Fairfield Reservoir 1 IA 03-SKU-909

Assessment Comments

Assessment if based on results of the "Iowa Voluntary Atrazine Monitoring Program" for 1999, 2000 & 2001.

Basis for Assessment

SUMMARY:  The Class B(LW) aquatic life uses and the fish consumption uses remain "not assessed."  The Class C (drinking water) uses remain assessed (evaluated) as "fully supported / threatened."  The source of data for this assessment is the results of the Iowa Voluntary Atrazine Monitoring Program conducted in 2000 and 2001 by Syngenta Crop Protection, Inc.  (formerly Novartis Crop Protection, Inc.).   EXPLANATION:  The Class B(LW) uses remain not assessed due to a lack of information on the aquatic communities of this lake.   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 this reservoir in these three calendar years were below the MCL of 3.0 ug/l.   The time-weighted mean of atrazine in 1999 (N=30) was 0.09 ug/l), in 2000 (N=30) was 1.6 ug/l, and in 2001 (N=31) was 1.2 ug/l.   Only one of the combined 91 samples collected from this reservoir in 1999, 2000, and 2001 exceeded the MCL of 3.0 ug/l with a value of 3.6 ug/l.   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, based on the single MCL violations in 2000, the Class C uses of Fairfield Reservoir No.  1 were assessed as "fully supported / threatened."  Fish consumption uses were "not assessed" due to the lack of fish contaminant monitoring at this lake.