Water Quality

Welcome to the NPDES Water Quality information page. Described below are the various water quality requirements that must be met throughout the project development and construction process. You will be provided a single point of contact during each of these phases. Should you have any questions, please contact our Customer Service line 714-667-8888

Discretionary Application Process:

  • Review of projects for water quality requirements
  • Application of Conditions of Approval

Plan Check:

  • Water Quality Management Plan (WQMP)
  • Erosion and Sediment Control Plan (ESCP)

Construction Site Inspections:

  • Implementation of construction phase BMPs
  • NPDES Inspections

Post-Construction Operation and Maintenance of BMPs:

  • 12-month post-construction inspection

The County’s NPDES Program enforces State mandated water quality regulations that apply to construction projects in the unincorporated area. These regulations are intended to minimize pollutants and runoff from both construction sites and completed project sites. The County has established requirements that owners, developers, contractors and builders must meet at each stage of the project development process in order to achieve compliance. These NPDES requirements have been integrated into the project application/permit approval process and construction site inspection system. These requirements include the following:

  • Non-exempt projects must prepare and submit a project specific Water Quality Management Plan (WQMP) prior to the issuance of any grading or building permit. The WQMP describes the permanent, post-construction Best Management Practices (BMPs) that will be constructed or utilized on the site and maintained during the life of the project.
  • An Erosion and Sediment Control Plan (ESCP) must be submitted with each set of grading and building plans submitted for Plan Check. The ESCP describes the appropriate BMPs that will be used throughout the construction (grading and building) phase.
  • NPDES inspections will be conducted on all construction sites to ensure that appropriate BMPs are kept in place throughout the construction phase. The frequency of these inspections is regulated by a State mandated schedule for both wet and dry seasons.
  • After construction has been completed, property owners are responsible for the ongoing operation and maintenance of all structural and non-structural water quality BMPs on their property and may be required to obtain a 12-month post-construction inspection of treatment control BMPs.
Not sure which region your property/project is in? Click here to use this link and your address to find out!

South Orange County (San Diego Region) Water Quality Requirements

South Orange County Hydromodification Requirements (April 1, 2015)

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.

North Orange County Revised Water Quality Requirements (effective august 17, 2011)

Water Quality (NPDES) Information

Top