Technology for protecting the environment in gasoline service stations has continued to develop through the use of containment sumps in the fill area, submersible pump area and under the dispenser for an underground storage tank and piping system. These containment sumps can be constructed of polyethylene, a material that is extremely resistant to gasoline and oil. Typically, these sumps are structured in one or several parts, depending on the application and the depth below the surface of the pavement. A typical fill area and submersible pump area sump is constructed in three parts for ease of installation, as shown in FIG. 1.
These three parts may be characterized as a lower portion, an upper portion, and an optional cover. The lower portion can be mounted to a flange and sealed using a rubber gasket. Installing the lower portion first allows easy access for piping and electrical connections to be made. The upper portion may be connected to the lower portion using metal rings, rubber gasklets and bolts, as shown in FIG. 1. Alternative designs include a tongue and groove joint in the two portions or a threaded joint. Piping penetrations are also sealed using metal rings or a hose clamp to secure a rubber boot to the sump side wall and the penetrating pipe or conduit.
While the initial assembly of these sumps provides effectively tight containment, the sump often is exposed to various stresses that result in movement of the polyethylene in such a way that a tight seal is no longer possible. This can occur due to upward forces during high water periods; settling or shifting of the underground tank and piping; and cold flow of the polyethylene in the gasket area due to stress created by the flanges and bolts used to effect the seal. Additionally, these sumps can crack due to the stresses described above.
Repair of a polyethylene sump has proven to be very time consuming with only marginal effectiveness. Patching materials fail to work because polyethylene is extremely resistant to bonding with any material. As a result, all of the effective repair methods require a "welding" of the polyethylene to occur before an effective repair can be made.