Abstract

Groundwater beneath a one acre site at Tinker Air Force Base has been heavily contaminated with No.2 fuel oil from underground storage tank releases. Over the past 40 years, the fuel product has leaked into the subsurface primarily from one 235,000 gallon tank and collected in a perched zone. The product was first discovered in 1983 during preliminary UST investigations and its overall extent has been the subject of continuing investigations and remedial activities since 1986. Early investigations assumed that the free product had accumulated on top of the water table and was unconfined. In 1992, a more thorough assessment revealed that two perched zones exist above a deeper and more extensive unconfined unit. The upper perched zone consists predominantly of unconsolidated to loosely consolidated sand and is unconfined. The lower perched zone is a sandstone with variable lithology that is confined by an overlying siltstone. The free product described above is now known to have accumulated principally in the lower perched zone and is trapped beneath the confining siltstone unit in a manner similar to a petroleum sandstone reservoir. As such, removal of the fuel oil has followed a strategy similar to a petroleum exploration/development program. A non-invasive 3-dimensional geophysical method has been used to define the limits of the free product layer and to select locations for extraction wells. In addition, a pneumatic fracturing technique was used to stimulate product yield from the lower perched zone.