Assessment Comments

Assessment is based on results from IDNR monthly monitoring at DeWitt and EPA/IDNR fish tissue (RAFT) monitoring north of Donahue (Scott Co.).

Basis for Assessment

[Note:  For the 2002 report, the previous waterbody segment IA 01-WPS-0010-0, which extended 95 miles from the mouth of Wapsipinicon River to its confluence with Buffalo Creek at Anamosa, was split into five subsegments:  (1) mouth to Silver Creek near DeWitt, Clinton Co.  (IA 01-WPS-0010-1), (2) Silver Creek to Rock Creek south of Wheatland, Clinton Co.  (IA 01-WPS-0010-2), (3) Rock Creek to Plum Creek southwest of Lost Nation in Clinton Co.  (IA 01-WPS-0010-3), (4) Plum Creek to Walnut Creek near Olin, Jones Co.  (IA 01-WPS-0010-4), and (5) Walnut Creek to Buffalo Creek at Anamosa (IA 01-WPS-0010-5).   The assessment information above applies to the original 95-mile waterbody segment (IA 01-WPS-0010-0).]

SUMMARY:  The Class A (primary contact recreation) uses were assessed as "fully supported."  The Class B(WW) aquatic life were assessed as "fully supported."  Fish consumption uses were assessed as "fully supported / threatened."  The sources of data for this assessments were (1) the results of montly monitoring at the IDNR fixed ambient station near DeWitt and (2) results of EPA/IDNR fish tissue (RAFT) monitoring north of Donahue in Scott County.   EXPLANATION:  The Class A uses were assessed as "fully supported."  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."  All 15 samples from the 2000 and 2001 recreational seasons were collected at flows not materially affected by surface runoff.   The geometric mean level of indicator bacteria (fecal coliforms) in these 15 non-runoff-affected samples (59 orgs/100ml) was well below the Iowa Class A water quality criterion of 200 orgs/100ml.   One of the 15 samples (8%) 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 10% or less of the 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).   The Class B(WW) aquatic life uses were assessed as "fully supported" due to (1) the lack of violations of Iowa Class B(WW) water quality criteria for dissolved oxygen and ammonia-nitrogen in the 24 samples collected from October 1999 through September 2001 at the IDNR fixed ambient station at DeWitt.  and (2) the lack of violations of Class B(WW) water quality criteria in the 4 samples from this station analyzed for toxic metals and toxic organic compounds during the 2000-2001 biennial period.   The only violation of a state water quality criterion during the biennial period at this station was for pH in one of the 24 samples collected (4.2% violation).   According to U.S.  EPA guidelines for Section 305(b) assessments, this frequency of violations does not suggest impairment of either primary contact or aquatic life uses (see U.S.  EPA 1997b, page 3-17).   Fish consumption uses were assessed as "fully supported / threatened."  EPA/DNR fish tissue (RAFT) monitoring conducted in 1998 and 2000 north of Donahue in Scott County showed that composite samples of whole-fish common carp contained technical chlordane at levels slightly greater than ½ the FDA action level of 0.300 ppm:  The 1998 sample contained 0.18 ppm and the 2000 sample contained 0.17 ppm of technical chlordane.   Although levels of organochlorine contaminants in whole-fish samples tend to overestimate levels in the edible portion of the fish, these levels of chlordane suggest that levels in edible portions may be greater than ½ of the FDA action level (0.30 ppm) for chlordane.   Thus, according to DNR's assessment methodology, the fish consumption uses should be assessed as "fully supported / threatened."  Additional whole-fish carp samples will be collected and analyzed from this stations as part of the 2002 and 2004 RAFT programs.