Assessment Comments
This assessment is based on results of (1) IDNR/UHL monthly monitoring from 2000-02 at the Highway 30 bridge downstream from Cedar Rapids and (2) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 1996.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses were assessed (monitored) as "not supported" due to high levels of indicator bacteria and violations of state water quality criteria. The Class B(WW) aquatic life uses were assessed (monitored) as "fully supported." Fish consumption uses were assessed (evaluated) as “fully supported” based on results of fish contaminant monitoring in 1996. The sources of data for this assessment include (1) the results of monthly monitoring from January 2000 through December 2002 at the IDNR ambient city monitoring station located at the Highway 30 bridge downstream from Cedar Rapids (station 10570001) and (2) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 1996.
EXPLANATION: The Class A uses were assessed as "not supported" based on results of ambient monitoring for indicator bacteria (fecal coliforms). For purposes of Section 305(b) assessments, DNR uses the long-term average monthly flow plus one standard deviation of this average to identify river flows that are materially affected by surface runoff. According to the Iowa Water Quality Standards (IAC 1990:8), the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) does not apply "when the waters are materially affected by surface runoff." Thirteen of the 16 samples collected from the Highway 30 station during the 2000, 2001, and 2002 recreational seasons were collected at flows not materially affected by surface runoff. The geometric mean level of indicator bacteria (fecal coliforms) in these 13 non-runoff-affected samples (208 orgs/100ml) is slightly above the Iowa Class A water quality criterion of 200 orgs/100ml. However, four of the 13 samples (31%) exceeded the U.S. EPA-recommended single-sample maximum value of 400 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting, if the geometric mean is greater than 200 orgs/100ml, the primary contact recreation uses are "not supported”; in addition, if more than 10% of the samples exceed the single-sample maximum value of 400 orgs/100 ml, the primary contact recreation uses are "partially supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, both the geometric mean of fecal coliforms (208 orgs/100ml) and the percentage of samples that exceed the single-sample maximum value of 400 orgs/100 ml (31%) suggest impairment of the Class A (primary contact recreation) uses of this river segment.
The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of monitoring from the IDNR ambient at Highway 30 from 2000 through 2002. Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 28 samples collected or for toxic metals and toxic organic compounds in the 28 samples analyzed during this assessment period. The levels of pH, however, violated the Class B(WW) criterion of 9.0 pH units in two of the 28 samples (7%). The sample collected on October 9, 2000, had a pH of 9.4 units which is greater than the Iowa water quality standard of 9.0 pH units; the sample collected on January 7, 2002 had a pH of 6.4 which is less than the Iowa water quality standard of 6.5 pH units. The violation on October 9, 2000, occurred on a day with an extremely high level of dissolved oxygen (20.3 mg/l) and a percent DO saturation of > 140%. These conditions suggest that the high level of primary productivity resulted in the high level of pH. Because this violation is more related to natural conditions than to pollution, the occurrence of this high level of pH in this river segment is not seen as a water quality impairment. The pH violation on January 7, 2002, occurred on the same day as the maximum ammonia level (1.3 mg/l) for the 2000-2002 period; this pH violation is likely not related to high primary productivity. Also, according to U.S. EPA assessment guidelines, if less than 10% of samples exceed state criteria for pH, the aquatic life uses should be assessed as "fully supported" (see pgs 3-17 of U.S. EPA 1997b).
Fish consumption uses are assessed as fully supported based on results of fish tissue monitoring in this river segment conducted in 1996 as part of the U.S. EPA/IDNR fish tissue (RAFT) monitoring program (see assessment for the 1998 report for more information). However, because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is changed from "monitored" (indicating an assessment with relatively high confidence) to "evaluated" (indicating an assessment with relatively lower confidence).
