Assessment Comments
Assessment remains based on results of Syngenta's Iowa Voluntary Atrazine Monitoring Program in 2000 and 2001.
Basis for Assessment
SUMMARY: The Class A (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 Class C (drinking water) uses remain assessed (monitored) as "fully supported/threatened" with a declining trend due to average levels of atrazine that appear to be approaching state water quality criteria and the U.S. EPA MCL. Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this river reach. The source of data for this assessment remains the results of the Iowa Voluntary Atrazine Monitoring Program conducted in 2000 and 2001 by Syngenta Crop Protection, Inc. (Loch Ayr was not sampled as part of the Syngenta program in 2002, 2003, or 2004).
EXPLANATION: The Class A and Class B(WW) uses remain "not assessed" due to the lack of water quality information for this lake.
Due to the lack of more recent data, the assessment developed for the previous (2004) Section 305(b) reporting cycle will be used for the current (2006) reporting cycle. According to U.S. EPA guidance and according to IDNR’s assessment/listing methodology, a Section 303(d) impairment cannot be removed due either to lack of more recent data or due to the age of the data upon which the impairment was based. The assessment of support of the Class C (drinking water) uses for the 2004 reporting cycle was based on the results of the Syngenta "Iowa Voluntary Atrazine Monitoring Program" in 2000 and 2001. This monitoring showed that the time-weighted mean levels of atrazine in samples collected from Loch Ayr in both calendar years 2000 and 2001 were below the MCL of 3 ug/l. The time-weighted mean of atrazine in 2000 (N=31) was 1.65 ug/l and in 2001 (N=29) was 2.94 ug/l. Yearly maximum values were 2.2 ug/l in 2000 and 7.2 ug/l in 2001. None of the 31 samples collected in 2000 exceeded the MCL; 13 of the 29 samples collected in 2001 did exceed the MCL. None of the 31 moving annual averages calculated for the 2000-2001 period exceeded the MCL of 3 ug/l (range: 1.4 to 3.2 ug/l). Note: 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 mean of atrazine for 2001 (0.00294 mg/l) rounds up to 0.003 mg/l, and the maximum moving annual average (0.0032 mg/l) rounds down to 0.003 mg/l; neither of these average values exceeds the MCL for atrazine. Thus, based on IDNR's Section 305(b) assessment methodology, if the average contaminant level in source water is less than the MCL, but the MCL is exceeded in one or more samples, the Class C (drinking water) uses of the source water should be assessed as "fully supported / threatened." However, if contaminant levels appear to be increasing, “threatened” waters can be considered as candidates for Section 303(d) listing.
Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring at this lake.
