Big Sioux River IA 06-BSR-1522

[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).]

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 Richland (STORET ID 460832) were as follows: the 2014 geometric mean was 249 orgs/100 ml, the 2015 geometric mean was 287 orgs/100 ml, and the 2016 geometric mean was 83 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 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."

The Class B(WW1) aquatic life uses remain assessed (monitored) as “partially supported” based on results of an DNR fish kill investigation in July 2002; fisheries staff from South Dakota also participated in the investigation. The kill occurred on July 12, 2002 downstream from the Westfield Access near the Highway 3 bridge; approximately seven miles of river was affected by the kill; a total of 144 fish were observed killed. Based on the condition of the fish, investigators estimated that the kill had occurred from two to three days prior to receiving the report of the kill on July 12. No source of the kill was identified, and investigators attributed the kill to “natural causes.” The level of dissolved oxygen measured in the river during the investigation, however, was 0.5 ppm. Such a daytime level of dissolved oxygen is extremely unusual for larger rivers, thus suggesting that a pollutant was responsible for the kill (the kill was investigated by boat, suggesting at least moderate flow in the Big Sioux River during the time of the kill). Due to these circumstances, the kill suggests a pollutant-caused water quality problem that is appropriate for Section 303(d) listing.

In addition to the fishkill, 2005, 2012 and 2013 biological sampling also indicate that the Class B(WW1) aquatic life uses are "partially supported" based on an evaluated assessment. This evaluated biological assessment was based on data collected in 2005, 2012 and 2013 as part of the DNR/SHL stream REMAP and large river sampling projects. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2005 FIBI score was 24 (poor) and the BMIBI score was 48 (fair). The 2012 BMIBI score was 42 (fair) and the 2013 BMIBI score was 56 (good). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The FIBI BIC for this ecoregion is 43 and the BMIBI BIC for this ecoregion is 54. This assessment is considered evaluated because the drainage areas (7600 and 7806 mi2) above the sampling sites were greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed the FIBI BIC (using 7 point uncertainty value applied to single samples) and failed the BMIBI BIC (1/3), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the sites used for the assessment don’t fall in the calibrated watershed size. According to DNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). DNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).

Despite the occurrence of the fish kill and the results of the biological sampling, the results of chemical/physical water quality monitoring at the Big Sioux River near Richland (STORET ID 460832) 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), 37 pH samples (range = 6.7 to 9), or 36 Temperature samples (maximum = 27 °C) occurred during monitoring from January 2014 to December 2016. One of the 36 samples (3%) analyzed for Dissolved Oxygen (minimum = 4.5 mg/L) 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 Dissolved Oxygen 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. Monitoring at the USGS station at Akron showed no violations of Class B(WW1) water quality criteria for 20 Temperature samples (maximum = 30.5 °C) occurred during monitoring from February 2014 to September 2015. 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 Dissolved Oxygen 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.

Fish consumption uses are assessed (monitored) as “fully supported” based on results of DNR fish contaminant monitoring on the Big Sioux River at Mill site Access near Westfield in 2013. 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: 0.08 ppm; total PCBs: <0.6 ppm; and technical chlordane: <0.2 ppm. 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 2013 show that the levels of contaminants do not exceed any of the DPH/DNR advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory.