Environmental Engineering Reference
In-Depth Information
TABLE 13.5
Pre- and Post-Treatment Total VOC Soil Concentrations
a
- Case Study #2
Pre-Treatment
Post-Treatment
Depth Interval
(m)
Conc.
(mg/kg)
Weight
(g)
Conc.
(mg/kg)
Weight
(g)
% Initial
Off-gas
-
-
-
50
c
0.4
Berm
-
-
2.39
70
d
0.55
0.0 - 0.9
48
1,860
b
-
252
e
2.0
0.9 - 2.1
84
4,380
b
5.04
252
e
2.0
2.1 - 3.4
106
5,515
b
3.14
180
e
1.40
3.4 - 4.6
20
1,050
b
-
180
e
1.40
Total
-
12,805
-
984
7.75
a
Total VOC concentration is defined as the summation of: trichloroethylene,
methylene chloride, 1,1,1-trichloroethane, trans1,2-dichloroethylene, cis 1,2-
dichloroethylene, 1,1-dichloroethane, and 1,2-dichloroethane. Values represent
the average of three soil columns.
b
Basis: Undisturbed soil bulk density = 1.95 kg/l.
c
Total VOC mass captured from off-gas for all three columns.
d
Basis: 50 vol% disturbed soil (bulk density = 1.4 kg/l) and 50 vol% grout
(bulk density = 1.515 kg/l).
e
Basis: mass of soil-grout column, exclusive of berm. VOC concentrations
were assumed uniform throughout the given depth intervals for samples from
1.2-1.5 m and 2.4-2.7 m intervals.
13.5, only 8% w/w of the pretreatment VOC mass vaporized during treatment. It is
speculated that as much as 90% of the pre-treatment VOC mass was captured in the
grout/soil mixture at the time of analysis. Drilling samples from the 1.2 to 1.5 m
and 2.4 to 2.7 m depth intervals were also tested using TCLP in an off-site laboratory.
These analyses indicate the treated material passed the accepted Toxicity Charac-
teristic (TC) limits for both organic and inorganic species.
Fifteen months after the demonstration, core samples were again collected using
a drill rig. These samples were sent to ORNL for physical and chemical analyses.
Visual evaluations were made of the samples at various depths, and photographs
were taken. Physical properties of the untreated and treated soils are given in Table
13.6. The apparent reduction in bulk density of the treated soil is due to the high
initial bulk density of this clay soil as a result of mixing, and may also be caused
by the large amount of water in the grout and entrapment of air during mixing.
Similarly, the increased hydraulic conductivity of the treated soil, in contrast to the
experience in most S/S applications, is likely due to the initial dense clay being
treated and its structural disruption caused by mixing. Most soils involved in S/S
projects have very high initial hydraulic conductivities. Compressive strength values
obtained were inversely proportional to the depth, although all of the values were
greater than the guideline for grouted material, 340 kPa (50 psi). The decrease in
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