Assessment Comments
Assessment is based on: (1) results of IDNR/UHL biological (biocriteria) monitoring in 1999-2002 and REMAP monitoring in 2004, (2) results of IDNR/UHL monthly ambient monitoring station on the Chariton River downstream from Rathbun Dam during the 2006-2008 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 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" based on monitoring for 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 2006-2008 assessment period (STORET station 10040001), (3) results from Rathbun Watershed station RA-28 at the reservoir outlet from 2004-2008, 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). The geometric mean level of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2006 through 2008 (90 orgs/100ml) is below, and meets, the Iowa Class A1 water quality criterion of 126 orgs/100ml. Four of the 22 samples (18%) 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 guidelines, however, also suggest that if more than 10% of samples exceed the single-sample maximum criterion for indicator bacteria, the primary contact recreation uses should be assessed as "partially supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, the monitoring data from 2006-08 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.”
A review of ambient monitoring data from Chariton River station 10040001 for the years 2000 through 2008 shows relatively low levels of indicator bacteria in this river segment and a tendency to meet the Class A1 geometric mean criterion of 126 orgs/100 ml. A comparison of geometric mean levels from previous listing cycles shows that geometric mean levels of E. coli for three of the four listing cycles since 2002 meet Iowa’s Class A1 geometric mean criterion of 126 orgs/100 ml: 2004 cycle: 110 orgs/100 ml (N=24); 2008 cycle: 119 orgs/100 ml (N=24); 2010 cycle: 90 orgs/100 ml (N=22). Only the geometric mean for the 2006 cycle (134 orgs/100 ml) slightly exceeded the Class A1 criterion. Similar to monitoring results from immediately downriver from Iowa’s other flood control reservoirs, the results for the Chariton River downstream from Rathbun Dam suggest that relatively low levels of indicator bacteria occur in Iowa rivers immediately downriver from Iowa’s federal flood control reservoirs.
The Class B(WW1) aquatic life uses remain assessed as "fully supporting" based on results of IDNR/UHL biological monitoring conducted from 1999-2002 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 1999-2002 BMIBI scores were 57 (good), 51 (fair), 45 (fair). 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 segment passed the FIBI BIC 1/1 times (using the uncertainty adjustment value (UAV) of seven points) in 2004 and passed the BMIBI BIC 4/4 times in the last 10 years. This assessment is considered evaluated because the drainage area (555 and 641 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.
This aquatic life assessment is now considered "evaluated" based on a change in the 2010 IDNR assessment methodology. IDNR now requires a segment have two or more biological samples collected from the segment in multiple years between 2004 and 2008 to be considered “monitored”. This segment had multiple BMIBI samples collected in the previous 10 years (1999-2008); however, the samples were not collected during 2004-2008. Despite this change in assessment methodology and type, this waterbody remains in IR Category (1) and remains on Iowa’s 2010 Section 303(d) list of impaired waters.
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 33 samples collected from 2006 through 2008 at the IDNR monthly ambient monitoring station that were analyzed for conventional parameters (dissolved oxygen, pH, and ammonia-nitrogen). In addition, none of the 11 samples analyzed for pesticides and neither of the two 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 2006-2008 assessment period and a relatively low average level of atrazine. The atrazine MCL violation (9.4 ug/l) occurred on May 2, 2006. The average level of atrazine in the 11 samples collected at the IDNR station during the 2006-08 period was 1.4 ug/l. Similarly, results from Rathbun Watershed station RA-28 at the reservoir outlet show low levels of atrazine. None of the nine samples collected at station RA-28 from 2004 through 2008 violated the U.S. EPA MCL for atrazine; the maximum atrazine concentration was 2.6 ppb on July 10, 2006. Regarding nitrate, none of the 33 IDNR samples analyzed for nitrate exceeded the EPA MCL of 10 mg/l (maximum value = 3.7 mg/l). Also, levels of nitrate at Rathbun Watershed station RA-28 were extremely low during this time period with a maximum value of 1.4 mg/l in the 16 samples collected from 2004 through 2008. 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. The fish contaminant data generated for this segment of the Chariton River from the 2003 RAFT show that the levels of contaminants do not exceed any of the IDPH/IDNR advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory.
