Odebolt Creek IA 06-LSR-1592

Assessment Comments

Assessment remains based 1997 IDNR/UHL biological monitoring data: FIBI = 42, 34 (fair); BMIBI = 58, 59 (good). FIBI BIC = 31, BMIBI BIC = 54.

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 remain assessed (evaluated) as "fully supported" based on results of IDNR/UHL biological (biocriteria) sampling in 1997.   The 1997 biological sampling data are greater than five years old; therefore, this assessment is now considered "evaluated" instead of "monitored".

EXPLANATION:  The Class B(WW2) aquatic life uses remain assessed as "fully supported" based on results of the IDNR/UHL biocriteria monitoring conducted on this stream segment in 1997.   Sampling was conducted at two sites on this stream segment.   The FIBI scores were 42 and 34 (both in the "fair" category); the BMIBI scores were 58 and 59 (both good).   The aquatic life use support was assessed (evaluated) as fully supported (=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 31 and the BMIBI BIC for this ecoregion is 54.   This segment passed the FIBI and BMIBI BICs 2/2 times in 1997.

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 1997; however, the multiple samples were not collected during 2004-2008 and were not collected in multiple years.   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.