Wettability Changes in Trichloroethylene-Contaminated Sandstone

Abstract

It is usually assumed that chlorinated solvent nonaqueous-phase liquids (NAPLs) are nonwetting with respect to water-saturated porous media. The focus of this work was to examine whether this supposition is appropriate for used trichloroethylene (TCE) samples. In this work, the term "used" indicates that the sample has been employed industrially and therefore contains solutes and breakdown products related to its previous use. The data obtained in this study indicate that exposure of initially water wet quartz slides to industrially used solvents can cause a contact angle change, measured through the aqueous phase, of 100 degrees with a maximum stable contact angle of 170 degrees (indicative of strong NAPL wetting characteristics) being recorded. The work on quartz slides was complemented by the use of sandstone cores. Wettability was measured using the Amott test. Used TCE again proved able to alter the wetting properties of sandstone to neutral wetting. The complexity of the industrially used samples precluded any realistic attempt to examine the agents causing these wetting changes. The data captured in these experiments were compared with laboratory grade TCE, and some attempts were made to synthesize known mixtures in order to replicate wetting changes. These experiments resulted in contact angle changes but did not alter the overall wettability of the quartz slides or sandstone cores. Finally the work reported here also demonstrates that increasing the duration of exposure to solvent has an important impact upon measured contact angle.

Controls on dense non-aqueous-phase liquid transport in Permo-Triassic sandstones, UK

“…Powers & Tamblin (1995) observed increases in contact angle for sands exposed to petroleum mixtures for between 14 and 60 days. Harrold et al (2001) noted an increase in contact angle from 20 ~ to 40 ~ over 24 h for a trichloroethene-sand system. In the present study, however, the sandstones were only exposed to solvent for relatively short times, typically of the order of 2 h. On the basis of the observations of Harrold et al (2001) and Powers & Tamblin (1995), it is unlikely that the length of exposure of the sandstones to PCE in the present study was sufficient to modify the contact angle significantly and hence to explain the observed entry pressures.…”

“…The contact angle provides the only direct measurement of wettability but is a difficult measurement to make under laboratory conditions without compromising the integrity of true environmental conditions. Recent work has shown the presence of subsurface chemical heterogeneities such as variations in aqueous-phase chemistry (Demond et al 1994), mineralogy (Anderson 1987a-c;Bradford et al 1998), organic matter distributions (Dekker & Ritsema 1994), and contaminant ageing (Harrold et al 2001) can substantially alter the wettability, and both water-and organic-wet solid surfaces occur within the same porous medium.…”

“…Employing a centrifuge method, Kinniburgh & Miles (1983) used an immiscible fluid to displace water from consolidated and unconsolidated media, but were not interested in investigating pore entry pressure relationships. It is only very recently that the centrifuge has been used to measure pore entry pressure for solvents in consolidated media (Pantazidou et al 2000;Harrold et al 2001). …”

“…A modified method for rapid determination of Pc(Sw) curves in DNAPL-water systems, developed and described by Gooddy et al (1999) and subsequently used by Harrold et al (2001), has been used in this study. A fully water saturated sample is placed in a tube in a centrifuge rotor (Fig.…”

Impact of Multi-Interface Surfactant Adsorption on Wettability in Dense Nonaqueous Phase Liquid Systems

“…The distribution of DNAPLs in the subsurface and the remediation efficiency are strongly affected by the system's wettability (Dwarakanath et al, 2002;O'Carroll et al, 2004), which is significantly different from their laboratory-grade counterparts (Harrold et al, 2001;Dwarakanath et al, 2002) because wastes often contain surface-active components that have the potential to adsorb at the interfaces and change the interfacial properties of the system. For example, organic bases render silica more oil-wet at low pH, which was attributed to the adsorption of the bases' cationic form (Standal et al, 1999;Lord et al, 2000).…”