Assessment Comments
Assessment is based on results of water quality monitoring by South Dakota DENR near Canton, SD, in 2000 & 2001.
Basis for Assessment
[NOTE: For the 2002 report, the previous waterbody segment for the Big Sioux River (IA 06-BSR-0020-0), which extended 54 miles from its confluence with the Rock River in Sioux County to the Iowa/Minnesota state line, was split into three subsegments: (1) from Rock River to Beaver Creek near Canton, SD and Beloit, IA (IA 06-BSR-0020-1), (2) (this one) Beaver Creek to Ninemile Creek ENE of Harrisburg, SD and west of Larchwood, IA (IA 06-BSR-0020-2), and (3) Ninemile Creek to the Iowa Minnesota state line (IA 06-BSR-0020-3). See assessment information found in subsegment IA 06-BSR-0020_1 for previous Section 305(b) assessments for the entire 54-mile reach.]
SUMMARY: The Class A (primary contact recreation) uses are assessed (evaluated) as "partially supported." The Class B(WW) aquatic life are assessed (monitored) as "fully supported." Fish consumption uses are assessed as "fully supported." The sources of data for this assessment include (1) results of monthly ambient water quality monitoring conducted on the Big Sioux River near Canton, SD, by the South Dakota Department of Environment and Natural Resources (DENR) from November 1999 through September 2001 and (2) results of U.S. EPA / IDNR fish tissue (RAFT) monitoring in September 2001. EXPLANATION: The Class A uses were assessed (evaluated) as "partially supported." The geometric mean of indicator bacteria (fecal coliforms) in the 7 samples not materially affected by surface runoff during the recreational seasons of 2000 and 2001 at the Canton monitoring station was below the Iowa water quality criterion (200 fecal coliform orgs/100ml) to protect primary contact recreation uses; the percentage of samples that exceeded the U.S. EPA-recommended single-sample maximum value, however, suggests "partial support" of the Class A uses. For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff. According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff." The geometric mean of fecal coliform bacteria in the 7 non-runoff-affected samples was 111 orgs/100 ml, with two samples (29%) exceeding the EPA-recommended single-sample maximum value of 400 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are "partially supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Because less than 10 non-flow affected samples were available for this assessment, the assessment type is considered "evaluated"; thus, this assessment is not of sufficient quality to support a Section 303(d) listing. Regarding support of the Class B(WW) aquatic life uses, results of monitoring at the Canton station also showed that two of the 24 samples collected from November 1999 through September 2001 (4%) violated the state Class A and Class B(WW) criterion for pH of 9.0 units: the pH of the sample collected on August 16, 2000 was 9.09 units, and the pH of the sample collected on September 12, 2000, was 9.1 units. 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 (8%) 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). These violations occurred on days with an high levels of dissolved oxygen (12.4 and 16.2 mg/l, respectively) and water temperatures (23.6 and 20.3 C, respectively) that indicate percent DO saturations in both samples of > 140%. These conditions suggest that the high level of primary productivity resulted in the high level of pH. Because these violations are more related to natural conditions than to pollution, the occurrence of the high level of pH in this river segment is not seen as a water quality impairment. No other violations of Class B(WW) criteria occurred at this station during the 2000-2001 biennial period. These results suggest "full support" of the Class B(WW) aquatic life uses. Fish consumption uses are assessed as "fully supported" based on results of EPA/DNR fish tissue (RAFT) monitoring in September 2001 near Hawarden in Sioux County. Results of this monitoring show that levels of all contaminants in the composite sample of fillets of common carp were far below ½ of the respective FDA action levels and IDNR levels of concern.
