Big Sioux River IA 06-BSR-1525

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 15 samples collected during the recreational seasons of 2012 through 2014 at the Big Sioux River near Canton were as follows: the 2012 geometric mean was 130 orgs/100 ml, the 2013 geometric mean was 57 orgs/100 ml, and the 2014 geometric mean was 68 orgs/100 ml.  One of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml.  Three of the combined 15 samples (20%) 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 at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”   

[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.   For the 2010 assessment and listing cycle, indicator bacteria levels were below the state's geometric mean criterion and this segment was moved from Category 4a (impaired; TMDL approved) to Category 1 (all designated uses met).   Because indicator bacteria levels again indicated impairment for the 2012 IR cycle, this segment was moved back to Category 4a (impaired; TMDL approved).   The assessment of Class A1 uses for the 2016 IR cycle continues to suggest that Category 4a is appropriate.] 

Regarding support of the Class B(WW1) aquatic life uses, results of monitoring at the Canton station during the 2012-2014 period show no violations of Class B(WW1) water quality criteria for 34 Ammonia samples (maximum = 1.8 mg/L), 36 Dissolved Oxygen samples (minimum = 5 mg/L), or 35 Temperature samples (maximum = 30° c) occurred during monitoring from January 2012 to December 2014. One of the 36 samples (3%) analyzed for pH (range = 7.5 to 9.4) violated the Class B(WW1) criteria during the 2012-2014 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of greater than 10% for conventional parameters such as pH suggests impairment of aquatic life uses.  Because the frequency of violations for this parameters is not greater than 10 percent, these results do not suggest impairment of the Class B(WW1) aquatic life uses.   Therefore the Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported." 

Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Hawarden in 2001.   The composite samples of fillets from common carp had low levels of contaminants.   [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 this site on the Big Sioux River near Hawarden.   Predator species, however, are sometimes difficult to capture, and RAFT status samples occasionally 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 levels of contaminants in the 2001 sample of common carp do not exceed any of Iowa's advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.   These data are over 10 years old and are thus of marginal use for characterizing current levels of fish contaminants; thus, the assessment type is considered "evaluated" (of lesser confidence).