Vertical Cross Contamination of Trichloroethylene in a Borehole in Fractured Sandstone

Abstract

Boreholes drilled through contaminated zones in fractured rock create the potential for vertical movement of contaminated ground water between fractures. The usual assumption is that purging eliminates cross contamination; however, the results of a field study conducted in a trichloroethylene (TCE) plume in fractured sandstone with a mean matrix porosity of 13% demonstrates that matrix-diffusion effects can be strong and persistent. A deep borehole was drilled to 110 m below ground surface (mbgs) near a shallow bedrock well containing high TCE concentrations. The borehole was cored continuously to collect closely spaced samples of rock for analysis of TCE concentrations. Geophysical logging and flowmetering were conducted in the open borehole, and a removable multilevel monitoring system was installed to provide hydraulic-head and ground water samples from discrete fracture zones. The borehole was later reamed to complete a well screened from 89 to 100 mbgs; persistent TCE concentrations at this depth ranged from 2100 to 33,000 microg/L. Rock-core analyses, combined with the other types of borehole information, show that nearly all of this deep contamination was due to the lingering effects of the downward flow of dissolved TCE from shallower depths during the few days of open-hole conditions that existed prior to installation of the multilevel system. This study demonstrates that transfer of contaminant mass to the matrix by diffusion can cause severe cross contamination effects in sedimentary rocks, but these effects generally are not identified from information normally obtained in fractured-rock investigations, resulting in potential misinterpretation of site conditions.

Novel Well Completions in Small Diameter Coreholes Created Using Portable Rock Drills

“…The bedrock underlying the site and surrounding areas consists of Late Cretaceous turbidite sandstones with shale interbeds, known as the Chatsworth Formation (Link et al 1984 ). The sandstone is highly fractured and has an average matrix porosity of 13% (Sterling et al 2005 ). The sandstone is composed mainly of quartz, plagioclase-and potassiumfeldspar, and minor phyllosilicates consisting of biotite and chlorite with iron oxide and calcite cement (Loomer andAl 2009 in Cherry et al 2009 ;Link et al 1984 ).…”

Assessment of Natural Attenuation Processes in the Groundwater Contaminated with Trichloroethylene (TCE) Using Multi-Species Reactive Transport Modeling

“…트리클로로에틸렌(trichloroethylene; TCE)을 포함한 염 소계 유기화합물은 가장 대표적인 지하수내 유기오염물로 서 (Sterling et al, 2005;Damagaard et al, 2013;Wanner et al, 2016), 국내에서도 산업단지를 중심으로 빈번하게 이로 인한 지하수 오염이 보고되고 있다 (Baek and Lee, 2011;Yang and Lee, 2012;Lee et al, 2015). ) in the study site.…”

Characterization of chlorinated solvent contamination in limestone using innovative FLUTe® technologies in combination with other methods in a line of evidence approach

“…The extraction technique for the limestone samples was adapted from a technique developed and previously used for solvents in clay till samples by Scheutz et al (2010), Damgaard et al (2013a+b), and Fjordbøge et al (2016). It exploits a combination of the water and matrix porewater miscibility and the efficiency of immiscible solvent (pentane) extractioncombining and refining the methods of Sterling et al (2005) and Lawrence et al (1990), respectively. Three subsamples of each extract were transferred to GC-MS vials.…”

“…A variety of methods are available for core sampling. Sterling et al (2005) used high-resolution subsampling of cores with an analytical method based on quantitative methanol (water miscible) extraction (Hewitt, 1998) for analysis of chlorinated VOCs in rock core matrices (dissolved and sorbed), and Lawrence et al (1990) used water immiscible solvent extractions of chalk core material (crushed in solvent).…”