Assessment Comments
Assessment is based on the results of monthly monitoring from January 2006 through December 2008 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).
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 2006 through 2008. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from 2006-2008. Fish consumption uses are “not assessed” due to the lack of recent fish contaminant monitoring in this river segment. The source of data for this assessment is the results of monthly monitoring from January 2006 through December 2008 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). 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.
Note: A TMDL for the bacteria impairment in this segment of Cedar River was prepared and was approved by EPA in February 2010. Thus, the Class A1 (primary contact recreation) uses this assessment segment will be placed in Category 4a (TMDL prepared and approved) for the current 2010 listing cycle.
EXPLANATION: The Class A1 uses are assessed (monitored) as "partially supported.” The geometric mean level of indicator bacteria (E. coli) in the 22 samples collected during recreational seasons of 2006 through 2008 (84 orgs/100ml) is well-below the Iowa Class A1 water quality criterion of 126 orgs/100ml. Three of the 22 samples (14%) 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 the geometric mean of E. coli is less than the applicable state criteria, the contact recreation uses should be assessed as "fully supported" (see pgs 3-33 to 3-35of U.S. EPA 1997b). These guidelines also suggest that if more than 10% of samples exceed the single-sample maximum criterion for indicator bacteria, 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, the monitoring data from 2006-08 suggest that the percentage of samples exceeding the single-sample maximum criterion is not significantly greater than 10%, thus suggesting that the Class A1 uses should be assessed as “fully supported.” Because however the IDNR assessment/listing methodology requires that the single-sample maximum criteria for E. coli be fully met over two assessment/listing cycles in order for de-listing, the Class A1 (primary contact recreation) uses this assessment segment will remain assessed as "partially supported/impaired" for the 2010 cycle.
This river segment has a history of geometric mean levels of E. coli that are well-below Iowa’s Class A1 criterion of 126 orgs/100ml. Geometric mean levels for recent assessment periods are as follow: 2004: 92 orgs/100 ml; 2006: 83 orgs/100 ml; 2008: 75 orgs/100 ml.
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 2006 through 2008. Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the 34 samples analyzed or of Class B(WW1) criteria for toxic metals in the five samples analyzed. Levels of pesticides in the three samples from this station were below Class B(WW1) criteria.
Fish consumption uses are “not assessed” due to the lack of recent fish contaminant monitoring in this river segment. Prior to the current (2010) assessment cycle, 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 more than 10 years old, they are now considered too old (greater than five years) to accurately characterize current water quality conditions; thus, the assessment is changed from “fully supported” to “not assessed.”
