In what seems like another lifetime, I used to be a geologist for an environmental consulting company here in the Bay Area. One of my biggest fears was drilling through a gas line.
We were often in the field, supervising remediation projects or gathering data in preparation for a remediation project. This often involved gathering soil and rock samples while drilling a series of boreholes that ranged anywhere from 3 feet in depth to around 100 feet in depth.
Before we ever drilled on a site, we consulted numerous maps and hired a company to carry out a USA (underground service alert) survey. The objective of a USA survey was to detect any utilities (gas, water, electricity) and mark them on the ground so that any drilling or excavation work wouldn’t impact said utilities.
This is what all the crazy markings you see all over a sidewalk or on a street mean.
While working on a project in Ukiah a few years ago, we marked a series of spots to drill and had a survey company make sure our spots were clear of any subsurface obstructions. Then we had a drill rig come out and start putting down boreholes.
Midway through the first day of drilling, we were sitting at our logging table when we heard a loud rushing sounds followed by frantic shouts. We looked up in time to see a 30 foot geyser of water shoot up through the top of rig’s tower and the workers scrambling away from the site.
We promptly contacted one of the property owners who turned off the water. After surveying the mess (a lot of muddy ground and a very wet drill rig), it turns out we had drilled right through the middle of an old asbestos cement water main about 6 feet below the surface. It never appeared on any site maps nor did the company conducting the USA survey detect it.
Since the pipe contained asbestos, special care had to be taken to clean up and repair the main, which involved masks for air filtration and disposable Tyvek suits.
Fortunately, it was only a water main (and not a very big one, at that), but it’s something that I was extremely paranoid about in future drilling operations that we conducted.
What if, through sloppy work, unmarked maps, or some other coincidence, it was a gas main? It’s a thought that still scares me today.