Assessment Comments

Assessment is based on results of IDNR/UHL ambient monthly monitoring during the 2006-2008 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 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 2006-2008 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).   The geometric mean level of indicator bacteria (E.   coli) in the 22 samples collected (537 orgs/100ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml.   Fourteen of the 22 samples (64%) 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 34 samples collected during the 2006-2008 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 two samples analyzed toxic metals.   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.