20
data provide weak support of this interpretation; borehole data in the marsh would be needed
to further constrain stratigraphy beneath the marsh.
Table 2.1. EM-31 west transect data with distance in ft and conductivity in mS/m.
Zero feet is located at the west end of the transect (Fig. 2.5). The east transect was similar to
the west, indicating slight increase in clay content toward the center of the marsh and was
therefore not recorded.
Distance Conductivity  Distance Conductivity  Distance Conductivity
0         39         150        49        280         46
10         39        160        48         290        46
20        37.5       170         47        300        48
30         39        180         46        310        48
40         39        180         45        320        47
50         37        200        45         330        48
60         38        210        46         340        47
70         42        220        46         350        49
80        41.5       230        46         360        48
90        42.5       240         47        370        48
100        43         250        46        380         48
110        46         260        45        390         48
120-140    culvert     270         44        400        48
USGS well WK-1301 was drilled as part of an earlier study of the Troy Valley
(Batten and Conlon, 1993) near the edge of the marsh along the Fox River (Fig. 2.5). The
well log is very general, with descriptions such as "sand, silty fine, gravel". Therefore, we
logged gamma radiation so that it could be compared to the boring log. Fig 2.6 shows part of
the gamma log next to the older drilling log. The high counts correspond to clay, while low
values are sand or sand and gravel. The gamma log correlates well with the boring log.
From 87-125 ft the boring log lists "clay, sandy, gravel", while the gamma log indicates areas
within this depth range that have higher clay content, such as at 113-114 ft deep. The gamma
log also shows a high clay content region around 10-15 ft deep, which agrees with the EM-3 1
measurements in the marsh that show silt and clay.