Millions of tons of drill cuttings generated from Marcellus shale gas development are currently disposed of in landfills, buried in-situ, or reused as road fill. This study conducted advanced solids characterization and leaching tests to allow consideration of more diverse disposal environments. Drill cutting samples with different mineralogical traits (e.g., high in pyrite and carbon, or high in calcite) from the lateral portion of Marcellus shale well in WV were studied. Solid characterization (e.g., elemental distribution and mineral composition) and geochemical leaching experiments (e.g., rainfall vs. landfill, wet vs. dry conditions) were conducted to evaluate trace metal mobility under different disposal scenarios. The effects of added drill cuttings on soil quality, plant germination and long-term plant growth were determined in the laboratory and on a building green roof. Results showed that although drill cuttings passed the regulatory short-term leaching tests for landfill disposal, long-term release of Ba in all samples and release of As, Ni, and Sb in high pyrite and low calcite samples were of environmental concern under simulated rainfall conditions. Selected trace metal release (e.g., Ba, V, Mo, Sr and Sb) increased 2–10 times when waste was first air-dried and subsequently underwent simulated rainfall leaching. Residual salt content in drill cuttings inhibited plant seed germination, but plant growth on green roofs in cuttings-amended soil was not inhibited once soluble salts were leached by rainfall. Our characterization better informs waste managers of the different geochemical factors that control trace metal release from drill cuttings and improves the ability to assess proposed methods of solid waste characterization and handling. Novel commercial uses, such as the addition of drill cuttings to green roof soils to offset costs, can be considered if the long-term safety of the material can be demonstrated.
Unconventional Marcellus shale gas development is extensive in the state of Pennsylvania, where 16,078 unconventional wells are permitted and 9,324 unconventional wells were drilled from 2004 to March 31, 2015 [1]. It has been estimated that over 2000 tons of Marcellus shale drill cuttings are produced from a typical 6000-ft horizontal well-drilling operation [2, 3]. As a result, millions of tons of drill cuttings generated from Marcellus shale gas development are currently disposed of in landfills, buried in-situ, or reused as road fill [3]. However, current waste management practices only focus on application of one regulatory test for waste evaluation, USEPA Method 1321 [4] simulating landfill conditions, and has not explored the potential for land application. These drill cuttings consist of residual drilling mud containing high barite (BaSO4) and fine-grained black shale rock cuttings, rich in organic matter and pyrite [5]. Secondary release of trace metals or barium from drill cuttings may be of environmental concern under different disposal scenarios.
