It was also covered with plastic sheeting. So far, so good. Reducing the parts per million of the gasoline would be irrelevant. I have consulted any number of engineers, geologists and biologists whom I consider professional and knowledgeable, and none are convinced that this procedure is fail-safe or cost effective. It must be irrigated, which means thorough containment of the material to prevent runoff and resulting contamination spread.
Weather obviously plays an important role in that volatilization is an inherent part of the process.
Only five months or so are effective for this purpose in the Inland Northwest. In this case, the stuff remained untouched and covered for over two years. Needless to say, the procedure was ineffective. Contamination levels averaged 12000 parts per million after the fact. Metals analyses showed cadmium levels over state cleanup levels, which requires disposal at a regulated problem waste facility.