The City of San Diego, CA, owns and operates the Pump Station No. 77 (PS77) force main which conveys untreated sewage 5+ miles through an environmentally sensitive habitat and beneath Lake Hodges, a regional drinking water
supply reservoir. Installation of the force main, constructed of ductile iron pipe, was completed in 1976.
The force main crosses underneath the lake in twin 2,000-foot long, 16-inch diameter parallel pipelines. In their 40-
plus-year operating history, there is no record of the pipelines having been cleaned or inspected.
While the City has performed condition assessment on the land-based portions of the force main at select locations utilizing traditional open-cut methods, the subaqueous portion had never been inspected – the condition of pipelines was unknown. And the City’s understanding was they could not be inspected.
The City tasked Brown and Caldwell (BC) to find a way to inspect the pipelines, accurately assess their condition,
and recommend whether maintenance, repair, or replacement was required. BC developed an innovative approach centered around the use of a cutting-edge, trenchless pipeline inspection technology.
BC selected an in-line inspection (ILI) tool, named the See Snake, because of its capability to measure pipe wall thickness for the entire length of the pipelines’ 360-degree circumference.
Executing a carefully orchestrated plan that included construction of pig launching and receiving facilities and performing pipeline cleaning via the progressive pigging method, the ILI tool was successfully deployed in a 100% free-swimming, non-tethered mode – a worldwide first for the See Snake in a force main beneath a body of water.