02.04 What are the site considerations for underground tanks?

The code requirements for underground tanks are typically 5 feet from building walls and 15 feet from property lines. Consideration should be given to the access for fuel delivery trucks to the tank area, and remote fill stations should be planned if needed.

The tanks may be located in paved areas, since properly installed they are not damaged from vehicle traffic. If located in unpaved areas or in areas of bituminous paving, it is typically important to install concrete collars around the fill point and manways. The concrete collars work to prevent damage to tank top equipment, and provide a barrier for small volumes of fuel that may be present from tank fill or maintenance operations.

Mechanical designers will typically locate the underground tanks in locations optimum for operational performance. This allows for a minimum of pipe length from the tanks to the building wall or point of use. However the excavation aspects of tank installations can have important impacts on the project costs and schedule, and these should be considered as well. The tank installation is often the deepest excavation associated with the construction, so it is worthwhile to do some preliminary planning. Some aspects of the tank excavation are as follows:

1. Large tank installations squeezed between buildings and property lines can restrict access to the building for construction operations.
2. Tank installations can impact building wall stability where the tank excavation is below the building footing wall elevation. Shoring, even where practical and cost effective, can increase the risk of building settlement. Buildings on adjacent properties can also be impacted in the same way.
3. Tank installations behind retaining walls can impact the stability of these structures if they are within the soil zone of influence for the wall footings.
4. Existing underground utilities in the tank area may require relocation or support, and the tank installation may increase the risk of utility service to the building.
5. A high water table at a proposed tank installation may require dewatering which can increase the installation costs, and increase the risk of ground settlement. Handling of dewatering discharges can also be problematic and may require special permits.
6. A high rock elevation at a facility will increase the costs of excavation and tank installation. And the construction aspects of rock removal can cause vibration that is detrimental to adjacent buildings or utilities.