The feeder takes advantage of large volumes of water when available from Northern California, depositing it in surface storage reservoirs, such as Diamond Valley Lake, and local groundwater basins for use during dry periods and emergencies.
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.
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.
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.
[2] The Arrowhead East Tunnel is 5.8 mi (9.3 km) long and 12 ft (3.7 m) in diameter and runs under McKinley Mountain.
The East tunnel was also constructed at a slight downhill grade to allow water to flow by gravity; from the time the water enters the Strawberry Portal until it exits the City Creek Portal, the tunnel will have dropped about 55 feet in elevation.
Original construction commenced in early 1997 at the City Creek Portal, and mining progressed along an uphill gradient from east to west.
Hand-mining efforts above the TBM shield were eventually employed to free the stuck machine.
[5] The $119 million Riverside Badlands Tunnel is 8 mi (13 km) long, the longest tunnel in the feeder project, with a diameter of 12 ft (3.7 m) and runs from Redlands, underneath the Crafton Hills and San Timoteo Badlands through to Moreno Valley.
[6][7] Construction of the tunnel began in October 1998 with the excavation of the Gilman Portal and dewatering work at the two intermediate shafts.
Special measures such as probing and grouting ahead of the TBM and, in particular, deep dewatering wells, were demonstrated to be effective for controlling adverse ground conditions.
The Gilman Portal site proved to be ideal, supporting very efficient mining and muck disposal operations and also allowing long pipe sections to be installed in the tunnel, significantly reducing the amount of field welding required.