Managing environmental risk has become an accepted cost of doing business. But a hazardous spill, leak or discharge has the potential to become an expensive, long-term problem. With proper site characterization and evaluation of remedial measures, these costs can be minimized.

In 1994, SME was hired to remediate a plume of natural gas condensate at a confidential natural gas compressor station in North Central Michigan. The contaminant plume, consisting of petroleum volatile organic compounds (VOCs), was venting into a river. At the time, plume venting was being addressed with a groundwater pump and treatment system, designed and installed by another consulting firm in 1991. Operation and maintenance of the system cost the client approximately $150,000 per year.

SME selected air sparging to remediate the source and main body of the plume. Air sparging involves injecting air into a contaminated groundwater zone. As the injected air moves horizontally and vertically, it “strips” the VOCs and provides oxygen to native bacteria which use the oxygen to reduce contaminants to acceptable levels. The initial remediation results indicated that air sparging could possibly replace the expensive groundwater pump and treatment system. SME obtained approval from the Michigan Department of Environmental Quality (MDEQ) to conduct a study to evaluate plume seepage control using air sparging.

SME’s study showed that the concentrations of petroleum hydrocarbons could be reduced to below groundwater surface water interface (GSI) criteria as set forth by the MDEQ. An air sparging system was installed at the site which increased the dissolved oxygen content of the groundwater. The increased oxygen levels promoted bacterial aerobic degradation of the contaminants. The use of air sparging reduced the clients operation and maintenance costs from $150,000 per year to $25,000 per year.

In 2007, SME upgraded the air sparging system to include a dissolved oxygen sensor. The oxygen sensor turns the air sparging system off and on, depending on the groundwater dissolved oxygen concentrations. This allowed operation of the air sparge system only when needed.

Currently air injection is only required for about two days out of about two weeks to maintain sufficient dissolved oxygen levels in the groundwater to degrade contamination. SME monitored groundwater concentrations in the spring and summer of 2015 in support of a No-Further Action (NFA) request.