Assessment Comments
Assessment remains based on results of (1) USGS ambient water quality monitoring in 1998 and 1999 near Mount Sterling and Milton and (2) UHL biological monitoring near the IA/MO state line in 1998.
Basis for Assessment
SUMMARY: The Class B(LR) aquatic life uses remain assessed as "fully supporting / threatened" (minor impacts) based on results of (1) ambient water quality monitoring conducted by the U.S. Geological Survey in 1998 and 1999 and (2) biological monitoring conducted by UHL in 1998 near the Iowa/Missouri state line.
EXPLANATION: Continued to use the assessment of support of the Class B(LR) uses developed for the 2000 report and also used for the 2002 reporting cycle. The data upon which this assessment was based were collected in 1998 and 1999. These data are less than five years old and are thus appropriate for characterizing current water quality conditions. The following is taken from the assessment developed for the 2000 reporting cycle: Results of water quality monitoring from two sources were used to develop this assessment of support of the Class B(LR) uses: (1) chemical water quality monitoring conducted in 1998 and 1999 by the U.S. Geological Survey at two stations (Milton and Mount Sterling) (see May et al. 1999 and Nalley et al. 2000) and (2) biological monitoring conducted approximately 3 miles south of the Iowa / Missouri state line in October 1998 by the University of Iowa Hygienic Laboratory (see Luzier and Miller 1999). USGS monitoring in 1998 and 1999 showed no violations of Class B(LR) water quality criteria for dissolved oxygen, pH, and ammonia-nitrogen in the approximately 12 samples collected at the Milton and Mt. Sterling stations. Of the 12 samples analyzed for toxic metals, one sample at each station exceeded a state water quality criterion. The samples collected on June 10, 1999 at Milton (60 ug/l) and June 11, 1999 at Mt. Sterling (100 ug/) both exceeded the Class B(LR) chronic water quality criterion for copper (55 ug/l). These samples were collected during a high flow event on the Fox River; the June 10 stream flow at the Milton station was 259 cfs; the June 11 stream flow at the Mt. Sterling station was 1010 cfs. According to U.S. EPA guidelines for Section 305(b) reporting (U.S. EPA 1997b, page 3-18), this one violation of a toxic contaminant does not suggest an impairment of the aquatic life uses. Based on DNR's assessment methodology for Section 305(b) reporting, however, this violation suggests that the Class B(LR) aquatic life uses should be assessed as "fully supported/threatened." Although not designated for Class C (drinking water) uses, from 40 to 50 percent of the 10 samples from each station analyzed for pesticides exceeded the U.S. EPA MCL of 3.0 ug/l. None of the approximately 12 samples at each station exceeded the nitrate MCL of 10.0 mg/l. Results of biological monitoring in 1998 by UHL showed a moderately diverse fish community for streams in the Central Irregular Plains ecoregion, with 15 species from 6 families and with a majority of the expected fish taxa (7 of 9) for Class B(LR) streams in this ecoregion. Based on DNR's assessment methodology for Section 305(b) reporting, the composition of the fish community suggests that the Class B(LR) uses are "fully supported / threatened." Thus, based on results of chemical and biological monitoring conducted in this river reach during the 1998-1999 biennial period, the Class B(LR) aquatic life uses are assessed as "fully supported / threatened."
