Is Installing a Cistern Under a Driveway a Good Idea?

Assessing Structural Integrity

Installing a cistern under a driveway can be feasible if the driveway is a solid concrete slab and the cistern is properly designed and engineered to transfer loads to the surrounding soil. A general rule of thumb is to limit the cistern to 1/3 of the driveway’s weight-bearing capacity. For a 4-inch-thick driveway, this translates to a 12-foot by 12-foot cistern, weighing around 20,000 pounds, filled with 10,000 gallons of water. A geotechnical engineer should be consulted to ensure the structure can handle the weight.

Water Quality and Maintenance Access

Water quality is a significant concern when burying a cistern under a driveway. The cistern should be lined with a durable, food-grade liner to prevent contamination from nearby fuel tanks, pesticides, or other pollutants. Maintenance access should be provided through a manhole or a removable cover, allowing for regular inspections and cleaning. The cistern should also be equipped with a sump pump and a backup power source, such as a battery or a generator, to ensure water can be removed in case of an emergency.

Concrete and Cistern Construction

When constructing a cistern under a driveway, it’s essential to consider the concrete’s compressive strength and the cistern’s material durability. A minimum 4-inch-thick concrete slab is recommended, with a compressive strength of at least 3,000 pounds per square inch (psi). The cistern itself should be made from a durable, corrosion-resistant material, such as stainless steel or fiberglass-reinforced plastic (FRP). A cathodic protection system can be installed to prevent corrosion and ensure the longevity of the cistern and the surrounding concrete.