Although not as common as backhoes or clamshells, because of depth constrictions, the continuous trencher is an option for composite barriers 35 to 40 ft deep. It is capable of simultaneously excavating a narrow, 12- to 24-in.-wide trench and immediately refilling it with either a reactive medium and/or a continuous sheet of impermeable, high-density polyethylene (HDPE) liner. The trencher operates by cutting through soil using a chain-saw type apparatus attached to the boom of a crawler-mounted vehicle. The boom is equipped with a trench box, which stabilizes the trench walls as a reactive medium is fed from an attached, overhead hopper into the trailing end of the excavated trench. The hopper contains two compartments, one of which can emplace up to gravel-size media. The other compartment is capable of simultaneously unrolling a continuous sheet of HDPE liner, if desired.