Unless an oil less compressor is used, the risk exists for introducing some
quantity of compressor oil into the borehole. This can occur even when oil 
removing filters are used, because their effectiveness depends on careful
maintenance. At best, the issue of whether oil has been introduced into the
aquifer will remain suspect. There is generally no way to tell when compressor
filters need changing because most drilling equipment has safety bypass valves
that route the air around plugged filters.
Control and containment of contaminated drill cuttings can be extremely
difficult, and could result in the spread of contamination at the ground surface.
Personnel safety considerations may require upgrading to higher levels of
respiratory and dermal protection due to the generation of dusts, mists, and
volatilization of organic compounds. Cuttings are difficult to contain and may
pose a safety threat to drill crews working on contaminated sites.
Although use of the air rotary drilling method should not be completely rejected,
owners/operators should take the following precautionary steps when using the air rotary
drilling method:
The air from the compressor should be filtered to ensure that compressor oil is
not introduced into ground water. The QAPjP should specify when and how
the filters will be monitored to prevent breakthrough.
Air rotary drilling should not be used in areas where upper soil horizons are
contaminated. In such settings, sloughing of the sidewalls of the borehole
would likely result in contamination of the ground water.
Air rotary drilling techniques should not be used in highly contaminated
environments. When air rotary is used in an environment where even minor
subsurface contamination is expected, shrouds, canopies, bluooey lines, or
directional pipes should be used to contain and direct the drill cuttings away
from the drill crew. Any contaminated materials (soil and/or water) should be
collected and properly treated or disposed of in an approved waste disposal
facility. Moreover, when drilling through potentially contaminated zones,
contaminants carried in the air flow can be introduced into other layers and
increase the zone of contamination. This problem can be lessened by installing
casing as the borehole is advanced.
The owner/operator should provide the Regional Administrator with a
discussion of the potential impact of the air rotary drilling method on the
physical and chemical characteristics of the subsurface and on ground water
November 1992
6 11






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