Environmental Engineering Reference
In-Depth Information
TABLE 13.4
Composition of Grout Used in Case Study #2
Fraction of Mixture
(wt%)
Mass Added Per Column
(kg)
Component
Water
31.4
5080
Retarder
a
< 0.10
10.2
Activated carbon
b
17.0
2724
Cement, Type I
41.3
6690
Flyash
10.4
1692
a
From the W.R. Grace Co., #WR-75-7250.
b
Calgon Type 220R, 30 × 100 mesh.
tightly onto the ground surface and penetration was initiated. The auger blade rotated
at approximately 10 rpm as it moved down the soil column. About 10 minutes of
mixing was required for the auger to reach the depth of 15 ft, and then the auger
was moved in a continuous upward/downward motion while rotating for a total of
45 minutes per column.
Because of the dense clay soil being treated, with the resultant low void content,
volume increase in the column due to the grout injection resulted in an aboveground
berm being created. The resultant berm was approximately 3 ft high, and the shroud
rose on the berm surface as it was formed. The shroud was kept under vacuum, but
the maintainable vacuum varied from about 155 Pa for two of the columns to only
about 17 Pa for the third. This may have been due to a relatively poorer seal with
the latter column due to resting on the berms of the two columns already formed.
After the demonstration, the berms were compacted and the geomembrane that
covered the surface of the site was repaired.
13.4.2.5
QC and Results
Off-gas was collected in the shroud over the column and the gas flow rate, temper-
ature, VOC content, and particulate content were monitored using appropriate in-
line instrumentation and sampling and analysis. Limited VOC removal was measured
during the processing, and no VOCs were detected until after about 10 minutes of
treatment. The application of grout onto the surface before penetration may have
limited the transfer of VOCs from the soil into the induced airflow caused by the
shroud vacuum. Also, the use of activated carbon in the grout formulation may have
enhanced sorption of VOCs into the treated soil.
Samples of untreated soil at various depths were taken prior to the demonstration
(Table 13.2). Within hours of the treatment operation, samples of the treated but
uncured soil were collected at various depths using a drill rig. Other samples were
collected from the berm using hand samplers. All solid samples were analyzed for
the seven target VOCs in an on-site laboratory using a heated headspace procedure
and gas chromatograph with electron capture detector. Results of this testing are
given in Table 13.5. From the mass balance computation on the data given in Table
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