Assessment Comments

Assessment remains based on: (1) results of IDNR/SHL ambient water quality monitoring downstream of Independence (station 10100002) from 2004 through 2006, (2) results of biological monitoring by IDNR Fisheries in 2002, (3) results of EPA/IDNR fish tissue (RAFT) monitoring in 2011 approximately 1 mile southeast of Independence, and (4) results of an IDNR fish kill investigation in August 2005.

Basis for Assessment

SUMMARY:  Class A1 (primary contact recreation) uses remain assessed (evaluated) as “fully supported” (IR 2a) based on results of bacterial monitoring from 2004-06.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" (IR 2b) based on occurrence of a fish kill in 2005.   Fish consumption uses are assessed (monitored) as "fully supported" based on results of U.S.  EPA/IDNR fish contaminant monitoring in 2011.   The sources of data for this assessment include (1) results of IDNR/SHL ambient water quality monitoring downstream of Independence (station 10100002) from 2004 through 2006, (2) results of fish sampling by IDNR Fisheries in 2002, (3) results of EPA/IDNR fish tissue (RAFT) monitoring in 2011 approximately 1 mile southeast of Independence, and (4) results of an IDNR fish kill investigation in August 2005.   (Note:  routine ambient monitoring at IDNR/UHL station 10100002 downstream from Independence was discontinued in 2006.)

EXPLANATION:  The Class A1 (primary contact recreation) uses remain assessed as “fully supported.”  The geometric means of indicator bacteria (E.  coli) in the 24 samples collected during the recreation seasons of 2004 through 2006 at IDNR ambient station 10100002 were as follows:  the 2004 geometric mean was 77 orgs/100 ml, the 2005 geometric mean was 34 orgs/100 ml and the 2006 geometric mean was 80 orgs/100 ml.   All three geometric means are well below the Class A1 criterion of 126 orgs/100 ml.   Two of the 24 samples (8%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric means are less than the respective water quality criterion, and less than 10% of samples exceed the respective single-sample maximum criterion, the contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because all recreation season geometric mean met Class A1 criteria, these uses are assessed as “fully supported.”  Because the data upon which this assessment is based are now more than five years old, the assessment type is changed from “monitored” (a higher confidence assessment) to “evaluated” (a lower confidence assessment).   As water quality data age, they are less able to represent current water quality conditions.   Despite the age of the data and the change from a “monitored” to an “evaluated” assessment type, these monitoring results suggest very low levels of indicator bacteria in this assessment segment.  

The results of IDNR/SHL ambient water quality monitoring from 2004 through 2006 also suggest "full support" of the Class B(WW1) uses due to the lack of violations of state water quality criteria for pH, dissolved oxygen, and ammonia-nitrogen in the approximately 35 samples collected during the 2004-2006 period.   In addition, no violations of Class B(WW1) chronic criteria occurred in the seven samples analyzed for the pesticide chlorpyrifos during this period.   None of the ten samples analyzed for toxic metals violated the respective Class B(WW1) criteria.  

Results of biological monitoring conducted in 2002 by the IDNR Fisheries Bureau suggest that the Class B(WW1) aquatic life use should be assessed (evaluated) as "fully supported."  A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the Fisheries sampling data.   The biological metrics are based on the numbers and types of fish species that were collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (FIBI).   The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2002 evaluated FIBI was 65 (good).   The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established for previous Section 305(b) reports.   The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.   The riffle site FIBI BIC for this ecoregion is 65.   The segment passed the FIBI BIC 1/1 times in 2002.  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 over a five-year period to be considered “monitored”.   This segment had a single sample collected in 2002.   Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).  

The occurrence of a fish kill in this river segment late August, 2005, however, suggests that the Class B(WW1) uses of this river segment should be assessed (evaluated) as impaired.   IDNR Fisheries staff investigated the kill.   Seventeen dead channel catfish ranging in length from 12 to more than 20 inches were found immediately downriver from the Independence Dam; only channel catfish appeared to have been affected by the kill.   The kill was attributed to stress associated with high water temperatures and was not caused by a pollutant.   According to IDNR’s assessment and listing methodology, a single fish kill attributed to non-pollutant sources within the most recent three-year period suggests that the aquatic life uses should be assessed (evaluated) as “partially supported.”  Due to lack of a pollutant source, this type of kill is not appropriate for Section 303(d) listing but is appropriate for Subcategory 2b of Iowa's Integrated Report.  

Fish consumption uses are assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring downstream from Independence in 2011.   The composite samples of fillets from channel catfish and smallmouth bass had low levels of contaminants.   The composite sample of fillets from channel catfish and the tissue plug samples from smallmouth bass had low levels of contaminants.   Levels of primary contaminants in the composite sample of fillets from channel catfish were as follows: mercury: 0.067 ppm; total PCBs: 0.09 ppm; and technical chlordane: < 0.031 ppm.   The average level of mercury in the tissue plug samples from five smallmouth bass was 0.245 ppm (standard deviation = 0.024 ppm; maximum =0.281 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 levels of contaminants in the samples from this assessment segment analyzed for the 2011 RAFT program do not exceed any of Iowa’s advisory trigger levels, thus indicating no justification for issuance of a consumption advisory for this waterbody and “full support” of fish consumption uses.