Case Studies: Full-Scale Operations and Delivery Systems - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 343

waste or damage the drilling equipment. Also, the grout that is pumped in can cause
ground swell unless inherent voids accommodate the increased volume; e.g., shallow
land burials contain large void volumes but tend to be rift with buried obstacles.
Ground swell may be undesirable in some situations, although in other remedial
actions the extra “fill” is welcome.
Jet grouting is a construction technique for consolidating or sealing soil in situ
where traditional excavation techniques are not practical; for example, where existing
buildings are too close. The grout is pumped to high pressure and then jetted into
the soil, with the potential energy of the high pressure transformed into and spent
as kinetic energy breaking up and mixing the soil with the grout. Obviously, this
mixing action is ideal for mixing stabilizing blends with contaminated media in situ .
However, the construction equipment and technique results in significant grout
returns to the surface (up to 100%; i.e., for every gallon in a soil-grout column, up
to another gallon flows to the surface). Although this extra soil-grout mixture causes
little more than inconvenience for construction work, returning this much contam-
inated material to the surface can be a serious disadvantage for an in situ remediation.
Fortunately, innovations and improvements have retained the advantage of inti-
mate mixing afforded by the use of such jets, while minimizing the amount of
material returned to the surface. For example, Multi-Point Injection (MPI™) had no
grout returns for shallow land burials, where significant void space existed to accom-
modate the volume of material injected. 2 Ground swell can be expected for such
injections into undisturbed soil, depending on the void volume and volume of
injected material. Also, injecting within about 2 feet of the surface can result in the
ground cover being incorporated into the grout mix. Thus, if contamination starts
at the surface and exposing the energetic mixing at the surface is undesired, a cover
of about 2 feet or more of clean soil may be required.
Liquid Injection Methods . In some situations stabilization can be accomplished
by just injecting a treatment solution or slurry into the contaminated area, in much
the same way that soil stabilization for construction purposes has been done for
many years. In a highly permeable material, such as sandy soil, injection may be
done using standard well injection points and injecting the solution/slurry under
pressure. In less-permeable formations, using one of the drilling augers described
above works better.
Area (Shallow) Methods . In many remedial projects, the sludge pond or con-
taminated soil depth is not great, often 5 feet or less. For these situations, the use
of modified agricultural soil conditioning equipment is efficient and cost-effective.
An example of such a system, using a tractor-mounted disk harrow, is shown in
Figure 13.6. The reagent can be spread on the surface followed by harrowing, or it
can be injected through nozzles mounted on the harrow. Similar systems use power-
driven, front-mounted augers or blades similar in operation to a roto-tiller.

13.3.2 F IXED I NSTALLATIONS

Fixed installations are those intended to be used at one site, either permanently or
for some singular purpose over a limited time span. Unlike the variety of delivery
systems encountered in mobile or portable systems, fixed installations are generally