Assessment Comments
Assessment based on (1) a pollutant-caused fish kill in July 2002 and (2) results of an IDNR/UHL biocriteria sampling in 1996 & 2002: FIBI = 34, 42 (fair), BMIBI = 82 (excellent), 59 (good). Non-riffle habitat FIBI BIC = 44, artificial substrate BMIBI BIC = 52.
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 "not assessed" due to the lack of information upon which to base an assessment. The Class B(WW2) aquatic life uses are assessed (evaluated) as “partially supported” based on results of IDNR/UHL biological monitoring conducted in 1996 and 2002 as part of the stream biocriteria project. Sources of data for this assessment include (1) results of IDNR/UHL biological monitoring conducted in 1996 and 2002 as part of the stream biocriteria project and (2) report of a fish kill that occurred on July 12, 2002.
EXPLANATION: The assessment of the Class B(WW2) aquatic life uses was based on biological data collected in 1996 and 2002 as part of the IDNR/UHL stream biocriteria project. The 1996 FIBI score was 34 (fair) and the BMIBI score was 82 (excellent). The 2002 FIBI score was 42 (fair) and the BMIBI score was 59 (good). 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 non-riffle habitat FIBI BIC for this ecoregion is 44 and the artificial substrate BMIBI BIC for this ecoregion is 52. This segment passed the FIBI BIC 0/2 times and passed the BMIBI BIC 2/2 times in the last 13 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 between 2004 and 2008 to be considered “monitored”. This segment had multiple samples collected in the previous 13 years (1996-2008); however, the multiple samples were not collected during 2004-2008 and/or were not collected in multiple years. 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). 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).
A fish kill occurred on in this stream segment on July 12, 2002. The kill affected 6 miles of this stream; an estimated 39,000 fish were killed. No cause was determined, but the investigator stated that the kill did not result from natural causes. According to IDNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill within the most recent three-year period indicates ongoing impairment of the aquatic life uses. However, the biological sampling was conducted in the same segment following the fishkill and the results indicated "partial support" of aquatic life uses. Therefore, this segment is appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation.
