Report of Flood, Oil Sheen, and fish Kill Incidents on East Fork Poplar Creek at the Oak Ridge Y-12 Plant

Water quality and plant opemtion irriiormation provided by the Y-12 Plant strongly suggest that a dechlorinating agent, applied to the raw water released below the North-South Pipes was responsible for the toxicity resulting in the fish kill of July 24. Dissolved oxygen (DO) measurements in upper EFPC indicai e that low oxygen levels (3-5 ppm) occurred for a period of up to 30 min. This slug of low DO water traveling down EFPC to the lake could easily explain the massive fish kill and the resulting observations. Dissolved oxygen levels of 5.2 ppm or lower are documented as causing problems for warmwater fish species (Heath 1995). The presence of other stressors, including a range of petrochemicals, tends to lower resistance to low oxygen conditions. Given the sequence of events in upper EFPC in the few days prior to July 24, where extremely high flows were followed by inputs of a wide range of low concentrations of oils, the sensitivity to low DO conditions might be heightened. The possible toxic impact of ::he oils and other contaminants reaching EFPC as a result of the heavy rainfidl on July 22 doesn't appear significant enough to be the sole cause of the kill on July 24. Even during the height of the kill, a large school of fish remained immediately downstream of the North-South Pipes. If the toxicity of waters flowing through this outlet were the primary cause of the kill, then it would be expected that this school of fish would not have been present immediately below the pipes. Any impact of waters entering from other sources, such as pumping of basements WOUIC1 have produced a staggered pattern of mortality, with fishing dying in different localities at different times and rates. Further, it would be expected that the morta.lhy observed would have continued over several days at least, as more resistant individuals succumbed slowly to the toxic exposure. This would have provided freshly dead or dying fish for the surveys of July 25 and 28. In previous fish kills in this stream section, the impact on the fish community has been judged to be short-term only, with no significant long-term ecological effects. In fact, the numerous fish kills over the past 7 years do not appear to have dampened the growth of the stream fish populations. The magnit~de of these kills was far less than that of the July 24 kill; maximum mortality of 10-20o/0 of th{~ total population above Lake Reality. Because the current kill has tiected a much larger proportion of the resident population, the impacts are expected to extend for a longer period in this situation, perhaps up to a year. Decreased population levels should be evident through the fhll 1997 and spring 1998 samples. Depending on the success rate of reproduction during the summer cf 1998, the recovery of fish populations should be observed in the fdl 1998 population sample. However, complete recovery may take several reproductive seasons to reach the densities seen in 1997. The cyprinid species occurring in upper EFPC have tremendous reproductive capacities and should be able to repopulate this area with little or no long-term ecological impact. Even the redbreast sunfish should, at the worst, only endure a narrowing of its available gene pool, with little if any long-term impacts