Iowa River IA 02-IOW-623

Assessment Comments

Assessment is based on results of IDNR ambient monthly water quality monitoring at Columbus Junction from 2000-02.

Basis for Assessment

SUMMARY:  Class A (primary contact recreation) uses are assessed (monitored) as "fully supported" based on results of ambient monitoring for indicator bacteria.   Class B(WW) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.   The source of data for this assessment is the results of monthly monitoring from 2000 through 2002 at the IDNR ambient station located at Columbus Junction (STORET station 10580001)

EXPLANATION:  Results of water quality monitoring during the 2000-2002 assessment period for indicator bacteria (fecal coliforms) at the IDNR ambient monthly station on the Iowa River at Columbus Junction show that the Class A (primary contact recreation) uses are "fully supported."  The geometric mean level of fecal coliform bacteria in the 18 non-runoff-affected samples collected during recreational seasons of 2000, 2001, and 2002 (78 orgs/100 ml) is well below the Iowa water quality criterion of 200 orgs/100 ml for protection of primary contact recreation uses.   One of the 18 samples (6%) had levels of fecal coliforms greater than the EPA-recommended single sample maximum value of 400 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting (pgs 3-33 to 3-35of U.S.  EPA 1997b), primary contact uses are "fully supported" if the geometric mean for fecal coliforms is less than 200 organisms/100 ml and if less than 10% of samples exceed U.S.  EPA's recommended single-sample maximum value of 400 orgs/100 ml.   Monitoring results for indicator bacteria during the 2000-2002 assessment period are consistent with the relatively low levels of fecal coliforms at the Columbus Junction station during recent biennial periods (see previous assessments for more information).  

The Class B(WW) aquatic life uses were assessed as "fully supported."  Results from DNR ambient monthly monitoring at this station during the 2000-2002 assessment period show no violations of Class B(WW) water quality criteria in the 36 samples analyzed for conventional parameters (e.g., dissolved oxygen, pH, and ammonia-nitrogen) or in the nine samples analyzed for pesticides.  

Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this river segment.