Assessment Comments
Assessment based on fish contaminant monitoring.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses and the Class B(WW) aquatic life uses are considered "not assessed." Fish consumption uses are assessed as "fully supported / threatened." EXPLANATION: Assessments of support of the Class A and Class B(WW) uses were not developed due to the lack of water quality monitoring data for this river reach. Fish consumption uses were upgraded from "not supporting" to "fully supported / threatened" due to lifting of the 10-year old fish consumption advisory in August 2000. This advisory was lifted after results of ALCOA-sponsored fish tissue monitoring in 1996 and 1998 showed that the average levels and upper 95% confidence limits of total PCBs (sum of Aroclors 1248, 1254, and 1260) in target species (common carp and river carpsucker) at all four sample sites in Pool 15 were below the FDA action level of 2.0 ppm (see URS Griener Woodward Clyde 2000a, 2000b). The decline in levels of PCBs in Pool 15 fish was attributed primarily to clean-up activities at the ALCOA plant but also likely reflects natural attenuation of PCBs as well as the potential influence of major flood events in the early 1990s on the Upper Mississippi River. Levels of PCBs remaining in Pool 15 fish are believed near background levels for this reach of the river. The assessment as "threatened" is due to the occurrence of average levels of total PCBs slightly above ½ of the FDA action level for common carp at two sites in 1996. According to DNR's Section 305(b) methodology, levels of fish contaminants above ½ the respective FDA action levels suggest a "threat" to the full support of the fish consumption use. The 1998 sampling showed that average levels of total PCBs plus the upper 95% confidence limits were below ½ of the FDA action level for both target species at all four sites.
