Page 557 - Materials Chemistry, Second Edition

CAT3525_C17.qxd 1/27/2005 12:44 PM Page 528
528 Waste Management Practices: Municipal, Hazardous, and Industrial

FIGURE 17.6 Sample of a geonet.

Events have been documented where landfill pipes have collapsed and failed. The ASTM D2412
test is used to measure the strength of pipe materials (ASTM, 2002).
Geonets are synthetic materials that require less space than perforated pipe or gravel, promote
rapid transmission of liquids, and, because of their relatively large openings, are less likely to clog
(see Chapter 10). They do, however, require geotextile filters above them and can experience prob-
lems with creep and intrusion.
Natural drainage materials should be tested to ensure that they will not dissolve in the leachate
or form a precipitate that might clog the system. ASTM D2434 evaluates the ability of the materi-
als to retain permeability characteristics (ASTM, 1968), while ASTM D1883 tests for bearing ratio,
or the ability of the material to support the waste unit (ASTM, 1999).

17.3.7 LEACHATE REMOVAL SYSTEMS
A sump is needed in the lowest portion(s) of the landfill to remove accumulated leachates. The
leachate removal standpipe must be extended through the entire landfill from the lowest liner to the
cover, and then through the cover itself. It must also be maintained for the entire postclosure care
period of 30 years or longer.

17.3.8 CLOSURE OF THE SECURE LANDFILL
Once a secure landfill or a cell is completed, it must be sealed off from its surroundings. Under the
Hazardous and Solid Waste Amendments (HSWA), there are numerous requirements for preventing
water entry into the landfill and for diverting and removing surface liquids.
A secure landfill cover consists of several layers. A dense clay cover is placed directly over the
waste. This is compacted by heavy machinery in order to decrease pore sizes and thus slow hydraulic
conductivity. After grading, a geomembrane cap is placed over the clay layer. A surface water col-
lection and removal (SWCR) system is installed above this composite liner system. Beyond this is a
soil layer that holds rooted vegetation.

17.3.9 GEOMEMBRANE CAPS
Geomembrane caps are synthetic membranes with chemical and physical properties similar to those
of geomembrane liners. The geomembrane cap, however, is one component of the cover. The