Reports
Geologic and hydrologic data from two core holes drilled through the Aquia Formation (Eocene-Paleocene), in Prince George's and Queen Anne's Counties, Maryland
1977, Harry J. Hansen
Miscellaneous Open File Report
Introduction
A start was made by Kapple and Hansen (1976) to develop a digital simulation model of the Aquia aquifer. It became apparent during the early stages of the investigation that the hydrologic properties of the confining beds were poorly known. Inasmuch as leakage through the confining beds represents an important source of recharge, a range of field-collected hydraulic conductivity and specific storage values were needed to make realistic trial runs during calibration of the model. In addition, relatively undisturbed cores were needed to investigate the transmissivity trends previously mapped by Hansen (1974) using geophysical logs, drillers’ logs, and drill cutting descriptions.
Core hole sites were selected in Prince George’s and Queen Anne’s Counties so that two distinct facies of the Aquia Formation could be sampled. Furthermore, since unconformities occurring between the two sites caused stratigraphic changes in the overlying units, two sets of upper confining bed data could also be collected. It should be noted that both sites were located near the Aquia outcrop to minimize drilling costs. To avoid sampling recently weathered materials, however, all cores were taken from below the water table.
The first core hole (PG-Df 35) was drilled in Prince George’s County during November and December, 1972 and was located approximately one mile south of the intersection of U.S. Rt. 301 and Md. Rt. 214 on vacant county land adjacent to Old Leeland Road (lat 38°52'59”N.; long 76°43'27”W.) (pl. 1). The Queen Anne’s County core hole (QA-Bg 54) was drilled in a sanitary landfill located southwest of Millington (lat 39°14'10”N.; long 75°51'12”W.) during September and October of the following year.
Core hole PG-Df 35 was drilled to a depth of 199.5 feet by National Foundation Engineering, Inc. of Lutherville, Maryland, in association with Allstate Drilling Co., of Providence, Rhode Island. It was planned to core continuously in three foot increments using a three-inch diameter, double-wall rotary core barrel (Denison barrel). Recovery was very good to a depth of about 145 feet. Below 145 feet a combination of formational and mechanical problems resulted in only sporadic recovery. A galvanized “stove-pipe” sleeve with a crimped seam was used as a liner in the inner tube of the Denison core barrel. Thus, the core could be extruded at the site simply by parting the seam with hand tools. Each core was then measured, described, wrapped in plastic, and stored in wooden boxes. In addition several Shelby samples were obtained by pressing 3 in x 2 ft steel tubes into the finer-grained confining beds above and below the Aquia Formation. Each Shelby tube was sealed at the site after inspecting the ends of the core to verify that “undisturbed” formation had been sampled. The Shelby samples were later sent to the U.S. Geological Survey Hydrologic Laboratory in Denver, Colorado, for testing.
Boring QA-Bg 54 was drilled to a depth of 310 feet by the Delmarva Drilling Co., Inc. of Bridgeville, Delaware. After setting casing through the Pleistocene, specifications required that five-foot Denison cores (5 in O.D.) be cut at 10-foot intervals until total depth was reached. Drill cuttings were also collected. Full core recovery was never realized but sufficient material (one to two feet) was generally retrieved to meet the objectives of the project. The Denison barrel was operated both with and without a brass sleeve (liner). Recovery was usually better with a sleeve in the barrel, but hydraulic extrusion of the core at the site was often impossible. In some cases the sleeve had to be cut longitudinally with an acetylene torch to the free the core. Again, as in PG-Df 35, several Shelby tube samples were obtained for hydrologic analysis. In addition parts of several Denison cores were left in the brass liners so that they could also be used for this purpose.
Geophysical logs were run in both core holes by the U.S. Geological Survey. Single-point resistivity, self-potential, and natural gamma ray logs were obtained from each hole. In addition the Birdwell Division of Seismograph Service Corporation ran a neutron log and a gamma-ray density log in QA-Bg 54 (pl. 1).
