METHODS OF
XX (XX) GPR Transect No./Year
INVESTIGATION
Birch Hill
GPR Transect
Road
Railroad
We have used several methods to
develop an understanding of per-
Tank Farm
0
200
400 m
mafrost distribution, ground water dis-
tribution and movement, and the area's
hydrogeology. These data are coupled
88 (94)
to in-situ, site-specific measurements
ad
Ro
ill
of ground water flow direction and ve-
H
h
rc
31 (93)
Bi
locity in monitoring wells.
Quarry
62 (94)
A
1 (93)
A'
65 (9
4)
100 (94)
Ground-penetrating
6 (93)
4)
)
50 (9
(93
11
radar (GPR)
2)
) 5 (9
(94
54
Ground-penetrating radar profiles
79 (94)
57
(94
N
)
were made along transects established
90 (94)
4 (93)
81 (94)
on existing trails in the Canol Road
8 (93)
34 (93)
3 (92)
area, some of which were cleared of
75 (94)
13 (93)
)
5 (94
5 (93)
6
)
recent vegetation by hydro-ax. Their
55 (94)
(94
Rd
58 (94)
70
9 (93)
r
ve
Ri
locations were subsequently surveyed
8 (93)59 (95)
(Fig. 6). We profiled each transect by
School
6 (93)
64 (94)
Che n
a
R
dragging antennas along the ground
5 (93)
13 (93)
4 (93)
behind a tracked vehicle at a constant
Tr
ai
Shannon Park
no
velocity of about 1 m/s. The antennas
rG
Subdivision
ate R ad
o
were situated approximately 67 m be-
ROLF
hind the vehicle. Event markers were
placed artificially on the records at 10-
m intervals. Scan durations, which are
Figure 6. GPR transects in the OU-3 area north of the Chena River.
related to depth, were set to encom-
Cross section AA' is illustrated in Figure 11.
pass the features of interest. Generally,
we used 600 to 1200 ns for profiles
with both 50- and 100-MHz antennas. The 1200-
rather than true depths. Borehole and GPR records
ns range penetrates approximately 40 m through
were subsequently combined to develop inter-
frozen ground, yielding data from the bottom
pretive cross sections of permafrost and aquifer
surface of permafrost. Scan durations of up to
distribution. Piezometric surface measurements
2000 ns were used with the 50-MHz antennas in
were also obtained from suprapermafrost, subper-
areas with much deeper (60-m) permafrost.
mafrost and unfrozen zone aquifers encountered
The radar system consisted of a Geophysical
by the drilling. Geologic logging of each borehole
Survey Systems, Inc., SIR Model 4800 control unit,
followed standard procedures.
assorted antennas, cables, a GSSI DT6000 digital
tape recorder, and a power supply. Appendix A
Monitoring wells
gives a more complete description of GPR meth-
Monitoring wells, generally in clusters of three
ods and theory.
at depths of about 10, 20 and 30 m, were drilled,
logged and developed for use with a ground wa-
ter flow system (see following section). Each moni-
Boreholes
We identified subsurface material types and
toring well cluster is located within thawed, per-
permafrost horizons by drilling boreholes in 1993
mafrost-free zones. Additional wells were drilled
and 1994. Drill sites (Fig. 7) were chosen accord-
to below permafrost into the subpermafrost aqui-
ing to the GPR data and preliminary interpreta-
fer and pressurized to prevent their closure by ice
tions of the site's geomorphic features based upon
growth (Fig. 8). Data from GPR surveys, borehole
ground observations and aerial photography. Geo-
logs and geomorphic features, and other geologi-
logic logs provided data necessary to quantify
cal data were used to select monitoring well loca-
GPR records, which provide vertical depths in
tions and provide representative ground water
terms of times of signal returns in nanoseconds,
flow data.
6