"We want the bacterial activity to eat these vapors before they reach us," Alvarez said. He said many factors, including shallow groundwater or soil with low permeability that is not easily ventilated, could stand in the way.
"The amount of oxygen allowed to diffuse in would determine the assimilative capacity of the soil and the degradation capability," he said. "The bacteria will be there, but they're not going to do you much good if they run out of oxygen. The problem is bacteria that eat the methane use up all the oxygen, and the ones you want to degrade benzene can't do their job because they don't have any oxygen left."
Benzene is a carcinogen. According to the federal Centers for Disease Control and Prevention, long-term exposure can harm bone marrow and cause a decrease in red blood cells, leading to anemia. It can also cause excessive bleeding and affect the immune system.
Alvarez said studies have assessed the amount of methane generated by spills, but none have directly addressed what happens when the highly flammable vapors rise into confined spaces, where they can accumulate. He said flux chambers have been used to measure methane in such spaces, but they don't account for building effects like typically lower interior pressure that would draw vapors in through cracked foundations.
So the Rice lab led by Alvarez, with the participation of researchers from Chevron, Shell and the University of Houston, programmed a three-dimensional vapor intrusion model to simulate the degradation, migration and intrusion pathways of methane and benzene under various site conditions. The program modeled a small building with a perimeter crack around the foundation, sitting in the center of an open field. The atmospheric pressure was assumed to be slightl
|Contact: David Ruth|