Assessment Comments
The source of data for this assessment is results of EPA/IDNR fish contaminant (RAFT) monitoring at Cedar Lake in 2006, 2008, 2010, and 2014, and turtle tissue 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 remain not assessed (IR Category 3a) due to the lack of information upon which to base an assessment. Fish consumption uses are assessed as fully supporting (IR Category 2a) due to the recent fish contaminant monitoring showing that levels of PCBs in fish are below the consumption advisory threshold. This assessment represents a de-listing of the previous impairment of fish consumption uses. The source of data for this assessment is results of EPA/IDNR fish contaminant (RAFT) monitoring at Cedar Lake in 2006, 2008, 2010, and 2014 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. Subsequently, levels of chlordane in Cedar Lake fish have fallen well-below IDNR/IDPH consumption advisory threshold.
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 are assessed (monitored) as “fully supported” based recent data for fish contaminants that shows declining levels of PCBs in Cedar Lake fish. 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 this lake since 1986, first due to high levels of chlordane and later due to high levels of PCBs. Because of this advisory, Cedar Lake has been monitored as part of the RAFT program on an approximately every-other-year basis since 1986. Results of ongoing U.S.EPA/IDNR fish contaminant (RAFT) monitoring in Iowa and at Cedar Lake have shown steady declines in these long-banned compounds in Iowa fish.
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 well below advisory trigger levels. Results from the 2008 monitoring showed that the level of technical chlordane in the composite sample of common carp fillets (0.034 ppm) was far below the advisory trigger level. The level of technical chlordane in channel catfish fillets in 2008 (0.18 ppm) was also well below the one meal per week consumption advisory trigger level of 0.6 ppm. Results from the 2010 monitoring showed that the level of technical chlordane in the composite sample of common carp fillets (<0.03 ppm) continued to be far below the advisory trigger level. The level of technical chlordane in channel catfish fillets in 2010 (0.093 ppm) was also well below the advisory trigger level. Based on these results, the consumption advisory at Cedar Lake based on chlordane remains rescinded.
Regarding PCBs, the levels of PCBs in the composite samples of common carp fillets in 2008 (0.105 ppm) and 2010 (0.19 ppm) were below the "one meal per week" advisory trigger level of 0.20 ppm. The level of total PCBs in the composite sample of channel catfish fillets in 2008 (0.39 ppm), however, again exceeded the advisory trigger level. Thus, continuance of the existing advisory and the impairment of fish consumption uses was justified. The level of total PCBs in the composite sample of channel catfish fillets in 2010 (0.191 ppm) was below the advisory trigger level. Based on IDNR's methodology, however, two consecutive samples with contaminant levels below the advisory trigger level are necessary before 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. A composite sample of channel catfish fillets was collected in 2014 at this lake. In addition to showing continued low levels of chlordane in Cedar Lake fish (0.07 ppm), the 2014 sample showed that the level of total PCBS (sum of Aroclors 1248, 1254, and 1260) was below the level of detection (0.06 ppm) and was thus well be low the one meal per week consumption advisory level of 0.2 ppm. Based on the results of two consecutive samplings that show levels of PCBs in bottom-feeding fish that are below the consumption advisory threshold, this impairment is proposed for de-listing.
Levels of mercury in Cedar Lake fish have generally been well below the "one meal per week" advisory threhsold of 0.3 ppm. In the 2010 sample, the level of mercury in composite samples of channel catfish (0.0507 ppm) and common carp (0.0104 ppm) were well below this advisory trigger level. The composite sample of channel catfish fillets collected for the 2014 sampling were not analyzed for mercury.
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.
