Assessment Comments
Assessment is based on results of (1) fish tissue monitoring conducted in August 2001 for U.S. EPA’s National Lake Fish Tissue Study and (2) U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2007.
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses remain "not assessed" due to the lack of water quality information upon which to base an assessment. Fish consumption uses are assessed (monitored) as "fully supported" based on results of fish U.S. EPA/IDNR fish contaminant (RAFT) monitoring in October 2007.
EXPLANATION: The Class B(LW) aquatic life uses remain "not assessed" due to the lack of water quality information upon which to base an assessment.
Fish consumption uses are assessed (monitored) as “fully supported” based on results of the U.S.EPA/IDNR fish contaminant monitoring conducted (1) as part of the U.S. EPA's National Lake Fish Tissue Study in 2001 and (2) as part of the Regional Ambient Fish Tissue (RAFT) monitoring program in 2007. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. Results of the 2001 sampling at Percival Lake suggest that levels of contaminants were sufficiently high for concern. The levels of at least one contaminant from past monitoring exceeded one or more advisory trigger levels, thus suggesting the need for additional (follow-up) monitoring to determine whether a consumption advisory should be issued. The composite samples of whole-fish common carp and largemouth bass fillets from the 2001 National Lake Fish Tissue Study had generally low levels of contaminants. Levels of primary contaminants in the composite whole-fish sample of common carp were as follows: mercury: 0.106 ppm; total PCBs: < detection. Levels of primary contaminants in the composite sample of largemouth bass fillets were as follows: mercury: 0.313 ppm; total PCBs: < detection. The level of at least one contaminant did, however, exceed one or more advisory trigger levels: the level of mercury in the sample of largemouth bass fillets (0.313 ppm) exceeds the one meal per week trigger level of 0.30 ppm.
In response to the elevated level of mercury in the 2001 sample of largemouth bass, follow-up monitoring was conducted at Percival Lake in 2007 as part of the annual EPA/IDNR RAFT program. Levels of primary contaminants in the composite sample of common carp fillets were as follows: mercury: 0.176 ppm; total PCBs: < 0.09 ppm; technical chlordane: <0.03 ppm. The levels of mercury in the composite sample of largemouth bass fillets was 0.170 ppm; this sample was not analyzed for other contaminants. Levels of all the contamiants from the 2007 samples, including mercury, are well-below the INDR/IDPH advisory trigger levels, thus suggesting that the fish consumption uses of this lake should be assessed (monitored) as "fully supported."
