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

SUMMARY:  The Class A (primary contact recreation) uses were assessed as "partially supported."  The Class B(WW) aquatic life were assessed as "fully supported."  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 Richland and Alcester, South Dakota.   The Class A uses were assessed as "partially supported"  Results of monitoring in summer 1998 showed that the geometric mean levels of indicator bacteria (fecal coliforms) in five samples from each station (388 orgs/100ml at Richland and 327 orgs/100 ml at Alcester) were greater than the Iowa Class A water quality criterion of 200 orgs/100ml.   Two of the five samples from the Richland station (40%) exceeded the U.S.  EPA-recommended single-sample maximum value of 400 orgs/100 ml; one of 5 samples from the Alcester station (20%) exceeded this level.   According to U.S.  EPA guidelines for Section 305(b) reporting, if the geometric mean level of fecal coliforms exceeds 200 orgs/100 ml, the primary contact recreation uses are "not 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 assessed (evaluated) as "partially supported."  Regarding support of the Class B(WW) aquatic life uses, results of monitoring at Richland and Alcester showed that one of the combined 20 samples collected from November 1997 through September 1998 (5%) violated the state Class A and Class B(WW) criterion for pH (9.1 units on July 15, 1998).   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), the percentage of violations for pH in this stream reach (5%) does not suggest a water quality impairment (the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated).   None of the combined 23 samples analyzed contained levels of ammonia-nitrogen above state chronic criteria for Class B(WW) waters.   Thus, the Class B(WW) aquatic life uses were assessed as "fully supported."  Fish consumption uses remain assessed as "fully supported" based on results of EPA/DNR fish tissue (RAFT) monitoring upriver from Hawarden (station 008316) 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.