Assessment Comments
Assessment is based on: (1) the results of IDNR/UHL biological monitoring conducted in 2005 as part of the stream biocriteria project and (2) the results of IDNR/UHL TMDL-related monitoring conducted in May and June 2005 at Site 32 south of Redfield (STORET station 11250001).
Basis for Assessment
[Note: Prior to the current (2008) Section 305(b) cycle, this stream segment was designated only for Class B(WW) aquatic life uses, including fish consumption 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) and the results of an Use Attainability Analysis, this segment is also now designated for Class A1 (primary contact recreation) uses. This segment remains designated for warmwater aquatic life use (now termed Class B(WW1) uses), and for fish consumption uses (now termed Class HH (human health/fish consumption uses).]
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (evaluated) as "not supported" due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW1) aquatic life are assessed as "fully supported" based on results of IDNR/UHL biological (biocriteria) monitoring in 2005. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this stream segment. The sources of data for this assessment are (1) the results of IDNR/UHL biological monitoring conducted in 2005 as part of the stream biocriteria project and (2) the results of IDNR/UHL TMDL-related monitoring conducted in May and June 2005 at Site 32 south of Redfield (STORET station 11250001).
EXPLANATION: The Class A1 uses are assessed (evaluated) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). Due to recent changes in Iowa’s Water Quality Standards, Iowa’s assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of Section 305(b) assessments and Section 303(d) listings.
The geometric mean level of indicator bacteria (E. coli) in the three samples collected in May and June at the IDNR/UHL TMDL Site 32 (6,734 orgs/100ml) far exceeds the Iowa Class A1 water quality criterion of 126 orgs/100ml. All three samples (100%) exceed Iowa’s single-sample maximum criterion of 235 orgs/100 ml. The three sample dates in 2005 and the associated E. coli levels are as follows: May 26: 680 orgs/100 ml; June 13: 30,000 orgs/100 ml; June 23: 420 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 amount of data (three samples) does not meet IDNR guidelines for Clean Water Act assessment and listing that require at least 10 samples be collected per site over a three-year period. Assessments based on data that do not meet IDNR assessment/listing guidelines are considered “evaluated” (i.e., of lower confidence); these assessments are not appropriate for adding waters to Iowa’s Section 303(d) list of impaired waters. Such assessments are, however, appropriate for addition of waters to IR subcategories 2b or 3b and to Iowa’s list of waters in need of further investigation.
Based on results of biological monitoring in 2005, the Class B(WW1) aquatic life uses are 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 2005 FIBI score was 59 (good) and the BMIBI score was 56 (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 FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51.
Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river segment.
