Assessment Comments
Assessment based on (1) results of IDNR/UHL biological (biocriteria) monitoring in 1999: FIBI = 50 (good), BMIBI = 62 (good); riffle habitat FIBI BIC = 53, BMIBI BIC = 62 and (2) results of monitoring from 2007 through 2008 by the National Laboratory for Agriculture and the Environment (NLAE), Ames, IA.
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 are assessed (monitored) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The source of data for this assessment is the results of monitoring from April 2007 through October 2008 conducted by the National Laboratory for Agriculture and the Environment (NLAE), Ames, IA, at station TC313 approximately 3 miles SWof Buckeye in Hardin County. The Class B(WW2) aquatic life uses remain assessed (evaluated) as "fully supported" based on results of IDNR/UHL biological (biocriteria) sampling in 1999.
EXPLANATION: The presumptive Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean of E. coli in the 15 samples collected at station TC313 (445 orgs/100 ml) exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. Ten of the 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 according to IDNR’s assessment/listing methodology, if the geometric mean level of E. coli is greater than the state criterion of 126 orgs/100 ml., the primary contact recreation uses should be assessed as "not supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b).
The Class B(WW2) aquatic life uses remain assessed (evaluated) as “fully supported” based on data collected in 1999 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 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 1999 FIBI score was 50 (good) and the BMIBI score was 62 (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 1994-2004. The riffle habitat FIBI BIC for this ecoregion is 53 and the BMIBI BIC for this ecoregion is 62. The FIBI score passed the FIBI BIC with the use of the FIBI UAV (+7) and met the BMIBI BIC.
This aquatic life assessment is considered "evaluated" because there were not two or more samples collected from this segment in multiple years from 2004-2008. 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). However, despite this change in assessment methodology and type, this assessment still suggests that this waterbody is fully supporting its' aquatic life uses.
