Above Ground Storage Tank or AST

Above Ground Storage Tank or AST Common Questions


Above Ground Storage Tank or AST, like an Underground Storage Tank (UST), contain heating oil for the purpose of heating homes and buildings. There are specific differences between the two tanks and these are some of the most common questions we are asked regarding ASTs.

What is an above ground storage tank or AST?

Homes, apartments, farms and some businesses that are currently or were heated using diesel heating oil, used an above ground storage tank (AST) to store the heating oil. ASTs are most commonly mounted on a stand or a ground pad either outside or in a basement. ASTs can also be partially buried in the ground, usually in a basement or crawlspace.

Since it isn’t underground, do I really need to be worried about an AST?

Yes, even above ground tanks can leak, resulting in contamination of soil and drinking water supplies. Any oil spill can pose a serious threat to human health and the environment, regardless of where the tank is located.

What is the difference between an AST and a UST?

The distinct difference between the two tanks is this:

  • If the tank and its piping is located 10% BELOW ground surface it is considered a UST, anything ABOVE 10% ground surface is considered an AST.
  • Another exception is that, ASTs are not regulated by the DEQ, therefore not governed the same way as a UST.

For example, if a UST is leaking above 50 PPM (parts per million) the contractor is required to report this to the DEQ and is subject to remediation, based on the level of contamination. After the clean-up has been completed, the UST is then decommissioned and registered with the DEQ. This scenario can also be compared for an out of service underground storage tank, once the tank has been decommissioned it can then be registered with the DEQ.

The circumstances for an AST are different. When an AST is or has leaked, is no longer in-service, or the homeowner is switching to a new heat source, the tank can simply be removed, no decommissioning or registration with the DEQ is required. However, like decommissioning an underground storage tank, each AST removal can bring about a different set of considerations.

What to do with an Above Ground Storage Tank AST when decommissioning is not an option

If you don’t decommission and register the AST with the DEQ, what do you do?

First, we would need to determine where is the tank located?

  • Outside the home
Above Ground Storage Tank or AST

Above Ground Storage Tank or AST – Exterior AST secured to concrete pad foundation.

  • In a basement or crawlspace, with a separate exterior access
Above Ground Storage Tank or AST

Above Ground Storage Tank or AST – AST located in basement with exterior access.

  • In a basement or crawlspace, with access through the home only
Above Ground Storage Tank or AST

Above Ground Storage Tank or AST – AST located within a crawlspace, no exterior access. For this AST to be removed, it will need to be cut into pieces.

Regardless of where the above ground storage tank or AST is located on your property, it is very important to have it removed by a licensed contractor with pollution insurance. If the AST is removed by a general contractor, and they usually DO NOT have pollution insurance, and heating oil is spilled in the house or the yard, the homeowner will be left with the clean-up, not the contractor.

Once the location has been determined:

  • All heating oil and sludge are pumped out, the tank removed and disposed of via recycling.
  • Depending if the tank is on the exterior or interior of the home determines if the tank can be removed as one piece or if it will need to be cut into portions and carried out of the home.
  • If applicable, the fill and vent are removed and holes would be patched.
    • Removing or concreting over the fill eliminates the possibility of an accidental fuel re-fill.
Above Ground Storage Tank or AST

Above Ground Storage Tank or AST – AST Vent (the larger pipe) and fill pipe.

When an Above Ground Storage Tank (AST) Leaks

What would cause an AST leak?

There are numerous reasons an AST can leak; improperly secured tanks, tank corrosion, equipment or support failure, overfilling the tank, or it could be as simple as human error.

Above Ground Storage Tank or AST

Above Ground Storage Tank or AST – Tank that has fallen down, if the contents are not pumped out, diesel fuel would be leaked into the yard.

My AST is leaking, what should I do?

  • Place a bucket underneath the tank to catch the release
    • If the AST is within the home, block all floor drains to prevent discharge into a drywell or sewer
  • Call a qualified heating oil tank provider that can respond to and clean-up a leaking tank
    • The AST would be pumped of all residual liquids
    • Clean-up would be performed to remove any heating oil contamination
Above Ground Storage Tank or AST

Above Ground Storage Tank or AST – Leaking AST, small bowl has been placed underneath the leak to catch the heating oil.

Washington Department of Ecology

State of Washington Department of Ecology

The Washington Department of Ecology does not regulate the use or operation of residential heating oil tanks, like the State of Oregon does. However, some local governments may have different requirements or guidelines that may apply to residential storage tanks. Regulations and policies vary from place to place and may change from time to time.

Are there specific concerns I should have as a homeowner if I have an abandoned oil tank on my property?

  • Tanks can develop holes and release heating oil into the soil. The released oil can contaminate groundwater, surface water, storm sewers, and cause vapor problems in nearby buildings. Under the state Model Toxics Control Act, the tank owner may be held liable for damage caused by a leaking tank.
  • Corrosion can cause underground tanks to deteriorate, making cave-ins a possibility. The homeowner could be held liable for injuries caused by a cave-in.
  • Before finalizing the sale of a house, lending institutions and home buyers may want sellers to remove or “close” unused heating oil tanks. To “close” a heating oil tank, the homeowner has the tank cleaned out and filled. The tank is then left buried in the ground.
Washington Department of Ecology

Washington Department of Ecology – tank found within a backyard in Vancouver, vent pipe can be found running along the side of the house to the left of the window. The sampling of this tank resulted in a Risk Based Clean-Up.

How does Ecology prefer decommissioning take place?

Ecology recommends that the tank is removed with proper soil samples taken, and remediation, if necessary. However, decommissioning the tank in-place is also acceptable, as long as soil samples take place and remediation is completed, if necessary.

Can I decommission my tank as a homeowner?

There is no law prohibiting homeowners from doing their own decommissioning. Although, Ecology does not recommend doing the tank work yourself because of the potential safety risks. Hiring an experienced contractor is advised, as working on an underground storage tank can be dangerous. Under certain conditions, tanks can explode. Working in the excavation pit, cutting open or handling heavy tanks, and using power equipment also pose risks to the homeowner. Ecology recommends that homeowners hire an experienced contractor to perform decommissioning work.

Leaking tanks and the State of Washington Department of Ecology

What if a tank has leaked?

Knowingly using a leaking tank is negligence. If you discover that your tank is leaking you must take immediate action to stop the leak. In most cases where a tank has leaked, only the soil near the tank is affected. Sometimes, however, the heating oil may also have contaminated groundwater or surface water. It is the homeowners or contractors responsibility to:

  • Evaluate the extent of contamination caused by the leak
  • Evaluate the extent of the contamination caused by the leak
  • Determine if it is a threat to human health and the environment
  • Clean-up any contamination caused by the leak

Should I report the leak to Ecology?

Minor Leaks or Spills that affect only the soil near the residential heating oil tank do not have to reported to the Department of Ecology.   However, if the minor leak was discovered during the process of the tank being decommissioned, Ecology does recommend reporting the minor spill through the ERTS program.

Contaminated Soil above 2000 PPM does need to be reported to the Department of Ecology. Any groundwater, surface water, free product or vapor intrusion should also be noted during the reporting process.

How do I report a leak to Ecology?

All confirmed releases must be reported to the Washington Department of Ecology within 24 hours to the ERTS SYSTEM. A leak can be reported via a phone call or through the online reporting system.

Should I clean-up contamination?

Absolutely, and the Department of Ecology recommends that homeowners hire a qualified clean-up contractor to perform the remediation. When the clean-up has been completed, the contractor should give the homeowner a copy of the clean-up report. Clean-up reports of minor leaks do not need to be sent to Ecology, as they do not track or report on these clean-ups. Clean-up reports on more extensive leaks do need to be sent to the Ecology regional office, as they do keep track of and report on these sites. All reports should be kept by the homeowner for their records and the remaining life of the property.

Does the Department of Ecology have a LUST list like the State of Oregon?

Yes, it is called the Confirmed and Suspected Contaminated Site List (CSCSL). However, the majority of the sites on this list are large properties, with larger leaks (i.e. gas stations). It is extremely rare when a residential property does appear on this list, reasons that a site would appear on CSCSL is as follows:

  • When a property has been reported, but after 90 days, no closure and/or continued work to complete the remediation has taken place.
  • If groundwater has been encountered, the property automatically gets put on the CSCSL. The homeowner/contractor then has to go through the voluntary clean-up to get taken off the list. Ecology then works with the homeowner/contractor to get off the list by providing opinions on the work being completed and to verify if meets the status of no further action.

Additional Website Links:

Generic Remedy Clean-Up

Generic Remedy Clean-Up

A Generic Remedy Clean-Up is considered a mid-level contamination, consisting of a release of 501 – 10,000 PPM. This remediation is a soil-only clean-up as long as there is no impact to groundwater, no free product is present and there is no vapor intrusion into the home or building. A generic remedy may require soil removal, as well as additional soil samples around the tank to determine the extent of the contamination. Total Petroleum Hydrocarbon (TPH) concentrations up to, but not exceeding, 10,000 PPM of soil may be left in place if:

  • There is at least three feet of clean soil over the contaminated soil
  • The volume of remaining contaminated soil (over 500 PPM) does not exceed 65 cubic yards
  • Analysis for the presence of benzene, ethylbenzene and naphthalene must be performed on all samples exceeding 2,500 PPM.
Generic Remedy Clean-Up

Generic Remedy Clean-Up – this is the fill cap from a tank that was decommissioned through a generic remedy remediation. The concrete was cut in order to gain access to the tank underneath the concrete patio.

Generic Remedy Clean-Up

Generic Remedy Clean-Up – Fill material from a tank that was being decommission through generic remedy remediation, this tank was found to have leaked at 5710 PPM

Once the investigation of the soils around the tank and the contaminated soil has been removed, the generic remedy clean-up decommissioning of the tank can continue.

In order to establish if a generic remedy is necessary, the DEQ requires a site assessment must be conducted to determine the source, nature, magnitude and extent of the contamination associated with a release from the underground storage tank. The site assessment must specifically address:

Generic Remedy Clean-Up Investigation

  • Determine the presence of free product
    • If there is pooling of liquid fuel in the tank excavation area or if there is clearly visible saturated soil, free product is present and a generic remedy remediation is no longer acceptable.
  • Determine if groundwater is affected and the depth to groundwater
    • During the tank excavation, if groundwater impact is discovered, the DEQ requires the water be pumped from the pit. If the pit remains dry for 24 hours, sampling and clean-up may proceed under the generic remedy. If water returns in less than 24 hours, it is presumed to be groundwater and the use of the generic remedy remediation is not allowed.
  • Determine the vertical and horizontal extent of the heating oil contamination
    • If decommissioning will be performed by removing the tank, two samples must be taken from each end of the excavation, at least 6 inches below the bottom of the excavation. If, by visual observations, additional contamination or odors are detected, samples must be collected from these areas as well.
    • If the decommissioned tank is to stay within the ground, two soil samples are to be taken from each end of the tank, as well as one below the tank bottom. The samples are to be taken no more than six inches from the tank end and at least one foot below the tank bottom. If contamination or odors are encountered, based on visual observations, samples must also be collected from these areas as well.
    • An estimated volume of contaminated soil proposed to remain at the site will be required to ensure that the 65 cubic yard limitation is not exceeded. Results of soil samples analyzed for the presence of heating oil are required to determine both the vertical and horizontal extent of contamination remaining above 500 PPM.

We have provided a link, this provides more insight to understanding more of the DEQs requirements regarding Generic Remedy Clean-Up remediation standards and guidelines.

Soil Matrix Cleanup

Soil Matrix Cleanup

A Soil Matrix Cleanup, which consists of a release of 500 PPM or less, lands within the DEQs simplest level of remediation. Pending that, during the decommissioning process, no holes within the tank are observed, the DEQ will not require any additional sampling or scope of work, in addition to the usual Soil Matrix Evaluation used to close the LUST file.

Standards for a Soil Matrix Cleanup

The standard by which the DEQ closes an open file for a Soil Matrix Cleanup is as follows:

  • Removal or treatment of the contaminated soil is not required
  • An abbreviated risk assessment is allowed for the site, which is called a Soil Matrix Evaluation
  • The tank and the contaminated soil will remain within the ground
  • The final steps include creating the Soil Matrix Report and submitting the report to the DEQ. Once reviewed and approved by the DEQ, the site will be considered DEQ Certified and the site will have a “Closed Status”.
Soil Matrix Cleanup

Soil Matrix Cleanup – Tank found and marked out for sampling. The small circle inside the right side of the marked tank is the fill pipe.

Soil Matrix Cleanup

Soil Matrix Cleanup – While excavating a tank during a soil matrix decommissioning, holes are found within the tank. These holes cause diesel heating oil to leak into the surrounding soils.

Soil Matrix Cleanup

Soil Matrix Cleanup – Excavation of a tank removal soil matrix decommissioning

For more information regarding Soil Matrix Cleanup, please see the DEQ UST Cleanup Manual.

Underground Storage Tank or UST Decommissioning

Underground Storage Tank or UST Decommissioning Common Questions


What does it mean to decommission a UST?

The most generic term, is to take the tank out of service.  Underground Storage Tank or UST decommissioning is accomplished by ensuring the tank has been properly cleaned and removed or completely filled with an inert material. The inert material consists either of perlite, a sand-like material or slurry, concrete.

If the tank is to be registered with DEQ, two soil samples will be taken from inside the bottom of the tank, after being pumped and cleaned, and analyzed for diesel and heavy oil. Each sample needs to be analyzed at an independent laboratory that is DEQ certified.

If the samples come back as non-detected, the tank can be then registered with the DEQ.

If the samples come back above the DEQ reporting limit (50.1 PPM), remediation will need to take place and once the corrective action has been completed, the tank will be registered with DEQ.  If soil remediation is need, please see our Decommissioning via Heating Oil Contaminated Soil Clean-Up page.

Why should homeowners decommission their UST and register it with the DEQ

I’ve emptied my tank of oil years ago and don’t use it any more, doesn’t that mean it is decommissioned?

No, in order to decommission the tank you will need to take the tank permanently out of service. This is completed by either removing the tank or filling it in place with an inert material.

Can I decommission my own UST?

According to the DEQ, it is legal for a homeowner to decommission their own UST, assuming that you perform the work yourself and comply with all applicable local, state and federal rules. Before deciding to decommission your own tank, the DEQ highly recommends that you read the DEQ Cleanup Guidance for Homeowners to understand the full scope of work involved in completing a decommissioning project. DEQ Decommissioning Guide for Homeowners

I’m selling my home and have switched over to gas years ago, should I decommission my tank?

It is not a requirement to decommission your tank before selling your home. Unfortunately in this highly active real estate market, many buyers will require at a minimum, proof of recent clean soil samples. Additionally, you will need to provide the buyer with documentation that the tank has been pumped of all of its contents. The documentation that the DEQ requires is dated receipts from the company that pumped the oil out of the tank; or receipts from the oil recycling company, if you pumped the tank yourself.

Do I have to decommission my UST?

No, it is not a requirement to decommission your tank once you stop using it.  However, if you are thinking about selling your home, most buyers and their agents request decommissioning and registration before closing. Per DEQ, you will need to ensure that the tank has been emptied of oil and you will need to provide that documentation to the new buyer.  DEQ Requirements for Tanks No Longer in Use

Do I have to register my UST?

It is not required by DEQ to register the tank, but it is highly recommended. However, if you are decommissioning the tank as part of the sale of the home, this is usually a prerequisite prior to closing.

Why should I register my UST?

There are three primary benefits of registering the UST decommissioning with the DEQ:

  1. The decommissioning becomes public record.  So, even if your copy of the paperwork is misplaced or the name of the contractor that performed the work is forgotten, the record remains in the DEQ files.
  2. When the DEQ changes any of their rules (i.e. reporting limits, remediation guidelines, etc.), previously closed or registered tanks are “grandfathered” in.  Tanks that were decommissioned and not registered are subject to the new rules.  For example, over time the DEQ required the locations of soil sampling to change.  Meaning a previously unregistered decommissioned tank, would need to obtain additional soil samples to bring the tank up to the new DEQ sampling requirements.
  3. Most buyers are requiring DEQ registration because they don’t want to deal with future DEQ rule changes.  Even if you don’t plan to sell the property any time soon, registering the tank now can prevent added costs prior to and during a future sale.

I have a tank that was decommissioned years ago, but never registered with the DEQ, how do I now get it registered?

In order to establish if the tank has been decommissioned properly, soil samples and a tank inspection would be required. Soil samples need to be taken in order to determine if the tank had leaked prior to decommissioning. A tank inspection is necessary to establish if the tank has been decommissioned properly.

If the soil samples are clean and the tank has been decommissioned properly, the tank then can be registered with the DEQ.

USTs that have been Decommissioned inproperly

What happens if it isn’t decommissioned properly?

There could be a couple of different reasons a tank has not been decommissioned properly.  There may be inadequate or contaminated fill material, water within the tank or simply something that shouldn’t be in the tank (i.e. paint cans, large rocks, etc.).  Besides what is inside the tank, the soil samples will need to be taken into consideration to allow the tank to be certified as decommissioned to register with the DEQ.

  • Fill Material:  If the fill material within the tank is not an approved by the DEQ, that material will need to be removed and the tank will be re-decommissioned to DEQ standards for certification.  The same reasoning will go with contaminated fill material, even if it is DEQ approved material.  The contaminated material will need to be removed and the tank will need to be re-decommissioned to DEQ standards for certification.
  • Water:  If there is water within the tank, all water will be pumped out of the tank and re-decommissioned in order to certify with the DEQ.
  • Unconventional Items:  From time to time, items are found within a tank that should NOT be there.  Items such as large boulders, paint cans, trash cans and even tires have been discovered within a tank.  If this situation does arise, all items will need to be removed and disposed of in a landfill and the tank will need to be decommissioned.
Underground Storage Tank or UST Decommissioning

Underground Storage Tank or UST Decommissioning – Concrete, pain cans and water found within a tank.

What exactly do you do to decommission a tank?

In order to decommission an underground storage tank, we need to follow some step-by-step processes to ensure that we are able to take soil samples and inspect the tank properly.  This is the process by which EcoTech begins each in-place underground storage tank decommissioning project:

1.  We dig down, expose the tank and cut it open.

Underground Storage Tank or UST Decommissioning

Underground Storage Tank or UST Decommissioning – Exposed tank top.

2.  All tank contents are removed; heating oil, residual liquids, sludge.

3.  Clean and dry the tank interior and inspect it for holes.

Underground Storage Tank or UST Decommissioning

Underground Storage Tank or UST Decommissioning – Holes from within a tank.

4.  Collect soil samples from the inside and through the bottom of the tank.

Underground Storage Tank or UST Decommissioning

Underground Storage Tank or UST Decommissioning – The technicians cut two holes in the bottom of the tank to expose the soil underneath, two samples are then “grabbed” underneath the tank bottom.

5.  Soil Samples are submitted to the lab the same day for analysis, with results typically back the next business day by noon.

6.  Pending favorable laboratory results (less than 50 PPM), the tank can be backfilled with perlite or slurry.

***If soil sample results come in above the 50 PPM, remediation would be required to bring the site up to DEQ requirements.  (Please see our Heating Oil Contaminated Soil Clean-Up section for additional information on remediation Clean-Up with Decommissioning).

Underground Storage Tank or UST Decommissioning

Underground Storage Tank or UST Decommissioning – Tank filled with slurry.

7.  After the tank has been filled, the tank is then covered back over with the previous landscape (i.e. grass, concrete, dirt, etc.).