Assessment of Advective Porewater Movement Affecting Mass Transfer of Hydrophobic Organic Contaminants in Marine Intertidal Sediment

摘要

Advective porewater movement and molecular diffusion are important factors affecting the mass transfer of hydrophobic organic compounds (HOCs) in marsh and mudflat sediments. This study assessed porewater movement in an intertidal mudflat in South Basin adjacentto Hunters Point Shipyard, San Francisco, CA, where a pilot-scale test of sorbent amendment assessed the in situ stabilization of polychlorinated biphenyls (PCBs). To quantify advective porewater movement within the top O-60 cm sediment layer, we used temperature as a tracer and conducted heat transport analysis using 14-day data from mulftidepth sediment temperature logging stations and one-dimensional heat transport simulations. The best-fit conditions gave an average Darcy velocity of 3.8cm/d in the downward vertical direction for sorbent-amended sediment with a plausible range of Ocm/d to Scm/d. In a limiting case with no net advection, the best-fit depth-averaged mechanical dispersion coefficient was 2.2 × 10~(-7)m~2/s with a range of 0.9 × 10~(-7)m~2/s to 5.6× 10~(-7)m~2/S.The Peclet number for PCB mobilization showed that moleculardiffusion would control PCB mass transfer from sediment to sorbent particles for the case of uniform distribution of sorbent However, the advective flow and mechanical dispersion in the test site would significantly benefit the stabilization effect of heterogeneously distributed sorbent by acting to smooth out the heterogeneities and homogenizing pollutant concentrations across the entire bioactive zone. These measurements and modeling techniques on intertidal sediment porewatertransport could be useful forthe development of more reliable mass transfer models for the prediction of contaminant release within the sediment bed, the movement of HOCs in the intertidal aquatic environment, and in situ sequestration by sorbent addition.