GEOCHEMICAL CHARACTERISTICS OF LEACHATE FROM THE MARCELLUS SHALE, OTSEGO COUNTY, NEW YORK; RESULTS OF A 100-DAY LABORATORY TEST

The potential environmental impacts of natural gas drilling in the Marcellus Shale have caused considerable public concern in New York State. One of the principle concerns is the potential for metals to be leached from drill cuttings, and the migration of this leachate into surface water and/or shallow groundwater. The purpose of this project is to characterize the geochemistry of leachate produced from Marcellus Shale over time. Three weathered rock samples were collected from the basal layer of the Marcellus Shale exposed in a road cut along U.S. Route 20 in Cherry Valley, New York, at the northern most boundary of the Allegheny Plateau. Samples were crushed by hand to a pebble size with a diameter ranging from 4.00 mm to 12.7 mm. X-ray fluorescence techniques identified the whole-rock composition of metals (i.e. Fe, Mn, Mg, Na, Cl, Ba, Sr, K, As, and Ca) in each sample prior to leaching. In the laboratory, 1000 mL of water was percolated through approximately 10 grams of crushed sample. The resulting leachate was collected and re-percolated through the sample once a day for 100 days at 25 °C. Water samples were collected at 25-, 50-, 75-, and 100-day intervals and analyzed for pH, electrical conductivity, dissolved metals (i.e. Fe, Mn, Mg, Na, Cl, Ba, Sr, K, and Ca) using an ICP-ES, anions (i.e. SO₄ and Cl) using an adsorption spectrophotometer, arsenic using a Hach test kit, and carbonate alkalinity by titration. The mobility of metals from drill cores will be determined by comparing the dissolved concentrations to the whole-rock concentrations for each species. The dissolved concentrations will also be compared to New York State water quality guidelines to identify potential contaminants of concern associated with Marcellus Shale drill core leachate.