Soap Creek IA 04-LDM-1032

Assessment Comments

Assessment is based on 1996 & 2002 IDNR/UHL biological monitoring data: FIBI = 41, 34 (fair), BMIBI = 55, 46 (fair). FIBI BIC = 33; BMIBI BIC = 41.

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 (see http://www.iowadnr.com/water/standards/files/06mar_swc.pdf), this segment is also now presumptively 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 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(WW1) aquatic life uses are assessed (evaluated) as "fully supported" based on results of IDNR/UHL biological (biocriteria) sampling in 1996 and 2002.   Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment.   This assessment is considered of lower confidence (evaluated) as opposed to higher confidence (monitored) because the data from the 2002 biological sampling are now older than five years, thus, these data are considered less able to accurately characterize current water quality conditions than would be more recent data.  

EXPLANATION:  The presumptive Class B(WW1) aquatic life uses remain assessed (evaluated) as “fully supporting” based on biological data collected in 1996 and 2002 as part of the IDNR/UHL stream biocriteria project.   The 1996 FIBI score was 41 (fair) and the BMIBI score was 55 (fair).   The 2002 FIBI score was 34 (fair) and the BMIBI score was 46 (fair).   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 33 and the BMIBI BIC for this ecoregion is 41.   This segment passed the FIBI and BMIBI BICs 2/2 times in the past 13 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 13 years (1996-2008); however, the multiple samples were not collected during 2004-2008.   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.