Assessment Comments
Assessment remains based on (1) a pollutant-caused fish kill in July 2002 and (2) results of an IDNR/SHL biocriteria sampling in 2002 & 2009: FIBI = 37, 42 (fair), BMIBI = 23 (poor), 62 (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, 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 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" (IR 3a) 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” (IR 3b-c) based on results of IDNR/SHL biological sampling conducted in 2002 and 2009 as part of the stream biocriteria project. Sources of data for this assessment include (1) results of IDNR/SHL biological sampling conducted in 2002 and 2009 as part of the stream biocriteria project and (2) report of a fish kill that occurred on July 12, 2002.
EXPLANATION: The Class B(WW2) aquatic life uses were assessed (evaluated) as “partially supporting” based on biological data collected in 2002 and 2009 as part of the IDNR/SHL stream biocriteria project. The 2002 FIBI score was 42 (fair) and the BMIBI score was 62 (good). The 2009 FIBI score was 37 (fair) and the BMIBI score was 23 (poor). 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 1994-2008. 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 1/2 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 11 years (2002-2012); however, the multiple samples were not collected during 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).
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). Because no additional kills have been reported for this stream for over 10 years, any fish kill-related impacts in this segment have likely dissipated; thus, this segment is being moved from IR Category 3b to IR Category 3a (not assessed).
