Assessment Comments
Assessment is based on results of IDNR ambient water quality monitoring in 2004.
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses are assessed (monitored) as "fully supported". The source of data for this assessment is the results of IDNR/UHL chemical/physical water quality monitoring conducted from May to December 2004 at the Maple Valley Road crossing (station 15960001).
EXPLANATION: The results of the IDNR/UHL water quality monitoring in 2004 show 3 violations of the Class B(LR) criteria for dissolved oxygen (5.0 mg/l) in the 26 samples (12%) collected. The minimum level of dissolved oxygen was 3.5 mg/l. According to U.S. EPA guidelines for Section 305(b) water quality assessments (U.S. EPA 1997b, page 3-17), "partial support" of aquatic life uses is indicated if criteria are exceeded in from 11 to 25% of the samples for conventional parameters (e.g., pH, temperature, or dissolved oxygen). Based on IDNR’s assessment methodology, however, these results do not suggest that significantly more than 10 percent of the samples exceed Iowa’s dissolved oxygen criteria and thus do not suggest an impairment of the Class B(LR) uses of this stream segment.
