Big Sioux River IA 06-BSR-1524

Assessment Comments

Assessment based on 1997/1998 monitoring conducted by South Dakota DENR at Hudson and Canton, SD and on results of EPA/DNR fish tissue (RAFT) monitoring upriver from the confluence with the Rock River (station 009836) in 1996.

Basis for Assessment

SUMMARY:  The Class A (primary contact recreation) uses were assessed as "fully supported."  The Class B(WW) aquatic life were assessed as "fully supported," and fish consumption uses were assessed as "fully supported."  EXPLANATION:  The assessments of support of the Class A and Class B(WW) beneficial uses are based on results of monthly water quality monitoring conducted from November 1997 through September 1998 by the state of South Dakota near the towns of Hudson and Canton, South Dakota.   The Class A uses were assessed as "fully supported"  Results of monitoring in summer 1998 showed that the geometric mean levels of indicator bacteria (fecal coliforms) in five samples from each station (194 orgs/100ml at Hudson and 57 orgs/100 ml at Canton) were less than the Iowa Class A water quality criterion of 200 orgs/100ml.   No samples from either station 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 levels of fecal coliforms are less than 200 orgs/100 ml, and if less than 10% of samples exceeds the EPA-recommended single sample maximum value of 400 orgs/100ml, the primary contact recreation uses are "fully supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).   Due, however, to 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), the Class A uses of this river reach were considered "evaluated: as "fully supported."  Additional data for indicator bacteria are needed to improve the confidence level for this assessment.   Regarding support of the Class B(WW) aquatic life uses, results of monitoring at Hudson and Canton showed no violations of Iowa Class B(WW) water quality criteria for pH, dissolved oxygen, or ammonia-nitrogen in the approximately 20 samples collected from November 1997 through September 1998 at these stations.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), these results suggest "full support" of the aquatic life uses.   Fish consumption uses were assessed as "fully supported" based on results of EPA/DNR fish tissue (RAFT) monitoring upriver from the confluence with the Rock River (station 009836) in 1996 that showed levels of all contaminants in the composite sample of carp fillets were less than ½ of the respective FDA action levels.