West Fork Cedar River IA 02-WFC-801

[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).]

The Class A1 uses are assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria (E. coli) during the 2012-2014 assessment/listing cycle.  The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2012 through 2014 at station 10070003 at Finchford were as follows:  the 2012 geometric mean was 108 orgs/100 ml, the 2013 geometric mean was 131 orgs/100 ml, and the 2014 geometric mean was 80 orgs/100 ml.  The 2012 and 2014 recreation season geometric means are below (meet) the Class A1 geometric mean criterion of 126 orgs/100 ml.  The 2013 geometric mean, however, very slightly exceeds the 126 orgs/100 ml geometric mean criterion.  Five of the 24 samples (21%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. 

Results of bacteria monitoring for the previous (2010-2012) assessment/listing cycle, however, suggested “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 were 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”.  Data for E. coli from the 2010-2012 period suggested “full support” of the Class A1 uses:  all geometric means were below the Class A1 criterion, and the percentage of samples exceeding the single-sample maximum criterion was not significantly greater than 10%.  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 remained in effect for the 2014 assessment/listing (IR) cycle.  Because at least one geometric mean exceeded the Class A1 criterion during the current (2012-2014) monitoring period, the Class A1 uses will remain assessed as impaired (partially supporting).  Also, the percentage violation of Iowa’s Class A1 single-sample maximum criterion during the 2012-2014 period (5 of 24 samples or 21%) is significantly greater than a 10% violation frequency and thus also indicates impairment of the Class A1 uses.  

None of the approximately 36 samples collected during the 2012-2014 assessment period at the IDNR monthly station violated Class B(WW1) water quality criteria for pH, ammonia-nitrogen, temperature, chloride, or sulfate.  One of the 36 samples collected, however, violated the state standard for dissolved oxygen (violation was 4.7 mg/l).  According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17), a violation frequency of less than 10 % for conventional parameters such as dissolved oxygen nonetheless suggests "full support" of aquatic life uses.  Thus, the percentage of violations of the dissolved oxygen criterion at this station (3%) does not suggest an impairment of aquatic life uses in this stream segment. 

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 2012-2014 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 2005 Fisheries FIBI score was 35 (fair).  The 2012-2014 BMIBI scores were 47 (fair) and 60, 72 (both good). 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 2/3 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 the sites used for the assessments don’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.