Post-Disaster Trenchless Installation of Water Pipelines in Napa, California: City of Napa Highway 29 Water Main Replacement Project

The City of Napa is located in northern California, approximately 50 miles north of San Francisco and is nearby several active earthquake faults. Napa’s water system serves a population of approximately 80,000 people through 370 miles of transmission and distribution pipelines. On August 24, 2014 at 3:20 a.m. the 6.0 magnitude South Napa Earthquake struck 5 miles south/southwest of Napa and 7 miles below ground. Ground shaking was recorded at 0.80g in the City of Napa. Vertical ground deformation was recorded up to 10 centimeters and horizontal deformation over 1 foot. This was the largest earthquake to hit the Bay Area since the Loma Prieta earthquake in 1989. The earthquake caused substantial damage to above ground structures  and more than 240 water pipeline leaks were identified. Luckily no damage occurred at the water treatment plants, pump stations, or dams and only 1 of the 12 storage tanks was damaged.

Several leaks were located beneath Highway 29 and because of their location beneath the highway, they were unable to be repaired and left isolated. This resulted in limiting the City’s ability to move water across the highway, which is a natural physical barrier in the distribution system. The pipelines that cross Highway 29 were originally installed when the highway was a rural two lane road, compared to it currently being a 4 line expressway. To restore water service, the City decided to abandon the isolated leaking sections of pipelines in place and install new highway crossings using horizontally directionally drilled pipelines.