Ill. Admin. Code tit. 77, pt. 905, app A, ILLUSTRATION I, exh. E
Example: Chamber systems shall be sized on the absorption area of the chamber that is equivalent to the bottom area of a gravel system. The equivalent chamber absorption area per lineal foot is equal to the average inside width of the chamber times an equivalency factor of 2.5. For example, a chamber that has an average inside width of 1.25 feet provides an equivalent absorption area of 3.125 square feet per lineal foot. (1.25 feet times the 2.5 equivalency factor equals 3.125 square feet per lineal foot.
To determine the length of chambers required, first calculate the absorption area required for a gravel system based on Appendix A, Illustration H, Exhibit A or Appendix A, Illustration M, Exhibit A. Then divide this area by the equivalent chamber absorption area per lineal foot. For example, if a 3 bedroom house requires 870 square feet of absorption field and chambers 1.25 feet wide are being used, then the length of chambers needed is 278 feet. (870 square feet divided by 3.125 square feet per lineal foot equals 278 feet.)
Chamber systems with an average inside dimension equal to or greater than 20 inches shall not be designed to receive an equivalent absorption area of greater than 5 square feet per lineal foot.
Ill. Admin. Code tit. 77, pt. 905, app A, ILLUSTRATION I, exh. E