Through the NM Water Quality Act, the State Legislature has empowered the Water Quality Control Commission with the authority to create such planning documents. The NMED is the agency responsible for implementing and enforcing the regulations adopted by the WQCC, including the development of TMDLs.
According to 40 Code of Federal Regulations (CFR) Part 130, TMDLs are the sum of the individual Waste Load Allocations (WLAs) for point sources and Load Allocations (LAs) for nonpoint sources (NPSs) and background conditions, and includes a margin of safety (MOS). A point source is a discrete discharge of pollution through a pipe or similar conveyance. A nonpoint source is any non-specific source of pollution (e.g. agricultural/rangeland runoff). Current estimates indicate that nonpoint sources are the cause of approximately 95% of the state’s water quality problem. The MOS accounts for uncertainty in the loading calculation. The MOS may not be the same for all waterbodies due to differences in the availability and strength of data used in the calculations. TMDLs are not regulatory documents, but they can be used to issue or modify permits for point sources. Non-point source pollution problems are addressed through non-regulatory programs including CWA §319(h) grants.
If there is adequate information provided to ensure that pollution control requirements other than TMDLs are stringent enough to achieve an applicable water quality standard, these assessment unit-pollutant combinations may be proposed for CWA 303d/305b Integrated Reporting (IR) Category 4b on the Integrated List. An IR Category 4b Demonstration must be prepared following the guidelines available in Appendix H of the Assessment Protocols in order to explain the regulatory controls, currently in place and planned, that are stringent enough to attain applicable Water Quality Standards within a reasonable time period, thus providing an alternative to development of a TMDL. IR Category 4b Demonstrations are also an important part of NM’s Water Quality Management Plan.