Assessment Comments
Assessment is based on (1) information from the IDNR Water Quality Bureau / Water Supply Section and (2) results of monitoring for Syngenta's "Iowa Voluntary Atrazine Monitoring Program" from 2000-2004.
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses and fish consumption uses remain "not assessed due to 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 notices of nitrate MCL violations issued in 2001. In addition, average levels of atrazine exceeded the MCL for atrazine during the 2002-2004 period and thus suggest an additional impairment of the Class C uses. The sources of data for this assessment include (1) the results of the Iowa Voluntary Atrazine Monitoring Program conducted in 2000 through 2004 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 as provided by IDNR staff and as summarized in annual compliance reports of Iowa’s public drinking water program.
Note: A TMDL for nitrate at Cedar Lake was prepared by IDNR and approved by EPA in 2005; thus, this lake was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle. Because the Section new 303(d) impairment due to atrazine was not addressed in the TMDL, this waterbody was moved from IR Category 4a to Category 5a (impaired; TMDL required) for the 2006 assessment/listing cycle.
EXPLANATION: The Class B(LW) uses and fish consumption uses remain not assessed due to the lack of water quality information needed to assess these uses.
The Class C (drinking water) uses were assessed as “not supported” due to notices of nitrate MCL violations issued for nitrate in 2001. Information from the Iowa DNR's Water Supply Section shows the issuance of notices of MCL violations for nitrate during April, May, and June of 2001; this advisory period lasted for 109 days (a previous advisory period in 1999 lasted 34 days from April 20 to May 23, 1999). No notices were issued in 2000 or 2002. 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 more per year suggests that the Class C use is "not 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 "not supported."
In addition, levels of atrazine in this lake also suggest impairment of the drinking water uses This assessment was based on the results of the Syngenta "Iowa Voluntary Atrazine Monitoring Program" in 2002, 2003, and 2004. This monitoring showed that although 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, moving annual average concentratins did exceed the MCL. The time-weighted mean of atrazine in 2002 (N=16) was 3.39 ug/l, in 2003 (N=27) was 2.6 ug/l, and in 2004 (N=33) was 2.0 ug/l. Eleven of the 66 moving annual averages calculated for the three-year period exceeded the MCL of 3 ug/l (maximum = 3.7 ug/l). Based on DNR's Section 305(b) assessment methodology, if the average contaminant levels in source water are greater than the MCL, the Class C (drinking water) uses of the source water should be assessed as "not supported." The high levels of atrazine (4 to 5.3 ug/l) that occurred in samples taken from mid-May to early November 2002 resulted in moving annual averages that exceeded the atrazine MCL. The very high spike of atrazine in the May 10, 2004 sample (47.5 ug/l), however, did not (yet) result in moving annual averages that exceeded the MCL.
Fish consumption uses were "not assessed" due to the lack of fish contaminant monitoring at this lake.
