Environmental Engineering Consulting

Among the primary issues those in the environmental engineering consulting field are tasked with addressing is water quality.  And, one of the hottest topics in the area of water quality is TMDL implementation, and permitting.  This post summarizes the origins  of TMDL and reviews the general regulatory process, and implementation.

Total Maximum Daily Loads (TMDLs) were first introduced in the Clean Water Act (CWA).  The CWA had its origins in legislation going all the way back to the 1899 Rivers and Harbors Appropriations Act.  The primary concern of that legislation was public health, but the CWA and its subsequent updates have expanded goals to areas outside human safety.  During the 1970s, emphasis was placed on establishing and enforcing effluent standards for point sources.

Ambient-based water quality standards are established by the individual states, and are subject to federal (EPA) approval.  Prior to the Federal Water Pollution Control Act Amendments of 1972, water quality standards were ambient-based.  However, 1972 Act introduced effluents standards for certain individual pollutants in order to avoid common problems associated with watersheds.  By setting water quality standards for streams or waterbodies, states found it difficult to limit discharges since they were not equipped to analyze the wide array of pollutants contributed by multiple discharges.

By setting effluent standards all dischargers had to follow, enforcement became less complicated.  The National Pollutant Discharge Elimination System (NPDES) addresses the point source water pollution directly by setting national effluent standards – or “end of pipe” standards.  The NPDES system is now considered successful in improving quality in waters of the nation; however, the end of pipe standards did not address necessarily address non-point source pollution.

Section 303d of the CWA mandates that all states set TMDLs for their streams and waterbodies; which is an ambient-based system, in that states do the determinations for their own waterbodies.  States must determine all sources of pollution, both point and non-point, and establish TMDLs for each waterbody, and then allocate responsibility for achieving those TMDLs to each of the waterbody’s dischargers.  The TMDL procedure is as follows:

• States must identify all waters of the state
• Determine correct designated uses
• List impaired waterbodies, by determining if standards are met for its designated use (impaired waterbodies must be submitted to EPA every two years, as part of the 1992 CWA update)
• Planning – TMDL calculation, allocation of loads among dischargers
• Implementation – enforcement of allocations as “point” sources (e.g., use of Best Management Practices [BMPs] to handle non-point sources)
• Monitoring to determine the effectiveness of the implementation process; a waterbody may be delisted if implementation is demonstrated, by monitoring, to be successful

The primary take-away from the TMDL process: regulating non-point sources is very difficult, therfore, the EPA and state regulatory agencies use TMDL allocation to treat non point source pollution as point source for individual dischargers to a waterbody.

This post summarizes the Introduction of the National Research Council’s “Assessing the TMDL Approach to Water Quality Management.”