Assessment Comments
Assessment is based on results of (1) IDNR/UHL ambient city monitoring upstream from Cedar Falls from 2000-04 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 during recreational seasons of 2002 through 2004. The Class B(WW) aquatic life uses were assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from 2002-2004. 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 2002 through December 2004 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. Note: this assessment is also used for the two adjacent upstream segments of the Cedar River: IA 02-CED-0060-1 and IA 02-CED-0060-2.
EXPLANATION: The Class A uses were assessed (monitored) as "partially supported” due to high levels of indicator bacteria. Due to recent changes in Iowa’s Water Quality Standards, Iowa’s 2006 assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A criterion for indicator bacteria (fecal coliforms) designed to protect primary contact recreation uses: the water quality criterion for fecal coliform bacteria (200 orgs/100 ml) did not apply "when the waters [were] materially affected by surface runoff." Due to a change in the Standards in July 2003, E. coli is now the indicator bacterium, and the high flow exemption was eliminated and replaced with language stating that the Class A criteria for E. coli apply when Class A1, A2, or A3 uses “can reasonably be expected to occur.” Because the IDNR Technical Advisory Committee on WQ Standards could not agree on what flow conditions would define periods when uses would not be reasonably expected to occur, all monitoring data generated for E. coli during the assessment period, regardless of flow conditions during sample collection, will be considered for determining support of Class A uses for purposes of the 2006 Section 305(b) assessments and Section 303(d) listings. The geometric mean level of indicator bacteria (E. coli) in the 24 samples collected during recreational seasons of 2002 through 2004 (83 orgs/100ml) is well-below the Iowa Class A water quality criterion of 126 orgs/100ml. However, six of the 24 samples (25%) contained a level of E. coli that exceeded Iowa’s single-sample maximum value of 235 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 should be assessed as "partially supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). According to IDNR’s assessment/listing methodology, these results suggest that significantly greater than 10% of the samples exceed IDNR’s single-sample maximum value, thus suggesting that the Class A uses should be assessed as “partially supported/impaired”.
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 2002 through 2004. 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 approximately 30 samples analyzed during this assessment period; no detected levels were reported in the seven samples from this station analyzed for pesticides.
Fish consumption uses were assessed (evaluated) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring upstream from Cedar Falls in 1997. Because these data are now considered too old (greater than five years) to accurately characterize current water quality conditions, the assessment category is considered “evaluated” (indicating an assessment with relatively lower confidence) as opposed to "monitored" (indicating an assessment with relatively higher confidence).
The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. Prior to 2006, IDNR used action levels published by the U.S Food and Drug Administration to determine whether consumption advisories should be issued for fish caught as part of recreational fishing in Iowa. In an effort to make Iowa’s consumption more compatible with the various protocols used by adjacent states, the Iowa Department of Public Health, in cooperation with Iowa DNR, developed a risk-based advisory protocol. This protocol went into effect in January 2006 (see http://www.iowadnr.gov/fish/news/consump.html for more information on Iowa’s revised fish consumption advisory protocol). Because the revised (2006) protocol is more restrictive than the previous protocol based on FDA action levels; fish contaminant data that previously suggested “full support” may now suggest either a threat to, or impairment of, fish consumption uses. This scenario, however, does not apply to the fish contaminant data generated from the 1997 RAFT sampling conducted in this assessment segment: levels of all contaminants from this monitoring were below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses.
