22.01 What is important about underground tank sumps?

Underground tank sumps allow for access to equipment such as submersible pumps that are directly installed above underground tanks. The most important aspect of the sumps is that they do not leak either fuel to the environment or water to the inside of the sump.

Tanks sumps are typically either fiberglass or HDPE plastic, and are circular or rectangular to resist soil loads. Sumps are typically 36” to 42” in diameter and 3’ to 6’ in depth. They connect to the tank either (a) by attachment to a collar which is integrally molded with the tank shell, (b) bolted to a tank manway, or (c) connected with bulkhead fittings through the sump floor to tank riser pipes. Alternative (a) has proven to have superior performance.

In California, tank sumps are required to be double walled and continuously monitored. Monitoring of the sump shell is typically by hydrostatic or vacuum methods

The most likely cause of water entry into tank sumps are (a) leaking piping penetration fittings, (b) leaking conduit penetration fittings or inflow through unsealed conduit, (c) leaking sump to tank seals, and (d) inflow through the sump led seal.