Assessment Comments
Assessment is based on the results of monthly ambient water quality monitoring conducted during 2010-12 on the Big Sioux River by three agencies: South Dakota Department of Environment and Natural Resources (DENR) near Richland, SD, (2) USGS at Akron (in 2010), and (3) IDNR/SHL also at Akron. Assessment is also based on results of a fish kill investigation in July 2002 and on resutls of IDNR/SHL stream biological sampling in 2005 and 2012.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses remain assessed (monitored) as "not supported" (IR 4a) due to levels of indicator bacteria (E. coli) that violate state water quality standards. The Class B(WW1) aquatic life remain assessed (monitored) as "partially supported" (IR 5b) based on results of a fish kill investigation in July 2002 and evaluated "partially supported" (IR 3b-u) based on 2005 and 2012 IDNR/SHL TMDL/large river biological samplings. Fish consumption uses remain "not assessed" (IR 3a) 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 2010 through 2012, (2) results of ambient water quality monitoring conducted by USGS at Akron in 2010, (3) results of ambient water quality monitoring conducted by IDNR/SHL at Akron from 2010 to 2012, (4) results of a fish kill investigation in July 2002, and (5) IDNR/SHL stream biological sampling in 2005 and 2012.
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 listing cycle.
EXPLANATION: Based on results of bacteria monitoring by three agencies at two locations during the 2010-12 period, the Class A1 (primary contact recreation) of this river segment are assessed as "not supported". All violations of the Class A1 geometric mean criterion during the 2010-12 period, however, were very slight, with recreation season geometric means largely meeing the Class A1 criterion during the recreation season of 2011.
The geometric means of indicator bacteria (E. coli) in the eight samples collected by USGS during the recreational season of 2010 at the Big Sioux River near Akron was 166 orgs/100 ml. This geometric mean slightly exceeds the Class A1 criterion of 126 orgs/100 ml. Two of the eight samples (25%) exceeded the 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 at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”
Results of ambient monitoring by the South Dakota DENR also suggest that the Class A1 uses be 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 15 samples collected during the recreational seasons of 2010 through 2012 at the Big Sioux River near Richland were as follows: the 2010 geometric mean was 349 orgs/100 ml, the 2011 geometric mean was 92 orgs/100 ml and the 2012 geometric mean was 102 orgs/100 ml. Only the geometric mean in 2010 slightly exceeded the Class A1 criterion of 126 orgs/100 ml. Seven of the 15 samples (47%) exceeded the 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 at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”
Similarly, results of ambient monitoring by the Iowa DNR/SHL at Akron also suggest that the Class A1 uses be 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 13 samples collected during the recreational seasons of 2010 through 2012 at the Big Sioux River at Akron were as follows: the 2010 geometric mean was 359 orgs/100 ml, the 2011 geometric mean was 61 orgs/100 ml and the 2012 geometric mean was 203 orgs/100 ml. The geometric means in 2010 and 2012 slightly exceeded the Class A1 criterion of 126 orgs/100 ml. Five of the 13 samples (38%) exceeded the 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 at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”
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 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 and 2012 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/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). 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 failed 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. According to IDNR’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). IDNR 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, 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 = 7.1 to 8.7), dissolved oxygen (minimum = 6.2 mg/L) or ammonia-nitrogen (maximum value = 0.89 mg/l) in the approximately 36 samples analyzed during the 2010-2012 period. Monitoring at the USGS station at Akron in 2010 showed no violations in the nine samples analyzed for ammonia, dissolved oxygen, and pH. None of the nine samples analyzed by USGS for chlorphyrifos, dieldrin, or DDE violated the respective Class B(WW1) criteria. Similarly, results of IDNR monitoring at Akron from 2010 to 2012 do not suggest impairment of the Class B(WW1) uses. No violations of chloride, ammonia, pH, or sulfate occurred in the 21 samples collected. One of the 21 samples (5%) violated the Class B(WW1) criterion for dissolved oxygen (4.8 mg/l). According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), the percentage of violations for dissolved oxygen in this stream reach (5%) does not suggest a water quality impairment (the EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated). None of the 99 samples analyzed for water temperature exceeded the Class B(WW1) criterion of 32C. 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.
