Assessment is based on results of (1) USGS/NAWQA monitoring at Wapello from Oct. 1998 to Sept. 2001 and (2) fish tissue (RAFT) monitoring in 1997 and 1999.
Basis for Assessment
SUMMARY: Both the Class A (primary contact recreation) uses and Class B(WW) aquatic life uses are assessed as "partially supported." Fish consumption uses are assessed as "fully supported." EXPLANATION: Results of monitoring conducted on the Iowa River at Wapello from March 1996 to August 1998 by USGS as part of the National Water Quality Assessment Program (NAWQA) (eastern Iowa river basins study unit, station 05465500) showed that levels of indicator bacteria suggest less than full support of the Class A (primary contact recreation) uses. In summer 1996, the geometric mean of fecal coliform bacteria in the 10 non-runoff-affected samples (130 orgs/100 ml) was less than the state criterion of 200 orgs/100 ml. Levels of bacteria in 3 of 10 samples (30%), 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 (pgs 3-33 to 3-35of U.S. EPA 1997b), "partial support" of primary contact uses is indicated if geometric mean for fecal coliforms is less than 200 organisms/100 ml but more than 10% of samples exceed the single sample maximum value of 400 orgs/100 ml. In summer 1997 USGS switched to E. coli as the bacteria indicator. The geometric mean of E. coli in the 12 samples (245 orgs/100 ml) was greater than the EPA-recommended criterion of 126 orgs/100ml, and 5 samples (42%) exceeded the EPA-recommended single sample maximum value (289 orgs/100 ml) for E. coli). According to the U.S. EPA guidelines, these results suggest "nonsupport" of the Class A uses. Because the Iowa water quality standards specify fecal coliforms as the bacterial indicator, the Class A uses for this river reach were assessed as "partially supported." Regarding support of the Class B(WW) uses, results of the USGS/NAWQA monitoring showed (1) no violations of Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen in the 53 samples collected, (2) a single violations of the Class B(WW) chronic water quality criteria for chlorpyrifos and DDE in the 52 samples analyzed, and (3) two violations of the Class B(WW) chronic water quality criterion for dieldrin in 52 samples analyzed. Although the results for pH, dissolved oxygen, and ammonia-nitrogen suggest full support of the aquatic life uses, the results of pesticide monitoring (dieldrin) indicate only partial support of these uses. According to U.S. EPA guidelines for Section 305(b) reporting (U.S. EPA 1997b, page 3-18), the single violations of the chronic criteria for chlorpyrifos and DDE do not suggest an impairment of the aquatic life uses. The EPA guidelines, however, specify that more than one violation of a water quality criterion for a toxic contaminant within a three-year period indicates that the aquatic life uses are not fully supported. Thus, the two violations of the chronic criterion for dieldrin (4% violation) indicate "partial support" of the Class B(WW) uses. Fish consumption uses are assessed as "fully supported" based on results of EPA/DNR fish tissue (RAFT) monitoring near Wapello in 1999 that showed levels of contaminants in the composite sample of whole-fish carp were below ½ of the respective FDA action levels and DNR levels of concern. The level of technical chlordane in the 1999 sample (0.11 mg/kg) is approximately half the level reported for the similar sampling in 1997 (0.21 mg/kg) and is less than ½ the FDA action level of 0.30 mg/kg.