Assessment Comments

Assessment is based on results of IDNR ambient monitoring north of Independence from 2000-02.

Basis for Assessment

SUMMARY:  Class A (primary contact recreation) uses are assessed (monitored) as “partially supported”; the Class B(WW) aquatic life uses are assessed as "fully supported."  Fish consumption uses were not assessed due to the lack of fish contaminant monitoring in this river reach.   The source of data for these assessments is results of IDNR monthly ambient water quality monitoring conducted on the Wapsipinicon R.  just north of Independence at the Otterville Access (STORET station 10100001) during the period from January 2000 through December 2002.    

EXPLANATION:  The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of monitoring for indicator bacteria (fecal coliforms) from 2000-02.   Of the 25 samples from this station analyzed for indicator bacteria (fecal coliforms) during recreational seasons of 2000, 2001, and 2002, seven samples were collected during conditions of high river flow.   These high flows resulted in monitoring at river discharges that exceeded the long-term monthly average flow plus one standard deviation of this average (flow statistics from Fischer et al.  1990 and Fischer and Eash 1998).   For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff.   According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff."  The geometric mean of fecal coliform bacteria in the 18 non-runoff-affected samples was 72 orgs/100 ml; this geometric mean is well below the Iowa water quality standard of 200 orgs/100 ml and suggests low levels of bacteria in this river reach.   Two of the 18 samples (11%), however, exceeded the EPA-recommended single-sample maximum value of 400 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are assessed as "partially supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b)  

Class B(WW) aquatic life uses were assessed as "fully supported" due to the lack of violations of state water quality criteria for pH, dissolved oxygen, and ammonia-nitrogen in the approximately 42 samples collected at the IDNR station during the 2000-2002 period.   In addition, no violations of Class B(WW) chronic criteria occurred in the 12 samples analyzed for pesticides during the assessment period.   The fish consumption uses were not assessed due to the lack of recent fish tissue monitoring in this river segment.