Case Studies: Full-Scale Operations and Delivery Systems - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 347

FIGURE 13.9 Photograph of the site operation for Case Study #1.

13.4.1.3 Delivery System

The physical setup for this project was basically as described in Section 13.3.2,
Mixer-Based Methods. A photograph of the actual site arrangement is shown in
Figure 13.9. In addition to the S/S treatment system, a size reduction and screening
operation was utilized prior to treatment. Such add-ons prevent equipment stoppages
due to jamming of feeder, conveyors, and mixers. The remediation contractor's
experience with this system contributed to operation with no major equipment
problems during the project. Portland cement was added at the soil feed point, a
somewhat unusual procedure, before conveying to the mixer. Thus, the only chemical
additions in the mixer were liquids (chemicals and water), allowing the use of a
smaller mixer and an overall faster processing rate.

13.4.1.4 Operations

A hazardous waste remediation subcontractor was chosen by the general contractor
to conduct the soil treatment phase of the project. The regulatory issues had been
addressed and resolved by the site owner, the general contractor, and the appropriate
regulatory agencies before the treatment phase was awarded and begun. Therefore,
the remediation contractor was able to proceed without delay. Prior to treatment,
the soil was excavated, stockpiled, and screened to less than 0.25 in. Oversized
material was crushed to less than 0.25 in. before processing. A front-end loader
placed screened soil from a stockpile into a feed hopper upstream from the pugmill.
Portland cement was added as the soil was fed onto a conveyor belt leading to the
pugmill. Water and a chemical solution were added in the pugmill and the combi-
nation mixed. The treated, semi-solid mixture was conveyed to and dumped on an
open space, where the product cured and the chemical reactions were allowed to
complete. This solid mound of treated material was used as “clean fill” stockpile
until the site grading was complete. After soil treatment and other site preparation
work were completed, the stockpiled, treated soil was used as engineered backfill
to form a berm. Trees and grass were planted on the treated soil to make a new park.