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.

Risk-Based Clean-Up

Risk-Based Clean-Up

Risk-Based remediation addresses the highest level of contamination from a leaking underground storage tank, with levels reported above 10,000 PPM. According to the DEQ, a risk-based clean-up offers the greatest amount of flexibility and adaptability to site-specific conditions. However, it is also the option that might require collecting additional site data and evaluation of more alternatives than a soil matrix or generic remedy clean-up. Risk-based clean-ups are the most rigorous option, with the collection of several soil samples to determine the magnitude and depth of contaminated soil, as well as how far the contamination has spread. The most important aspect of a risk-based clean-up is the evaluation of current and reasonably likely future risks to human health and the environment.

A risk-based remediation involves a soil investigation, which examines the pathways the contamination has likely spread. This pathway evaluation determines where the contaminants were released, how the contaminants can be transported to new locations and the reasonably likely ways that people may come into contact with them. Tests need to be conducted on enough samples to determine the lateral extent, as well as the depth of the petroleum contamination.

There are three investigative phases of concern while conducting a risk-based clean-up, phase two and three may not be necessary if the area of contaminated soil is limited enough in extent. Below are the steps, in order, that are required by the DEQ in order to close a risk-based clean-up:

Risk-Based Clean-Up and Free Product, Groundwater and Soil Vapor Gas

Petroleum Contaminated Soil (PCS) and/ or Free Product:

Up to seven (7) soil samples are taken to establish a representative sample and delineate the vertical and lateral extent of the pocket of petroleum-impacted soil, and potential or actual groundwater impacts. If it is determined that there is free product or large volumes of heavily contaminated soil, from which product may continue to migrate, mitigating the risk by excavation and off-site removal would be required, to the maximum extent practicable.

Risk-Based Clean-Up

Petroleum Contaminated Soil (PCS) seen during an excavation. The PCS is pictured here in the greyish color.

Risk-Based Clean-Up

The side view of the PCS, here you can see the coloration difference between the contaminated and the native soil.

Risk-Based Clean-Up

Free Product refilling into a sample boring hole

Risk-Based Clean-Up

Free Product within a sampling tube

Groundwater:

Has groundwater at the site at risk or has it been impacted by the diesel contamination?

In order to determine if groundwater has been or could be potentially encountered, a 10’ separation is required by the DEQ between the vertical extent of the contaminated soil and any potential shallow groundwater.

If there is no impact or potential impact to groundwater?

The groundwater investigation is now completed, no further action would be required.

If groundwater has been or has the potential to be impacted, what are the next steps?

A representative well will be installed in the source area to determine if groundwater has been impacted by the release. The installation of the representative well is designed to obtain a groundwater sample to measure, if any, the water level elevation in the contaminated water or soil.

If the samples in the representative well have detections that exceed the DEQs Ingestion and Inhalation from Tap Water Risk-Based Clean-Up levels, a groundwater investigation is necessary. The groundwater investigation determines the extent of the contaminated groundwater, and whether it is limited only to the property of the leaking UST or if extends to neighboring properties.

If the samples in the representative well meet the DEQ Ingestion and Inhalation from Tap Water Risk Based Clean-Up levels, no further action would be required.

The 10’ separation boring cannot be obtained due to site conditions, what happens to the investigation?

If a 10’ separation boring cannot be completed due to examples like refusal (rocky soil, etc.) or if the tank is too deep, per the DEQ a Beneficial Well Survey would need to be conducted.

A Beneficial Well Survey determines if a release of hazardous substances has impacted or has the potential to impact groundwater or surface water, through contaminant migration. These determinations will be used for evaluating exposure pathways in human health and ecological risk assessment; for identifying hot spots of contamination; and for selection or approval of remedial actions at hazardous substance clean-up sites.

The DEQ requires the survey to identify all properties that are in proximity to the site with the leaking underground storage tank, which may be utilizing a water supply well. The well may be used for drinking water, irrigation, etc. DEQ regulations considers that any well on a property that is for domestic use, be accounted for. These surveys can and are conducted within and outside city limits.

Grd Water

Groundwater encountered within an opening within an underground storage tank.

Vapor Intrusion from soil or groundwater:

Vapor intrusion is the migration of Volatile Organic Compounds (VOCs) from the subsurface into buildings. Per the DEQ, vapors released from volatile substances can be slowly released from underground spills. These volatile constituents move upward through the pores in the soil, when the soil is exposed during excavation, as well as, from contaminated groundwater. The DEQ requires Soil Vapor Gas sampling (SVGs) to assess the potential of carcinogenic vapors entering residential buildings. When certain constituents of interest, such as benzene, ethylbenzene and naphthalene concentrations exceed the DEQ Vapor Intrusion into Residential Buildings Standards, soil vapor gas sampling would be required.

To assess the potential cancer risks from vapor intrusion into homes, soil vapor gas sampling is triggered if any of the following variables apply:

  • The plume of contamination exceeds 65 cubic yards
  • There are, or likely to be, buildings within 30 feet of Volatile Organic Compounds (VOCs)
  • A 10’ separation cannot be established between the vertical extent and any potential shallow groundwater

Due to site specific factors, the number and sample locations may vary. Sampling may be conducted within the home or on the exterior of the building, either through the sub-slab and/or the soil.

Risk-Based Clean-Up

Soil Vapor Gas Sampling at the exterior of the property

Risk-Based Clean-Up

Sub-Slab Sampling, in the interior of the building

For a more in-depth overview of the DEQs requirements and standards regarding Risk-Based Clean-Up and leaking tanks, please visit their Leaking Underground Storage Tank Program (LUST site) DEQ LUST Site.

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.

Septic Tank Decommissioning

Septic Tank Decommissioning Common Questions

What is a septic tank?

A septic tank processes wastewater from the home and consists of two main parts, the tank and a drain field.  It encompasses a piping connection, allowing the waste to flow from the home, through the tank and into the drain field, these connections are made through a T pipe, allowing liquid to enter and exit without disturbing the surface above.  The septic tank treats the wastewater and allows the separation of solids and liquids, once broken down the solids remain in the tank while the liquids drain into the leach field.

Septic tanks may be concrete or metal, 5 to 7 feet long and 5 to 7 feet deep, and will be located 5 to 30 feet away from the home.

Are there dangers associated with abandoned septic tanks?

Septic tanks that are buried underground are susceptible to corrosion, thus weakening the stability of the structure. The instability can cause the system to collapse, causing serious injury or death. Septic tanks contain dangerous gases due to the breakdown of decomposing matter, falling into a tank can cause the possibility of being overcome by noxious gases.

How do I know if I have a cesspool or septic tank on my property?

Within the Portland Metro area, there are two methods that may help determine if you have a cesspool or septic tank on your property:

  • For a general rule:
    • If your home is east of the Willamette River, most systems installed were cesspools.
    • If your home is west of the Willamette River, most systems installed were septic tanks.

How do you find a septic tank?

The location of the system would need to be determined by sending out a technician to the property.  The technician locates the main plumbing stack that comes through the roof and visually extends a straight line from the exterior foundation line.  From the foundation, the technician would follow the visual straight line out to the septic tank, between 5 to 30 feet from the home.

Decommissioning of a septic tank

How do you decommission a septic tank?

The proper septic tank decommissioning permit will need to be obtained for the city and/or the county the septic system is located in.

EcoTech uses excavation equipment to dig to the top of the structure to expose and open the septic system.  Once accessed and per OSHA regulation, shoring of the area around the system is completed to prevent collapse of the shaft and to ensure the safety of our technicians.

Our technicians will then inspect the interior of the tank, and pump any liquid or sludge that may be present.

Contingent on the city and/or county permitting process, inspection of the system may need to take place prior to filling the tank.  Inspection may also need to take place after the tank has been filled, depending on permit requirements.

When the tank has been pumped of all sludge, and all relevant inspections completed, the tank can be filled with either sand or gravel.  Once the septic tank is decommissioned, the technicians would replace the soil overburden, bringing the area back to surface grade, along with a closed permit for the decommissioned septic tank.

Septic Tank Decommissioning

Septic Tank Decommissioning – Dug down and exposed septic tank

Septic Tank Decommissioning

Septic Tank Decommissioning – Roped off septic pit for safety

Septic Tank Decommissioning

Septic Tank Decommissioning – Broken terracotta pipe, this is part of the system that allows wastewater to drain from the home. When the pipe is broken, this allows waste to seep into the yard.

Septic Tank Decommissioning

Septic Tank Decommissioning – Filled septic tank, with T piping junction of metal pipe to terracotta pipe.

Septic Tank Decommissioning

Septic Tank Decommissioning – Filled septic tank, with T piping junction of metal pipe to terracotta pipe.

Septic Tank Decommissioning

Septic Tank Decommissioning – Filled septic tank, ready for overburden to be replaced

For more information on local cities requirements on septic tank decommissioning within the Portland Metro area, please click on the following links: