Assessment Comments

Assessment is based on: (1) the results of IDNR/UHL ambient monthly monitoring during the 2008-2010 assessment period at STORET station 10440001 approximately 3 miles southwest of Oakland Mills in Henry County (formerly station number 821004) and (2) results of IDNR/UHL biological monitoring conducted in 2000 and 2008.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this river segment was designated only for Class B(WW1) 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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf) and due to the completion of a Use Attainability Analysis prepared in 2007, 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 remain assessed (evaluated) as "partially supported" based on results of biological monitoring conducted in 2002.   Fish consumption uses remain “not assessed” due the lack of recent fish contaminant monitoring in this assessment segment.   The sources of data for this assessment include (1) the results of IDNR/UHL ambient monthly monitoring during the 2008-2010 assessment period at STORET station 10440001 approximately 3 miles southwest of Oakland Mills in Henry County (formerly station number 821004) and (2) results of IDNR/UHL biological monitoring conducted in 2000 and 2008.  

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 22 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10440001 near Oakland Mills were as follows:  the 2008 geometric mean was 563 orgs/100 ml, the 2009 geometric mean was 540 orgs/100 ml and the 2010 geometric mean was 1,010 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Fifteen of the 22 samples (68%) 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.”  

Results of ambient chemical/physical water quality monitoring suggest “full support” of the Class B(WW1) aquatic life uses.   None of the approximately 30 samples collected during the 2008-2010 assessment period at the IDNR/UHL monthly station violated Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen.  

The results of biological monitoring conducted in 2000 and 2008 as part of the IDNR/UHL stream biocriteria project also suggest “full support” of the aquatic life 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 fish species and benthic macroinvertebrate taxa that were collected in the stream sampling reach.   The biological metrics were combined to form a fish index of biotic integrity (FIBI) and a benthic macroinvertebrate index of biotic integrity (BMIBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 2000 FIBI score was 30.   The 2008 BMIBI scores were 49 (fair) and 57 (good).   The aquatic life use support was assessed (evaluated) as fully supported (=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 1994-2004.   The FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41.   This segment passed the FIBI BIC (using the uncertainty adjustment value (UAV) of 7 points) 1/1 times in 2000 and passed the BMIBI BIC 2/2 times in 2008.   This assessment is considered evaluated because the drainage area (533.2 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 FIBI BIC (using the UAV +7) 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.  

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 multiple BMIBI samples collected in the previous five years (2006-2010); however, the samples were not collected in multiple years.  

Fish consumption remain are “not assessed” due to the lack of recent fish contaminant monitoring in this river segment.   Previous assessments were based on results of fish contaminant monitoring conducted by USGS in 1995 as part of the NAWQA project.   These data are now considered too old (greater than 10 years) to accurately characterize current water quality conditions.