Big Sioux River IA 06-BSR-1523

[Note: A TMDL for pathogen indicators in this segment of the Big Sioux River was prepared by DNR and the South Dakota Dept.of Environment & Natural Resources; this TMDL was approved by EPA in January 2008. Because all Section 303(d) impairments identified for the current assessment/listing cycle were addressed by the TMDL, this waterbody remains in IR Category 4a (impaired; TMDL approved).]

The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 15 samples collected during the recreational seasons of 2014 through 2016 at the Big Sioux River near Alcester (STORET ID 460667) were as follows: the 2014 geometric mean was 13 orgs/100 ml, the 2015 geometric mean was 514 orgs/100 ml, and the 2016 geometric mean was 69 orgs/100 ml. One of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Four of the combined 15 samples (27%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as "partially supported."

Results of chemical/physical water quality monitoring at the Big Sioux River near Alcester (STORET ID 460667) suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 35 Ammonia samples (maximum = 1 mg/L), 36 Dissolved Oxygen samples (minimum = 5.6 mg/L), 36 pH samples (range = 7.3 to 9), or 36 Temperature samples (maximum = 27 °C) occurred during monitoring from January 2014 to December 2016. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” of the Class B(WW1) aquatic life uses.

Fish consumption uses are assessed (monitored) as “fully supported” based on results of U.S.EPA/DNR fish contaminant (RAFT) monitoring on the Big Sioux River north of Hawarden in 2011. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.056 ppm; total PCBs: <0.09 ppm; and technical chlordane: <0.03 ppm. [Note:Typically, samples of both bottom-feeding fish (e.g., common carp) and predator species (e.g., largemouth bass) are collected at RAFT status sites such as the Big Sioux River near Hawarden. Predator species, however, are naturally rare in rivers of southern and western Iowa, and RAFT status samples from these rivers typically contain only the bottom-feeder sample.] The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. The fish contaminant data generated for this segment of the Big Sioux River from the 2011 RAFT show that the levels of contaminants do not exceed any of the DPH/DNR advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory.