Assessment Comments

Assessment is based on: (1) results of IDNR/UHL monthly ambient monitoring conducted from 2008 through 2010 on Indian Creek at a bridge 4.8 miles north of Colfax and 1.8 miles east of Green Castle in Jasper County (station 10500001) and (2) IDNR/UHL biological (REMAP) monitoring near Mingo in 2003.

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:  The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria.   The Class B(WW2) aquatic life uses are assessed (evaluated) as "fully supported" based on results of ambient chemical/physical water quality monitoring and on results of biological monitoring results from a 2003 REMAP site.   The sources of data for this assessment are (1) results of IDNR/UHL monthly ambient monitoring conducted from 2008 through 2010 on Indian Creek at a bridge 4.8 miles north of Colfax and 1.8 miles east of Green Castle in Jasper County (station 10500001) and (2) IDNR/UHL biological (REMAP) monitoring near Mingo in 2003.  

EXPLANATION:  The presumptive Class A1 uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E.  coli).   The geometric means of indicator bacteria (E.  coli) in the 21 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10500001 near Colfax were as follows:  the 2008 geometric mean was 254 orgs/100 ml, the 2009 geometric mean was 476 orgs/100 ml and the 2010 geometric mean was 1,868 orgs/100 ml.   All three geometric means exceed the Class A1 criterion of 126 orgs/100 ml.   Twelve of the 21 samples (57%) exceeded the 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 are "not supported" (see pgs 3-33 to 3-35 of U.S.  EPA 1997b).   Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.”

The Class B(WW2) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient chemical/physical water quality monitoring.   Results of chemical/physical monitoring at the IDNR/UHL station show no violations of Class B(WW2) criteria for dissolved oxygen, pH, or ammonia nitrogen (maximum value = 0.35 mg/l) in the approximately 30 samples analyzed during the 2008-2010 assessment period.   This assessment is consistent with the assessment developed for this assessment segment for previous Section 305(b) reporting cycles.  

Additionally, the Class B(WW2) aquatic life uses remain assessed as “fully supporting” based on data collected in 2003 as part of the IDNR/UHL stream REMAP 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 2003 FIBI score was 30 (fair) and the BMIBI score was 58 (good).   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 biological impairment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2004.   The non-riffle habitat FIBI BIC for this ecoregion is 32 and the BMIBI BIC for this ecoregion is 62.   The assessment is considered FS-evaluated because both the FIBI and BMIBI scores met the respective BICs with the use of the UAVs (used on single samples): FIBI = 7 points and BMIBI = 8 points.  

This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years over 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).