Ill. Admin. Code tit. 35, § 817.407 – Leachate Drainage System

a) The leachate drainage system shall be designed and constructed to be capable of operation throughout the entire design period.
b) The system shall be designed in conjunction with the leachate collection system required by Section 817.408:
1. 1) To maintain a maximum head of leachate 3.0 meters (10 feet) above the liner; and
2. 2) To operate during the month when the highest average monthly precipitation occurs and, if the liner bottom is located within the saturated zone, under the condition that the groundwater table is at its seasonal high level. In addition, the following design assumptions shall apply:
  1. A) The unit is assumed to be at field capacity; and
  2. B) The final cover is in place.
c) A drainage layer shall overlay the entire liner system. This drainage layer shall be no less than 0.30 meter (one foot) thick and shall have a hydraulic conductivity equal to or greater than 1x10^-3 centimeters per second.
d) The drainage layer shall be designed to maintain laminar flow throughout the drainage layer under the conditions described in subsection (b).
e) The drainage layer shall be designed with a graded filter or geotextile as necessary to minimize clogging and prevent intrusion of fine material.
f) Materials used in the leachate collection system shall be chemically resistant to the wastes and the leachate expected to be produced.