Assessment Comments
Assessment is based on the results of monthly monitoring from January 2010 through December 2012 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" (IR 5a) based on results of ambient monitoring for indicator bacteria during recreational seasons of the previous (2008-2010) assessment period: results of monitoring from 2010-2012 do not suggest a bacteria impairment. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" (IR 2a) based on results of ambient water quality monitoring from 2010-2012. 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 2010 through December 2012 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 downstream segments (IA 02-CED-0060-2 and IA 02-CED-0050-L_0).
Note: A TMDL for the bacteria impairment in this segment of Cedar River was prepared and was approved by EPA in February 2010. This TMDL, however, did not cover this assessment segment (IA 02-CED-0060_2). Thus, the Class A1 (primary contact recreation) uses for this assessment segment will remain Section 303(d)-impaired and will thus remain in Category 5a (impaired and TMDL required) for the current listing cycle.
EXPLANATION: Despite the low levels of indicator bacteria in this segment of the Cedar River during the current (2010-2012) assessment period, the Class A1 uses remain assessed (monitored) as "not supported" based on results of monitoring during the previous (2008-2010) assessment period at the IDNR ambient monitoring station upstream from Cedar Falls (STORET station 10700005). For the current (2010-2012) assessment period, all Class A1 criteria for indicator bacteria (E. coli) (geometric mean of 126 orgs/100 ml and single-sample maximum of 235 orgs/100 ml) were met. The geometric means of indicator bacteria (E. coli) in the 24 monthly samples collected during the recreational seasons of 2010 through 2012 at IDNR station 10700005 were as follows: the 2010 geometric mean was 78 orgs/100 ml, the 2011 geometric mean was 56 orgs/100 ml and the 2012 geometric mean was 26 orgs/100 ml. Only one of the 24 samples collected (4%) exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. These geometric means are well-below the Class A1 criterion of 126 orgs/100 ml, and the percentage of samples exceeding the Class A1 single-sample maximum criterion of 235 orgs/100 ml was far below the impairment threshold of 10%. Based on U.S. EPA guidelines and the IDNR assessment/listing methodology, these results suggest “full support” of the Class A1 uses.
Because, however, IDNR’s assessment/listing methodology requires that standards be met for two consecutive assessment cycles (total of five years) before an impairment can be removed, the impairment of the Class A1 uses will remain based on the 2008 and 2009 geometric means that slightly exceeded the Class A1 geometric mean criterion. The geometric means of indicator bacteria (E. coli) in the monthly samples collected at station 10700005 during the recreational seasons of 2008 and 2009 were as follows: the 2008 geometric mean was 146 orgs/100 ml and the 2009 geometric mean was 150 orgs/100 ml. Thus, the 2008 and 2009 geometric means very slightly exceed the Class A1 criterion of 126 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 should be assessed as "not supported". Thus, the Class A1 uses were assessed as "not supported" for the 2012 Integrated Reporting cycle. Despite the recent 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 current (2010-2012) assessment period are consistent with that history. If bacteria levels remain low during the next (2012-14) assessment period, this impairment should be considered for removal.
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 2010 through 2012. Monitoring at this station showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, ammonia-nitrogen, chloride or sulfate in the 36 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.”
