Organic compounds in soils and sediments from unlined waste disposal pits for natural gas production and processing

Abstract

Samples of soil in dry waste pits and of sediment from waste pits currently in-use for natural gas production in the San Juan Basin of northwest New Mexico were collected for characterization of the presence and concentration of organic compounds. Samples were dried at 25 °C and about 50 g were extracted successively in a Soxhlet apparatus using hexane, benzene, and methanol. Extracts were filtered and condensed to 10 mL. Analyses of hexane extracts of samples using high-resolution gas chromatography showed presence of a complex mixture of 40 to 50 organic compounds in dry soil and in sediment from in-use pits. The range of size for compounds was C10 to C25. Although no compounds were detected in GC analyses of subsequent benzene and methanol extracts of the same soil samples, these extracts were highly colored and contained 5 to 10% of total absorptivity at 254 nm. Total extractable residues in the hexane extracts ranged from 49 to 110 mg g−1 of soil. Polycyclic aromatic hydrocarbons were detected in hexane extracts at concentrations of 270 to 870μg g−1 of dry sample.