MONITORING THE WATER TABLES IN MULTI-LEVEL GROUND WATER SAMPLING SYSTEMS

SURVEILLANCE DES NAPPES PHREATIQUES DANS LES SYSTEMES D'ECHANTILLONNAGE DE L'EAU SOUTERRAINE MULTI-NIVEAUX

English Abstract

An apparatus and method for monitoring the water tables in boreholes, such as boreholes used as sampling wells for sampling contaminants in ground water. Fluctuations in one or more ground water levels can be monitored and recorded using transducers, and the changes in the water levels evaluated and considered, particularly in the context of sampling for contaminants where subsurface pollution remediation is contemplated or ongoing. The changes in ground water levels can be tracked in time and correlated, as desired, with the water sampling regime. The transducers used for monitoring pressure changes attributable to water table changes are located advantageously above the surface of the ground, where they are accessible for re-use, replacement, or repair. Apparatus and method for providing an air-coupling between the transducers and subsurface sampling points is disclosed.

French Abstract

Un appareil et un procédé servant à mesurer les nappes phréatiques dans les puits de forage, comme des puits de forage utilisés en tant que puits déchantillonnage pour échantillonner des contaminants dans leau souterraine. On peut surveiller et enregistrer les fluctuations dun ou de plusieurs niveaux deau souterraine à laide de transducteurs et évaluer et considérer les changements des niveaux deau, particulièrement dans le contexte dun échantillonnage des contaminants dans le cadre duquel une dépollution de subsurface est envisagée ou en cours. Les changements dans les niveaux deau peuvent être suivis dans le temps et corrélés, le cas échéant, avec le régime déchantillonnage de leau. Les transducteurs utilisés pour surveiller les changements de pression attribuables aux changements dans les nappes phréatiques sont situés avantageusement au-dessus de la surface du sol où ils sont accessibles à des fins de réutilisation, de remplacement ou de réparation. Un appareil et un procédé assurant un accouplement par air entre les transducteurs et les points déchantillonnage de subsurface sont décrits.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEDGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An apparatus for monitoring changes in a level of a fluid in a
formation, there
being a borehole extending into the formation from a formation surface, the
apparatus having
at least one tubing system comprising:
a transducer tube extending in the borehole and having a top end above the
formation
surface and a bottom end below the fluid level in the formation;
a transducer above the formation surface and in closed fluid communication
with the
top end of the transducer tube, for measuring a gas pressure within an upper
portion of the
transducer tube; and
a port tube in fluid communication with the fluid in the formation and with
the bottom
end of the transducer tube, via which port tube the fluid flows between the
formation and a
lower portion of the transducer tube, whereby a level of the fluid in the
transducer tube tends
to equilibrate with the level of the fluid in the formation;
wherein the level of fluid in the transducer tube affects the gas pressure
within the upper
portion of the transducer tube, and wherein further a change in gas pressure
measured by the
transducer indicates a change in the level of the fluid in the formation.
2. An apparatus according to claim 1 further comprising a flexible liner
everted
into the borehole to a depth below the level of the fluid in the formation,
the liner
substantially sealing the borehole walls against the flow of fluid between the
formation and
the borehole interior to the liner; wherein the transducer tube and the port
tube are situated
within the interior of the everted flexible liner.
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3. An apparatus according to claim 2 wherein the tubing system further
comprises:
a pump tube within the everted flexible liner and having a top end above the
formation surface and a bottom end below the level of the fluid in the
formation, the pump tube
bottom end in fluid communication with the port tube;
a sample tube within the everted flexible liner and having a top end above the
formation surface and a bottom end in fluid communication with the bottom end
of the pump
tube;
a port in the everted flexible liner at a sampling location elevation and in
fluid
communication with the port tube, wherein fluid in the formation flows into
the pump tube via
the port and port tube; and
a check valve between the bottom end of the pump tube and the port tube for
regulating fluid flow from the pump tube into the port tube;
wherein when a gas pressure is supplied to the top end of the pump tube, the
check valve closes and a fluid sample within the pump tube is expelled above
the formation
surface via the sample tube.
4. An apparatus according to claim 1, wherein the transducer tube
comprises:
a dilated portion having a first diameter, extending from the level of the
fluid in the
formation up to a transition elevation; and
a narrow portion, above the transition elevation, having a second diameter
smaller than
the first diameter of the dilated portion, the narrow portion extending up to,
and connected to, the
transducer;
wherein a change in a fluid level within the dilated portion of the transducer
tube creates an
amplified change in gas pressure within the narrow portion proportional to the
difference
between the first and second diameters.
5. An apparatus according to claim 1 further comprising an enclosure about
the
transducer for insulating the transducer from temperature changes.
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6. An apparatus according to claim 5, wherein the enclosure comprises:
a borehole well casing having a top opening; and
a layer of insulating material disposed across the top opening of the casing;
wherein the transducer is fluidly connected to the transducer tube via a
disconnectable
connecting union and an intermediate tube, whereby the transducer is removably
disposable
within the well casing prior to the disposition of the layer of insulating
material.
7. An apparatus according to claim 5, wherein the enclosure comprises:
a thermally insulated housing located outside a borehole well casing;
a disconnectable connecting union at the top of the transducer tube; and
a thermally insulated intermediate tube;
wherein the transducer is located within the housing and is in fluid
communication with
the transducer tube via the connecting union and intermediate tube.
8. An apparatus according to claim 1 further comprising an enclosure about
the
transducer tube, the enclosure comprising a slender casing around the
transducer tube, wherein
the transducer is in fluid communication with the transducer tube via a
disengageable connecting
union sealably attached to the top of the transducer tube and an intermediate
tube extending
between the transducer and the connecting union.
9. An apparatus according to claim 1, wherein the at least one tubing
system
comprises a plurality of tubing systems.
10. A method for monitoring changes in a level of a fluid in a formation,
there being a
borehole extending into the formation from a formation surface, comprising the
step of situating
at least one tubing system in the borehole, wherein the step of situating at
least one tubing system
comprises:
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extending a transducer tube in the borehole such that a top end of the
transducer tube is
above the formation surface and a bottom end of the transducer tube is below
the fluid level in
the formation;
disposing a transducer above the formation surface and in closed fluid
communication
with the top end of the transducer tube;
providing a port tube in fluid communication with the fluid in the formation
and with the
bottom end of the transducer tube;
allowing fluid to flow, via the port tube, between the formation and a lower
portion of the
transducer tube, whereby a level of the fluid in the transducer tube tends to
equilibrate with the
level of the fluid in the formation;
permitting any change in the level of fluid in the transducer tube, resulting
from a change
in the level of the fluid in the formation, to affect the gas pressure within
an upper portion of the
transducer tube, any change in gas pressure indicating a change in the level
of the fluid in the
formation; and
measuring with the transducer a change in the gas pressure within the upper
portion of
the transducer tube.
11. The method of claim 10 further comprising the steps of:
everting a flexible liner into the borehole to a depth below the level of the
fluid in the
formation to substantially seal, with the liner, the borehole walls against
the flow of fluid
between the formation and the borehole interior to the liner; and
situating the transducer tube and the port tube within the interior of the
everted flexible
liner.
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12. The method of claim 11 further comprising the steps of:
disposing a pump tube within the everted flexible liner such that a top end of
the
pump tube is above the formation surface and a bottom end of the pump tube is
below the level
of the fluid in the formation;
placing the pump tube bottom end in fluid communication with the port tube;
situating a sample tube within the everted flexible liner such that a top end
of the
sample tube is above the formation surface;
placing a bottom end of the sample tube in fluid communication with the bottom
end of the pump tube;
providing at a sampling location elevation a port in the everted flexible
liner in
fluid communication with the port tube;
allowing fluid in the formation to flow into the pump tube via the port and
port
tube;
disposing a check valve between the bottom end of the pump tube and the port
tube, and regulating with the check valve the fluid flow from the pump tube
into the port tube;
and
supplying a gas pressure to the top end of the pump tube, thereby closing the
check valve and expelling, via the sample tube and to above the formation
surface, a fluid sample
from within the pump tube.
13. The method of claim 10 further comprising the step of determining, from
a
measured change in the gas pressure within the upper portion of the transducer
tube, a change in
the level of fluid in the formation.

14. The method of claim 13, wherein the step of determining a change in the
level of
fluid in the formation comprises calculating the change in level of fluid
using the formula
<IMG>
where .DELTA.WT is the change in the formation fluid level, .DELTA.Pg is the
measured change in the gas
pressure in the upper portion of the transducer tube, c is a constant to
convert from pressure to
hydraulic head, n is the number of moles of gas in the upper portion of the
transducer tube, R is
the universal gas constant, T is the absolute temperature, Po is a first
absolute pressure in the
transducer tube, Pg is a subsequent second absolute pressure in the transducer
tube, and A is a
radial cross sectional area of the transducer tube.
15. The method of claim 10, wherein the step of extending a transducer tube
comprises:
defining in the transducer tube a dilated portion, having a first diameter
extending from
the level of the fluid in the formation up to a transition elevation, and a
narrow portion above the
transition elevation, having a second diameter smaller than the first diameter
of the dilated
portion; and
extending the narrow portion up to, and connecting the narrow portion to, the
transducer;
wherein a change in a fluid level within the dilated portion of the transducer
tube creates an
amplified change in gas pressure within the narrow portion proportional to the
difference
between the first and second diameters.
16. The method of claim 10 further comprising the step of insulating the
transducer
from temperature changes.
17. The method of claim 16, wherein the step of insulating the transducer
comprises
disposing an enclosure around the transducer by:
placing the transducer within a borehole well casing having a top opening;
disposing a layer of insulating material across the top opening of the casing;
26

fluidly connecting the transducer to the transducer tube via a disconnectable
connecting
union and an intermediate tube; and
removably disposing the transducer within the well casing prior to disposing
the layer of
insulating material.
18. The method of claim 16, wherein the step of insulating the transducer
comprises
disposing an enclosure around the transducer by:
locating a thermally insulated housing outside a borehole well casing;
locating the transducer inside the housing;
securing a disconnectable connecting union at the top of the transducer tube;
and
placing the transducer in fluid communication with the transducer tube by
extending a
thermally insulated intermediate tube between the connecting union and the
transducer.
19. The method of claim 10, wherein the step of extending the transducer
tube
comprises:
placing the transducer tube within the interior of a slender casing within the
borehole; and
further comprising the steps of:
sealably attaching a disengageable connecting union to the top of the
transducer tube; and
placing the transducer in fluid communication with the transducer tube by
extending an
intermediate tube between the connecting union and the transducer.
20. The method of claim 10, wherein the step of situating at least one
tubing system
comprises situating a plurality of tubing systems.
27

Description

CA 02714692 2015-09-22
MONITORING THE WATER TABLES IN
MULTI-LEVEL GROUND WATER SAMPLING SYSTEMS
FIELD OF THE INVENTION
This invention relates generally to borehole liners, and more particularly to
pore fluid
sampling and other similar uses for everting flexible borehole liners, and
specifically to the
measurement of water table fluctuation histories at many elevations in a
borehole.
BACKGROUND OF THE INVENTION
Flexible borehole liners are installed by the eversion process to seal a
borehole against
flow into or out of the borehole, which flow can cause the spread of ground
water
contamination. The installation method as commonly practiced propagates an
everting
borehole liner into the hole by adding water to the interior of the everting
liner, which dilates
the liner and, as the liner is everted into the borehole, causes the liner to
displace the borehole
fluids (usually water or air) into the adjacent surrounding subsurface
formation. The
installation of the liner, and/or its placement after installation, permits
the gathering of a
variety of useful data regarding subsurface conditions in the vicinity of the
borehole. Aspects
of the data-gathering process may include measuring or monitoring water
level(s) in the
borehole; some boreholes are in fact monitoring "wells." Helpful and general
background
regarding the utility and function of everting flexible borehole liners is
provided by
applicant's previously issued U.S. Patents Nos. 5,176,207, No. 6,283,209, and
No. 6,910,374.
Most water level measurements in traditional wells are performed by lowering a
pressure transducer beneath the water surface to monitor the pressure history
of water level
changes. A multi-level sampling system in a single borehole does not allow
such a simple
measurement of the formation head at different levels in the formation.
Previously known
flexible liner systems for multi-level water sampling and head measurements in
a single
borehole use pressure transducers dedicated to the system and located
significant distances
(e.g., 100-200 feet) below the water table in a borehole in the geologic
formation. Such
pressure transducers monitor the hydraulic head in the formation at many
different elevations.
However, if one (or more)
transducer should fail, the entire multi-level system must be removed from the
borehole to
access
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CA 02714692 2015-09-22
and replace the failed transducers. This removal, besides causing delay and
expense, can
result in damage to other functioning transducers, as well as to the flexible
liner sampling
system.
Flexible liner designs for a multi-level sampling system have been known for
years,
but previous designs have involved deep transducer locations, with transducers
inaccessibly
situated down-well, sometimes hundreds of feet, and more or less permanently
dedicated to
the system. Applicant's previously known "Water FLUTe" system is described at
http://www.flut.com/sys 1.html. Certainly the multi-level
water sampling system has been improved beyond the teachings of applicant's
U.S. Patent
No. 5,176,207, or of applicant's co-pending U.S. Patent Application Serial No.
12/001,801
entitled -Pore Fluid Sampling System with Diffusion Barrier." The cost of
removal and
repair of failed transducers in known systems, however, can be a major expense
of the design.
Also, the dedication of the transducers to the system is a very expensive
feature of the
system, and the transducers are not available for reuse in other applications.
Improvements in transducer accuracy, and the recent addition of data recording
capability in an individual transducer, increase significantly the
practicality of the presently
disclosed apparatus and method compared to systems using formerly utilized,
less-accurate,
transducers. That fact, coupled with the peculiar needs of the multi-level
sampling system,
were the background for the formulation of the useful devices and methods
hereinafter
disclosed.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided an apparatus for
monitoring changes in a level of a fluid in a formation, there being a
borehole extending into
the formation from a formation surface, the apparatus having at least one
tubing system
comprising:
a transducer tube extending in the borehole and having a top end above the
formation
surface and a bottom end below the fluid level in the formation;
a transducer above the formation surface and in closed fluid communication
with the
top end of the transducer tube, for measuring a gas pressure within an upper
portion of the
transducer tube; and
a port tube in fluid communication with the fluid in the formation and with
the bottom
end of the transducer tube, via which port tube the fluid flows between the
formation and a
lower portion of the transducer tube, whereby a level of the fluid in the
transducer tube tends
to equilibrate with the level of the fluid in the formation;
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CA 02714692 2015-09-22
wherein the level of fluid in the transducer tube affects the gas pressure
within the upper
portion of the transducer tube, and wherein further a change in gas pressure
measured by the
transducer indicates a change in the level of the fluid in the formation.
According to a further aspect of the invention, there is provided a method for
monitoring changes in a level of a fluid in a formation, there being a
borehole extending into
the formation from a formation surface, comprising the step of situating at
least one tubing
system in the borehole, wherein the step of situating at least one tubing
system comprises:
extending a transducer tube in the borehole such that a top end of the
transducer tube
is above the formation surface and a bottom end of the transducer tube is
below the fluid
level in the formation;
disposing a transducer above the formation surface and in closed fluid
communication
with the top end of the transducer tube;
providing a port tube in fluid communication with the fluid in the formation
and with
the bottom end of the transducer tube;
allowing fluid to flow, via the port tube, between the formation and a lower
portion of
the transducer tube, whereby a level of the fluid in the transducer tube tends
to equilibrate
with the level of the fluid in the formation;
permitting any change in the level of fluid in the transducer tube, resulting
from a
change in the level of the fluid in the formation, to affect the gas pressure
within an upper
portion of the transducer tube, any change in gas pressure indicating a change
in the level of
the fluid in the formation; and
measuring with the transducer a change in the gas pressure within the upper
portion of
the transducer tube.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and form a part of the
specification, illustrate embodiments of the present invention and, together
with the
description, serve to explain the principles of the apparatus and method. In
the drawings:
Figure I is a diagrammatic view (not all elements to scale), in vertical
section, of a
prior-art multi-level sampling and monitoring system with transducers in a
borehole deep
below the ground surface;
Figure 2 is a diagrammatic view (not all elements to scale), in vertical
section, of a
multi-level sampling and monitoring apparatus according to the present
invention, with
transducers above the ground surface;
Figure 3 is a schematic side view depicting the geometry of a monitoring
system
apparatus according to the present invention;
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CA 02714692 2010-09-09
Figure 4 is an algorithm usable to calculate changes in water table levels
from pressure
data obtained from the method and apparatus of the present invention;
Figure 5 is a schematic side view, similar to that of Fig. 3, depicting the
geometry of an
alternative embodiment of a monitoring system apparatus according to the
present invention,
having a transducer tube specially configured to increase the sensitivity of
pressure change
measurements;
Figure 6 is a schematic side view of a portion of an alternative embodiment of
a
monitoring system apparatus according to the present invention, showing the
protected location
of the pressure transducer;
Figure 7 is a schematic side view of a portion of an alternative embodiment of
a
monitoring system apparatus according to the present invention, showing the
protected location
of the transducer tube in an open slender casing; and
Figure 8 a diagrammatic view (not all elements to scale), in vertical section,
of a
multi-level sampling and monitoring apparatus according to the present
invention, with
transducers above the ground surface but in a protective housing outside the
borehole.
Like numerals label like elements throughout the several views.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
(BEST MODE FOR PRACTICING THE INVENTION)
Flexible liners in boreholes have been designed by the applicant as shown in
Fig. 1 for
the purpose of extracting from the borehole a ground water sample by gas
displacement of the
water in the tubing. Only a single port is shown in Fig. 1 for clarity of
illustration; the entire
tubing system seen in Fig. 1 is duplicated for additional sampling elevations
located on and
within the same liner.
The sampling and monitoring system usually is emplaced into the borehole by an
eversion process known in the art. The continuous impermeable liner 1 is
installed by eversion
into a borehole 13 in the geologic formation 14 as described generally in, for
example, U.S.
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CA 02714692 2010-09-09
Patents No. 5,176, 207. The liner 1 is pressurized by the liner's interior
water level 15 being
above the formation water level 6 in the adjacent geologic formation 14. Once
emplaced, the
sample tubing of the system fills with water from the formation 14. Ambient
water in the
formation 14 moves into the spacer 2. The formation water is conducted from
the spacer 2 via
the port19 and the port tube 3, then through the first check valve 4, to fill
the interior volume of
the pump tube 17 until it reaches equilibrium level 5 with the existing water
level 6 in the
formation 14. The formation water level 6 can be determined by lowering an
electric water level
meter through the top 7 of the pump tube 17 to the water surface at pump tube
water level 5.
Water in the pump tube 17 is pumped to the surface by application of a gas
pressure at the top 7
of the pump tube 17. Upon application of such a sufficient and regulated gas
pressure, the first
check valve 4 closes, and the water in the pump tube 5 is expelled through the
second check
valve 8, through the sample tube 9, and to the surface container 10 (e.g., for
sampling analysis).
In previously known systems, a continuous history of the water pressure in the
formation 14 is obtained by monitoring a pressure transducer 11 connected to
the port tube 3 and
situated beneath the first check valve 4, at the connection location 16 seen
in Fig. 1. Connection
location 16 ordinarily is underwater, and often is a hundred feet or more
below the ground
surface. The transducer's electrical connection to the surface is via the
cable 12. The
immediately foregoing design and function typifies the current multi-level
sampling and
formation water pressure measurement system. The problem addressed by the
inventive multi-
level system described hereinafter is that the transducer 11 is not easily
accessible for removal
for reuse or repair. Also, the dedication of the expensive transducers (e.g.,
five to fifteen
transducers 11 per system) is a major investment in a multi-port system.
Attention is invited to Fig. 2, showing the presently disclosed apparatus and
method.
While there are numerous ports 19, and numerous sampling, pumping, and
pressure monitoring
tubing systems (including collectively 2, 3. 4, 8, 9, 17, 21, 24) in a typical
multi-level sampling
and monitoring system, for the sake of simplicity of expression only one
sampling and pressure
measurement tubing system is described. Description of one sampling and
pressure
measurement system according to the present invention suffices to describe a
plurality. It is
understood by any person skilled in the art that a complete monitoring system
may and normally
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CA 02714692 2010-09-09
will have a plurality (often up to fifteen, sometimes even more) of sampling
and pressure
measurement tubing assemblies disposed in a given borehole.
The complete sampling system of Fig. 2 is a non-obvious improvement to that
illustrated
in Fig. 1. In the apparatus of Fig. 2 a transducer tube 21 is connected to the
port tube 3 at the
connection location 16. The transducer tube 21 extends to the surface at the
top of the
borehole 13. The water in the transducer tube 21 rises to level 22 (as it
likewise rises to the
elevation 5 in the pump tube 17). The upper portion of the transducer tube 21
above the water
level 22 is filled with a columnar volume of ambient air 23 (a typical gas,
although other gasses
could be supplied). After the water level 22 in the transducer tube 21 has
equilibrated with the
water level 6 in the formation 14, a pressure transducer 24 having a pressure
low range (e.g. 30
psi) and high resolution (e.g., 0.05% of full scale) is securely connected
with a gas-tight seal to
the top end of the transducer tube 21. This sealing action defines and
establishes the original or
baseline water level 22, the original gas volume 23, and the initial gas
pressure in the transducer
tube 21. After several hours have elapsed, the relative humidity in the
transducer tube gas
volume 23 approaches equilibrium with the water surface 22 (at the temperature
of the interior of
the borehole 13). At that time, the elevation of the water level 5 in the pump
tube 17 is
measured. At the same time, the gas pressure in the upper portion of the
transducer tube 21 is
noted and recorded; this is the initial baseline pressure condition of the gas
volume 23 in the
upper portion of the transducer tube 21, when the initial water level in the
formation 14 is at
level 6, as measured at pump tube water level 5.
In time, the water level 6 in the formation 14 typically changes. It often is
desirable to
monitor and consider such changes. According to the invention, the water level
22 in the
transducer tube 21 tends to follow or "track" the fluctuations in the
formation water level 6.
However, if the water level 22 in a transducer tube 21 rises, for example, the
air column 23 in the
interior volume of the upper portion of the transducer tube 21, above the
water level 22, tends to
be compressed. Such compression resists the further rise of the water level 22
in the transducer
tube 21, hampering the achievement of complete equilibration with the
formation water level 6.
In such case, neither the water level 22 in the transducer tube 21, nor the
pressure increase in the
air column 23 in the upper portion of the transducer tube, is a direct
indication of the change in
water level 6 within the formation 14. Nevertheless, by accounting physically
and
6

CA 02714692 2010-09-09
mathematically for both the change of the water level 22 in the transducer
tube 21 and the
pressure change measured in the air column 23 in the transducer tube upper
portion (adjacent the
transducer 24), an elevation change to a new water table level 6 in the
formation 14 can be
determined with reasonable accuracy.
By measuring the air pressure of the air column 23 within the upper portion of
the
transducer tube 21, a user of the present invention can deduce or calculate
the rise and the fall of
the formation water table 6. This method and apparatus configuration allows
the transducer 24
to be located at or near the surface at the top of the borehole 13, where it
can be easily repaired if
needed, or reused at another installation. The easier access for repair may
greatly reduce the cost
of the warranty services to the transducers 24 deployed in a particular
monitoring system
according to the present disclosure.
Referring additionally to Fig. 3, fundamental aspects of the configuration and
function of
presently disclosed apparatus and method are: The original gas volume 23 in
the upper portion of
the transducer tube 21; the elevation of the water level 5 in the pump tube
17; and the barometric
air pressure above the ground surface 37 at the time the transducer 24 is
sealably attached to the
top end of the transducer tube 21. The initial gas volume 23 is simply
calculated from the known
inside diameter of the transducer tube 21, the water level 22 below the
reference level 37, and the
elevation of the transducer 24 connection. (At initial conditions, the fluid
levels 5 and 22 are
approximately the same elevation.) The barometric pressure at the surface is
measured with an
independent transducer (not shown) located above the surface of the formation
14.
The pressure at the connection 16 to the pumping system (seen in Fig. 2) is
equal to the
hydrostatic head from that elevation at connection position (16) to the water
table 6 in the
formation 14, plus the barometric pressure above the water table. The pressure
at elevation of
connection 16 also is equal to the hydrostatic head from that connection 16 to
the water level 5 in
the pump tube 17 (which can be measured as the distance 36 measured from the
formation
surface with an electric water level meter), plus the barometric pressure at
the surface 37. The
pressure at the connection 16 also is equal to the hydrostatic head of the
current water level 22 in
the transducer tube 21, plus the gas pressure in the air volume 23 above the
water level 22 in the
transducer tube 21. It is noted that the water level 5 in the pump tube 17
will not follow
formation water level 6 if the formation water level 6 drops at a later time,
due to the function of
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CA 02714692 2010-09-09
the check valve 4 below the bottom end of the pump tube. However, for the ease
of this
description, it is assumed that the water level will remain constant or rise.
If the water level 6
should fall, the pump tube 17 can be purged to allow the pump tube water level
5 to decrease to
match the formation water level 6.
Fig. 3 illustrates diagrammatically the principal aspects of the hydraulic
function of the
presently disclosed apparatus and method. If the water level 6 in the
formation 14 rises to a new
formation level 66, the water level 5 in the pump tube 17 likewise rises to a
new pump tube
level 32 equal to the new formation level 66. However, the water level 22 in
the transducer
tube 21 rises to a new transducer tube level 31 which is lower than the new
level 32 in the pump
tube 17. The lesser rise in the transducer tube water level is due to the
closed gas volume 23,
which gas is compressed by the water rising in the transducer tube 21. As the
pressure in the gas
volume 23 increases, it resists any rise in the transducer tube water level
31.
By adding the hydrostatic head in the transducer tube 21 to the pressure in
the gas
volume 23, and equating it to the hydrostatic head in the formation 14 (which
equals the head at
the accessible pump tube level 5), one can solve for the water table level 6
in the formation 14 as
a function of the gas pressure in volume 23 of the transducer tube 21 (as
measured by the
transducer 24). This is possible because a change in the gas pressure in the
upper portion of the
transducer tube 21 is directly related to a change in the gas volume 23, which
in turn is directly
related to the transducer tube's water level rise to new level 31. Therefore,
both the new water
level 31 and the pressure in the gas volume 23 can be determined from the gas
pressure
measurement at the transducer 24. Notably, the new water level 31 in the
transducer tube 21
does not match the new water level 32 in the pump tube 17 after the change in
the formation
water level 6. Despite this difference, the new formation water level 66 can
be determined from
the change in pressure in the transducer gas volume 23. In the course of the
practicing of the
invention, the pressure values measured by the transducer 24 are periodically
or continually
recorded for input into algebraic formulae for calculating water level
changes. Differences in
water level in the formation, such as a rise in formation water level from a
selected first level 6 to
an immediately subsequent level 66, can be determined from the difference
between the
corresponding measured gas pressures in the upper portion of the transducer
tube.
Correspondence is provided by time correlation.
8

CA 02714692 2010-09-09
Fig. 4 is an algebraic expression of the result of equating the pressure in
the tube tubes 21
to the pressure at the level of connection 16 and that relationship to the
water level 66 in the
formation 14. The expression of Fig. 4 permits the calculation, from the
measured pressure
change in the gas volume 23, of a change in elevation (e.g. to 66) of the
formation water level 6.
In the equation of Fig. 4, AWT is the change in the formation water level from
its first (e.g.,
initial) level (i.e., 6 in Fig. 3) to a second subsequent level (e.g., 66 in
Fig. 3), APg is the
measured change in gas pressure in the transducer tube upper portion gas
volume 23 due to the
change in fluid level from the first level 6 to a second level 66, c is a
constant to convert from
pressure to hydraulic head, n is the number of moles of gas in the gas volume
23 in the
transducer tube, R is the universal gas constant, T is the absolute
temperature, Po is the initial
absolute pressure in the transducer tube 21, Pg is the subsequent absolute
pressure measured by
the transducer 24, and A is the cross sectional area of the transducer tube 21
at the new water
level 31 in the tube. As is convenient, the user can test check the calculated
water level 6 by
comparing it with the new level 32 measured in the pump tube 17.
It is noted that to determine correctly the current water level (i.e., as
changed from the
baseline level) in the transducer tube 21 from the gas pressure in volume 23,
one must employ a
representative equation of state for the gas to determine a volume change from
the gas pressure
change. For this illustration, the simple ideal gas equation of state, PV =
nRT, was used, where
P is the absolute pressure, V is the gas volume 23 in the transducer tube, n
is the number of
moles of gas in the volume 23, R is the universal gas constant, and T is the
absolute temperature.
Other equations of state may be useful for higher resolution. The number of
moles of gas, n, is
determined from the initial conditions at the moment the transducer 24
initially is connected to
the transducer tube 21. It is worthy of further note that variations of the
barometric pressure on
the water surface at level 5 in the pump tube 17, and also on the water table
surface at formation
level 6, can cause changes in the water level 22 in the transducer tube
without any change in the
actual formation water level 6. For that reason, the pressure measured by the
transducer 24 in
the gas 23 in the upper portion of the transducer tube 21 preferably is
corrected for changes in
the barometric pressure, in order to not confuse atmospheric barometric
pressure effects with a
change in the formation water level 6.
9

CA 02714692 2010-09-09
The foregoing mathematical formulae are known from gas physics, and are not
unique to
the present invention. The data processing procedure includes obtaining the
periodically or
continuously recorded pressure (and temperature) history from the transducer
24, via the
transducer cable 12, and entering that data together with the original or
initially measured
baseline parameters (as described above) for the calculation, by the equation
of Fig. 4, of the
system response. Measured raw data may be input into a digital computer
processor 27 for rapid
calculation of AWT by routines known or readily provided by the software
programming arts.
The net result is the compiled history of the formation water level 6 for each
port 19 for which an
air-coupled transducer tubing system has been employed. It is preferable that
the data reduction
process is convenient for the method to be practical.
Of further note is that the number of moles, n, of gas in volume 23 is
modified slightly by
the effect of water vapor evolving, with changes in temperature or pressure,
from the surface of
the water 22 and into the air volume 23 in the upper portion of the transducer
tube 21. This effect
has been measured to be most significant at the time the transducer 24 is
first attached to the
tube 21, when the air in the tube volume 23 is not fully saturated with water
vapor. After the
relative humidity in the closed air volume 23 has been permitted to stabilize,
the effect of water
vapor pressure changes is small. Still, it is preferable to maintain the
transducer 24 at a relatively
constant temperature to minimize the temperature effects, even though the
transducer 24
typically records both pressure and temperature at the transducer's location.
Again, the tubing system described with reference to Figs. 2 and 3 may be
reproduced for
several different port elevations, and their associated sampling systems,
within a single flexible
liner 1 for a multi-level sampling system in a common borehole 13. These
several tubing
systems are bundled in the interior of the liner 1 and the several transducers
24 are located at the
top of the borehole, with one tubing system assembly associated with each
respective spacer 2
and port 19 through the liner 1. Each tubing system assembly in the plurality
has an associated
spacer 2 with an adjacent port 19 permitting fluid to enter an associated port
tube 3 through
which fluid is transported to the tube connection 16. Each tube system
assembly likewise
includes a pump tube 17, a sample tube 9, and a transducer tube 21, as well as
a transducer 24
and other associated components such as check valves 4 and 8 as described
above. Accordingly,
it is understood by a person skilled in the art that in a preferred embodiment
of the invention, a

CA 02714692 2010-09-09
single borehole 14 may have a plurality of tubing system assemblies installed
within the common
flexible liner 1 situated in the borehole. Each tube system assembly is
substantially similar to the
others in the plurality, except that the spacer 2, port 19, and connection 16
for each tube system
assembly are disposed at a different borehole elevation. The transducer 24
corresponding to
each tube system assembly is at the ground surface for easy access.
Fig. 5 shows an embodiment having a similar tubing geometry to the embodiment
of
Fig. 3, except that a dilated first portion of the transducer tube 21 features
a greater diameter,
extending up to a transition elevation 36. Below the transition elevation 36,
the dilated portion
of the transducer tube 21 has a first diameter 33 that is larger than the
second, smaller
diameter 34 of the tube above the transition elevation 36 at a distance 35
below the surface 37.
The narrow portion of the tube 21 having the smaller diameter 34 extends up
to, and is connected
to, the transducer 24. With the use of a lower dilated tube segment having a
diameter 33
substantially larger than a diameter 34 of an upper narrow tube segment, a
change in the
transducer tube water level from a first level 22 to a second level 31
produces a comparatively
larger change in gas pressure in the upper tube gas volume 23. This relatively
larger change is
due to the ratio of the volume change in the dilated portion of tube 21 to the
original volume 23
in the higher, narrow portion of the tube being greater for a given
incremental change of the
water level (e.g., first level 22 to second level 31), than the one-to-one
ratio if the transducer tube
has a constant diameter. It is observed here that the calculation of the
initial gas volume 23 in
this embodiment requires a slightly different formula than the formula for a
simple cylinder of
constant diameter, to account for the affect upon volume 23 of the differing
diameters
(i.e., 33, 34).
The pressure amplification geometry of Fig. 5 is especially helpful for
practicing the
invention in very deep water tables, in which the air-filled volume 23 in the
transducer tube 21 is
large relative to that for shallow water tables. The dilated geometry is
helpful because the
resolution of a pressure change depends upon the fractional change in gas
pressure. A deep
water table has a relatively larger initial volume of gas in volume 23, hence
the advantage of the
larger volume change with a dilated tube at the levels 22 and 31. The use of a
second upper
portion of the tube having a smaller diameter 34 at the transducer 24 also
minimizes the
undesirable effect of a temperature change at the top of the borehole 13,
because the gas volume
11

CA 02714692 2010-09-09
affected by the temperature change in the second, narrow portion of the tube
21 having the
smaller diameter 34, is small relative to the total gas volume contained in
the volume 23, which
includes gas contained in the dilated portion of the tube below the transition
level 36.
Because it is convenient to locate the transducers in the top of the borehole
13, a tubing
geometry at the ground's surface such as that depicted in Fig. 6 allows easy
access to a
disengageable connecting union 51 which fluidly couples the transducer 24 to
the transducer
tube 21 via a very flexible, small-diameter intermediate tube 52. In this
embodiment, the
transducer 24 can be lowered into the protective interior of the well casing
53 (and inside the
liner 1) prior to the engagement of the union 51. It is desirable to provide
the transducer, and at
least a portion of the upper portion of the transducer tube 21 (particularly
that upper portion
containing the gas volume 23) with an insulated enclosure. The interior of the
borehole, within
the casing 53, is at a more nearly uniform temperature than the outside
environment above the
surface 37. Further, it is preferable to maintain the interior of the casing
53 at a relatively
uniform temperature, to reduce the temperature effects on the air volume 23 in
the transducer
tube. A layer of insulating material 54, for example a rigid foam, may be
placed in the top of the
casing 53 to prevent large temperature effects within the casing interior due
to thermal variations
in the atmosphere above the casing. Other insulation geometries or enclosure
means may be
more useful for different wellhead configurations.
Yet another alternative embodiment of the apparatus and method seen in Fig. 7
involves
lowering the transducer tube 21 into a slender tube or small-diameter well
casing 61 (e.g., the
pump tube 17). The diameter of the slender casing 61 is less than adequate to
allow the
installation of a pressure transducer 24 beneath the water level 5 in the
slender casing 61. Thus,
in order to determine the original water level 5, the water level 5 in the
slender casing 61 must be
measured before the transducer tube 21 is lowered into the slender casing 61.
For this geometry
to be effective in a pump tube 17, the check valve 4 (Fig. 2) is removed from
the system to allow
the fluctuations in the water level 5 to "track" or follow the formation water
level 6. Also, the
number of moles of gas 23 in the transducer tube 21 will be that contained in
the tube before it is
lowered into the water in the slender casing 61. A weight 63 disposed on the
bottom of the
transducer tube 21 may be required to prevent the transducer tube from
floating or rising due to
the buoyancy of the air trapped inside the tube.
12

CA 02714692 2010-09-09
Another possible alternative embodiment of the present apparatus and method
includes
the sealed attachment of the transducer 24 directly (or via a short coupling
tube) to the top 7 of a
pump tube 17 (or similar slender tube or casing 61) for monitoring water level
fluctuations.
However, the conditions and environment at the ground's surface need to be
stable or controlled
so that temperature changes at the transducer 24, or in the air volume in the
tube 21 connected to
the transducer 24, are minimal so as not to be detrimental to the measurement
accuracy. Also, it
is important that the transducer tube 21 must be nearly absolutely air tight;
there very preferably
exists no loss, or gain, of gas in air volume 23 in the upper portion of the
transducer tube 21,
which fluctuations can cause a gas pressure change, over time, that is
unrelated to changes in the
formation water level 6.
Another useful variation on the present design and process locates the
transducer 24 in a
nearby volume (e.g., enclosed housing near the top of the borehole 13)
protected from
temperature effects, which does not include the placement of the transducer in
the volume of the
well casing or borehole. For example, as seen in Fig. 8, a protective
enclosure for the
transducer 24 features a thermally insulated housing 50 located outside the
borehole well casing
(53 in Fig. 6). The disconnectable connecting union 51 is sealed secured to
the top of the
transducer tube 21 within the borehole well casing. An intermediate tube 52,
well thermally
insulated, extends between the transducer 24 and the disengageable connecting
union 51. The
transducer 24 thus is located within the insulated housing 50 and is in fluid
communication with
the top of the transducer tube 21 via the connecting union 51 and intermediate
tube 52.
Accordingly, there is disclosed by collective reference to the drawing figures
an
apparatus for monitoring changes in the level 6 of a fluid (typically ambient
water) in the
formation 14, there being the borehole 13 extending into the formation 14 from
the formation
surface 37, with the apparatus having one, and preferably more than one,
tubing system. A
tubing system according to the apparatus includes the transducer tube 21
extending in the
borehole 13 and having its top end located above or near the formation surface
37, and its bottom
end below the fluid level 6 in the formation 14. Each tubing system also has
the transducer 24
positioned above the formation surface 37 and in closed fluid communication
with the top end of
the transducer tube 21, whereby the gas pressure within the volume 23 in the
upper portion of the
transducer tube 21 can be measured. The transducer tube 21 is together with
the port tube 3, the
13

CA 02714692 2010-09-09
latter being in fluid communication with the fluid in the formation 14, and
also in fluid
communication with the bottom end of the transducer tube 21. Fluid flows, via
the port tube 3,
between the formation 14 and a lower portion of the transducer tube 21,
whereby the level 22 of
the fluid in the transducer tube 21 tends to equilibrate with the existing
level 6 of the fluid in the
formation 14. Further to a key feature of the apparatus, the level 22 of fluid
in the transducer
tube 21 affects the gas pressure within the upper portion of the transducer
tube; a change in fluid
level within the transducer tube 21 (e.g., from first level 22 to second level
31) changes the
pressure in the gas volume 23, as measured by the transducer 24, to indicate
the change in the
level of the fluid in the formation 14 (e.g., from first formation level 6 to
second formation
level 66).
The very preferred embodiment of the apparatus has the flexible liner 1 that
is everted
into the borehole 13 at least to a depth below the level 6 of the fluid in the
formation 14. The
liner 1 substantially seals the borehole walls against the flow of fluid
between the formation 14
and the borehole interior to the liner 1, except where ports 19 are provided
(adjacent spacers 2 on
the outside of the liner 1). The transducer tube 21 and the port tube 3 are
situated within the
interior of the everted flexible liner 1.
The apparatus very preferably also provides a means for sampling ambient fluid
from the
formation 14. The sampling means is a part of the tubing system, and includes
the pump tube 17
within the everted flexible liner 1, the top end 7 of the pump tube 17 being
above the formation
surface 37 and the bottom end being below the level 6 of the fluid in the
formation 14; the pump
tube bottom end also is in fluid communication with the port tube 3. There is
also provided in
the tubing system the sample tube 9 at least partially within the everted
flexible liner 1 and
having a top end above the formation surface 37 and a bottom end in fluid
communication with
the bottom end of the pump tube 17. Each port 19 is defined through the
everted flexible liner!
at a sampling location elevation and in fluid communication with the port tube
3, whereby fluid
in the formation 14 flows into the pump tube 17 via the port 19 and port tube
3. In the sampling
means there is the check valve 4 between the bottom end of the pump tube 17
and the port tube 3
for regulating (preventing) fluid backflow from the pump tube 17 into the port
tube 3. When a
gas pressure is supplied to the top end 7 of the pump tube 17, the check valve
4 closes and a fluid
14

CA 02714692 2010-09-09
sample from within the pump tube 17 is expelled above the formation surface 17
via the sample
tube 9.
Returning attention more particularly to Fig. 5, an alternative embodiment of
the
apparatus has the transducer tube 21 featuring a dilated portion having a
first diameter 33,
extending from the level of the fluid in the formation 6 (a level
approximately equal to the fluid
level 22 in the tube) up to the transition elevation 36, and a narrow portion,
above the transition
elevation 36, having a second diameter 34 smaller than the first diameter 33
of the dilated
portion. The narrow portion of the transducer tube extends up to, and connects
to, the
transducer 24. Accordingly, a change in the fluid level (e.g. 22) within the
dilated portion of the
transducer tube 21 creates an amplified change in gas pressure within the
narrow portion of the
tube proportional to the difference between the first 33 and second 34
diameters.
The apparatus in alternative embodiments has an enclosure about the transducer
24 for
insulating the transducer 24 from deleterious temperature changes. Referring
again to Fig. 6, one
version of the enclosure is composed of the borehole well casing 53, and the
layer of insulating
material 54 disposed across the top opening of the casing. In this embodiment,
the transducer 24
is fluidly connected to the transducer tube 21 via the disconnectable
connecting union 51 and the
intermediate tube 52. This way, the transducer 24 is removably disposable
within the well
casing 53 prior to the disposition of the layer of insulating material 54, but
remains protected yet
easily accessible at the surface 37 of the ground.
Alternatively, the transducer enclosure may be a thermally insulated housing
50 located
outside the borehole well casing 53, yet quite proximate to the top of the
borehole 13, as
suggested in Fig. 8. The disconnectable connecting union 51 is at the top of
the transducer
tube 21. The transducer is within the protected confines of the housing 50.
The transducer 24 is
in fluid communication with the transducer tube 21 via the connecting union 51
and a heavily
insulated intermediate tube 52.
The embodiment of Fig. 7 manifests an enclosure about the transducer tube 21
for
enclosing the transducer tube, wherein the enclosure is the slender casing 61
within the borehole
well casing 53 and around the transducer tube. In certain instances, it may be
desirable to
deploy a pump tube 17 but without a sample tube 9, and with no check valve 4.
Such an
alternative configuration permits the use of a different pumping system, and
the water level in

CA 02714692 2010-09-09
the pump tube 17 follows the water table level 6 without the need for purging.
The
transducer 24 is in fluid communication with the transducer tube 21 via the
disengageable
connecting union 51 (which is sealably attached to the top of the transducer
tube), and an
intermediate tube 52 extending between the transducer 24 and the connecting
union 51.
Element 61 is a slender casing (e.g., about 1/2-inch inside diameter) which
can be sampled, but
the air-coupled tube 21 lowered into the casing 61 allows the water level to
be monitored.
Normally, the casing 61 is too small to allow the transducer 24 to be lowered
into the water (5) in
the casing. For example, the tube 21 may be lowered into the pumping tube 17
in situations
where there are no current transducers in the system. The main feature of this
embodiment is the
air-coupled transducer geometry shown in the Fig. 7.
In most practical and preferable embodiments of the apparatus, there is a
plurality (e.g.,
two to fifteen, typically between five and ten) of tubing systems (including
at least the port
tube 3 and transducer tube 21 and associated ports, connections, and valves as
described) within
a single borehole 13.
The methodology of the invention is apparent from the foregoing, but is here
summarized. The method for monitoring changes in the level 6 or 66 of a fluid
in a formation 14,
(there being a borehole 13 extending into the formation 14 from a formation
(ground) surface 37,
includes the basic step of situating at least one tubing system in the
borehole 13. This step of
situating at least one tubing system features the steps of extending a
transducer tube 21 in the
borehole 13 such that a top end of the transducer tube is above the formation
surface 37 and a
bottom end of the transducer tube is below the fluid level 6 in the formation,
disposing a
transducer 24 above the formation surface 37 and in closed fluid communication
with the top end
of the transducer tube 21, providing a port tube 3 in fluid communication with
the fluid in the
formation 14 and with the bottom end of the transducer tube 21, allowing fluid
to flow, via the
port tube 3, between the formation 14 and a lower portion of the transducer
tube 21 whereby a
level of the fluid in the transducer tube tends to equilibrate with the level
of the fluid in the
formation, permitting any change in the level 22 of fluid in the transducer
tube 21 resulting from
a change in the level 6 of the fluid in the formation 14 to affect the gas
pressure within an upper
portion of the transducer tube (any change in gas pressure indicating a change
in the level of the
16

CA 02714692 2010-09-09
fluid in the formation, and measuring with the transducer 24 a change in the
gas pressure within
the upper portion of the transducer tube.
The method preferably also has the steps of everting the flexible liner 1 into
the
borehole 13 to at least a depth below the level 6 of the fluid in the
formation 14 to substantially
seal, with the liner, the borehole walls against the flow of fluid between the
formation 14 and the
borehole interior to the liner 1, and (simultaneously or subsequently)
situating the transducer
tube 21 and the port tube 3 within the interior of the everted flexible liner.
To enable fluid sampling processes, the method includes disposing a pump tube
17 within
the everted flexible liner 1 such that a top end 7 of the pump tube is above
the formation
surface 37 and a bottom end of the pump tube is below the level 6 of the fluid
in the
formation 14. The bottom end of the pump tube 17 is placed in fluid
communication with the
port tube 3, and a sample tube 9 is situated within the everted flexible liner
1 such that a top end
of the sample tube is above the formation surface. The bottom end of the
sample tube 9 is placed
in fluid communication with the bottom end of the pump tube 17. This method
includes the
provision at a sampling location elevation of a port 19 through the everted
flexible liner 1 and in
fluid communication with the port tube 3, thereby allowing fluid in the
formation 14 to flow into
the pump tube 17 via the port 19 and the port tube 3, and the disposition of a
check valve 4
between the bottom end of the pump tube and the port tube, and thereby
regulating with the
check valve the flow of fluid from the pump tube into the port tube. By
supplying a gas pressure
to the top end 7 of the pump tube 17, thereby closing the check valve 4 and
expelling, via the
sample tube 9 and to above the formation surface 17, a fluid sample can be
retrieved from within
the pump tube 17 for analysis at the ground's surface 37 or in a remote
laboratory.
A key act is the step of determining, from a measured change in the gas
pressure within
the volume 23 within the upper portion of the transducer tube 21, a change in
the level of fluid in
17

CA 02714692 2010-09-09
the formation 14. This determination fundamentally is the calculation of the
change in level of
fluid by using the formula
n (¨ ¨ ¨
APg Po Pg,
2,117 = ¨c +
in which AWT is the change in the formation fluid level, APg is the measured
change in the gas
pressure in the upper portion of the transducer tube, c is a constant (known
from the art of gas or
hydraulic physics) to convert from pressure to hydraulic head, n is the number
of moles of gas in
the upper portion of the transducer tube, R is the universal gas constant, T
is the absolute
temperature, Po is a first absolute pressure in the transducer tube, Pg is a
subsequent second
absolute pressure in the transducer tube, and A is a radial cross sectional
area of the transducer
tube.
In the method, extending a transducer tube 21 optionally means defining in the
transducer
tube a dilated portion, having a first diameter 33 extending from the level of
the fluid in the
formation up to a transition elevation 36, and defining a narrow portion above
the transition
elevation 36, having a second diameter 34 smaller than the first diameter of
the dilated portion,
and extending the narrow portion up to, and connecting the narrow portion to,
the transducer 24.
In this version of the method, any change in a fluid level within the dilated
portion of the
transducer tube creates an amplified change in gas pressure within the narrow
portion, the
amplification being substantially proportional to the difference between the
first and second
diameters (33, 34).
An alternative method optionally includes the step of insulating the
transducer 24 from
temperature changes. This may mean disposing an enclosure around the
transducer by placing
the transducer within the borehole well casing 53 having a top opening,
disposing the layer of
insulating material 54 across the top opening of the casing, fluidly
connecting the transducer 24
to the transducer tube 21 via the disconnectable connecting union 51 and an
intermediate
tube 52, and removably disposing the transducer 24 within the well casing 53
prior to disposing
the layer of insulating material 54 across the open top.
18

CA 02714692 2010-09-09
Alternatively, insulating the transducer 24 may mean disposing an enclosure
around the
transducer by locating a thermally insulated housing 50 outside a borehole
well casing 53, then
locating the transducer 24 inside the housing 50, securing a disconnectable
connecting union 51
at the top of the transducer tube 21, and placing the transducer in fluid
communication with the
transducer tube by extending a thermally insulated intermediate tube 52
between the connecting
union and the transducer.
In another possible embodiment, the transducer tube 21 is placed within the
interior of a
slender casing 61 within the borehole 13, sealably attaching the disengageable
connecting
union 51 to the top of the transducer tube, and placing the transducer in
fluid communication
with the transducer tube by extending an intermediate tube 52 between the
connecting union and
the transducer. This alternative methodology permits a person practicing the
inventive process to
use an air-coupled transducer 24 located in a slender casing 61 such as the
tube 17 for such
systems not equipped with a separately situated transducer tube.
All versions of the method may have the step of situating a plurality of
tubing systems
into a common borehole.
The foregoing description of the system and method describes only the basic
system.
The actual use may be numerous duplications of the basic monitoring system,
that is, a plurality
of tube assemblies disposed in a single borehole. Other obvious embodiments
such as pre-
pressurizing the gas volume 23 in the transducer tube, the use of other gases,
other thermal
insulations, vented versus unvented transducers, and the like are within the
scope of the present
invention.
There accordingly have been disclosed an apparatus and method for monitoring
water
tables in multi-level ground water sampling systems. The method and apparatus
are basic in
concept, although somewhat more sophisticated in implementation, but with
significant
advantages. The inventor of the flexible liner multi-level sampling system
described would have
enjoyed the advantages for this design long ago if had he recognized the
nonobvious utility of the
present invention. The gas physics and the necessary mathematics particular to
this invention
obscured the feasibility of the design, slowing its innovation. Further, only
relatively recent
improvements in high-resolution pressure measurements have rendered practical
the present
19

CA 02714692 2010-09-09
invention for the broad range of borehole and water level conditions found in
typical monitoring
and measurement environments.
Laboratory tests of the present apparatus have revealed that numerous
hypothetical
perturbations are not important, and that the variations of partial pressure
of the water vapor in
the gas column 23 and temperature effects can be controlled to obtain
calculations of better than
one-inch resolution of water level changes in the subsurface environment. An
additional
advantage of the presently disclosed invention for the described multi-level
system is that the
transducer-derived water level change can be independently verified as often
as desired by
manually measuring the water level 5 in the pump tube 17. The manual level
check is done after
the pump tube 17 has been purged, and after the water level 5 has equilibrated
at the current
water level 6 in the geologic formation. Otherwise, the check valve 4
interferes with the manual
verification check of the air-coupled system. The invention does not, however,
interfere with the
normal water sampling system, or manual water level measurement, as described
herein with
reference to Fig. 1.
Although the invention has been described in detail with particular reference
to these
preferred embodiments, other embodiments can achieve the same results. The
present invention
can be practiced by employing conventional materials, methodology and
equipment.
Accordingly, the details of such materials, equipment and methodology are not
set forth herein in
detail. In the previous description, specific details are set forth, such as
specific materials,
structures, chemicals, processes, etc., in order to provide a thorough
understanding of the present
invention. However, as one having ordinary skill in the art would recognize,
the present
invention can be practiced without resorting to the details specifically set
forth. In other
instances, well known processing structures have not been described in detail,
in order not to
unnecessarily obscure the present invention.
Only some embodiments of the invention and but a few examples of its
versatility are
described in the present disclosure. It is understood that the invention is
capable of use in various
other combinations and is capable of changes or modifications within the scope
of the inventive
concept as expressed herein. Modifications of the invention will be obvious to
those skilled in
the art and it is intended to cover in the appended claims all such
modifications and equivalents.

Representative Drawing