Patent ID: 8297880

Claim:
A method for treating wastewater in a leaching field, which comprises forming and burying in soil a molded thermoplastic leaching chamber having an arch shape cross section, opposing lengthwise ends having openings, for connecting to other chambers, sidewalls rising upwardly from opposing side base flanges toward the top of the chamber, a multiplicity of alternating peak and valley corrugations running transverse to the length of the chamber from vicinity ofone flange to vicinity of the opposing side base flange; wherein the chamber is formed by hte step of molding a chamber as a one piece structure in combination with simultaneously carrying out at least the following steps: (a) forming opposing portions of the sidewalls so they curve inwardly as they rise upwardly toward the top of the chamber; (b) forming a curved top with connects said opposing portions of sidewalls, to thereby make the arch shape cross section of the chamber a continuous curve which runs upwardly from one base flange, across the top, and downwardly to the opposing base flange; (c) forming a multiplicity of vertically spaced apart horizontal slots in the curved portions of the sidewalls at places where said peak corrugations and valley corrugations are present, for flow of water through the sidewalls of the chamber; (d) forming the sidewalls and top so that peak corrugations are spaced apart from each other with a center to center distance of less than 8 inches ; (e) making the interior of the chamber free of strengthening ribs, (f) making the wall thickness of the chamber in the range 0.090 inches to 0.125 inches; wherein the chamber has a leaching area of at least 100 square inches per pound of chamber weight; and wherein the thermoplastic material of the chamber has properties which impart to the chamber strength sufficient to meet an H-10 rating of American Association of State Highway and Transport Officials (AASHTO).