Observed Migration of a Controlled DNAPL Release by Geophysical Methods

Abstract

Seven hundred seventy liters of a dense nonaqueous phase liquid (DNAPL), tetrachloroethylene (PCE), were released into an isolated volume of a completely saturated natural sandy aquifer. The release was monitored over a period of 984 hours with a variety of geophysical methods including ground penetrating radar, time domain reflectometry, in situ resistivity, and a neutron soil moisture probe. The PCE formed a pool on a low permeability layer at approximately 1 m depth and spread over an area exceeding 32 m2. In its course of downward migration, the PCE subsequently formed eight smaller pools. At the end of the experiment an estimated 41 percent of the total PCE volume remained trapped in the upper pool. The PCE mass and its spatial moments were calculated from radar reflection amplitudes. Between 48 and 100 percent of the PCE mass was accounted for by radar measurements. The center of mass moved a total of 0.5 m south southeast and 1.3 m downward. Spatial variances showed that the greatest lateral spreading occurred in the east‐west direction. The results demonstrate that natural heterogeneities, even in a relatively homogeneous aquifer, can cause DNAPLs to spread laterally over large areas in the subsurface. This experiment also demonstrated that while the ability of geophysics to uniquely measure the presence of DNAPL is limited, certain techniques are well‐suited to monitoring changes in DNAPL saturation.

Quantification of Degradation of Chlorinated Hydrocarbons in Saturated Low Permeability Sediments Using Compound-Specific Isotope Analysis

“…25 The aquifer consist of primarily horizontal, discontinuous lenses of medium grained, fine-grained, and silty fine-grained sand 26 with a mean porosity of 0.33 (n = 36; standard deviation (SD) of 0.017). 27 Despite the observed variability, the sandy aquifer is considered as relatively homogeneous.…”

Subsoil heterogeneities controlling porewater contaminant mass and microbial diversity at a site with a complex pollution history

“…Borden (Ontario, Canada), where many experiments have been performed with DNAPLs. These experiments have shown that, after its injection, DNAPL is distributed horizontally, forming pools on the horizontal layers with lowest conductivity and vertical trails where the DNAPL free-phase passed during its descent (Kueper et al, 1993 andBrewster et al, 1995).…”

Characterization And Monitoring Of Natural Attenuation Of Chlorinated Solvents In Ground Water: A Systems Approach

“…The first two techniques are active, in that they require electrical current to be injected into the earth; selfpotential is passive, and uses naturally occurring electrical potentials. Other geophysical techniques used to monitor contaminant migration in the subsurface include ground penetrating radar and time domain reflectometry (TDR) (Brewster et al 1995). WSRC-STI-2006-00084, Rev Geophysical monitoring techniques require: (1) a conceptual and theoretical framework that supports the method, (2) demonstrated effectiveness, (3) cost-efficient performance, and (4) the ability to be used for a reasonable time period.…”