Cal. Code Regs. tit. 23 § 3939.48
On June 10, 2015, the Los Angeles Regional Water Quality Control Board (Los Angeles Water Board) adopted Resolution No. R15-005, amending the Water Quality Control Plan for the Los Angeles Region (Basin Plan) to incorporate a total maximum daily load (TMDL) for indicator bacteria in the San Gabriel River, Estuary and tributaries. The State Water Resources Control Board (State Water Board) approved the amendment under Resolution No. 2015-0067 on November 17, 2015.
The TMDL sets numeric targets for indicator bacteria based on numeric water quality objectives provided in the Basin Plan. The TMDL assigns waste load allocations (WLAs) and load allocations (LAs) to municipal separate storm sewer system (MS4) discharges, other non-MS4 National Pollutant Discharge Elimination System (NPDES) discharges, and nonpoint source discharges to attain water quality objectives for bacteria set to protect public health based on the water contact recreation and non-contact recreation beneficial uses of these waterbodies.
There are two types of numeric targets: single sample limits and geometric mean limits. Final allocations to achieve the single sample limits numeric targets are expressed as "allowable exceedance days" and only apply to days in which single sample limits are exceeded and do not apply to days where geometric mean limits are exceeded. Allowable exceedance days are further separated into two time periods (1) dry weather and (2) wet weather for San Gabriel River and its tributaries and into three time periods (1) summer dry-weather, (2) winter dry-weather, and (3) wet-weather for San Gabriel River Estuary. No exceedance days of the geometric mean targets are allowed at any time. The TMDL requires the MS4 dischargers and nonpoint source dischargers to achieve the final WLAs and LAs within 10 years for the dry-weather and 20 years for the wet-weather condition.
Compliance with the MS4 WLAs is assessed through compliance with MS4 permits. The MS4 WLAs will be implemented by permittees through their Watershed Management Programs or Enhanced Watershed Management Programs, which have to be approved by the Los Angeles Water Board. Compliance with the WLAs assigned to non-MS4 point source dischargers is assessed through NPDES permits with effluent limits for bacteria that are equal to the existing effluent limits for bacteria. Non-MS4 dischargers that do not have existing effluent limits for bacteria are not assigned WLAs. If reasonable potential analysis during the permitting process indicates a reasonable potential for the discharge to be a source of bacteria, then effluent limits must be included in the permit.
Compliance with the LAs is assessed through compliance with the Conditional Waiver for Irrigated Lands (Order No. R4-2010-0186 or other successor order), Waste Discharge Requirements, Waivers of Waste Discharge Requirements, Memoranda of Understanding or other appropriate mechanisms consistent with the State Water Board's Nonpoint Source Implementation and Enforcement Policy.
Cal. Code Regs. Tit. 23, § 3939.48