Shoal Creek IA 05-CHA-1342

Assessment Comments

Assessment based on 1999 & 2006 IDNR/UHL biological monitoring data: FIBI = 58, 51 (good), BMIBI = 34 (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(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 (2012) assessment, the available water quality monitoring data will be compared to the applicable Class A1 and Class B(WW2) water quality criteria.]

SUMMARY/EXPLANATION:  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 biological data collected in 1999 and 2006 as part of the IDNR/UHL stream biocriteria project.   A series of biological metrics which reflect 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 and fish species collected in the stream sampling reach.   The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI).   The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).   The 1999 FIBI score was 58 (good) and the BMIBI score was 34 (fair).   The 2006 FIBI score was 51 (good) and the BMIBI score was excluded from this assessment due to poor sample quality.   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 FIBI BIC for this ecoregion is 33 and the BMIBI BIC for this ecoregion is 41.   This segment passed the FIBI BIC 2/2 times and passed the BMIBI BIC 1/1 times (using the BMIBI uncertainty adjustment value of 8 points applied to single samples) in the last 12 years.   The biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.  

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 12 years (1999-2010); 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).