Assessment Comments
Assessment is based on (1) 2001 Biocriteria: Fish IBI= 65(good), 46(fair); BM-IBI= 36(fair),30(poor) and (2) results of IDNR/UHL monitoring in support of TMDL development.
Basis for Assessment
[Note: For the 2002 report, the previous waterbody segment IA 02-CED-0432-0, which extended 18 miles from the mouth of Middle Fork South Beaver Creek to its headwaters, was split into two subsegments: (1) mouth to unnamed tributary approximately 4 miles NW of Wellsburg, upstream from Grundy County road T13 (IA 02-CED-0432-1) and (2) unnamed tributary in Grundy County to headwaters in NW 1/4, S15, T89N, R19W, Hardin Co. (IA 02-CED-0432-2). See assessments for previous Section 305(b) reporting cycles above for historical assessments developed for the entire 18-mile stream reach.]
SUMMARY: The general (aquatic life) uses continued to be assessed as "partially supporting (=PS)." The sources of data for this assessment are: (1) Biological sampling data collected in 2001 as part of the DNR/UHL stream biocriteria and TMDL development projects. 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 (F-IBI) and a benthic macroinvertebrate index (BM-IBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2001 Fish IBI scores were 65 (good) and 46 (fair); the BM-IBI scores were 36 (fair) and 30 (poor). The aquatic life use support was assessed as partially supporting (=PS), 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. (2) Sampling results of monthly monitoring conducted by IDNR and UHL at one location approximately 4 miles NW of Wellsburg from March to November 2001 as part of monitoring in support of TMDL development. Because the stream segment is classified only for general uses, and because general uses are not supported by numeric water quality criteria for conventional or toxic pollutants, Class B(LR) aquatic life criteria were used to estimate any potential water quality impairments for this stream reach. EXPLANATION: The previous assessment of support for the general beneficial uses of this stream ("partially supported") was based on the occurrence of repeated fish kills from 1991 to 1997 (see assessment developed for the 1998 report above). The most recent kill occurred in September 1997. According to DNR's assessment methodology for Section 305(b) reporting, the lack of fish kills during the most recent three-year period suggest that the stream has fully recovered from fish kill-related impacts. Results TMDL-related monitoring in 2001, however, suggest the potential for water quality impacts to the general aquatic life uses. One of the nine samples (11%) violated the Class B(LR) chronic water quality criterion for ammonia nitrogen: the sample collected on March 6, 2001 contained 3.1 mg/l of ammonia-nitrogen and exceeded the criterion of 1.32 mg/l based on temperature and pH of that sample. According to U.S. EPA guidelines for Section 305(b) reporting, if, for a dataset where at least 10 samples have been collected over a three-year period, more than 10% of the samples exceed state criteria for toxics (including ammonia-nitrogen), the aquatic life uses are "not supported" (see pg 3-18 of U.S. EPA 1997b). However, because less than 10 samples were available for this assessment, the assessment type is considered "evaluated"; and the degree of support of the aquatic life uses was considered "fully supported/threatened." According to IDNR assessment guidelines, "evaluated" assessments are not of sufficient quality to support a Section 303(d) listing.
