PAHs in sediment pore water can be sequestered before upwelling water reaches the sediment-water interface using amended sand caps with amendments such as activated carbon and biochar. Passive samplers offer a method to monitor remedy effectiveness.
A key condition for using passive samplers to directly estimate hydrophobic organic compounds (HOCs) pore water concentrations is that the concentrations of the HOCs being sampled are in equilibrium between the sampler and the pore water. The time to achieve equilibrium between the passive sampler and the surrounding pore water is dependent on both the hydrophobicity of the HOC and the surrounding chemical environment. The loss of performance reference compounds (PRCs) during deployment of a passive sampler allows for the estimation of the degree of equilibrium achieved or confirmation of the achievement of equilibrium. If the passive sampler is found not to be at equilibrium with the surrounding pore water, then the PRC data can provide an estimation of passive sampler uptake rates for calculation of the equilibrium pore water HOC concentrations.
This presentation will show theoretical and empirical data demonstrating the difference in estimated equilibration times for various PAH compounds in different amended sediment cap environments. The equilibration times measured ranged from ~20 days in a powdered activated carbon (PAC) amended cap environment to ~200+ days in a sand only cap with no flowing water. Equilibration times were determined using deuterated PAH and hydrophobic dye PRCs. The results of the research can be used to determine if PRCs are required in passive sampling programs depending on the cap conditions (e.g. PAC or no PAC), HOCs of interested being measured and estimated sample deployment time.