What is the Model Water Quality Management Plan (WQMP)?
The Model WQMP has been developed to aid the County of Orange, the Orange County Flood Control District, and cities of Orange County (the Permittees) and development project proponents with addressing post-construction urban runoff and stormwater pollution from new development and significant redevelopment projects that qualify as Priority Projects. Priority Projects include development that creates new impervious surface and significant redevelopment that adds or replaces 5,000 or more square feet of impervious area on an already developed site.
The Model WQMP describes the process that Permittees will employ for developing a Project WQMP for individual new development and significant redevelopment projects. A Project WQMP is a plan for minimizing the adverse effects of urbanization on site hydrology, runoff flow rates and pollutant loads. Development of a Model WQMP to provide guidance for preparation of a Project WQMP is required by the two National Pollutant Discharge Elimination System (NPDES) permits held jointly by the Permittees administered by two Regional Water Quality Control Boards. The permits also require development of Conceptual or Preliminary WQMPs prior to submission of a Project WQMP.
Orange County is split into two Regional Water Quality Control Board jurisdictional areas. North and Central Orange County (any area north of El Toro Road) is part of the Santa Ana Regional Water Quality Control Board (SARWQCB). South Orange County (any area South of El Toro Road) is part of the San Diego Regional Water Quality Control Board (SDRWQCB). The County of Orange (Unincorporated area) and cities of Laguna Hills, Laguna Woods and Lake Forest have land area in both Regions.
Not sure which Regional Water Quality Control Board has jurisdiction over where your project is located located? (Click here to find out
)Watershed Infiltration and Hydromodification Management Plan (WIHMP)
To assist with preparing a project WQMP, physiographic data is now available through the County's Georesearch tool (click the map below to access the tool): Santa Ana Regional Water Quality Control Board (SARWQCB) – North of El Toro Road
In response to permit requirements from the SARWQCB, the County of Orange has prepared a 2011 Model WQMP
to assist with project development in North and Central Orange County. Consistent with the 2011 Model WQMP, a Project WQMP may include:
- Site design measures
- Low Impact Development (LID) Best Management Practices (BMPs)
- Participation in sub regional/regional BMPs
- Hydromodification BMPs
- Use of alternative programs or treatment control BMPs, and
- Applicable source control BMPs
This updated 2011 Model WQMP was approved by the SARWQCB on May 19, 2011 and became effective on August 17, 2011. To assist with compliance with the SARWQCB permit requirements and to explain aspects of the Model WQMP, a Technical Guidance Document (updated Dec 2013)
is available for project proponents.
A Project WQMP template has been prepared to help guide you through the process. Go to the city website in which your project is located and you will be able to access their WQMP template. If your project is located in unincorporated county land, simply click on the OC Community Development Water Quality website
. San Diego Regional Water Quality Control Board (SDRWQCB) – South of El Toro Road
In response to permit requirements from the SDRWQCB, the County of Orange has prepared a 2013 Model WQMP
to assist with project development in South Orange County. To assist with compliance with the SDRWQCB permit requirements and to explain aspects of the Model WQMP, a Technical Guidance Document
is available for project proponents. When using the Technical Guidance Document
for projects in South Orange County, please refer to this memorandum, “Guidance for Applying the TGD in South Orange County,"
for a summary of key differences between Santa Ana Region and San Diego Region Permit Areas.
Check with the city in which your project is located in order to comply with their local Project WQMP requirements. Each city’s requirements are currently based on the 2003 Model WQMP and may vary slightly so it is important that you contact the city in which your project is located before planning your project. A Project WQMP template has been prepared to help guide you through the process. Go to the city website in which your project is located and you will be able to access their WQMP template.
For a project in unincorporated County area south of El Toro Road, the document that explains the requirements placed upon all new development and significant redevelopment projects can be found by clicking on the County of Orange Local WQMP (Exhibit A-7.VI of the County’s Local Implementation Plan
). If your project is located in unincorporated county land, simply click on the OC Community Development Water Quality website
. Hydromodification Criteria for Priority Development Projects in the San Diego Regional Water Quality Control Board Jurisdiction
In addition to preparing a Project WQMP for Priority Development Projects, all Priority Development Projects* in the San Diego Region are required to comply with hydromodification criteria. The goal of hydromodification control is to integrate hydrologic controls into a proposed project such that the flow duration curve corresponding to the post project condition agrees with the baseline condition curve over the range of flows of interest. This range is 10% of the 2-year peak flow (0.1Q2) to the 10-year peak flow (Q10). The baseline condition is the pre-development condition, which is typically oak grassland habitat.
The south Orange County HMP went into effect on April 1, 2015.
A hydrologic model called the south Orange County Hydrology Model (SOCHM) has been developed to assist project proponents in selecting and sizing hydromodification controls.
*Hydromodification control criteria does not apply to Priority Development Projects where the project discharges (1) storm water runoff into underground storm drains discharging directly to bays or the ocean, or (2) storm water runoff into conveyance channels whose bed and bank are concrete lined all the way from the point of discharge to ocean waters, enclosed bays, estuaries, or water storage reservoirs and lakes. Additionally, Order R9-2013-0001, as amended by Order R9-2015-0001 allows for two additional interim exemptions, at the Permittees discretion. These exemptions include discharges to an engineered channel conveyance system with a capacity to convey peak flows generated by the 10-year storm event all the way from the point of discharge to water storage reservoirs, lakes, enclosed embayments, or the Pacific Ocean; and large river reaches with a drainage area larger than 100 square miles and a 100-year flow capacity in excess of 20,000 cubic feet per second, provided that properly sized energy dissipation is included at all Priority Development Project discharge points. These interim exemptions will remain in place until the Permittees have updated their BMP Design Manual. t is the project proponent’s responsibility to field verify the condition of the downstream channel.
Environmentally Sensitive Areas (ESAs)
Your project may be subject to additional requirements if it:
- Replaces or adds 2,500 square feet or more of impervious surface, or increases impervious surface by 10% or more, and,
- Is directly adjacent to (located within 200 feet) or is discharging directly into an ESA, defined as an area such as those coastal areas designated in the Ocean Plan as an Area of Special Biological Significance, preserves or their equivalent under the Natural Communities Conservation Program (NCCP) or a waterbody listed on the Clean Water Act Section 303(d) list of impaired waters.
Please click here for a map of Environmentally Sensitive Areas (as defined in the MS4 Permits) in Orange County:
2003 Drainage Area Management Plan (DAMP)
The documents for the 2003 Drainage Area Management Plan (DAMP) are listed below.
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- DAMP Section 7, New Development/Significant Redevelopment
- DAMP Section 7, Exhibit 7.I, CEQA Guidance
- DAMP Section 7, Exhibit 7.II, Model WQMP Text (For projects in Santa Ana Region through August 16, 2011)
- DAMP Section 7, Exhibit 7.II, Model WQMP Attachments (For projects in Santa Ana Region through August 16, 2011)
- County of Orange Local Implementation Plan (LIP) Section 7, Exhibit 7.VI, County of Orange Local WQMP: (For projects in the unincorporated areas of the County of Orange located south of El Toro Road in the San Diego Regional Water Quality Control Board area)
In order to provide land developers, project proponents, and associated consultants and organizations with an overview of the new land development requirements in Orange County in the area under the jurisdiction of the Santa Ana Regional Water Quality Control Board, training modules
have been developed to orient readers to the contents of both the updated Model WQMP and the Technical Guidance Document. The training modules provide an overview of the level of detail that must be included at each phase of the WQMP preparation process, site and watershed assessment methods, LID BMP selection and prioritization methods, LID BMP design standards and performance criteria, regional LID BMP options, watershed-based plans and LID alternative compliance options.
OC Watersheds has also prepared a Frequently Asked Questions (FAQs)
page to address common questions that arise regarding the new land development requirements. If you have a specific question that is not addressed in the training modules or the FAQs, please use our comment form
to submit your question, or any comments or concerns. Please note that it may take up to three business days to respond to your question.