Assessment Comments

Assessment based on (1) 2001 and 2010 IDNR/SHL biological sampling data: FIBI = 73, 76, 78, 81 (excellent), and BMIBI = 58, 70, 73 (good) and 80 (excellent) (riffle habitat FIBI BIC = 65, natural substrate BMIBI BIC = 70) and (2) results of chemical WQ monitoring from May 2011 to November 2012.

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 (2014) 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 are assessed (monitored) as “partially supported” (IR 5p) due to violations of Iowa water quality criteria for indicator bacteria.   This is a new impairment for this assessment segment.   The Class B(WW2) aquatic life uses are assessed (monitored) as “fully supported” (IR 2a) based on results of biological sampling and chemical/physical monitoring.   The sources of data for this assessment are the results of (1) IDNR/SHL biological sampling in 2001 and 2010 and (2) chemical/physical monitoring from May 2011 to November 2012 at station VR40 at Q Avenue (STORET station 15330013).  

EXPLANATION:  The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria.   The geometric means of indicator bacteria (E.  coli) in the seven monthly samples collected during the recreational season of 2011 (482 orgs/100 ml), and the geometric mean of the eight samples collected during 2012 (259 orgs/100 ml) both exceeded the Class A1 criterion of 126 orgs/100 ml.   Ten of the combined 15 samples (67%) exceeded Iowa’s 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 the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).  

The Class B(WW2) uses remain assessed as “fully supported” based on both biological sampling and on results of chemical/physical water quality monitoring.   Results of biological sampling in 2001 and 2010 conducted as part of the IDNR/SHL stream biocriteria project suggest that the Class B(WW2) aquatic life uses should be assessed as “fully supported”.   A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data.   The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were 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 2001 FIBI scores were 78 and 81 (excellent); the 2010 FIBI scores were 73 and 76 (excellent).   The 2001 BMIBI scores were 80 (excellent) and 73 (good); the 2010 BMIBI scores were 58 and 70 (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 1994-2008.   The riffle habitat FIBI BIC for this ecoregion is 65 and the natural substrate BMIBI BIC for this ecoregion is 70.   This segment passed the FIBI BIC 4/4 times and passed the BMIBI BICs 3/4 times in the last 12 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 last 12 years; 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.

Results of chemical/physical water quality monitoring at station VR 40 (STORET station 15330013) also suggest “full support” of the aquatic life uses.   No violations of Class B(WW2) water quality criteria for ammonia, dissolved oxygen, pH, or temperature occurred in the approximately 15 samples analyzed from May 2011 to November 2012.