Publications

Paine, J. G., Harris, S. T., and Phelan, J. M., 2004, Assessing groundwater perching horizons using synthetic, ground, and airborne TDEM data at the Pantex Plant, Texas, in Proceedings, Symposium on the Application of Geophysics to Engineering and Environmental Problems: Environmental and Engineering Geophysical Society, p. 874-889 (CD-ROM).
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 [Abstract in Word format]

At the U.S. Department of Energy's Pantex Plant near Amarillo, Texas, recharging groundwater encounters a perching fine-grained zone (FGZ) above the main Ogallala (High Plains) aquifer, which is a critical source of agricultural, municipal, and industrial water. In March, airborne geophysical surveys were conducted to measure the magnitude and variation of apparent electrical conductivity of the subsurface to help assess the extent and integrity of the FGZ. We obtained time-domain electromagnetic induction data along flight lines totaling 1,243 km in length within four survey blocks located north, east, south, and west of the main Pantex Plant.

Preliminary results include the observation that the conductivity structure beneath surveyed playa basins differs from that outside the basins. In particular, playas have high higher apparent electrical conductivities than do interplaya areas at shallow depths, and lower apparent conductivities at equivalent deeper depths. This observation is consistent with the dissolution-induced subsidence model of playa formation, where the shallow, more conductive material represents lacustrine basin fill with high clay content and the deeper, less conductive material may represent deposits disturbed by subsidence. These data will be integrated with available geological and hydrological data from survey area wells and borings to establish the relationship between stratigraphic and hydrologic characteristics and measured apparent conductivity.