Monitoring A Permeable Reactive Iron Wall Installation In Unconsolidated
Sediments By Using A Cross-Hole Radar Method
By John W. Lane, Jr., Peter K. Joesten, and Jennifer G. Savoie
ABSTRACT
Cross-hole common-depth (CD) radar scanning was used at the Massachusetts
Military Reservation (MMR) in Cape Cod, Massachusetts, to monitor pilot-scale
testing of a hydraulic-fracturing method to install permeable reactive zero-valent
iron walls in unconsolidated sediments. The pilot-scale study was undertaken
to assess the feasibility of using zero-valent iron to remediate ground water
that is contaminated with chlorinated solvents at depths exceeding the range
of conventional iron wall installation methods. The pilot-scale test was conducted
at the site near the source area of Chemical Spill 10 (CS-10), a chlorinated-solvents
plume that underlies the MMR. Two iron walls 5 meters (m) apart and 12 m long
were designed to intersect the contaminated ground water at depths ranging
from 24 to 37 m below land surface.
A series of post-installation cross-hole CD radar-scanning surveys were conducted
in boreholes installed on opposite sides of the walls. The presence of iron
significantly reduces the radar-pulse amplitude and can be identified using
CD radar scanning. Significant decreases in cross-hole radar-pulse amplitude
were observed in field data after the iron walls were installed. Changes in
cross-hole radar-pulse amplitudes observed in the field data were compared
to results of two-dimensional finite-difference time-domain models used to
predict the effects of holes in the wall and wall edges. Analysis of these
data from the south wall indicates the presence of an irregularly shaped wall
about 8 m wide, extending from about 27 to 37 m below land surface. Analysis
of data from the north wall is presently underway.