Assessment Comments
Assessment is based on (1) information from the DNR Water Quality Bureau / Water Supply Section and (2) Syngenta's "Iowa Voluntary Atrazine Monitoring Program."
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses and fish consumption uses remain "not assessed." The Class C (drinking water) uses remain assessed as "partially supported." The sources of data for this assessment include (1) the results of the Iowa Voluntary Atrazine Monitoring Program conducted in 1999, 2000, and 2001 by Syngenta Crop Protection, Inc. (formerly Novartis Crop Protection, Inc.) and (2) information from the Iowa DNR's Water Supply Section on violation of MCLs in finished water. EXPLANATION: The Class B(LW) uses are 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 1999, 2000, and 2001. This monitoring showed that the time-weighted mean levels of atrazine in samples collected from Cedar Lake in these three calendar years were below the MCL of 3.0 ug/l. The time-weighted mean of atrazine in 1999 (N=31) was 1.6 ug/l, in 2000 (N=30) was 2.42 ug/l, and in 2001 (N=31) was 1.61 ug/l. Five of the 31 samples collected in 1999 exceeded the MCL of 3 ug/l with a maximum value of 8.0 ug/l; three of the 30 samples collected in 2000 exceeded the MCL, with a maximum value of 7.2 ug/l; none of the 31 samples collected in 2001 exceeded the MCL. Based on DNR's Section 305(b) assessment methodology, if the average contaminant level in source water is less than the MCL, but a level in one or more samples is above the MCL, the Class C (drinking water) uses of the source water should be assessed as "fully supported / threatened." Thus, the occurrence of the combined four MCL violations in 2000 and 2001 suggest that the Class C uses of Cedar Lake should be assessed as "fully supported / threatened." Information from the Iowa DNR's Water Supply Section, however, shows the issuance of notices of of MCL violations for nitrate during April, May, and June of 2001. According to EPA and DNR methods for assessing support of Class C (drinking water) uses, one or more drinking water advisory lasting 30 days or less per year suggests that the Class C use is only "partially supported" (see pages 3-38 to 3-44 of U.S. EPA 1997b and the DNR assessment methodology for Section 305(b) reporting). Thus, the Class C (drinking water) uses for this lake are assessed as "partially supported." Fish consumption uses were "not assessed" due to the lack of fish contaminant monitoring at this lake.
