Since 1988, Weston has been conducting site investigation and long-term monitoring activities at a 200-acre parcel consisting of three separate landfill disposal areas that resulted in groundwater impacted by volatile organic compounds and 1,4-dioxane. The presence of waste below the water table causes reducing conditions, which have mobilized naturally occurring arsenic. Despite the complex hydrogeology of the site, Weston developed Conceptual Site Models and a hydrogeologic framework to determine that downgradient receptors have not been impacted by arsenic to date. In the last 4 years, Weston has expanded investigations to include a targeted groundwater sampling program to determine if emerging contaminants, such as 1,4-dioxane and PFAS, are present. Although these emerging contaminants are present in groundwater, the impacts of potentially site-related 1,4-dioxane and PFAS are limited; however, upgradient and off-site PFAS detections suggest regional impact from other sources. Weston’s long-term monitoring approach saves the client millions of dollars as compared to an active remediation alternative, such as ex-situ groundwater treatment or relocating the landfill waste.