Cedar River IA 02-CED-470

[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/IA 02-CED-470). 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).]

Despite the continued low levels of indicator bacteria in this segment of the Cedar River during the previous (2010-2012) and current (2012-2014) monitoring periods, the Class A1 uses are assessed (monitored) as "partially supported" based on results of monitoring at the DNR ambient monitoring station upstream from Cedar Falls (STORET station 10700005). For the current (2012-2014) monitoring period, all recreation season geometric means met the Class A1 criteria for indicator bacteria (E. coli) (geometric mean of 126 orgs/100 ml. The geometric means of indicator bacteria (E. coli) in the 22 monthly samples collected during the recreational seasons of 2012 through 2014 at DNR station 10700005 were as follows: the 2012 geometric mean was 26 orgs/100 ml, the 2013 geometric mean was 99 orgs/100 ml, and the 2014 geometric mean was 58 orgs/100 ml. These geometric means indicate very low levels of E. coli in this river segment. Five of the 22 samples (21%), however, exceeded Iowa’s single-sample maximum criterion of 235 orgs/100 ml. According to Iowa DNR’s assessment/listing methodology, the percentage of samples exceeding the Class A1 single-sample maximum criterion of 235 orgs/100 ml was significantly greater than 10%, thus suggesting that the Class A1 uses should be assessed as “partially supporting. Despite this impairment, levels of indicator bacteria in this river segment are very low for an Iowa river.

Based on the results of monitoring from the DNR ambient station at Cedar Falls from 2012 through 2014, 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, ammonia-nitrogen, chloride or sulfate in the 33 samples analyzed. One of the 33 samples (3%) violated the Class B(WW1) criteria for pH. According to U.S. EPA guidelines for Section 305(b) reporting, if more than 10% of samples exceed state criteria for conventional parameters such as pH and dissolved oxygen, the aquatic life uses should be assessed as "impaired" (see pgs 3-33 to 3-35of U.S. EPA 1997b). According to DNR’s assessment/listing methodology, however, the results from station 10070005 do not indicate that significantly greater than 10% of the samples exceed either the Class B(WW1) criteria for dissolved oxygen or pH. Thus, these results do not suggest impairment of the Class B(WW1) aquatic life uses.

In agreement with the water quality data and assessment, the evaluated biological assessment based on data collected in 2009 as part of the DNR Fisheries Bureau sampling project also suggests "full support" of the aquatic life uses. 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 fish species collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI). The index ranks the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2009FIBI score was 61 (good). The aquatic life use support was assessed (evaluated) as fully supporting (=FS), based on a comparison of the FIBI score with biological impairment criteria (BIC) established from a statistical analysis of biological data collected at stream ecoregion reference sites from 1994-2008. The riffle habitat/non-riffle habitat FIBI BICs for this ecoregion are 65/44. While the riffle status of the sampling site is still undetermined, the FIBI score passed both BICs (using the FIBI UAV applied to single samples for the riffle habitat BIC). This assessment is considered evaluated because the drainage area (4318 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site passed the FIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria becausethe site used for the assessmentdoesn’t fall in the calibrated watershed size.

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/DNR 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.”