Groundwater flow and transport modeling of MTBE at Rocky Mount, Virginia, USA
Keywords:
Flow model, Transport model, MTBE, Litigation.Abstract
Groundwater flow and transport modeling conducted for court litigation at Plateau Plaza, Rocky Mount, VA, USA. In October 1999 about 6,500 to 7,500 liters of petroleum released to the subsurface. Many residential and commercial water supply wells impacted by dissolved phase MTBE. The study objective is to evaluate travel time of dissolved phase MTBE from site to individual properties of supply wells, MS-7 and MS-9. Groundwater flow and dissolved phase transport models were constructed using MODFLOW and MT3D. The two-layered model was conceptualized and constructed using historical drilling data, groundwater gauging, sampling, slug-testing, and geophysical studies. Flow and transport models calibrated to historical groundwater levels and concentrations. Sensitivity analysis conducted to evaluate uncertainty in hydraulic conductivity, dispersivity, and source concentration. The conclusions based on geologic, hydrogeologic, geophysical and dissolved concentration data spanning over eight years that portray actual field conditions. The specific dates of dissolved MTBE movement and to approach the boundaries of individual properties based on modeling and professional expertise. The model is sensitive to change in any parameter that would affect the plume speed. Any changes to those parameters, including changes that would slow the migration of the simulated plume were detrimental to the calibration of the model. It is appraised that the dissolved MTBE entered the property of Well No. MS-7 in the deep and upper zones in December 31, 2001, and February 24, 2002, respectively. The plume in the property of Well No. MS-9 entered in deeper and upper zones in September 11, 2002, and October 13, 2002
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