Assessment Comments

Assessment based on: (1) IDNR/SHL biological sampling in 1996, 2003 & 2011 and (2) IDNR/sHL monthly ambient monitoring conducted during the 2010-2012 assessment period near Milford (STORET station 10300001 (formerly station 920450)); this station is located approximately 1.2 miles west of Milford and is approximately 0.5 miles upstream from the confluence with Milford Creek.

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 the 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 uses are assessed (evaluated) as "fully supported” (IR 2a) based on results of biological monitoring in 1996, 2003 and 2011.   Results of ambient chemical/physical water quality monitoring near Milford from 2010-12 do not suggest a water quality concern.   Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this river segment.   This assessment is based on results of (1) IDNR/SHL biological (biocriteria) sampling in 1996, 2003 and 2011 and (2) IDNR/SHL monthly ambient monitoring conducted during the 2010-2012 assessment period near Milford (STORET station 10300001 (formerly station 920450)); this station is located approximately 1.2 miles west of Milford and is approximately 0.5 miles upstream from the confluence with Milford Creek.  

EXPLANATION:  The Class A1 (primary contact recreation) are assessed as "not supported" based on levels of indicator bacteria that exceeded state water quality criteria.   The geometric means of indicator bacteria (E.  coli) in the 24 samples collected during the recreational seasons of 2010 through 2012 at Little Sioux River near Milford were as follows:  the 2010 geometric mean was 428 orgs/100 ml, the 2011 geometric mean was 152 orgs/100 ml, and the 2012 geometric mean was 102 orgs/100 ml.   The 2010 and 2011 geometric means exceeded the Class A1 criterion of 126 orgs/100 ml.   Twelve of the 24 samples (50%) 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 assessment of the Class B(WW1) aquatic life uses was based on data collected in 1996, 2003 and 2011 as part of the IDNR/SHL stream biocriteria project.   The 1996 FIBI score was 56 (good) and the BMIBI score was 67 (good).   The 2003 FIBI score was 31 (fair) and the BMIBI score was 65 (good).   The 2011 FIBI score was 60 (good) and the BMIBI score was 54 (fair).   The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.  The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008.   The riffle site FIBI BIC for this ecoregion is 53 and the BMIBI BIC for this ecoregion is 62.   This segment passed the FIBI BIC 2/3 times and passed the BMIBI BIC 2/3 times in the last 17 years.  

This aquatic life assessment is also considered "evaluated" because of 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 in a recent five year period to be considered “monitored”.   This segment had multiple samples collected in the previous 17 years (1996-2012); however, the multiple samples were not collected during a five year period.  However, despite this change in assessment methodology and type, this waterbody remains in IR Category 5a and remains on Iowa’s 2010 Section 303(d) list of impaired waters because of the Primary Contact Recreation use impairment.

Ambient chemical/physical water quality monitoring at the IDNR/SHL station near Milford show no violations of Class B(WW1) water quality criteria during the 2010-2012 assessment period for dissolved oxygen (minimum = 5.6 mg/L), pH (range = 7.4 to 8.8 units), temperature (maximum = 28.7C), ammonia-nitrogen (maximum value = 0.41 mg/l), chloride, or sulfate in the approximately 36 samples analyzed.   Although violations of the Class B(WW1) criteria for dissolved oxygen have occasionally (historically) occurred in this assessment segment, there has not been a dissolved oxygen violations in results of ambient monthly monitoring since February 2004.  

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