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PREDICTING DIVING PLUME BEHAVIOR
Citation:
Acree*, S, J T. Wilson*, AND G. Alvarez*. PREDICTING DIVING PLUME BEHAVIOR. Presented at NGWA 2003 Conf. on MTBE Assessment, Baltimore, MD, 06/4-6/2003.
Description:
The United States Environmental Protection Agency has responded to a number of multi media environmental issues surrounding the use of methyl tertiary butyl ether (MTBE) and other fuel oxygenates. In Region 5, MTBE from various sources - but mainly from leaking underground storage tanks (LUST) - has contaminated groundwater. In some cases, drinking water has been impacted resulting in communities being forced to adopt expensive alternatives (Island Lake, Illinois; East Alton, Illinois; Mishawaka, Indiana, Spring Green, WI, Milford, MI and others). One of the physical properties of MTBE, especially when compared with other petroleum hydrocarbon chemicals of concern (COCs), is that it is very soluble in water. Traditionally, LUST site characterizations have focused on the upper portion of the groundwater table. It has been demonstrated that MTBE can "dive" below monitoring well networks that are designed to detect petroleum COCs near the surface - thereby leading some sites to be falsely perceived as not being a threat. We believe the diving is controlled both by MTBE solubility and recharge effects (fresh rainwater infiltrating and mixing with groundwater to push a plume deeper into the water table).
Our study selected 3 LUST sites with MTBE groundwater contamination with varying patterns of local recharge and land use patterns (i.e., sites surrounded by tightly paved areas with less dominant recharge vs. sites surrounded by open areas with more dominant recharge). The hypothesis was that the MTBE plumes dive further and faster in areas where patterns of local recharge are dominant.
This project attempts to provide end users (state & federal regulatory agencies, environmental consultants and responsible parties) with tools to help identify diving MTBE plumes and possibly predict their behavior. If our study shows that open settings do in fact contribute to diving plumes with some measure of predictability, then we can alert our state regulatory agencies to fine tune their site characterization polices and guidance to account for this phenomenon. The result would be an increase in three dimensional groundwater profiling site characterizations, which would lead to enhanced protection of potentially impacted drinking water sources. Combining this with an effective UST regulatory enforcement component, MTBE sources can be better controlled.