Cal. Code Regs. tit. 23 § 3939.46
On June 6, 2013, the Los Angeles Regional Water Quality Control Board (Regional Board) adopted Resolution No. R13-004, amending the Water Quality Control Plan for the Los Angeles Region (Basin Plan) by establishing implementation plans and schedules for the Los Cerritos Channel Metals TMDL and the San Gabriel River and Impaired Tributaries and Selenium TMDL. The Los Cerritos Channel Metals TMDL and the San Gabriel River and Impaired Tributaries and Selenium TMDL were previously established by the United States Environmental Protection Agency (U.S. EPA).
The implementation plans for the Los Cerritos Channel and San Gabriel River Metals TMDLs require MS4 permittees (including Caltrans) to demonstrate a progressive reduction in pollutant loading at milestones in 2017, 2020, and 2023, and must meet both the dry-weather and wet-weather waste load allocations (WLAs) for copper, lead, and zinc by September 30, 2026.
The U.S. EPA-established TMDLs assign dry-weather WLAs equal to zero to unauthorized non-storm water discharges. Authorized non-storm water discharges from construction or industrial activities must comply with concentration-based limits equal to the WLAs assigned to the "other NPDES permits", as defined in the U.S. EPA-established TMDLs. The implementation plans clarify that WLAs will be incorporated into permits as effluent limitations consistent with the assumptions and requirements of the WLAs.
The implementation plans specify effluent limitations that are consistent with the concentration-based WLAs established for non-storm water point sources in the TMDLs. For the major, minor, and general NPDES permits, WLAs may be translated into daily maximum and monthly average effluent limitations by applying appropriate methodologies subject to Los Angeles Water Board Executive Officer approval, such as procedures from the State Water Board's Policy for Implementation of Toxics Standards for Inland Surface Waters, Enclosed Bays, and Estuaries of California.
The implementation plans explain that nonpoint sources will be regulated through the authority contained in the California Water Code, in conjunction with the State Water Board's Policy for Implementation and Enforcement of the Nonpoint Source Pollution Control Program.
Cal. Code Regs. Tit. 23, § 3939.46