How to Recognize and Avoid False Violations When Using Whole - PDF document

tmoore@risk-sciences.com 8/21/2013 How to Recognize and Avoid False Violations When Using Whole Effluent Toxicity (WET) Test Methods to Evaluate Stormwater Samples Timothy F. Moore Risk Sciences Rockvale, TN No Toxics… …In Toxic Amounts (c) 2013, Risk Sciences 1

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tmoore@risk-sciences.com 8/21/2013 100% 90% 80% 70% Probability of Passing All Tests 60% 50% 40% 30% 20% 10% 0% 0 10 20 30 40 50 60 70 80 90 100 110 120 130 Number of Tests Performed (c) 2013, Risk Sciences 6

tmoore@risk-sciences.com 8/21/2013 1) Random, Unusual, & Rare 3) NOEC Not Consistent w/ IC25 (c) 2013, Risk Sciences 7

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tmoore@risk-sciences.com 8/21/2013 DMR Certification Statement “I certify under penalty of law that this document and all attachments were prepared under my direction or supervision in accordance with a system designed to assure that qualified personnel properly gather and evaluate the information submitted. Based on my inquiry of the person or persons who manage the system, or those persons directly responsible for gathering the information, the information is, to the best of my knowledge and belief, true, accurate, and complete. I am aware that there are significant penalties for submitting false information, including the possibility of fine and imprisonment for knowing violations.” 40 CFR 122.22(d) Systematic WET Test Review 1) Know the Expected Total Number of False Positives 2) Run a Full Dilution Series, Not a Screening Test 3) Use Multiple Control Waters for Ionic Imbalance 4) Calculate and Compare Both the NOEC and the IC25 5) Demand Comprehensive Laboratory Control Charts 6) Perform Stats Using 95% and 99% Confidence Levels 7) Analyze Identical Split Samples in Accelerated Testing 8) Consider Using Alternate Test Species 9) Develop Written Data Quality Objectives and Checklist (c) 2013, Risk Sciences 11

HOW TO RECOGNIZE AND AVOID FALSE VIOLATIONS WHEN USING WHOLE EFFLUENT TOXICITY (WET) TEST METHODS TO EVALUATE STORMWATER SAMPLES. Timothy F. Moore 1 INTRODUCTION Federal and state law universally prohibits the discharge of "toxic substances in toxic amounts." For the first twenty years following adoption of the Clean Water Act compliance was determined using chemical analyses to demonstrate that pollutant concentrations were within allowable limits. However, it was impractical to develop numeric water quality criteria for the many thousands of different chemicals in routine use. Nor would individual water quality criteria address the synergistic effects that may occur when aquatic organisms are exposed to a complex mixture of several different chemical pollutants simultaneously. Whole Effluent Toxicity ("WET") testing was developed to address these concerns. In the mid-1990's EPA promulgated standard methods for conducting toxicity tests using sensitive aquatic organisms. Since then, these methods have come into widespread use - particularly for municipal and industrial wastewaters. It is only recently that this trend has expanded to include stormwater discharges. Many MS4 permittees are now required to perform routine WET tests on samples of stormwater and receiving water. Most are only required to monitor and report the results of such testing. But, a few are now required to rely on WET testing to demonstrate compliance with narrative or numeric effluent limits prohibiting toxic discharges. And, that number is expected to increase with time. As the very name suggests, WET test methods were originally designed to evaluate municipal and industrial effluents. Using the standard test procedures and organisms to assess potential toxicity in stormwater samples poses unique challenges. Chief among these is the elevated risk of false test failures caused by various interference factors such as the low conductivity and pH levels found in natural rainfall. When negotiating monitoring requirements or discharge limitations in an MS4 permit, or contracting with a laboratory to perform WET tests, great care must be taken to consider the special demands associated with evaluating potential toxicity in stormwater samples. EPA guidance provides considerable flexibility to address such concerns but, because most MS4 agencies are relatively new to WET testing, few permittees are fully aware of their implementation options. The purpose of this paper is to describe some of the most useful alternatives. 1 Risk Sciences, 125 New Dawn Rd., Rockvale, TN 37153; (615) 274-2745; tmoore@risk-sciences.com

WHAT IS A "FALSE" TEST FAILURE? Most toxicity tests proceed by exposing standardized organisms (primarily fish and macroinvertebrates) to an effluent or receiving water sample and comparing the rate of survival, reproduction and/or growth to that observed for identical organisms that have been exposed to non- toxic laboratory control water. Any statistically-significant reduction in survival, growth or reproduction is deemed to be evidence that the sample water is probably "toxic." Chemical toxicity can, indeed, inhibit reproduction or growth and increase the risk of mortality. But, statistically-significant differences can also occur due to other factors outside a dischargers control. When a test fails, it is often difficult to distinguish between genuine toxicity and artifactual causes. Consequently, preferring to err on the side of caution, regulators are initially predisposed to consider all such failures as potential exceedances of state water quality standards. Even where a WET test failure is not automatically deemed to be a permit violation, it will often trigger expensive and time-consuming follow-on testing (called a "Toxicity Identification Evaluation") to determine what is causing the toxicity or to demonstrate the initial test failure was an anomaly. And, for MS4 agencies that are in the early phases of WET monitoring where they are only required to "Monitor-and-Report" results, false test failures may lead to an incorrect conclusion that there is Reasonable Potential for toxicity at their outfalls and, eventually, actual effluent limits for WET. WHAT CAUSES FALSE TEST FAILURES? As with any other form of chemical analysis, toxicity testing is vulnerable to sample contamination, laboratory error, and similar phenomenon that can produce incorrect data. However, because WET testing relies on living organisms as the primary instrument of detection, natural biological variability is also an important source of potential error. By definition, when one uses a 95% confidence level to identify statistically-significant changes in survival, reproduction or growth, one is also accepting the small (5%) chance that some large differences may be due to nothing more than random chance. A 5% risk of error is relatively low for any individual test. But, the risk adds up over time. If a discharger is required to perform quarterly chronic toxicity tests then a total of 20 samples will be analyzed during the course of a normal 5-year permit term. Most toxicity tests will evaluate two species (a fish and an invertebrate) and two endpoints for each species (mortality and a sublethal metric such as reproduction or growth). Consequently, the testing laboratory will perform a total of 80 statistical analyses (20 samples x 2 species x 2 endpoints) during the 5-year period. Since 5% of all tests are expected to fail due to random chance alone, then it is likely that most dischargers engaged in a similar monitoring program will observe and report 1 false failure in every 20 tests. It is easy to see why such a record might lead state authorities to conclude that there is Reasonable Potential for toxicity and include a WET limit in subsequent NPDES permits.