West Fork Cedar River IA 02-WFC-802

Assessment Comments

Assessment is based on results of (1) IDNR/UHL biocriteria sampling in 1999 and 2006 and (2) U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2002.

Basis for Assessment

Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption 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 completion of a use attainability analysis (UAA), 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), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]

SUMMARY:  The Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as fully supporting based on results of IDNR/UHL biological monitoring in 1999 and 2006.   Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of U.S.  EPA/IDNR fish contaminant monitoring near Allison in July 2002.  

EXPLANATION:  The Class B(WW1) aquatic life usess remain assessed (evaluated) as "fully supporting" based on biological data collected in 1999 and 2006 as part of the IDNR/UHL stream biocriteria 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 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 1999 FIBI score was 70 (good) and the BMIBI score was 55 (fair).   The 2006 FIBI score was 65 (good) and the BMIBI score was not available due to flooding removing the artificial substrates.   The aquatic life use support was assessed 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 1994-2004.   The non-riffle site FIBI BIC for this ecoregion is 44 and the BMIBI BIC is 52.   This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 1/1 times in the last 10 years.   This assessment is considered evaluated because the drainage area (554 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 the FIBI BIC, 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 FIBI samples collected in the previous 10 years (1999-2008); however, the multiple samples were not collected during 2004-2008.  Despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.  

Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Allison in 2002.   The composite samples of fillets from channel catfish and smallmouth bass had very low levels of contaminants.   Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.105 ppm; total PCBs: 0.094 ppm; and technical chlordane: 0.045 ppm.   Levels of primary contaminants in the composite sample of smallmouth bass fillets were as follows: mercury: 0.080 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 levels of contaminants in the samples from the 2002 sampling near Allison do not exceed any of Iowa’s advisory trigger levels, thus suggesting no justification for issuance of a consumption advisory for this waterbody.   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).