Assessment Comments

Assessment is based on results of IDNR/UHL ambient water quality monitoring in 2004.

Basis for Assessment

SUMMARY:  The Class B(CW) aquatic life uses are assessed (monitored) as "not supported" due to violations of the water quality criterion for dissolved oxygen.   Fish consumption uses were “not assessed” due to the lack of fish contaminant monitoring in this stream segment.   Sources of data for this assessment include the results of IDNR/UHL chemical/physical water quality monitoring conducted from May to December 2004 at the County Road W4B crossing (station 15030008).  

EXPLANATION:  The results of the IDNR/UHL water quality monitoring in 2004 show 9 violations of the Class B(CW) criteria for dissolved oxygen (7.0 mg/l) in the 26 samples (35%) collected.   The minimum level of dissolved oxygen was 5.2 mg/l.   According to U.S.  EPA guidelines for Section 305(b) water quality assessments (U.S.  EPA 1997b, page 3-17), "nonsupport" of aquatic life uses is indicated if criteria are exceeded in more than 25% of the samples for conventional parameters (e.g., pH, temperature, or dissolved oxygen).   Thus, the percentages of violations of the dissolved oxygen criterion in this stream segment (35%) suggests an impairment of coldwater aquatic life uses.   Violations occurred in throughout the May-December period of 2004.  

Fish consumption uses remain “not assessed” due to the lack of fish contaminant monitoring in this stream segment.