monitoring wells (4 out of 6) while parent atrazine was present in one well at 0.14 ppb
(Tables 4 - 9). By 2/4/91, parent atrazine was found in two of the wells and by 3/25/91,
about 11 months after the first application, parent atrazine was found in 4 of the-6 wells.
Numerical results were available for the two metabolites, deethyl and
deisoproplyatrazine by 3/25/91. On this date 5 of the 6 wells had deethylatrazine
concentrations ranging from 0.73 ppb to 1.5 ppb while parent atrazine was usually less
than half the levels of deethylatrazine. There was no deisoproplyatrazine in any of the
wells. Not one of the wells exceeded the ES although 5 of the wells exceeded the PAL.
The highest total atrazine concentration (parent atrazine and 2 metabolites) was 2.17
ppb for well 5. This was reached less than 1 year after the initial application. There
wasn't any clear connection between the 2 different application rates and the atrazine
concentrations found in the groundwater samples. Additionally there wasn't any clear
connection between atrazine levels in groundwater and deep percolation events. Under
conditions at the study site, deethvlatrazine, although the most leachable, still took about
7 months to reach the groundwater even with numerous large rainfall events (Table 1)
which increased the water table elevation by at least 2 feet.
Atrazine was applied for the second growing.season on 5/8/91 at similar rates to
1990 (1 lb/A by wells 1, 3, and 5 and 0.5 lbs/A near wells 2, 4, and 5). By 8/28/91, 5 of
the 6 wells had total atrazine concentrations exceeding 2 ppb. Well 1 exceeded the ES
at 8.8 ppb. (for unexplained reasons atrazine concentrations were often much higher in
this well). By 10/8/91, 3 of the wells exceeded the ES. After this time total atrazine
concentrations dropped slowly over the next year or so and by 3/25/92 only well 1