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Septic Decommissioning Permits in Multnomah County

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Learn about septic decommissioning permits and inspections for cesspools, septic tanks, and seepage pits that were abandoned or are no longer in use. You need these permits when connecting to a public sanitary sewer from an active septic system, and often for demolition permits or building permits.
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The City of Portland has an intergovernmental agreement with Multnomah County and the State of Oregon Department of Environmental Quality to conduct septic decommissioning inspections for all of Multnomah County.

Search historic plumbing records for septic system locations

You might find records showing septic system locations on Portland Maps. Enter an address to begin your search. Then select Permits under the "Permits and Zoning" section. You can find any available historic plumbing records here. If there is not a historic plumbing record with a cesspool location on Portland Maps, please call 503-823-6892 or email septic@portlandoregon.gov for assistance. Occasionally there may be cesspool records hiding somewhere that city septic staff may be able to locate for you. Please note that if there is not an open permit on the property, all public records requests must go through GovQA.
 

Decommissioning permit application and important information   

When you need a septic decommissioning permit

Please note: Septic decommissioning is not required for a real estate transaction.

If a structure had interior plumbing before it was connected to a sanitary sewer, the structure used a septic system. Historically there are many homes in the Portland area that used septic systems before connecting to a sanitary sewer, and many of these septic systems have not been decommissioned. Septic decommissioning permits are required upon connection to a public sanitary sewer from a live septic system and may be required as part of building demolitions, building permits, land divisions, property line adjustments, and to abate a property nuisance due to a collapsed or open septic feature. Septic decommissioning will require excavation of the existing yard.

You must have a septic decommissioning permit for any cesspool, septic tank, or seepage pit (septic system) when:

  • A property connects to a public sanitary sewer and the active septic system is removed from service.
  • The source of the sewage is permanently eliminated. For example, demolishing the structure served by a septic system.
  • New construction is proposed within 10 feet of an abandoned septic system.
  • Prior to the approval of a land division of a property with an abandoned septic system.
  • Prior to the approval of a property line adjustment that will result in an abandoned septic system being located on a different lot than the structure it served or located within five feet of a proposed property line.
  • To fill a sink hole resulting from a collapsed or open septic feature.
  • Final inspection approval of a City of Portland septic decommissioning permit is required to have a septic decommissioning on record in Multnomah County.

Apply for a septic decommissioning permit  

Please complete the information in the left-hand column of the Septic Evaluation Application:

  • Job Site Information and Location
  • Property Owner Information
  • Project/System Description
  • Applicant Information
  • Check Decommissioning box on top right

You don't have to include a building permit or engineered drawings with the application. You can email us your completed application. The septic decommissioning permit will be set up within 1-2 business days. We'll contact the applicant with information about how to make fee payment using a credit card. The septic decommissioning permit will be issued upon payment.
 

Who can do the work 

Many types of contractors can perform septic decommissioning work including excavation companies, sanitary sewer contractors, specialty companies for home sales, and septic professionals. Homeowners and others may also perform the decommissioning work. You do not need a trade license to get a decommissioning permit.
 

Decommissioning terms

Cesspool

This is a photo of a cesspool constructed with a red brick lining.
This is a cesspool constructed with a red brick lining.

A cesspool is a large hole that receives combined solid and liquid sanitary waste generated by the plumbing fixtures in a structure. The solids settle to the bottom and remain in the hole while the liquid seeps out into the surrounding soil. The average size is approximately 3-4 feet in diameter and 8-15 feet deep. The top of a cesspool is usually 2-3 feet below the depth of the sanitary sewer line exit at the house. The top of a cesspool may be 10 feet or more below ground surface with basement-level plumbing. Cesspools are usually found east of the Willamette River where soils are typically well-drained.

This is a photo of a cesspool constructed with pre-cast concrete rings.
This image depicts a cesspool constructed with pre-cast concrete rings.

Cesspools constructed before the 1950s were commonly made of stacked brick. Brick may be red (any era) or grey (cement brick typically used from 1940s-1950s).  Brick cesspool lids are often domed brick with a concrete cap. 4” or 6” sanitary lines are typically installed with a 90-degree fitting into the top of the cesspool cone or are run into the side of the cesspool.

This is a photo of an unlined cesspool.
This is a photo of an unlined cesspool.

Cesspools built after the 1950s are usually made of pre-cast concrete rings with a slab concrete lid; 4” or 6” sanitary lines are typically installed with a 90-degree fitting into a square hole in the cement lid.

Cesspools can also be unlined holes dug into silt soils or cobbles. Lid construction may consist of a thin layer of concrete over a wooden platform.

Septic Tank

This is a photo of an old two-compartment septic tank.
This is a large old two-compartment concrete septic tank that previously served a school in East Multnomah County.

A septic tank is a watertight receptacle that receives sewage generated by the plumbing fixtures in a structure. The sewage sits in the septic tank for a period of time, which allows the solids to settle to the bottom and the fats, oils, and greases (call the “scum layer”) to rise to the top. A septic tank has an outlet tee that pulls liquid sewage (called “septic effluent”) from a clear zone between the solids at the bottom of the tank and the scum floating on top. A septic tank always needs a place for the liquid to go – either a seepage pit or a drainfield. If there is a septic tank east of the Willamette River in the City of Portland or Gresham, it typically outlets to one or more seepage pits because the soils are well-drained. A septic tank west of the Willamette River or in east unincorporated Multnomah County typically outlets to a drainfield.

Old septic tanks were made from concrete or metal. Old metal septic tanks can be very degraded and may collapse, and care must be taken when working around old metal septic tanks. Modern septic tanks are usually concrete or made of composite or plastic materials.
 

Seepage Pit

This is a photo of an old "crock" septic tank.
Old 250-gallon cement “crock” septic tanks that were often placed in a series

A seepage pit looks like a cesspool but it is connected to a septic tank before it. A seepage pit only receives liquid sewage from the clear zone in a septic tank. A septic tank may discharge to a concrete box called a distribution unit which may have a few pipes going out of it that lead to multiple seepage pits. Seepage pits may be constructed of the same materials as a cesspool including red or grey brick, concrete rings, or unlined. Residential seepage pits may be smaller than cesspools. Commercial or industrial seepage pits can be very deep (20-30 feet or more). Seepage pits must be decommissioned along with the septic tank.

Drainfield

A drainfield is a system of open-jointed or perforated piping that is connected to a septic tank before it. The drainfield receives liquid sewage from the clear zone in a septic tank. A septic tank may discharge to a concrete box called a distribution unit which may have a few pipes going out of it that lead to multiple drainfield lines. Open jointed piping is usually seen in older septic drainfields (approximately 1960s and before) and consist of one-foot sections of terra cotta or cement pipe stacked end to end in a line and often surrounded by drain rock or gravel. Drainfields installed from the 1970s to early 1990s are usually perforated plastic or corrugated pipe wrapped in drain rock. Drainfields from the early 1990s to present may be made of perforated pipe with drain rock, plastic chambers, or corrugated plastic pipe wrapped in a drain media similar to Styrofoam packing peanuts. Drainfields do not need to be decommissioned, but the septic tank preceding a drainfield does need to be decommissioned.
 

Decommission

The act of pumping and/or filling an abandoned septic system with documentation of the work on permit record with an approved inspection by the City of Portland. Septic tanks, cesspools, and seepage pits must be pumped by a licensed sewage disposal service to remove all sewage (if present). Tanks, cesspools, and seepage pits must be filled with sand, gravel, or concrete density fill or slurry.
 

Abandonment

An abandoned septic system was removed from service and left in place, with no documentation that the septic feature was pumped and filled on permit record. An abandoned septic system is not decommissioned on permit record. Sewer connection records where abandonment without decommissioning occurred will be stamped “Decommissioning Released”, “Release Letter signed”, etc., or have a note “Abandonment $35”. These stamps indicate that at the time of sewer connection these features were released from the decommissioning requirement, and there is no documentation that the septic feature(s) were decommissioned and filled.

Get ready for septic decommissioning permit inspections

Cesspools

Step 1: Locate

Locate a cesspool by following or uncovering the sanitary pipe exiting the building to the end of the pipe either at the cesspool or the property line. The sanitary pipes are typically 4 to 6 inches in diameter. If the sanitary line exiting the building is now connected to sanitary sewer, look for the cesspool behind any pipe fittings that turned the original sanitary line towards the street in line with the main plumbing vent stack of the structure.

This is a diagram illustrating typical locations of original and replacement cesspools.
Diagram of typical primary and replacement cesspool locations
  • Original: Most original cesspools have been constructed directly in line with the main 4” plumbing vent stack visible at the roof and 10-12 feet away from the original building foundation.
  • Replacement: Most replacement cesspools are usually located 10 feet straight out from the original cesspool (20 feet from the original building foundation) or offset at a 45-degree angle.

Step 2: Excavate and remove the top of the cesspool    

In the approximate location of the cesspool, the top of the cesspool should be approximately 2-3 feet below the depth of the sanitary sewer pipe existing the building. Carefully remove the top and expose the cesspool. If the building has basement level plumbing, the top of the cesspool may be 10-12 feet below the ground surface.  

Step 3: Pump out any sewage 

If any residual solid or liquid sanitary waste is in the cesspool it must be pumped by a licensed DEQ pumper. If a cesspool has been abandoned for several years, it will likely be dry. If a cesspool is dry, pumping and a pump receipt are not required. 

If pumping is necessary, a copy of the pump receipt will be required for inspection approval. 

Step 4: Backfill  

Backfill the cesspool using clean ¾-inch minus crushed rock, gravel, masonry or playground sand, or concrete slurry. Native silty or clay soils, debris, and/or garbage cannot be used.

Leave the upper 12-18 inches of the cesspool lining and the piping entering the cesspool exposed. The inspector will document the piping, cesspool construction as brick, concrete ring, or unlined soil, and type of fill materials. The inspector will also sketch the location of the cesspool(s) on the property.

You may be required to remove fill if these elements are not visible during inspection.  For fill using sand or gravel, it is recommended to fill in lifts of 6-12 inches thick and water down and/or tamp for proper compaction.

If a new foundation will be constructed within 10 feet of the onsite septic system, the fill may need to be placed as structural fill with compaction testing by an engineer or testing agency. Please consult with your engineer or building inspector. 

Septic tanks 

Step 1: Locate  

Locate a septic tank by following or uncovering the sanitary pipe exiting the building to the end of the pipe either at the septic tank or the property line.  The sanitary pipe to a septic tank is typically 4 inches in diameter. If the sanitary line exiting the building is now connected to sanitary sewer, look for the septic tank behind any pipe fittings that turned the original sanitary line towards the street in line with the main plumbing vent stack of the structure.  Occasionally septic tanks may have a riser to ground surface. If the septic tank is east of the Willamette River, the inspector will ask that the septic tank outlet is followed to confirm whether the tank outlet connect to a seepage pit or drainfield. If the septic tank is connected to a seepage pit, the seepage pit must be decommissioned following the cesspool instructions above.

Most septic tanks have been constructed directly in line with the main 4” plumbing vent stack visible at the roof and 5-20 feet away from the original building foundation. Septic tanks are usually located in an area downslope of the house to accommodate gravity flow to the drainfield or seepage pit.

Step 2: Pump out any sewage if applicable  

If any residual solid or liquid waste is in the tank it must be pumped by a licensed DEQ pumper. Septic tanks typically must be pumped and are infrequently dry.

Please keep a copy of the pump receipt. It is required prior for inspection approval.

Step 3: Remove or decommission in-place  

To decommission a septic tank in place, it may be possible to fill the septic tank through an existing riser opening. In other situations, the top may need to be broken open to fill the septic tank. To ensure drainage, break up, punch, or drill holes in the bottom of the tank. Backfill the tank with sand, ¾-inch minus gravel, or concrete slurry. The top of the tank must be visible at the time of inspection so the tank construction, depth below grade, and fill material can be documented.  The inspector will also sketch the location of the septic tank(s) on the property. 

You can remove tanks if desired and backfill the excavation with sand, gravel, slurry, or according to an engineer’s recommendation. If you pull a septic tank before inspection, please make sure the tank remains on-site for inspection or photos are available showing the empty septic tank prior to removal.

If a new foundation will be constructed within 10 feet of the onsite septic system, the fill may need to be placed as structural fill with compaction testing by an engineer or testing agency. Please consult with your engineer or building inspector. 
 

Schedule a septic decommissioning permit inspection, get inspection results and make corrections 

To schedule a septic decommissioning inspection, call the automated Requests for Inspection phone number at 503-823-7000. You need your IVR number and the three-digit code for the inspection. The IVR code for septic decommissioning is 842.

Our inspection staff will call between 7 and 9 a.m. on the day of the inspection. We'll confirm the site is accessible and the work is ready for inspection. We'll also provide an inspection window for arrival.

The inspector will come to the property prepared with historic septic and plumbing records for the property. They will inspect the uncovered septic feature location(s), pipe type(s), and dimensions and compare to the available permit records. The inspector will sketch an as-built of the septic system feature(s) and document septic feature dimensions and backfill material. If a septic feature was not located, excavation efforts will be inspected and similarly documented. Keep all excavation efforts open for inspection. The inspector will collect the pump receipt to confirm the removal of septage.  Also:

  • If a pump receipt is unavailable at the time of the inspection, or other corrections are required, a list of the corrections will be documented on the inspection report.
  • Get the results of the inspection on Portland Maps permit/case search the next day. Read more about why work does not get approved and how to schedule a reinspection.
  • A reinspection fee may be charge if the inspector needs to perform three or more inspections on site. The fee must be paid prior to inspection approval.
  • When the inspection has been approved, you may cover the cesspool or septic tank.

Contact septic inspectors 

If you have questions about septic inspections, please call Onsite Septic Permits and Inspections at 503-823-6892.