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Underground Storage Tanks

There are a variety of issues surrounding underground storage tanks (USTs)—environmental, safety, economic and legal. Such issues have increased concerns among homeowners, home buyers, lenders and real estate agents…and for good reason. Among the more pressing issues involving USTs are: soil and groundwater contamination; fire risk and tank collapse; high maintenance costs; contamination cleanup; and third party damages.

Before purchasing a home, it is strongly recommended that buried tanks be tested. The liability surrounding a leaking tank becomes the responsibility of the new owner after the property is purchased. The cost for testing a residential tank generally ranges from $500 to $800.

The USTs that were installed in the 1970s and 1980s had been installed by people who were less concerned about installation and environmental issues, and by those using old technology. Present day concerns, such as contaminated soil, may have never been anticipated. In fact, many tanks are not designed to be stored underground. Consequently, many tanks encountered today are defective.

Leaks in USTs can be attributed to improper installation, corrosive soils, and tank and piping defects. In addition, if tanks are not carefully lowered into an excavated hole, they are susceptible to damage by dropping or pushing them. Today, USTs generally have a corrosion-resistant exterior as well as components that deter the effects of pressure, vibration and movement.

Inside the tank, moisture in the oil encourages tank failure by enhancing corrosive action. The moisture joins with sulfur and other components in the oil to become acidic and corrosive. Water can enter the tank from:

  • an improperly sealed fill box
  • a missing fill pipe or vent pipe caps;
  • loose pipe fittings;
  • water delivered with fuel from an improperly maintained bulk storage facility; and
  • ground water through a damaged tank wall.

Rust damage is the most common cause of UST failure—moisture inside the tank corrodes the tank from the inside out. The combination of water with sulfur in heating fuel, bacterial action, and other non-compatibility factors may also be considered contributing factors to tank failure. Since water corrodes the tanks, buried tanks should be tested to determine the amount of water present in the tank bottom, and the water should be pumped out.

Components of Residential Underground Systems
Oil Tank – Underground Oil Storage Tanks (USTs) are typically used in the northern regions of the nation to hold home heating fuel oil underground and out of sight. The typical residential storage tank can hold up to 1,000 gallons and is commonly buried within 4 to 8 feet of the property’s foundation. Although most underground tanks today are typically constructed of a fiberglass-based composite material, they have historically been constructed of steel. The primary concern with steel tanks is deterioration, leakage, and soil contamination surrounding the tank.

  • Fill Pipe – The fill pipe is the access by which the underground tank is filled with fuel oil. The fill pipe is generally located directly above the tank.
  • Vent Pipe – The vent pipe provides a means for air to escape the tank when it is being filled with fuel oil. If the tank were air tight, then it would not accept additional product. The vent pipe may be further from the tank than the fill pipe, but usually at a location near a building where it can be supported as it is extended above ground. The vent pipe should have a cap or some other means to prevent rainwater from entering the tank.
  • Supply Line – The supply line is the copper tube, which delivers the fuel oil from the underground tank to the furnace. The supply line may run through the wall or under and up through the floor to the furnace.

Testing Methods
UST Soil Test – The Underground Storage Tank (UST) soil evaluation is designed to test for total petroleum hydrocarbons (TPH) in the soil surrounding an abandoned or in-use underground oil tank. Most states do not have regulations governing residential underground oil tanks. Therefore, U.S. Inspect has limited this evaluation to detecting levels of TPH. In states where residential USTs are regulated, U.S. Inspect will report on TPH and all other contaminants required by the state. U.S. Inspect’s on-site evaluation is based upon what the licensed technician is able to detect from field screening and soil samples sent to the lab. The evaluation is not exhaustive, and is only intended to determine if petroleum has contaminated the surrounding soil at the time of the evaluation. In instances where soil contamination has been confirmed, U.S. Inspect will recommend proper abandonment or removal of the underground tank. U.S. Inspect will also recommend removal and disposal of all contaminated soil.

Tank Tightness Testing:

  • Volumetric – Designed to test the liquid portion of an in-use underground storage tank. A minimal amount of product (usually about 20%) must be in the tank in order to perform a test. The test will also take simultaneous readings of the ullage (air) space to determine if a leak exists within the tank above the product line. Most states do not regulate resident underground oil tanks, therefore U.S. Inspect will report on all leaks associated with the integrity of the tank, abiding by EPA leak regulations. The on-site evaluation is based upon what the licensed technician is able to detect from the readings at the time of the inspection. This evaluation is not exhaustive, since it will only determine if a leak exists, not if any contamination has occurred. In instances where an underground storage tank is leaking, U.S. Inspect will recommend proper abandonment or removal of the underground tank, and the removal and disposal of any contaminated soil.
  • Vacuum Testing – Designed to test the ullage portion of an active underground storage tank. This test is performed by closing off all tank openings and inserting a high-resolution electronic sensor and microprocessor through the fill pipe of the tank. The technician then pulls a slight vacuum (generally -.5 to 2.0 psi) from the tank. The sensors and microprocessors detect the ingress of air into the tank to determine if a leak is present. Simultaneously, the liquid portion of the tank is tested in order to determine the integrity of the tank. In instances where tank is found to be leaking, U.S. Inspect recommends proper abandonment and/or removal of the tank. This investigation is not exhaustive, since it does not determine the presence or extent of soil contamination, only whether a leak exists. If a leak is found, U.S. Inspect also recommends removal and disposal of the contaminated soil.
  • Tracer Testing – Involves injecting a rare gas isotope into the UST and planting soil monitors in the soils around the UST to monitor amounts of the gas, if any, that pass through the leak and into the soil. The disadvantage of using tracer testing is that the ability to place the probes into the soil can be limited. In addition, the test can take approximately 10 days to produce results, depending on factors such as solid permeability, which affects the rate at which the isotope is released. The denser the soil conditions, the greater the time involved.

Tank Closure Methods and Requirements
A proper abandonment procedure involves pumping out remaining fuel, confirming that there has been no leakage, cleaning the tank, and filling the tank with an approved filler, or removing it entirely. The only underground storage tanks that are typically recommended for abandonment in-place are tanks that are under a building or would endanger a building structure if removed.

Removal of USTs
The Maryland Department of the Environment recommends the following course of action for removing an underground tank.

  • Notify the oil supplier – Call your oil distributor and ask them to discontinue the oil service to your home if you are converting to gas or electric heat, or if you are replacing the tank.
  • Obtain a contractor – Find a competent contracting company to do the job for you. Your oil supplier may be able to provide a list of contractors certified by the State to perform the job.
  • Local permit – Before any excavation work can be started, a permit to abandon the underground tank may be required from your local fire department, health department, or other county agency.
  • Remove product – All product should be removed from the tank and lines before pulling the tank. Your oil supplier may pump out the reusable oil and credit your account. An explosion-proof or air-driven pump or vacuum truck should be used to remove the liquid in the tank.
  • Excavation – Excavate to the top of the tank and expose the piping.
  • Disconnect all piping and drain – All piping should be disconnected, drained, and capped (if it cannot be removed); this includes the tank fill line.
  • Tank cleaning – Oil sludge or residue should be removed and disposed of properly.
  • Tank removal – Once the tank is cleaned, it may be removed from the ground and disposed of properly.
  • Tank disposal locations – There are a number of locations, such as dismantling yards, landfills, and local scrap yards.
  • Reporting and disclosure – You and your contractor may be required to report contamination of soil if it is discovered following the removal of the underground tank.

EPA Regulations – Residential USTs
Since most states do not regulate USTs that have a tank volume less than 1,100 gallons, a majority of residential USTs, which typically carry between 250 and 750 gallons, evade regulation. Furthermore, tanks with home heating oil also typically evade regulation. The U.S. Environmental Protection Agency (EPA) mandate that testing methods be evaluated against a .10 gallons per hour leakage rate at a probability of detection of 95%, and a probability of false alarms of 5%.

It is important to note that meeting federal, state, and local regulatory standards may not meet the highly discriminating standards of home buyers. As long as the tank’s leakage rate does not exceed .10 gallons per hour, it satisfies the legal requirements. Nonetheless, some homebuyers may not settle for a tank that “legally” loses up to nearly 2 gallons of fuel each day into the soil.

In compliance with federal regulations, if a tank is determined to leak more than .10 gallons per hour, the leak must be corrected, a site characterization completed, remediation undertaken, and the incident reported.