Nature and Extent of Toluene Contamination in a Shallow Dolostone Aquifer using High Resolution Methods for Assessing Natural and Anthropogenic Influences

A groundwater study was conducted using multiple, high-resolution methods at an urban site with decades-old toluene contamination in a shallow fractured dolostone aquifer. Key methods included continuous coring and logging of fracture and matrix variability, core sampling for physical and chemical analyses, borehole geophysical / hydrophysical logging for multilevel system design. Toluene concentrations at aqueous solubility occurs in the low permeability, porous rock matrix in a thin horizon near top of bedrock, decreasing with depth with 95% of mass within 2.3 to 3.5 m bgs, coincident with the mean water table position. The source zone has minimal residual NAPL which remains due to large sorbed and aqueous mass in the matrix. Anthropogenic features have influenced contaminant nature and extent, however, matrix diffusion with sorption exert the strongest influences on contaminant phase and mass distribution, keeping 80% of total contaminant mass proximal to the source area, where phytoremediation has been implemented.