The Delaware Basin is a broad asymmetric sedimentary trough in southeastern New Mexico and west Texas. Basin subsidence occurred from the Pennsylvanian into the Triassic. The basin also underwent tilting since the early Cenozoic. Layered evaporite units of Ochoan age in the basin are 1000 m thick. These evaporites are divided into three stratigraphic units (listed in order of increasing age): the Rustler Formation, the Salado Formation, the Castile Formation. These units, especially the Castile, are deformed along portions of the margin of the Delaware Basin and in some areas internal to the basin. In the northern Delaware Basin adjacent to the WIPP site, the term "Disturbed Zone" (DZ) has been applied to an area in which deformation structures are found in boreholes and from which chaotic seismig reflection data were obtained. The origin and timing of this deformation is considered important for the determination of This docunlent is PUBLI&'L%7 RELEASABLE Authorizing Official Date: 81/31 / W O d

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Data from selected drill holes spaced at intervals of 1.5 to 15 km (5,000 to 50,000 ft) in southeastern New Mexico demonstrate a progressive removal of halite by dissolution, hydration of anhydrite to gypsum, and removal of gypsum by dissolution in the Permian Rustler Formation. Thickness of the Rustler decreases as halite is removed, but increases after complete removal due to the hydration of anhydrite to gypsum.

Drillhole DOE-2 was drilled to investigate a structural depression marked by the downward displacement of stratigraphic markers in the Salado Formation -2 mi north of the center of the WIPP site. This depression was named informally after the shallow borehole FC-92 in which the structure was described. The presence of the depression was confirmed by drilling. Contrary to several hypotheses, halite layers were thicker in the lower part of the Salado, not thinner as a result of any removal of halite. The upper Castile anhydrite in Drillhole DOE-2 is anomalously thick and is strongly deformed relative to the anhydrite in adjacent drillholes. In contrast, the halite was t 8 f t thick and significantly thinner than usually encountered. The lower Castile anhydrite appears to be normal. The depression within the correlated marker beds in the Salado Formation in Drillhole DOE-2 is interpreted as a result of gravity-driven deformation of the underlying Castile Formation.Several stratigraphic units were hydrologically tested in Drillhole DOE-2. Testing of the unsaturated lower portion of the Dewey Lake Red Beds was unsuccessful because of exceptionally small rates of fluid intake. Drill-stem tests were conducted in five intervals in the Rustler Formation, over the Marker Bed 138-139 interval in the Salado Formation, and over three sandstone members of the Bell Canyon Formation. A pumping test was conducted in the Culebra Dolomite Member of the Rustler Formation. Pressure-pulse tests were conducted over the entire Salado Formation. Fluid samples were collected from the Culebra Dolomite Member and from the Hays Member of the Bell Canyon Formation.