Note: Descriptions are shown in the official language in which they were submitted.
Doc. No. 328-14 CA
Green Tech Patent
METHOD AND SYSTEM FOR FORMING A PERMEABLE
REACTIVE BARRIER IN THE GROUND
FIELD
The present invention relates generally to methods and systems for in situ
construction of a
subsurface containment region for containing hazardous waste or contaminated
soil buried
under in the ground, and more particularly to a method and system for forming
an
underground permeable reactive barrier.
BACKGROUND
Dr. Robert Gillham of the University of Waterloo, decades ago, discovered a
method of in-
situ treatment of chlorinated solvents by introducing iron filings into a
polluted ground source
of ground water.
Sayles et al. (Environmental Science and Technology, 1997) investigated the
utility of using
zero-valent iron (e.g., granular iron filings and the like) to dechlorinate
DDT and related
compounds in an anaerobic aqueous environment. Sayles et al. also acknowledged
the
importance of providing for a large surface-area of reactive iron, such as
that which could be
facilitated by the use of a fine particulate or powdered forms of iron. This
method became
popular and was used later by mixing iron filings with sand.
Currently, various techniques are known for forming zero-valent iron permeable
reactive
barriers. These known techniques can be classified based on whether placement
of the barrier
requires digging a trench or is achieved without digging a trench. Those
techniques that do
not require digging a trench may be further classified based on whether a
continuous or
discontinuous barrier is formed.
As will be apparent, barrier placements that require digging a trench are
limited to relatively
shallow depths, cause considerable disruption of the surface and subsurface,
and are not well
suited for areas in which the subsurface contains large cobbles or
consolidated rock
formations. On the other hand, barrier placements involving the drilling of
boreholes into the
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ground can be used to form barriers to deeper depths than is possible using
trenched
techniques, and the presence of cobbles or consolidated rock formations is not
a major
concern.
One approach involves drilling a series of large diameter boreholes, which are
spaced closely
together such that adjacent boreholes overlap with one another. When a barrier
material is
placed into the boreholes, the resulting barrier is continuous along the
length of the series of
boreholes. Alternatively, a series of smaller diameter boreholes may be
drilled in a spaced-
apart arrangement and fracturing techniques may be used to open a space
between the
adjacent boreholes. Once again, when a barrier material is placed into the
boreholes, the
resulting barrier is continuous along the length of the series of boreholes.
Yet another
approach involves drilling an array of spaced-apart boreholes, which is
arranged in a plurality
of staggered rows. When a barrier material is placed into the boreholes, the
resulting barrier
is discontinuous, but the array is designed such that contaminated groundwater
must flow
through the barrier material in at least one of the boreholes in at least one
of the rows.
The use of staggered rows of boreholes to form a permeable reactive barrier is
particularly
attractive because greater depths may be reached, the barrier may be
constructed close to
property lines, and the subsurface composition is not problematic.
Unfortunately, the
boreholes tend to be relatively small in diameter (e.g., 6 inches), which
causes problems when
filling the boreholes with a substantially dry barrier-forming material, such
as for instance a
sand/iron filing mixture with a humidity level of about 20%. Typically, the
substantially dry
barrier-forming material is fed through a conduit that is inserted into the
borehole. The
borehole is filled from the bottom up, and the conduit is withdrawn as the
level of the
substantially dry barrier-forming material in the borehole rises. The barrier-
forming material
is normally entrained in a flow of a gas, such as for instance air, and is fed
into the borehole
with a high flow velocity. This may result in a significant amount of the
barrier-forming
material being blown back up the borehole and into the surrounding
environment. In
addition, the height of the barrier-forming material in the borehole may rise
faster than the
conduit is being withdrawn from the borehole, causing the outlet end of the
conduit to become
stuck in the borehole.
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The need thus exists for an improved method and system that addresses the
above-mentioned
drawbacks.
SUMMARY
In accordance with an aspect of at least one embodiment there is provided a
method of
forming a permeable reactive barrier in the ground for remediating
groundwater, comprising:
drilling a plurality of holes in the ground; and introducing a substantially
dry barrier-forming
material into two holes of the plurality of holes in a simultaneous fashion,
comprising:
positioning a filling tool relative to the two holes such that an outlet end
of a first conduit of
the filling tool is proximate a bottom of a first one of the two holes and an
outlet end of the
second conduit of the filling tool is proximate a bottom of a second one of
the two holes;
providing a flow of the substantially dry barrier-forming material at an
initial flow velocity
through a source conduit and into a flow divider, the flow divider having a
first outlet in fluid
communication with an inlet end of the first conduit and a second outlet in
fluid
communication with an inlet end of the second conduit; and withdrawing the
filling tool out
of the two holes while continuing to introduce the substantially dry barrier-
forming material
into the two holes, wherein a final flow velocity of the substantially dry
barrier-forming
material exiting from the outlet ends of the first and second conduits is at
least about 30% less
than the initial flow velocity, and wherein withdrawing the filling tool is
performed at a rate
that is substantially equal to a rate of filling the two holes with the
substantially dry barrier-
.. forming material.
In accordance with an aspect of at least one embodiment there is provided a
system for
forming a permeable reactive barrier in the ground for remediating
groundwater, comprising:
a source conduit for providing a substantially dry barrier-forming material at
an initial flow
velocity; a flow divider having an inlet in fluid communication with an outlet
end of the
source conduit, and having a first outlet and a second outlet, wherein the
flow of the
substantially dry barrier-forming material exits the flow divider via the
first and second
outlets at a flow velocity that is lower than the initial flow velocity; a
first conduit having an
inlet end in fluid communication with the first outlet and having an outlet
end opposite the
inlet end thereof; a second conduit having an inlet end in fluid communication
with the
second outlet and having an outlet end opposite the inlet end thereof; wherein
the first and
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second conduits each comprise one or more openings defined in respective
sidewalls thereof
for venting air that is entrained in the flow of the substantially dry barrier-
forming material for
reducing the flow velocity of the substantially dry barrier-forming material
from the
intemiediate flow velocity to a final flow velocity.
In accordance with an aspect of at least one embodiment there is provided a
system for
forming a permeable reactive barrier in the ground for remediating
groundwater, comprising:
a source conduit for providing a substantially dry barrier-forming material at
an initial flow
velocity; and a delivery conduit arrangement in fluid communication with the
source conduit
and having a first delivery conduit and a second delivery conduit, the first
and second delivery
conduits each having an outlet end for being positioned proximate a bottom of
respective
spaced-apart holes drilled into the ground, and the first and second delivery
conduits each
having one or more openings defined in respective sidewalls thereof proximate
the outlet
ends thereof for venting air that is entrained in the flow of the
substantially dry barrier-
forming material, wherein a total cross-sectional area of a flow path of the
substantially dry
barrier-forming material increases between the source conduit and the outlet
ends of the first
and second delivery conduits, and wherein during operation a final flow
velocity of the
substantially dry barrier-fomiing material exiting via the outlet ends of the
first and second
delivery conduits is at least about 30% less than the initial flow velocity.
BRIEF DESCRIPTION OF THE DRAWINGS
The instant disclosure will now be described by way of example only, and with
reference to
the attached drawings, in which:
FIG. 1 is a simplified diagram of a system or filling tool according to an
embodiment.
FIG. 2 is an enlarged partial view of the system or filling tool of FIG. 1.
FIG. 3 is a simplified view showing the system or filling tool of FIG. 1
positioned within two
adjacent boreholes of an array of boreholes.
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FIG. 4 is a simplified side view showing the system or filling tool of FIG. 1
positioned within
two boreholes prior to filling with substantially dry barrier-fanning
material.
FIG. 5 is a simplified side view showing the system or filling tool of FIG. 1
positioned within
two boreholes during filling with substantially dry barrier-fanning material.
FIG. 6 is a simplified side view showing the system or filling tool of FIG. 1
positioned within
two boreholes after filling with substantially dry barrier-fanning material.
DETAILED DESCRIPTION
While the present teachings are described in conjunction with various
embodiments and
examples, it is not intended that the present teachings be limited to such
embodiments. On
the contrary, the present teachings encompass various alternatives and
equivalents, as will be
appreciated by those of skill in the art. All statements herein reciting
principles, aspects, and
embodiments of this disclosure, as well as specific examples thereof, are
intended to
encompass both structural and functional equivalents thereof. Additionally, it
is intended that
such equivalents include both currently known equivalents as well as
equivalents developed
in the future, i.e., any elements developed that perfonn the same function,
regardless of
structure.
As used herein, the tenns "first", "second", and so forth are not intended to
imply sequential
ordering, but rather are intended to distinguish one element from another,
unless explicitly
stated. Similarly, sequential ordering of method steps does not imply a
sequential order of
their execution, unless explicitly stated.
Referring now to FIG. 1, shown is a simplified diagram of a system or filling
tool according
to an embodiment. The system 100 includes a source conduit 102 as well as a
delivery
conduit arrangement, which is shown generally at 104. The delivery conduit
arrangement 104
includes a flow divider 106, a first delivery conduit 108 and a second
delivery conduit 110,
each of which has a wall thickness of about 0.6 cm. The flow divider 106 has
an inlet 112
that is in fluid communication with the source conduit 102 for receiving a
flow of a
substantially dry barrier-fonning material. The flow divider 106 divides the
flow of the
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Green Tech Patent
substantially dry barrier-fanning material into two, approximately equal flows
out of first and
second outlets 114 and 116 and into the first and second delivery conduits 108
and 110,
respectively.
A first sensing ring 118 is provided proximate the outlet end of the first
delivery conduit 108
.. and a second sensing ring 120 is provided proximate the outlet end of the
second delivery
conduit 110. In an embodiment, the sensing rings 118 and 120 are approximately
30 cm in
length and have a wall thickness of 2.5 to 3 cm. Since the sensing rings 118
and 120 have the
same inside diameter as the first and second delivery conduits 108 and 110,
the sensing rings
118 and 120 protrude outwardly from the outer surface of the first and second
delivery
conduits 108 and 110. The sensing rings 118 and 120 may be joined to the
outlet end of the
first and second delivery conduits 108 and 110 by a weld bead.
A first plurality of openings 122 is provided through the sidewall along a
length of the first
delivery conduit 108 that is above the sensing ring 118. Similarly, a second
plurality of
openings 124 is provided through the sidewall along a length of the second
delivery conduit
110 that is above the sensing ring 120. Additional openings (not illustrated)
are also fanned
on the sides of the first and second delivery conduits that are opposite the
openings 122 and
124 shown in FIG. 1. Alternatively, the openings 122 and 124 are provided in
the fonn of
elongated slots, or the number and/or size and/or distributions of the
openings 122 and 124
may be selected for a particular application.
Attachment points 126 and 128 are provided for the purpose of attaching
lifting cables (not
shown in FIG. 1), which allow a crane to be used to lower and raise the system
100 along a
substantially vertically path. Preferably, the source conduit 102 is flexible
and the delivery
conduits 108 and 110 are rigid and parallel to one another, to facilitate a
straight up-and-down
insertion and withdrawal of the system 100 into and out of boreholes that are
to be filled with
.. the substantially dry barrier-fanning material.
Referring now to FIG. 2, shown is an enlarged partial view of the system or
filling tool 100 of
FIG. 1, which shows more detail of the flow divider 106 and first delivery
conduit 108.
During operation, an inlet end (not shown in FIG. 2) of the source conduit 102
is in fluid
communication with a source of the substantially dry barrier-fanning material.
By way of a
specific and non-limiting example, the substantially dry barrier-fanning
material comprises
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sand, such as for instance silica sand or quartz sand, mixed with iron
particles and a
thixotropic rheology modifier such as for instance attapulgite or Acti-Gel
(purified
magnesium aluminosilicate). In a specific implementation, 4 parts sand are
mixed with 1 part
iron particles and thixotropic rheology modifier. By way of a specific and non-
limiting
example, the source conduit 102 has an inside diameter of approximately 5 cm
and provides
an initial flow fT of the substantially dry barrier-fanning material with an
initial velocity v,.
The flow fT enters the flow divider 106 via inlet 112 and is divided into two
approximately
equal flows f; and f2. In the example that is shown in FIG. 2, the flow
divider 106 has an
inside diameter of approximately 7.5 cm. The combined effect of i) dividing
the initial flow
fT into two flows f/ and f2 and ii) providing a larger inside diameter within
the flow divider
106 compared to the source conduit 102 is to increase the total cross-
sectional area of a flow
path of the substantially dry barrier-forming material. In the instant
example, the total cross-
sectional area increases from about 19.5 cm2 in the source conduit 102 to
about 88.3 cm2 in
the flow divider 106. According to Bernoulli's principle, since the total
volumetric flow rate
of the substantially dry barrier-forming material is constant along the flow
path, the flow
velocity of the two flows fi and f2 in the flow divider 106 will be lower than
the flow velocity
within the source conduit 102, i.e., reduced from v, to an intermediate
velocity vm.
Referring still to FIG. 2, the flow fi passes along the length L of the first
delivery conduit,
which is typically 5 m to 15 m, through sections 200 and 202, each of which
has an inside
diameter approximately equal to the inside diameter of the flow divider 106,
i.e., an inside
diameter of about 7.5 cm. The plurality of openings 122 defined through the
sidewall of
section 202 vent a portion of the gas G within which the substantially dry
barrier-fanning
material is entrained. In some embodiments, the openings 122 are about 2.5 cm
in diameter
and are spaced apart from one another by about 15 cm. In some embodiments, two
rows of
openings 122 are provided along opposite sides of the section 202. Venting gas
G via the
openings 122 further reduces the velocity of the two flows fi and f2 from the
intermediate
velocity v,õ to a final velocity vf. By way of a few non-limiting examples,
the final velocity vf
of the flows fi and f2 exiting from the outlet ends of the first and second
delivery conduits 108
and 110, respectively, is at least 30% less, at least 40% less, at least 50%
less, or at least 60%
less than the initial flow velocity v, within the source conduit 102.
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Now referring also to FIG. 3, the system or filling tool 100 may be used for
forming a
permeable reactive barrier in the ground for remediating groundwater, in which
an array of
boreholes 300 is formed in a plurality of staggered rows r1-r3 and then filled
with a barrier-
forming material. By way of a specific and non-limiting example, the bore
holes are
approximately 15 cm in diameter and are separated by a center-to-center
distance d of
approximately 45 cm. As will be apparent, the boreholes in the array 300 are
formed, e.g., by
drilling, such that the center-to-center separation corresponds to the center-
to-center
separation between the substantially parallel first and second delivery
conduits 108 and 110 of
the system 100. If the system 100 has a different configuration, such as for
instance a flow
divider that spaces the first and second delivery conduits 108 and 110 either
more closely
together or further apart, then the spacing between the adjacent boreholes in
the array 300 is
adjusted accordingly.
Of course, the depth of the boreholes in the array 300 depends on various
factors that are
specific to the site that is being remediated. A depth of about 5 m to 15 m
below ground
surface is typical. As will be apparent, one or more of the diameter, the
spacing, and the
depth of the boreholes may be smaller or larger than the above-mentioned
example
dimensions, e.g., depending on the particular constraints and requirements.
The boreholes
300 may be drilled or bored etc. through various types of subsurface
structures, including
consolidated rock formations or soils that contain cobbles of various sizes.
The formation of
a suitable array 300 of boreholes may be achieved using techniques that are
generally well
known to one of ordinary skill in the art and will not be discussed further
herein.
Now referring also to FIGS. 4-6, the system or filling tool 100 is positioned
within two
adjacent boreholes 302 and 304, such that the sensing rings 118 and 120 at the
outlet ends of
the first and second delivery conduits 108 and 110 are proximate the bottoms
400 and 402 of
the boreholes 302 and 304, respectively (FIG. 4). The boreholes 302 and 304
are filled with a
substantially dry mixture of sand, iron particles, granular iron or iron
filings, and a thixotropic
rheology modifier suspension stabilizer such as Acti-Gel . Some water may be
added to
mixture to dampen it, however the dry mixture will over time acquire moisture
in-situ in the
ground after the boreholes 302 and 304 are filled. Preferably quartz sand, or
silica sand is
used in the mixture. In operation the mixture may be added to a hopper and fed
into the
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source conduit 102 using e.g., a not illustrated shotcrete compressed air
delivery system
capable of moving the mixture with the high initial velocity v,.
As the boreholes 302 and 304 are filled with the substantially dry barrier-
forming material
500 (FIGS. 5 and 6), the system 100 is withdrawn substantially vertically
upwards, as
indicated by the block arrow, at a rate that is approximately the same as the
filling rate of the
boreholes 302 and 304. For instance, cables 404 and 406 are attached to the
system 100 via
the attachment points 126 and 128, respectively, and a not illustrated crane
is used to lift the
system 100 out of the boreholes 302 and 304.
Referring again to FIGS. 1 and 2, the sensing rings 118 and 120 have the same
inside
diameter as the first and second delivery conduits 108 and 110, respectively,
but a larger
outside diameter. For instance, the outside diameter of the sensing rings 118
and 120 is
approximately 2.5 cm larger than the outside diameter of the first and second
delivery
conduits 108 and 110. The sensing rings 118 and 120 therefore protrude
outwardly from the
outer surfaces of the first and second delivery conduits 108 and 110. If the
crane operator
raises the system 100 at a rate that is slower than the rate at which the
boreholes 302 and 304
are being filled, then the protruding sensing rings 118 and 120 will become
buried in the
substantially dry barrier-forming material and the crane operator will sense
an increased
resistance to continued raising of the system 100. With experience, the crane
operator will
learn to vary the rate of raising the system 100 in response to sensed
feedback provided by the
sensing rings 118 and 120.
Advantageously, the reduced flow velocity that is achieved using the system
100, combined
with vertically lifting the system 100 during filling of the boreholes 302 and
304, results in the
simultaneous formation of void-free columns of the substantially dry barrier-
forming material
within the boreholes 302 and 304. The system 100 may then be positioned into
another pair
of adjacent boreholes, such as for instance boreholes 306 and 308, and the
boreholes 310 and
312 are filled, etc., and the process is repeated until all of the boreholes
of the array 300 are
filled. Advantageously, two boreholes may be filled at the same time, which
may reduce the
total time required to construct the permeable reactive barrier, since the
system 100 does not
need to be lowered into and withdrawn from each borehole individually.
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As discussed above, the depth of the boreholes in the array 300 depend on the
constraints and
requirements of the site that is being remediated. Typical depths are in the
range of 5 m to 15
meters, but other depths are possible. The system 100 may be made in different
sizes to
accommodate different depth boreholes, for instance the length L in FIG. 2 may
be 5 m or the
length L may be 10 m or the length L may be 15 m. The relative sizes of the
sections 200 and
202 may be different in systems 100 having different lengths L. For instance,
the section 202
may have a length of about 3 m, and the section 200 may have a length that is
selected to
provide the desired total length L, e.g., 2 m or 7 m or 12 m. Alternatively,
the relative sizes of
the sections 200 and 202 may be the same in different systems 100 having
different lengths L.
Optionally, the system 100 may be disassembled to allow sections 200 and/or
202 of different
lengths to be used to suit the requirements for a particular application. For
instance, boreholes
having a depth of 15 m may be filled when the system 100 is assembled using a
section 200 of
12 m in length and a section 202 of 3 m in length. When it becomes necessary
to fill
boreholes that are only 10 m in depth, the section 200 of 12 m in length may
be "swapped
out" for a different section 200 of only 7 m in length. A kit of parts may
include a flow
divider, a pair of sections 202 of 3 m in length, and a plurality of pairs of
sections 200 of
various lengths. Optionally, the kit of parts further includes additional
pairs of sections 202 of
various lengths.
Throughout the description and claims of this specification, the words
"comprise",
"including", "having" and "contain" and variations of the words, for example
"comprising"
and "comprises" etc., mean "including but not limited to", and are not
intended to, and do not
exclude other components.
It will be appreciated that variations to the foregoing embodiments of the
disclosure can be
made while still falling within the scope of the disclosure. Each feature
disclosed in this
specification, unless stated otherwise, may be replaced by alternative
features serving the
same, equivalent or similar purpose. Thus, unless stated otherwise, each
feature disclosed is
one example only of a generic series of equivalent or similar features.
All of the features disclosed in this specification may be combined in any
combination, except
combinations where at least some of such features and/or steps are mutually
exclusive. In
particular, the preferred features of the disclosure are applicable to all
aspects of the
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disclosure and may be used in any combination. Likewise, features described in
non-essential
combinations may be used separately (not in combination).
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