If your sewer line is clogged, it could be because there is a gas line running through the middle of it. Yes, you read that correctly.

The City of Palo Alto Utilities Department has launched a gas safety initiative to visually inspect sewer lines throughout the city after learning that some of those lines may have been inadvertently drilled through during gas line installations—a condition known as a crossbore. Crossbores are not typically dangerous when left undisturbed, according to a statement released today by CPAUD. But when someone tries to unclog a sewer line with a snake or a cutter, that device may sever a gas line and cause a dangerous leak.

"The key message for our customers is this: if you believe you have a sewer blockage problem, call the City of Palo Alto Utilities Department first at (650) 496-6995," said Javad Ghaffari, Manager of Water, Gas and Wastewater Operations. "We will have trained staff available to respond 24x7. They will assess the area for crossbore and determine additional precautions or next steps," he said.

Concern over crossbores arose as a result of the Utility reviewing its operations and best practices and in response to overall heightened concerns over gas system safety, according to Water, Gas and Wastewater Engineering Manager Greg Scoby. "Although the issue of crossbore safety is a national one, CPAU is among the first utilities in the country to undertake a very aggressive crossbore safety program," said Scoby.

CPAU has already begun inspecting high-occupancy buildings, such as churches, hospitals, nursing homes, and has completed 26 schools. The program is expected to be completed by January 2013.

"This is an abundance of caution situation," said Utilities Communications Manager Mary Coady.

The Utility has so far found eight crossbores since 2000. Across the country, such instances are rare, according to a CPAU statement. Crossbores began occuring in the 1970's, when trenchless drilling allowed utility companies to bore into the ground to install flexible, low-pressure, plastic gas lines. During that time the industry undertook "all standard precautions" to place new pipes in areas free of other underground utilities, the statement said. But not all sewer lines were placed where the utilities thought, the result of landscaping or other improvements.