Effect of NAPL Dissolution on NAPL-Water Interfacial Area
EMSL Project ID
16721
Abstract
The release of nonaqueous-phase liquids (NAPL) into soils and aquifers is a widespread and serious environmental problem. The typically low solubilities of NAPL cause them to dissolve slowly; thus NAPL act as a long-term source of groundwater contamination. In addition to the NAPL’s solubility, NAPL-water interfacial area is an important parameter that influences the rate of NAPL dissolution in porous media. While many studies have focused on NAPL dissolution phenomena, there are few experimental studies on determining interfacial area in two-phase NAPL-water systems. In particular, the change of interfacial area as a consequence of continuous dissolution of immobile, entrapped NAPL blobs has yet to be investigated experimentally. Information on this phenomenon should be of substantial relevance to predicting the efficiency of aquifer remediation methods such as surfactant or co-solvent flushing and other pump-and-treat techniques.The main objective of this work is to experimentally investigate the effect of NAPL dissolution on specific entrapped NAPL-water interfacial area in well-characterized porous media. We want to generate a base line data set of specific interfacial area as a function of entrapped NAPL saturation during NAPL dissolution. This data can aid in the calibration and validation of existing and future models attempting to predict the efficacy of various aquifer remediation techniques. In particular, we want to compare our experimental results with numerical simulations employing the STOMP simulator (under development at PNNL), to test the simulator’s capability of predicting NAPL dissolution and associated NAPL-water interfacial area.
Experimental Methods. We will perform column experiments to quantify specific NAPL-water interfacial area as function of NAPL saturation during entrapped-NAPL dissolution into the aqueous phase. Experiments will be performed for a set of well-characterized silica sands while using trichloroethene (TCE) as NAPL. The sand-packed column will be initially water-saturated. NAPL will be entrapped in the column through a sequence of imbibition and drainage steps. NAPL dissolution will then be initiated by flushing the column with an aqueous solution of fixed ionic strength at high flow rate.
Prior to and at specific time intervals during NAPL dissolution, we will determine entrapped-NAPL saturations along the column length using a dual-energy gamma radiation system. At the same time intervals we will perform interfacial tracer tests to quantify specific NAPL-water interfacial area within the sand-pack. To this end we will inject an aqueous solution of fixed ionic strength containing a conservative tracer (e.g., pentafluorobeonzoic acid, PFBA) and a surfactant (e.g., Aerosol MA80-I) at low flow rate into the column and determine the surfactant’s retardation relative to the conservative tracer from samples collected at sampling ports installed along the column length. To compute specific NAPL-water interfacial area from these data, separate measurements of NAPL-water interfacial tension will be required for varying surfactant concentrations. The latter measurements will be performed using a De-Noüy ring tensiometer.
Apart from dual-energy gamma radiation and interfacial tension measurements, analytical procedures will involve the quantification of TCE, PFBA and MA80-I in aqueous samples collected from either the column effluent or from the sampling ports along the column length. Analysis of these compounds will be performed by high-performance liquid chromatography with photo-diode array detection.
Project Details
Project type
Exploratory Research
Start Date
2005-11-19
End Date
2007-06-07
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members