A protocol for assessing the biotreatability of hydrocarbon contaminated exploration and production site soils

It is estimated that there are over 260,000 natural gas production wells in the continental United States. At many of these locations, production or reserve pits exist which may require remediation depending on several conditions such as : the manner in which they were initially closed ; whether or not they were lined ; and the local climate, soil type, and depth to groundwater. As part of the Gas Research Institute (GRI) research program on exploration and production (E&P) site remediation, a treatability protocol is being developed to facilitate the rapid assessment of the amenability of the contaminated soils to remediation by biological processes. This paper describes the treatability protocol and the results of a series of treatability tests on a spectrum of hydrocarbon contaminated E&P soils collected from various operating locations throughout the United States. The soils are subjected to physical and chemical characterization prior to treatability testing. Potential biotoxic characteristics of the soils are determined by a respirometry screening technique. Presuming that the soils are not toxic to aerobic soil microorganisms, 20 percent by weight aqueous slurries of the soils are prepared and subjected to continuous batch aeration for a six week period. Conditions favorable to microbial growth are maintained in the reactors by monitoring and augmentation as needed of pH, microbial nutrients and oxygen for microbial respiration. The extent of microbial degradation of the contaminant hydrocarbons is monitored by periodic measurement of total petroleum hydrocarbons (TPH), oil and grease, and individual hydrocarbon compounds as determined by gas chromatography. Microbial plate counts are prepared to document the biological viability of the treatment process. This paper includes the treatability results obtained from subjecting a number of E&P pit soils to the treatability protocol. The factors influencing the amenability of these soils to bioremediation as determined from the test results are discussed.