Assessment Comments
Assessment based on: (1) the results of IDNR/SHL biological sampling conducted in 2005 & 2012 as part of the stream biocriteria project and (2) the results of IDNR/SHL 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 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 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 remain assessed (evaluated) as "not supported" (IR 2b) due to levels of indicator bacteria that violate state water quality criteria. The Class B(WW1) aquatic life remain assessed (evaluated) as "fully supported" (IR 2a) based on results of IDNR/SHL biological (biocriteria) sampling in 2005 and 2012. Fish consumption uses remain "not assessed" (IR 3a) due to the lack of fish contaminant monitoring in this stream segment. The sources of data for this assessment remain (1) the results of IDNR/SHL biological sampling conducted in 2005 and 2012 as part of the stream biocriteria project and (2) the results of IDNR/SHL TMDL-related monitoring conducted in May and June 2005 at Site 32 south of Redfield (STORET station 11250001).
EXPLANATION: The Class A1 uses remain assessed (evaluated) as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric mean level of indicator bacteria (E. coli) in the four samples collected in May and June 2005 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 four samples (100%) exceed Iowa’s single-sample maximum criterion of 235 orgs/100 ml. The four sample dates in 2005 and the associated E. coli levels are as follows: May 26: 680 orgs/100 ml; June 12: 240,000; 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 (four 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. This amount of data also fails to meet IDNR guidelines for overwhelming evidence of impairment which requires at least five samples over a three-year period such that the geometric mean criterion would be exceeded even if the remaining five samples were all less than the level of detection (i.e., 10 orgs/100 ml). 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 and 2012, the Class B(WW1) aquatic life uses remain assessed (evaluated) 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 54 (good). The 2012 FIBI score was 53 (good) and the BMIBI score was 65 (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 FIBI BIC for this ecoregion is 36 and the BMIBI BIC for this ecoregion is 51. 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 over a five-year period to be considered “monitored”. This segment had multiple samples collected in the previous eight years; however, the multiple samples were not collected during a recent five-year period. Despite this change in assessment methodology and type, this waterbody remains in IR Category 2b based on the bacteria sampling data.
Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this river segment.
