Opinion ID: 519994
Heading Depth: 2
Heading Rank: 2

Heading: Remedy for Unavoidable Exceedances

Text: 268 Petitioners PPG and Dow assert that the EPA's statistical model demonstrates that a well-operated plant using BAT can be expected to perform within the daily effluent limitations only 99 percent of the time and within the monthly effluent limitations only 95 percent of the time. They contend that the regulations are unachievable, hence arbitrary, because the model implies that exceedances, i.e., toxic discharges in excess of the BAT limitations, can be expected to occur an average of one percent of the time on a daily basis and five percent of the time on a monthly basis. The regulations, they assert, do not provide a remedy for such unavoidable exceedances. 269 This argument is based on an apparent misunderstanding of the EPA's statistical model. The EPA developed two variability factors for each pollutant--a maximum daily variability factor and a maximum monthly variability factor. To develop the variability factors, the EPA fit the data for each pollutant at each plant to a statistical distribution curve that graphed discharge levels (represented on the horizontal axis) against the probability of the particular discharge occurring (represented on the vertical axis). For the daily data distributions, the EPA estimated both the mean and the level below which 99 percent of the discharge measurements fell for each pollutant at each plant; for the monthly data, the EPA estimated both the mean and the level below which 95 percent of the discharge measurements fell for each pollutant at each plant. The EPA then divided the 99th and 95th percentile figures by the respective means of daily and monthly distributions to determine plant-specific daily and monthly variability factors. 204 Finally, the EPA averaged plant-specific variability factors for all of the plants in the data base to determine a daily and monthly variability factor for each pollutant. 205 270 The data points reflecting discharge levels in excess of the 99th and 95th percentiles represent extreme departures from the mean and were not used by the EPA in calculating the variability factors. The industrial petitioners apparently argue that, because the model technology produced these data points and because these points were not used in determining the variability factors, the limitations are not achievable using the model technology. 271 The EPA did not use the data points in excess of the 99th and the 95th percentiles in calculating the variability factors because it thought that these extremes were due to plant quality-control problems, not unavoidable exceedances. It determined that these variations could be controlled by quality-control methods such as frequent inspection and repair of equipment, use of back-up systems, operator training and performance evaluations, management control, careful communications and coordination among production and wastewater treatment personnel, spill diversion and holding systems, and equalization basins to make wastewater flow and quality more uniform. The EPA also determined that use of these techniques should result in compliance at all times apart from instances of upsets. 206 272 The industrial petitioners argue that the EPA has not adequately demonstrated that the data points exceeding the 99th and 95th percentiles represent controllable rather than uncontrollable variability. The EPA's conclusion that these data points result from quality-control problems is, however, reasonable because these points are isolated and extreme departures from average performance. The purpose of these variability factors is to account for routine fluctuations that occur in plant operation, not to allow for poor performance. 207 The data points exceeding the 99th and 95th percentiles, by definition extreme, do not reflect routine performance, and were reasonably excluded. 273 In any event, the EPA has provided an exception for unavoidable exceedances. The regulations provide that an unavoidable exceedance caused by an upset is an affirmative defense in an action for non-compliance. 208 The regulations define an upset as: 274 an exceptional incident in which there is unintentional and temporary noncompliance with technology-based permit effluent limitations because of factors beyond the reasonable control of the permittee. An upset does not include noncompliance to the extent caused by operational error, improperly designed treatment facilities, inadequate treatment facilities, lack of preventive maintenance, or careless or improper operation. 209 275 It is not clear whether upsets were included in the data used by the EPA to calculate the variability factors. At one point the record states that upsets were edited from the data; however, the record also states that the EPA used all data collected from the data-base plants. 210 We need not resolve this discrepancy. The EPA reasonably concluded that the data points exceeding the 99th and 95th percentiles represent either quality-control problems or upsets because there can be no other explanation for these isolated and extremely high discharges. If these data points result from quality-control problems, the exceedances they represent are within the control of the plant. If, however, the data points represent exceedances beyond the control of the industry, the upset defense is available.