Brush Creek IA 01-VOL-317

The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceed state water quality criteria.  The geometric means of indicator bacteria (E. coli) in the 23 samples collected during the recreational seasons of 2012 through 2014 at the station BRU-10 (STORET station 15330002) were as follows:  the 2012 geometric mean was 113 orgs/100 ml, the 2013 geometric mean was 211 orgs/100 ml, and the 2014 geometric mean was 38 orgs/100 ml.  Only the 2013 recreation season geometric mean exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml and then only very slightly.  Four of the combined 23 samples (17%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml.  According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).  Regardless of this impairment, this segment of Brush Creek has exceptionally low levels of indicator bacteria for an Iowa stream.  

Results of both chemical/physical and biological monitoring suggest that the Class B(WW2) aquatic life uses of this segment of Brush Creek should be assessed as “fully supporting”.  Results of chemical/physical water quality during the 2012-2014 period do not suggest impairment of the Class B(WW2) aquatic life uses.  Monitoring at station BRU 10showed no violations of Class B(WW2) water quality criteria for ammonia (16 samples), dissolved oxygen (24 samples) pH (24 samples), temperature (24 samples), or chloride (16 samples).  Thus, the Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported”. 

In addition to results of chemical/physical monitoring, results of IDNR/SHL biological sampling conducted in 2005 and 2012 as part of the stream biocriteria project also suggest “full support” of the aquatic life uses.  A series of biological metrics that 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 fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum).  The 2005 FIBI score was 80 (excellent) and the BMIBI score was 62 (good).  The 2012 FIBI score was 75 (excellent) and the BMIBI score was 77 (excellent).  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 1994-2008.  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 eight 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 10 years (2005-2014); however, the multiple samples were not collected during a five-year period.  Despite this change in assessment methodology and type, this waterbody remains in IR Category 2a.