(a) Requirements for all Development Projects:
(1) Follow as applicable the approach and criteria described in the State Water Resources Control Board General Permit for Storm Water Discharges Associated with Construction and Land Disturbance Activities.
(2) Except as noted in Section 67.811(b), submit a Standard Stormwater Quality Management Plan (SWQMP), with an application for a County permit or other County approval, identifying the measures that will be used for stormwater and non-stormwater management for the project consistent with the County BMP Design Manual.
(3) General Requirements. BMPs shall be designed, constructed and maintained as follows:
(A) Onsite BMPs must be located so as to remove pollutants from runoff prior to its discharge to any receiving waters, and as close to the source as possible;
(B) Structural BMPs may not be constructed in receiving waters; and
(C) Onsite BMPs must be designed and implemented with measures to avoid the creation of nuisance or pollution associated with vectors (e.g., mosquitos, rodents, or flies).
(4) Source Control BMP Requirements. Where applicable and feasible, the following source control BMPs must be implemented at all development projects:
(A) Prevention of illicit discharges into the stormwater conveyance system;
(B) Stenciling and marking of all storm drains in accordance with the BMP Design Manual;
(C) Protection of all outdoor material storage areas from rainfall, run-on, runoff, and wind dispersal including the following:
• Storage areas must be paved and sufficiently impervious to contain leaks and spills, where necessary.
• The storage area shall be sloped towards a sump or another equivalent measure that is effective to contain spills.
• Runoff from downspouts/roofs must be directed away from storage areas.
• The storage area must have a roof or awning that extends beyond the storage area to minimize collection of storm water within the secondary containment area. A manufactured storage shed may be used for small containers.
• Use other methods approved by the County.
(D) Protection of materials stored in outdoor work areas from rainfall, run-on, runoff, and wind dispersal including the following:
• Create an impermeable surface such as concrete or asphalt, or a prefabricated metal drip pan, depending on the size needed to protect the materials.
• Cover the area with a roof or other acceptable cover.
• Berm the perimeter of the area to prevent water from adjacent areas from flowing on to the surface of the work area.
• Directly connect runoff to sanitary sewer or other specialized containment system(s), as needed and where feasible. Approval for this connection must be obtained from the appropriate sanitary sewer agency.
• Locate the work area away from storm drains or catch basins.
• Use other methods approved by the County.
(E) Protection of trash storage areas from rainfall, run-on, runoff, and wind dispersal including the following:
• Design trash container areas so that drainage from adjoining roofs and pavement is diverted around the area(s) to avoid run-on. This can include berming or grading the waste handling area to prevent run-on of storm water.
• Ensure trash container areas are screened or walled to prevent offsite transport of trash.
• Provide roofs, awnings, or attached lids on all trash containers to minimize direct precipitation and prevent rainfall from entering containers.
• Locate storm drains away from immediate vicinity of the trash storage area and vice versa.
• Post signs on all dumpsters informing users that hazardous material are not to be disposed.
• Use other methods approved by the County.
(F) Implementation of additional BMPs as the County determines necessary to minimize pollutant generation.
(5) Site Design Requirements. Where applicable and feasible, the following Site Design BMPs must be implemented at all development projects:
(A) Natural storage reservoirs and drainage corridors (including topographic depressions, areas of permeable soils, natural swales, and ephemeral and intermittent streams) must be maintained or restored;
(B) Buffer zones must be provided for natural water bodies whenever technically feasible. When buffer zones are technically infeasible, other buffers such as trees and access restrictions are required;
(C) Natural areas within the project footprint should be conserved whenever possible;
(D) Streets, sidewalks, and parking lot aisles shall be constructed to the minimum widths necessary consistent with public safety;
(E) The impervious footprint of the project shall be minimized;
(F) Soil compaction to landscaped areas shall be minimized where doing so does not create an excessive risk of slope failure or erosion;
(G) Impervious surfaces shall be disconnected by disturbed pervious areas that can be used to infiltrate runoff;
(H) Landscaped or other pervious areas shall be designed and constructed to effectively receive and infiltrate, retain, and/or treat runoff from impervious areas prior to discharging to the stormwater conveyance system;
(I) Small collection strategies shall be located at, or as close as possible to, the source of the discharge;
(J) Permeable materials shall be used for projects with low traffic areas and appropriate soil conditions;
(K) Native or drought tolerant landscaping shall be used; and
(L) Precipitation shall be harvested and used for landscaping or other permitted use.
(b) Additional Requirements for Priority Development Projects. These requirements apply only to projects west of the Pacific/Salton Sea Divide. In addition to meeting the BMP requirements applicable to all other development projects as required by the NPDES Order and set forth above, the following are applicable to Priority Development Projects.
(1) Priority Development Projects include:
(A) New development projects that create 10,000 square feet or more of impervious surfaces (collectively over the entire project site). This includes commercial, industrial, residential, mixed-use, and public development projects on public or private land.
(B) Redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface (collectively over the entire project site on an existing site of 10,000 square feet or more of impervious surfaces). This includes commercial, industrial, residential, mixed-use, and public development projects on public or private land.
(C) New and redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface (collectively over the entire project site), and support one or more of the following uses:
i. Restaurants. This category is defined as a facility that sells prepared foods and drinks for consumption, including stationary lunch counters and refreshment stands selling prepared foods and drinks for immediate consumption (SIC code 5812).
ii. Hillside development projects. This category includes development on any natural slope that is twenty-five percent or greater.
iii. Parking lots. This category is defined as a land area or facility for the temporary parking or storage of motor vehicles used personally, for business, or for commerce.
iv. Streets, roads, highways, freeways, and driveways. This category is defined as any paved impervious surface used for the transportation of automobiles, trucks, motorcycles, and other vehicles.
(D) New or redevelopment projects that create and/or replace 2,500 square feet or more of impervious surface (collectively over the entire project site), and discharging directly to an ESA. "Discharging directly to" includes flow that is conveyed overland a distance of 200 feet or less from the project to the ESA, or conveyed in a pipe or open channel any distance as an isolated flow from the project to the ESA (i.e., not commingled with flows from adjacent lands).
(E) New development projects, or redevelopment projects that create and/or replace 5,000 square feet or more of impervious surface, that support one or more of the following uses:
i. Automotive repair shops. This category is defined as a facility that is categorized in any one of the following Standard Industrial Classification (SIC) codes: 5013, 5014, 5541, 7532-7534, or 7536-7539.
ii. Retail gasoline outlets (RGOs). This category includes RGOs that meet the following criteria:
a. 5,000 square feet or more; or
b. A projected Average Daily Traffic (ADT) of 100 or more vehicles per day.
(F) New or redevelopment projects that result in the disturbance of one or more acres of land and are expected to generate pollutants post construction.
(2) The following projects shall not be considered priority development projects:
(A) New or retrofit paved sidewalks, bicycle lanes, or trails that meet the following criteria:
i. Designed and constructed to direct stormwater runoff to adjacent vegetated areas, or other non-erodible permeable areas; or
ii. Designed and constructed to be hydraulically disconnected from paved streets or roads; or
iii. Designed and constructed with permeable pavements or surfaces in accordance with USEPA Green Streets guidance.
(B) Retrofitting or redevelopment of existing paved alleys, streets or roads that are designed and constructed in accordance with the USEPA Green Streets guidance. Compliance with any Green Street guidance developed by the County shall be deemed to satisfy this requirement as long as that guidance is as protective of water quality as the USEPA Green Streets guidance. Green Streets projects are subject to County review and approval.
(3) Special considerations for redevelopment projects:
(A) Where redevelopment results in the creation or replacement of impervious surface in an amount of less than fifty percent of the surface area of the previously existing development, then the structural BMP performance requirements defined in the BMP Design Manual apply only to the creation or replacement of impervious surface, and not the entire development; or
(B) Where redevelopment results in the creation or replacement of impervious surface in an amount of more than fifty percent of the surface area of the previously existing development, then the structural BMP performance requirements defined in the BMP Design Manual apply to the entire development.
(4) Priority Development Projects must submit a PDP Stormwater Quality Management Plan (PDP SWQMP), with an application for a County permit or other County approval, identifying the measures that will be used for stormwater and non-stormwater management for the project consistent with the County BMP Design Manual, and implement structural BMPs that conform to performance requirements described below:
(A) Each PDP must implement BMPs that are designed to retain (i.e., intercept, store, infiltrate, evaporate, and evapotranspire) onsite the pollutants contained in the volume of stormwater runoff produced from a 24-hour 85th percentile storm event (design capture volume); or
(B) If retaining the full design capture volume onsite is not technically feasible, biofiltration BMPs may be used. Biofiltration BMPs must be designed to have an appropriate hydraulic loading rate to maximize stormwater retention and pollutant removal, as well as to prevent erosion, scour, and channeling within the BMP, and must be sized to:
i. Treat 1.5 times the design capture volume not reliably retained onsite, or
ii. Treat the design capture volume not reliably retained onsite with a flow-thru design that has a total volume, including pore spaces and pre-filter detention volume, sized to hold at least 0.75 times the portion of the design capture volume not reliably retained onsite.
(C) If the County determines that biofiltration is not technically feasible, then a PDP may be allowed to utilize flow-thru treatment control BMPs to treat runoff leaving the site, AND mitigate for the design capture volume not reliably retained onsite pursuant to the requirements in Section 67.811(b)(6). Flow thru treatment control BMPs must be sized and designed to:
i. Remove pollutants from storm water to the MEP;
ii. Filter or treat either: 1) the maximum flow rate of runoff produced from a rainfall intensity of 0.2 inch of rainfall per hour, for each hour of a storm event, or 2) the maximum flow rate of runoff produced by the 85th percentile hourly rainfall intensity (for each hour of a storm event), as determined from the local historical rainfall record, multiplied by a factor of two;
iii. Be ranked with high or medium pollutant removal efficiency for the PDP's most significant pollutants of concern. Flow-thru treatment control BMPs with a low removal efficiency ranking will only be approved by the County if a feasibility analysis has been conducted which exhibits that implementation of flow-thru treatment control BMPs with high or medium removal efficiency rankings are infeasible for the applicable portion of a PDP.
(5) Hydromodification Management BMP Requirements. Priority Development Projects must implement onsite BMPs to manage hydromodification that may be caused by stormwater runoff discharged from a project as follows:
(A) Hydromodification BMPs must be sized and designed such that post-project runoff conditions (flow rates and durations) will not exceed pre-development runoff conditions by more than 10 percent (for the range of flows that result in increased potential for erosion, or degraded instream habitat downstream of Priority Development Projects).
i. In evaluating the range of flows that results in increased potential for erosion of natural (non-hardened) channels, the lower boundary must correspond with the critical channel flow that produces the critical shear stress that initiates channel bed movement or that erodes the toe of channel banks.
(B) A Priority Development Project may be exempted from the hydromodification management BMP performance requirements where the project discharges stormwater runoff to:
i. Existing underground storm drains that discharge directly to water storage reservoirs, lakes, enclosed embayments, or the Pacific Ocean; or
ii. Conveyance channels whose bed and bank are concrete lined all the way from the point of discharge to water storage reservoirs, lakes, enclosed embayments or the Pacific Ocean; or
iii. An area identified by the County as appropriate for an exemption through a Watershed Management Area Analysis incorporated into a Water Quality Improvement Plan accepted by the RWQCB.
(C) PDP projects must avoid critical coarse sediment yield areas as identified by the County unless measures are implemented consistent with the BMP Design Manual that allow critical coarse sediment to be discharged to receiving waters, such that there is no net impact to the receiving water.
(6) A PDP may be allowed at the County's discretion to utilize offsite alternative compliance in lieu of complying with the storm water pollutant control and hydromodification BMP performance requirements in Section 67.811(b)(4)-(5). The PDP must mitigate for the portion of the pollutant load in the design capture volume not retained onsite and/or post-project runoff conditions not fully managed onsite consistent with a Water Quality Equivalency (WQE) Guidance Document accepted by the RWQCB. If a PDP is allowed to utilize offsite alternative compliance, flow-thru treatment control BMPs must be implemented to treat the portion of the design capture volume that is not reliably retained onsite. Flow-thru treatment control BMPs must be sized and designed in accordance with the requirements of Section 67.811(b)(4)(C). An offsite alternative compliance project for a private PDP may be partially or wholly located within the County Right-of-way upon approval of the Authorized Enforcement Officer. Any and all costs associated with the project shall be the sole responsibility of the applicant, including design and installation and the effective operation and maintenance in perpetuity of any and all treatment and hydromodification controls required under this Chapter. The County shall retain the authority to recoup as necessary any and all such costs.
(7) The following requirements apply to the use of infiltration BMPs:
(A) Infiltration BMPs shall not cause or contribute to an exceedance of applicable groundwater quality objectives as set out in the RWQCB "Basin Plan" for the San Diego area;
(B) Runoff must undergo pretreatment such as sedimentation or filtration prior to infiltration;
(C) Pollution prevention and source control BMPs must be implemented at a level appropriate to protect groundwater quality at sites where infiltration BMPs are to be used;
(D) Infiltration BMPs must be adequately maintained to remove pollutants in stormwater to the MEP;
(E) The vertical distance from the base of any infiltration BMP to the seasonal high groundwater mark must be at least 10 feet. Where groundwater basins do not support beneficial uses, this vertical distance criteria may be reduced, provided groundwater quality is maintained;
(F) The soil through which infiltration is to occur must have physical and chemical characteristics (e.g., appropriate cation exchange capacity, organic content, clay content, and infiltration rate) which are adequate for proper infiltration durations and treatment of runoff for the protection of groundwater beneficial uses;
(G) Infiltration BMPs must not be used for areas of industrial or light industrial activity, and other high threat to water quality land uses and activities as designated by the County, unless source control BMPs to prevent exposure of high threat activities are implemented, or runoff from such activities is first treated or filtered to remove pollutants prior to infiltration; and
(H) Infiltration BMPs must be located a minimum of 100 feet horizontally from any water supply wells and 25 feet from any septic system or as prescribed by County of San Diego Department of Environmental Health and Quality.
(8) A priority development project shall not receive a certificate of occupancy or other final approval allowing use of the project site or any portion thereof, until after all required structural BMPs have been constructed in accordance with the PDP SWQMP, BMP Design Manual, this Chapter, and the NPDES Order.
(c) Grandfathering under Previous Land Development Requirements. The requirements of Sections 67.811(a) and (b) apply to all development projects unless a prior lawful approval to proceed under the provisions of a prior MS4 Permit has been obtained from the County. The Authorized Enforcement Official may partially or wholly waive these requirements for any private or public development project meeting the conditions of either Section 67.811(c)(1) or (2) below.
(1) Previous land development requirements may be allowed to apply to any portion or phase of a development project for which the Authorized Enforcement Official determines the County lacks the land use authority or legal authority to require the project to implement the requirements of Sections 67.811(a) and/or (b).
(2) At its discretion, the Authorized Enforcement Official may allow the requirements of the immediately prior MS4 Permit to apply to any portion or phase of a Priority Development Project for which all of the conditions below have been satisfied.
(A) Initial Approvals. Prior to the effective date of the current MS4 Permit provisions, the applicant must have:
i. Obtained an approval of a design that incorporates the storm water drainage system for the Priority Development Project in its entirety, including all applicable structural and hydromodifica-tion management BMPs consistent with the requirements of the prior MS4 permit. For public projects, a design stamped by the County Engineer or engineer of record for the project is considered an approved design; and
ii. Been issued a project permit or approval that authorizes the commencement of construction activities based on the design approved in Section 67.811(c)(2)(A)i;
For purpose of Section 67.811(c), the effective date of the 2013 MS4 Permit provisions is February 26, 2016.
(B) Demonstrated to the County's satisfaction that construction activities have commenced on any portion of the Priority Development Project site within 365 days prior to, or 180 days after, the effective date of the current MS4 Permit provisions, where construction activities are undertaken in reliance on the permit or approval.
(C) Subsequent Approvals. Within five years of the effective date of the current MS4 Permit provisions, the applicant must have obtained all subsequent project permits or approvals that are needed to implement the design initially approved in conformance with Section 67.811(c)(2)(A)i. After that time, any portion or phase of a Priority Development Project for which subsequent approvals have not been obtained is required to meet the updated requirements of Section 67.811(a) and (b).
(D) Substantial Conformance. The storm water drainage system for the Priority Development Project in its entirety, including all applicable structural pollutant treatment control and hydromodi-fication management BMPs must remain in substantial conformity with the design initially approved in conformance with Section 67.811(c)(2)(A)i. Any portion or phase of a Priority Development Project not maintaining substantial conformity with this design is required to meet the updated requirements of Sections 67.811(a) and (b).
(Added by Ord. No. 10385 (N.S.), effective 6-12-15; amended by Ord. No. 10410 (N.S.), effective 2-26-16; amended by Ord. No. 10709 (N.S.), effective 1-15-21)