Assessment Comments

Assessment is based on results of IDNR ambient monitoring north of Independence.

Basis for Assessment

[Note:  For the 2002 report, the previous waterbody segment IA 01-WPS-0020-1, which extended 108 miles from the confluence with Buffalo Creek at Anamosa to Snyder Access in Bremer County, was split into seven subsegments:  (1) Buffalo Creek at Anamosa to Walton Creek  in Linn County (IA 01-WPS-0020-1), (2) Walton Creek to Pine Creek in Buchanan Co.  (IA 01-WPS-0020-2), (3) Pine Creek to Harter Creek in Buchanan Co.  (IA 01-WPS-0020-3), (4) Harter Creek to L.  Wapsipinicon River in Buchanan Co.  (IA 01-WPS-0020-4), (5) L.  Wapsipinicon River to Crane Creek in Black Hawk Co.  (IA 01-WPS-0020-5), (6) Crane Creek to East Fork Wapsipinicon River in Bremer Co.  (IA 01-WPS-0020-6), and (7) East Fork Wapsipinicon River to Snyder Access in Bremer Co.  (IA 01-WPA-0020-7).   See assessment information for segment IA 01-WPS-0020-1 (Buffalo Creek to Walton Creek, Linn Co.) for previous Section 305(b) assessments for this river reach.]

SUMMARY:  Class A (primary contact recreation) uses and the Class B(WW) aquatic life uses were assessed as "fully supported."  Fish consumption uses were not assessed.   The source of data for these assessments is results of IDNR monthly water quality monitoring conducted on the Wapsipinicon R.  just north of Independence at the Otterville Access during the biennial period from October 1999 through September 2001.   EXPLANATION:  The Class A (primary contact recreation) uses remain assessed as "fully supported."  Of the 16 samples from this station analyzed for indicator bacteria (fecal coliforms) during recreational seasons of 2000 and 2001, six 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 nine non-runoff-affected samples was 86 orgs/100 ml; one of the ten samples (10%) exceeded the EPA-recommended single-sample maximum value of 400 orgs/100 ml.   The geometric mean (86 orgs/100 ml) is well below the state water quality criterion of 200 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if no more than 10% of samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are "fully 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 30 samples during the biennial period.   In addition, no violations of Class B(WW) chronic criteria occurred in the four samples analyzed for toxic metals during the biennial period.   The fish consumption uses were not assessed due to the lack of recent fish tissue monitoring in this river segment.