Assessment Comments

Assessment is based on results of IDNR/UHL monthly ambient monitoring from 2008 through 2010 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, 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 2008 through 2010.   The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring from 2008-2010.   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 2008 through 2010 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 means of indicator bacteria (E.  coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10460001near Humboldt were as follows:  the 2008 geometric mean was 211 orgs/100 ml, the 2009 geometric mean was 112 orgs/100 ml, and the 2010 geometric mean was 160 orgs/100 ml.   The 2008 and 2010 geometric means slightly exceed the Class A1 criterion of 126 orgs/100 ml.   Nine of the 21 samples (43%) 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.”  

Monitoring at the IDNR/UHL station south of Humboldt showed no violations of Class B(WW1) water quality criteria during the 2008-2010 assessment period for dissolved oxygen, pH, or ammonia-nitrogen in the 32 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.