SWI NAPL Recovery represented by Cemcor Environmental Services Contact: Craig Marlow Phone 419.867.8966 Cell 419.349.7970 Email cemarlow@att.net
Physical mechanisms of SWI Injection in the saturated zone of water that is supersaturated with CO 2 to introduce gas into contaminated porous media Gas bubbles grow in situ by advective diffusion allow gas to appear in pore space that is not possible by other methods such as air sparging Growing gas bubbles volatilize and mobilize the NAPL upwards toward the vadose zone where it can be soil vapor extracted
Conceptual model Injection well Extraction well Water is supersaturated with CO2 in the gpro mass transfer system Supersaturated water is then injected into the aquifer through injection points CO2 bubbles nucleate at various points in the aquifer 0 0.7 1 2 3 4 Clay layer Gravel Unsaturated Sand Residual Hydrocarbons Saturated Sand 7
Conceptual Model Injection well Extraction well 0 Clay layer Gravel When the rising CO 2 bubbles contact hydrocarbons they cause volatilization of the hydrocarbons Groundwater and soil vapour (including CO 2 and volatilized hydrocarbons) are removed through wells 0.7 1 2 3 Unsaturated Sand Residual Hydrocarbons Saturated Sand 4 7
Direct pore-scale evidence- Volatilization A CO 2 bubble growing by mass transfer from the injected supersaturated aqueous phase. Upon contact with the bubble, NAPL spontaneously spreads over water. Volatile components of the NAPL are readily transferred into bubble.
Recovery by mobilization of NAPL ganglia Demonstration of nonvolatile NAPL (Soltrol) recovery by SWI
Gas sparging limitations (Ji et al., 1993)
In situ gas evolution in the presence of impermeable barriers SWI
Proof of concept in the lab: In situ gas saturation development and rate of gas ebullition Bubble flow meter V g1 V g2 V g3 Water outlet and level control V w Injection Saturated porous medium Production Supersaturated water, C
Gas evolution during SWI: Experiment 60 54 52 41 36 33 31 28 26 24 21 17 12 9 10 0 min sec
Recovery of residual hexane by SWI
Recovery of residual hexane by SWI
Modeling of lab experiments 125 cm 125 cm Inlet 45 cm Outlet Inlet Boundary 45 cm Outlet Boundary Experimental Apparatus FEMLAB Simulation Domain
Comparison of simulation to experiment kl 0.01S g s 1 41 31 17 60 91 24 4 min 0 min min 60 41 31 24 17 94 10 min v in = 0.078 cm/s, C 0 = 5.44 g/l
Proof of concept in the field 200 L of hydrocarbon (mixture of pentane, hexane and Soltrol) existing as residual NAPL in the saturated zone (enclosed cell in the sand pit at Borden)
Field Experimental Cell Vapors and Water out Injection well Extraction well Saturated Water in Air vent well 5 m Spilled Residual NAPL 1 m
Cumulative Mass Removal 25 20 15 10 pentane hexane 5 0 0 2000 4000 6000 8000 10000 12000 14000 16000 Elapsed Time (min)
NAPL recovery results after one week of SWI Removed Mass (kg) PID/samplin g Pentane 21.5 50.3 Hexane 13.4 28.6 % Removed Pentane : Hexane Total 34.8 39.0 1.6:1
Average concentrations: Core 1: 151, 360 Core 4: 55, 134 Core 5: 562, 751 Evidence of very good recovery in the regions probed by core 1 and core 4
Soil Coring Results Average concentrations: Core 2: 1445, 1706 Core 3: 1011, 1326 Evidence of poor recovery in the regions probed by core 2 and core 3
Success of SWI linked to hydraulic control Supersaturated water must sweep the contaminated zone for effective remediation well placement in relation to contamination is important Computed SWI flow paths corroborate superior remediation effectiveness in contaminated areas swept by gas-infused water
CO2 SWI ECS Boston - Well Layout Field Trial Area RW-6 Horizontal Multi-phase Extraction Well CO 2 SWI Wells
ECS BostonExtraction Well Profile Notes: Groundwater in silty sand formation Depth to groundwater ~ 10 ft Depth to impermeable clay ~16 to 20 ft
PCE Mass Removal in SVE During SWI Injection to Monitoring Wells (101 and 205)
iti Microporous Hollow Fiber Gas Mass Transfer Modules
Mobile gpro HP Setup
gpro HP in Remediation Container
Conclusions SWI is a significant improvement over direct gas injection (sparging) into a porous medium: Greater zone of influence, higher sweep efficiency NAPL spreads upon contact with gas bubbles Gas bubbles are a sink for volatile NAPL NAPL can be mobilized upwards by gas bubbles In addition to recovery of source NAPL, another potential application of SWI is the generation of a zone of trapped gas (oxygen for bioremediation)
Conclusions Pore-scale, lab-scale and field-scale studies confirm SWI for source zone remediation to be potentially advantages: Higher recovery rate Shorter duration for recovery projects Low tech existing equipment (besides Gas infusion technology) Reduced lingering operational costs