The Bethesda Metro station Credit: FILE PHOTO

Metro announced Thursday it will expand a pilot program to waterproof the leaky Red Line tunnel in the Bethesda area, which will cause service disruptions in October and November.

Metro began testing an injectable waterproof membrane material on the tunnel between the Medical Center and Bethesda stations in July. After testing it, the transit operator determined it was working and that the tunnel was remaining “relatively dry” even with excess rains in July and August.

As a result, Metro is going to expand the “curtain grouting” technique to a 4,000-foot section of inbound track between the Medical Center and Grosvenor-Strathmore stations.

Metro plans the following service changes to install the waterproofing material:

­To install the waterproofing material, crews drill into the tunnel and inject a polymer-based material that flows down the walls of the tunnel. The technique is designed to prevent water from leaking into the tunnel—a notorious problem for the tunnel that stretches from Dupont Circle to Grosvenor. It’s the only stretch of Metro’s tunnels built before the widespread use of a method in which a waterproof membrane is installed.


The track in the leaky tunnel is prone to corrosion and arcing insulator incidents, when debris or water is in contact with the electrified third rail and causes smoke or fire. The tunnel is beneath the water table and most prone to leaking during and after heavy rains.