Brush Creek IA 01-VOL-317

Assessment Comments

Assessment is based on 2000 & 2005 IDNR/UHL biological monitoring data: FIBI = 83, 80 (excellent), BMIBI = 67, 62 (good). FIBI BIC = 52, BMIBI BIC = 61.

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, 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 (2012) 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 remain assessed (evaluated) as "fully supporting"  based on results of IDNR/UHL biological (biocriteria) sampling in 2000 and 2005.  

EXPLANATION:  The assessment of the Class B(WW2) aquatic life uses (“fully supporting”) was based on data collected in 2000 and 2005 as part of the IDNR/UHL stream biocriteria project.   The 2000 FIBI score was 83 (excellent) and the BMIBI score was 67 (good).   The 2005 FIBI score was 80 (excellent) and the BMIBI score was 62 (good).   The aquatic life use support was assessed 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 FIBI BIC for this ecoregion is 52 and the BMIBI BIC for this ecoregion is 61.   This segment passed the FIBI and BMIBI BICs 2/2 times in the last 11 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 over a five-year period to be considered “monitored”.   This segment had multiple samples collected in the previous 11 years (2000-2010); however, the multiple samples were not collected during a five-year period.   Additionally, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).   Despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.