Total Maximum Daily Loadings
The State of Georgia assesses its waterbodies for compliance with water quality standards as required by the Federal Clean Water Act (CWA) and 40 CFR 130.7. Assessed waterbodies are placed into one of three categories: 1) supporting, 2) assessment pending, or 3) not supporting. If a waterbody is not supporting its Designated Use and does not have a Total Maximum Daily Load (TMDL), it is placed on the 303(d) List and will require a TMDL be developed. The 303(d) List contains the list of waters, pollutants causing the impairments, and a priority ranking.
TMDLs are frequently developed using Water Quality Models. This process establishes the allowable pollutant loadings that can be discharged into a waterbody and still meet the water quality standards. TMDLs are described by the following equation:
TMDL = ∑WLA + ∑LA + MOS
WLA = Waste Load Allocation assigned to existing and future point sources and constitutes a water quality based effluent limit.
LA = Load Allocation attributed to existing or future nonpoint sources of pollution and to natural background sources, tributaries, and adjacent segments.
MOS = Margin of Safety that can be either implicit or explicit.
If Best Management Practices (BMPs) or other nonpoint source controls make the LA more stringent, then the WLAs can be made less stringent. Therefore, the TMDL process provides for pollutant trading.
Prior to 2012 individual TMDL Implementation Plans were prepared for each impaired stream segment. After 2012 a more detailed Implementation Plan was included in the TMDL documents. Resources regarding Watershed Assessment and Planning can be found below.