Storing Diesel Fuel for Generators – Above Ground or Underground Tanks?

With increasing fluctuation in the cost of diesel, lots of sites which operate a diesel generator are buying in bulk when the price is low and storing it away in large storage tanks. Many sites will have the choice between above ground storage tanks (AST) and underground storage tanks (UST) for diesel fuel.

Making the decision about how to store your diesel can be a challenging one because so many factors play a role in this process. There are benefits of both underground and above ground storage. Before you can choose, be sure to consider your location and any local ordinances.


Weighing Up Pros & Cons

Both above ground and underground systems can be beneficial. While some sites will clearly favor one over the other, it’s often a delicate game of balancing risks and costs. Before making the decision, consider each one of these key factors.



The costs associated with underground tanks are significantly higher than those for setting up an above ground tank. Underground tanks require expensive excavation work. This may include a variety of permits and specialized equipment.

By comparison, assembling and positioning an above ground tank may be faster and less expensive. However, some still need more attention paid to the details to ensure they keep the property aesthetically appealing.

When maintenance is necessary, it is less expensive (and faster) to make repairs on an above ground tank rather than one positioned underground. Repairs are a key concern for long-term costs. For installation, above grounds tend to be slightly less expensive overall.

Also, consider secondary containment requirements – different for above ground and underground – and EPA rules in your area for the type of tank (and size of tank) for your needs.


Contamination and Leak Risks

Both types of fuel storage solutions can suffer contamination and leaks, for which exist severe financial penalties for the perpetrator and damage to water supplies, soils and local ecosystems. The cleanup operation alone can run into six figures with potential legal battles, insurance hikes and reduced property values on top. The big risk with underground tanks is the difficulty in spotting the leak early enough before significant damage is done.

However, designed well, underground tanks are less likely to suffer damage. Whereas an above ground tank is always susceptible to interactions with people and vandals, those under the ground are less accessible overall. Above ground tanks are also easier to monitor for leaks. This may mean you can spot them early on and rectify the problem long before it becomes a contamination risk. However, many will require a vapor recovery system to be installed.

Contamination from storage tank to environment is not the only risk – the diesel itself runs the risk of contamination. Prime causes of fuel contamination are water, heat and air which all pose more of a threat to above ground tanks. Contamination by these elements takes months off diesel’s shelf life, defeating the purpose of buying fuel in bulk and storing it in large quantities.


Fire and Explosion Risks

Fire and explosion risks can occur in both cases. They are more likely with an above ground tank than an underground model, though. Because of this, above ground tanks have to pass more stringent local regulations such as distance to other tanks or buildings and have to demonstrate higher fire resistance levels. Above ground tanks may also require a vapor recovery system to minimize some of these risks. Those exposed to pressure and temperature fluctuations are going to be more likely to explode than others.

Underground tanks have lowered fire risks. They are also less likely to explode due to the limited amount of tension and pressure. However, backup solutions and maintenance remain important.


Security Threats from Vandals or the Elements

Security threats are an ongoing concern for many locations. Protecting any fuel tank is going to be a big part of the work you do. In an above ground system, there’s more to protect. You may need to spend a bit more on security systems (alarms, CCTV, lighting) to protect an above ground system – something you should be doing already with a generator on-site. It is also an increased risk for accident vehicular collision.

Weather conditions can also impact above ground systems more often. This can mean more instances of repairs necessary. Tanks exposed to the weather are specifically likely to wear down sooner than those enclosed or underground. Underground tanks have a significantly higher level of protection because they are sheltered well. When factoring in weather, also consider piping. When piping is underground, freezing conditions may cause breakage and cracks. Above ground systems, on the other hand, can be better maintained in an enclosure that offers more temperature protection.


Mobility Concerns

For those who need a fuel storage tank that’s mobile, underground tanks are limited. Simply, there is no easy way to move these. However, above ground tanks can be designed for more mobility. If there is a need to move the tank to a specific location or to change its position for refueling, above ground systems are far more versatile overall.

More portable above ground tanks also benefit areas whose needs and equipment are in flux. An underground tank is no good if you need to frequently shuffle around equipment. It’s also important to think long-term and consider future placements since there are regulations, varying by state, to determine exactly how close a storage tank can be to other tanks, buildings and property lines. Once a tank is placed underground it’s a much harder task to uproot it to a new position.


Space Limitations

All tanks need enough room, but underground tanks take up no amount of above ground space. Without any surface space used for the tank, this option can be a better fit for those areas with limited space for operations. There is still the need to properly vent and create access points, but overall underground tanks have far less demand on your property space.


Aesthetics Needs

It’s true that an above ground tank can be enclosed or made to look better. However, it will still be present on the surface and within the view of those who pass by. Underground tanks are less of an aesthetic concern. This may mean they require less maintenance to keep up on the overall look of the tank as well.


Shelf Life

Overall, both tanks can last for decades if well maintained. A variety of factors determine how long the tank will be used. However, in terms of day-to-day use, underground tanks suffer less wear and tear. This may mean they can last longer and perform well for you throughout that time. The lack of weather and vandalism risks increases the lifespan of most underground tanks. At the same time, they are harder to inspect, which makes it harder to pinpoint problems sooner.


Which Tank Is Best for You?

There’s no solution that is best for all needs. It’s up to you to determine which option fits with the type of layout you have as well as your concerns. Mobility, space, and overall safety concerns vary from one location to the next. Financial concerns matter, too. Work closely with the manufacturer as well. Be sure to consider the type of site ideal for the tank you plan to purchase, including how you plan to use it long term. Both options can be the ideal fit in some cases.