Assessment Comments
Assessment is based on: (1) results of IDNR/UHL biological (biocriteria) monitoring in 2002 and REMAP monitoring in 2004, (2) results of IDNR/UHL monthly ambient monitoring station on the Chariton River downstream from Rathbun Dam during the 2004-2006 assessment period (STORET station 10040001), (3) results from Rathbun Watershed station RA-28 at the reservoir outlet, and (4) results of U.S. EPA / IDNR fish contaminant (RAFT) monitoring north of Centerville in 2003.
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this river segment was designated for Class B(WW) aquatic life uses, including fish consumption uses and for Class C (drinking water) 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), and due to the completion of a Use Attainability Analysis in 2006, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), for fish consumption uses (now termed Class HH (human health/fish consumption uses), and for Class C (drinking water) uses.]
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" due to high levels of indicator bacteria (E. coli). The Class B(WW1) aquatic life uses are assessed (evaluated) as "fully supporting" based on results of chemical, physical, and biological monitoring. The Class C (drinking water) uses are assessed (monitored) as "fully supporting" based on results of ambient water quality monitoring for pesticides, toxic metals, and nitrate. Fish consumption uses remain assessed (monitored) as "fully supported" based on results of fish contaminant monitoring in 2003. The sources of data used for this assessments include (1) results of IDNR/UHL biological (biocriteria) monitoring in 2002 and REMAP monitoring in 2004, (2) results of IDNR/UHL monthly ambient monitoring station on the Chariton River downstream from Rathbun Dam during the 2004-2006 assessment period (STORET station 10040001), (3) results from Rathbun Watershed station RA-28 at the reservoir outlet, and (4) results of U.S. EPA / IDNR fish contaminant (RAFT) monitoring north of Centerville in 2003.
EXPLANATION: The Class A1 uses are assessed (monitored) as "partially 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 24 samples collected during the recreational seasons of 2004 through 2006 (119 orgs/100ml) is below, and meets, the Iowa Class A1 water quality criterion of 126 orgs/100ml. Seven of the 24 samples (29%) 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 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). These EPA guidelines state, however, that if more than 10% of the samples exceed the state’s single-sample maximum criterion, 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 criterion, thus suggesting that the Class A1 uses should be assessed as “partially supported/impaired.”
The Class B(WW1) aquatic life uses remain assessed as "fully supporting" based on results of IDNR/UHL biological monitoring conducted from 2000-2002 as part of the stream biocriteria project and sampling conducted in 2004 as part of the REMAP project. A series of biological metrics which 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 that were collected in the stream sampling reach. The biological metrics were combined to make a benthic macroinvertebrate index (BMIBI) and fish index of biotic integrity (FIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2004 REMAP FIBI score was 26 (fair) and the BMIBI score was 47 (fair). The 2002 BMIBI score was 45 (fair). The BMIBI average was 46. The aquatic life use support was assessed (evaluated) as fully supporting (= FS), 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. The FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41. This assessment is considered evaluated because the drainage area (537 and 700 mi2) above the sampling sites was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site met both the FIBI (using the UAV of 7 points) 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.
Results of ambient chemical/physical water quality monitoring conducted by IDNR/UHL do not suggest any water quality impacts in this river reach. No violations of Class B(WW1) water quality criteria occurred in the 36 samples from the IDNR monthly ambient monitoring station analyzed for conventional parameters (dissolved oxygen, pH, and ammonia-nitrogen). In addition, none of the 8 samples analyzed for pesticides and none of the ten samples analyzed for toxic metals violated the respective Class B(WW1) criteria. These results suggest no impairments of the Class B(WW1) aquatic life uses in this river segment.
Class C (drinking water) uses are also assessed (monitored) as "fully supporting." Results from the IDNR ambient station show the occurrence of a single violation of the U.S. EPA MCL for atrazine (3 ug/l) during the 2004-2006 assessment period and a relatively low average level of atrazine (0.9 ug/l). The atrazine MCL violation (9.4 ug/l) occurred on May 2, 2006. The average level of atrazine in the 35 samples was 0.9 ug/l. None of the 36 IDNR samples analyzed for nitrate exceeded the EPA MCL of 10 mg/l (maximum value = 3.7 mg/l). Similarly, results from Rathbun Watershed station RA-28 at the reservoir outlet show low levels of atrazine. None of the 20 samples analyzed from 2002 through 2006 violated the U.S. EPA MCL for atrazine; the maximum atrazine concentration was 2.6 ppb on July 10, 2006. Also, levels of nitrate at station RA-28 were extremely low during this time period with a maximum value of 0.8 mg/l in the 23 samples collected from 2002 through 2006. Based on DNR's Section 305(b) assessment methodology, the results of the IDNR/UHL and Rathbun watershed monitoring both suggest that the Class C (drinking water) uses should be assessed as fully supported.
Fish consumption uses remain assessed (monitored) as "fully supported" based on results of the U.S. EPA/IDNR fish tissue (RAFT) monitoring north of Centerville in 2003. The composite samples of fillets from channel catfish had very low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.119 ppm; total PCBs: 0.09 ppm; and technical chlordane: <0.03 ppm. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa. In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol. This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol). Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses. This scenario, however, does not apply to the fish contaminant data generated from the 2003 RAFT sampling conducted in this assessment segment: the levels of contaminants do not exceed any of the new (2006) advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory.
