AREA A/B ENGINEERING REPORT - Waste Management

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hundreds to thousands of years. For a CCL under these same design and construction constraints,
the service life is even longer, on the order of thousands of years 9 . This is the reason that CCLs
are used in the encapsulation liner systems of more “critical” waste management units (e.g.,
radioactive waste), and that a well maintained liner can be protective in a MSW landfill far
beyond the time the contained waste would be of potential environmental concern. 10
3.3 Leachate Management System
The purpose of a leachate management system (LMS) is to collect leachate from the base of a
landfill and convey the leachate away for safe discharge or disposal. In general, a LMS includes
the following three major components:
• A leachate collection and recovery system (LCRS) directly above the liner system, which is
sloped and graded to provide positive leachate drainage under gravity to a sump fitted
with a riser pipe (see Figure 3-2);
• A leachate transmission and storage system featuring a pipeline network, pumps, and
storage tanks, sumps, or lagoons; and
• A treatment and/or disposal system.
These components are integrated and serve complementary functions for environmentally
protective leachate management at a modern landfill. The type and complexity of each
component system is dependent on local climate conditions and operational design, as well as
other site-specific factors. Selection of an appropriate LMS is discussed in Section 3.3.4.
3.3.1 Leachate Collection and Recovery System
In most cases, the LCRS overlies the low permeability liner system in a modern
managed landfill. The LCRS normally comprises a 12 to 24 inch layer of porous
sand or gravel, the purpose of which is to collect and remove leachate generated
in the landfill, although the sand/gravel layer also serves to protect the liner
system from damage during initial waste placement. A specifically designed openweave
plastic mesh termed a geonet (GN) or synthetic drainage material termed a geocomposite
(GC) is sometimes installed above the liner instead of, or in conjunction with, a sand/gravel
drainage layer to improve LCRS drainage performance. The LCRS is overlain by a geotextile
(GT) fabric or similar permeable barrier to minimize intermixing of overlying waste and
protective soil layers. The first two to four feet of waste disposed of in the landfill are carefully
9 The service life of HDPE geomembranes and composite liner systems has received significant attention in the
technical literature (e.g., Koerner, et al, 1990; Hsuan & Koerner, 1998; Rowe, 1998; Rowe & Sangam, 2002;
Sangam & Rowe, 2002; Hsuan & Koerner, 2005; Rowe, 2005) and has been the focus of a recent USEPA-sponsored
study (Koerner & Hsuan, 2002). See also Appendix B.
10 Discussion of the use of geosynthetic and natural soil systems for very long term waste encapsulation is beyond the
scope of this document. However, seminal references include Reith & Caldwell (1993) and Bechai, et al (1986).
MD10186.doc 39 29 March 2009