West Branch Buttrick Creek IA 04-RAC-1151

Assessment Comments

Assessment is based on 1995, 2001 and 2008 IDNR/UHL biological monitoring data: FIBI = 63, 61 (good), 79 (excellent); BMIBI = 68, 74, 59 (good). Riffle habitat FIBI BIC = 53, BMIBI BIC = 62.

Basis for Assessment

Note:  Prior to the 2008 Section 305(b) cycle, this stream segment was designated only for Class B(LR) aquatic life 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), this segment is now presumptively designated for Class A1 (primary contact recreation) uses.   The stream remains designated for aquatic life uses (now termed Class B(WW2) aquatic life uses).   Thus, for the current (2010) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]

SUMMARY:  The presumptive Class A1 (primary contact recreation) uses remain "not assessed" due to the lack of information upon which to base an assessment.   The Class B(WW2) aquatic life uses are assessed (evaluated) as "fully supported"  based on results of IDNR/UHL biological (biocriteria) sampling in 1995, 2001 and 2008.  

EXPLANATION:  The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supported” based on biological data collected in 1995, 2001 and 2008 as part of the IDNR/UHL stream biocriteria project.   The 1995, 2001 and 2008 FIBI scores were 63, 61 (good) and 79 (excellent).   The 1995, 2001 and 2008 BMIBI scores were 68, 74, 59 (good).   The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI and BMIBI scores with biological impairment criteria (BIC) established for previous Section 305(b) reports.   The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The riffle habitat FIBI BIC for this ecoregion is 53 and the BMIBI BIC for this ecoregion is 62.   This segment passed the FIBI BIC 3/3 times and passed the BMIBI BIC 2/3 times in the last 14 years.

This aquatic life assessment is now 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 between 2004 and 2008 to be considered “monitored”.   This segment had multiple samples collected in the previous 14 years (1995-2008); however, the multiple samples were not collected during 2004-2008.   Despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.