Natural Discharge of Volatile Organic Compounds from Contaminated Aquifer to Surface Waters

Little attention is usually given to estimating the importance of natural discharge in cleanup efforts, although it has long been recognized that volatile organic compounds (VOCs) can be discharged from a contaminated aquifer under natural gradient conditions. In this study, concentrations and total fluxes of VOCs in the ground water discharging to streams were estimated in the headwaters of the heavily industrialized Aberjona eastern watershed in Massachusetts by measuring the concentrations of VOCs and two injected tracers (one conservative, the other volatile), and simultaneously solving the mass balance equations for the tracers and VOCs in the reach. Measurements were made throughout 2 years, with spatial resolution ranging from tens to hundreds of meters. Concentrations in the inflow as low as 0.05 μg/L of benzene could be reliably detected; the largest inflow observed was 2,200 μg/L of trichloroethene. The estimated natural discharge rate of all identified VOCs from all tested sites was 140 kg/yr, an annual amount of similar magnitude to the mass of VOCs removed by ongoing remediation efforts at a Superfund site in the watershed. Results suggest that the natural discharge rates of contaminated aquifers under natural gradient conditions can and should be considered in developing remediation strategies.