adjacent to the transmitter annex (Ecology and
northern edge of the Fort Richardson cantonment
Environment 1990, 1996). Subsequently, the Corps
(Fig. 6). The moraine runs from the Chugach
of Engineers contracted for the removal of 150 tons
Mountains to the east, extending along the north
of PCB-contaminated soil in 1988 and another 600
edge of Elmendorf Air Force Base and across Knik
tons in 1992. PCB-contaminated oils in the bun-
Arm into the Susitna Lowland. This moraine was
deposited between 14,000 and 13,000 14C years BP
ker complex were not removed, but the damaged
transformers were taken away and the bunker was
at the termination of the last major glacial
reportedly sealed.
readvance into the Knik Arm region (Reger et al.
In June of 1996, CRREL conducted a reconnais-
1995). The multiple ridges and terraces in the
sance survey of the Fort Richardson cantonment
moraine were formed by local fluctuations in the
area using ground-penetrating radar (GPR) to
ice margin and by discharging ice marginal
determine if it could delineate the subsurface
streams. The southernmost ridge represents the
geology (Strasser et al. 1996, Hunter et al. 1997).
maximum position of ice advance. The end-
As part of that study, the Roosevelt Road Trans-
moraine is composed of juxtaposed sequences of
mitter Site was analyzed to define the extent of
laterally discontinuous coarse gravel, fine well-
buried structures. This report presents the results
sorted sand, dense silt and clay, and diamictons
of these surveys and demonstrates the utility of
(mixed coarse to fine material with a fine-grained
GPR in defining buried structures.
matrix).
Surficial mapping by Yehle et al. (1990) shows
that the transmitter site is located on a kame-
terrace. Kame-terraces form as a result of water
SITE DESCRIPTION
running along the glacier margin, depositing long,
The Roosevelt Road Transmitter Site is located
narrow strips of sand and gravel between the gla-
on the northern side of the Elmendorf Moraine,
cier and local topographic highs (Fig. 6). Its sur-
about 1 km southeast of the Eagle River Flats and
face is generally smooth and gently sloping. Split-
3 km north of the main cantonment of Fort
spoon samples collected on-site record gravely
sand and silty to sandy gravel down to a depth of
Richardson. The bunker and transmitter annex are
located on a level, low-relief ridge at an elevation
about 15 m, with 10 to 30% silt and clay (Ecology
and Environment 1996). Further details on sub-
of 78 m above sea level. A gravel road, two large
surface materials cannot be assessed from the
concrete foundations, four small concrete pads,
existing borehole logs; however, rapid vertical and
and one concrete cesspool are located above
lateral changes in materials are common in nearby
ground (Fig. 2). A second cesspool is buried west
bluff exposures (e.g., Miller and Dobrovolny 1959,
of the bunker. The area was cleared of trees dur-
Yehle et al. 1990) and are typical of ice-proximal
ing site operations (Fig. 3). Following decommis-
deposits (e.g., Lawson 1979). The depth to ground
sioning, the site has revegetated with alder and
water at the transmitter site is near 54 m above
cottonwood. Growth is especially thick along the
sea level.
western edge of the bunker. Two sinkholes occur
there (Fig. 4); their openings are about 0.6 m square
and expose the concrete walls of utilidors. Rail-
road ties in the utilidor ceiling had collapsed, pos-
METHODS
sibly because of heavy vehicle traffic during the
1988 and 1992 remediations. The thick overgrowth
Ground-penetrating radar (GPR)
Our GPR system consists of a digital control
limited the westward extent of our radar analyses
unit (GSSI System 10+) and transducer manufac-
(Fig. 5). Other sinkholes were observed along the
tured by Geophysical Survey Systems Inc. (GSSI)
eastern and western edges of the transmitter
of North Salem, New Hampshire (Fig. 7). The
annex foundation, and the utilidor extending from
radar control unit was set to trigger pulses at a
the annex to a power hut to the north.
selected repetition rate of 50 kHz during the study.
The received radar signals were sampled in pro-
gressive time steps and converted to audio fre-
GEOLOGY
quency scans for display and storage at a rate of
32 scans per second. The scans were digitally
As mentioned above, the Roosevelt Road Trans-
stacked to improve signal quality and reduce the
mitter Site is located on the Elmendorf Moraine,
amount of stored information. Each recorded scan
which is a major topographical feature along the
3
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