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DISCUSSION
Followup Investigations
About 36 farms with the highest concentrations of one or more pesticides
were visited by staff from the ARM Division. Each farmer was interviewed
about pesticide use and handling history and about construction of the sampled
well. More detailed investigations were conducted at each farm where an ES
was exceeded. Soil samples were collected from areas of historic pesticide
mixing and loading and analyzed for the compound(s) found in the well. One
warning letter was issued to a farmer where illegal pesticide container disposal
practices were observed and significant concentrations of atrazine were detected
in soil samples. Of the 36 farmers interviewed, about 50% mix and load
pesticides on the farm, about 40% hire commercial applicators and about 10%
mix and load pesticides at a farm other than the one sampled. About 70% of
the farmers are themselves certified applicators.
Well Construction
The well on a Wisconsin Grade A dairy farm is required to meet the
standards in Ch. NR 112 of the Wisconsin Administrative Code for such things
as minimum setback distances from septic tanks and barnyards, minimum casing
depth and well depth, and proper plumbing. When a well is drilled the driller
submits the well log to the WDNR and leaves a copy with the well owner. The
original well construction records are maintained by the Wisconsin Geological
and Natural History Survey (WGNHS). For a variety of reasons it was very
difficult to locate well construction records for the Grade A dairy farm wells.
Of the 71 wells that contained pesticides a well construction record could be
confidently associated with only 16 wells. The following statements apply only
to this set of records.
These wells were generally high quality, properly constructed wells. The
pesticide detections in these wells cannot be attributed to improper well
construction or inadequate casing depth. The contaminated wells range in
depth from 62 to 200 feet. The casing depth in these wells ranges from 37 to
117 feet. Eighty percent of these wells were finished in bedrock formations
and 20% were finished in unconsolidated materials such as sand and gravel.
None of the farmers who were interviewed were able to produce a well
construction report for their well.
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