ExampleThree1

EXAMPLE NO. 3: A FORENSIC STUDY TO DIFFERENTIATE TWO DISSOLVED GASOLINE PLUMES AT ADJOINING SERVICE STATIONS

Three gasoline service stations are present at a highway intersection in central New Jersey. In the mid- to late- 1980s, service station “B” began to notice large discrepancies in their gasoline inventory. The USTs were removed in 1988 and a significant release was discovered. Separate-phase gasoline, as much as 1.5 feet (0.5 m) thick was present on the water table for about an area of one acre. Monitoring wells were installed and a plume extending downgradient by as much as 300 feet (100 m) was found. Downgradient potable wells were also impacted and had to be replaced. An upgradient well was installed and this well also contained separate-phase gasoline. Accordingly, station “B” began to petition the state regulatory agency to include station “A” in the cleanup.

Based on a calculation using the product thickness, porosity of the soil and the area affected (among other parameters), the quantity of gasoline released was in the hundreds of thousands of gallons (>one million litres).

Monitoring wells were installed at station “A” and a release from underground piping was discovered. However, except for the one well installed between the two sites, separate-phase gasoline was not detected at station “A”.

In the mean time, station “B” undertook a ground-water cleanup. Several recovery wells were installed and a treatment system was built. The treated effluent was then directed to an infiltration gallery installed into the former UST excavation. Unfortunately, this area was still underlain by separate-phase petroleum and the infiltration of effluent caused the gasoline to be flushed radially in all directions, including upgradient.