Environmental Engineering FOURTH EDITION

Hazardous Waste 309

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Level 3

J

>I Control Monltoring Monitoring Monltoring

Level 1

Level 2

fl Imperviouslayer

Level 3

Liner plus leachate

collectionkreatment

Backup liner plus

leachate collection/

treatment

Wells to monitor and,

if needed, control

leachate plume

Figure 15-5. Three levels of safeguard in hazardous waste landfills.

facilities, as well as the correct procedure to follow during the operation and postclosure
phase of the facility’s life, are discussed next.
Design. The three levels of safeguard that must be incorporated into the design of
a hazardous landfill are displayed in Fig. 15-5. The primary system is an impermeable
liner, either clay or synthetic material, coupled with a leachate collection and treatment
system. Infiltration may be minimized with a cap of impervious material overlaying
the landfill, and sloped to permit adequate runoff and to discourage pooling of the
water. The objectives are to prevent rainwater and snow melt from entering the soil
and percolating to the waste containers and, in case water does enter the disposal
cells, to collect and treat it as quickly as possible. Side slopes of the landfill should be a
maximum of 3: 1 to reduce stress on the liner material. Research and testing of the range
of synthetic liners must be viewed with respect to a liner’s strength, compatibility with
wastes, costs, and life expectancy. Rubber, asphalt, concrete, and a variety of plastics
are available, and such combinations as polyvinyl chloride overlaying clay may prove
useful on a site-specific basis.
A leachate collection system must be designed by contours to promote movement
of the waste to pumps for extraction to the surface and subsequent treatment. Plas-
tic pipes, or sand and gravel, similar to systems in municipal landfills and used on
golf courses around the country, are adequate to channel the leachate to a pumping
station below the landfill. One or more pumps direct the collected leachate to the
surface, where a wide range of waste-specific treatment technologies are available,
including:

0 Sorbent material: Carbon and fly ash arranged in a column through which the
leachate is passed.
a Packaged physical-chemical units: This includes chemical addition and flash
mixing, controlled flocculation, sedimentation, pressure filtration, pH adjustment, and
reverse osmosis.