A Modified Triaxial Permeameter for Physical Characterization of Parameters Affecting Contaminant Transport through Wetland Deposits

The Wells G and H Superfund site, located in the Aberjona watershed in Woburn, Massachusetts, has been studied by a number of MIT research groups since 1987. Initial research conducted to characterize the hydraulic properties of the wetland deposits, did not indicate the classical trend linking changes in hydraulic conductivity to changes in total porosity. It was hypothesized, therefore, that hydraulic conductivity was changing in response to changes in the effective porosity of the deposits. Equipment was developed to enable measurement of hydraulic conductivity, as well as the measurement of breakthrough curves resulting from pulses of a conservative tracer solution, while controlling the flow rate and effective stress acting on a soil specimen. The breakthrough curves (concentration vs. time data) could then be analyzed with a curve fitting package to obtain estimates of the hydrodynamic dispersion coefficient, effective porosity, and the mass transfer coefficient governing the transport of contaminants between the mobile and immobile regions in the soil. A preliminary set of experiments was performed using two specimens of uniform silica sand, followed by two specimens of the Aberjona wetland deposits. While there were not enough data to confirm the presence or absence of the anticipated trends, the suitability of the equipment for use in obtaining the hydrologic properties of the wetland deposits was established. Thesis Co-Supervisor: Dr. Patricia J. Culligan-Hensley Title: Assistant Professor of Civil and Environmental Engineering Thesis Co-Supervisor: Dr. John T. Germaine Title: Principle Research Associate in Civil and Environmental Engineering