Assessment Comments
Assessment is based on (1) results of IDNR/UHL biological (biocriteria) monitoring in 1997 (Fish IBI= 20 (poor), BM-IBI= 42 (fair)) and (2) results of an IDNR investigation of a fish kill in August 1999.
Basis for Assessment
SUMMARY: The general aquatic life uses are assessed (monitored) as "paritally supported" based on results of an IDNR investigation of a fish kill in August 1999. Results of IDNR/UHL biological (biocriteria) sampling in 1997 suggest "non-support" of the general uses of this stream segment.
EXPLANATION: As stated in the assessment developed for the 2000 report, a fish kill occurred on DD-71 on August 19, 1999 at the north side of Jewell in Hamilton County. This kill was attributed to agricultural fertilizer: a brief, hard rain washed a slug of ammonia into DD-71. Approximately ½ mile of stream was affected; an estimated 9,300 fish were killed. No responsible party for this kill was identified. An additional kill occurred in DD-71 near Jewell on August 7, 1995. According to DNR's assessment methodology for Section 305(b) reporting, occurrence of a single pollution-caused fish kill within the most recent three-year period (2000-2002) indicates that the aquatic life uses of a waterbody are only "partially supported."
In addition, this assessment is based on result of biological monitoring conducted in 1997 as part of the IDNR/UHL stream biocriteria project. The F-IBI score was 20 (poor), and the BM-IBI score was 42 (fair). Results of this monitoring suggested that the aquatic life use support should be assessed as "not supporting" (=NS), based on a comparison of the F-IBI and BM-IBI scores with biological assessment criteria established specifically for the 2002 Section 305(b) report. The biological assessment criteria were determined from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2001. The assessment type for this assessment is considered "evaluated" (relatively lower confidence assessment) due to the uncertainty of using biological assessment methods developed for Class B(LR) and wadable Class B(WW) streams for assessing aquatic life conditions in general use-only stream segments.
The primary basis of this assessment is the fish kill that occurred in August 1999. IDNR assessment guidlelines state that if a kill occurred more than three years ago, and additional kills have not occurred, the impacts from the kill have likely dissipated. However, the lack of responsible party for this pollutant-caused kill, combined with results of IDNR/UHL biological monitoring in 1997 strongly suggest the possibility that the aquatic life uses of this general use stream segment remain impaired.
The assessment based on results of DNR/UHL biocriteria sampling ("not supported"), however, is more restrictive; thus, the final assessment of the general aquatic life uses is "not supported."
