In an effort to preserve water quality, these techniques aim to reduce storm water runoff volume and rate. The discharge of surface water contaminants from the project site into receiving waterways can be avoided by making sure that there is no detectable increase.

CALGreen Code Section A5.106.2: Storm water design.

Design storm water runoff rate, and quantity, and quality in conformance with Section A5.106.3 Low impact development (LID) or by local requirements, whichever are stricter.

Intent:

The intent of these measures is to limit the amount and rate of storm water runoff, in an attempt to maintain water quality. Ensuring that no measurable increase occurs will help prevent the discharge of surface water pollutants from the project site into receiving waters. These provisions make exception for impervious areas that cannot retain all of the storm water on site.

The quality of the storm water runoff can be increased by incorporating treatment control best management practices (BMPs) through recommendations for project maintenance.

Compliance Method:

The design plan should ensure that storm water runoff quality is not compromised and that the rate does not increase from existing conditions. BMPs for storm water treatment control should be employed during construction. Recommendations for continuing treatment control should be included in the operation and maintenance manual.

Enforcement:

Plan intake: The plan reviewer should examine the construction documents for BMPs to control the storm-water runoff rate, quantity and quality.

On-site enforcement: The inspector should verify the approved plans that on-site treatment controls meet with design criteria. Check the operations and maintenance manual for recommendations concerning ongoing compliance.

(Excerpted from ‘Guide to the 2022 California Green Building Standards Code Nonresidential’ – Appendix A5)