Assessment Comments
Assessment is based on results of water quality monitoring at two stations in this segment from May 2011 to November 2012. Assessment also remains based on results of 2002 IDNR/SHL biological sampling data: FIBI = 84 (excellent), BMIBI = 71 (good).
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 the completion of a Use Attainability Analysis, 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 "partially supported” (IR Category 5a) due to levels of indicator bacteria that slightly exceed Iowa water quality criteria. This is a new impairment for this assessment segment. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" (IR Category 2a) based on results of IDNR/SHL biological monitoring in 2002 and based on results of water quality monitoring in 2011 and 2012. The fish consumption uses remain "not assessed” (IR Category 3a) due to the lack of recent fish contaminant monitoring in this river segment. The sources of data for this assessment include (1) results of monitoring at station TR60 at the Great River Road (STORET station 15330010) from May 2011 to November 2012, (2) results of monitoring at station TR50 at the Great River Road (STORET station 15330011) from May 2011 to November 2012, and (3) results of 2002 IDNR/SHL biological sampling.
EXPLANATION: The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria at two monitoring stations that exceed state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 15 samples collected during the recreational seasons of 2011 and 2012 at station TR50 (STORET station 15330010) were as follows: the 2011 geometric mean was 146 orgs/100 ml and the 2012 geometric mean was 107 orgs/100 ml. Four of the 15 samples (27%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. The geometric means of indicator bacteria (E. coli) in the 15 samples collected during the recreational seasons of 2011 and 2012 at station TR60 (STORET station 15330011) were as follows: the 2011 geometric mean was 168 orgs/100 ml and the 2012 geometric mean was 270 orgs/100 ml. Five of the 15 samples (33%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. Three of the four recreation season geometric means exceed the Class A1 criterion of 126 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 impaired (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” (IR Category 5a).
Results of chemical/physical water quality monitoring in 2011 and 2012 do not suggest impairment of the Class B(WW1) aquatic life uses. Monitoring at stations TR50 and TR60 showed no violations of Class B(WW1) water quality criteria for conventional pollutants or ammonia, dissolved oxygen, or pH in the approximately 15 samples analyzed at each station. Thus, the Class B(WW1) aquatic life uses are assessed (monitored) as “fully supported”.
The assessment of the Class B(WW1) aquatic life assessment remains based on biological data collected in 2002 as part of the IDNR/SHL REMAP 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 2002 FIBI score was 84 (excellent) and the BMIBI score was 71 (good). The aquatic life use support was assessed as fully supporting (=FS), 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 FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61. This assessment is considered evaluated because the drainage area (667 mi2) above this sampling site was greater than the maximum limit (500mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed both 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 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 5 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).
Due to the age of the data (>10 years) upon which previous assessments were based, the fish consumption uses for this segment are considered “not assessed.” Prior to the current (2014) assessment/listing cycle, these uses were assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring near Clermont in 1999. Because these data are now considered too old (greater than ten years) to characterize current water quality conditions, the fish consumption use remains “not assessed.”
