North Skunk River IA 03-NSK-853

Assessment Comments

Assessment is based on results of IDNR ambient monthly monitoring near Sigourney in 2000 & 2001.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses were assessed as "fully supporting / threatened."  Fish consumption uses remain "not assessed."  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.  during the 2000-2001 biennial period (station 10540001).   EXPLANATION:  None of the 24 samples collected during the 2000-2001 biennial period violated Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen.   Violations did occur, however, for Class B(WW) criteria for toxic metals and for pesticides.   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.