The most common causes of underground tank leaks are pressure created by water in the soil surrounding the foundation. Cracks within the underground tanks, loose plaster, damaged chamfers and dry soil can cause the water leakage outwards similarly during periods of heavy or persistent rain, the soil can become saturated, creating hydrostatic pressure (or water pressure) that can push moisture and water through your underground tank walls and floor. The looser soil around the foundation tends to absorb more water. The area around the structure is often flooded with rainwater from clogged gutters or downspouts that are discharging water right next to the foundation. When the soil expands, it creates lateral (or sideways) pressure against the foundation. This can cause damage to the underground tank and any structure it is supporting.