From the mid 1800s through early 1900s, before natural gas was available as an energy source, manufactured gas plants (MGPs) were operated throughout the United States. These plants used coal, coke and oil to produce gas for lighting, heating and cooking. At that time, this technology was a major step forward as it revolutionized street lighting, enhanced public safety, and enabled businesses to work into the night.

In addition to gas, the manufacturing and purification processes at these plants yielded byproducts or residues that included tars, sludges, lampblack, light oils, spent oxide wastes, and other hydrocarbon products. Most of the MGP sites were closed and dismantled more than 50 years ago, however research conducted by the U.S. Environmental Protection Agency found that contaminated residues remained at many of the abandoned sites and required remediation.

SME has extensive experience providing services at former MGP sites for energy companies. We have conducted remedial investigations, defined the extent of MGP residual and non-aqueous phase liquids (NAPL, light and dense), performed risk evaluations, evaluated remedial alternatives, and implemented selected remedies. Risk evaluations were performed to adequately characterize sites and involved evaluating the risk to relevant pathways,, including drinking water, direct contact, indoor air inhalation (vapor intrusion), ambient air inhalation, and surface water. Remedial investigation activities have also included geotechnical surveys, soil borings, use of vertical profiling technologies, laser induced fluorescence, rotosonic drilling, monitor well installation and sampling, multilevel piezometers, surface soil sampling, soil gas sampling, and sub-slab vapor sampling. Remedies have included:

  • In situ remediation – in situ chemical oxidation and air sparging to treat contaminated soil and groundwater
  • Excavations – planned, developed specifications, and monitored the removal of tens of thousands of tons of impacted soil and sediment, many under challenging geotechnical conditions.
  • Geotextile tubes – to facilitate sediment dewatering as part of dredging efforts, treated dredged slurry with ionic polymers prior to discharge into geotextile tubes, which allowed for the discharge of millions of gallons of effluent water into public waste water treatment facilities without additional treatment
  • Storm sewers – assessed, excavated, and replaced or repaired affected storm sewers, including the use of cured in-place pipe lining material.
  • Exposure barriers – developed caps of soil and gravel covers or asphalt and concrete pavements to prevent direct contact with contaminated soil
  • Restrictive covenants – developed pioneering language for clients of impacted sites

SME is currently assisting clients in completing remediation of their former MGP sites. As part of our efforts, we are assisting with the use of cost models to help with financial planning for characterization, remediation and monitoring. We are also preparing No Further Action (NFA) submittals for those sites ready for closure.

SME has provided services for a total of ten former MGP sites in the Midwest.