Assessment Comments
Assessment is based on results of IDNR/UHL ambient monthly monitoring from 2000-02 west of Jefferson.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses are assessed (monitored) as "partially supported" due to high levels of indicator bacteria. The Class B(WW) aquatic life uses are assessed (monitored) as "fully supported" based in results of ambient chemical/physical water quality monitoring. Support of fish consumption uses remains "not assessed" due to the lack of fish contaminant monitoring in this river segment. The source of data for this assessment is the results from the IDNR/UHL ambient monthly monitoring station near Jefferson in Greene County (STORET station 10370001 (formerly station 700101)).
EXPLANATION: The Class A uses are assessed (monitored) as "partially supported" due to levels of indicator bacteria (fecal coliforms) that exceed U.S. EPA assessment guidelines. 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." Eighteen of the 21 samples collected from the Jefferson station during the 2000, 2001, and 2002 recreational seasons were collected at flows not materially affected by surface runoff. The geometric mean level of indicator bacteria (fecal coliforms) in these 18 non-runoff-affected samples (122 orgs/100ml) is below the Iowa Class A water quality criterion of 200 orgs/100ml, and thus does not suggest an impairment of the Class A uses. Two of the 18 samples (11%), however, exceeded the U.S. 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 the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are only "partially supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW) uses are assessed (monitored) as "fully supported." Results of IDNR/UHL ambient chemical/physical monitoring at the Jefferson station during the 2000-2002 assessment period show no violations of Class B(WW) (aquatic life) water quality criteria in the 36 samples analyzed for dissolved oxygen, pH, and ammonia or in the nine samples analyzed for pesticides and other toxic organic compounds. These results suggest that the aquatic life uses of this river segment are "fully supported."
Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
