A Division of the Georgia Department of Natural Resources

Total Maximum Daily Loadings

The State of Georgia assesses its waterbodies for compliance with water quality criteria established for Designated Uses as required by the Federal Clean Water Act (CWA) and 40 CFR 130.7. Assessed waterbodies are placed into one of three categories with respect to Designated Uses: 1) supporting, 2) assessment pending more data, or 3) not supporting. These waterbodies are found on Georgia’s 305(b) list as required by that section of the CWA that defines the assessment process, and are published in the Water Quality in Georgia report.  If a waterbody is not supporting its Designated Use and does not have a TMDL, it is placed on the 303(d) List and will require a Total Maximum Daily Load (TMDL) to be developed. The 303(d) List contains the list of waters, pollutants causing the impairments, and a priority ranking.  EPD has developed a Draft Priority Framework that describes how GA EPD will prioritize waters on the 303(d) list for development of TMDLs or TMDL alternatives. 

TMDLs are frequently developed using Water Quality Modeling.  The process establishes the allowable pollutant loadings or other quantifiable parameters for a waterbody based on the relationship between pollutant sources and instream water quality conditions.  TMDLs are described by the following equation:

TMDL = ∑WLA + ∑LA + MOS

  • WLA is the Waste Load Allocation, which is the portion of a receiving water’s loading capacity that is allocated to existing and future point sources and constitutes a water quality based effluent limit.
  • LA is the Load Allocation, which is the estimated portion of a receiving water’s loading capacity that is attributable to existing or future non-point sources of pollution and to natural background sources, tributaries, and adjacent segments. 
  • MOS is the Margin of Safety, which can be either implicit or explicit.

If Best Management Practices (BMPs) or other non-point source controls make more stringent LA practical then WLAs can be made less stringent.  Thus, the TMDL process provides for non-point source control tradeoffs or 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.

TMDLs

TMDL Alternatives

TMDL Implementation Plans and BMP Resources