Loring Air Force Base

A major contaminant present at the Loring site was tetrachlorethylene (also called perchloroethylene (PCE), with additional fuel-related compounds such as benzene and toluene. EPA regulates PCE in public drinking water supplies and has established a maximum contaminant level (MCL) for drinking water at five parts per billion (ppb).

At the Loring site, Steam Enhanced Remediation (SER) was applied to fractured bedrock to remediate the contaminants that were present in the form of dense non-aqueous phase liquids (DNAPLs). Contamination in fractured bedrock has historically been very challenging to address, because fractures allow contaminants to move through rock formations, limiting the ability of standard remediation systems to capture them. DNAPLs are particularly challenging to remediate in groundwater because they exhibit:

• Low viscosities which allow them to migrate rapidly in subsurface
• Low solubilities which allow them to sink to the base of aquifers where they form pools that can remain in place for many years.
• Low degradability which gives them the potential to remain in groundwater for a very long time

The SITE program demonstration looked at the ability of SER to remediate the contaminants that were present with particular interest in its utility in fractured rock environments. Bedrock at the Loring site was sparsely fractured and had low transmissivity, limiting the ability of steam or other materials to penetrate the fractures and to move contaminants from the fractures into the aqueous phase from which they could be captured or removed. SER is an in-situ thermal cleanup technology that reduces organic contaminants. Steam is injected into the contaminated area and vapor, water and contaminants are removed from the extraction wells. The system showed limited effectiveness early on; however, after approximately three weeks of operations, the extraction rates increased and continued to increase for the duration of the project.