| The contamination of soil by light hydrocarbons such as gasoline or diesel fuel represents a major environmental problem. It is estimated that there are over 400,000 contamination sites in the United States alone resulting from spillage from underground storage tanks or associated infrastructure at consumer refueling stations. There are other sites resulting from above ground storage at bulk terminals, such as airport or refinery tank farms. The remediation of each site varies, ranging from {dollar}15,000 (U.S.) to well over {dollar}125,000 (U.S.).; To investigate the potential application of a water and gas displacement method, Gravity Assisted Immiscible Gas Injection (“GAIGI”), for remediation of such sites, laboratory experiments and numerical simulation studies have been performed. The scope of the study is the remediation of the area of the soil where the contaminant has contacted the groundwater. This is where the highest percentage of a spill will be located for large volume releases. The laboratory studies investigate aspects of the contamination and subsequent remediation processes, in one and two dimensional sand packs. The sand packs have been constructed with sands of various grain sizes, as well as mixtures of sand and clay, and sand coated with humic acid. The numerical simulation studies have investigated the performance of the water and gas displacement process for field scale operations.; It has been found that extremely high recoveries, better than 70%, can be attained in any type of one dimensional laboratory sand pack porous media by the GAIGI process. In cases of high permeability, the recoveries can be better than 95%. In two dimension sand packs with large buoyancy traps in the model, experimental data demonstrates contaminant recovery of 98%. Numerical simulation of a field scale operation demonstrate that the lack of conformity of the soil leads to lower contaminant recovery. Numerical simulation studies demonstrate that secondary contamination of pristine soil during the remediation process is a large factor responsible for the lower recoveries. This secondary contamination will occur despite efforts to contain the soil plume using perimeter water injection wells to push all fluid flow inward toward the remediation site. |
