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
- 2018
- Release Status
- Final
- Overall IR
- 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
- Trend
- Unknown
- Created
- 7/10/2019 12:09:38 PM
- Updated
- 7/30/2019 12:23:12 PM
The Class A1 (primary contact recreation) uses are assessed as "partially supported" due to violations of Iowa’s water quality criteria for indicator bacteria. The Class B(WW1) aquatic life are assessed as "fully supported" based on results of ambient chemical/physical water quality monitoring from 2014 through 2016. Fish consumption uses remain "not assessed" 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 2014 through 2016.
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 Hudson (STORET ID 460666) were as follows: the 2014 geometric mean was 14 orgs/100 ml, the 2015 geometric mean was 902 orgs/100 ml, and the 2016 geometric mean was 65 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." [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).] Results of chemical/physical water quality monitoring at the Big Sioux River near Hudson (STORET ID 460666) also/ however/ suggest “full support” of the aquatic life uses. Monitoring showed no violations of Class B(WW1) water quality criteria for 36 Ammonia samples (maximum = 0.9 mg/L), 36 Dissolved Oxygen samples (minimum = 5.5 mg/L), or 36 Temperature samples (maximum = 28 °C) occurred during monitoring from January 2014 to December 2016. Two of the 37 samples (5%) analyzed for pH (range = 7.3 to 9.2) violated the Class B(WW1) criteria during the 2014-2016 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17) and Iowa DNR's assessment/listing methodology, a violation frequency of significantly greater than 10% for conventional parameters such as pH suggests impairment of aquatic life uses. Because the frequency of violations for this parameter is not greater than 10 percent, these results do not suggest impairment of the Class B(WW1) aquatic life uses.