Chemical Oxidation to Achieve Site Closure
A petroleum marketer made the business decision to close an existing retail operation and relocate its convenience store and gas station operations, including the site’s underground storage tanks (USTs). Management of environmental liabilities dictated closure of an existing petroleum release case as soon as possible. State regulators had disapproved a proposed remedial action plan developed by the client’s previous consultant. An innovative, least-cost yet effective approach was required to meet the company’s business objectives.
Closure sampling had reported concentrations of petroleum constituents (benzene and MTBE) in exceedance of the state residential limits. GES recognized that site lithology and conditions appeared receptive to treatment via aggressive in-situ chemical oxidation injection (ISCO). Average depth to groundwater was 12 feet, with an average overburden thickness of 28 feet. Overburden materials consisted of sandy gravel, silty clays, sand, and cobbles. GES’ patented HypeAir injection technology was demonstrated to stakeholders – client, regulator, and state UST reimbursement fund – as an effective remediation method that would eliminate the need for an installed system at the site.
The ISCO solution was pilot-tested, using mobile injection technology to inject hydrogen peroxide, air, and oxygen into the subsurface through two new injection points. Soil vapor extraction technology was used to prevent ozone accumulation near the station’s underground structures.
Dissolved oxygen, temperature, pH, and oxygen reduction potential in groundwater were evaluated prior to and following the pilot study injection event. Three months after the injection event, groundwater samples demonstrated decreased levels of the petroleum contaminants and increased levels of oxygen in groundwater. Based on these results, GES completed three additional ISCO injection events, utilizing six injection points at key locations across the site. Following ten quarters of attainment sampling, the site had achieved the statewide regulatory health standards and the state granted “no further action” classification to the site.
Successful management of similar retail petroleum sites enabled GES to efficiently evaluate site conditions and to develop and implement an approach that met the needs of various stakeholder groups. By using mobile HypeAir technology, the client avoided the need to invest in an installed remediation system. The non-operational liability was removed from the site with limited cost to the client or to the state UST fund.