West Fork Cedar River IA 02-WFC-801

Assessment Comments

Assessment is based on results of (1) IDNR ambient monthly monitoring at Finchford.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses were assessed as "fully supported / threatened.   Fish consumption uses remain "not assessed."  EXPLANATION:  The assessments of support of beneficial uses are based (1) on results of DNR monthly water quality monitoring conducted on the West Fork Cedar River at Finchford during the 1998-1999 biennial period and (2) on results of pesticide monitoring conducted 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 05458900).  Extrapolated results from the September 1995 DNR stream use assessment conducted upstream from this waterbody segment were used for the 1996 and 1998 assessments (see above) but were not used for the 2000 assessment.   None of the 26 samples collected during the 1998-1999 biennial period at the DNR monthly station violated Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen; no violations occurred in the two samples analyzed for toxic metals.   Although these results suggest "full support" of the Class B(WW) uses, results of the USGS/NAWQA pesticide monitoring suggest that these uses be assessed as "fully supported / threatened."  One of 26 samples analyzed for pesticides contained DDE above the Class B(WW) chronic criterion.   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."  Support of the fish consumption uses remains "not assessed" due to the lack of recent fish contaminant monitoring in this river reach.