Summary
Drilling operations for unconventional gas reservoirs generate large amounts of drill cuttings for landfill disposal, in-situ burial and reuse as road fill. Understanding the leaching characteristics of drill cuttings under different geochemical conditions will assist in making waste management decisions. In this study, leaching experiments to simulate different disposal scenarios were conducted on one Marcellus shale outcrop sample from NY, one oil-based and two water-based drill cuttings from PA and WV. These experiments include: (1) short-term leaching tests, such as the Toxicity Characteristic Leaching Procedure (TCLP) simulating leaching conditions in municipal solid waste landfills at different pHs, the Synthetic Precipitation Leaching Procedure (SPLP) simulating leaching exposed to acid rain and extraction tests using real rain water; (2) 10-time TCLP test to evaluate long-term release from acetogenic landfill conditions at different pHs. Our results indicate that all drill cuttings passed regulatory SPLP and TCLP for in-situ burial and landfill disposal. High release of total dissolved solids (e.g., Na, Ca and chloride) released at g/L level became the major environmental concern on water quality for short-term leaching from drill cuttings. In-situ burial may result in a lower potential effect on water quality, as trace metal release from TCLP is 10 times higher than that from SPLP. The 10-time TCLP test revealed that Ba, Co, Ni, Cu, Pb and Zn were of longterm release concern. The oil-based drill cutting released more oxyanions (e.g., As, Sb, Mo, V) compared to the other samples. This research improves the understanding of heavy metal mobility from different types of drill cuttings under different disposal scenarios and can inform future waste management options for drill cuttings.
