Assessment Comments

Assessment is based on results of IDNR/UHL ambient monthly monitoring during the 2008-2010 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, 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 2008-2010 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 means of indicator bacteria (E.  coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10630002 near Bussey were as follows:  the 2008 geometric mean was 1,474 orgs/100 ml, the 2009 geometric mean was 902 orgs/100 ml and the 2010 geometric mean was 235 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Sixteen of the 22 samples (73%) 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 Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported.”  None of the approximately 30 samples collected during the 2008-2010 assessment period at the IDNR/UHL monthly station violated Class B(WW1) water quality criteria for dissolved oxygen, pH or ammonia-nitrogen.   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.