1887

Abstract

A model is proposed for the spatial distribution of electrical earth conductivity in the volume in and around Light Non-Aqueous Petroleum Liquid (LNAPL) spills. Because of vertical and lateral movement of subsurface liquids, the dimension of time must also be included in any model. The subsurface is a complex system and therefore some principles from biology, geochemistry, and hydrogeology are reviewed. A number of contaminant plumes have been recognized (Bennett, et. aI., 1993) emanating from a single spill, each of which may evolve different geophysical properties with time. In the vadose zone is the freelresidual product plume in which sediments have been directly impacted by free hydrocarbons. Surrounding and above this is the vapor phase plume composed of volatiles derived from the free product plume. Below the water table is the dissolved plume where relatively low concentrations of hydrocarbons disseminate into the upper part of the aquifer. The dissolved plume can be subdivided into an aerobic upper and outer boundary, and an anerobic inner core. Another diffuse gaseous plume can be defined in the vadose zone above zones of biologic degradation of hydrocarbons. This plume is enriched in carbon dioxide and may also contain methane, both products of bacterial metabolism. The vadose zone plumes will affect the electrical conductivity in a highly variable manner, depending upon volume of the spill, surface area of the spill, composition of the spill, thickness of the vadose zone, sediment mineralogy, grain size distribution, and rainfall regime. Initially a lowered conductivity may be observed. However, within the residual product and the aquifer plumes, the biodegradation will produce organic acids which very aggressively leach inorganic salts from the soil or sediment grains. Additionally, bacterial evolution of carbon dioxide gas can lead to carbonic acid production in the overlying vadose zone. This will also produce an inorganic leachate.

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/content/papers/10.3997/2214-4609-pdb.299.161
1997-11-07
2024-03-28
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