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

quality.

November 1992

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