Assessment Comments
Assessment is based on the results of monthly monitoring from January 2008 through December 2010 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 "not supported" based on results of ambient monitoring for indicator bacteria during recreational seasons of 2008 through 2010. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring from 2008-2010. Fish consumption uses remain “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 2008 through December 2010 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 listing cycle.
EXPLANATION: The Class A1 uses are assessed (monitored) as "not supported.” The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at IDNR station 10070005 upstream from Cedar Falls were as follows: the 2008 geometric mean was 146 orgs/100 ml, the 2009 geometric mean was 150 orgs/100 ml and the 2010 geometric mean was 78 orgs/100 ml. The 2008 and 2009 geometric means very slightly exceed the Class A1 criterion of 126 orgs/100 ml. Five of the 22 samples (23%) exceeded the Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and IDNR’s assessment/listing methodology, if a recreation season geometric mean exceeds the respective water quality criterion, the contact recreation uses are "not supported" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as “impaired.” Despite the 2010 and 2012 assessments of the Class A1 uses as impaired, this river segment has a history of low E. coli levels, and the monitoring results from the 2008-2010 assessment period are consistent with that history.
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 2008 through 2010. Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the 33 samples analyzed or of Class B(WW1) criteria for toxic metals and pesticides in the three samples analyzed.
Fish consumption uses remain “not assessed” due to the lack of recent fish contaminant monitoring in this river segment. The most recent fish contaminant monitoring in this assessment segment was conducted in 1997 as part of the U.S.EPA/IDNR fish contaminant (RAFT) monitoring program. 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 was changed from “fully supported” to “not assessed.”
