at Old Waterman Canyon Road and California State Route 18. The tunnel was constructed with a grade to allow water to flow by gravity; from the time the water enters the Devil Canyon Portal until it exits the Waterman Portal, the tunnel will have dropped about 31 feet in elevation. The west tunnel was the most difficult of the three tunnels to excavate. It was excavated using a tunnel boring machine (TBM) that took over four years to bore its way through the mountain. The TBM was launched from the Waterman Portal and tunneled in a westerly direction toward the Devil Canyon portal at a slight uphill gradient of approximately 2 inches per 100 linear feet (0.17%). Crews faced many challenges during the excavation, including the 2003 Old Fire that destroyed construction equipment at the Waterman Portal and halted tunneling for ten days. Later that year, a flash flood engulfed the Waterman Portal site and submerged the TBM. It took four months to restore operations in the aftermath of the flooding. The TBM faced many challenges during the tunneling. Much of the tunneling took place in water-bearing strata of metamorphic and granitic rock. The presence of water, coupled with the depth of the tunnel, up to 1,100 feet underground, forced the tunneling team to deal with water pressures in excess of 150 pounds per square inch. Additionally, the tunnel alignment crossed or traversed near several significant faults and shear zones, including branches of the San Andreas and Arrowhead Springs Faults. In these faulted areas, the massive blocks of rock were broken into fine debris that were treated with grout before tunneling could safely cross through these zones. A particularly challenging reach of the tunnel alignment was encountered in the last 1,500 feet of the tunneling work as the TBM crossed five significant fault and shear zones along the tunnel alignment on its way to completion at the Devil Canyon Portal. While tunneling in this zone in mid-2008, the TBM began dipping as it encountered a 40-foot-wide fault zone of completely crushed, weak rock. Concrete and steel foundation pads were constructed in front of the cutter head to stabilize the TBM and correct the alignment of the machine as it crossed the weak ground within the fault zone. The tunnel was completed in August 2008, with installation of pipeline being completed in 2009. Arrowhead East Tunnel The Arrowhead East Tunnel is