Assessment Comments
Assessment is based on results of (1) water quality monitoring conducted by South Dakota DENR near Richland, SD, from 2000-02 and (2) an IDNR investigation of a fish kill in July 2002.
Basis for Assessment
[NOTE: For the 2002 report, the previous waterbody segment for the Big Sioux River (IA 06-BSR-0010-0), which extended 82 miles from its mouth at Sioux City to confluence with the Rock River in Sioux County, was split into four subsegments: (1) mouth to Broken Kettle Creek in southwestern Plymouth County (IA 06-BSR-0010-1), (2) Broken Kettle Creek to Brule Creek near Richland, SD (and near Westfield, IA) (IA 06-BSR-0010-2), (3) (this one) Brule Creek to Indian Creek in northwestern Plymouth Co. (IA 06-BSR-0010-3), and (4) Indian Creek to the Rock River in Sioux Co. (IA 06-BSR-0010-4). See assessment information found in this subsegment (IA 06-BSR-0010_4 for previous Section 305(b) assessments for the entire 82-mile reach.]
SUMMARY: The Class A (primary contact recreation) uses remain assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality standards. The Class B(WW) aquatic life are assessed (monitored) as "partially supported" based on results of a fish kill investigation in July 2002. 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 March 2000 through December 2002 and (2) results of a fish kill investigation in July 2002.
EXPLANATION: The Class A uses were assessed (monitored) as "not supported" due to levels of indicator bacteria (fecal coliforms) that violate state water quality standards. The geometric mean of indicator bacteria (fecal coliforms) for the 14 of 15 samples not materially affected by surface runoff during the recreational seasons of 2000, 2001, and 2002 at the Richland monitoring station exceeded the Iowa water quality criterion (200 fecal coliform orgs/100ml) to protect primary contact recreation uses. For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff. According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff." The geometric mean of fecal coliform bacteria in the 14 non-runoff-affected samples was 341 orgs/100 ml, with seven samples (50%) exceeding the EPA-recommended single-sample maximum value of 400 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, if the geometric mean level of fecal coliforms exceeds 200 orgs/100 ml, the primary contact recreation uses are "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
The Class B(WW) aquatic life uses are 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; the kill occurred 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.
Despite occurrence of the fish kill and indications of degraded chemical water quality, results of monthly ambient monitoring on the Big Sioux River at Richland suggest relatively good water quality. This monitoring showed that one of the 33 samples collected during the 2000-2002 assessment period (3%) violated the Class B(WW) criterion for ammonia-nitrogen. The sample collected on March 27, 2001 contained 1.26 mg/l of ammonia-nitrogen; this level exceeded the Class B(WW) temperature/pH-dependent chronic criterion of 0.71 mg/l. Violations also occurred on this date at two other stations (Alcester and Hudson) on the Iowa reach of the Big Sioux River that are monitored by the South Dakota DENR. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-18), however, one violation of a water quality criterion for a toxic pollutant in an abundant data set (at least 10 samples over at three-year period) set does not indicate an impairment of aquatic life uses. Based on Iowa DNR's assessment methodology for Section 305(b) reporting, this violation suggests that the Class B(WW) aquatic life uses should be assessed as "fully supported/threatened." No other violations of Class B(WW) criteria occurred at this station during the 2000-2002 assessment period.
Fish consumption uses remain "not assessed" due to a lack of fish contaminant monitoring in this river segment.
