Case study: the septic tank was under the new addition

A homeowner called us shortly after buying a house. The property had been renovated before the sale and they simply wanted to know where the septic tank was, which is a reasonable thing to want to know about a system you now own.

We flushed a sonde, a small transmitter, down a toilet and tracked it from the surface as it travelled the line. It stopped under the new addition.

What that means for the owner

A septic tank needs to be reachable. It has to be pumped on a regular cycle, inspected when there is a problem, and eventually repaired or replaced. A tank under a structure is difficult to access at best and can require removing part of the building at worst.

There are also permitting and setback rules for septic systems, which vary by county and are worth confirming with the local health or environmental department before deciding what to do. What we can tell a homeowner is precisely where the tank is. What the county requires about a structure sitting over it is their determination to make.

Why it was not found sooner

A standard home inspection does not locate a septic tank. A septic inspection usually does, but it is ordered separately and is often skipped in a quick sale or waived on a property that appears to be in good order.

Renovation work can bury a tank lid under a slab, deck or addition without anyone involved realising what is beneath. The crew works from the plans they were given, and those plans rarely show the septic system.

Worth doing before you close

Locating the septic system is inexpensive relative to the cost of discovering a problem after the sale, and it is far easier to negotiate before closing than after.

• Where the tank, lines and drainfield actually are.

• Whether anything has been built over any part of the system.

• Whether the system matches the as-built the seller provides, if one exists.

• Where the private water, electric and gas lines run, while somebody is already on site.

Related reading: an unmapped septic line under a planned shop and common private utility locating mistakes on rural properties.

Septic and private utility locating

Advanced Underground Utility Locating has been locating private utilities since 2002. We locate septic tanks, lines and drainfields using sonde tracing, ground penetrating radar and electromagnetic locating, along with private water, electric, gas and communications lines that 811 will not mark.

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.