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Issues discussed concern the design and construction of a subway system in Los Angeles, California, focusing on the design challenge posed by anticipated earthquakes and hazardous subsurface gases. Topics addressed include the structural integrity of the tunnels, and the use of high-density polyethylene membranes to keep dangerous gases out of the system.

The Inland Feeder designed to increase the amount of state-produced water for Southern California comprises of the Arrowhead East and Arrowhead West Tunnels. The tunnels incorporate structural features like impermeable lining, unique seismic sections and extensive probing and grouting to account for earthquakes and a ground-water monitoring program with 100 monitoring sites. The use of thick-walled steel pipes in fault zones serves a means of protection for the tunnel-workers during earthquakes.