Big Sioux River IA 06-BSR-1524
from confluence with Rock R. (S1 T95N R48W Sioux Co.) to confluence with Beaver Cr near Canton SD in S36 T98N R49W Lyon Co.
Assessment Comments
Assessment based on monitoring conducted by South Dakota DENR at Hudson and Canton, SD.
Basis for Assessment
Used results of WQ monitoring at Hudson and Canton, SD, to assess support of Class A primary contact uses as PS due to approximately 40% of the samples coll. during summers of 1996 and 1997 that exceeded the 200 organisms/ 100 ml Iowa WQ criterion at each site. Too few non flow-affected samples were collected at each site (5), however, to make a "monitored" Section 305(b) assessment. Thus, made the "evaluated" assessment of PS. Two Class B(WW) WQ criteria were exceeded in the approximately 48 samples collected at the two stations: the sample collected on June 24, 1997 at Hudson contained 2.4 mg/l of dissolved oxygen and thus violated the Iowa WQ criterion of 5.0 mg/l, and a sample from Hudson on Nov. 1, 95 contained 0.33 ug/l of mercury, thus exceeding the chronic WQ criterion of 0.05 ug/l. Neither of these violations suggests WQ impairment according to U.S. EPA guidelines for Section 305(b) reporting. Thus, assess Class B(WW) aquatic life uses at FST. Approx. 50% samples > 750 mg/l TDS; sources believed natural.