7.4.5.1 Leachate Generation. Leachate is generated from moisture passin
through the solid waste. It may be a result of moisture already present
the refuse, or from rainfall or irrigation infiltrating into and through
fill area. Regulations in most states require that sanitary landfills ha
facilities both to monitor for the presence of leachate and to control
leachate that may otherwise adversely affect local water quality. There
are presently no federal regulations concerning specific treatment or
disposal methods for leachate generated at nonhazardous waste disposal
sites. Some state agencies have implemented regulations governing leacha
collection, treatment, and disposal methods. In addition, landfill leach
itself could be classified as a hazardous waste under RCRA, depending on
chemical characteristics. Leachate that is classified as a hazardous
waste would require treatment or disposal at a licensed hazardous waste
facility.
A basic goal of a landfill design is to provide for features that
minimize leachate production. In general, leachate generation can be
minimized (or even eliminated in arid regions where evaporation
significantly exceeds rainfall) by avoiding contact between waste materia
and groundwaters or surface waters; diverting offsite runoff away from th
landfill; diverting onsite runoff away from active fill areas and minimiz
runoff travel distances over filled surfaces; minimizing direct infiltrat
of precipitation into the fill by properly covering the solid waste with
suitable soil or other material; and properly applying, compacting, and
grading final soil cover (minimum 2- to 3-foot [0.6- to 0.9-meter] depth)
filling is completed in portions of the site.
Methods for mitigating adverse environmental effects of leachate incl
the use of a site that is hydrologically isolated from local aquifers or
where natural conditions promote attenuation of leachate constituents via
"filtering" through insitu soils, and the installation of a system to
collect and subsequently treat the leachate generated before it contacts
groundwaters or surface waters.
When natural conditions and contaminant attenuation through soils are
proposed for mitigation of leachate impacts, the primary factors to be
considered are the hydrogeological characteristics of the site, especiall
the hydraulic conductivity of the underlying strata, soil characteristics
and the depth to usable groundwater. A soil that offers low permeability
high clay content, high cation exchange capacity (CEC), and relatively hi
pH (> 7.0) is preferred over soils composed of coarse-grained particles w
high permeabilities and low CEC values.
The long-term effectiveness of contaminant removal via soil interacti
processes is not verified, since the attenuating capacity of a soil is
finite and not necessarily permanent. Further, if chemical loading rates
exceed the soil's attenuative capacity, the quality of regional ground wa
could be affected.
For site-specific information, subsurface investigations and soils te
should be performed onsite by qualified hydrogeologists and soil scientis
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