A sudden heating oil release occurred below a concrete slab of a residence in Massachusetts. The oil entered an open sump in the basement and migrated to a nearby stream. Remediation included deployment of absorbent booms, limited soil excavation, and in-situ treatment with hydrogen peroxide. Soil, sediment, groundwater, and indoor air samples were analyzed to delineate the extent of contamination, verify that remedial efforts were successful, and determine if a vapor intrusion pathway existed. Indoor air samples were collected on three events: at the time of release, after remedial activities, and four months later.

Indoor air analytical results were compared to the new draft Threshold Values published by the MassDEP Indoor Air Working Group (June 2008). In each sampling event, various compounds were detected above the applicable Threshold Values. As suggested by the MassDEP, multiple lines of evidence were investigated to determine whether the exceedances were attributable to the release. The presence of mothballs, the construction and operation of the home heating system, analytical evidence of a potential historical release, and soil and groundwater analytical data were used as lines of evidence that a vapor intrusion pathway did not exist.