Screening reactive materials as permeable barriers to treat lead and benzene contaminated groundwater

Laboratory batch experiments were performed to: (i) select two individual and two mixtures of potential reactive materials for permeable barriers to treat groundwater contaminated with benzene and soluble lead (Pb²⁺); (ii) investigate the involved contaminant removal mechanisms; and (iii) determine the permeability and assess the environmental compatibility of the selected materials. Five individual reactive materials (zeolite, diatomaceous earth, brown coal, compost, and zero-valent iron as control) and four mixtures (compost:brown coal, compost:zeolite, compost:mulch, and mulch:diatomaceous earth) in different ratios were investigated. Benzene and Pb²⁺ were investigated separately using Pb²⁺/benzene spiked deionized water. Zeolite and brown coal were selected as individual materials for Pb and benzene based on their removal efficiencies. For the material mixtures, compost:brown coal (1:3) and compost:zeolite mixtures (1:3) were selected for Pb, whereas compost:zeolite (1:1) and compost:brown coal (1:5) were selected for benzene. The sequential extraction of Pb from these selected reactive materials showed that Pb was held mainly in the exchangeable fraction (52%–76%). Benzene was removed by biodegradation and sorption, with the latter contributing most to its removal (60%–99%). The selected materials were compatible with the environment considering the amounts of toxic metals leached from them, and their permeabilities were in the range of 4.2 × 10⁻⁵–2.14 × 10⁻³ m s⁻¹.