Assessment Comments
Assessment is based on results of (1) IDNR/UHL biological (biocriteria) monitoring in 2002 (Fish IBI= 61 (good), BM-IBI= 63 (good)), (2) IDNR/UHL ambient water quality monitoring conducted in 2001 in support of TMDL development, and (3) U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 1998.
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported / threatened" (minor impacts) based on results of IDNR/UHL biological (biocriteria) sampling in 2002. This assessment is also based on results of IDNR/UHL ambient monthly water quality monitoring conducted from March to November 2001 in support of TMDL development. Fish consumption uses remain assessed (monitored) as "fully supported" based on results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 1998.
EXPLANATION: The assessment of the Class B(WW) aquatic life uses was based on data collected in 2002 as part of the DNR/UHL stream biocriteria project. The 2002 Fish IBI score was 61 (good) and the BM-IBI score was 63 (good). The aquatic life use support was assessed as Fully Supported/Threatened (=FS/T), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established for previous Section 305(b) reports. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001.The Class B(WW) uses are assessed as "fully supported/threatened" based on results of IDNR/UHL biological monitoring conducted in 2002. Results of monitoring conducted in 2001 in support of TMDL development for the downstream segment of Black Hawk Creek, however, show no violations of state water quality criteria for conventional parameters in the nine monthly samples collected between March and November 2001. Biological monitoring is better able to reflect cumulative impacts of water quality over time and thus is believed to more accurately represent water quality conditions of this segment of Black Hawk Creek than do results from the monthly TMDL monitoring site.
Fish consumption uses remain assessed (monitored) as "fully supported" based on results of U.S. EPA/IDNR fish tissue (RAFT) monitoring in 1998 near Hudson that showed levels of contaminants in composite samples of fillets from channel catfish were less than ½ the respective FDA action levels and DNR levels of concern. Levels of the primary contaminants of concern in the 1998 sample were as follows (all values are wet weight): technical chlordane: 0.055 mg/kg; dieldrin: 0.096 mg/kg; PCB-Aroclor 1260: 0.016 mg/kg (Aroclors 1248 and 1254 were not found above detection levels); and mercury: 0.102 mg/kg.
Although this segment is not designated for Class A (primary contact recreation) uses, the levels of fecal coliform bacteria in the six non-flow affected samples from the TMDL monitoring station 1 mile SW of Hudson (Site 17) were very high, with a six-sample geometric mean for the 2001 recreational season of 1,005 orgs/100 ml; all six samples exceeded the U.S. EPA's recommended single-sample maximum value of 400 orgs/100ml.
