Assessment Comments
Assessment is based on: (1) results of chemical/physical water quality monitoring conducted from 2004 through 2006 on Wolf Creek near Chariton (station RA-41; lower segment) and near Humeston (station RA-44; upper segment) by Iowa State University under contract with the U.S. Army Corps of Engineers-Kansas City District as part of the Rathbun Water Quality Project, (2) results of IDNR/UHL biocriteria and REMAP monitoring in 2005, and (3) results of biological monitoring by the IDNR Fisheries Bureau in 2002.
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life uses. Due to changes in Iowa’s surface water classification that were approved by U.S. EPA in February 2008 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is now presumptively designated for Class A1 (primary contact recreation) uses. The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses). Thus, for the current (2008) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]
SUMMARY: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW2) aquatic life uses are assessed (monitored) as "partially supported" based on results of chemical/physical water quality monitoring and on results of biological monitoring. The sources of data for this assessment include (1) results of chemical/physical water quality monitoring conducted from 2004 through 2006 on Wolf Creek near Chariton (station RA-41; lower segment) and near Humeston (station RA-44; upper segment) by Iowa State University under contract with the U.S. Army Corps of Engineers-Kansas City District as part of the Rathbun Water Quality Project, (2) results of IDNR/UHL biocriteria and REMAP monitoring in 2005, and (3) results of biological monitoring by the IDNR Fisheries Bureau in 2002.
EXPLANATION: The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 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 Section 305(b) assessments and Section 303(d) listings.
The geometric mean level of indicator bacteria (E. coli) in the approximately 20 samples collected at both the lower (RA-41) monitoring station (373 orgs/100 ml) and upper (RA-44) monitoring station (202 orgs/100 ml) on Wolf Creek during recreational seasons of 2004 through 2006 exceeded the Iowa Class A1 water quality criterion of 126 orgs/100ml. Thirteen of 21 samples (62%) at the lower station, and 12 of 22 samples (55%) at the upper station, exceeded Iowa’s single-sample maximum criterion 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 level 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).
Regarding support of the Class B(WW2) aquatic life uses, none of the nine samples collected in 2004 at (downstream) station RA-41 during the 2004-2006 period violated Class B(WW2) criteria for ammonia-nitrogen (maximum level = 0.79 mg/l). Similarly, none of the 10 samples collected in 2004 from the upstream station (RA-44) violated ammonia criteria. One of the 24 samples collected (4%) at station RA-41, and 3 of 24 samples collected at station RA-44 during the 2004 through 2006 assessment period violated the Class B(WW2) water quality criterion for dissolved oxygen. Minimum dissolved oxygen values were 4.2 mg/l at the downstream station and 3.6 mg/l at the upstream station. Only one of the combined 50 samples collected from both station during the 2004-2006 period violated the Class B(WW2) criterion for low pH (6.5 units); this sample contained a pH of 6.2 units. The isolated violations of the criteria for dissolved oxygen and pH that occurred during the 2004-2006 period do not suggest an impairment: according to U.S. EPA assessment guidelines, if 10% or less of the samples exceed state criteria for conventional parameters such as dissolved oxygen and pH, the aquatic life uses should be assessed as "fully supported" (see pgs 3-17 of U.S. EPA 1997b). And, according to IDNR’s assessment/listing methodology, these results do not suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum value, thus suggesting that the Class B(WW2) aquatic life uses should be assessed as “fully supported.”
Although this stream segment has a history of problems with low levels of dissolved oxygen and pH, levels of these parameters over the last six years of monitoring appear to have improved. The bulk of the violations of Class B(WW2) water quality criteria that led to this waterbody being assessed as impaired occurred in the dry summer of 2000 and were thus likely related to naturally-occurring low flow conditions. Since 2000, violations of the Class (WW2) criteria for dissolved oxygen and pH have been relatively rare, although they have continued to be associated with dry weather and low flow conditions, especially at the monitoring station (RA-44) in the upper segment of Wolf Creek. Thus, based on results of recent monitoring, this stream segment does not currently show impairments of the Class B(WW2) uses related to either dissolved oxygen or pH.
Results of biological monitoring from IDNR/UHL biocriteria sampling and from IDNR Fisheries monitoring suggest that the Class B(WW2) uses should be assessed (monitored) as "partially supported." This biological assessment was based on data collected in 2005 as part of the DNR/UHL stream biocriteria and REMAP projects and 2002 Fisheries bureau data. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biological 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 IDNR/UHL biocriteria average (n=2) FIBI score was 18 (poor) and the single biocriteria BMIBI score was 31 (fair). The evaluated Fisheries average FIBI score (n=3)was 21 (poor). The aquatic life use support was assessed as partially supporting (=PS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports. The FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41. The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.
Although this stream reach is not designated for Class C drinking water uses, Wolf Creek does flow into Rathbun Reservoir which is used as a source of drinking water for a public water supply. The seasonal elevation of pesticide levels in the Chariton River and other tributaries of Rathbun Reservoir presents a continuing concern for full support of the Class C (drinking water) uses designated for the Chariton River immediately downriver from Rathbun Reservoir. Fortunately, however, the levels of atrazine in Wolf Creek during the 2004-2006 period do not suggest a serious threat to support of drinking water uses in Rathbun Reservoir. For example, the mean level of atrazine in the 11 samples collected in 2004 at Station RA-41 (1.2 ug/l) is well-below the atrazine MCL of 3 ug/l. Similarly, at station RA-44, the mean level of atrazine in the 11 samples collected in 2004 (1.3 ug/l) was well-below the atrazine MCL of 3 ug/l.
