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Fate of the MTBE Plume

During the early stages of the investigation, vapor issues were evaluated in cooperation with the County health department. This was accomplished by sampling the indoor ambient air in homes located either in close proximity to the source, or those in which contaminated water was actively seeping into the basement. After a thorough sampling program, the health department concluded that vapors were a potential concern only in those homes located within the area of sorbed contamination and in those where contaminated water was entering the structure.

Exposure Pathways: As the investigation proceeded the water table declined, effectively eliminating the concern of vapors associated with impacted water within a residence. The potential for vapor transfer from the groundwater plume was reduced with distance from the source, as clean water from recharge accreted above the plume. Groundwater ingestion had not been a concern since there were no public or private wells within the existing or projected path of the plume.

There was, however, a surface water boat channel located approximately 1,000 feet downgradient from the edge of the MTBE plume. Since the regulatory limit for discharge of MTBE to surface waters (marine or fresh)at this site is 50 ppb, this pathway would have to be evaluated before developing a remedial plan for the site.

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