Assessment Comments
Assessment is based on: (1) the results of monthly monitoring from January 2010 through December 2012 at the IDNR/SHL ambient city monitoring station located at the Highway 30 bridge downstream from Cedar Rapids (station 10570001) and (2) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2006.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses are assessed (monitored) as "not supported" (IR 4a) due to levels of indicator bacteria that very slightly exceed state water quality criteria. Results of ambient chemical/physical water quality monitoring suggest that the Class B(WW1) aquatic life uses should be assessed (monitored) as "fully supported.” Fish consumption uses are assessed (monitored) as “fully supported” (IR 2a) based on results of fish contaminant monitoring in 2006. The sources of data for this assessment include (1) the results of monthly monitoring from January 2010 through December 2012 at the IDNR/SHL ambient city monitoring station located at the Highway 30 bridge downstream from Cedar Rapids (station 10570001) and (2) results of U.S. EPA/IDNR fish contaminant (RAFT) monitoring in 2006.
Note: A TMDL for indicator bacteria in this segment of Cedar River was prepared and approved by EPA in February 2010. The approval of this TMDL moves the bacterial impairment for this segment from Iowa's list of Section 303(d) waters (Category 5a of the Integrated Report) to IR Category 4a (impaired; TMDL not required).
EXPLANATION: The Class A1 uses are assessed as "not supported" based on results of ambient monitoring for indicator bacteria (E. coli). The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2010 through 2012 at station 10570001 downstream from Cedar Rapids were as follows: the 2008 geometric mean was 145 orgs/100 ml, the 2011 geometric mean was 79 orgs/100 ml and the 2012 geometric mean was 56 orgs/100 ml. Only the 2010 geometric mean exceed the Class A1 criterion of 126 orgs/100 ml and then only slightly. The 2011 and 2012 geometric means were well below the Class A1 criterion. Four of the 24 samples (17%) 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 ongoing impairment of the Class A1 uses in this river segment, levels of indicator bacteria are very low. If levels remain similarly low over the next assessment cycle (2012-2014), the bacterial impairment of the Class A1 uses should be considered for removal.
The results of monitoring from the IDNR/UHL ambient station 10570001 at Highway 30 from 2010 through 2012 suggest "full support" of the Class B(WW1) aquatic life uses. Monitoring at this station showed no violations of Class B(WW1) water quality criteria for ammonia-nitrogen, chloride, or sulfate in the 36 samples collected, and only one of the approximately 36 samples (3%) violated the Class B(WW1) criteria for pH and dissolved oxygen. 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 IDNR’s assessment/listing methodology, however, the results from station 10570001 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.
Fish consumption uses remain assessed (monitored) as “fully supported” based on results of U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Cedar Rapids in 2006. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of support of fish consumption uses in Iowa’s rivers and lakes. The composite samples of fillets from channel catfish and freshwater drum had low levels of contaminants. Levels of primary contaminants in the composite sample of channel catfish fillets were as follows: mercury: 0.0803 ppm; total PCBs: 0.091 ppm; and technical chlordane: 0.03 ppm. Levels of primary contaminants in the composite sample of freshwater drum fillets were as follows: mercury: 0.104 ppm; total PCBs: 0.09 ppm; and technical chlordane: 0.03 ppm. All levels of these contaminants from this monitoring are below advisory trigger levels, thus suggesting the continued “full support” of fish consumption uses in this segment of the Cedar River.
