Environmental Engineering Reference
In-Depth Information
TABLE 5.16. Capillary Rise in Unconsolidated Materials
TABLE 5.17. Parameters (
α
,
β
)
Grain Size
Capillary Rise
LnAPL Density (kg/m
3
)
material
(mm)
(cm)
Soil Texture
700
775
850
Fine gravel
2-5
2.5
Sand
(0.10, 0.397)
a
(0.20, 0.391)
(0.30, 0.384)
Very coarse sand
1-2
6.5
Loamy sand
(0.175, 0.363)
(0.25, 0.352)
(0.40, 0.344)
Coarse sand
0.5-1
13.5
Sandy loam
(0.325, 0.340)
(0.44, 0.324)
(0.65, 0.310)
medium sand
0.2-0.5
24.6
Loam
(0.65, 0.303)
(0.85, 0.278)
(1.10, 0.247)
Fine sand
0.1-0.2
42.8
Sandy clay loam (0.55, 0.252)
(0.69, 0.232)
(0.90, 0.211)
Silt
0.05-0.1
105.5
Silt loam
(1.00, 0.273)
(1.25, 0.237)
(1.60, 0.195)
Silt
(1.12, 0.273)
(1.45, 0.234)
(1.80, 0.183)
Source of data
: Lohman (1979).
Clay loam
(1.07, 0.195)
(1.35, 0.166)
(1.75, 0.134)
Sandy clay
(1.07, 0.159)
(1.35, 0.134)
(1.75, 0.110)
Silty clay loam
(1.47, 0.150)
(1.85, 0.116)
(2.50, 0.083)
Clay
(1.52, 0.071)
(2.02, 0.052)
(2.90, 0.036)
aquifer. The relationship between the free product
thickness in the recovery well,
H
w
, and the equivalent
free product thickness in the aquifer,
H
a
, can be esti-
mated by the relation (Kemblowski and Chiang, 1990)
Silty clay
(1.90, 0.056)
(2.65, 0.038)
(4.20, 0.024)
a
α
is in meters and
β
is dimensionless.
Source of data
: Charbeneau (2000).
H H
=
− 3
h
(5.85)
a
w
s
well may not contain any nAPL if the screened interval
contains only residual nAPL.
where
h
s
is the capillary rise of water in the soil, which
can be estimated using Table 5.16.
Since the capillary rise increases for finer aquifer
materials, in fine-grained aquifers, the free product
thickness measured in a monitoring well can overesti-
mate the actual free product thickness in the aquifer by
tens of centimeters. Equation (5.85) also demonstrates
that for the same amount of nAPL in the groundwater,
wells surrounded by fine-grained material will show a
greater free product thickness than wells surrounded by
coarse-grained material. An alternative relation pro-
posed by Hampton and miller (1989) is
EXAMPLE 5.19
Several monitoring wells surrounding a gas station show
a 30-cm-thick layer of gasoline in wells covering an area
of 2500 m
2
. The gasoline has a density of 750 kg/m
3
, the
temperature of the groundwater is 15°C, the aquifer
material consists of medium sand with a (water) capil-
lary rise of 8 cm, and the porosity of the aquifer is
0.23. Estimate the volume of gasoline floating on the
water table.
ρ
−
ρ
w
f
H
=
H
(5.86)
a
w
ρ
w
Solution
where
ρ
w
is the density of water (mL
−3
), and
ρ
f
is the
density of the LnAPL (mL
−3
). Charbeneau (2000) con-
sidered the role of soil texture on the relationship
between aquifer free product thickness,
H
a
, and the
monitoring well thickness,
H
w
, and suggested the
relation
From the data given,
H
w
= 30 cm = 0.30 m,
A
spill
=
2500 m
2
,
h
s
= 8 cm = 0.08 m,
n
= 0.23,
ρ
f
= 750 kg/m
3
,
and at 15°C
ρ
w
= 999.1 kg/m
3
. Interpolating from
Table 5.17 for sand texture gives
α
= 0.167 m and
β
=
0.393. According to Kemblowski and Chiang (1990),
Equation (5.85) gives the thickness
H
a
of gasoline in the
aquifer as
H
=
β
(
H
−
α
)
(5.87)
a
w
where
α
(L) and
β
(dimensionless) are empirical con-
stants given in Table 5.17 for LnAPLs of various densi-
ties. The parameter
α
in Equation (5.87) represents the
minimum thickness of LnAPL in the well for the
LnAPL to flow freely between the well and the aquifer.
Typically, the free product thickness in a recovery well
is 2-10 times thicker than the free product thickness in
the aquifer. It is important to note that a monitoring
H H
=
−
3
h
=
0 30 3 0 08
.
−
( .
)
=
0 06
.
m
=
6
cm
a
w
s
Using the relation proposed by Hampton and miller
(1989), Equation (5.86) gives
ρ
−
ρ
999 1 750
999 1
.
−
w
f
H
=
H
=
( .
0 30
)
=
0 075
.
m
=
7 5
.
cm
a
w
ρ
.
w
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