Patent ID: 7491015

Claim:
A combination of an arch shape cross section chamber having opposing side base flanges, for receiving and dispersing water when buried in water permeable medium, and an end plate, for closing off the end of the chamber and preventing the entry of said medium; wherein the endplate comprises: a dished portion; a flange running around the periphery of the dished portion, wherein said flange is configured to associate with the end of the chamber and the opposing side base flanges, to close off the end of the chamber; and a plurality of strengthening ribs running between the arch shaped flange of the endplate on the concave side of the dished portion; and an arch shaped rib running between a first base portion of the endplate and a second base portion of the endplate on the concave side of the dished portion, the arch shaped rib having a smaller radius than the arch shaped flange and having substantially the same shape as the arch shaped flange.