Assessment Comments

Assessment is based on: (1) the results of IDNR/SHL ambient monthly water quality monitoring conducted at Finchford (station 10070003) during the 2010-2012 assessment period, (2) results of IDNR/SHL biological sampling conducted in 2008 and 2012, (3) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring near Allison in 2011 and 2012 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" (IR 5a) due to levels of indicator bacteria during the previous (2012) assessment period that violated state water quality criteria.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported" (IR 3b-u) based on results of biological monitoring.   Fish consumption uses remain assessed (monitored) as “fully supported” (IR 2a) based on fish contaminant monitoring in 2011 and 2012.   Sources of data for this assessment include (1) the results of IDNR/SHL ambient monthly water quality monitoring conducted on the West Fork Cedar River at Finchford (IDNR station 10070003) during the 2010-2012 assessment period, (2) results of IDNR/SHL biological monitoring conducted in 2008 and 2012, (3) results of U.S.  EPA/IDNR fish contaminant (RAFT) monitoring near Allison in 2011 and 2012, and (4) IDNR Fisheries Bureau fish sampling conducted in 2005.  

EXPLANATION:  The Class A1 uses remain assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E.  coli) during the previous (2012) assessment/listing cycle.   Results of bacteria monitoring for the current (2014) listing cycle, however, suggest “full support” of the Class A1 uses.   The geometric means of indicator bacteria (E.  coli) in the 24 samples collected during the recreational seasons of 2010 through 2012 at station 10070003 at Finchford were as follows:  the 2010 geometric mean was 118 orgs/100 ml, the 2011 geometric mean was 103 orgs/100 ml, and the 2012 geometric mean was 108 orgs/100 ml.   All three recreation season geometric means are below the Class A1 geometric mean criterion of 126 orgs/100 ml.   Four of the 24 samples (17%) 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 all recreation season geometric means are below the respective water quality criterion, the contact recreation uses are should be assessed as "fully supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   In addition, according to the IDNR assessment/listing methodology, if the percentage of samples that exceed Iowa’s single-sample maximum criterion (235 orgs/100 ml) is not significantly greater than 10%, then the Class A1 uses should be assessed as “fully supported”.   The percentage of samples exceeding the single-sample maximum criterion during the 2010-2012 period is not significantly greater than 10%.   Thus, these results suggest “full support” of the Class A1 primary contact recreation uses.   Because, however, the IDNR assessment/listing methodology requires that, before a bacterial impairment can be de-listed, geometric mean levels of E.  coli must all be less than the applicable state water quality criteria for two consecutive listing cycles (i.e., five consecutive years), the impairment of the Class A1 uses will remain in effect.   Of the monitoring results from this station over the last five years, the 2008 recreation season geometric mean (451 orgs/100 ml) and the 2009 geometric mean (161 orgs/100 ml) both exceeded the Class A1 criterion.   If sufficient additional data are collected during the 2013-2014 period that show a continued decline in bacteria levels and compliance with the Class A1 water quality criterion, this impairment may be removed.

None of the 36 samples collected during the 2010-2012 assessment period at the IDNR monthly station violated Class B(WW1) water quality criteria for dissolved oxygen, pH, ammonia-nitrogen, chloride, or sulfate.   These results suggest “full support” of the Class B(WW1) aquatic life uses.

Despite results of chemical/physical monitoring which suggest “full support” of the Class B(WW1) aquatic life uses, results of IDNR/SHL biological monitoring from 2008 and 2012 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 2008 BMIBI score was 63 (good) and the 2012 BMIBI score was 60 (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 1994-2008.   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 2/2 times in the last five years.   This assessment is considered evaluated because the drainage areas (824 and 850 mi2) above the 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 BIC and passed the BMIBI 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.  

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 2011 and 2012.   In the 2011 samples, the composite samples of fillets from channel catfish had low levels of contaminants:  mercury: 0.136 ppm; total PCBs: 0.091 ppm; and technical chlordane:  <0.03 ppm.   The average level of mercury in the tissue plugs from four smallmouth bass was 0.415 ppm (SD=0.099 ppm).   This level of mercury exceeded Iowa's threshold for a one-meal per week consumption advisory of 0.3 ppm.   According to Iowa’s fish consumption advisory protocol, however, two consecutive samplings that show contaminant levels above an advisory threshold are needed to confirm that an advisory should be issued.   Thus, follow-up sampling was conducted in 2012.   The results of this follow-up sampling showed that the average level of mercury in the tissue plugs from four smallmouth bass (0.182 ppm; SD=0.077 ppm) was well below the advisory threshold of 0.3 ppm, thus suggesting no justification for issuance of a consumption advisory for this river segment.   These results suggest continued full support of the fish consumption uses.