Big Sioux River IA 06-BSR-1526
from confluence with Ninemile Cr. (S25 T100N R49W Lyon Co.) to the Iowa / Minnesota state line at N line of S4 T100N R49W Lyon Co.
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trend
- Stable
- Created
- 9/1/2016 2:08:37 PM
- Updated
- 9/1/2016 2:08:37 PM
The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” (IR 4a) due to violations of Iowa’s water quality criteria for indicator bacteria. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" (IR 2a) based on results of ambient chemical/physical water quality monitoring from 2012 through 2014. Fish consumption uses remain not assessed (IR 3a) due to a lack of information upon which to base an assessment. The source of data for this assessment is results of monthly ambient water quality monitoring conducted on the Big Sioux River near Brandon, SD, by the South Dakota Department of Environment and Natural Resources (DENR) from 2012 through 2014.
The Class A1 (primary contact recreation) are assessed as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. Due to the 2008 approval of the TMDL for bacteria impairments in the Big Sioux River, however, this impairment is placed in Category 4a of Iowa's Integrated Report (impaired but TMDL not required). 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 Brandon were as follows: the 2012 geometric mean was 116 orgs/100 ml, the 2013 geometric mean was 194 orgs/100 ml, and the 2014 geometric mean was 238 orgs/100 ml. Two of the three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Five of the combined 15 samples (33%) 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 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.” [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. Because all Section 303(d) impairments identified for the current (2014) assessment/listing cycle are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).] Regarding support of the Class B(WW1) aquatic life uses, results of monitoring at the Brandon station during the 2012-2014 period show no violations of Class B(WW1) water quality criteria for 36 Ammonia samples (maximum = 2.1 mg/L), 36 Dissolved Oxygen samples (minimum = 7.5 mg/L), 37 pH samples (range = 7.3 to 9), or 36 Temperature samples (maximum = 30° c) occurred during monitoring from January 2012 to December 2014. These results suggest that the Class B(WW1) aquatic life uses should be assessed as "fully supported." Fish consumption uses remain not assessed (IR 3a) due to a lack of information upon which to base an assessment.