Assessment Comments
Assessment is based on: (1) the results of monthly monitoring from January 2004 through December 2006 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.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on results of ambient monitoring for indicator bacteria during recreational seasons of 2004 through 2006. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from 2004-2006. 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 2004 through December 2006 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 A1 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 assessment methodology for indicator bacteria has changed. Prior to 2003, the Iowa WQ Standards contained a high-flow exemption for the Class A1 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 A1 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 A1 uses for purposes of 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 2004 through 2006 (75 orgs/100ml) is well-below the Iowa Class A1 water quality criterion of 126 orgs/100ml. However, five of the 24 samples (21%) contained a level of E. coli that exceeded Iowa’s single-sample maximum criterion 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 criterion, 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 criterion, thus suggesting that the Class A1 uses should be assessed as “partially supported/impaired”. Note: one less violation of the single-sample maximum criterion for E. coli during the 2004-2006 period would have resulted in an assessment of “fully supported” for the Class A1 uses for this river segment.
The Class B(WW1) aquatic life uses are assessed as "fully supported" based on results of monitoring from the IDNR ambient station at Cedar Falls from 2004 through 2006. Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the 36 samples analyzed or of Class B(WW1) criteria for toxic metals in the 14 samples analyzed. Levels of pesticides in the nine samples from this station were below Class B(WW1) criteria.
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.
