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.
- Cycle
- 2016
- Release Status
- Final
- Overall IR
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trend
- Unknown
- Created
- 9/1/2016 8:52:16 AM
- Updated
- 1/13/2017 8:58:09 AM
The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 4a) due to violations of Iowa’s water quality criteria for indicator bacteria. The Class B(WW1) aquatic life 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 the lack of fish contaminant monitoring in this river segment. The source of data for this assessment is the results of monthly ambient water quality monitoring conducted on the Big Sioux River near Hudson, 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 "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 during the recreational seasons of 2012 through 2014 at the Big Sioux River near Hudson were as follows: the 2012 geometric mean was 75 orgs/100 ml, the 2013 geometric mean was 36 orgs/100 ml, and the 2014 geometric mean was 28 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.] Regarding support of the Class B(WW1) aquatic life uses, results of monitoring at the Hudson station showed no violations of Class B(WW1) water quality criteria for 35 Ammonia samples (maximum = 1.9 mg/L), 36 Dissolved Oxygen samples (minimum = 5.5 mg/L), or 36 Temperature samples (maximum = 29°c) occurred during monitoring from January 2012 to December 2014. One of the 36 samples (3%) analyzed for pH values (range = 7.3 to 9.2) 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. Fish consumption uses remain "not assessed" due to a lack of fish contaminant monitoring in this river segment.