Assessment Comments
Assessment is based on results of IDNR ambient city monitoring upstream from Marshalltown in 2001.
Basis for Assessment
[NOTE: For the 2002 report, the previous waterbody segment IA 02-IOW-0060-1, which extended 61 miles from Salt Creek (Benton Co.) to Asher Creek at Marshalltown, was split into four subsegments: (1) Salt Creek to Richland Creek in Tama Co. (IA 02-IOW-0060-1), (2) Richland Creek to Deer Creek at Tama (IA 02-IOW-0060-2), (3) Deer Creek to Timber Creek in Marshall Co. (IA 02-IOW-0060-3), and (4) Timber Creek to Asher Creek at Marshalltown (IA 02-IOW-0060-4). See assessment information for segment IA 02-IOW-0060-1 (Salt Creek to Asher Creek) for previous Section 305(b) assessments for this river reach.] As part of this splitting, the previous identification number for segment IA 02-IOW-0060-2 (from Asher Creek to Minerva Creek) was changed to IA 02-IOW-0060-5. The distance of this segment did not change.]
For the 2002 report: SUMMARY: The Class A (primary contact recreation) uses were assessed (evaluated) as "partially supported," and the Class B(WW) aquatic life uses were assessed as "fully supported." Fish consumption uses were not assessed. The source of data for this assessment is the results of monthly monitoring from April 2000 through September 2001 at the IDNR ambient city monitoring station located upstream from Marshalltown at the state highway 330 bridge northwest of Marshalltown. 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 10 samples collected from the Highway 330 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 7 non-runoff-affected samples (251 orgs/100ml) is above the Iowa Class A water quality criterion of 200 orgs/100ml. 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 the geometric mean is greater than 200 orgs/100ml, the primary contact recreation uses are "not 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." Monitoring at the Highway 330 station showed no violations of Class B(WW) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the 14 samples collected, for toxic metals in the 14 samples collected, and for toxic organic compounds in the six samples analyzed, during the 2000-2001 biennial period. Fish consumption uses remain "not assessed" due to lack of recent fish tissue monitoring in this river segment.
