Case Studies: Full-Scale Operations and Delivery Systems - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 351

The proportion of unmixed soil, as determined from visual observations made
during the size-reduction process, ranged from less than 10% to greater than 20%.
The diameter of the unmixed soil chunks ranged from less than 1/8 in. in diameter
to greater than 1 / 4 in. in diameter. Visual observations were made during the course
of the stabilization activities. In each instance the solidified waste form formed a
monolith with a high degree of cohesion and no free liquid.

13.4.2.3 Delivery System

The mechanical system used in this project was described in Section 13.3.1.1 and
is shown in Figures 13.4 and 13.5, a schematic and an actual photograph, respec-
tively, of the system at the X-231B site. The availability of the hood mentioned
briefly in Section 13.3.1.2 was a major element in the decision to use this equipment
for the project because of the VOC concentrations in the soil. The auger drilled holes
10 ft in diameter, producing overlapping columns of treated soil 7.0 ft on center,
which provided a 3-ft overlap. The rows of columns were staggered to provide
complete treatment of all the soil volume; this resulted in double treatment of the
overlapping areas. The grout was prepared at a local concrete batch plant and
delivered to the site in 7-yd 3 concrete transit mixers. The grout was then deposited
from the mixer into a grout hopper with 0.25-in. screen to remove any large particles
upstream from the grout pump. A progressive cavity grout pump with a maximum
capacity of approximately 50 ft 3 per minute was used to deliver grout to the “Kelly
bar” and hence to the hollow auger of the system (“MecTool”), which injected the
grout and mixed it into the soil. During shakedown tests at the onset of the demon-
stration, mechanical problems encountered with the grout delivery system were
resolved through grout reformulation and mechanical modifications.

13.4.2.4 Operations

After shakedown tests at the site, substituting granular activated carbon for the
original powdered carbon and adding flyash to increase the consistency and fluidity
of the grout modified the formulation. A retarder was also added to increase working
time about 2 hours, since the grout was to be mixed in a transit mixer on the way
to the injection point. The final formulation of the grout used for injection into the
soil is shown in Table 13.4.
The auger was positioned above the column to be treated. Auger position was
determined and monitored by a geologger on the MecTool that was connected to a
data acquisition system (DAS). Grout delivery rate was controlled and monitored
by a flow meter on the grout pump, and the number and capacity of the grout delivery
trucks controlled the volume of grout added. Additional water was added at the site
to further increase workability. Approximately 14 yd 3 of grout was injected into each
of three columns, yielding a grout-soil combination of approximately 30% v/v, 20%
w/w grout. Two of the three columns were surrounded by undisturbed soil, while
the third (central) column overlapped the other two columns by 3 ft, about 15% of
the column area. At the start of each test, grout was pumped out of the auger at
ground level to wet the ground area prior to penetration. A steel shroud was lowered