USING PXRF IN CONJUNCTION WITH OTHER TECHNIQUES TO ANTICIPATE METAL RELEASE FROM DRILL CUTTINGS OF THE MARCELLUS SHALE

Analysis using a Bruker Tracer III portable XRF was used in consort with a suite of techniques to anticipate the extent to which metals from Marcellus Shale drill cuttings and surrounding units are affected by drilling operations and subsequent disposal. 10 m composite samples from 600 m of stratigraphic section were obtained using dry drilling techniques. The samples were analyzed using the portable XRF to quantify total metal concentrations for 28 elements using shale specific calibration techniques. The samples were microwave digested in a 1% HCl and 10% HNO₃ solution to determine acid extractable metal concentrations under elevated temperature and pressure conditions. The drill cuttings were also leached under anaerobic conditions using either 1% HCl or deionized H₂0 to determine the quantity and kinetics of metal release under conditions that simulate typical drilling operations and landfill disposal after one, thirty, and 120 days of leaching. The combination of these analytical techniques and XRD results were used to establish how mineralogy related differences affected metal concentration and subsequent release. The metal concentrations from the XRF results were examined using EPA Unmix 6.0 and Positive Matrix Factorization (PMF) 5.0 statistical techniques to determine factors contributing to metal sequestration under changing depositional environment conditions and subsequent diagenesis in mudstone and carbonate units. Results indicate that the Marcellus Shale contains as well as releases larger amounts of As, Cd, Cu, Mo, Ni, and Zn than the surrounding rock units. The quantity of some of the metals that are released from drill cuttings into landfill leachate could have differing toxicology impacts on short and long term time scales because of pH related changes in mineral dissolution and desorption rates.