Surgical Site Closure: Integrating Natural Attenuation and Focused Source Treatment (PDF)

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“Surgical site closure” is an innovative remedial strategy designed to intelligently integrate natural attenuation, risk-based cleanup goals, and focused source removal/treatment to cost-effectively remediate hydrocarbon-impacted sites. The first step in a surgical site closure is to develop a thorough understanding of site-specific groundwater geochemistry, via an evaluation of the presence and relative contribution of intrinsic bioremediation processes. The primary intent of this initial step is to demonstrate the stability or regression of a dissolved-phase groundwater plume, eliminating the need for off-site or plumewide remedial efforts and/or plume containment. Application of risk assessment principles, including a detailed evaluation of potential receptors and associated exposure pathways and possible development of site-specific, risk-based cleanup objectives, is the second key component in the surgical site closure process. In many cases, actual potential receptors are limited, and/or potential exposure pathways are incomplete, resulting in a significant reduction in risk and facilitating a much less aggressive closure approach. The third step in the surgical site closure process involves focused source removal (e.g., soil excavation), where necessary, accompanied by enhanced aerobic biodegradation to degrade the remaining dissolved-phase groundwater impacts to concentrations at or below closure levels.

“Surgical site closures” have been completed at nine sites, and are in progress at 10 additional sites in Indiana for a major oil company. Groundwater geochemistry evaluations demonstrated plume stability and eliminated the need for remediation of off-site groundwater impacts, but also demonstrated that most of the dissolvedphase plumes were predominantly anaerobic, supporting the use of enhanced aerobic biodegradation to accelerate remedial efforts.

Limited, focused soil excavation then successfully eliminated or significantly reduced the source area(s) for groundwater impacts at all of the sites. Oxygen release compound (ORC) slurry injections were subsequently completed in and near the source areas and resulted in reduced target constituent concentrations in groundwater at nearly all of the sites. Necessary data were collected during remedial activities to permit use of Indiana’s proposed Risk-Integrated System of Closure (RISC) policy, as appropriate, when it becomes effective.

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