Transport and fate of a LNAPL in fractured clayey till
Bruce H. Kjartenson
Flow through interconnected fractures and fissures in an otherwise "tight" formation can lead to increased mobility and spreading of contamination. To investigate the potential for increased mobility of a LNAPL, gasoline, in fractured clayey till, a series of laboratory flexible wall permeability tests (column tests) were performed on undisturbed samples of fractured clayey till at confining pressures equal to the measured in situ lateral earth pressures. The column tests were performed using a CaSO4 solution, a CaCl2 solution, and gasoline as the permeants;Results of the tests with CaSO4 and CaCl2 solutions indicate that the fractured and fissured till has a hydraulic conductivity on the order of 10-6 cm/s and an effective porosity significantly less than the total porosity. The hydraulic conductivity using gasoline as the permeant is approximately the same as using water as the permeant. Following the hydraulic conductivity testing stage, air was forced through the gasoline soaked samples to investigate air venting as a remedial technology for this material. This study allowed determination of an effective air permeability and the immobile gasoline fraction. The amount of immobile gasoline was determined by measuring residual concentrations of Benzene, Ethyl benzene, Toluene, and Xylene from soil samples taken from the "remediated" samples. Results indicate that the gasoline flow occurs only through a small portion of the total porosity (~10%) inferring the potential for a significant decrease in travel time, and that fractured clayey till should not be considered as a significant barrier against groundwater contamination. Other results indicate that air venting effectively removes approximately 60% of the mobile gasoline from the sample and may be a viable in situ remedial technology for this material.