Theme: 06. Petroleum and Heavy Hydrocarbon Site Strategies

Topic Area: 6c. LNAPL Recovery/Remediation Technology Transitions

Formatted Title:

Reevaluating Mass Removal Efficiency Metrics Using Environmental Footprint Data

Background/Objectives:

A primary objective of sustainable remediation is to remediate contaminated sites using the least impactful technologies available to provide the most overall protection to human health and the environment. This study looked back at mass removal data for soil and groundwater remediation systems at petroleum-contaminated sites and the environmental footprint data, primarily greenhouse gas (GHG) emissions, associated with each system’s operation, maintenance, and monitoring (OM&M). The objectives were to retroactively measure environmental footprint metrics, such as GHG, per mass of contaminant removed for individual systems over time to compare the ratio of remediation footprint per mass removal for different systems and sites.

Approach/Activities:

Various sites were included in this evaluation, including bulk fuel storage and distribution terminals and underground storage tank (UST) gas station sites. The remedial technologies that were evaluated included dual-phase extraction (DPE), soil vapor extraction (SVE), oxygen injection (OI), in situ chemical oxidation (ISCO), monitored natural attenuation (MNA), and natural source zone depletion (NSZD).

Contaminant mass removal was calculated using different methods. DPE and SVE mass removal rates were calculated using standard equations for vapor-phase contaminant removal and results of laboratory vapor samples. ISCO mass removal was calculated based on the mass of the applied oxidant and stoichiometric balancing. To estimate contaminant degradation via OI and MNA, the Ricker Method^® of Groundwater Plume Analytics was used to calculate changes in groundwater contaminant mass over time. Environmental footprint metrics for each technology/site were measured using SiteWise™.

Results/Lessons Learned:

Environmental footprint data provide an additional line of evidence to aid in determining when to shut down remediation systems or transition to lower energy technologies. For the systems included in this evaluation, there was significant variation in the magnitude of GHG emissions per unit of hydrocarbon mass removal. This was often related to the specific objective of the system and where it was designed to operate in context of the release (i.e., source area, plume, boundary/plume control). The results also showed variability in the rate of increase in emissions over the lifespan of the system, ranging from a factor of 2 to over 14. Tracking and reporting these metrics can be useful in determining when the external environmental effects of system operation exceed the benefits of continued remediation.

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Chris Schultz