Petrologic, Mineralogic, and Ion Exchange Characteristics of the Rome Formation and Pumpkin Valley Shale on the Oak Ridge National Laboratory Reservation, Oak Ridge, Tennessee

Two outcrops of the Rome Formation and lower Conasauga Group, located on the Oak Ridge National Laboratory Reservation were studied with respect to their petrologic, mineralogic, and ion exchange characteristics. Twenty-eight sample pairs (a pair consisted of a fresh and weathered segment) were taken from each outcrop.

The agrillaceous samples were analyzed by x-ray diffraction and the remaining samples by thin section analysis. Using an ammonia electrode, CEC values were determined for all argillaceous samples and selected non-argillaceous samples. Porosity determinations of the fresh segments of the sandstones and siltstones were made, using 100to 12 micron thick petrographic sections.

X-ray analysis established the presence of illite, glauconite, kaolinite, chlorite, biotite, muscovite, quartz, hematite, calcite, dolomite, Kspar, and plagioclase. Quantification of the shales is complicated by the clay minerals, therefore data is strictly qualitative. The presence of randomly interstratified clays, discrete crystallites, or a combination was suggested by a few broad peaks on the diffractograms. The exact nature of these peaks was undeterminable in this study.

For the argillaceous samples, CEC's ranged from 5.52 to 33.61 meq/100g. A few sandstones analyzed generally had values at or below the lowest value of the siltstones. Clay mineral content (by visual estimates) appeared to be directly proportional to CEC values.

Quartz, Kspar, matrix, cement (quartz overgrowths, hematite, calcite), glauconite, plagioclase, muscovite, and biotite were the mineral components of the sandstones and siltstones. Based on modal analysis, the flowoing "average" composition for all non-argillaceous samples was calculated: quartz-58%, Kspar-20%, matrix-10%, cement-4%, glauconite-3%, plagioclase-2%, muscovite-1%, miscellany-1%, and biotite-trace.

The "typical" Rome sandstone is mature, well-sorted, subarkosic, and a very fine sandstone to silty sandstone. Sandy siltstones to silty sandstones, which were moderately sorted immature, are the "average" non-argillaceous unites of the Conasauga.

The porosity of the samples examined can be attributed to four factors: deterioration of glauconitic and micaceous grains, microscopic voids, discontinuous microscopic cracks, and macroscopic fractures. Values ranged from 0-10%. A notable difference was observed in the average porosities between samples from the two outcrops: 0.7% at the Comparative Animal Research Lab and 3.7% at the Fuel Reprocessing Road Outcrop. The slightly higher degree of weathering at the FR location is believed responsible for the sizeable variations.

Samples from the fresh and weathered segments of all lithologies exhibited little or no mineralogical variation.

The data gathered in this investigation provide information concerning the lithologies directly at or adjacent to waste burial sites. From this data, it is possible to assess the potential for the development of an aquifer, should any material seep from the Pumpkin Valley Shale (where some waste is buried) into the Rome Formation. The uppermost portion of the Rome (thick layers of sandstones) is bound above and below by shale layers. In the event of seepage of waste fluid, shales are significantly more effective in removing cations than sandstones, and are fairly impervious. If any fluid does reach the Rome sandstones, it is unlikely that an aquifer would develop, since the sandstones have low absolute porosities, thus suggesting low permeabilities.