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

SUMMARY:  The Class A (primary contact recreation) uses were assessed as "partially supported."  The Class B(WW) aquatic life were assessed as "fully supported."  Fish consumption uses were assessed as "fully supported / threatened."  EXPLANATION:  The assessments of support of the Class A and Class B(WW) beneficial uses are based on results of (1) DNR quarterly water quality monitoring conducted on the Wapsipinicon River near DeWitt during the 1998-1999 biennial period (October 1997 through September 1999) and (2) USGS monitoring near DeWitt from March 1996 through September 1998 as part of their National Water Quality Assessment (NAWQA) program monitoring in the eastern Iowa river basins study unit (station 05422000).   Data from the DNR quarterly monitoring station near Olin (station 300520) were last collected from October 1993 through September 1995 and are thus considered too old (greater than five years) for characterizing current water quality conditions.   The Class A uses were assessed as "partially supported"  Results of USGS/NAWQA monitoring in 1996 showed that the geometric mean level of indicator bacteria (fecal coliforms) in the 5 non-runoff-affected samples (154 orgs/100ml) was less than the Iowa Class A water quality criterion of 200 orgs/100ml.   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."  One of the five samples (20%) 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 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 3-35of U.S.  EPA 1997b).   Due, however, to (1) the lack of sufficient data points for developing a "monitored" assessment (according to DNR's 305(b) assessment methodology, "monitored" assessments require at least 10 non-runoff-affected samples), and (2) the relatively low geometric mean, the Class A uses of this river reach would have been assessed (evaluated) as "fully supporting" for the 1996 assessment.   DNR quarterly monitoring near DeWitt during the 1998-1999 biennial period, however, showed that the geometric mean of the five non-flow-affected samples (255 orgs/100 ml) was greater than the Iowa Class A water quality criterion of 200 orgs/100 ml; in addition, one of the five samples (20%) 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 the geometric mean exceeds 200 orgs/100 ml, the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   Because less than DNR-required 10 non-runoff-affected samples were collected during the 1998-1999 biennial period, the Class A uses were assessed (evaluated) as "partially supported."  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 pH, dissolved oxygen, and ammonia-nitrogen in the 35 samples collected from March 1996 to September 1998 as part of the USGS/NAWQA monitoring and in the 8 samples collected during the 1998-1999 biennial period as part of DNR quarterly monitoring, (2) the lack of violations of Iowa Class B(WW) water quality criteria for toxic organic compounds and pesticides in the 22 samples collected from March 1996 to September 1998 as part of USGS/NAWQA monitoring, and (3) the lack of violations of Class B(WW) water quality criteria in the 2 samples analyzed for toxic metals during the 1998-1999 biennial period as part of DNR quarterly monitoring.   This assessment was based, in part, on results of quarterly monitoring.   Results from stations monitored monthly or more frequently, however, are preferred for Section 305(b) assessments in order to improve the accuracy and confidence level of the assessment.   As part of DNR's expanded water quality monitoring program, monthly monitoring at the DeWitt station began in October 1999.   Fish consumption uses were assessed as "fully supported / threatened."  EPA/DNR fish tissue (RAFT) monitoring in 1998 north of Donahue in Scott County showed that composite samples of whole-fish common carp contained 0.18 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 2000 RAFT program.