Post-Construction Storm Water Management Requirements

On July 13, 2013, the Central Coast Regional Water Quality Control Board adopted Post-Construction Storm Water Management Requirements (Resolution R3-20132-0032025).

Post-Construction Storm Water Compliance

The Central Coast Regional Water Quality Control Board recognizes that it is necessary to protect watershed processes so that beneficial uses of receiving waters are maintained and, where applicable, restored. The primary objective of these Post -Construction Stormwater Management Requirements is to ensure reduction of pollutant discharges to the Maximum Extent Practicable and preventing storrnwater discharges from causing or contributing to a violation of receiving water quality standards in all applicable development projects that require approvals and/ or permits issued under the planning, building or other comparable authority. To address the impacts of development on water quality, the National Pollutant Discharge Elimination System (NPDES) Small Municipal Separate Storm Sewer System (MS4) General Permit requires the City of Arroyo Grande to develop and implement a Guidance Document that includes specific Best Management Practices (BMPs).


A project is exempt if it retains 100% of stormwater on site for all storms or if the project consist of only one of the items listed in Draft Resolution No. R3- 2013- 0032, Section B. Post - Construction Requirements 1b. Typically, maintenance and utility projects are also considered " exempt" from post-construction requirements specified by the Regional Board.

Examples of exempt maintenance projects include routine overlays and slurry seals. Examples of utility projects that are "exempt" include:

  • Installation of an ADA ramp
  • Solar panels on rooftops
  • Repair of roads or aerial utilities
If the project meets the criteria to be considered "Exempt", project applicants are still encouraged to implement practices that will reduce stormwater impacts associated with their proposed development.

Regulated Projects

Regulated Projects include all New Development or Redevelopment projects that create and/or replace >2,500 square feet of impervious surface (collectively over the entire project site). Use the Performance Requirement Flow Chart below to determine if a project is regulated and subject to one or more performance requirements, or exempt.

Performance Requirement Flow Chart

 If the project is considered to be a Regulated project, the regulated project will be required to meet Performance Requirement 1 (PR 1). Many regulated projects are required to meet additional performance requirements. To determine if the project must meet additional requirements, you must determine the Net Impervious Area.

The Net Impervious Area is the total ( including new and replaced) post-construction impervious areas, minus any reduction in total imperviousness from the pre-project to post-project conditions. Permeable pavements may only be excluded from the impervious surface area calculation if they are designed to infiltrate.

Performance Requirements

Click the links below to learn more about each Performance Requirement.

PR1: Site Design and Runoff Reduction
PR2: Water Quality Treatment
PR3: Runoff Retention
PR4: Peak Management
PR5: Special Circumstances