Two pilot-scale tests of surfactant-modified zeolite (SMZ) permeable barriers were conducted at the Large Experimental Aquifer Facility of the Oregon Graduate Institute. The tests were performed in an 8.5-m-wide, 8.5-m-long, 3-m-deep concrete tank. The SMZ was installed in a 1-m-wide, 6-m-long, 2-m-deep barrier frame in the center of the tank. The rest of the tank was filled with sand to form a simulated aquifer. A three-dimensional sampling array consisting of 405 sampling points was installed in the tank. Controlled water flow across the tank was maintained using ten upgradient injection wells and ten downgradient withdrawal wells. A specific discharge of 0.17 m day−1 was imposed, resulting in an average linear groundwater velocity of approximately 0.5 m day−1 in the sand. The upgradient wells allowed injection of a three-dimensional contaminant plume composed of 10 mg L−1 (0.19 mmolL−1) Cr, in the form of chromate, and 1.8 mg L−1 (0.011 mmol L−1) perchloroethylene (PCE).
In the first pilot test, 12 metric tons of 14–40 mesh (1.4−0.4 mm) SMZ, manufactured at a cost of about $460 per metric ton, was used as the barrier material. Intensive sampling showed that much of the contaminant plume was being deflected under and around the SMZ barrier. Hydraulic testing failed to conclusively isolate the cause(s) of the flow restriction but suggested that a partially plugged barrier frame, along with a possible decrease in SMZ permeability, were responsible.