Assessment Comments
Assessment 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) and on IDNR/SHL biological sampling conducted in 2012.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" (IR 4a) 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 (evaluated) as "partially supported" (IR 3b-u) based on results of 2012 IDNR/SHL biological sampling. Fish consumption uses remain “not assessed” due to the lack of recent fish contaminant monitoring in this river segment. The source sof 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) and 2012 IDNR/SHL biological sampling conducted upstream of Waterloo. Note: this assessment is also partially 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: 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 "partially 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 "impaired". 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.
Based on the results of monitoring from the IDNR ambient station at Cedar Falls from 2010 through 2012, the Class B(WW1) aquatic life uses should be assessed as "fully supported" . 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.
In contrast to the water quality aquatic life assessment, the aquatic life assessment based on biological sampling suggests the aquatic life uses are "partially supporting". This evaluated biological assessment was based on data collected in 2012 as part of the IDNR/SHL stream nutrient sampling project. A series of biological metrics that reflect stream water quality and habitat integrity were calculated from the biological sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa collected in the stream sampling reach. The biological metrics were combined a benthic macroinvertebrate index (BMIBI). The index rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012 BMIBI scores were 58 (good) and 62 (good). The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. The artificial substrate BMIBI BIC for this ecoregion is 52 and the natural substrate BMIBI BIC is 70. This assessment is considered evaluated because the drainage area (4734 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. The BMIBI score of 58 was a natural substrate sample and failed the natural substrate BIC of 70. The 62 score was an artificial substrate score and passed the artificial substrate BIC of 52.
Even though this site failed the BMIBI BIC (1/2), it is uncertain as to whether or not this segment is meeting the aquatic life criteria because it doesn’t fall in the calibrated watershed size. According to IDNR’s assessment/listing methodology, impairments based on “evaluated” assessments are of lesser confidence and are thus not appropriate for Section 303(d) listing (Category 5 of the Integrated Report). IDNR does, however, consider these impairments as appropriate for listing under either Category 2b or 3b of the Integrated Report (waters potentially impaired and in need of further investigation).
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.”
