Two Rapid Enhanced Flushing NAPL Recovery Methods James A. Jacobs (Environmental Bio-Systems, Inc.), Lief Nelson (Worley Parsons Komex ) and Jim Begley ( inVentures Technologies of Canada). Abstract:. Gas Mass Transfer.
Two Rapid Enhanced Flushing NAPL Recovery Methods
James A. Jacobs (Environmental Bio-Systems, Inc.), Lief Nelson (Worley Parsons Komex) and Jim Begley (inVentures Technologies of Canada)
Gas Mass Transfer
EBS Biosolvent Actions To Remove Heavy Free Product (Diesel, Motor Oil, Hydraulic Oils, Bunker-C Oils, Heavy Oils)
1. Dissolves petroleum and lowers viscosity
2. Decreases adhesion to grain surfaces
3. Reduces density of weathered oil, allowing recovery by HVDPE
4. Consolidates the oil into floating globules and patches for easier recovery
5. Enhances the biodegradation of the residual petroleum hydrocarbons
Lab and Field Tests
Two Rapid Enhanced Flushing NAPL Recovery Methods
Rapid free product removal of hydrocarbons and solvents has been a major challenge over the past three decades of remediation. Long-term product only or pump-and-treat systems are commonly used for removal of NAPLs. Failing rapid removal of free product allows for long-term dissolution around the edges of the NAPL, providing a continuing and unabated source of dissolved groundwater contamination. Two different enhanced flushing methods have been developed within the past two years to rapidly remove gasoline free product from within an aquifer. Recovery Method 1 involves a field trial in Ontario, Canada. Supersaturated Water Injection (SWI) technology was used with carbon dioxide saturated water injection for controlled mobilization of VOCs to the water table for collection with soil vapor extraction (SVE) or dual phase extraction where NAPL was present. In the SWI process, water was supersaturated with CO2 in a patented gas-liquid mass transfer system. The saturated water was injected into an aquifer test cell were a 200 liter hydrocarbon mixture had been placed forming a residual NAPL zone. CO2 bubbles nucleated at the targeted area of the aquifer. The rising CO2 bubbles contact with VOC NAPL ganglia in the saturated zone and cause volatilization of the VOCs into the vapor phase and mobilization of NAPL trapped in pores.
Extraction and reinjection wells were used to recirculate the CO2 saturated water.. The CO2 is distributed by flowing water resulting in effective gas distribution followed by heterogeneous bubble nucleation and continuous growth of gas bubbles in situ. A gas saturation front developed which expanded laterally and vertically towards the water table. VOCs mobilized to soil gas were extracted with a SVE system. Results indicated a significant proportion of VOCs were removed by SVE.
Recovery Method 2 was performed at a former tank pit at a northern California containing used hydraulic oil that was trapped beneath the saturated zone. Recovery Method 2 used a two-step flushing process which included high-pressure air injection and biosolvent injection to thin and mobilize the heavy oil, which was measured up to 41 cm in height in one well. The high-pressure air injection and biosolvents were used with high-vacuum extraction to recover both the used hydraulic oil and the biosolvent. The final stage separated the heavy oil from the unspent biosolvent and groundwater. Over 11 barrels of free product were removed and a similar volume of biosolvent was recovered during the one week process. Site closure is imminent. These two remedial methods show rapid removal of free-product that was trapped within the pore spaces of the saturated zone.
Recovery of 100% of residual hexane by CO2 Supersaturated Injection
in lab scale experiment in 65 minutes
at up to 600 psi
With high vacuum
Removes the used
As an example of gas mass transfer into water, oxygen (O2) mass transfer chart above shows flow rates and water flow. Other gases such as carbon dioxide (CO2) have been used as well.
SWI Process with CO2
EBS Biosolvent Flushing
Below left, 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, Ontario. Field experimental process (right)
CASE 1 – FREE PRODUCT REMOVAL USING CO2 FLUSHING (gPRO System)
A CO2 bubble growing by mass transfer from the injected
supersaturated aqueous phase.
CASE 2 – FREE PRODUCT REMOVAL USING EBS BIOSOLVENT FLUSHING
Lift draws the CO2 bubbles upward.
Upper left panel, gPRO mass transfer module with iSOC gas delivery tool on right (same technology), gPRO module in lower left panel. Right panel shows gPRO demo unit
with pump, controller, high-pressure mass transfer unit.
Collection of used hydraulic oil (left). Extraction of oil using HVDPE (right)
CASE 1 –CO2 Flushing for Free Product Removal: Pilot Testing at Several Sites
CASE 2 – EBS Biosolvent Flushing for Free Product Removal:
Site Status (3/2/08) Site Closure granted early 2008, well abandonment planned.
James Jacobs, Environmental Bio-Systems, Inc., 707 View Point Road, Mill Valley, CA 94491 USA, Tel: 415-381-5195; [email protected]; www.ebsinfo.com
Leif Nelson, Worley Parsons Komex; Suite 100, 4500 16th Ave. NW, Calgary, Alberta, T3B0M6 Canada, Tel: 403-247-0200; [email protected]
Jim Begley, inVentures Technologies of Canada, www.isocinfo.com; Tel: 647-477-2394; [email protected]
EBS Biosolvent is available from Environmental Bio-Systems, Inc.
gPROHP System developed by inVentures Technologies, Inc.
Mobilization of NAPL ganglia for recovery: LIFT
The CO2 bubbles as they nucleate in the target area, the contaminants dissolve in the more soluble CO2 bubbles. Then the CO2 bubbles with dissolved contaminant inside are lifted to the surface, where they are removed by soil vapor extraction.
gPROHP System Schematic - Control
Data of free product thickness in RW-4 shows reduction on 4/15/06.