Water levels were continuously monitored prior to the SVE experiments. Figure 14 shows water depth data from the time of the spill in September, 1992 until the initiation of SVE.
Precipitation was not measured at the site prior to remediation. The data indicate that the water table fluctuated between ground surface to -2.6 ft (0.8 m) below ground surface.
29
Copyright American Petroleum Institute Provided by IHS under license with API
--`,,-`-`,,`,,`,`,,`---
Approximaợe location
/ of gasoline plume
? 1.2 rn 0.6m
HF well Approximate location
of the hydraulic fracture
ground surface bentonite
V-wells
Io PVC
ir-wells
1
B -10 m
AS - Air sparging well V - Vapor monitoring well W - Vertical 2" vapor extraction well HF - Hydrofracture well
Figure 12. Cross-section view of the experimental cell showing the locations of the trenches, wells, hydrofiacture and the hydrocarbon plume.
30
Copyright American Petroleum Institute Provided by IHS under license with API
Not for Resale No reproduction or networking permitted without license from IHS
--`,,-`-`,,`,,`,`,,`---
MW-1 0
N
Scale
O 1 2 m
r
Legend O
O MW - Groundwater Sample location Trench location
IW - Gasoline injection wel:
monitoring well
- . - .
- . - . -
I I I I
L.-.-
I I I I I
! N-3 N- 1 I
. .
MW-2 O
. .
. . . . . . . .
. .
. .
. .
. .
. .
. .
. .
. .
. . . .
. .
. .
. .
. . .. ..
. .
. .
. .
. .
. .
. .
. .
. .
. .
. . . .
:.s : : g :
! z i
: = :
. o .
. . . . . .
. .
. . . .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
. .
.. ..
. .
. . . .
. .
. .
. .
. .
. .
. .
. .
. .
Figure 13. Plan view of the test cell showing the locations of the sampling trenches and the specific sample locations.
31
Copyright American Petroleum Institute Provided by IHS under license with API
--`,,-`-`,,`,,`,`,,`---
S T D . A P I / P E T R O P U B L DR 2 2 5 - E N G L I1998 0 7 3 2 2 9 0 ObL228Y 975 W
400
a rn
m E -200 a e
e
blD
E -400 cw
E
d
a2
-2 c, -600
m $
-800
I I
t
t 1
-1000 I I l I
O 1 O0 200 300
time, days since spill
Figure 14. Water table depths measured inside and outside the test cell for the time of release to the initiation of remediation (- 1 O months).
32
Copyright American Petroleum Institute Provided by IHS under license with API
Not for Resale No reproduction or networking permitted without license from IHS
--`,,-`-`,,`,,`,`,,`---
S T D . A P I / P E T R O P U B L DR 225-ENGL 1998 O732290 ObL2285 B O L
VII. DETERMINATION OF AIR PERMEABILITY AND EFFECTIVE POROSITY In order to assess the impact of the fractures and water on air flow, air permeability and effective porosity, measurements were made using three wells within the experimental test cell (Figure 15). Pneumatic tests were conducted by pumping air from one of the wells and measuring the reduction in pressure at all three wells. As discussed below, those data were used to graphically estimate the radius of influence of the extraction well and from that the air permeability was calculated.
As seen in Table V, the pneumatic pumping test flows were generally in the range of 2 scfìn.
The vacuum at the extraction well was maintained at 0.5 atm. Vacuums at the other two wells were 1 inch of water (0.003 atm). The radius of influence for these tests was estimated to be 10 ft (3 m). The air permeability of the fractured clay was calculated using the in-situ air permeability test protocol developed by the U.S. Air Force (Hinchee et al., 1992). The protocol recommends the following equation for estimating air permeabiliíy :
where: Q = volumetric flow rate from the venting well (m3/s) p = viscosity of air
Rw = radius of the venting well (m)
RI = radius of venting influence at steady-state (m) H = depth of screen (m)
Pw = absolute pressure at the venting well (Pa) Palm = ambient pressure (1 .O 1 xl O5 Pa)
kgím-s)
Air permeabilities calculated for the test site using equation 1 range from an average value of - 5 ~ 1 0 - l ~ m2.
to m2, with The data contained in Table V, along with the general fracture orientation at the Sarnia site (McKay et al., 1993a) are shown in Figure 16. Generally, the highest vacuums were generated at wells oriented in the same plane as a set of fractures. For example, pumping to or from P1 and P2 (Test 1 and Test 2, respectively) results in the highest (0.002 atm) vacuum through the clay till, and P1 and P2 are oriented along the general direction of a set of fractures. On the other hand, the smallest vacuum results from pumping to or from P1 and P3 (Test 1 and Test 3, respectively) which are not aligned with a fracture set. Also, the hydrocarbon source zone is slightly elliptical in the direction of the northwest-southeast fracture set (see Appendix A). This may suggest that northwest-southeast is the major fracture direction while the northeast- southwest fractures are secondary fractures. Major and minor fracture directions have not been verified, however, McKay et al., (1993a) suggest a slight fracture domination in the northwest- southeast direction. Based on the above discussion, if a trench is to used in an SVE system, it
t
33
Copyright American Petroleum Institute Provided by IHS under license with API
--`,,-`-`,,`,,`,`,,`---
S T D . A P I / P E T R O PUBL DR 225-ENGL L978 0732270 ObL228b 748 =
Test 1 Test 2 Test 3
N
P1 Y2 P3
2.0 scfin 0.33" water 0.92" water 0.3" water 1.9 s c h 1.1 'I water 0.86" water 1.1 water 2.0 s c h 10 m
Figure 15. Plan view of cell showing the locations of the wells used for effective porosity and air permeability tests.
Table V. Pneumatic pumping test measured flows and pressures.
34
Copyright American Petroleum Institute Provided by IHS under license with API
Not for Resale No reproduction or networking permitted without license from IHS
--`,,-`-`,,`,,`,`,,`---
S T D . A P I / P E T R O P U B L DR 225-ENGL 1778 0 7 3 2 2 9 0 Ob32287 6 8 4
General orientation offiactures -