In geological settings where the water table is a subdued replica of the ground surface, cokriging can be used to estimate the water table elevation at unsampled locations on the basis of values of water table elevation and ground surface elevation measured at wells and at points along flowing streams. The ground surface elevation at the estimation point must also be determined. In the proposed method, separate models are generated for the spatial variability of the water table and ground surface elevation and for the dependence between these variables. After the models have been validated, cokriging or minimum variance unbiased estimation is used to obtain the estimated water table elevations and their estimation variances. For the Pits and Trenches area near Oak Ridge National Laboratory, water table estimations along a linear section, both with and without the inclusion of ground surface elevation as a statistical predictor, illustrate the advantages of the cokriging model.

The authors are very grateful to the many people who made this work possible. The many efforts of Kip Solomon and RaNaye Dreier facilitated the work of this project. Kip • Solomon and Norman Farrow designed the packer/pressure transducer assembly that allowed us to monitor pressure variations in the deep wells with high resolution. Scott Gregory assisted with setting the pressure transducers and with data logging and de,',nloading. Bob Kennard and Kim Davis helped in the logging of the deep wells. Andy Hunt assisted with setting the packers. Kip Solomon and Andy Hunt designed the purging system of the deep wells. Tom Zondlo and Scott Gregory prepared Figs. 1 and 7, respectively. RaNaye Dreier,

Various geologic, hydrologic, and geochemical methods were used to assess active ground‐water circulation in a brine‐filled, deep (> 50 m below land surface) aquitard underlying the Oak Ridge Reservation, Tennessee. In places, the brine which was presumed to be stagnant in the past, contains various contaminants. If ground‐water circulation is viable in the brine‐containing formations, then remediation or containment of the deep‐seated contaminants should be considered a high priority. Data used to determine this included (1) spatial and temporal pressures and hydraulic heads measured in the aquitard, (2) hydraulic parameters of the formations in question, (3) vertical temperature gradients, and (4) spatial and temporal chemical and isotopic composition of the saline ground water. Conclusions suggest that the saline water contained at depth is not isolated (in terms of recharge and discharge) from the overlying active and fresh‐water‐ (< 500 mg/1) bearing units. Consequently, influx of young water (and contamination) from land surface does occur. Potential discharge into the shallow aquifers was assumed where the hydraulic head of the saline water was higher than that in the shallow aquifers, accounting for temperature and salinity anomalies observed close to land surface. The confined water (and dissolved solutes) move along open conduits at relatively high velocity into adjacent, more permeable units.

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