Assessment Comments
The source of data for this assessment is results of EPA/IDNR fish contaminant (RAFT) monitoring at Cedar Lake in 2006, 2008, and 2010, and turtle contaminant monitoring in 2009.
Basis for Assessment
Note: This waterbody is not in Iowa's current surface water classification (http://www.iowadnr.gov/water/standards/files/swcdoc2.pdf) and is thus classified only for general uses. As such, only the general use protection for aquatic life will be assessed. Due to existence of a fish consumption advisory, the fish consumption uses are assessed as well.
SUMMARY: The general aquatic life uses were not assessed due to the lack of information upon which to base an assessment. Fish consumption uses remain assessed as impaired due to the continuance of the fish consumption advisory at this lake: levels of PCBs in bottom-feeding fish suggest the need to continue the existing fish consumption advisory at this lake. The source of data for this assessment is results of EPA/IDNR fish contaminant (RAFT) monitoring at Cedar Lake in 2006, 2008, and 2010 and the results of turtle tissue monitoring in 2009.
Note: A TMDL for chlordane at Cedar Lake was prepared by IDNR and approved by EPA in 2001; thus, this lake was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle. Because the impairment due to PCBs was not addressed in the chlordane TMDL, this waterbody remains in IR Category 5a (impaired; TMDL needed) for the 2012 assessment/listing cycle.
EXPLANATION: Because data are not available to develop an assessment of support of the Class B(LW) (aquatic life) uses, these uses are considered "not assessed."
Fish consumption uses were assessed (monitored) as “partially supported” based the existence of a fish consumption advisory at this lake and on results of ongoing U.S.EPA/IDNR fish contaminant (RAFT) monitoring at Cedar Lake in 2006 and 2008. The existence of, or potential for, a fish consumption advisory is the basis for Section 305(b) assessments of the degree to which Iowa’s lakes and rivers support their fish consumption uses. A fish consumption advisory has existed at Cedar Lake since 1986. Because of this advisory, Cedar Lake has been monitored as part of the RAFT program on an every-other-year basis since 1986. The fish consumption advisory for chlordane was removed from this lake for the 2008 assessment/listing cycle and results from 2008 and 2010 monitoring also suggest that levels of chlordane in composite samples of bottom feeding fish are below advisory trigger levels. Results from the 2008 monitoring show that the level of technical chlordane in the composite sample of common carp fillets (0.034 ppm) was below the advisory trigger level. The level of technical chlordane in channel catfish fillets in 2008 (0.18 ppm) was also below the advisory trigger level. Results from the 2010 monitoring show that the level of technical chlordane in the composite sample of common carp fillets (<0.03 ppm) was below the advisory trigger level. The level of technical chlordane in channel catfish fillets in 2010 (0.093 ppm) was also below the advisory trigger level.
However, levels of PCBs exceeded the advisory trigger level in 2008, therefore continuance of the existing advisory, and the impairment of fish consumption uses is justified. The level of total PCBs in the composite sample of channel catfish fillets in 2008 (0.39 ppm) again exceeded the advisory trigger level. The level of total PCBs in the composite sample of channel catfish fillets in 2010 (0.191 ppm) was below the advisory trigger level. However, based on IDNR's methodology, two consecutive samples with contaminant levels below the advisory trigger level are necessary before suggesting removal of a fish consumption advisory. Therefore, the fish consumption uses of Cedar Lake remain impaired due to the fish consumption advisory at this lake. The level of PCBs in the composite sample of common carp fillets in 2008 (0.105 ppm) and 2010 (0.19 ppm) were below the advisory trigger level.
Levels of mercury in composite samples of channel catfish (0.0507 ppm) and common carp (0.0104 ppm) were well below the advisory trigger level (0.30 ppm) in 2010.
In addition to fish tissue monitoring, turtle tissue samples were collected in 2009. Levels of primary contaminants in the shoulder tissue of snapping turtle were all below the advisory trigger level. Results from the 2009 turtle tissue monitoring were as follows: mercury: 0.0486 ppm; total PCBs: 0.113 ppm; and technical chlordane: <0.03 ppm. These results do not suggest an impairment of the fish consumption uses at Cedar Lake.
