Multicomponent NAPL composition dynamics and risk

This paper presents a numerical simulation of multicomponent non-aqueous phase liquid (NAPL) dissolution and biodegradation. The model system is a liquid-liquid system consisting of water and a NAPL that is a mixture of polycyclic aromatic hydrocarbons (PAHs). The dynamic processes include dissolution from the NAPL phase, biodegradation in the aqueous phase, and flushing in the aqueous phase. The model was applied to describe composition dynamics in a NAPL containing seventeen soluble compounds and a stable fraction, and uses a numerical solution procedure to solve a system of 36 coupled differential equations. Parameters describing biodegradation and mass transfer kinetics were estimated from literature data. Simulation results demonstrate the dependence of aqueous concentrations on NAPL composition dynamics, and the resulting interdependence of PAH behavior. Thirty year time-averaged aqueous concentrations were used to estimate carcinogenic risk associated with ingestion of the contaminated water. Only during the first five years do the lower molecular weight compounds contribute significantly to risk, after which the risk is dominated by compounds such as benzo[a]pyrene.