Case study: an unmapped septic line under a planned shop

A homeowner planning a new shop needed to know exactly where their septic system ran before siting the building. They had the as-built from the original installation and a reasonable belief that it told them what they needed.

We located the system with ground penetrating radar and electromagnetic locating. Most of it matched the drawing. One line did not appear on the as-built at all, and it ran directly through the planned footing of the shop.

What that line would have cost

Found during construction, an unmapped septic line in a footing is not a small problem. The excavation is already open, the concrete is scheduled, and the options are all expensive: redesign the footing, reroute the line, or stop while somebody works out which is permissible.

Found beforehand, it is a site plan revision. The homeowner shifted the shop, kept their schedule, and avoided a change order and a damaged septic system.

Why the as-built was incomplete

As-builts record what was installed on the day. They do not record what happened afterwards, and septic systems get added to: a line to a new outbuilding, a replaced run on a different route with the original left in place, a repair that shortened a lateral. Decades of ordinary property changes accumulate, none of which update the original drawing.

Treat an as-built as the best available starting point, not as the record of what is in the ground.

Why septic is worth locating before you build

• Tanks and drainfields are easy to drive over with equipment and expensive to repair.

• Septic line is private line. 811 will not mark any of it.

• Setbacks from tanks and drainfields affect where a structure can legally sit, not just where it can physically fit.

• Damage often shows up months later as a failing system rather than immediately.

Related reading: common private utility locating mistakes on rural properties and what happens during a private utility locate.

Locate before you site the building

Advanced Underground Utility Locating has been locating private utilities since 2002. We locate septic tanks, lines and drainfields, private water and electric, and everything else 811 will not mark, and can capture the results as survey-grade points with RTK collection so the record is there for the next project.

Spokane, Coeur d'Alene and the Idaho panhandle: 509-710-2621. Seattle, Tacoma and Portland: 509-954-8623. Bend, Medford and northern California: 541-678-0629. Eugene and Roseburg: 541-780-4149. Coos Bay and the Oregon Coast: 541-315-6728.