Cox Creek IA 01-VOL-304

Assessment Comments

Assessment based on 2011 IDNR/SHL biological sampling data: CBI = 47; CW BIC = 60.

Basis for Assessment

[Note: Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(CW) aquatic life 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) and Class A2 (secondary contact recreation) uses.  This segment remains designated for coldwater aquatic life use (now termed Class B(CW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption) uses.  

SUMMARY: The presumptive Class A1 (primary contact recreation) uses and the presumptive Class A2 (secondary contact recreation) uses are "not assessed" (IR 3a) due to the lack of data for indicator bacteria upon which to base an assessment.  The Class B(CW1) coldwater aquatic life uses are assessed (evaluated) as "partially supported" (IR 3b-c) based on 2011 IDNR/SHL biological sampling data.   Fish consumption (Class HH) uses are "not assessed" (IR 3a).  

EXPLANATION: The assessment of the Class B(CW1) aquatic life uses was based on data collected in 2011 as part of the IDNR/SHL coldwater stream sampling project.  A series of biological metrics which reflect coldwater stream water quality and habitat integrity were calculated from the biological sampling data.  The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa that were collected in the stream sampling reach.  The biological metrics were combined to make a coldwater benthic index (CBI).  The index ranks the biological integrity of a coldwater stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).  The 2011 CBI score was 47.  The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the CBI score with biological impairment criteria (BIC) established for the 2012 Section 305(b) report.  The biological impairment criteria were determined from a statistical analysis of data collected at coldwater stream reference sites from 1994-2011.  The CW BIC is 60 and this segment passed the CW BIC 0/1 times in 2011.  

This aquatic life assessment is considered "evaluated" based on a change in the 2010 IDNR assessment methodology.  IDNR now requires a segment have two or more biological samples collected from the segment in multiple years over a five-year period to be considered “monitored”.  This segment had a single sample collected in 2011.  According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report).   IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).

Fish consumption uses remain "not assessed" due to lack of fish tissue monitoring in this stream reach.