Assessment Comments
Assessment is based on results of IDNR/UHL ambient monthly monitoring near Sigourney from 2000-02.
Basis for Assessment
SUMMARY: The Class B(WW) aquatic life uses are assessed as "fully supporting / threatened" due to a single violation of the chronic water quality standard for lead. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment. The assessments of support of beneficial uses are based on results of IDNR ambient monthly water quality monitoring conducted on the North Skunk River southwest of Sigourney in Keokuk Co. (STORET station 10540001) during the 2000-2002 assessment period.
EXPLANATION: None of the 36 samples collected during the 2000-2002 assessment period violated Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen. None of the 9 samples analyzed for pesticides violated state water quality criteria. Violations did occur, however, for Class B(WW) criteria for toxic metals. One of the four samples analyzed for toxic metals exceeded the Class B(WW) chronic criterion for lead. The sample collected on July 5, 2000, contained 40 ppb of lead, thus exceeding the Class B(WW) chronic criterion of 30 ppb. According to U.S. EPA guidelines for Section 305(b) reporting (U.S. EPA 1997b, page 3-18), the single violation of chronic criterion for lead does not suggest an impairment of aquatic life uses. Based on DNR's assessment methodology for Section 305(b) reporting, however, this violation suggests that the Class B(WW) aquatic life uses should be assessed as "fully supported / threatened." Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this river segment.
