Chariton River IA 05-CHA-1307

Assessment Comments

Assessment remains based on results of USGS chemical/physical water quality monitoring near Moulton from March 2004 through September 2004.

Basis for Assessment

[Note:  Prior to the 2008 Section 305(b) cycle, this river 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, 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 remain “not assessed” (IR 3a) due to the lack of information upon which to base an assessment.   The Class B(WW1) aquatic life uses remain assessed (evaluated) as “fully supporting” (IR 2a) based on results of chemical/physical monitoring in 2004.   Fish consumption uses remain “not assessed” (IR 3a) due to lack of fish contaminant monitoring data upon which to base an assessment.   The source of data for this assessment remains the results of USGS chemical/physical water quality monitoring near Moulton from March 2004 through September 2004.  

EXPLANATION:  The Class A1 uses remain “not assessed” due to the lack of water quality monitoring and other water quality information for this river segment upon which to assess support of these uses (USGS monitoring in this river segment did not include analysis for indicator bacteria).  

The Class B(WW1) aquatic life uses remain assessed (evaluated) as "fully supported" based on results of water quality monitoring by the U.S.  Geological Survey near Moulton in 2004.   No violations of state water quality criteria occurred in the seven samples analyzed for dissolved oxygen, pH, ammonia, chlorpyrifos, DDE, and dieldrin.   Although these results indicate “full support” of the aquatic life uses of this river segment, the number of samples is relatively low and does not meet IDNR guidelines for developing a “monitored” (i.e., higher confidence) assessment.   Thus, the assessment type is considered “evaluated” (lower confidence).   Also, because these data are now more than five years old, and because as data age beyond five years they are less able to represent current water quality conditions, the assessment type is considered “evaluated” (lower confidence assessment) rather than “monitored” (a higher confidence assessment).

The fish consumption uses remain “not assessed” due to the lack of information upon which to base an assessment.