Abstract
Well injection depth extraction (WIDE) is a hybrid in situ subsurface remediation technology applicable for liquid and gas extraction in fine-grained soils. A finite element model is developed to study the impact of the extraction process, using WIDE, on the groundwater head distribution and contaminant transport. An optimization process is employed to develop an operating schedule to control groundwater elevations and therefore improve removal efficiency of a given contaminant phase. The model results showed that groundwater elevation was lowered at the rate of approximately 30 mm/h at an extraction rate of 0.125 m(3)/h. The transport model is analyzed for three scenarios: (1) applying a continuous source of benzene concentration to provide information on the required time for mobilization of benzene due to the presence of a constant source at the top of the water table; (2) applying an initial pulse concentration of benzene at the top of the groundwater table to show the reduction rate of soluble benzene concentration with time, once the liquid free product is removed, and the soluble phase is removed from within the sand seam but remains above it in the lower-permeability layer; and (3) applying a uniform distribution of the soluble phase of benzene within the geologic medium between the wells to investigate progressive contaminant removal from the hydro-geologic domain, given that groundwater is contaminated with soluble phase. Effluent concentration equal to the initially assumed constant source of 0.3 mg/L of benzene leaking into a 0.08 m thick sand lens was obtained after 18 h of system operation. On the other hand, once the source ceased to exist, and considering an initial pulse concentration of benzene on top of the groundwater level, 125 h of continuous system operation was needed to lower the benzene concentration to less than 0.005 mg/L (maximum concentration level for drinking water standards) within the flow domain. Results from the optimization study showed that an operation schedule of 3 h 'on' and 21 h 'off' can enhance the efficiency of WIDE extraction of subsurface contaminants in various phases.
