Assessment Comments

Assessment is based on results of (1) IDNR/UHL biological sampling in 2000-2002 and 2004, (2) IDNR/UHL ambient monitoring from 2002-04, and (3) Rathbun Watershed project monitoring at outlet of Rathbun Reservoir from 2002-04, and (4) U.S. EPA/IDNR fish contaminant monitoring in 2003.

Basis for Assessment

SUMMARY:  The Class B(WW) aquatic life uses are assessed (evaluated) as "fully supporting" based on results of biological monitoring.   The Class C (drinking water) uses were assessed (monitored) as "fully supporting" based on results of ambient water quality monitoring for atrazine.   Fish consumption uses are 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 2000-2002 and REMAP monitoring in 2004, (2) results of IDNR/UHL monthly ambient monitoring station on the Chariton River downstream from Rathbun Dam during the 2002-2004 assessment period (STORET station 10040001), (3) results of monitoring during 2002-2004 at the outlet of Rathbun Reservoir (station RA-28) as part of the Rathbun Reservoir Water Quality Project, and (4) results of U.S.  EPA / IDNR fish contaminant (RAFT) monitoring north of Centerville in 2003.  

EXPLANATION:  The Class B(WW) aquatic life uses were assessed (evaluated) 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 48 (fair).   The 2000-2002 BMIBI scores were 52 (fair), 51 (fair) and 45 (Fair).   The BMIBI average was 49.   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 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site passed both the FIBI 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 and by ISU/ACOE do not suggest any water quality impacts in this river reach.   No violations of Class B(WW) 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 the approximately 10 samples analyzed for pesticides and toxic metals during the 2002-2004 period, the only violation of a Class B(WW) criterion was for DDT.   This violation occurred on May 5, 2003; the level of DDT in the sample was 0.062 ug/l and exceeded the Class B(WW) criterion of 0.001 ug/l.   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) does not indicate an impairment of aquatic life uses.   Although only seven samples were analyzed for pesticides during the assessment period, IDNR considers the available data sufficient to characterize levels of DDT in is reach of the Chariton River.   No violations of Class B(WW) criteria for dissolved oxygen, pH, or ammonia-nitrogen occurred in the 12 samples collected from Rathbun Project station RA-28 during the 2002-2004 period.  

Class C (drinking water) uses were also assessed (monitored) as "fully supporting".   Results from the IDNR ambient station show the occurrence of a single violations of the U.S.  EPA MCL for atrazine during the 2002-2004 assessment period and a relatively low average level of atrazine (0.9 ug/l).   The atrazine MCL violation occurred on May 5, 2003 (3.9 ug/l).   The average level of atrazine in the 36 samples was 0.9 ug/l.   Monitoring at Rathbun Project station RA-28 produced similar results:  none of 13 samples analyzed exceeded the atrazine MCL (maximum level = 2.9 ug/l).     The average level of atrazine in the 13 samples was 1.4 ug/l.   None of the 36 IDNR samples analyzed for nitrate exceeded the EPA MCL of 10 mg/l (maximum value = 2.8 mg/l).   Similarly, none of the 13 samples from Rathbun Project site RA-28 exceeded the MCL (maximum value = 0.6 mg/l)  The only other violation of a Class C water quality criterion was for DDT:  the sample collected on May 5, 2003 contained 0.062 ug/l of DDT with exceeded the Class C (Human Health) criterion of 0.0059 ug/l.     Based on DNR's Section 305(b) assessment methodology, the results of the IDNR/UHL and ISU/ACOE monitoring suggest that the Class C (drinking water) uses are fully supported:  average levels of all pesticides are well below their respective MCLs and Class C criteria.    

Fish consumption uses are 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.