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'This research project addresses the nature and and distribution of DNAPL sources (typically chlorinated solvents) in fractured clays or shales and the potential for natural attenuation of plumes derived from these sources. Specific goals include: (1) determining whether typical DNAPLs can penetrate fractures and the fine-grained matrix pore structure for head values within the range expected for a typical DNAPL spill; (2) investigate methods of measuring or estimating fracture or matrix entry pressure and pressure-saturation curves for these materials; (3) experimentally determine whether DNAPL residuals in fractures can be significantly depleted by dissolution and diffusion into the fine-grained matrix over the time-frame relevant to many contaminant investigation and remediation programs; and (4) assess potential for natural attenuation of common DNAPLs (TCE and its degradation products) in these deposits. Preliminary investigations indicate that DNAPL source removal will be a much more difficult and slower process for fractured clay-rich deposits than for granular deposits. These basic research investigations are needed to build the scientific framework for assessment of remediation options or for determining whether remediation, at least for the source zone, should be considered Technically Impractible (TI). This report summarizes progress made during the first 1.7 years of a 3-year project. The project investigates the behavior of DNAPLs in two fractured clay-rich materials: weathered shales at Oak Ridge National Lab. in east Tennessee; and weathered glacial till in southern Ontario. The materials, although very different in origin, are similar in terms of fracturing, porosity and hydraulic conductivity and DNAPLs are expected to behave in similar fashions in the two materials. This allows the researchers to share their expertise, as well as helping to determine whether the findings of these studies are applicable to a broader spectrum of fractured clay-rich materials. Results to date for the major sub-projects are briefly described.

Behavior of dense, immiscible solvents in fractured clay-rich soils. 1998 annual progress report