The significance of buried landscape in subsurface migration of dense non-aqueous phase a liquids: The case of perchloroethylene in the Sussex aquifer, New Brunswick

At Sussex, New Brunswick, dissolved perchloroethylene (PCE) as high as 28.0 mug/liter, was detected within the upper aquifer and in concentrations to 1.6 mug/liter within the lower aquifer that serves as the main source of mu nicipal water supply. Predominantly formed as an esker ridge, the lower aqu ifer consists of well-sorted, glaciofluvial/ice-contact, sand and gravel la yers mostly confined by underlying till and/or bedrock and an overlying uni t of laminated silt-clay glaciolacustrine sediments (middle aquitard). The middle aquitard is in turn overlain by an upper aquifer of variable thickne ss, extending from a depth of about 18 m to near surface, consisting of coa rsening-upward sand and gravel, with occasional lenses of clay, silt and di amicton. A dispersal plume was identified by contouring PCE concentrations from 72 s amples from the upper aquifer; PCE was not detected in 16 surface soil samp les. The highest concentrations imply that the PCE originated from a surfac e spill near the urban business center and that subsurface migration was in fluenced significantly by a buried relict river channel cut into the middle aquitard. Scouring along the channel bottom cut through the middle aquitar d and intersected the esker ridge of the underlying water supply aquifer, f orming windows through the aquitard. Contamination of the lower aquifer has likely originated from the PCE being drawn through these windows during pu mping of a water-supply well that is now out of service. Results indicate t hat withdrawal rates and placement of original municipal water wells, as we ll as the stratigraphy, conductivity and topography of subsurface units are controlling factors in Dense Non-Aqueous Phase Liquid migration at this si te.