Assessment Comments
Assessment is based on results of the Iowa Voluntary Atrazine Monitoring Program in from 2000-2002.
Basis for Assessment
SUMMARY: The 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 "not supported" due to average levels of atrazine that exceed state water quality criteria and the U.S. EPA’s MCL. The source of data for this assessment is the results of the Iowa Voluntary Atrazine Monitoring Program conducted in 2000, 2001, and 2002 by Syngenta Crop Protection, Inc. (formerly Novartis Crop Protection, Inc.). Note: The Syngenta data are presented as being taken from Morris and Ellis lakes near Centerville.
EXPLANATION: The Class B(LW) uses remain not assessed due to the lack of water quality information needed to assess these uses.
The assessment of support of the Class C (drinking water) uses was based on the results of the Syngenta "Iowa Voluntary Atrazine Monitoring Program" in 2000, 2001, and 2002. This monitoring showed that the time-weighted mean levels of atrazine in samples collected from Lake Morris in calendar years 2000, 2001, and 2002 were below the MCL of 3.0 ug/l. The time-weighted mean of atrazine in 2000 was 2.69 ug/l (N=31), in 2001 was 2.99 ug/l (N=31), and in 2002 was 2.1 ug/l (N=16). Rounding is required when comparing levels of atrazine to the MCL. Because the MCL, as published by U.S. EPA, is 0.003 mg/l, any values compared to the MCL must be in the proper MCL units and compared at the same number of significant figures. Thus, the annual time-weighted means of atrazine for 2000 (0.00269 mg/l) and 2001 (0.00299 mg/l) both round up to 0.003 mg/l; neither of these three annual means exceed the MCL for atrazine. Nine of the 31 samples collected in 2000 exceeded the MCL of 3.0 ug/l with a maximum value of 4.6 ug/l; 13 of the 31 samples collected in 2001 exceeded the MCL for atrazine (maximum value = 9.6 ug/l). Seven of the 47 moving annual averages calculated for the 2000-2002 period were above the MCL of 3 ug/l (range: 1.9 to 3.7 ug/l). These elevated running annual averages resulted from high levels of atrazine that occurred from May through September of 2001; the 13 samples collected during these months contained atrazine at levels ranging from 4.4 to 12 ug/l. Based on DNR's Section 305(b) assessment methodology, if the average contaminant level in source water is greater than the MCL, the Class C (drinking water) uses of the source water should be assessed as "not supported."
Fish consumption uses were "not assessed" due to the lack of fish contaminant monitoring at this lake.
