Assessment Comments
Assessment remains based on 1994, 2000 & 2007 IDNR/UHL biological monitoring data: FIBI = 39, 35 (fair); BMIBI = 46, 43 (fair). FIBI BIC = 31, BMIBI BIC = 54.
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 remain "not assessed" due to the lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses remain assessed (evaluated) as "partially supported" based on results of IDNR/UHL biological (biocriteria) sampling in 1994, 2000 and 2007.
EXPLANATION: The Class B(WW2) aquatic life uses are assessed as “partially supported” based on biological data collected in 1994, 2000 and 2007 approximately 4.5 miles northeast of Avoca as part of the IDNR/UHL stream biocriteria project. The 1994 FIBI score was 39 (fair) and the BMIBI score was not calculated due to low numbers of benthic macroinvertebrates. The 2000 FIBI score was 35 (fair) and the BMIBI score was 46 (fair). The 2007 BMIBI score was 43 (fair) and fish were not collected. The aquatic life use support was assessed as partially supporting (=PS), 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 31 and the BMIBI BIC for this ecoregion is 54. This segment passed the FIBI BIC 2/2 times in the last 17 years and passed the BMIBI BIC 0/2 times in the last 11 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 previous 17 years; however, the multiple samples were not collected during over a five-year period. According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).
