US Patent 7637691 Multiple layer wall water storage chambers

A storm water and septic system using plastic galleries that have multiple layers provided having differing hardness characteristics, the exterior layer having a lower hardness rating than an inner layer; and a multi-layer gallery where the inner layer is treated to be resistance to degradation to a selected chemical that would otherwise degrade polyethylene. The gallery may further be provided with an interior layer having defined dielectric properties such that a fluid level measurement can be made of fluid in the galleries.