California Storm Water TMDLs Explained

California is divided into nine regional Water Quality Control Boards (Boards), governed by the State Water Board, that exercise rulemaking and regulatory activities in their respective basins. The Storm Water Program branch of these Boards regulates storm water discharge from industrial facilities, construction sites, and municipal systems. The most recent Statewide Industrial Storm Water General Permit, Order 2014-0057-DWQ (Industrial General Permit) became effective on July 1, 2020 and included updates to the total maximum daily load (TMDL) implementation requirements. If a facility is covered under the Industrial General Permit and discharges to a waterbody with a Clean Water Act (CWA) section 303(d) listed impairment, the facility is subject to a TMDL for the pollutant(s) causing the water quality to be impaired.

TMDL is defined in 40 CFR §130.2(i) as “the sum of the individual wasteload allocations for point sources and load allocations for nonpoint sources and natural background.” The State Water Board develops TMDL requirements and wasteload allocation limits that are specific to each impaired waterbody. The current list of waterbodies with CWA section 303(d) listed impairment can be found in Appendix 3 of the Industrial General Permit. As TMDLs are approved by the State or Regional Water Boards, they are incorporated into the Industrial General Permit via the process detailed in Section VII of the Industrial General Permit. Attachment E of the General Industrial Permit lists the current waterbodies with issued TMDLs.

Facilities or Responsible Dischargers, capable of discharging pollutants of concern into impaired waterbodies must meet the approved TMDL requirements and limits. The waste load allocation limits are categorized into two levels: TMDL-specific Numeric Action Levels (TNALs) and Numeric Effluent Limitations (NELs). Should stormwater discharges from a facility indicate a TNAL exceedance, the Exceedance Response Action (ERA) Process must be initiated. However, if a NEL exceedance is reported, a violation is immediately triggered and may result in the assessment of a mandatory minimum penalty (MMP). MMPs can add up quickly for each occurrence of a TMDL exceedance.

Due to the novelty of these TMDL requirements and the fact that more are being incorporated into the Industrial General Permit, storm water compliance can seem almost unmanageable to facilities. ALL4 is familiar with the Industrial General Permit and is able to assist facilities in understanding storm water quality characteristics at their location, navigating their site-specific TMDL requirements, and determining what action to take should a TMDL limit be exceeded. Contact Anna Richardson or our California office with any questions you may have.