Assessment Comments

Assessment is based on: (1) the results of IDNR/UHL ambient monthly water quality monitoring conducted at Finchford (station 10070003) during the 2008-2010 assessment period, (2) results of IDNR/UHL biological monitoring conducted from 1999-2002 and 2008 as part of the IDNR biocriteria project, (3) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring near Allison in 2002 and (4) IDNR Fisheries Bureau fish sampling conducted in 2005.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this river 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, 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 are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of biological monitoring.   Fish consumption uses remain assessed (monitored) as “fully supported” based on fish contaminant monitoring in 2002.   Sources of data for this assessment include (1) the results of IDNR/UHL ambient monthly water quality monitoring conducted on the West Fork Cedar River at Finchford (IDNR station 10070003) during the 2008-2010 assessment period, (2) results of IDNR/UHL biological monitoring conducted from 1999-2002 and 2008 as part of the IDNR biocriteria project, (3) results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring near Allison in 2002 and (4) IDNR Fisheries Bureau fish sampling conducted in 2005.  

EXPLANATION:  The Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E.  coli).   The geometric means of indicator bacteria (E.  coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at station 10070003 at Finchford were as follows:  the 2008 geometric mean was 451 orgs/100 ml, the 2009 geometric mean was 161 orgs/100 ml and the 2010 geometric mean was 118 orgs/100 ml.   The 2008 and 2009 geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Eight of the 21 samples (38%) 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 mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”  

None of the 32 samples collected during the 2008-2010 assessment period at the IDNR monthly station violated Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen.   No violations occurred in the two samples analyzed for pesticides.  

Despite results of chemical/physical monitoring which suggest “full support” of the Class B(WW1) aquatic life uses, results of IDNR/UHL biological monitoring from 1999-2002 and 2008 and IDNR Fisheries monitoring in 2005 suggest (evaluated) “partial support” of these uses.   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 1999-2002 and 2008 BMIBI scores were 51, 43, 50, 55 (fair) and 63 (good).   The 2005 Fisheries FIBI score was 35 (fair).   The aquatic life use support was assessed (evaluated) as partially supporting (=PS), 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 non-riffle FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52.   This segment passed the FIBI BIC 0/1 times in 2005 and passed the BMIBI BIC 2/5 times in the last 12 years.   This assessment is considered evaluated because the drainage areas (824 and 850 mi2) above this sampling sites were greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria.   Even though this site failed to meet 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.  

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 over a five-year period to be considered “monitored”.    This segment had multiple BMIBI samples collected in the previous 12 years (1999-2010); however, the samples were not collected during the most recent five-year period.   According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report).   IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).  

Fish consumption uses remain assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Allison, Iowa, in 2002.   This assessment is considered of lesser confidence (evaluated) because the data are more than five years old and are thus less able to represent current water quality conditions.   The composite samples of fillets from channel catfish and smallmouth bass had 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: 0.08 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 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.