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Preventing Contamination


Protect the Environment and Product Quality

Providing high quality, uncontaminated petroleum products is vital in today's business climate. Customers expect their cars and trucks to perform flawlessly on the gasoline or diesel fuel they buy. They expect their vehicles to start, accelerate, and deliver good mileage.

The operator of a retail petroleum business plays an important role in maintaining the level of product quality that helps develop and keep satisfied customers. Clean, uncontaminated petroleum products contribute to a cleaner and healthier environment, and to automotive safety.

Handling and disposal of contaminated fuel can contribute to long term environmental damage. It can also be costly to station owners.

  • In the short term, it is expensive to repair fuel-related damage to customers' cars. A station owner's insurance rates can increase as a result of repeated problems.

  • In the mid term, failure to care for the environment will cost customers. Many customers are increasingly aware of the need to preserve the environment -- they will not patronize a business that is careless about the environment.

  • In the long term, any environmental damage affects station owners and their children and grandchildren. Petroleum products spilled in the ground will end up in the water supply. Station owners who don't want to drink gasoline, should not spill any.

Prevent Storage Tank Leaks

Tank maintenance is the first step toward preventing petroleum product contamination. Tanks must be leak free. Above ground and underground storage tanks are subject to U.S. Environmental Protection Agency regulations, enforced by the Minnesota Pollution Control Agency (MPCA).

Station owners must regularly monitor tanks for leaks. Procedures for detecting leaks and preventing corrosion and spills are specified in federal regulations. The procedures vary depending on the age, type, and size of the tanks, and the type of piping between the tanks and pumps.


Avoid Water Entry into Storage Tanks

In Minnesota's climate, water is the most common contaminant in petroleum storage tanks. Water in tanks requires cleanup actions that range from pumping the water out of the tank, to removing all the product stored in the tank . It is critically important to keep water out of tanks.

To prevent water contamination:

Make sure that fill pipes are located on high ground, and that snow melt and runoff are directed away from them.

Check fill pipe caps. They must be water tight. Seals and latches must be in excellent condition. Replacing a fill cap is a lot less expensive than replacing a tank full of contaminated product, or paying to repair fuel-related damage to a customer's car.

Check vent pipes. They must have special caps to allow ventilation and prevent rain water entry. Faulty or missing vent caps are a common, but frequently overlooked, source of water contamination.

Newer tank installations have large catch basins surrounding the fill pipe openings. These basins are designed to catch product spills and overflow during tank filling. They're also great for catching and holding water. Catch basins must be kept clean and dry.

Many catch basins are equipped with a drain valve. This is not a water drain. It was designed to drain spilled product back into the storage tank. Water and dirt drained from catch basins will drain directly into storage tanks. Water and dirt must be removed from catch basins with a pump, mop, or sponge.

Water lying at the bottom of the storage tank can cause rust-through and leaking. Water removed from the bottom of a storage tank is loaded with toxic substances. Please don't pump water or petroleum products onto the apron, or into a storm sewer or drainage ditch.


Avoid Unloading Errors

Unloading the wrong product into a storage tank is another common cause of product contamination. To help prevent these errors, state law requires an identification tag which must be constructed of one 3-1/2 inch by 3-1/2 inch piece of aluminum or stainless steel. All surfaces of the tag must be coated with a permanent enamel paint or powder coating. The coating must be light blue for gasoline and alcohol products and dark green for petroleum distillate products. Lettering must be at least three-eighths of one inch high, and printed on the tag with permanent enamel paint or powder coating. Lettering must be black for gasoline and alcohol products and white for petroleum distillate products.

To help the transport driver avoid overfilling, the department recommends that the capacity of each storage tank be marked on the fill pipe. When an unloading error occurs, the mixed or contaminated product must be removed from the storage tank. Pumping is a potential source of spills. The easiest way to avoid a spill is to prevent unloading errors by clearly marking tanks.

Please note: Color-coded or marked storage tank covers are not acceptable. Covers are often lost during snow plowing, exchanged during inventory checking, or flipped over when product is delivered.


Store Oxygenated Gas Properly

Oxygenated gasoline is more prone to contamination than straight gasoline. It requires special handling. Gasoline sold in Minnesota must be blended with ethanol.  Ethanol is the only oxygenate used in Minnesota.

There are two important factors to consider when storing oxygenated gasoline:

  • Ethanol and other oxygenates act as solvents, or cleaning agents. Storage tanks must be clean before filling with oxygenated gasoline.

  • Gasoline will not mix with water -- oxygenates will. Ethanol has a higher water tolerance than other oxygenates, but ethanol's ability to absorb water is limited. When storing oxygenated gasoline, tanks must be dry before filling, and must be kept dry.

If there is too much water in storage tanks, the oxygenate will separate from the gasoline. This is called a phase separation and will cause a layer of gasoline on top of a layer of oxygenate/water blend. The amount of water needed to cause a phase separation is temperature related. If the oxygenate/water blend is deep enough, it will be picked up by the pumps and delivered into customers' cars.

When a water/oxygenate blend develops at the bottom of a storage tank, it must be pumped out. Again, pumping is a potential source of spills and subsequent environmental contamination. The easiest way to avoid a spill is to prevent water problems. Check tanks, fill caps, and fill pipe vents regularly.


What to Do if Contamination Occurs

Water contamination in storage tanks. Water pumped from the bottom of a storage tank may be considered a hazardous waste, depending on the level of dissolved contaminants like rust, dirt, and petroleum products.

In most cases, this liquid will have to be treated as hazardous waste. For information on handling and disposal of wastes, station owners should contact:

  • the county Environmental Health office, if they live in the Twin Cities area;

  • the MPCA Hazardous Waste Generator Unit (651-297-8332) in the Twin Cities or 1-800-657-3864 statewide);

  • the Minnesota Technical Assistance Program (612-624-1300) in the Twin Cities, or 1-800-247-0015 statewide).

For assistance in having tanks pumped, station owners should contact their petroleum equipment repair company.

Oxygenated fuel that has separated. Station owners experiencing a phase separation problem should follow the recommendations above to dispose of water and water/oxygenate mixtures pumped from tanks. In addition, the gasoline that remains in tanks after removing a water/oxygenate mixture will not meet state requirements for oxygenated gasoline. The fuel supplier should be contacted for assistance in blending and handling the remaining product.

Product unloading errors. A contaminated product may have to be pumped from a storage tanks if a transport driver has unloaded the wrong product into the tank. When an unloading error occurs, contact the fuel supplier for assistance in correcting the problem.


For complete information on regulations and procedures, contact the MPCA. In the Twin Cities, call 651-297-8679. From outside the Twin Cities, call 1-800-657-3864.