Assessment Comments
Assessment is based on results of the Iowa Voluntary Atrazine Monitoring Program conducted in 2000-01 and 2010-12 sponsored by Syngenta Crop Protection.
Basis for Assessment
SUMMARY: The Class A1 (primary contact recreation) uses and the Class B(LW) aquatic life uses remain "not assessed" due to the lack of water quality information upon which to base an assessment. The assessment of the Class C (drinking water) uses is changed from "fully supported/threatened" (IR Category 5a) to “fully supported” (IR Category 2a) based on results of atrazine monitoring from 2010-12. This change in IR category represents a delisting of the atrazine impairment of drinking water uses for this former water supply reservoir. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake. The source of data for this assessment is the results of atrazine monitoring from October 2010 to October 2012 as part of Syngenta’s voluntary monitoring program. This monitoring was conducted through a cooperative sampling arrangement between Syngenta and Iowa DNR.
EXPLANATION: The Class A1 and Class B(WW) uses remain "not assessed" due to the lack of water quality information for this lake upon which to base an assessment.
The assessment of support of the Class C (drinking water) uses is changed from “fully supporting/threatened” (IR Category 5a) to “fully supporting” (IR Category 2a) based on results of atrazine monitoring conducted as part of Syngenta’s voluntary monitoring program through a cooperative arrangement with Iowa DNR. The long-standing impairment of drinking water uses at this former water supply reservoir was based on the results of Syngenta-sponsored atrazine monitoring in 2000 and 2001. These data showed that while average levels of atrazine were below the MCL, data from monitoring in 2001 suggested an increasing (worsening) trend such that full support of the Class C uses was “threatened” (see assessment narratives for previous assessments for the details of this assessment). According to IDNR's Section 305(b) assessment methodology, if the average contaminant levels in source water are less than the MCL, but average levels appear to be trending upward, the Class C (drinking water) uses of the source water should be assessed as "fully supported / threatened". Thus, this impairment was added to Iowa’s 2002 Section 303(d) list.
No additional data for atrazine have been generated from Loch Ayr from 2002 through 2009, and this former water supply reservoir has remained assessed as Section 303(d) impaired. Syngenta-sponsored monitoring began again in 2010 through a cooperative arrangement with Iowa DNR. Twenty-five monthly samples were collected from October 2010 through October 2012. None of the 25 samples collected exceeded the atrazine MCL of 3 ppb (maximum = 0.92 ppb). All of the 14 moving annual averages were well below the MCL (maximum = 0.35 ppb). According to Iowa DNR’s assessment/listing methodology, the Class C (drinking water) uses should be assessed as “fully supporting” if all moving annual average levels of atrazine are less than the maximum contaminant level (MCL) of 3 ug/l. Thus, the drinking waters uses for Loch Ayr are assessed as “fully supporting” for the current (2012) IR cycle, and the previous atrazine impairment is removed.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
