Abandoned Cesspools
What May Still Be Under the Yard
Tens of thousands of Portland homes drained to a cesspool before the sewer reached them. Most of those pits were supposed to be pumped and filled at hookup. The records don’t always show that it happened, and most cesspools leave no trace at the surface.
Why this is a Portland problem
- Before the sewer reached a neighborhood, houses east of the Willamette usually drained to a cesspool. The City of Portland says cesspools are most common east of the river, where the soils drain well. West of the river, septic tanks were more common.
- There are two big groups. Close-in east side houses from the early 1900s often had a cesspool until the sewer arrived. Then came the postwar houses of mid-Multnomah County, mostly east of 82nd Avenue, which stayed on cesspools for decades. The Mid-County Sewer Project connected about 54,000 of those properties between 1986 and 2001.
- Oregon’s rules say a cesspool has to be pumped and filled once the house connects to a sewer. Whether that actually happened at a given house, and whether anyone wrote it down, is a separate question.
- The City’s own guidance is blunt about it: if the historic plumbing record doesn’t clearly say the system was decommissioned and filled, assume it wasn’t.
What a Portland cesspool actually is
A cesspool is a lined pit that took raw sewage straight from the house. Solids settled to the bottom and stayed there. Liquid seeped out through gaps and holes in the lining into the soil around it. There was no tank ahead of it and no drain field after it.
Portland’s cesspools aren’t the wide, shallow pits most people picture. City guidance describes a typical one as a cylinder about 3 to 4 feet across and roughly 8 to 15 feet deep. Before the 1950s they were usually laid up in brick. After that, stacked precast concrete rings became the norm.
Two related terms show up in old permit records. A septic tank is a watertight box that holds solids before the liquid moves on to a drain field or a pit. A seepage pit is basically a cesspool with a septic tank in front of it. When any of these is taken out of service, Oregon’s rules treat them the same way.
Where abandoned cesspools are most likely
The close-in east side. Houses built before the sewer lines reached them had to put their waste somewhere. In February 2014, after a wet stretch of weather, a woman and her dog fell into a hole that opened in a backyard on SE 38th Avenue. City records showed the house was built in 1909 with a cesspool. The hole was about 20 feet deep and 3 1/2 feet across. Both were pulled out unhurt.
Mid-Multnomah County. This is where most of Portland’s cesspools were. Much of the area east of 82nd Avenue was built up after World War II without sewers, and by 1984 the county was warning that groundwater there couldn’t be counted on as safe to drink. Portland annexed the area through the 1980s and early 1990s. The Mid-County Sewer Project then ran sewer to about 54,000 properties across 28 square miles, starting in 1986 and finishing in 2001. The project’s stated purpose was to replace the cesspools those houses had been using.
A second pit. Cesspools clogged and got replaced. City guidance says a replacement was usually dug about 10 feet from the original, either straight out or at an angle. The City’s own example is a house built in 1943 with a new cesspool on record in 1971. That property has two pits to account for, one brick and one concrete.
Outside Portland. Older homes in Clackamas County, Clark County, and the rest of the metro that predate their sewer connection can have the same leftovers. The county septic programs, not Portland, keep those records.
Why an unfilled cesspool matters
An unfilled cesspool is a deep, narrow hole with a lining that was built to leak. Over decades, brick and open-jointed rings can let soil wash in, and the lining itself can weaken. The City’s disclaimer for properties with a possible abandoned system says these features may collapse, settle, or cause the ground to subside, and that this can damage structures.
Keep that in proportion. When the SE 38th Avenue hole made the news in 2014, a city development services official said cesspools that were never decommissioned are common, and that a cesspool sinkhole is rare. Most of these pits sit quietly for decades.
Where it really comes up is building. Portland requires an abandoned system within 10 feet of new construction to be decommissioned first. That covers additions, ADUs, garages, and decks. If a new foundation is going within 10 feet, the City notes the fill may need to be placed as structural fill with compaction testing, which brings an engineer into the picture.
Why you usually can’t see one
Most abandoned cesspools leave no mark on the surface at all. According to City guidance, the top of a typical cesspool sits about 3 to 5 feet below grade when the house has no plumbing in the basement, and about 8 to 10 feet down when it does. A rule of thumb from the same guidance: the top is roughly where the sewer line leaves the building, plus 2 feet.
The City also tells owners where to look. Find the main plumbing vent stack on the roof, usually a 4-inch pipe. Picture a straight line from it out through the foundation. The original cesspool is typically 10 to 12 feet out along that line.
Things that point toward a cesspool:
- A house built before the sewer reached its street. If a house was built with plumbing before public sewer was available, the City says it had an onsite system.
- A historic plumbing record that shows a cesspool, especially one without a note that it was decommissioned and filled.
- A settled or sunken spot in the yard roughly in line with the main vent stack.
- A hole or depression that opens up after heavy rain.
None of these proves anything by itself, and a yard with none of them can still have a pit under it.
Checking the records first
Portland has better paper on this than most people expect. On PortlandMaps, search the address, open Permits and Zoning, then Permits, and scroll to Historic Plumbing. Each record can run several pages. The front usually has a table and a short description, and the back often has a hand drawing of the plumbing, sometimes with the cesspool sketched in.
Read those records for two things. First, any mention of a cesspool, original or replacement. Second, whether the record says the system was decommissioned and filled. If it doesn’t say that clearly, the City’s guidance is to treat it as not done. If nothing shows up online, the City’s septic program answers questions at septic@portlandoregon.gov.
Where a home inspection fits
A home inspection doesn’t look for cesspools. It doesn’t include anything underground, so it can’t find a cesspool, confirm one is there, or tell you whether it was filled. For an older east side house, the historic plumbing records are the place to answer that question.
A sewer camera inspection, arranged separately through a plumber, looks at the line the house uses today. It isn’t designed to find or evaluate an old cesspool. If someone needs to know exactly where a pit is and what condition it is in, that’s a job for a locating company or a contractor who does decommissioning.
How decommissioning is supposed to be done
Oregon’s onsite rule, OAR 340-071-0185, requires an owner to decommission a cesspool, seepage pit, or septic tank once the house is connected to a sewer. In Portland, the process runs through the City’s septic program:
- Get a decommissioning permit.
- Find the pit. Digging along the original sewer line from the house is the method the City calls most reliable.
- If any sewage is left, have it pumped by a DEQ-licensed pumper and keep the receipt. A dry cesspool doesn’t need pumping.
- Fill it with 3/4-inch-minus gravel, masonry or playground sand, or concrete slurry. Sand and gravel go in lifts and get watered or tamped. Native soil and debris aren’t allowed.
- Leave the top 12 to 18 inches open, with the old pipe exposed, and call for the City’s decommissioning inspection.
- After it passes, fill to grade.
An inspection is required even if the pit can’t be found, so the City can document how hard someone looked. The permit also puts the location on record, which is exactly what was missing for so many houses connected during the Mid-County project.
Outside Portland, the steps are close to the same. Clackamas County uses a certification form built on the same DEQ standard: pumped by a licensed pumper, then filled with sand or gravel, or removed. In Clark County, Washington, Clark County Public Health asks for the waste to be pumped by a certified pumper, the lid removed or destroyed, the void filled, and a written abandonment notice sent in.
| Item | Cost |
|---|---|
| Decommissioning permit, no site visit | $486 |
| Decommissioning permit, site visit with no other septic permit | $982 |
| Locating, excavation, pumping, and fill | Contractor quote |
Questions worth asking
- Do the historic plumbing records show a cesspool, and do they say it was decommissioned and filled?
- Was the house built before the sewer reached the street? If so, when was it connected?
- Is there more than one cesspool on record, an original and a replacement?
- Is an addition, ADU, garage, or deck in your plans? If so, anything within 10 feet of an old pit will need to be dealt with first.
If the answers point toward an old pit, the historic plumbing records and the City’s septic program are the next stop.
Abandoned Cesspools FAQ
