"Certain types of machinery used by homeowners and plumbers to repair clogged sewers, such as snake machines and cutters, could cut the gas line intersecting the lateral, causing a gas leak," said Tomm Marshall, assistant director of Utilities.
"This is why it is important for residents who believe that they have a sewer blockage to contact the CPAU (City of Palo Alto Utilities) on a phone line that we have set up," he said.
The city will have engineers and contractors available at all times to be on site for crossbore inspection within two hours.
The department will run specialized miniature video cameras from the city's sewer mains through customers' individual sewer lines to search for crossbores.
The primary focuses for inspections are gas service that were installed or repaired between 1971 and 2001. It was during this period that the utilities department began to install gas service lines through horizontal or directional drilling, a technique that involved the digging of small underground tunnels through which new gas lines were pulled. While this process avoided the disruption caused by the digging of larger trenches, it is possible that on rare occasions the new gas pipes might have unintentionally bored through sewer lines that were placed differently than originally planned.
A total of $3.8 million has been budgeted to cover the costs of the inspections, which will run through 2013. Though officials noted that they do not expect a vast amount of crossbores to be identified, if one is located, the city will remove and reroute the gas line and repair the sewer line, at no cost to customers.
The department has already begun inspections at high-occupancy buildings such as schools, hospitals and places of worship.
"So far, we have inspected 26 schools and found no evidence of crossbores," Marshall said. This phase of the project is expected to be completed by the end of summer.
The second phase will target commercial and residential locations, beginning in the middle of summer and ending by January 2013. A full schedule will be made available on the department's website.
"Crossbores are a safety risk across the country, and Palo Alto is one of the first utilities departments nationwide to have started a program specific to the problem," said Greg Scoby, engineering manager for Water, Gas and Wastewater.
Several measures have already been taken by the department to tackle the problem, he added. These have included the installation of new gas lines (beginning in 1999) that, if broken, immediately shut off the excess flow valve to reduce gas flows.
Residents can report a sewer blockage problem or suspected gas leak by calling 650-496-6995.