Is Wet All Wet?

Alexandra Dapolito Dunn

Under the Clean Water Act (CWA), the U.S. Environmental Protection Agency (EPA) must promulgate guidelines establishing test procedures for the analysis of any pollutants that must be included in National Pollutant Discharge Elimination System (NPDES) permits. See CWA § 304(h). EPA recently ratified several whole effluent toxicity (WET) test methods for effluents and receiving waters, withdrew two test methods, and revised other methods to increase confidence in the test results. 67 Fed. Reg. 69,952 (Nov. 19, 2002). EPA’s action was designed to satisfy obligations under a 1998 Settlement Agreement related to litigation over the original 1995 WET methods (60 Fed. Reg. 53,529) (Edison Electric Institute et al. v. EPA, No. 96-1062, D.C. Cir.).

In WET testing, acute and chronic tests are performed on wastewater samples using surrogate organisms as test species. Exposure durations for the organisms range from a day or more for acute tests, to over seven days for chronic tests. NPDES permits must contain WET limits (typically expressed as “toxic units”) where the permitting authority determines the discharger has a “reasonable potential” to cause an excursion above numeric or narrative WET criteria. 40 CFR § 122.44(d)(1)(iv)-(v).

WET Regulatory History

In the mid- to late-1970s, EPA published various acute toxicity methods but methods to detect long-term chronic effects on aquatic life, such as reduced growth and reproduction, were not generally available. By the 1980s, new chronic methods allowed the detection of some adverse effects on freshwater and marine organisms. In 1984, EPA published a national statement entitled “Policy for the Development of Water Quality-Based Permit Limitations for Toxic Pollutants” (WET Policy). 49 Fed. Reg. 9,016 Mar. 9, 1984. The WET Policy recommended the use of toxicity data to assess and control the discharge of toxic pollutants to the nation’s waters through the NPDES program, and addressed technical approaches for doing so. EPA’s 1989 surface water toxics control program rule defined WET and described the procedures for determining whether a particular NPDES permit must include a water quality-based effluent limitation. 54 Fed. Reg. 23,868. Later that year, EPA took a major step forward by proposing to add specific acute and chronic WET methods to Table IA, 40 CFR Part 136. 54 Fed. Reg. 50,216.

Permittee Concerns

As more permitting authorities began to include WET limits in permits, NPDES permittees expressed concern that technical problems in WET methods undermined the methods’ accuracy and predictive capabilities. These technical limitations included a high degree of variability in the test methods and a general inability to draw clear relationships between effluent toxicity, overall ambient toxicity, and receiving water impacts attributable to WET. While WET tests had a valuable role as informative tools, permittees questioned their use to set enforceable permit limits. To respond to these concerns, EPA released a National Policy on WET Enforcement (Enforcement Policy) in August 1995. Under the Enforcement Policy, a single exceedance of a WET permit limit causing no environmental harm was not to be treated as a civil penalty violation, and citizens could not bring suits against a discharger on the basis of a single WET violation.

In 1995, EPA finalized the 1989 proposed WET test methods, requiring that all WET testing be conducted according to the codified protocols. 60 Fed. Reg. 53,529. Litigation over the final methods was filed, resulting in a stalemate on WET permitting activity in some EPA Regions, and having no effect in others. After significant negotiations, EPA agreed under a 1998 Settlement Agreement to: publish a technical correction notice and method guidance and variability guidance documents, conduct an interlaboratory variability study and publish a peer-reviewed report on the study, address pathogen contamination; propose specific technical method changes, and ratify or withdraw test methods evaluated in the study.

EPA published a proposed rule to address these issues in September 2001. Comments by NPDES permittees noted lingering concerns, including: the poor level of accuracy expected for WET test methods, the methods’ failure to ensure consistent results between and within laboratories, the methods’ failure to contain adequate quality assurance and quality control requirements, the methods’ lack of clear reporting requirements; and the lack of correlation between effluent toxicity and in-stream impairment.

The Future

EPA’s November 2002 final rule was intended to complete EPA’s obligations in response to the litigation. Now that final Part 136 methods are available to the states, WET limits will become more common in many NPDES permits. The changes EPA made in its November rule do not enhance the accuracy of the WET test methods – particularly the chronic, sub-lethal methods. EPA believes that lingering WET concerns can be addressed through reasonable WET implementation and enforcement discretion. Whether this is an acceptable solution for the future for NPDES permittees is unclear.