Problem: Gasoline "free product" was found in a Telephone Company (TC) manhole. Inquiries made to the adjacent three service stations revealed that two of the three had some onsite contamination problems, however according to the assessments made by their Environmental Engineers, none of their contamination had migrated offsite. The presence of extensive concrete cover further complicated the determination of the source of the "free product". After suffering significant damage from the "free product" in their manhole, TC contracted Exploration Technologies, Inc. (ETI) to conduct a soil gas geochemical assessment over the street right-of-ways in order to determine the source of the gasoline.

Approach: A soil vapor survey was initially conducted over the street right-of ways in order to determine the likely sources. This initial survey indicated that both of the stations which had onsite contamination problems, also had offsite contaminant plumes. A failure to respond to this initial soil gas evidence required TC and ETI to go to court to obtain permission to extend the initial soil gas survey onto the adjacent properties owned by the service stations. This follow-up soil gas survey linked the gasoline contamination in the subsurface soils and groundwater on the stations to the offsite plumes. The soil vapor data were also utilized to determine if there were any "new" releases, or if the "free product" in the TC cable manhole was the result of older release(s) not previously delineated by the service stations Environmental Engineers during their assessments.

Results: Soil vapor analytical results and contoured plume maps indicated the presence of subsurface petroleum product contamination off-site as well as on the service station's property. Off-site migration of gasoline contamination into the telephone right-of-way was proven by the soil gas data. Constituent plume maps confirmed a source of gasoline contamination had been released from both of the offending service stations. The soil vapor data also found a "new" release on one of the two stations that had not been discovered by the stations Environmental Engineers. The soil gas surveys proved that the initial assessments were not comprehensive and had not identified the full extent of the contamination on either of the two offending service stations. Following depositions, the two service station operators paid for the damages caused to the Telephone Company.