GEOCHEMICAL IMPLICATIONS OF DRILL CUTTINGS ON LANDFILL LEACHATE FROM UNCONVENTIONAL ENERGY DEVELOPMENT IN THE APPALACHIAN BASIN

Unconventional drilling for oil and natural gas within the Appalachian Basin produces millions of tons of drill cuttings that are disposed of in landfills. For this study, dry drilled cuttings from Tioga County, NY that included the overlying undifferentiated Hamilton Group and the Marcellus Shale drilling target were selected for analysis. Leaching methods included TCLP (Toxicity Characteristic Leaching Procedure, a dilute acetic acid leach) which many landfills require before accepting drill waste. A modified BCR (Community Bureau of Reference) sequential extraction (a determination of acetic acid soluble, reducible, and oxidizable fractions) was also used to further characterize leaching behavior. The acetic acid leaching experiments were designed to simulate percolation through landfills and involved collection and analysis of the leachates at 1, 7, 30, and 120 day intervals. The concentrations of elements in the leachates were measured using ICP-OES. From the BCR results the elements primarily liberated by the acetic acid were Ca, K, Mg, Mn, Na, and Sr; while the reducible component contained more Al, As, Ba, Cr, Pb, V and Zn; and the oxidizable fraction released most of the Cd, Co, Cu, Fe, Ni, and Sb. The results of the acetic acid leach indicate that most elements were quickly released (1-day leach); whereas the concentrations of Al, Co, Ni, and Zn increased as the leach duration progressed. Notably, higher levels of elements of interest were released by the Hamilton Group cuttings (Al, Ba, Co, Fe, K, Mn, Pb) rather than the Marcellus Shale cuttings (Ca, Cd, Cu, Mg, Mo, Ni, Sr, Zn); suggesting that in some cases element concentrations in landfill leachates could be strongly influenced by drill cuttings from other formations besides the Marcellus. This investigation suggests that the mineralogy of the cuttings and the pH of the leachate are both significant factors in controlling element solubility related to mineral dissolution and lithological dependent adsorption-desorption kinetics.