Assessment Comments

Assessment is based on results of IDNR/UHL monthly ambient monitoring from 2006 through 2008 approximately two miles south of Humboldt (STORET station 10460001 (formerly station 444061)).

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), and due to the completion of a Use Attainability Analysis in 2007, 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" based on results of ambient monitoring for indicator bacteria (E.   coli) during recreational seasons of 2006 through 2008.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring from 2006-2008.   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 IDNR/UHL monthly ambient monitoring from 2006 through 2008 approximately two miles south of Humboldt (STORET station 10460001 (formerly station 444061)).  

EXPLANATION:  The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" based on results of monitoring for indicator bacteria (E.   coli).   The geometric mean level of indicator bacteria (E.   coli) in the 20 samples collected (136 orgs/100ml) during the recreational seasons of 2004 through 2006 exceeds Iowa’s Class A1 water quality criterion of 126 orgs/100ml.   Six of the 20 samples (30%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml.   According to U.S.  EPA guidelines for Section 305(b) reporting, if the geometric mean level of E.   coli exceed Iowa’s geometric mean 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).  

Monitoring at the IDNR/UHL station south of Humboldt showed no violations of Class B(WW1) water quality criteria during the 2006-2008 assessment period for dissolved oxygen, pH, or ammonia-nitrogen in the 33 samples analyzed or for toxic metals in the two samples analyzed.   These results suggest "full support" of the Class B(WW1) aquatic life uses.  

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