Flood Creek IA 02-SHL-788

Assessment Comments

Assessment is based on results of (1) USGS/NAWQA water quality monitoring near Powersville from 1996-98.

Basis for Assessment

SUMMARY:  The Class B(LR) aquatic life uses are assessed as "fully supported / threatened."  EXPLANATION:  The assessments of support of beneficial uses are based on results of water quality monitoring conducted on Flood Creek near Powersville (Floyd County) from March 1996 to September 1998 by USGS as part of the National Water Quality Assessment Program (NAWQA) (eastern Iowa river basins study unit, station 05461390).   Monitoring at this USGS/NAWQA station showed (1) no violations of Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen in the 34 samples collected, and (2) a single violation of the Class B(WW) chronic water quality criterion for DDE in the 21 samples analyzed.   Although the results for pH, dissolved oxygen, and ammonia-nitrogen suggest full support of the Class B(LR) aquatic life uses, the single violation of the water quality criterion for DDE suggests that these uses should be assessed as "fully supported / threatened."  According to U.S.  EPA guidelines for Section 305(b) reporting (U.S.  EPA 1997b, page 3-18), this one violation of a toxic contaminant does not suggest an impairment of the aquatic life uses.   Based on DNR's assessment methodology for Section 305(b) reporting, however, this violation suggests that the Class B(WW) aquatic life uses should be assessed as "fully supported/threatened."  In addition, the inconclusive results of the DNR stream use assessment in 1992 suggests that additional biological monitoring should be conducted to better determine the status of the aquatic communities of this stream reach.   Results of USGS/NAWQA fish tissue monitoring in September 1995 showed that levels of organochlorine contaminants were less than ½ of the respective FDA action levels and DNR levels of concern (see assessment for the 1998 report above).   Although results of this monitoring suggest that fish consumption uses are "fully supported," Iowa's Class B(LR) streams are not considered designated for fish consumption uses.   Thus, these uses were "not assessed."