(a) Surface impoundments should be sited and
(3) Each disposal type has its own soil requirements
for construction and operation. Although all materials
designed with maximum protection of ground water
can be imported from off-site sources, project costs can,
provided by liners, low permeability clay (10-8 cm/sec)
as a result, become prohibitive. In sites located in areas
underlying soils, and maximum separation.
underlain by shallow cemented bedrock, nearly all soil
hydraulic head formed in the impoundment provides for a
materials may need to be imported; as a result, costs for
high potential for liquid seepage and subsurface
landfilling in such areas can be prohibitive.
(b) Since potential for buildup of hydraulic head
underlain by clay deposits significantly reduce the cost of
construction of all types of disposal facilities. Below is a
in landfills and waste piles is much less than for
summary of soil needs for different disposal methods:
impoundments, siting criteria can be somewhat relaxed
for these facilities. With liners beneath the waste, soils
with permeabilities in the vicinity of 10-6 cm/sec (silts,
Daily and intermediate cover;
silty clays) may be acceptable separation materials.
(c) In land treatment facilities little or no
a variety of soil types are
hydraulic head buildup is created; however, strict
Final cover soils must be low
operational criteria are required by RCRA to ensure their
protection. Such facilities can be located in most locales
Liner soil must be clay.
Liner soil must be low
approximately 10 feet, and moderately low permeability
soils (10-4 to 10-5 cm/sec-silty sands, silts).
Liner soil must be low per-
(d) Limitations in locating injection wells are
discussed in paragraph 5-5.
Treatment zone must have
(2) Isolation of wastes from surface water is a major
minimum of 5 feet of suitable
concern in the design and locating of all disposal
soil, as described in section
methods. It is highly recommended that disposal units
5-4 b (2).
be located out of a 100-year flood plain and away from
topographic areas prone to flash flooding and/or severe
erosion; avoidance of flood plain areas may be
3-6. Design requirements imposed by hydrogeologic
mandatory for certain types of hazardous wastes. All
disposal modes (landfills, impoundments, etc.) should be
Less than ideal hydrogeologic conditions can be
designed with drainage diversion and surface run on
overcome by engineering designs in all but the most
protection and isolation facilities (i.e., berms, dikes, etc.).
extreme conditions. However, the site owner/operator
High design and construction costs may be associated
must be aware that great expense may be involved in
with sites located within flood areas and/or in areas
these engineering solutions, and may make the project
requiring diversion of surface runoff from large
economically unfeasible. Table 3-2 summarizes the
upgradient watersheds. With proper facility design,
major design/operational requirements imposed by
surface water conditions should not be a major factor in
unfavorable hydrogeologic conditions.
selection of a disposal type, but only in selection of