Page 553 - Materials Chemistry, Second Edition

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524 Waste Management Practices: Municipal, Hazardous, and Industrial
● Designed and operated to minimize clogging during the active life and postclosure care
period.
● Constructed with sumps and pumps of sufficient size to remove liquids from the sump
and prevent liquids from backing up into the drainage layer. Each unit must have its own
sump. All pumpable liquids must be removed in the leak detection system sumps to min-
imize the head on the bottom liner.

Alternative designs and operating practices are allowed by the permitting agency if they ade-
quately prevent the migration of hazardous constituents into groundwater or surface water. Factors
to consider with alternative designs include the characteristics and quantity of the wastes and the
hydrogeologic setting of the facility, including the ability of liners and soils to attenuate any con-
taminants which may leach from the facility. The double-liner requirement may be waived for a
hazardous waste facility under certain conditions, for example if the landfill:

● Contains only hazardous wastes from foundry furnace emission controls or metal casting
molding sand
● Has at least one intact liner
● Is located more than one-quarter mile from an underground source of drinking water
● Is in compliance with applicable groundwater monitoring requirements

Precautions are also required for the proper management of surface liquids including run-on
and runoff. The facility must design, construct, and operate a run-on control system capable of pre-
venting flow onto the active portion of the landfill during peak discharge from at least a 25-year
storm. Also, a runoff management system must be installed to collect and control the water volume
resulting from a 24-h, 25-year storm. These design aspects will be discussed below.

17.3.2 SECURE LANDFILL DESIGN, CONSTRUCTION, AND OPERATION

Many of the requirements for secure landfill design and construction are similar to those for Subtitle
D (sanitary) landfills; therefore, several sections will be discussed briefly below. Details appear in
Chapter 10.

17.3.3 LINER MATERIALS

17.3.3.1 Clay Liners
As discussed in Chapter 10, clay is an important component of soil liners due to its ready avail-
ability and its tendency to be accomodating to mechanical and other stresses. Clay materials, being
natural, incorporate readily with native soil materials and are obviously very durable. Additionally,
the clay fraction of the soil ensures low hydraulic conductivity. For the secure landfill, the U.S. EPA
requires that clay liners be constructed so that hydraulic conductivity is less than 1 10 7 cm/sec.

17.3.3.2 Synthetic Liner Materials
Synthetic liner materials (geomembrane liners) are composed of polymers, which are either natural
or synthetic compounds of high molecular weight. Different polymeric materials may be used in the
construction of geomembranes (U.S. EPA, 1989), including:

● Thermoplastics — polyvinyl chloride (PVC)
● Crystalline thermoplastics — high-density polyethylene (HDPE) and linear low-density
polyethylene (LLDPE)