Page 560 - Materials Chemistry, Second Edition

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Land Disposal of Hazardous Waste 531
17.3.13 VEGETATIVE LAYER

The uppermost layer in the closed landfill profile is the vegetative layer. This layer is often planted
with a bed of dense-rooted grasses and legumes. The vegetative layer prevents wind and water erosion,
minimizes the percolation of surface water into the waste layer, and maximizes evapotranspiration, i.e.,
the loss of water from soil by evaporation combined with plant-induced transpiration. The vegetative
layer also enhances aesthetics and promotes a self-sustaining ecosystem on top of the landfill.
There are problems in maintaining a vegetative layer on top of a landfill site, especially in arid
or semiarid regions. A vegetative layer built upon a surface water collection and removal system
composed of well-drained stone and synthetic material may be unable to support crops of any kind
because insufficient soil moisture will be available. In arid regions a continuous sprinkler system
may be needed to maintain plant growth, even if the soil is sufficiently deep and fertile.

17.4 DEEP WELL INJECTION OF HAZARDOUS WASTES
Deep well injection, also known as underground injection, involves the injection of liquid hazardous
wastes into confined geologic formations deep below the surface. A geologic formation considered
suitable for injection is one having sufficient permeability and porosity surrounded by thick imper-
meable strata.
Injection well disposal places treated or untreated liquid waste into geologic formations that are
considered to have no potential for migration of contaminants into potential potable water aquifers.
Injection wells have been used for the disposal of industrial and hazardous wastes since the 1950s;
therefore, the equipment and methods are readily available and well known. Use of injection wells,
however, continues under strict regulatory control. The overriding environmental concern regarding
underground disposal of hazardous wastes is the potential for contamination of drinking water. For
this reason, legislation was enacted under the Safe Drinking Water Act (SDWA) of 1974 to protect
underground drinking water sources from contamination that may be caused by the disposal of haz-
ardous liquids in injection wells (U.S. ACE, no date).

17.4.1 THE UNDERGROUND INJECTION CONTROL PROGRAM

One component of the SDWA required the EPA to report to Congress on waste disposal practices
and to develop minimum federal requirements for injection practices that protect public health by
preventing wells from contaminating an underground source of drinking water (USDW). A USDW
is defined as an aquifer that:

● Supplies any public water system or contains sufficient water to supply a public water
system
● Currently supplies drinking water for public consumption
● Contains fewer than 10,000 mg/L total dissolved solids and is not an exempted aquifer

The EPA established the underground injection control program (UIC) program to set minimum
federal requirements for all injection wells that discharge hazardous and nonhazardous liquids
above, below, or into USDW. The requirements affect the siting, construction, operation, mainte-
nance, monitoring, testing and closure of injection wells. The program is also designed to provide
a safe and cost-effective means for industries, municipalities, and small businesses to dispose of
their wastewater, extract mineral resources, and store water for the future. All operational wells
require authorization under general rules or specific permits.
Under the UIC program, a well is defined as:

● A bored, drilled, or driven shaft whose depth is greater than the largest surface dimension
● A dug hole whose depth is greater than the largest surface dimension