Assessment Comments

Assessment is based on results of IDNR/UHL ambient monthly monitoring during the 2004-2006 assessment period at STORET station 10630002 (formerly station 500680) at the Highway 156 bridge approximately 1.5 miles northwest of Bussey.

Basis for Assessment

[Note:  Prior to the current (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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is also now presumptively 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 presumptive 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 are assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.   The source of data for this assessment is the results of IDNR/UHL ambient monthly monitoring during the 2004-2006 assessment period at STORET station 10630002 (formerly station 500680) at the Highway 156 bridge approximately 1.5 miles northwest of Bussey.  

EXPLANATION:  The presumptive 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 (256 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Ten of the 24 samples (42%) 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 Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported."  None of the 37 samples collected during the 2004-2006 assessment period at the IDNR/UHL monthly station violated Class B(WW1) water quality criteria for pH or ammonia-nitrogen; no violations occurred in the approximately 10 samples analyzed toxic metals or in the eight samples analyzed for pesticides.   One of the 37 samples analyzed for dissolved oxygen, however, violated the Class B(WW1) criterion of 5.0 mg/l (this sample contained a dissolved concentration of 4.9 mg/l).   According to U.S.  EPA guidelines (U.S.  EPA 1997b, page 3-17), however, a violation frequency of less than 10% for conventional parameters such as dissolved oxygen nonetheless suggest "full support" of aquatic life uses.   Thus, the percentage of violations of the dissolved oxygen criterion at this station (3%) does not suggest an impairment of aquatic life uses in this stream segment.   These results suggest that the Class B(WW1) aquatic life should be assessed as "fully supported."

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