Marathon Oil Company, of Houston, Texas, has reached an agreement with EPA Region 7 to conduct a cleanup study and implement a remedy for groundwater contamination at its former West Sidney Gas Plant in Sidney, Neb.
Under an administrative order on consent, filed in Kansas City, Kan., Marathon will first conduct a study of alternative remedies for the groundwater contamination, and then recommend one or more preferred remedies for addressing the contamination. EPA would then review the proposed remedy or remedies, and if the Agency approves, Marathon would proceed to develop a plan to implement the work.
Marathon will fund all costs associated with the study, the proposed remedy and the subsequent environmental remediation work, according to the order, which was issued under the authority of the federal Resource Conservation and Recovery Act (RCRA).
Marathon owns the property at 2829 Road 111, southwest of Sidney, where beginning in 1954 it operated the West Sidney Gas Plant, a facility that processed natural gas. The plant produced a variety of waste streams, including used absorption oil, wet glycol, produced water and an unidentified hydrocarbon liquid. Those waste streams were recovered or recycled at the facility, or were disposed into an onsite injection well, or from approximately 1964 to 1982, were disposed into three unlined surface impoundments at the site.
In 2003, EPA ordered Marathon to perform groundwater sampling, analysis and monitoring to determine the nature and extent of hazardous releases from the site. Sampling and monitoring have shown groundwater at the site to be contaminated with benzene, ethylbenzene, toluene, xylene and other light non-aqueous phase liquids (LNAPLs), which are organic substances that are relatively insoluble in water. Since 2003, the dissolved phase contamination of benzene, ethylbenzene and xylene has steadily decreased to below drinking water standards, although LNAPLs are still present.
Groundwater contamination from the former West Sidney Gas Plant has been identified in the Brule formation, an aquifer that serves as a source of irrigation water, livestock water and potable drinking water for farmers, ranchers and other rural users in the Lodgepole Creek drainage basin west of Sidney. The Brule formation also provides a portion of the municipal water supply for the City of Sidney, although municipal wells are not affected by the contamination.