Handbook of Solvents - George Wypych - ChemTech - Ventech!

17.2 Fate-based management 1163
data for the leachate-site system. A given land-disposal site has a finite capacity to attenuate
organic solvents in solution to environmentally acceptable levels. If the attenuation capacity
of a site can be estimated, then the resulting information can be used as criteria to make
decisions as to what wastes should be landfilled, and what quantities of solvent in a given
waste can be safely accepted. The purpose of this section is to summarize studies 1-3 that
were conducted that illustrate how knowledge of the environmental fate and movement of
the solvents in Section 17.1 can be used in managing solvent-containing wastes. These studies
were conducted by using computer simulations to assess the fate of organic compounds
in leachate at a waste-disposal site.
17.2.1.1 The waste disposal site
There are three major factors that will ultimately determine the success of a land-disposal
site in being protective of the environment with respect to groundwater contamination by
organic solvents: (1) the environmental fate and toxicity of the solvent; (2) the mass loading
rate, i.e., the amount of solvent entering the subsurface during a given time, and (3) the total
amount of solvent available to leach into the groundwater. The environmental fate of the
solvents was discussed in 17.1.
The hypothetical waste-disposal site used in this evaluation (Figure 17.2.1) had a single
waste trench having an area of 0.4 hectare. Although site-specific dimensions may be assigned
with actual sites, this hypothetical
site was considered representative of many
situations found in the field. The trench was
12.2 meters (40 ft) deep and was constructed
with a synthetic/compacted-soil
double-liner system. The bottom of the
trench was in direct contact with a sandy
aquifer that was 6.1 meters (20 ft) thick.
The top of the water table was defined as
being at the top of the sandy aquifer. Thus,
this site was designed as a worst-case scenario.
The sandy aquifer directly beneath
the hazardous-waste trench would offer little
resistance to the movement of contaminants.
To further compound a worst-case
situation, it was also assumed that the entire
trench was saturated with leachate, generating
a 12.2 meter (40 ft) hydraulic head
through the liner. This could correspond to
a situation where the trench had completely
filled with leachate because the leachate
collection system had either failed or the
site had been abandoned.
The following aquifer properties, typical
of sandy materials, 1 were used in the
study:
Figure 17.2.1. Design of the waste-disposal site model
used in the simulations (Roy et al. 1 ).