GROUNDWATER CLEANUP BY IN-SITU SPARGING .6. A SOLUTION DISTRIBUTED DIFFUSION-MODEL FOR NONAQUEOUS PHASE LIQUID REMOVAL

A microcomputer model for the sparging of aquifers contaminated with v olatile organic compounds (VOCs) is presented which includes the kinet ics of solution of nonaqueous phase liquid (NAPL) droplets and of diff usion from low-permeability porous layers. The well configuration mode led is a horizontal slotted pipe. Modeling results lead to the followi ng conclusions. 1) The presence of low-permeability porous lenses of c lay, till, silt, etc. results in marked increases in cleanup times. Th e extent of the increases depends strongly on the thickness of the str uctures. NAPL droplets of large size also result in marked increases i n cleanup time. 2) Increases in air flow rate do not yield correspondi ng decreases in cleanup time if the system is limited by solution/diff usion kinetics. 3) The rate of induced water circulation plays a minor role in determining cleanup time. 4) Wells should be sufficiently dee p and operated at an air flow rate such that air is delivered to the e ntire zone of contamination, 5) The spatial distribution of the VOC ha s little effect on the cleanup time as long as air is delivered to the entire contaminated zone. 6) Cleanup times increase roughly proportio nally to increasing initial VOC concentration. 7) The terminal phase o f cleanup typically shows substantial tailing as water containing VOC must circulate into the zone of aeration for the VOC to be stripped. 8 ) VOCs having Henry's constants of 0.05 or larger can readily be remov ed by sparging.