&EPA
United States
Environmental Protection
Agency
EPA/540/SR-93/509
August 1993
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Technology Demonstration
Summary
Accutech Pneumatic Fracturing
Extraction and Hot Gas Injection,
Phase I
Herbert S. Skovronek
The Accutech Pneumatic Fracturing
Extractionf™* (PFE)™ process evalu-
ated in a SITE Program demonstration
improves bedrock permeability for va-
por extraction of volatile organic com-
pounds by injecting bursts of com-
pressed air into wells in the vadose
zone, thereby creating new fractures
and/or enlarging pre-existing fractures.
Based on 4-hr tests, fracturing in-
creased the extracted air flow rate 400%
to 700%, averaging 600%. With the in-
creased air flow rate and improved ac-
cessibility, trichloroethene mass re-
moval rate increased about 675% over
that observed in a 4-hr test before frac-
turing. When extracting from radially
located monitoring wells, fracturing in-
creased the extracted air flow rates
450% to 1,400% at wells 10 ft from the
fracture well and 200% to 1,100% in
wells at 20 ft, providing a significant
improvement in the effective radius for
extraction. With monitoring wells open
as a passive source of air, even larger
increases in air flow rate and TCE mass
removal rate were achieved. The pro-
cess is particularly useful where the
vadose zone permeability is so low that
conventional vapor extraction would
not be effective.
Using data developed in the 4-hr
postfracture test, the estimated cost
for a hypothetical 1-yr cleanup would
be $307/kg ($140/lb) of TCE removed,
including capital cost amortization. La-
bor was the major cost factor (29%),
followed by capital equipment (22%),
collection and disposal of extracted
VOCs (19%)f«ite preparation (11%), and
residuals disposal (10%).
Experiments to evaluate the effects
of injecting heated air (-200 to 250 °F)
into the vadose zone gave inconclu-
sive results.
This Summary was developed by
EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the SITE program dem-
onstration that is fully documented in
two separate reports (see ordering in-
formation at back).
Introduction
The Superfund Innovative Technology
Evaluation (SITE) Program was instituted
in 1986 to promote the development and
application of innovative technologies to
Superfund and other sites contaminated
Printed on Recycled Paper
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with hazardous wastes. This project was
carried out under a New Jersey Environ-
mental Cleanup Responsibility Act (ECRA)
Cleanup Plan for an industrial site in
Somerville, NJ where the soil and
groundwater were found to be contami-
nated with VOCs, primarily trichloroethene
(TOE). The Plan calls for decontamination
of the vadose zone by vapor extraction,
where the formation is a shale with very
limited air permeability.
Process Description
With Pneumatic Fracturing Extraction
(PFE), new fractures may be created and
existing fractures may be enlarged and/or
extended by injecting bursts (10 to 20V
sec) of compressed air (up to 500 psig)
into narrow (2 ft) intervals of one or more
wellbores. Each interval is isolated by a
proprietary injector unit equipped with
packers during pneumatic injection. The
new fractures provide increased connec-
tions and an enlarged radius of influence,
thus making vapor extraction from the va-
dose zone more efficient. Vapor extrac-
tion can be carried out from all wells, or
with some wells either left open to allow
passive air introduction or capped to di-
rect the subsurface air flow.
The developer, Accutech Remedial Sys-
tems, Inc., also is developing a catalytic oxi-
dation system for the aboveground destruc-
tion of chlorinated hydrocarbons, which may
be investigated in a Phase II study. Accutech
hypothesizes that further improvements in
VOC removal rates can be achieved by in-
jecting the hot exhaust gas (600 to 1000 °F)
into one or more wells. The catalytic unit is
not yet available, consequently a compressor
was used in this Phase I study to produce hot
air (200 to 250 °F) in order to develop and
calibrate a model for hot gas injection and to
evaluate the effects of injecting heated air.
Test Program^
A series of radially placed, 6-in. diam-
eter monitoring wells, and a central 4-in.
diameter fracture well (FW), were drilled
to a depth of about 20 ft (Figure 1).
Each well was cased to about 8 ft be-
low land surface (bis) and left open bore
for the remaining depth. Approximately 2-
ft intervals of the fracture well (FW) were
sequentially isolated by packers and frac-
tured by injecting a burst of compressed
air (<500 psig) into each interval for 10 to
20 seconds. The packer assembly was
then moved to the next interval and the
fracturing process repeated.
Strike
BuMng
Foundation
O FMW5(20-)
Dip •
O
FMW4(10')
TMW3(T) TMW2(5')
® © © TMW1 (7')
FMW3(10') FW FMW6(7.5')
O © • O
IW2(18')
FMW8 (28')
O
FMW7(20')
TMW4 (S-)
O
FMW2(W)
FMW1 (10')
LEGEND:
• FW=Fracture Well
O FMW = Fracture Monitoring Well
© TMW - Thermal Monitoring Well
© IW= Injection Well
( -') Distance to Fracture Well
Pressures at monitoring wells (capped)
and at the extraction well, extracted air
flow rates, and TCE mass removal rates
were compared before and after fractur-
ing. A second prefracture test was carried
out after a 24-hr dormant period to docu-
ment the recharge effect commonly ob-
served when vapor extraction is interrupted
and then restarted. Samples of the ex-
tracted gas were collected using EPA
Method 18 and analyzed onsite by gas
chromatography for TCE concentrations.
These values were converted to TCE mass
removal rates using the air flow rates.
Surface heave during each fracture event
was estimated with electronic tiltmeters.
Pressures and air flow rates also were
measured while extracting individually from
each monitoring well to determine whether
fracturing had established connections
between the fracture well and the moni-
toring wells and to provide information on
the radius of influence created by fractur-
ing. The effectiveness of passive air inlet
was evaluated by uncapping from one to
four monitoring wells while extracting from
the fracture well. Pressures, air flow rates,
and TCE removal rates were determined.
Two experiments were carried out to
evaluate the effects of hot gas injection.
Compression heated air (~200 to 250 °F)
was injected into a central well while ex-
tracting from one or more monitoring wells.
Temperatures in selected monitoring wells
were measured and pressures, air flow
rates, and TCE mass removal rates were
determined for the extracted air.
Results—Pneumatic Fracturing
Extraction Tests
A comparison of the 4-hr postfracture
data with the data from the restart test
demonstrated an air flow rate increase of
between 400% and 700%, averaging about
600%. Although TCE concentrations after
fracturing were only slightly higher than
before fracturing (58 ppmv vs. 50 ppmv,
avg), when coupled with increased air flow
rates, the mass removal rate was in-
creased by about 675% (Table 1 and Fig-
ure 2).
Table 1. Effects of Fracturing, Capped 4-hr
Tests
Test Pressure, Air Flow, TCE,
psia scfm Ib x 1O6/min
Prefracture
Restart
Postfracture
Increase, %
11.0
11.1
11.4
—
<0.6*
<0.6*
4.2
>600*
<10.8±1.0
<10.8±1.6
83.S±30.8
>67&>
Figure 1. Well location diagram.
* Accutech data indicate prefracture air flow
rate <0.6 scfm.
* % Increase = 100 x (Post - Pre)/Pre.
-------
I
I
e
8
180
170
160
150
140
130
120
100
90
80
70
60
50
40
30
20
10
postfracture
prefecture restart
prefrai
\cture
j_
0 20 40 60 80 100 120 140 160 180 200 220 240
Elapsed time, min
Figure 2. TCE mass removal comparison—4-hr test.
It was also found that a more complex
gas mixture was extracted after fracturing,
with higher concentrations of benzene,
chloroform, and tetrachloroethene (Table
2). Fracturing may have improved con-
nection with pockets of these compounds,
making them more accessible for extrac-
tion.
Extraction at each peripheral monitor-
ing well individually before and after frac-
turing confirmed that connections were sig-
nificantly improved even at wells 20 ft
from the fracture well, as shown by ex-
tracted air flow rates (Table 3).
Attempts were made to determine
whether vertical connections existed or
were created by fracturing between adja-
cent 2-ft intervals, but the data were in-
conclusive, probably because of perched
water in the vadose zone and the wellbore.
Additional tests were carried out with
monitoring wells left open as passive air
inlets while extracting from the fracture
well. In these experiments, even larger
increases in air flow rates and TCE mass
removal rates were observed after fractur-
ing (Table 4).
Results—Hot Air Injection Tests
During the first hot gas injection test
(90-hr), temperatures in the monitoring
wells remained essentially constant over
the first 10 hr at approximately 58°F. At
that time the thermocouples were raised
Table 2. VOCs in Extracted Air, Before and
After Fracturing
Contaminant
Concentration, ppmv
Before After
Fracturing Fracturing
Methylene chloride
Chloroform
c-1 ',2-Dichloroethene
Trichloroethene
Benzene
Tetrachloroethene
Toluene
Xylene, m/p-
Xylene, o-
1.4
3.5
U*(<3)
59.4
5.4
3.3
U (<3.3)
U (<2.8)
U (<2.8)
26.0
108.5
U (<12.5)
113.4
412.7
220.4
5.2J>
U (<11.4)
U(<11.4)
* U = below detection limit.
* J = estimated, below quantitation limit.
Table 3. Monitoring Well Extraction Tests
from 14 ft bis to 8 ft bis. Elevated tem-
peratures were immediately observed and
continued to increase over the next 10 hr
before stabilizing (Table 5). It is unknown
whether one or more thermocouples was
immersed in water in the well at the 14 ft
depth.
In addition, only very low concentra-
tions of TCE (~1 ppmv) were found in the
extracted air, both before and during hot
air injection. Even with the increased air
flow rates during injection, the calculated
TCE mass removal rate actually decreased
during hot air injection (Table 6), possibly
due to changes in the subsurface air flow
directions when the system configuration
was changed from extraction only to ex-
traction and injection.
A second experiment, lasting 24 hr, was
carried out in another area of the site
where higher TCE concentrations were
anticipated. A new hot gas injection well
and an additional extraction well were in-
stalled (IW2, FMW8). Air was extracted
from two wells (FMW6 and FMW8), each
10 ft from the injection well (see Figure 1).
Although initial temperatures in the ex-
traction wells were somewhat higher (~65
to 75 °F) than in the first hot gas injection
test, well temperatures did not increase
further in this case. Compared to an ex-
traction-only pretest, TCE mass removal
rate did increase about 50%, reflecting
both increased airflow rates and increased
TCE concentration in the extracted air
(Table 7).
Perched water in the wells may explain
some of the inconsistencies in the air flow
rate and temperature results from the two
hot air injection experiments.
Costs
Operating and capital equipment costs
provided by Accutech were coupled with
the demonstration study to estimate the
cost for remediation of a hypothetical site
comparable to the demonstration site, with
an estimated area of 100 ft by 150 ft or
15,000 ft2. With an effective extraction ra-
Distance
from
FW.ft
10s*
10o/s
10 d
10s
20s
7.5 d
20 d
Well
No.
FMW1
FMW2
FMW3
FMW4
FMW5
FMW6
FMW7
Air Flow,
scfm
pre-
<.62*
<.62-.88
<.62
<.62
<.62
<.88
<.62
post-
5.15-6.36
6.99-5.22
5.11-9.35
5.7-8.11
5.48-7.46
4.83-7.1
1.94-1.96
Increase,
(post-pre)
pre
>7.3 - 9.2
>4.9 -10.3
>7.2-14.1
>8.2-12.1
>7.8-11.0
>4.5-7.1
>2.1 -2.2
* s = strike; d = dip; o/s = off strike and dip.
" Some prefracture air flows are based on Accutech data.
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Table 4. Passive Air Inlet Tests
Test
Prefecture
Postfractura
Increase, %
Pressure,
psia avg
10.8
14.6
Air Flow, TCE Mass Removed,
scfm avg Ib x 10^/min
0.39tO.04
76.4±4.8
19,500
4.9*1.4
116±91.0
2,270
Table 5. Hot Air Injection Well Temperatures, 90 hr
Well
TMW2
TMW4
TMW1
TMW3
FMW4
FMW2
Distance
from Injection
Well, ft
5
5
7
7
10
10
Monitorinp Well Temperature. °F
Initial
to 10 hr
@14ft
59
58
57
58
57
56
After
11 hr,
@8ft
72
71
75
75
65
64
After
21 hr,
@8ft
77
74
75
76
70
68
After
89 hr,
,@8ft
75
73
72
74
71
69 ,
dlus of 25 ft and 15% to 20% overlap,
about 15 wells would be needed.
Although serious limitations are recog-
nized with such an approach to a cost
analysis, the results of the 4-hr tests were
extrapolated to a 1-yr cleanup effort. It
was also assumed that the observed TCE
concentration and mass removal rate
would continue unchanged for a full year,
even though a decrease in the rate of
removal as the concentration in the for-
mation decreases is more realistic.
Accutech estimates that a fracturing sys-
tem consisting of two injector/packer as-
semblies, a bank of 12 air cylinders, a 12-
hp compressor to recharge cylinders be-
tween fractures, and auxiliary equipment
would cost about $7,131/wkfor 2 wk while
the 15 wells were fractured. A monitoring
and analysis system (including a field GC,
tiltmeters, datalogger, and supporting mi-
crocomputers) would add an additional
$6,656/Wk.
The vacuum extraction system for si-
multaneous extraction from 15 wells con-
sists of a 40-hp vacuum blower capable
of 500 scfm, associated piping, instrumen-
tation, and a water knock-out vessel. The
estimated cost for this system is $1,0907
wk, for the entire year of operation.
The cost for pumping perched water
out of the formation was included, but the
cost of disposal was not since it was as-
sumed that it would be air stripped to-
gether with contaminated groundwater and
the incremental cost would be very small.
Well cuttings and a small amount of pro-
tective gear will require disposal. The total
cost for dewatering of the vadose zone
and disposal of these materials was esti-
mated at $37,200.
Since Accutech's proposed catalytic oxi-
dation unit is not yet available and has not
been evaluated, carbon adsorption was
selected for the extracted VOCs. The cost
to adsorb the calculated 1209 kg (2,660
Ib) of TCE to be extracted over the year of
operation and to remove and replace the
carbon is estimated at about $70,000/yr.
Personnel will be required throughout
the year (24 hr/wk for 49 wk) to oversee
the ongoing extraction and a more inten-
sive effort (120 hr/wk) will be required
during the 2 wk of fracturing. At an aver-
Table 6. Hot Air Injection Test, 90 hr
age rate of $65/hr, the total labor cost is
estimated at $107,640/yr.
The resulting cost for 1 yr of operation,
during which 1209 kg (2,660 Ib) of TCE
would be removed, is estimated at
$371,364, equivalent to about $307/kg or
$140/lb of TCE removed. Table 8 pro-
vides a summary of the costs and the
percent each subcategory contributes to
total cost.
No cost estimate was developed for the
effect of hot gas injection; the planned
catalytic oxidation unit was not used as
the source of hot gas.
Applicability to Other Sites
Based on the demonstration and other
information, the PFE process would ap-
pear to be attractive for VOC-contami-
nated formations with low permeability,
such as most clays and shales. Studies
have suggested that improvements in VOC
extraction rates are also obtained with
more permeable formations such as sands
and silts, but the effects are not as great.
There is no a priori reason to expect a
fracture necessarily to intersect a pocket
of contamination. And, as observed in this
demonstration, fractures do not always
propagate in the direction or to the dis-
tances expected. Natural and man-made
obstacles such as boulders, building foun-
dations, buried pipelines, etc., can affect
fracture propagation, provide undesirable
paths, or decrease resistance to fractur-
ing. This can result in surface failures
during fracturing or the unexpected es-
cape of vapors, as occurred during the
SITE demonstration. Perched water also
may hamper fracturing and/or interfere with
Test
Pre-hot air
Hot air injection
(one well extraction)
Hot air injection
(four wells extraction)
Air Flow,
Inject.
69.3*5.4
73.043.4
scfm avg
Extract
11.6±1.S
55.8±3.4
82.6±7.1
TCE Mass Removed,
Ib x 10*/min
172±18
20.4±32.0
31.2±10.3
Table 7. Second Hot Air Injection Test, 24 hr
Test
Air Flow,
Inject.
scfm avg
Extract.
TCE Mass Removed,
Ib x 10*/min
Pre-hot air inject
Hot air inject
(2 wells)
Increase, %
to26.r
3.7±1.8
9.2±4.7
150
63±27
97133
54
' Some data lost due to leak in manifold; measured values ranged from 10.9 to 26,1.
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Table 8. Operating Cost of Full Scale Pneumatic Fracturing Extraction
Cost Item
Site preparation
Permitting/regulatory
Capital equipment (1.5yr)
Startup
Labor salary
Consumables/supplies
Utilities
Emission control
Residuals (water, etc.)
Analytical services
Repair, replacement
Demobilization
Total
Total Cost,
$
42,000
1,750
82,074
8,200
107,640
4,000
17,000
70,000
37,200
N/A
N/A
1,500
$371,364
Cost/lb TCE,
$/lb
15.79
0.66
30.85
3.08
40.47
1.50
6.39
26.32
13.98
_
—
0.56
139.60
% Of Total
11.3
0.5
22.1
2.2
29.0
1.1
4.6
18.8
10.0
—
0.4
100.0
air flow through the formation, thereby de-
creasing VOC removal rates while increas-
ing cost.
Conclusions
For properly selected formations, PFE
can significantly improve vapor extraction
effectiveness. The nature of the forma-
tion, moisture content, air permeability,
uniformity, water table, and the presence
of obstacles or potential sources of short
circuits must all be considered when evalu-
ating PFE as a remediation option.
In the demonstration, Accutech's claims
were far exceeded: fracturing increased
extracted air flow rates 400% to 700%
and TCE mass removal rates by almost
700% when operating with a single frac-
ture/extraction well and no air inlet sources.
With passive air inlets, the air flow rate
and the TCE mass removal rate after frac-
turing are increased even more, 19,000%
and 2,300%, respectively, when compared
with the prefracture results.
The radius of influence can be increased
significantly by fracturing, with 1,100% to
1,400% increases in extracted air flow
rates in wells at distances of 10 ft and
200% to 1,100% even in wells at 20 ft.
The estimated cost for PFE remediation
of a site such as that in Somerville, NJ, is
$307/kg or $140/lb of TCE removed. La-
bor, capital equipment, and emissions con-
trol are the three major cost factors.
The effects of hot air injection are in-
conclusive. Increases in the temperature
of the formation may be produced if suffi-
cient heat is introduced, but this does not
necessarily increase the TCE mass re-
moval rate.
•&U.S. GOVERNMENT PRINTING OFFICE: 1993 - 750-071/80050
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Herbert S. Skovronek is with Science Applications International Corporation,
Hackensack, NJ 07601
Uwa Frank is the EPA Project Officer (see below).
The complete report, entitled 'Technology Evaluation Report: SITE Program
Demonstration Test—Accutech Pneumatic Fracturing Extraction and Hot
Gas Injection—Phase I," (Order No. PB93-216596/AS; Cost: $17.50, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
A related report discusses the applications of the demonstrated technology:
"SITE Program Applications Analysis Report: Accutech Pneumatic Fracturing
Extraction and Hot Gas Injection—Phase I" (EPA/540/AR-93/509).
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency (MS-106)
Edison, NJ 08837-3679
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/540/SR-93/509
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