Existing wells are required by law only to meet separation requirements in effect at the time of well construction. Make every effort, however, to exceed the regulations whenever possible. One gallon of gasoline containing one percent benzene can contaminate about two-million gallons of groundwater. Preventing spills and leaks is especially important because of how quickly gasoline can move through the soil. Although diesel fuel and fuel oil are more dense than gasoline and move more slowly through the soil, they too will eventually reach groundwater.
Every site has unique geologic and hydrologic conditions that can affect groundwater movement.
How quickly the petroleum product reaches groundwater will also depend upon local soils. You may choose to locate a new tank at least 200 to 400 feet away from your well, to provide reasonable assurance that subsurface flow or seepage of contaminated groundwater will not reach your well. If possible, the tank should also be located downslope from the well. Aboveground Fuel Storage Aboveground fuel storage tanks are those in which more than 90 percent of the tank volume, including piping, is located aboveground or above the floor of an underground chamber, such as a basement. New aboveground fuel tank installations of over 1100 gallons, or modifications to existing systems, must also be approved in advance by the State Fire Marshall's office to verify the tank meets applicable fire codes.