volume of stormwater runoff produced by the design storm, using a ratio of two (2) to one (1) contributing impervious area to pervious area. Examples include graded depressions with landscaping, pervious pavement, a natural or horticultural grassland, or other landscaped area. Specific requirements for design measures for self-retaining areas are found in the Mendocino County LID Manual.

(J) "Site Design Strategies for Runoff Management" means project and site planning approaches that integrate existing site characteristics that affect runoff (such as topography, drainage patterns, vegetation, soil conditions, natural hydrologic features, and infiltration conditions) into the design of strategies aimed at preventing or reducing adverse impacts of stormwater pollutants of concern and changes in the runoff flow regime (i.e., flow rate, volume, timing, and duration) on coastal and groundwater water quality, coastal resources, and beneficial uses. Site Design strategies include, for example, minimizing impervious surfaces, maintaining or enhancing on-site infiltration, preserving existing vegetation, protecting natural hydrologic features, maximizing setbacks from sensitive resources, and avoiding construction on steep slopes with erodible soils. Additional site design measures and techniques are listed in the Mendocino County LID Manual.

(K) "Source Control Best Management Practice (BMP)" means a land use or site planning practice, including structural and operational measures, that aims to prevent runoff pollution by reducing the potential for contact between pollutants and runoff at the source of pollution. Source control BMPs are aimed at minimizing the transport of pollutants in both stormwater and urban dry weather runoff. Source control measures include, for example, covering outdoor storage areas, using efficient irrigation, proper application and clean-up of potentially harmful chemicals and fertilizers, following spill prevention plans, and proper disposal of waste. Additional source control measures are listed in the Mendocino County LID Manual.

(L) "Developments of Water Quality Concern" means certain categories of development, specified in section 20.717.010 (B)(3)(a)—(m), that have a greater potential for adverse impacts to water quality and hydrology, due to the extent of impervious surface area, type of land use, and/or proximity to coastal waters. Applicants for a Coastal Development Permit for a Development of Water Quality Concern are required to submit a Water Quality Mitigation Plan and comply with additional long-term post-development requirements to protect coastal resources.

(M) "Treatment Control BMP" means any structural system, method, or technique designed to remove pollutants and/or solids from polluted stormwater or non-stormwater runoff by processes such as gravity settling of particulate pollutants, filtration, biological uptake, media absorption, or other physical, biological, or chemical process. Examples include vegetated swales, detention basins, and storm drain inlet filters.

(Ord. No. 4395, § 2, 11-17-2017)

(A) Requirements of Construction Pollution Prevention Plan. The Construction Pollution Prevention Plan (CPPP) shall describe the temporary BMPs the development will implement to minimize erosion and sedimentation during construction, and to minimize pollution of runoff and coastal waters by construction chemicals and materials. The level of detail provided to address the plan's requirements shall be commensurate with the type and scale of the development, and the potential for adverse water quality and hydrologic impacts to coastal waters. The CPPP shall demonstrate that the development complies with the following requirements:

(1) Minimize Erosion, Pollutant Discharge, and Non-Stormwater Runoff. During construction, development shall minimize erosion, the discharge of sediment and other pollutants, and non-stormwater runoff resulting from construction activities, through the use of temporary BMPs. Development shall implement the following types of construction-phase BMPs, as applicable to the project:

(a) Erosion and Sediment Control BMPs. BMPs to minimize soil erosion and the discharge of sediment off-site or to coastal waters, including:

i. Erosion control BMPs to prevent soil from being eroded by water or wind (such as mulch, soil binders, blankets or mats, or temporary seeding).

ii. Sediment control BMPs to trap and remove eroded sediment (such as fiber rolls, silt fences, straw bales, and sediment basins).

iii. Tracking control BMPs to prevent vehicles leaving the construction area from tracking sediment off-site (such as a stabilized construction exit, and street sweeping).

(b) Pollutant Control BMPs. BMPs to minimize the discharge of other pollutants resulting from construction activities (such as chemicals, vehicle fluids, petroleum products, asphalt and cement compounds, trash, and debris) off-site or to coastal waters, including:

i. Materials management and waste management BMPs to minimize the discharge of pollutants from staging, storage, and disposal of construction chemicals and materials (such as stockpile management practices, and a debris disposal plan).

ii. Site management "good housekeeping" BMPs to minimize the discharge of pollutants from construction activities (such as maintaining an inventory of chemicals used on site, and having a written plan for the clean-up of spills and leaks).

(c) Non-Stormwater Runoff Control BMPs. BMPs to retain, infiltrate, or treat non-stormwater runoff resulting from construction activities (such as a concrete washout facility, dewatering tank, or dedicated vehicle wash area), to minimize the discharge of polluted runoff.

(2) Stabilize Soil as Soon as Feasible. Soil stabilization BMPs (such as mulching, soil binders, erosion control blankets, or temporary seeding) shall be implemented on graded or disturbed areas as soon as feasible during construction, where there is a potential for soil erosion to lead to discharge of sediment off-site or to coastal waters.

(3) Minimize Land Disturbance and Soil Compaction. Development shall minimize land disturbance during construction (e.g., clearing, grading, and cut-and-fill) and shall phase grading activities, to avoid increased erosion and sedimentation. Development shall minimize soil compaction due to construction activities, to retain the natural stormwater infiltration capacity of the soil.

(4) Minimize Damage or Removal of Vegetation. Development shall minimize the damage or removal of non-invasive vegetation (including trees, native vegetation, and root structures) during construction, to achieve water quality benefits such as transpiration, vegetative interception, pollutant uptake, shading of waterways, and erosion control.

(5) Use Designated Fueling and Maintenance Areas. Conduct fueling and maintenance of construction equipment and vehicles off-site, if feasible. Any fueling and maintenance of mobile equipment conducted on-site shall take place at a designated area located at least fifty (50) feet from coastal waters, drainage courses, and storm drain inlets, if feasible (unless these inlets are blocked to protect against fuel spills). The fueling and maintenance area shall be designed to fully contain any spills of fuel, oil, or other contaminants. Equipment that cannot be feasibly relocated to a designated fueling and maintenance area (such as cranes) may be fueled and maintained in other areas of the site, provided that procedures are implemented to fully contain any potential spills.

(6) Avoid Plastic Netting in Temporary Erosion and Sediment Control Products. Development shall avoid the use of temporary erosion and sediment control products (such as fiber rolls, erosion control blankets, mulch control netting, and silt fences) that incorporate plastic netting (such as polypropylene, nylon, polyethylene, polyester, or other synthetic fibers), in order to minimize wildlife entanglement and plastic debris pollution.

(7) Use Additional BMPs for Construction Over, In, or Adjacent to Coastal Waters. Development shall implement additional BMPs for construction taking place over, in, or adjacent to coastal waters (including wetlands), if there is a potential for construction chemicals or materials to enter coastal waters. BMPs shall include, where applicable:

(a) Tarps to Capture Debris and Spills. Use tarps or other devices to capture debris, dust, oil, grease, rust, dirt, fine particles, and spills to protect the quality of coastal waters.

(b) BMPS for Use of Preservative-Treated Wood in Aquatic Environments. If preservative-treated wood is used, implement appropriate BMPs that meet industry standards for selection, storage, and construction practices for use of preservative-treated wood in aquatic environments. At a minimum, implement the standards identified by the Western Wood Preservers Institute, et al. in: Treated Wood in Aquatic Environments: A Specification and Environmental Guide to Selecting, Installing and Managing Wood Preservation Systems in Aquatic and Wetland Environments (2012, or current revision thereof).

(c) Non-Petroleum Hydraulic Fluids. Use non-petroleum hydraulic fluids in principal heavy equipment operated for one (1) week or longer over, in, or adjacent to coastal waters (including wetlands and intertidal areas), if leaks or spills of hydraulic fluid from this equipment cannot be contained and could potentially enter coastal waters.

(8) Avoid Grading During the Rainy Season. Development shall avoid grading during the rainy season (from October 15 th through May 15 th ), unless the Planning Director determines one (1) of the following:

(a) Extension. If the Director grants an extension for a specific length of time, based on an inspection of the site, and a determination that conditions at the project site are suitable for continued work with appropriate erosion and sedimentation control measures that will be maintained during the activity; or

(b) Emergency. If the Director allows grading under emergency conditions, and BMPs to protect coastal resources are implemented where feasible.

(9) Manage Construction-Phase BMPs. Appropriate protocols shall be implemented to manage construction-phase BMPs (including installation, ongoing operation, inspection, maintenance, and training), to protect coastal water quality.

(10) Use an Appropriate BMP Guidance Manual. The selection of BMPs for the Construction Pollution Prevention Plan shall be guided by the current edition of the California Stormwater Quality Association (CASQA) Construction BMP Handbook, or by the current edition of a BMP manual that has been designed to address local or regional runoff conditions and has been approved by the North Coast Regional Water Quality Control Board.

(B) Requirements of Post-Development Runoff Plan. The Post-Development Runoff Plan (PDRP) shall describe the runoff management Site Design strategies, pollutant Source Control BMPs, and other measures the development will implement to minimize stormwater pollution and changes in runoff flows from the site after development is completed, in order to protect and, where feasible, restore the quality of coastal waters. The level of detail provided to address the plan's requirements shall be commensurate with the type and scale of the project, and the potential for adverse water quality and hydrologic impacts to coastal waters. The PDRP shall demonstrate that the development complies with the following requirements:

(1) Address Runoff Management Early in Site Design Planning. All development shall address runoff management early in site design planning and alternatives analysis, and shall implement appropriate and feasible site design strategies for runoff management.

Site design strategies for runoff management are project design and site layout techniques that integrate existing site characteristics that affect runoff (such as topography, drainage patterns, vegetation, soil conditions, natural hydrologic features, and infiltration conditions) into the design of strategies to minimize post-development changes in the runoff flow regime, control pollutant sources, and where necessary remove pollutants.

Applicants shall implement LID site design strategies and Best Management Practices (BMPs)to minimize post-development changes in stormwater runoff flows, and minimize post- development polluted runoff, to the extent appropriate and feasible. Site design BMPs may reduce the need for Treatment Control and Runoff Control BMPs, and thus shall be integrated into the project design at the earliest planning stage, prior to the integration of Treatment Control and Runoff Control BMPs.

(2) Give Precedence to a Low Impact Development Approach to Stormwater Management. All development shall give precedence to the use of a Low Impact Development (LID) approach to stormwater management, to preserve the natural hydrologic functions of the site and minimize post-development changes in the site's runoff flow regime. LID emphasizes preventive site design strategies, integrated with small-scale, distributed BMPs that replicate the site's pre-development hydrologic balance through infiltration, evapotranspiration, harvesting for later on-site use, detention, or retention of stormwater close to the source.

In implementing an LID approach, priority shall be given to the use of LID site design strategies (such as reducing impervious surface area) to minimize post-development changes in the site's stormwater flow regime, supplemented by the use of structural LID BMPs (such as a bioretention system) if needed to mitigate any unavoidable changes in runoff flows. Use of LID site design strategies can reduce the volume of stormwater runoff generated, and thus reduce the need for and size of structural LID BMPs required.

LID Site Design Strategies and BMPs include, but are not limited to, the following:

(a) Protect and Restore Natural Hydrologic Features. Site and design development to protect and, where feasible, restore the site's natural hydrologic features and drainage patterns that provide stormwater infiltration, treatment, storage, or conveyance. Examples include:

i. Preserve natural drainage patterns, drainage swales, groundwater recharge areas, floodplains, and topographical depressions that can provide storage of small storm volumes.

ii. Preserve natural stream corridors, rivers, and wetlands, and establish appropriate setback and buffer areas.

(b) Preserve or Enhance Vegetation. Site and design development to preserve or enhance non-invasive vegetation, in order to achieve water quality benefits such as transpiration, interception of rainfall, pollutant uptake, shading of waterways to maintain water temperature, and erosion control. Examples include:

i. Minimize removal of natural non-invasive vegetation.

ii. Plant non-invasive trees, shrubs, and herbaceous vegetation, preferentially native plants.

iii. Plant and preserve healthy established trees that include both evergreens and deciduous species, as applicable.

iv. Preserve vegetation that exists or is established to protect a stream, river, lake, reservoir, or coastal area.

(c) Maintain or Enhance On-Site Infiltration. Site and design development to maintain or enhance on-site infiltration of runoff, where appropriate and feasible, in order to preserve natural hydrologic conditions, recharge groundwater, attenuate runoff flows, retain dry-weather runoff on-site, and minimize transport of pollutants. Examples include:

i. Locate new development to preserve infiltration capacity at the site and/or in other areas of the Town that are capable of receiving additional infiltration.

ii. Concentrate development on portions of the site with less permeable soils, and preserve areas that can promote infiltration.

iii. Minimize unnecessary soil compaction, which can greatly reduce the infiltrative capacity of soils.

iv. Maintain or improve soil quality through soil amendments and enhancement of the microbial community, to enhance the soil's infiltration and pollutant removal capacity.

v. Install an infiltration/evapotranspiration BMP such as a bioretention system, vegetated swale, or rain garden.

(d) Minimize Impervious Surface Area. Site and design development to minimize overall impervious coverage of the site, by minimizing the installation of impervious surfaces (including pavement, sidewalks, driveways, patios, parking areas, streets, and roof-tops), in order to reduce runoff. Where feasible, increase the area of pervious surfaces in re-development. Examples include:

i. Downsize impervious coverage by minimizing the footprint of buildings and impervious pavement (such as a shorter driveway, narrower road, or smaller parking lot).

ii. Where pavement is required, install a permeable pavement system (e.g., interlocking concrete pavers, porous asphalt, permeable concrete, or reinforced grass or gravel), where appropriate and feasible. Design permeable pavements so that runoff infiltrates into a subsurface recharge bed and the underlying soil, if feasible, thereby reducing the runoff from a site, filtering pollutants, and enhancing groundwater recharge.

(e) Disconnect Impervious Surface Areas from Storm Drain System. Site and design development to minimize directly-connected impervious areas, which are areas covered by a building, impermeable pavement, or other impervious surfaces that drain directly into the storm drain system without first flowing across permeable areas (such as vegetative landscaping). Convey runoff from impervious surfaces into permeable areas in a non-erosive manner. Examples include:

i. Direct roof-top runoff into self-retaining areas, such as permeable landscaped areas, instead of to the storm drain system.

ii. Direct runoff from impervious pavement into distributed permeable areas such as turf, recreational areas, medians, parking islands, and planter boxes.

iii. Design curbs, berms, and similar structures to avoid isolation of vegetative landscaping and other permeable areas, and allow runoff to flow from impervious pavement to permeable areas for infiltration.

iv. Install an infiltration BMP such as a vegetated swale or filter strip to intercept runoff sheet flow from impervious surfaces.

v. Install a rainwater harvesting BMP, such as a rain barrel or cistern, to capture and store runoff from roof-tops for later use in on-site irrigation.

(f) Protect Natural Landforms: Development shall define the development envelope and protected areas, identifying areas that are most suitable for development and areas to be left undisturbed.

(g) Participate in the Town Stormwater Drainage Management System. Development shall participate in the Town stormwater drainage management system, when it is established by the County, the Mendocino City Community Services District, or others, in consultation with Town residents, business owners, State Parks, and other stakeholders.

(3) Use Alternative BMPs Where On-Site Infiltration is Not Appropriate. If on-site infiltration of runoff may potentially result in adverse impacts (including, but not limited to, geologic instability, flooding, or pollution of coastal waters), the development shall substitute alternative BMPs that do not involve on-site infiltration, to minimize changes in the runoff flow regime to the extent appropriate and feasible. Alternative BMPs shall also be used where infiltration BMPs are not adequate to treat a specific pollutant of concern attributed to the development, or where infiltration practices would conflict with regulations protecting groundwater. Examples of alternatives to infiltration BMPs include:

(a) Install a Green Roof or Flow-through Planter. Install a vegetated "green roof" (e.g., roof-top garden) or flow-through planter box that does not infiltrate runoff into the ground, and instead uses evapotranspiration to reduce runoff.

(b) Install Rainwater Harvesting System. Install a rainwater harvesting system (such as a rain barrel or cistern) to capture and store roof-top runoff for later on-site use of non-potable water that drains to the sanitary sewer or storm drain system (such as flushing toilets).

(c) Direct Runoff to Off-site Infiltration Facility. Direct runoff from the development to an off- site regional infiltration facility.

(d) Direct Runoff to Storm Drain System. If appropriate and feasible BMPs have been implemented to reduce runoff volume, velocity, and flow rates, direct runoff to the storm drain system.

(4) Use Source Control BMPs. All development shall implement appropriate and feasible long-term, post-development pollutant Source Control BMPs to minimize the transport of pollutants in runoff from the development.

Source Control BMPs are structural features or operational practices that control pollutant sources and keep pollutants segregated from runoff. Examples include covering outdoor storage areas, using efficient irrigation, proper application and clean-up of potentially harmful chemicals and fertilizers, and proper disposal of waste.

(5) Address Runoff from Impervious and Semi-Pervious Surfaces. Runoff from all new and/or replaced impervious and semi-pervious surfaces shall be addressed in the plan. For sites where the area of new and/or replaced impervious and semi-pervious surfaces is greater than or equal to fifty (50) percent of the pre-existing impervious and semi-pervious surfaces, runoff from the entire developed area, including the pre-existing surfaces, shall be addressed in the plan.

(6) Prevent Adverse Impacts to Environmentally Sensitive Habitat Areas from Runoff. In areas in or adjacent to an Environmentally Sensitive Habitat Area (ESHA), development shall be sited and designed to protect the ESHA from any significant disruption of habitat values resulting from the discharge of stormwater or dry weather flows.

(7) Minimize Discharges of Dry Weather Runoff to Coastal Waters. Development shall be planned, sited, and designed to minimize discharges of dry weather runoff to coastal waters, to the maximum extent feasible. Examples include:

(a) Use Efficient Irrigation. Use efficient irrigation techniques that minimize off-site runoff.

(b) Design Vehicle Washing Areas to Minimize Runoff. Design vehicle washing areas so that wash water is conveyed to an infiltration system, recycling system, or sanitary sewer system, to minimize off-site runoff.

(8) Minimize Adverse Impacts of Discharges from Stormwater Outfalls. Development shall be planned, sited, and designed to avoid the adverse impacts of discharging concentrated flows of stormwater or dry weather runoff through stormwater outfalls to coastal waters, intertidal areas, beaches, bluffs, or stream banks. Development shall comply with the following requirements:

(a) Avoid Construction of New Stormwater Outfalls. Avoid construction of new stormwater outfalls, and direct stormwater to existing facilities with appropriate treatment and filtration, where feasible.

(b) Minimize Adverse Impacts to Coastal Resources from Unavoidable Stormwater Outfalls. Where new development or redevelopment of a stormwater outfall that discharges directly to coastal waters, intertidal areas, beaches, bluffs, or stream banks cannot be avoided, plan, site, design, and manage outfalls to minimize adverse impacts to coastal resources. To minimize adverse impacts, development shall:

i. Consolidate existing and new stormwater outfalls, where appropriate.

ii. Implement design and management features to minimize discharges of dry weather runoff through stormwater outfalls.

iii. Implement design and management features to minimize adverse impacts to coastal resources resulting from discharges of stormwater or dry weather runoff through stormwater outfalls.

(9) Prevent Erosion at Stormwater Outlets. Protective measures shall be used to prevent erosion at stormwater outlets (including outlets of pipes, drains, culverts, ditches, swales, or channels), if the discharge velocity will be sufficient to potentially cause erosion from concentrated runoff flows. The type of measures selected for outlet erosion prevention shall be prioritized in the following order, depending on the characteristics of the site and the discharge velocity:

(a) Use Vegetative Bioengineered Measures. Vegetative bioengineered measures for outlet protection (such as plant wattles) shall be given preference, rather than hardened structures, where site conditions are favorable for these measures to be feasible and effective. Where plant wattles are not feasible, other bioengineered measures (such as rock and plant pole cuttings) shall be considered for outlet erosion prevention.

(b) Use Hardened Structure Consisting of Loose Material. Where a vegetative bioengineered measure is not feasible or effective, a hardened structure consisting of loose material (such as a rip-rap apron or rock slope protection) shall be considered for outlet erosion prevention.

(c) Use Fixed Energy Dissipation Structure. Where none of the above measures would be feasible or effective, a fixed energy dissipation structure (such as a concrete apron, grouted rip-rap, or baffles) designed to handle the range of flows exiting the outlet shall be used for outlet erosion prevention. It is anticipated that larger outlets will require a fixed energy dissipation structure.

(10) Manage BMPs for the Life of the Development. Appropriate protocols shall be implemented to manage post-development BMPs (including ongoing operation, maintenance, inspection, and training) in all development, to protect coastal water quality for the life of the development.

(11) Use an Appropriate BMP Guidance Manual. The current edition of the Mendocino County Low Impact Development (LID) Manual shall be used for selecting and sizing of BMPs for the Post-Development Runoff Plan. The selection of BMPs may also be guided by the current edition of the California Stormwater Quality Association (CASQA) New Development and Redevelopment BMP Handbook (https://www.casqa.org/resources/bmp-handbooks/new-development-redevelopment-bmp-handbook), or by the current edition of a BMP manual that has been designed to address local or regional runoff conditions and has been approved by the North Coast Regional Water Quality Control Board.

(C) Requirements of Water Quality Mitigation Plan (WQMP). Developments of Water Quality Concern shall be designed using site design measures, Source Control BMPs, LID BMPs, and Treatment Control BMPs (when additional pollutant removal is required). Where required, Runoff Control BMPs shall be designed, installed, and maintained to retain runoff from the applicable design storm on-site, to minimize post-development changes in runoff volume, flow rate, timing, and duration. Incorporating these measures into the project design will help to minimize the amount of pollution and runoff leaving the site, resulting in the overall objective of coastal water and ground water quality protection, and coastal resource protection.

The WQMP shall demonstrate that a Development of Water Quality Concern complies with the following requirements:

(1) Prepare Plan by a Qualified Licensed Professional. A California-licensed professional (e.g., Registered Professional Civil Engineer, Geotechnical Engineer, Geologist, Engineering Geologist, Hydrogeologist, or Landscape Architect) qualified to complete this work shall be in responsible charge of preparing the Water Quality and Hydrology Plan for a Development of Water Quality Concern.

(2) Conduct a Polluted Runoff and Hydrologic Site Characterization. A polluted runoff and hydrologic characterization of the existing site (e.g., potential pollutants in runoff, soil properties, infiltration rates, depth to groundwater, and the location and extent of hardpan and confining layers) shall be conducted, as necessary to design the proposed BMPs.

(3) Address Runoff from Impervious and Semi-Pervious Surfaces. Runoff from all new and/or replaced impervious and semi-pervious surfaces shall be addressed in the plan. For sites where the area of new and/or replaced impervious and semi-pervious surfaces is greater than or equal to fifty (50) percent of the pre-existing impervious and semi-pervious surfaces, runoff from the entire developed area, including the pre-existing surfaces, shall be addressed in the plan.

(4) Size LID, Runoff Control, and Treatment Control BMPs Using the 85 th Percentile Design Storm Standard. Any LID, Runoff Control, or Treatment Control BMP (or suite of BMPs) implemented to comply with WQMP requirements shall be sized, designed, and managed to infiltrate, retain, or treat, at a minimum, the stormwater runoff produced by the 85 th percentile twenty-four (24) hour design storm event at the Town for volume-based BMPs, or two (2) times the 85 th percentile one (1) hour design storm event for flow-based BMPs. The standards and specifications for Regulated Projects found within the current edition of the Mendocino County Low Impact Development (LID) Manual (http://www.co.mendocino.ca.us/planning/pdf/MC\_Lid\_Manuel\_2015.pdf) shall be used for guidance in designing BMPs.

(5) Use an LID Approach to Retain the Design Storm Runoff Volume On-Site. The development shall implement an LID approach to stormwater management that will retain on-site (by means of infiltration, evapotranspiration, or harvesting for later on-site use) the runoff volume produced by the 85 th percentile twenty-four (24) hour design storm (see 20.717.020 (C)(4)), to the extent appropriate and feasible.

(6) Conduct an Alternatives Analysis if the Design Storm Runoff Volume Will Not be Retained On-Site Using an LID Approach. If the proposed development will not retain on-site the runoff volume produced by the 85 th percentile twenty-four (24) hour design storm (see 20.717.020 (C)(4)), using an LID approach, an alternatives analysis shall be conducted. The alternatives analysis shall demonstrate that:

(a) There are No Feasible Alternative Project Designs. Demonstrate that there are no appropriate and feasible alternative project designs (such as a reduced project footprint) that would enable on-site retention of the runoff volume produced by the 85 th percentile twenty-four (24) hour design storm, giving precedence to an LID approach.

(b) On-Site Runoff Retention is Maximized. Demonstrate that on-site runoff retention is maximized to the extent appropriate and feasible, giving precedence to an LID approach.

(c) Feasibility of Off-Site Runoff Retention is Considered. If 20.717.020 (C)(6)(a) and (b), above, are demonstrated, some or all of the runoff volume produced by the 85 th percentile twenty-four (24) hour design storm may be retained off-site, if it is demonstrated that off-site options will feasibly contribute to meeting the development's runoff retention and treatment requirements.

(7) Use Treatment Control BMPs to Remove Pollutants if Necessary. Treatment Control BMPs shall be implemented, if needed, to remove a specific pollutant of concern attributed to the development. Treatment Control BMPs shall treat runoff prior to conveyance off-site.

Treatment Control BMPs are structural systems designed to remove pollutants from runoff by processes such as gravity settling of particulate pollutants, filtration, biological uptake, media adsorption, or other physical, biological, or chemical process. Examples of these BMPs include vegetated swales, detention basins, bioretention facilities, and storm drain or trench drain inlet filters.

Combinations of structural and operational BMPs, with monitoring and reporting to assure BMP functionality over the economic life of the proposed development, may be required to avoid significant adverse coastal water quality and hydrologic impacts from stormwater runoff.

The following applicability and performance standards shall be required for Treatment Control BMPs:

(a) Use Treatment Control BMPs to Remove Pollutants from any Design Storm Runoff Not Retained On-Site. The development shall implement a Treatment Control BMP (or suite of BMPs) to remove pollutants of concern from any portion of the runoff produced by the 85 th percentile twenty-four (24) hour design storm (see 20.717.020 (C)(4)) that is not retained on-site using an LID or comparable approach.

(b) Use Treatment Control BMPs Prior to Infiltration Where Necessary and Effective. Where infiltration BMPs are not adequate to remove a specific pollutant of concern attributed to the development, an effective Treatment Control BMP (or suite of BMPs) shall be required prior to infiltration of runoff, or else an alternative BMP that does not involve infiltration shall be substituted for the infiltration BMP.

(c) Select Treatment Control BMPs Effective for Pollutants of Concern. Where a Treatment Control BMP is required, a BMP (or suite of BMPs) shall be selected that has been shown to be effective in reducing the pollutants of concern generated by the proposed land use.

(d) Implement Site Design and Source Control BMPs First. Site design measures and Source Control BMPs shall be implemented, as applicable, to reduce runoff and reduce pollutant loads, prior to designing and implementing Treatment Control BMPs.

(e) Give Preference to Bioretention Facilities. Bioretention facilities (designed using the specifications found in the Mendocino County LID Manual) shall be used to treat, infiltrate, or evapotranspire the runoff produced by the 85 th percentile, twenty-four (24) hour design storm, as a preference to directing stormwater runoff to existing stormwater outfalls.

(f) Size Flow-Through BMPs Properly. Flow-through BMPs shall be designed to treat two (2) times the runoff produced by the 85 th percentile one (1) hour storm event.

(8) Runoff Control BMPs. Runoff Control BMPs shall be implemented, if needed, when site design measures and LID BMPs are not adequate to minimize adverse post-development changes in runoff volumes, flow rate, timing, and duration, which may adversely impact coastal waters, habitat, and real property through hydromodification.

Runoff Control BMPs are structural systems designed to minimize post-development changes in runoff flow characteristics using processes such as infiltration, evapotranspiration, harvesting for later on-site use, detention, or retention of runoff. Examples include retention structures such as basins, ponds, topographic depressions, and stormwater vaults.

(a) Runoff Control BMPs Using Flow Retention Techniques. A proposed development that will add a net total of fifteen thousand (15,000) square feet or more of impervious surface area shall implement a Runoff Control BMP that uses Flow Retention techniques to capture and retain any portion of the runoff volume produced by the 85 th percentile, twenty-four (24) hour design storm (see 20.717.020 (C)(4)) that will not be retained on-site using an LID approach. LID has proven to be an effective approach to stormwater management in other parts of the country, and is seen in California as the preferred alternative to conventional stormwater management. Flow Retention techniques shall optimize on-site infiltration, and shall use stormwater storage, harvesting for later on-site use, and/or evapotranspiration to address any of the required runoff flow retention volume that cannot be infiltrated.

(b) Runoff Control BMPs Using Peak Management Techniques. In addition to using Flow Retention techniques, a proposed development that will add a net total of twenty-two thousand five hundred (22,500) sq. ft. or more of impervious surface area shall also implement a Runoff Control BMP that uses Peak Management Techniques to prevent the volume of post-development runoff peak flows discharged from the site from exceeding pre-project peak flow volumes for the two (2) year through ten (10) year recurrence storm events at the Town of Mendocino (or its reference rain measurement location).

(9) Use Appropriate BMPs For High-Pollutant Land Uses. Commercial and industrial developments with a potential for a high concentration of pollutants (including, but not limited to, outdoor work and storage areas, restaurants, roads and highways, parking lots, and vehicle service facilities) shall implement appropriate Site Design and Source Control BMPs to keep pollutants out of stormwater, and shall either use Treatment Control BMPs to remove pollutants of concern before discharging runoff to coastal waters or the storm drain system, or shall connect the pollutant-generating area to the sanitary sewer.

(a) Source Control BMPs for Specific Land Uses:

i. Outdoor Materials Storage. In outdoor areas used for storage of materials that may contribute pollutants (e.g., debris, sediment, and chemicals) to the stormwater conveyance system, these materials shall be placed in an enclosure (e.g., cabinet or shed) that prevents contact of the pollutants with runoff, and prevents spillage to the stormwater conveyance system; alternatively, the materials shall be protected by secondary containment structures such as berms, dikes, or curbs. Also, the storage area shall be graded to prevent run-on or run-off and sufficiently impervious to contain leaks and spills, and shall have a roof or awning to minimize collection of stormwater within the secondary containment area.

ii. Outdoor Solid Waste Storage Areas. Solid waste and recycling receptacle areas shall be designed to divert runoff drainage from adjoining roofs and pavements away from the receptacle. The solid waste and recycling container shall be screened or walled to prevent off-site transport of trash, including transport by wind. Solid waste and recycling receptacles shall also be covered when not in use, and during storm events.

iii. Large Commercial/Industrial Developments. In large commercial developments, the following shall be required: loading dock areas shall be covered, or else designed to minimize run-on and runoff of stormwater drainage; direct connections to storm drains from depressed loading docks (e.g., truck wells) shall be prohibited; repair/maintenance bays shall be indoors, or else designed to not allow stormwater run-on or contact with stormwater runoff; the drainage system for a repair/maintenance bay shall capture all wash water, leaks, and spills, and shall connect to a sump for collection and disposal; direct connection of the sump to the storm drain system shall be prohibited. If proposed as a necessary component in a development, require an area for washing/steam cleaning of vehicles and or equipment to be self-contained and/or covered, is equipped with a clarifier or other pre-treatment facility, and is properly connected to a sanitary sewer or other appropriately-permitted disposal facility.

iv. Food Service. An area for the washing/steam cleaning of equipment and accessories that is self-contained, equipped with a grease trap, and properly connected to a sanitary sewer is required, unless an alternative equivalent is approved by the Mendocino County Department of Environmental Health. If the washing/steam cleaning area is located outdoors, the area shall be covered, paved, have secondary containment, and be connected to the sanitary sewer or other appropriately-permitted disposal facility.

v. Fuel Dispensing Areas. For a petroleum products service station or other land use uses with on-site fueling system stations, the following shall be required: the fuel dispensing area shall be covered with an overhanging roof structure or canopy with minimum dimensions, if feasible, equal to or greater than the area within the grade break. Such canopy shall not drain onto the fuel dispensing area, and the canopy downspouts must be routed to prevent drainage across the fueling area; the fuel dispensing area must be paved with Portland cement concrete or equivalent smooth impervious surface; use of asphalt concrete shall be prohibited.

vi. Vehicle Repair and Maintenance Shops. For vehicle repair and maintenance shops, the following shall be required: repair/maintenance bays shall be indoors, or designed to not allow stormwater run-on or contact with stormwater runoff; the drainage system for a repair/maintenance bay shall capture all wash water, leaks, and spills, and connect to a sump for collection and disposal; direct connection to the storm drain system shall be prohibited; an area for washing/steam cleaning of vehicles and equipment shall be required, and the area shall be self-contained and/or covered, equipped with a clarifier or other pre-treatment facility, and properly connected to a sanitary sewer or other appropriately-permitted disposal facility; loading dock areas shall be covered, or else designed to minimize run-on and runoff of stormwater drainage; direct connections to storm drains from depressed loading docks (e.g., truck wells) shall be prohibited.

vii. Repair and Maintenance Bays. For repair and maintenance bays, the following shall be required: repair and maintenance bays must be indoors, or else designed to not allow stormwater run-on or contact with stormwater runoff; repair and maintenance bays shall be designed to capture all wash water, leaks, and spills. All bay drains shall be connected to a sump for collection and disposal. A direct connection of the bays to the storm drain system is prohibited.

viii. Vehicle and Equipment Wash Areas. For vehicle and equipment wash areas, the following shall be required: the area for washing/steam cleaning of vehicles and equipment is required to be self-contained and/or covered, and equipped with a clarifier or; the area shall be properly connected to a sanitary sewer or other appropriately-permitted disposal facility; commercial vehicle washing in areas without specially designed wash areas is prohibited.

Additional examples of Source Control BMPs can be found in the California Stormwater Quality Association Stormwater Best Management Practice Handbook for New and Redevelopment (https://www.casqa.org/resources/bmp-handbooks/new-development-redevelopment-bmp-handbook) and in the Mendocino County LID Manual.

(10) Design and Manage Parking Lots to Minimize Polluted Runoff. A parking lot over five thousand (5,000) square feet in area shall be designed to minimize impervious surfaces, and the parking lot runoff shall be treated and/or infiltrated before it discharges to coastal waters or the storm drain system, so that heavy metals, oil and grease, and polycyclic aromatic hydrocarbon pollutants on parking lot surfaces will not enter coastal waters. Parking lot design and management shall include:

(a) Parking Lot Landscaping. The design of landscaped areas for parking lots shall consider, and may, where appropriate, be required to include provisions for the on-site detention, retention, and/or infiltration of stormwater runoff, in order to reduce and slow runoff, and provide pollutant cleansing and groundwater recharge. Where landscaped areas are designed for detention, retention, and/or infiltration of stormwater runoff from the parking lot, recessed landscaped catchments (below the elevation of the pavement) shall be required. Curb cuts shall be placed in curbs bordering landscaped areas, or else curbs shall not be installed, in order to allow stormwater runoff to flow from the parking lot into landscaped areas. All surface parking areas shall be provided a permeable buffer between the parking area and adjoining streets and properties.

(b) Parking Lot Vacuuming. Accumulations of particulates that may potentially be contaminated by oil, grease, or other pollutants shall be removed from heavily used parking lots (e.g., fast food outlets, lots with twenty-five (25) or more parking spaces, sports event parking lots, shopping malls, grocery stores, and discount warehouse stores) by dry vacuuming or equivalent techniques.

(c) Filter Maintenance. Filter treatment systems, particularly for hydrocarbon removal BMPs, shall be adequately maintained.

(11) Manage BMPs for the Life of the Development. Appropriate protocols shall be implemented to manage BMPs (including ongoing operation, maintenance, inspection, and staff training), to protect coastal water quality for the life of the development.

(a) Operation and Maintenance Plan for All BMPs. All post-development BMP's shall be inspected, cleaned, and repaired when necessary prior to September 30 th of each year; additional inspections should occur after storms as needed throughout the rainy season. Owners, heirs, and assigns of parcels (lots) with BMPs shall be responsible for ensuring that all BMPs continue to function as intended for the economic life of the development. Repairs, modifications, or installation of additional BMPs, as needed, shall be carried out prior to the next rainy season. The Planning Director, or his/her designee who reviews the required post-development plans for a proposed development project shall determine if the development's post-development BMPs require monitoring to maintain their effectiveness, and shall specifically require such a monitoring program be included in the project development application before it may be deemed complete for filing and processing. The template for operation and maintenance plans in the current version of the Mendocino County LID Manual shall be used to detail such plans for each required BMP.

(Ord. No. 4395, § 2, 11-17-2017)

(A) Information about Existing Project Site Conditions. In addition to the required content for each water quality protection plan specified in sections 20.717.025 (B)—(D), below, the following information about the existing project site conditions shall be submitted, if applicable to the project, to enable evaluation of the project's potential water quality and hydrologic impacts:

(1) Location Map. A location map, drawn to scale, showing the location of the development, and the distance from the development to the nearest coastal waters and other natural hydrologic features.

(2) Description of Existing Project Site Conditions. A site plan that illustrates and describes the following existing project site conditions:

(a) Topography and Drainage. General site topography and drainage, including natural hydrologic features that may provide stormwater infiltration, treatment, storage, or conveyance (such as groundwater recharge areas, stream corridors, floodplains, and wetlands), and any existing structural stormwater conveyances or BMPs.

(b) Nearby Coastal Waters and ESHA. Location of coastal waters and Environmentally Sensitive Habitat Areas (ESHA) within two hundred (200) feet of the project site, indicating whether site runoff drains to these areas.

(c) Discharges to Impaired Waters or ASBS. Whether runoff discharges to receiving waters listed for water quality impairment on the most recent Clean Water Act Section 303(d) list, or to an Area of Special Biological Significance (ASBS).

(d) Structures and Pavement. Existing structures, impervious surface areas, permeable pavements, utilities, and vegetated areas. An accompanying table shall quantify the extent of such areas.

(e) Potential Contamination. Any previous land use on the site with a potential for a historic source of contamination, and any known soil or water contamination.

(B) Construction Pollution Prevention Plan Application Requirements:

(1) Submittal of Construction Pollution Prevention Plan (CPPP). An applicant shall submit a preliminary CPPP (based on site conditions and project features known at the time of application) with the CDP application, and shall submit a final CPPP for approval prior to construction. The information provided to address the plan's requirements may be submitted as a stand-alone document, or incorporated into the CDP application materials. Any changes to the final CPPP after issuance of the Coastal Development Permit shall be subject to additional authorization by the Planning Director.

To comply with the California State Water Resources Control Board (SWRCB) stormwater permit requirements, an applicant proposing certain size or types of development, including industrial facilities, may be required to develop and implement a Stormwater Pollution Prevention Plan (SWPPP) that addresses construction activities. Applicants submitting a SWPPP to meet SWRCB requirements shall also submit a CPPP to meet the Town's requirements for review of a Coastal Development Permit application. Applicable information provided in the SWPPP may also be included as part of the CPPP.

(2) Content of Construction Pollution Prevention Plan (CPPP). To comply with the CPPP requirements listed in 20.717.020 (A), above, the CPPP shall include a construction site map and a narrative description addressing, at a minimum, the following required components, if they are applicable to the development. The level of detail provided to address the plan's requirements shall be commensurate with the type and scale of the project, and the potential for adverse water quality or hydrologic impacts to coastal waters.

(a) Construction Site Plan Map. A map delineating the construction site, construction phasing boundaries, and the location of all temporary construction-phase BMPs (such as silt fences, inlet protection, and sediment basins).

(b) Construction Phasing Schedule. A construction phasing schedule, with a description and timeline of significant land disturbance activities.

(c) Description of BMPs to be Implemented to Meet All CPPP Requirements. A description of the BMPs that will be implemented to meet all the CPPP requirements listed in section 20.717.020 (A), above, and how these BMPs will minimize pollution of runoff and coastal waters. Include calculations that demonstrate proper sizing of the BMPs. The CPPP shall contain a site-specific erosion control plan that includes controls on grading (i.e., timing and amounts); BMPs for staging, storage, and disposal of construction materials; design specifications for BMPs such as sedimentation basins, and landscaping or revegetation of graded or disturbed areas; and specific measures for protecting any Environmentally Sensitive Habitat Areas (ESHAs) on the project site or on an adjacent (contiguous) parcel or lot against potential project erosion or sedimentation effects.

(d) Construction-Phase BMP Management Plan. A description and schedule for the management of all construction-phase BMPs (including installation and removal, ongoing operation, inspection, maintenance, and staff training) as needed to ensure protection of coastal resources. Identify any temporary BMPs that will be converted to permanent post-development BMPs.

(C) Post-Development Runoff Plan Application Requirements:

(1) Submittal of Post-Development Runoff Plan (PDRP). An applicant shall submit a preliminary PDRP (based on site conditions and project features known at the time of application) with the Coastal Development Permit application, and shall submit a final PDRP prior to issuance of the Coastal Development Permit.

(2) Content of Post-Development Runoff Plan (PDRP). The PDRP shall include a site plan, site design measures, source control BMPs and, if necessary treatment control and baseline hydromodification BMPs. Post-development plans detailing how stormwater and polluted runoff will be managed or mitigated shall be included, as applicable, in the design of all projects that require a Coastal Development Permit or approval by the Mendocino Historic Review Board. At the earliest stage, post-development site design measures, including the Town stormwater management system after it is adopted and approved consistent with applicable County, State, and Federal standards, shall be considered and integrated into all required development project design plans. Required development project applications shall include relevant details identifying how the project will use applicable treatment control BMPs and baseline hydromodification BMPs, designed, installed, and maintained for the 85 th percentile, twenty-four (24) hour storm event (for volume-based BMPs) or the 85 th percentile, one (1) hour storm event (with a safety factor of two (2) or more, for flow-through BMPs), to minimize the project's adverse effects on water quality and runoff flow regime to the extent feasible. The following information shall be included in the submitted design plans (for which the Storm Water Control Plan methodology of the Mendocino County LID Manual constitutes guidance), if applicable to the development. The level of detail provided to address the plan's requirements shall be commensurate with the type and scale of the project, and the potential for adverse water quality or hydrologic impacts to coastal waters.

(a) PDRP Site Plan. A site plan that shows post-development structural BMP's, stormwater conveyances and discharges, structures, pavements, and utilities, with contour intervals appropriate to identify post-development topography, finished grades, and drainage patterns;

(b) Conformance with Town Stormwater Management System. A description of how the development will be planned, sited, and designed to conform to the Town stormwater management system, including, but not limited to, through avoidance of adverse impacts of discharging concentrated flows of stormwater or dry weather runoff through stormwater outfalls to coastal waters, intertidal areas, beaches, bluffs, or stream banks;

(c) Description of BMPs to be Implemented to Meet All PDRP Requirements. A description of the BMPs that will be implemented to meet all the PDRP requirements listed in 20.717.020 (B), above, and how these BMPs will minimize stormwater pollution and post-development changes in runoff flows from the development. Include a schedule for installation or implementation of all post-development BMPs. The PDRP shall include a site-specific polluted runoff control plan that demonstrates how runoff will be (a) diverted from impermeable surfaces into permeable areas of the property in a non-erosive manner, or otherwise contained and disposed of consistent with this Chapter, and/or (b)(1) filtered and, as feasible, infiltrated either prior to conveyance off-site, or (2) filtered, and retained for later on-site use, consistent with applicable County and State stormwater quality protection and beneficial use standards. The PDRP shall also include specific source control measures, both structural and operational, designed and implemented to minimize polluted runoff;

(d) Description of Low Impact Development Approach to Stormwater Management to be Implemented. A description of the Low Impact Development (LID) approach to stormwater management (see 20.717.020 (B)(2), above) that will be implemented, or a justification if an LID approach is not selected;

(e) Source Control BMPs. Source Control BMPs that will be implemented to minimize polluted stormwater runoff;

(f) Identification Pollutants Potentially Generated. Identification of pollutants potentially generated by the proposed development that could be transported off the site by runoff;

(g) Site Design Measures. Site design measures that will be implemented to maximize the feasible retention, on-site use, and infiltration of post-development stormwater runoff. Include methods to accommodate on-site infiltration, revegetation of disturbed portions of the site, address on-site and/or off-site impacts, and construction of any necessary improvements; drainage improvements designed to retain and/or treat 85 th percentile design storm; and, as applicable, conform the development project stormwater runoff controls to the town stormwater management system;

(h) Estimate of Changes in Impervious and Semi-Pervious Surface Area. A quantification of any proposed changes in impervious surface area on the site, including pre-project and post-project impervious coverage area and the percentage of the parcel or lot that will be covered with impervious surfaces after development project completion. Include an estimate of proposed changes in the amount of directly-connected impervious areas, which drain directly into the storm drain system without first flowing across permeable areas, and an estimate of changes in site coverage with permeable pavement; and,

(i) BMP Management Plan. A description of the proposed ongoing management of post-development BMP's (including operation, maintenance, inspection, and staff training, as applicable) that will be performed for the economic life of the development, if required for the BMPs to function properly; provided, that such description may reference the Town stormwater management system when it has been adopted and implemented.

[(D)]

Water Quality Mitigation Plan Application Requirements.

(1) Submittal of Water Quality Mitigation Plan (WQMP). An applicant for a Development of Water Quality Concern shall submit a preliminary WQMP (based on site conditions and project features known at the time of application) with the Coastal Development Permit application, and shall submit a final WQMP prior to issuance of the Coastal Development Permit.

(2) Content of Water Quality Mitigation Plan (WQMP). For "Developments of Water Quality Concern," a WQMP shall be required that demonstrates how Treatment Control and/or Runoff Control BMPs will be implemented (in addition to Site Design and Source Control BMPs) as needed to minimize the discharge of polluted runoff from the development project site and to minimize post-development changes in the site's runoff flow regime. The WQMP shall be signed and stamped by a California Registered Civil Engineer, or by another professional with comparable expertise, and be approved by the Department of Planning and Building Services. The following information shall be included in a WQMP (the Regulated Project Storm Water Control Plan methodology of the Mendocino County LID Manual constitutes guidance) if applicable to the development:

(a) Post-Development Runoff Plan Information. All of the information required for the Post-Development Runoff Plan (see section 20.717.025 (C), above), including Site Design strategies and pollutant Source Control BMPs.

(b) Documentation of Polluted Runoff and Hydrologic Site Characterization. Documentation of a polluted runoff and hydrologic characterization of the existing site (e.g., potential pollutants in runoff, soil properties, infiltration rates, depth to groundwater, and the location and extent of hardpan and confining layers) as necessary to design the proposed BMPs.

(c) Description of BMPs to be Implemented to Meet All WQHP Requirements. A description of the BMPs that will be implemented to meet all the WQHP requirements listed in section 20.717.020 (C), above, and how these BMPs will minimize stormwater pollution and changes in runoff flows from the development. Include documentation of the expected effectiveness of the BMPs, a characterization of post-development pollutant loads, and calculations of changes in the stormwater runoff flow regime (i.e., volume, flow rate, timing, and duration of flows) resulting from the proposed development when implementing the proposed BMPs. The description of the BMPs shall include, as applicable:

i. Site Design Measures to maximize the retention and infiltration of post- development stormwater runoff, including:

(a) Methods to accommodate on-site infiltration, when feasible and not determined to adversely impact groundwater, landform stability, or revegetation of disturbed portions of the site;

(b) Measures to address on-site and/or off-site impacts, and construction of any necessary improvements;

(c) Drainage improvements designed to retain and/or treat the 85 th percentile design storm event (e.g., locations of diversions/conveyances for upstream runoff);

(d) Feasible measures to infiltrate and/or treat runoff from impervious surfaces (e.g., roads, driveways, parking structures, building pads, roofs, patios, etc.) on the subject parcel(s), and to discharge the runoff in a manner that avoids erosion, gullying on or downslope of the subject parcel or other discharge areas provided by the Town stormwater management system.

ii. Source Control BMPs to:

(a) Feasibly minimize polluted stormwater runoff; and

(b) Identify pollutants of concern generated by the proposed development.

iii. Treatment Control BMPs to minimize the transport of pollutants in stormwater runoff from the site, which (a) shall include calculations describing how the BMPs (or suites of BMPs) have been designed to infiltrate and/or retain, and treat the stormwater runoff produced by the 85 th percentile, twenty-four (24) hour recurrence storm event for volume-based BMPs, or the 85 th percentile one (1) hour storm event (with an appropriate safety factor of two (2) or greater) for flow-based BMPs; and (b) may include the use of structures (alone or in combination) such as biofilters, grassy swales, desilting basins, and detention ponds. Alternatively, Treatment Control BMPs may be provided by the Town stormwater management system, consistent with applicable County, State, and Federal standards. Bioretention facilities, using the Mendocino County Design Criteria, shall be given preference within the Plan design.

iv. Runoff Control BMPs (e.g., a bioretention facility) to minimize post-development changes in the site's runoff flow regime, by retaining the design storm runoff volume on-site: (a) For development projects adding a net total of fifteen thousand (15,000) sq. ft. or more impervious surface area, calculations shall be required that demonstrate appropriate sizing and design of the proposed Runoff Control BMPs (e.g., retention facilities) to capture and retain, at a minimum, the stormwater runoff produced by the 85 th percentile twenty-four (24) hour storm event, and demonstrate that on-site infiltration has been optimized; (b) For development projects adding twenty-two thousand five hundred (22,500) sq. ft. or more impervious surface area, calculations shall be required that demonstrate appropriate sizing and design of the proposed Runoff Control BMPs (e.g., retention facilities) to capture and retain, at a minimum, the peak stormwater runoff flow from the two (2) year through ten (10) year storm event, and demonstrate that on-site infiltration has been optimized. Alternatively, Runoff Control BMPs may be provided by the Town stormwater management system, consistent with applicable County and State standards.

v. Pre-development runoff rates from the parcel (lot), on which the development is proposed, during the twenty-four (24) hour, two (2) year, five (5) year, and ten (10) year storm events, and average discharge volume from the parcel (lot) perimeter.

(d) Calculations for Sizing BMPs Using the 85 th Percentile Design Storm Standard. Calculations that demonstrate that the proposed BMP (or suite of BMPs) implemented to comply with WQMP requirements (see 20.717.020 (C), above) has been sized and designed to infiltrate, retain, or treat, at a minimum, the runoff produced by the 85 th percentile twenty-four (24) hour storm event for volume-based BMPs, or two (2) times the 85 th percentile one (1) hour storm event for flow-through BMPs.

(e) Documentation that Runoff from Impervious and Semi-Pervious Surfaces is Addressed. A table quantifying the site's proposed new, replaced, and pre-existing impervious and semi-pervious surface areas. Documentation that runoff from all new and/or replaced impervious and semi-pervious surfaces is addressed. For sites where the area of added and/or replaced impervious and semi-pervious surfaces is greater than or equal to fifty (50) percent of the pre-existing impervious and semi-pervious surfaces, documentation that runoff from the entire developed area, including pre-existing surfaces, is addressed (pursuant to 20.717.020 (C)(3), above).

(f) Description of the LID Approach Used to Retain the Design Storm Runoff Volume On-Site. A description of the LID approach to stormwater management to be implemented, documenting that LID Site Design strategies have been given priority, and a description of the LID BMPs that will be used to retain on-site (by means of infiltration, evapotranspiration, or harvesting for later on-site use) the runoff produced by the 85 th percentile twenty-four (24) hour design storm (see 20.717.020 (C)(5), above), to the extent appropriate and feasible.

(g) Alternatives Analysis Documenting Site-Specific Constraints. Where an alternatives analysis is required (pursuant to 20.717.020 (C)(6), above), document the site-specific engineering constraints and/or physical conditions to justify the determination that there are no appropriate and feasible alternative project designs that would retain on-site the runoff produced by the 85 th percentile twenty-four (24) hour design storm, giving precedence to an LID approach. Also demonstrate that on-site runoff retention is maximized to the extent appropriate and feasible, and that the feasibility of off-site runoff retention is considered.

(h) BMP Management Plan. A description and schedule of the ongoing management of post-development BMPs (including operation, maintenance, inspection, and staff training) that will be performed for the life of the development, as needed for the BMPs to function properly.

(i) Potential Flow Paths. Potential flow paths on and from the parcel where erosion may occur after completion of construction. Alternatively, a flow path analysis may be provided by the Town stormwater management system.

(j) Needed Storm Drain System Upgrades. The need for upgrades to municipal storm drain systems, for discharge of pollutants (e.g., oil, heavy metals, toxics) to coastal waters, or to avoid or mitigate other potentially significant adverse stormwater runoff impacts from the proposed development project. Alternatively, the Town stormwater management system may provide for a suite of structural and operational stormwater quality best management upgrades by Town zoning district, hydrologic subarea, or in and for the entire Town.

[(E)]

Environmental Review: Provisions of this section shall be complementary to, and shall not replace, any applicable requirements for stormwater mitigation required under the California Environmental Quality Act.

(Ord. No. 4395, § 2, 11-17-2017)

(A) All applicants for a coastal development permit or for approval by the Mendocino Historical Review Board of development in Historic Zone A or Historic Zone B shall provide written verification, as part of any such application, of proposed post- development operation, maintenance, inspection and, as applicable, training and management of all BMPs. Such written verification may be by recorded legal agreement, covenant, CEQA mitigation requirement, or other device that assures that the written verification runs with the land and applies to all heirs, successors, or assigns. Verification at a minimum shall include the property owner's/developer's signed statement accepting responsibility for maintenance until the responsibility is legally transferred; in addition, one (1) of the following long-term maintenance agreements shall be submitted:

(1) A signed statement from the public entity assuming responsibility for structural and treatment control BMP maintenance and that it meets all local agency design standards; or

(2) Written text in project conditions, covenants, and restrictions (CCRs) for residential properties assigning responsibilities to the homeowners' association for maintenance of the BMP's; or

(3) Any other legally enforceable agreement that assigns responsibility for the maintenance of post- development BMPs.

(B) In addition to, or in the alternative to, subpart (A), where a development project is proposed to discharge any stormwater runoff to the Town stormwater management system, the applicant for that development project shall submit as part of the application for that development a "will serve" letter from the public agency that implements the system and has agreed to operate, inspect, and maintain it for the economic life of the development project.

(Ord. No. 4395, § 2, 11-17-2017)