Scientists call for better quality science in EPA water quality management

The Council has been examining the scientific basis of the Total Maximum Daily Load (TMDL) programme authorised by the US Environmental Protection Agency (EPA), which involves a calculation of the maximum amount of a pollutant that a water body can receive whilst still meeting water quality standards.

“Using current science, we recommend several changes in how EPA and the state conduct the TMDL programme that can be immediately implemented, leading to improvements in the TMDL programme,” Council Chairman Kenneth Reckhow told the House Subcommittee on Water Resources and Environment. “Many of these recommendations simply involve changes in the techniques used in the TMDL process, not development of new techniques.”

In July 2000, the EPA revised its TMDL regulations. However, controversy over cost estimates and the adequacy of the use of science under the rules led Congress to prohibit the EPA from using any funds during the past two fiscal years in order to implement the new rules. As a result of the new NAS report, Congress is still unwilling to provide extra funds until the TMDL problem is solved.

“There are several changes that EPA and the states could immediately implement to improve the science underlying the TMDL program,” said Reckhow. “As part of the TMDL, EPA requires a margin of safety factor that is protective of water quality. This factor is intended to reflect the uncertainty in the TMDL forecast. However, EPA allows the margin of safety to be arbitrarily chosen, resulting in a variable level of protection. We can do better; techniques exist now to base the margin of safety on an explicit calculation of uncertainty.”

“In many ways, the NAS report confirms the fears expressed by stakeholders about EPA’s TMDL program and its new rules governing this programme,” said Subcommittee Chairman Representative John Duncan. “The NAS report verifies that many water bodies are brought into the TMDL program without any water quality data showing that the waters are impaired. The report also confirms that, under pressure from unrealistic deadlines, the TMDL programme is becoming an administrative exercise. Many states are focusing on numbers of permits issued and numbers of TMDLs completed, and are not focusing on actual improvements in water quality.”

The report also suggests that EPA should adopt both a preliminary list and an action list, instead of one list of impaired waters. Many waters now on state lists were placed there without the benefit of adequate water quality standards or data. These potentially erroneous listings contribute to a large backlog of TMDL segments and foster the impression of a problem that is larger than it may actually be. States could move those waters for which there is a lack of data to the preliminary list.