[en] A series of laboratory gas-flow tests has been performed on interfaces comprised of concrete, very low-density polyethylene membrane, and halite. These tests were conducted to (1) evaluate whether a meaningful test can be run to quantify the effectiveness of a membrane, and (2) aid in the design of an Alcove Gas Barrier at the Waste Isolation Pilot Plant (WIPP), where membranes of this type are being considered for use at the interface between the concrete or grout of the gas barrier structure and the surrounding halite. Over 400 longitudinal transient-flow and steady-state radial-flow tests have been completed. However, it is not clear from these tests that the test results can be meaningfully applied to the full-scale Alcove Gas Barrier configuration because the measured permeabilities are several orders of magnitude higher than the meter-scale in situ concrete seal tests conducted at the WIPP as part of the Small-Scale Seal Performance Tests. Results show that the membranes decrease gas permeability along the concrete/halite interface by one to two orders of magnitude to below 10^-15 m² for the simplified test configurations. 28 refs., 11 figs., 16 tabs