Assessment Comments
Assessment is based on: (1) the results of monthly ambient water quality monitoring conducted on the Big Sioux River near Richland, SD, by the South Dakota Department of Environment and Natural Resources (DENR) from 2006 through 2008, (2) results of ambient water quality monitoring conducted by USGS at Akron from January 2006 to September 2008, (3) results of a fish kill investigation in July 2002, and (4) IDNR/UHL stream TMDL biological sampling in 2005.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses remain assessed (monitored) as "not supported" due to past levels of indicator bacteria (E. coli) that violate state water quality standards. The Class B(WW1) aquatic life remain assessed (monitored) as "partially supported" based on results of a fish kill investigation in July 2002 and evaluated "partially supported" based on 2005 IDNR/UHL TMDL stream biological monitoring. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment. The sources of data for this assessment include (1) the results of monthly ambient water quality monitoring conducted on the Big Sioux River near Richland, SD, by the South Dakota Department of Environment and Natural Resources (DENR) from 2006 through 2008, (2) results of ambient water quality monitoring conducted by USGS at Akron from January 2006 to September 2008, (3) results of a fish kill investigation in July 2002, and (4) IDNR/UHL stream TMDL biological sampling in 2005.
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, however, the Section 303(d) impairment related to a 2002 fish kill caused by unknown toxicity was not addressed in the TMDL, this waterbody was placed in IR Category 5b (impaired) for the 2006 assessment/listing cycle and remains in IR Category 5b for the current (2010) listing cycle.
EXPLANATION: The Class A1 uses are assessed (monitored) as "not supported" due to levels of indicator bacteria (E. coli) that violate state water quality standards. Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed. The geometric mean level of indicator bacteria (E. coli) in the nine samples collected by the South Dakota DENR during the recreational seasons of 2006, 2007, and 2008 (66 orgs/100ml) was below the Iowa Class A1 water quality criterion of 126 orgs/100ml. Three of the fifteen samples (20%) exceeded Iowa’s single-sample maximum value of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, and according to IDNR’s assessment/listing methodology, if the geometric mean of E. coli is less than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). However, based on IDNR's assessment methodology two assessment/listing cycles with indicator bacteria levels below the geometric mean criteria are necessary to suggest de-listing of a bacteria impairment. Therefore, the Class A1 uses will remain assessed as "not supported" for the 2010 assessment/listing cycle. If bacteria levels remain below the geometric mean criterion for the 2012 assessment/listing cycle, the bacteria impairment at this river segment will be suggested for de-listing. The USGS monitoring conducted at Akron, IA, did not include analysis for indicator bacteria.
The Class B(WW1) aquatic life uses remain assessed (monitored) as “partially supported” based on results of an IDNR 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 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 biological sampling also indicate that the Class B(WW1) aquatic life uses are "partially supported" based on an evaluated assessement. This evaluated biological assessment was based on data collected in 2005 as part of the IDNR/UHL stream REMAP project. 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 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 1994-2004. Both IBI scores required the use of the UAV to pass the BICs and the FIBI scored was in the "poor" category. 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 area (8264 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site failed both the FIBI and BMIBI BICs, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size.
Despite the occurrence of the fish kill, the indications of degraded chemical water quality, and the results of the 2005 biological sampling, the results of monthly ambient monitoring by the South Dakota DENR on the Big Sioux River at Richland suggest relatively good water quality. Results of this monitoring show no violations of Class B(WW1) water quality criteria for pH (range = 7.3 to 8.7), dissolved oxygen (minimum = 8.3 mg/L) or ammonia-nitrogen (maximum value = 0.85 mg/l) in the approximately 36 samples analyzed during the 2006-2008 period. Monitoring at the USGS station at Akron showed no violations in the 33 samples analyzed for ammonia, dissolved oxygen, and pH during the 2006-2008 period. There was one violation of the Class B(WW1) chronic criterion for chlorpyrifos in 33 samples. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the percentage of samples that violated criteria for chlorpyrifos in this river reach (3%) does not suggest a water quality impairment: EPA guidelines allow up to 10% violations of chronic water quality standards parameters before impairment of water quality is indicated. Thus, these results thus suggest “full support” 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.
