Equilibrium passive sampling devices consisting of 17-mu m thick polyoxymethylene (POM) were in situ deployed as a novel technique for landfill groundwater leachate water sampling of freely dissolved poly-cyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). POM was deployed in two groundwater leachate wells (flow around 100 m y(-1)) and an effluent leachate tank. The dissipation of >90% of spiked performance reference compounds and comparison between 60 d and 140 d of equilibration confirmed that POM-water equilibrium was reached for all PAHs and most PCBs within 60 d. Comparison of total and freely dissolved concentrations yielded dissolved organic carbon-water distribution ratios that were on average 0.4 log-unit below amorphous organic carbon-water distribution ratios and in accordance with literature values. Particle-bound fractions ranged from 50% (small PAHs) to 99.9% (large PCBs), and were >95% for most compounds. It was concluded that POM-17 equilibrium passive samplers provide a facile method to measure freely dissolved concentrations of PAH and PCB in groundwater leachate, which will yield valuable information on its ecotoxicological risk for aquatic and benthic organisms.