Iowa River IA 02-IOW-623

Assessment Comments

Assessment is based on results of IDNR ambient monthly monitoring at Columbus Junction.

Basis for Assessment

Used results from the DNR monthly WQ monitoring station at the Hwy 92 bridge at Columbus Junction to develop assessments of use support.   The Class B(WW) aquatic life uses were assessed as FS due to lack of violations for either conventional or toxic pollutants in the 24 samples collected from October 1995 to September 1997.   The Class A primary contact uses were assessed as PS:  the geometric mean of the 11 non-flow affected samples collected during summers of 1996 and 1997 was 104 orgs/100 ml (<200 orgs/100 ml WQS = FS), but 18% of the samples had levels of fecal coliforms > 400 orgs/ 100 ml (=PS, see p.  3-34 of the Supplement to the U.S.  EPA Guidelines for preparation of the 1998 Section 305(b) reports).  Assess overall support as FST due to known threats from nonpoint source pollutants.