Assessment Comments
Assessment is based on results of (1) IDNR ambient city monitoring upstream from Cedar Falls from 2000-02 and (2) U.S. EPA/IDNR fish tissue (RAFT) monitoring in 1997.
Basis for Assessment
SUMMARY: The Class A (primary contact recreation) uses were assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria. The Class B(WW) aquatic life uses were assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from 2000-2002. Fish consumption uses remain assessed (evaluated) as "fully supported" based on results of fish contaminant monitoring in 1997. The sources of data for this assessment are (1) the results of monthly monitoring from January 2000 through December 2002 at the IDNR ambient city monitoring station located at upstream from Cedar Falls at the old highway 218 bridge at Cedar Falls (STORET station 10070005) and (2) the results of U.S. EPA/IDNR fish tissue (RAFT) monitoring at Cedar Falls in September 1997.
EXPLANATION: The Class A uses were assessed (monitored) as "partially supported” due to high levels of indicator bacteria. 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." Fifteen of the 16 samples collected from the Cedar Falls 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 the 15 non-runoff-affected samples (92 orgs/100ml) is well-below the Iowa Class A water quality criterion of 200 orgs/100ml. However, two of the fifteen samples (13%) contained a level of fecal coliform bacteria that 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 samples exceed this single-sample maximum value, the primary contact recreation uses are "partially supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b).
The Class B(WW) aquatic life uses were assessed as "fully supported" based on results of monitoring from the IDNR ambient station at Cedar Falls from 2000 through 2002. Monitoring at this station showed no violations of Class B(WW) water quality criteria for dissolved oxygen, pH, ammonia-nitrogen, toxic metals, and toxic organic compounds in the 28 samples analyzed during this assessment period; no detected levels were reported in the nine samples from this station analyzed for pesticides.
Fish consumption uses remain assessed (evaluated) as "fully supported" based on results of U.S. EPA/IDNR fish tissue (RAFT) monitoring at Cedar Falls in 1997 that showed levels of all contaminants were less than ½ of the respective FDA action levels and IDNR levels of concern (see assessment for the 2000 and 1998 reports). 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).
