Assessment Comments
Assessment is based on results of IDNR ambient monthly monitoring at the Highway 30 bridge at Cedar Rapids. See attached document for details.
Basis for Assessment
[Note: For the 2002 report, the previous waterbody segment IA 02-CED-0020-0, which extended 52 miles from Mud Creek (aka Sugar Creek) in Muscatine Co. to its confluence with Prairie Creek at Cedar Rapids, was split into three subsegments: (1) Mud Creek to Rock Run Creek in Cedar Co. (IA 02-CED-0020-1), (2) Rock Run Creek to Highway 30 at Cedar Rapids (IA 02-CED-0020-2), and (3) Highway 30 to Prairie Creek at Cedar Rapids (IA 02-CED-0020-3). See assessment information for segment IA 02-CED-0020-1 (Mud Creek to Rock Run Creek) for previous Section 305(b) assessments for this river reach.]
SUMMARY: The Class A (primary contact recreation) uses were assessed as "partially supported," and the Class B(WW) aquatic life uses were assessed as "fully supported." Fish consumption uses were not assessed. The sources of data for this assessment is the results of monthly monitoring from October 1999 through September 2001 at the IDNR ambient city monitoring station located at the Highway 30 bridge downstream from Cedar Rapids.
EXPLANATION: The Class A uses were assessed as "partially supported." 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." Seven of the 9 samples collected from the Highway 30 station during the 2000 and 2001 recreational seasons were collected at flows not materially affected by surface runoff. The geometric mean level of indicator bacteria (fecal coliforms) in these seven non-runoff-affected samples (111 orgs/100ml) is below the Iowa Class A water quality criterion of 200 orgs/100ml. However, two of the 7 samples (29%) 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 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). Because less than 10 non-flow affected samples were available for this assessment, the assessment type is considered "evaluated"; thus, this assessment is not of sufficient quality to support a Section 303(d) listing. The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of monitoring from the IDNR ambient at Highway 30 in 2000 and 2001. Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen or ammonia-nitrogen in the 14 samples collected or for toxic metals and toxic organic compounds in the 14 samples analyzed during this biennial period. The levels of pH, however, violated the Class B(WW) criterion of 9.0 pH units in one of the 14 samples (7.1%). 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. This violation 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 the high level of pH in this river segment is not seen as a water quality impairment. 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 were not assessed due to lack of recent fish tissue monitoring in this river segment. The most recent fish tissue monitoring was conducted in 1996 as part of the U.S. EPA/IDNR fish tissue (RAFT) monitoring program. These data are not more than five years old and are considered too old for characterizing current water quality conditions.
