National Pollutant Discharge Elimination System (NPDES) permitting requirements are mandated by the Federal Clean Water Act (CWA). In 1987, the CWA was amended by the Water Quality Act to require the U.S. Environmental Protection Agency (EPA) to develop discharge permits under the NPDES program. In California, the municipal permit program is overseen by the State Water Resources Control Board and Regional Water Quality Control Boards (RWQCB) in accordance with the November 1990 Federal Regulations (40 CFR Part 122) and the Porter-Cologne Act. These regulations require all municipal separate storm sewer systems (MS4s) that serve populations over 100,000 to obtain coverage under an NPDES discharge permit. In the San Diego area, the San Diego Regional Water Quality Control Board (RWQCB) oversees the NPDES permit program.
The County of San Diego, the City of San Diego, the San Diego Unified Port District, the San Diego Regional Airport Authority and 17 other cities (collectively referred to as Copermittees) are covered under a municipal NPDES permit for discharge of runoff to waters of the United States. The participating Copermittees share the costs of monitoring required for compliance with this permit.