Assessment Comments
Assessment is based on results of IDNR/UHL ambient water quality monitoring from 2008 through 2010 near Palo.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as “not supported”. The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of ambient water quality monitoring. Fish consumption uses remain not assessed due to the lack of 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 County Road E36 east of Palo (STORET station 10570002).
Note: A TMDL for the bacteria impairments in the two downriver assessment segments of the Cedar River was prepared and approved by EPA in February 2010. This TMDL addressed bacteria impairments in Cedar River segments IA 02-CED-0030_1 and -0030_2 but did not include this segment of the Cedar River (IA 02-CED-0030_3). The bacteria impairments in all three segments, however, are based on the same monitoring data from the same Iowa DNR ambient water quality monitoring station: Cedar River at County Road E36 east of Palo (STORET station 10570002)). As noted in comments from U.S. EPA in May 2011, however, the failure of the TMDL to include segment CED-0030_3 require that this segment remain on Iowa's Section 303(d) list.
EXPLANATION: The Class A1 uses are assessed (monitored) as "not supported" based on results of monitoring for indicator bacteria (E. coli) at the IDNR/UHL ambient monitoring station on the Cedar River east of Palo. The geometric means of indicator bacteria (E. coli) in the 22 samples collected during the recreational seasons of 2008 through 2010 at station 10570002 upstream from Cedar Rapids were as follows: the 2008 geometric mean was 202 orgs/100 ml, the 2009 geometric mean was 63 orgs/100 ml and the 2010 geometric mean was 122 orgs/100 ml. Only the 2008 geometric means exceed the Class A1 criterion of 126 orgs/100 ml, thus suggesting that extreme flooding in the Cedar River in summer 2008 contributed to this impairment. Seven of the 22 samples (32%) 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.”
Since Iowa’s adoption of E. coli as an indicator bacterium in 2003 until summer 2008, geometric mean levels at IDNR monitoring station 10570002 had fully met Iowa’s geometric mean criterion of 126 orgs/100 ml. This segment of river has some of the lowest geometric means of any free-flowing rivers segment in the state of Iowa. Regardless of the recent (2010 and 2012) impairments, levels of indicator bacteria in this segment of the Cedar River have been and continue to be very low relative to levels of bacteria in other Iowa rivers, and thus this bacterial impairment should be considered very slight in magnitude.
The Class B(WW1) aquatic life uses are assessed (monitored) as "fully supported" based on results of water quality monitoring 2008-2010 from (1) the IDNR ambient station near Palo and (2) the USGS stations at Edgewood Road and Blairs Ferry Road. Monitoring at these stations showed no violations of Class B(WW1) water quality criteria for dissolved oxygen, pH, or ammonia-nitrogen in the approximately 40 samples analyzed, for toxic metals in the approximately ten samples analyzed, or for the approximately five samples analyzed for pesticides during this assessment period.
Fish consumption uses remain “not assessed” due to lack of recent fish tissue monitoring in this river segment.
