Big Sioux River IA 06-BSR-1523

The Class A1 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.  The geometric means of indicator bacteria (E. coli) in the 14 samples collected by the South Dakota DENR during the recreational seasons of 2012 through 2014 at the Big Sioux River near Alcester were as follows: the 2012 geometric mean was 87 orgs/100 ml, the 2013 geometric mean was 113 orgs/100 ml, and the 2014 geometric mean was 25 orgs/100 ml.  None of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml.  Three of the combined 14 samples (21%) 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 IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because none of recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “fully supported.”  However, in the 2014 assessment/listing cycle, the Class A1 uses were listed as "not supported" due to geometric mean and single sample maximum exceedances.  According to IDNR's methodology, streams must meet water quality standards for two consecutive assessment/listing cycles to suggest de-listing.  Therefore, the Class A1 uses will remain listed as "not supported" for the 2016 cycle.

[Note:  A TMDL for pathogen indicators in this segment of the Big Sioux River was prepared by IDNR and the South Dakota Dept.  of Environment & Natural Resources; this TMDL was approved by EPA in January 2008.]

Despite the historical occurrence of several isolated violations of Class B(WW1) criteria for ammonia, dissolved oxygen, and pH, the results of ambient water quality monitoring from 2012-14 suggest “full support” of the aquatic life uses of this segment of the Big Sioux River.   Results of monitoring at the Alcester station by the South Dakota DENR showed no violations of Class B(WW1) water quality criteria for 34 Ammonia samples (maximum = 2.2 mg/L), 35 Dissolved Oxygen samples (minimum = 5.6 mg/L), 35 pH samples (range = 7.3 to 8.8), or 35 Temperature samples (maximum = 28°c) analyzed during monitoring from January 2012 to December 2014. These results are similar to those from the previous IR assessment periods.

Fish consumption uses are assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR 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 IDPH/IDNR advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory.