Assessment Comments

Assessment is based on: (1) IDNR/UHL biological (biocriteria) monitoring in 2003 and (2) IDNR/UHL monthly ambient monitoring conducted during the 2004-2006 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 current (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 2003.   Results of ambient chemical/physical water quality monitoring near Milford from 2004-06 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 2003 and (2) IDNR/UHL monthly ambient monitoring conducted during the 2004-2006 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 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E.  coli).   Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed.   Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses:  the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff."  Due to a change in the Standards in July 2003, E.  coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E.  coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.”  Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E.  coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.  

The geometric mean level of indicator bacteria (E.  coli) in the 24 samples collected at the IDNR/UHL ambient monitoring station near Milford during summer recreational seasons of 2004-2006 (377 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Fifteen of the 24 samples (62%) exceed Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting and according to IDNR’s assessment/listing methodology, if the geometric mean level of E.  coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S.  EPA 1997b).  

The assessment of the Class B(WW1) aquatic life uses remains based on data collected in 2003 as part of the DNR/UHL stream biocriteria project.   The 2003 FIBI score was 31 (fair) and the BMIBI = 66 (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 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.

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 2004-2006 assessment period for pH (range = 7.7 to 9.0 units) or ammonia-nitrogen (maximum value = 0.58 mg/l) in the 36 samples analyzed.   Levels of pesticides in the seven samples analyzed, and levels of toxic metals in the ten samples analyzed, were all below their respective Class B(WW1) water quality criteria.   Monitoring results for dissolved oxygen showed that one of the 36 samples analyzed (3%) violated the Class B(WW1) water quality criterion for dissolved oxygen:  the level of dissolved oxygen in the sample collected on February 9, 2004 (0.9 mg/l) was well below the Class B(WW1) criterion of 5.0 mg/l.   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.