10-2 cm/sec. A slope of 2 to 5 percent must be
collection system, or a leak detection system will be
provided to maintain flow velocity during leachate
required as determined by the responsible agency.
collection so that solids do not settle out.
A discussion of such systems may be found in TM
Maintaining velocity will also help prevent biolog-
(6) Transport for Treatment The using service
ical and chemical processes that produce additional
solids. Collection pipes should be placed in a trench
will determine the method of leachate disposal.
where the top of the pipe is no more than one pipe
Therefore, requirements for transporting leachate
diameter below grade, and the entire trench is
should be a part of that decision process.
d. Leachate Treatment
wrapped in a geotextile blanket. (See fig 3-11).
Collection pipes should be situated where leachate
(1) Before a treatment plan can be formulated,
will travel no more than 200 feet (preferably 100
the quantity and quality of leachate should be
feet or less) through the drainage layer before being
determined. Factors which influence leachate qual-
(5) Additional Protection. If leachate is ex-
(b) Landfill age.
pected to be extremely hazardous, or if the landfill
(c) Refuse depth.
is located in an environmentally sensitive area, then
(d) Refuse permeability.
either a double composite liner with backup