screened to allow for a broader distribution of gas or liquid injec-
tion or extraction. The positioning of horizontal wells can be planned to conform to the distribution of subsurface contamination, optimiz-
ing the remediation system design by providing more surface area to contact the contaminant plume. Because most water-bearing for-
mations are deposited in relatively thin but extensive zones and their transmissivity in the horizontal direction normally exceeds their capability to transmit fluids verti-
cally, horizontal wells provide more efficient fluid delivery and hence improve contaminant recovery.

Because the borehole in the hori-
zontal section of directionally dril-
led wells is unstable, particularly in unconsolidated sediments, the

borehole must be stabilized in some manner. The traditional methods for borehole stabilization are to use high density drilling fluid or to drive casing behind the drill bit as it advances. Because the drilling used in drilling in con-
taminated sites must often be treated as hazardous waste, it is desirable to use drilling methods that do not require the use of fluids. Because of the curvature of the drilling assembly in directional drilling, casing driven after the drill bit can be damaged or ruin-
ed. To address these problems, cryogenic drilling is being devel-
oped in order to stabilize bore-
holes penetrating unconsolidated sediments. This technology freezes the moisture in the vicinity of the borehole to form an ice stabilized borehole while drilling is occurring.