A need became apparent in the 1980's for a reliable underground bulk storage tank system. The then industry standard storage tanks were single wall. A major leak or tank wall collapse could result in 20,000 or more gallons of liquid, e.g. gasoline, being spilled. Even a minor leak could cause substantial environmental damage over time.
When the leakage problem inherent with the single wall storage tank systems became apparent, the tank industry began building double wall storage tank systems. An inner wall contains the stored liquid while an outer wall encompassing the single wall provides back-up or secondary containment capability. A space between the walls is monitored for wall leakage. Examples of such double wall tank systems are found in U.S. Pat. Nos. 4,653,312, 4,739,659, 4,875,361, 4,925,046, 5,017,044, 5,020,358 and 5,167,142. Such systems have proved reliable. Many of the double wall storage tank systems now being sold are based on their designs.
Now that the reliability of double wall tank systems have been generally recognized, the industry has begun to focus on producing the tanks more economically. A savings in raw material costs and a savings in labor costs are possible.
In accord with a need for a more economical storage tank system, there has now been developed a method of building a composite storage tank. The tank is built by a method which results in a savings in both raw material and labor costs. The resultant storage tank has double wall characteristics which gives it performance attributes that make it a viable alternative to current double wall storage tank systems.