Assessment Comments
Assessment is based on: (1) the results of the Iowa Voluntary Atrazine Monitoring Program conducted from 2010 through 2012 by Syngenta Crop Protection, Inc. and (2) information from the Iowa DNR's Water Supply Section on violations of MCLs in finished water as provided in Iowa DNR annual compliance reports of Iowa’s public drinking water program.
Basis for Assessment
SUMMARY: The Class B(LW) aquatic life uses and fish consumption uses remain “not assessed” (IR 3a) due to lack of water quality information upon which to base an assessment. The Class C (drinking water) uses are assessed (monitored) as "fully supporting" (IR 2a) due to low level of the monitored contaminants (atrazine and nitrate). This assessment represents removal of the IR Category 4a impairment for nitrate. The sources of data for this assessment include (1) the results of the Iowa Voluntary Atrazine Monitoring Program conducted from 2010 through 2012 by Syngenta Crop Protection, Inc. and (2) information from the Iowa DNR's Water Supply Section on violations of MCLs in finished water as summarized in annual compliance reports of Iowa’s public drinking water program from 2007 through 2013.
Note 1: 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. This impairment remained in IR Category 4a through the 2012 IR cycle. Due to lack of subsequent nitrate MCL violations, this assessment is moved to IR Category 2a for the current (2014) IR cycle.
Note 2: A TMDL for atrazine at Cedar Lake was prepared and approved by EPA in 2010; thus, this lake was placed in IR Category 4a (TMDL approved) for the 2010 assessment/listing cycle. Because atrazine data over the 2010 and 2012 Integrated Reporting cycles showed “full support” of the drinking water uses, this assessment was moved to IR Category 2a (fully supported) for the 2012 IR Cycle.
EXPLANATION: The Class B(LW) (aquatic life) uses and fish consumption 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 is changed from “partially supporting (IR Category 4a) to "fully supporting" (IR 2a) due to lack of nitrate MCL violations during the period 2008 through 2012. The continuance of the IR 4a impairment had been based on a May 2007 nitrate MCL violation and advisory for nitrate from the Winterset Municipal Waterworks (see Appendix B (page 56) of Iowa DNR’s 2007 annual compliance report for the State of Iowa Public Drinking Water Program). The advisory lasted approximately 30 days before compliance was achieved. According to IDNR’s assessment/listing methodology, one drinking water advisory lasting 30 days or less per year indicates impairment (“partial support”) of the Class C uses. Thus, the assessment of the TMDL-covered drinking water uses were considered appropriate for IR Category 4a (i.e., impaired but TMDL not required due to existence of an EPA-approved TMDL). As documented in subsequent Iowa DNR drinking water program compliance reports, no violations of the nitrate MCL occurred at this utility in calendar years 2008 through 2013 (covering IR Cycles 2012 and 2014). Because the trend of lower nitrate levels and no nitrate advisories has continued through two IR cycles, this impairment is moved from IR Category 4a (impaired; TMDL completed) to IR Category 2a indicating “full support” of the Class C (drinking water) uses.
Regarding atrazine, the results of monitoring from 2010-12 are similar to those from previous IR monitoring periods and continue to show generally low levels of atrazine in this reservoir. Although seven of the 65 samples (11%) collected during the 2010-12 period exceeded the Class C criterion for atrazine of 3 ug/l, none of the 65 moving annual averages for this dataset exceeded the Class C criterion. Based on IDNR’s assessment methodology, if none of the moving annual mean contaminant level in source water is greater than the MCL, the Class C uses of the source water should be assessed as “fully supported.”
