The Crossville Storage Cavern was a shallow cavern which had been dug to a depth of approximately 200 feet and experienced some leakage over most of its 30 year life.  The purpose of our investigation was to determine if leakage was associated mainly with the cavern shaft or if leakage from one or more of the cavern drifts was also significant.  Observation was made from some 400 wells installed to depths of 10 – 12 feet.  When the cavern was filled with propane, the observations revealed a spot of contamination roughly 600 feet in diameter which was not symmetrical about the shaft.  When the cavern was emptied of propane, it was filled with nitrogen to which was added a cylinder of helium to use as a tracer.  The helium spot developed during the first day around the shaft and required about 15 days to reach the peripheral areas of the former hydrocarbon spot. 

At this cavern, we also were able to determine that contaminant not only existed in the near surface sediments, but also migrated through the surface into the atmosphere as a function of rising and falling barometric pressure.  We concluded from our measurements at Crossville that the cavern leakage was largely associated with the cavern shaft rather than leakage from one or more of the drifts (Robert J. Pirkle, Proceedings of the American Gas Association Meeting, Chicago, IL, April 1986).

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