|The master control valve was rusty but|
gave way to determination + a pipe wrench
I turned off the valve to the house, but the water continued to flow. A fairly desperate call (it was Friday, remember) at 4:35 to the city water department, now closed, referred me to the Foster City Fire Department. And so it was that a fire truck with five firefighters pulled up, surely an inefficient use of public resources but I certainly wasn't complaining.
After 15 minutes of fiddling with various valves and connections, the firefighters unlocked the master control valve near the curb and shut off the water to the property. Apparently the developer in his haste had run a water line directly to the sprinklers without going through the house system.
On a serious note, the problem of undocumented underground utility lines is a nationwide problem:
Failure to locate underground utilities before you dig can result in disruption of services to individual homes or entire neighborhoods. Even worse, cutting into some buried cables or pipes can result in injury or death. But, underground pipes and cables can be hard to find. In some instances, they have been recorded on GIS [geographic information system] mapping. In many cases, however, there is no record of where this underground infrastructure has been buried.
|Glue gets it done|
[Update - 3/1/15: fortunately the leak was from a PVC pipe and I was able to replace the section myself on Sunday morning.
(BTW, I found that so-called "glue-free" lockable couplings weren't leak-free under continuous water pressure)]