Legacies from three former manufactured-gas plants: impacts on groundwaterquality

Groundwater contamination due to accidental releases of mono- and polycycli c aromatic compounds (MAHs and PAHs) from decommissioned manufactured-gas p lants is an ongoing and litigious problem. The MAHs and PAHs are derived fr om coal tar, which was a by-product of the gas-manufacturing process. While originally designed to contain coal tar, the manufactured-gas plant struct ures that remain today have often degraded over time and are not completely leak-proof. Over a period of many years, subsurface water has seeped into and out of the structures, resulting in groundwater contamination. This was particularly true once the tops of the structures were removed. In this st udy, process-based simulations were conducted to estimate the groundwater-q uality impacts of accidental releases of dissolved naphthalene (C10H8) from the sites of three former manufactured-gas plants. The results from one-di mensional, transient, unsaturated, near-surface fluid-flow and solute-trans port simulations served as input to three-dimensional saturated subsurface fluid-flow and solute-transport simulations. The simulation results and sen sitivity analysis reported here indicate that accidental releases of naphth alene had significant, negative impacts on groundwater quality at each of t he three sites.