Characterization and Quantification of Pneumatic Fracturing Effects at a Clay Till Site

Abstract

Environmental fracturing offers assistance to remediation efforts at contaminated, low-permeability sites via creation of active fracture networks, and hence, reduction of mass transport limitations set by diffusion in low-permeability matrices. A pilot study of pneumatic fracturing, focusing on direct documentation of fracture propagation patterns and spacing, was performed at a typical basal clay till site. The study applied a novel package of documentation methods, including injection of five tracers with different characteristics (bromide, uvitex, fluorescein, rhodamine WT, and brilliant blue), subsequent tracer-filled fracture documentation via direct and indirect methods, and geological characterization of the fractured site. The direct documentation methods consisted of Geoprobe coring, augering, and excavation. A mass balance and conceptual model have been established for the distribution of the injected tracers in the subsurface. They reveal that tracer was distributed within 2 m of the fracturing well, mainly in existing fractures above the redox boundary (2 to 4 m.b.s.; 5 to 10 cm spacing). Spacing of observed tracer-filled fractures was large (>1 m) at greater depths. The number of fractures induced/activated could possibly be increased via adjustments to the fracturing equipment design.

Identification of chlorinated solvents degradation zones in clay till by high resolution chemical, microbial and compound specific isotope analysis

“…Fig. 1b) is highly fractured due to freeze and thaw processes and contains many worm and root holes (Christiansen et al, 2008). This is reflected in the contaminant distribution by the presence of chlorinated solvents in most of the clay till matrix.…”

“…Fewer fractures are present below 3-5 m b.s. (Christiansen et al, 2008). In some places the upper clay till is separated from the lower clay till by sand lenses and stringers, which possibly have resulted in horizontally more widespread contamination around this interface.…”

In situ bioventing of the vadose zone of multi-scale heterogeneous soils

“…An effective ''in situ'' remediation of a contaminated fractured site is accordingly dependent on accessing the natural fractures and mobilizing/degrading the pollutants within the matrix. For this purpose various stimulation technologies such as hydraulic fracturing may be adopted (Murdoch 1995;Bradner and Murrdoch 2005;Christiansen et al 2008;Nilsson et al 2011).…”

Release of contaminants from a heterogeneously fractured low permeability unit underlying a DNAPL source zone

“…Efforts to address contaminants in low permeability zones have included use of pneumatic and hydraulic fracturing (Christiansen et al, 2008;Slack et al, 2000).…”