Assessment Comments

Assessment is based on: (1) IDNR/UHL biological (biocriteria) monitoring in 1996 & 2003 and (2) IDNR/UHL monthly ambient monitoring conducted during the 2008-2010 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" due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as "partially supported” based on results of biological monitoring in 1996 and 2003.   Results of ambient chemical/physical water quality monitoring near Milford from 2008-10 do not suggest a water quality concern.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river segment.   This assessment is based on results of (1) IDNR/UHL biological (biocriteria) monitoring in 1996 and 2003 and (2) IDNR/UHL monthly ambient monitoring conducted during the 2008-2010 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 21 samples collected during the recreational seasons of 2008 through 2010 at Little Sioux River near Milford were as follows:  the 2008 geometric mean was 78 orgs/100 ml, the 2009 geometric mean was 180 orgs/100 ml and the 2010 geometric mean was 428 orgs/100 ml.   The 2009 and 2010 geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Eleven of the 21 samples (52%) 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 and 2003 as part of the IDNR/UHL 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 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 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 1994-2004.   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 1/2 times and passed the BMIBI BIC 2/2 times in the last 13 years.   This assessment is considered evaluated because of the documented sampling problems encountered during the 2003 biological sampling.   Field staff rated the fish sampling quality as "fair" and listed depth, daylight limiting visibility, turbidity, width, and equipment malfunction as the reasons for the fair fish sampling quality.   Combining this knowledge with the fact that the BMIBI at this site passed the BMIBI BIC, there is reason to believe that with all the problems encountered during the fish sampling that the sample collected was not representative of the reach.   This site is a reference site and will be sampled in the near future.

In addition to the explanation above, 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 five year period to be considered “monitored”.   This segment had multiple samples collected in the previous 15 years (1996-2010); however, the multiple samples were not collected during a five year period.   Additionally, because these data are now considered too old (greater than five 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).   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).   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/UHL station near Milford show no violations of Class B(WW1) water quality criteria during the 2008-2010 assessment period for dissolved oxygen (minimum = 7.0 mg/L), pH (range = 7.4 to 8.6 units) or ammonia-nitrogen (maximum value = 0.39 mg/l) in the 29 samples analyzed.   (Note: pesticides and toxic metals were not monitored during the 2008-2010 period.)  While monitoring results for dissolved oxygen from 2008 through 2010 showed no violations of the Class B(WW1) water quality criteria, there have been occasional violations of the dissolved oxygen criteria at this station.   According, however, to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), if 10% or less of samples exceed criteria for conventional parameters (e.g., dissolved oxygen and pH), aquatic life uses should be assessed as “fully supported.”  Over the five-year period since monthly monitoring was implemented at this IDNR/UHL station, levels of dissolved oxygen have occasionally violated the Class B(WW1) criterion of 5.0 mg/l; usually these samples are collected in late winter or early spring.   In addition to the February 2004 sample, samples collected on January 9, 2001 and March 13, 2001 also violated the Class B(WW1) criterion for dissolved oxygen.   While not indicating impairment of aquatic life uses, the magnitude and timing of these violations suggest some type of reoccurring condition, whether natural or man-made, that contributes to these violations.    

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