Assessment Comments
Assessment is based on results of (1) water quality monitoring conducted by South Dakota DENR near Richland, SD, from 2002-04, (2) USGS ambient monitoring in 2004, and (3) an IDNR investigation of a fish kill in July 2002.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses remain assessed (monitored) as "not supported" due to levels of indicator bacteria (E. coli) 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 2002 through 2004, (2) results of ambient water quality monitoring conducted by USGS at Akron from May 2002 to September 2004, and (3) 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 (E. coli) that violate state water quality standards. Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of the 2006 Section 305(b) assessments and Section 303(d) listings.
The geometric mean level of indicator bacteria (E. coli) in the 14 samples collected during the recreational seasons of 2002, 2003, and 2004 (128 orgs/100ml) slightly exceeded the Iowa Class A water quality criterion of 126 orgs/100ml. Six of the 14 samples (43%), however, 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 greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). Also, the U.S. EPA guidelines state that if levels of E. coli exceed the single-sample maximum criterion in more than 10% of the samples, the primary contact recreation uses should be assessed as “partially supported.” According to IDNR’s assessment/listing methodology, these results suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum value, thus suggesting that the Class A uses should be assessed as “partially supported/impaired”. Thus, regardless of whether 2000-04 geometric mean actually exceeds Iowa’s Class A criterion, the occurrence of over 40% of the samples greater than Iowa’s single-sample maximum value suggests continued impairment of the Class A uses in this assessment segment.
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 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. Monitoring at the South Dakota station near Richland showed no violations of Class B(WW) water quality criteria for pH or ammonia-nitrogen (maximum value = 1.2 mg/l) in the approximately 30 samples analyzed during the 2002-2004 period. The maximum value of ammonia-nitrogen was 1.2 mg/l. One of the 35 samples contained a level of dissovled oxygen (4.6 mg/l on February 9, 2004) that violated Iowa's Class B(WW) criterion of 5.0 mg/l, and one of 35 samples contained a level of pH that violated Iowa's Class A,B(WW) criterion of 9.0 pH units (9.2 units on September 2, 2003). Similarly, monitoring at the USGS station at Akron showed no violations in the nine samples analyzed for ammonia and only one violation each for dissolved oxygen (4.6 mg/l on September 12, 2003) and pH (9.2 units on July 30, 2002) in the approximately 25 samples analyzed during the 2002-2004 period. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), however, the percentages of samples that violate criteria for dissolved oxygen and pH in this river reach (from 3 to 4%) do not suggest water quality impairments: EPA guidelines allow up to 10% violations of these conventional parameters before impairment of water quality is indicated. These results thus suggest “full support” of the Class B(WW) aquatic life uses.
Fish consumption uses remain "not assessed" due to a lack of fish contaminant monitoring in this river segment.
