Assessment Comments
Assessment is based on: results of the Iowa Voluntary Atrazine Monitoring Program conducted from 2004 through 2006 by Syngenta Crop Protection, Inc.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation), Class B(LW) (aquatic life) uses and fish consumption uses remain "not assessed" due to the lack of water quality information upon which to base an assessment. The Class C (drinking water) uses are assessed (monitored) as "fully supported" due to continued decrease in average levels of atrazine. The source of data for this assessment is the results of the Iowa Voluntary Atrazine Monitoring Program conducted from 2004 through 2006 by Syngenta Crop Protection, Inc.
EXPLANATION: The Class A1 and Class B(LW) uses remain not assessed due to the lack of water quality information needed to assess these uses. This lake is not monitored as part of Iowa's ambient statewide lake monitoring network.
The Class C (drinking water) uses are assessed (monitored) as “fully supported” based on results of the Syngenta “Iowa Voluntary Atrazine Monitoring Program” from 2004 through 2006. This monitoring showed that the time-weighted mean levels of atrazine in the samples were well below the MCL of 3.0 ug/L. The mean and median atrazine concentrations over this three-year period (N= 82) were 1.0 ug/L and 0.9 ug/L, respectively. The maximum value for this period was 2.5 ug/L. None of the 49 moving annual averages for atrazine for 2004, 2005, or 2006 at Centerville Reservoir exceeded the MCL of 3.0 ug/L. Based on IDNR’s assessment methodology, if the average contaminant level in source water is less than the MCL, the Class C uses of the source water should be assessed as “fully supported.”
The Class C (drinking water) uses were assessed as “not supported” for the 2004 assessment/listing cycle based on results of sampling conducted as part of the Iowa Voluntary Atrazine Monitoring Program in 2000, 2001, and 2002 by Syngenta Crop Protection, Inc. Results of this program from 2000 through 2002 showed thirty-two of the 48 moving annual averages calculated for the 2000-02 period were above the MCL of 3 ug/l (range: 3.5 to 4.9 ug/l). Based on DNR's Section 305(b) assessment methodology, the Class C (drinking water) uses of Lower Centerville Reservoir were assessed as "not supported" for the 2004 reporting cycle. Data used for the 2006 assessment/listing cycle suggested that levels of atrazine were below the MCL and suggested “full support” of the Class C uses. Centerville Reservoir, however, remained on the 303d list to ensure that atrazine levels were consistently below the MCL. Results from 2004-2006 again suggest that annual average levels of atrazine have not exceeded the MCL. Therefore, based on continued low levels of atrazine at Centerville Reservoir, the Class C uses are assessed as “fully supported” and the lake is proposed for removal from the state’s 303d list.
Fish consumption uses remain not assessed due to a lack of fish tissue data at this lake.
