Big Sioux River IA 06-BSR-1523

Assessment Comments

Assessment is based on results of water quality monitoring conducted by South Dakota DENR near Alcester, SD, Richland, SD, and Akron, IA.

Basis for Assessment

No violations of Class B(WW) WQ criteria for either toxic or conventional contaminants in samples collected monthly at the Richland and Alcester stations during the Oct 95 to Sep 97 period.   Approximately one third of the samples exceeded the general class criterion of 750 mg/l for total dissolved solids.   Based on conversations with WQ staff from other Region VII states, attribute these violations to naturally occurring conditions.   Based on assessment methods recommended in U.S.  EPA guidelines for preparation of the 1998 section 305(b) reports, the Class A primary contact recreation uses were assessed as PS due to (1) geometric mean levels of fecal coliform bacteria at both stations (360/100 ml at Richland; 244/100 ml at Alcester) that exceeded the Iowa WQ criterion of 200 organisms/100 ml and (2) 20% of the five non-flow affected samples at each site exceeded 400 organisms/100 ml.   Because data from too few non-flow affected samples were available (i.e., less than 10 samples), support of the Class A primary contact recreation uses was assessed as PS.   Monitoring for the 1996 U.S.  EPA/DNR Regional Ambient Fish Tissue (RAFT) monitoring prog.  showed all contams < 1/2 FDA action levels in carp (=FS).