Assessment Comments

Assessment is based on results of (1) IDNR/SHL ambient monthly monitoring during the 2010-2012 assessment period at STORET ambient monitoring station 10250001 (formerly station 429340) located near Redfield approximately 1 mile downriver from the confluence of Middle Raccoon and South Raccoon rivers and (2) 2012 IDNR/SHL biological sampling conducted near Redfield.

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 and results of an 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 "not supported" (IR 5a) due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life are assessed (monitored) as "fully supported” (IR 2a) based on results of ambient chemical/physical water quality monitoring from 2010 through 2012 and on 2-12 IDNR/SHL biological sampling.   Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this river segment.   The source of data for this assessment are the results of (2) IDNR/SHL ambient monthly monitoring during the 2010-2012 assessment period at STORET ambient monitoring station 10250001 (formerly station 429340) located near Redfield approximately 1 mile downriver from the confluence of Middle Raccoon and South Raccoon rivers and (2) 2012 IDNR/SHL biological sampling conducted near Redfield.    

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 24 samples collected during the recreational seasons of 2010 through 2012 at IDNR station 10250001 near Redfield were as follows:  the 2010 geometric mean was 1,425 orgs/100 ml, the 2011 geometric mean was 160 orgs/100 ml, and the 2012 geometric mean was 157 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml, with the 2010 geometric mean far exceeding the criterion and the 2011 and 2012 geometric means very slightly exceeding the criterion.   Ten of the 24 samples (42%) 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.”

The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported” based on results of IDNR/UHL ambient chemical/physical water quality monitoring from 2010 through 2012.   None of the 36 samples collected during the 2010-2012 assessment period at the IDNR ambient monthly station violated Class B(WW1) water quality criteria for ammonia, pH, or dissolved oxygen.  

This evaluated biological assessment was based on data collected in 2012 as part of the IDNR/SHL large river sampling project.   A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa collected in the stream sampling reach.   The biological metrics were combined to make a benthic macroinvertebrate index (BMIBI).   The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2012 BMIBI scores were 53 (fair) adnd 59 (good).  The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008.   The BMIBI BIC for this ecoregion is 51.   This assessment is considered evaluated because the drainage area (988 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 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.

Fish consumption uses remain "not assessed" due to the lack of recent fish contaminant monitoring in this stream segment.