SYSTEM FOR DETERMINING RATE OF GROUND WATER RE-CONTAMINATION DUE TO ROCK MATRIX BACK DIFFUSION

Abstract

The present invention is a low permeability rock matrix back diffusion testing system and method which enables contaminant concentrations and hydraulic pressure values to be independently tested. This system includes specially configured packer components which allow precise placement and maintain test conditions for the duration of a study to accurately measure and predict the rate of back flow diffusion over time in low permeability zones.

Description

FIELD OF INVENTION

This invention relates to the field of ground water testing and more specifically to a testing procedure that measures matrix back diffusion of contaminants in open boreholes of existing rock wells.

BACKGROUND OF THE INVENTION

The Environmental Protection Agency (EPA) currently manages over 1,300 groundwater remediation projects. The U.S. Geological Survey supports the EPA in developing technological solutions for initial groundwater remediation and to address naturally occurring recontamination of previously remediated sites.

Recontamination of “low permeability” well borehole sites often occurs when long after remediation projects have been deemed complete. Low permeability sites characterized by fractures that are very small. Recontamination can occur slowly and reach prohibited levels years after remediation.

Most recontamination is caused by back diffusion of contaminants from the rock into well water. The rate of back diffusion is expressed as a ratio of contaminant concentration levels over time for a borehole having a known volume based on its radius.

Back diffusion in low permeability sites is currently monitored by testing core rock samples drilled from an existing borehole. The drilling permanently alters the undergoing testing.

The core rock samples are tested by submerging in water. The surrounding water is repeatedly tested to determine the change in the concentration level of the contaminant over time, δC₁/δt, to estimate the rate of back diffusion recontamination for the borehole from which the sample was obtained.

Various diffusion coefficient equations are known in the art for extrapolating laboratory results to estimate the rate of back diffusion for an actual borehole having a known radius.

One formula known in the art is used to estimate a diffusion rate coefficient (Di) for a volume of water in a cylinder. (Crank, The Mathematics of Diffusion, 1975) This formula is expressed as follows:

$R_1\theta \frac{\partial C_1}{\partial t}=\frac{1}{r}\frac{\partial }{\partial r}\left(r\theta D_1\frac{\partial C_1}{\partial r}\right)-{\stackrel{\_}{\lambda }}_1{\rho }_bK_{d,1}C_1$

In addition to the ratio (δC₁/δt) of initial concentration to concentration at time (t) and the radius of the borehole (r), this formula requires the use assumed constant values to reflect assume borehole conditions. For example, constant values may be used to reflect the porosity (8) of the rock, and retardation (R) to calculate a diffusion rate coefficient (Di). These constant values may not equate to actual conditions.

It is a problem known in the art that the use of core sampling techniques formulas used to estimate back diffusion based may not accurately represent the actual conditions of the borehole.

There is an unmet need for in situ testing methods which can be used to directly measure the rate of diffusion in boreholes, without the need for costly core sampling and the margin of error associated with testing methods known in the art.

SUMMARY OF THE INVENTION

The present invention is a low permeability rock matrix back diffusion testing system which includes upper and lower conformable barriers that form a seal when in contact with the inner surface of a borehole. The seals are used to isolate test zones of varying dimensions and with varying data point resolutions, for the duration required for conducting testing of low permeability test sites.

Testing zones include a lower test zone, a central isolated test zone and an upper test zone. Each zone has chemical concentration values and hydraulic pressure values which may be independently measured.

An air sparging conduit is operatively coupled with a pressurized air source to expel contaminants from the central isolated test zone. The air sparging conduit passes through the upper conformable barrier.

A water line operatively coupled with a test zone pump enables the extraction of water from the test zone in which the pump is located.

The system further includes a sparged contaminant conduit which passes though said upper barrier and said lower barrier to conduct sparged contaminants from the central isolated test zone out of the borehole. The system may further include sensors and a computer processor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary embodiment of a system for determining the rate of ground water re-contamination due to rock matrix back diffusion.

FIG. 2 is a cross-sectional view of an exemplary back diffusion test system placed within a borehole.

FIG. 3 illustrates an exemplary method for testing rock back-diffusion in a low permeability zone.

FIG. 4 illustrates hydraulic and chemical zone classifications for open-boreholes.

TERMS OF ART

As used herein, the terms “conformable” refers to the quality of conforming to dimensions and contours.

As used herein, the term “rock matrix diffusion coefficient” means a quantitative value that indicates the rate of increase in contaminant concentration in groundwater, caused by diffusion of contaminants from the walls of a borehole.

As used herein, the term “sample collection interface” means a structural feature which allows access to the central isolated test zone for extraction of isolated test fluid.

As used herein, the term “sparge” or “sparging” means increasing the quantity of an inert gas to remove or decrease the quantity of other dissolved gases including but not limited to oxygen, methane, and volatile organic compounds from the liquid.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an exemplary embodiment of a system for determining the rate of ground water re-contamination due to rock matrix back diffusion.

Visible in FIG. 1 are upper conformable barrier 10a, lower conformable barrier 10b, inflatable portion 11, lower test zone air line 14b, lower test zone water line 16b, barrier inflation line 18, perforated section 24, sparging conduit 50, sample collection interface 80, and sparged contaminant conduit 70.

In the exemplary embodiment shown, lower test zone air line 14, lower test zone water line 16, barrier inflation line 18 sparging conduit 50, and sample collection interface 80 pass through inflatable portion 11 of barriers 10a and/or 10b and may be welded together. In the exemplary embodiment shown, inflatable portion 11 is a flexible inflatable bladder.

In the exemplary embodiment shown, the portion of sparged contaminant conduit 70 that passes through barrier 10 is sample collection interface 80 which has an end below barrier 10b that is closed with an end cap. Sample collection interface 80 with a perforated section 24 allows contaminant gases to exit borehole 99 and allows the user to retrieve samples from borehole 99.

In the exemplary embodiment shown, barrier inflation line 18 is operatively coupled with a source of pressurized air to inflate barriers 10a and 10b.

In the exemplary embodiment shown, lower test zone air line 14 and barrier inflation line 18 are ¼ inch national pipe thread couplings that operatively couple with an air line hose.

In the exemplary embodiment shown, lower test zone water line 16 is a ⅜ inch national pipe thread coupling that operatively couples with a hose.

In the exemplary embodiment shown, sparging conduit 50 is a ⅜ inch national pipe thread coupling that operatively couples with an air line hose.

In alternative embodiments, sparging conduit 50 may be used to supply air to a bladder pump and sampling line 16 may be used to conduct water from a bladder pump located within the central isolated test zone (optional) to the ground surface.

In the exemplary embodiment shown, barrier 10 is an inflatable packer measuring approximately 4-8 inches in diameter when inflated and 3.5 inches when deflated. This diameter allows the packer to create a seal in a borehole of standard dimensions and allows back diffusion testing System 100 to be easily portable. These packers are configured for longer studies that require a hydraulic seal to last for months. The small size of these packers also allows the distance between the packers to be as small as 1 foot, which creates a smaller central isolated test zone 20 and increased data point resolution.

In alternative embodiments, barrier 10 may be a commercially available packer. In alternative embodiments, a stronger hydraulic seal can be created by partially filling the inflatable component of the packer with water or other liquid while placing System 100 in borehole 99 and completing the inflation with gas.

FIG. 2 is a cross-sectional view of exemplary back diffusion test system 100 placed within borehole 99.

In various embodiments, System 100 includes upper conformable barrier 10a and lower conformable barrier 10b, central isolated test zone 20, sparging conduit 50, sparged contaminant conduit 70, sample collection interface 80, contaminant concentration and hydraulic pressure sensors 85, computer processor 60, and borehole 99.

In the exemplary embodiment shown, conformable barriers 10a and 10b each include an outer perimeter surface that is in contact with an inner surface of borehole 99. Conformable barriers 10a and 10b create a hydraulic seal which prevents the water in borehole 99 from moving into or out of central isolated test zone 20.

The volume and interior of central isolated test zone 20 is a space defined by the dimensions of the walls of borehole 99 and the distance between barriers 10a and 10b. Central isolated test zone 20 contains isolated test fluid. The distance between barriers 10a and 10b can be configured to alter the size of central isolated test zone 20 to test boreholes at intervals of varying dimensions and with varying data point resolutions. Decreasing the size of isolated test zone 20 allows higher data point resolution by testing more intervals of borehole 99, which facilitates locating the precise location of contaminants in borehole 99. In contrast, the number of testing iterations required to capture data on the full depth of the bore hole can be reduced by increasing the size of central isolated test zone 20. In various embodiments, components connecting barriers 10a and 10b are interchangeable and varying lengths of these components determines the distance between the barriers. In alternative embodiments, barriers 10a and 10b may slide along sample collection interface 80 to increase or decrease the distance between the barriers.

Central isolated test zone 20 is an area between upper conformable barrier 10a and lower conformable barrier 10b. Central isolated test zone 20 contains a quantity of isolated test fluid, which has a quantifiable concentration of contaminants.

Sparging conduit 50 is operatively coupled with a pressurized air source. In the exemplary embodiment shown, sparging conduit 50 conducts argon or another inert gas or contaminant-free air into central isolated test zone 20 to force contaminants out of the water in gas form. In various embodiments, contaminants include but are not limited to oxygen, methane, and volatile organic compounds.

In the exemplary embodiment shown, sparged contaminant conduit 70 is a pipe that conducts sparged gas contaminants from central isolated test zone 20 out of borehole 99 but may be any structure suitable for conveying contaminants from central isolated test zone 20.

Sample collection interface 80 may be any component or assembly of components for removing samples before and after sparging. In the exemplary embodiment shown, sample collection interface 80 is a pipe that passes though upper conformable barrier 10a and lower conformable barrier 10b to conduct contaminants and samples from central isolated test zone 20 to sparged contaminant conduit 70. In the exemplary embodiment shown.

In the embodiment shown, sample collection interface 80 includes perforated section 24. Perforated section 24 includes small apertures which allow water from central isolated test zone 20 to enter sparged contaminant conduit 70 and sampling containers within sparged contaminant conduit 70. In the exemplary embodiment shown, perforated section 24 is perforated by drilled holes. In alternative embodiments, perforated section 24 is a screen or another permeable material that allows the passage of water.

In the exemplary embodiment shown, sparged contaminant conduit 70 may function as sample collection interface 80, by inserting a sample collection receptacle in sparged contaminant conduit 70. In various embodiments, sample collection interface 80 is a tube. In alternative embodiments, sample collection interface 80 is a pipe. Sparged contaminant conduit 70 and sample collection interface 80 have a diameter sufficiently large enough to allow the retrieval of samples, but small enough to enter borehole 99.

In various embodiments, System 100 includes optional barrier inflation lines 18a and 18b, test zone pumps 12a and 12b, upper and lower test zone air lines 14a and 14b, upper and lower test zone water lines 16a and 16b, central isolated test zone 20, upper test zone 22, perforated section 24, lower test zone 26, dye pouches 23 and 27, gas sampling containers 30a through 30i, water sampling containers 40a through 40g, and sample retrieval lines 32, 42, 52.

In the exemplary embodiment shown, barrier 10a is operatively coupled with upper test zone pump 12a, upper test zone air line 14a, and upper test zone water line 16a. In the exemplary embodiment shown, lower conformable barrier 10b is operatively coupled with lower test zone pump 12b, lower test zone air line 14b, and lower test zone water line 16b. In the exemplary embodiment shown, barrier inflation lines 18a and 18b are each connected to a gas cylinder at the ground surface and allow pressurized gas to fill the inflatable component of barriers 10a and 10b. Barrier inflation lines 18a and 18b are each operatively coupled with a pressure gauge to indicate the pressure in barriers 10a and 10b. In the exemplary embodiment shown, barriers 10a and 10b are inflated to a pressure that is approximately 20 pounds per square inch (PSI) higher than the pressure exerted by the water surrounding barriers 10a and 10b, to create a hydraulic seal in borehole 99. In alternative embodiments, one gas cylinder and one gas line operatively couples with both barriers 10a and 10b to inflate the barriers. In the exemplary embodiment shown, the gas cylinders contain pressurized nitrogen. In alternative embodiments, the gas cylinders contain other pressurized gases.

In one exemplary embodiment, upper and lower test zone pumps 12a and 12b are bladder pumps that are operatively coupled with air lines 14a and 14b that inject nitrogen into the pumps to activate the bladder and start pumping action. Then, pumps 12a and 12b conduct water from above or below central isolated test zone 20 to the ground surface through sampling lines 16a and 16b. If this directional pumping causes a rapid reduction in the water level in central isolated test zone 20, this indicates a leak in the hydraulic seal created by barriers 10a and 10b. If the reduction in water level is slow, this indicates that fractures in the rock allow water to move out of central isolated test zone 20. In alternative embodiments, peristaltic pumps, other pumps or other devices are employed to collect water and gas samples from central isolated test zone 20, upper test zone 22 and lower test zone 26.

In the exemplary embodiment shown, dye pouches 23 and 27 are used to detect the movement of water from central isolated test zone 20 to other areas of borehole 99. In the exemplary embodiment shown, dye pouch 23 is attached to sparged contaminant conduit 70, proximate to the lower surface of upper barrier 10a. Dye pouch 27 is attached to sparged contaminant conduit 70, proximate to the upper surface of lower barrier 10b. Dye pouches 23 and 27 are mesh bags that contain frozen, colored dye that melts during use. In various embodiments, the dye may be blue food-grade dye. In various embodiments, dye pouches contain other chemically neutral, non-reactive and non-hazardous substances that can act as conservative tracers, including but not limited to Sodium Bromide. In alternative embodiments, dye pouches 23 and 27 are holsters that hold replaceable cartridges filled with tracers.

In the exemplary embodiment shown, upper test zone pump 12a is located above upper conformable barrier 10a, outside of central isolated test zone 20 and lower test zone pump 12b is embedded below lower conformable barrier 10b, outside of central isolated test zone 20. Upper and lower test zone pumps 12a and 12b draw water up to the ground surface from outside of central isolated test zone 20. If dye or another tracer is detected in this water, it indicates that water can exit central isolated test zone 20 and/or that barriers 10a and 10b have not successfully formed a hydraulic seal to create central isolated test zone 20. The timing and distribution of the appearance of the dye is indicative of the nature of transport either via the borehole or externally through microcracks. In the exemplary embodiment shown, sparging conduit 50 injects contaminant-free air into the water in central isolated test zone 20 to force gas contaminants out of the water.

In various embodiments, System 100 may include pressure sensor 85 located below barrier 10b that monitors pressure changes in lower test zone 26. If there are pressure changes, it can demonstrate if there is a leak in the hydraulic seals.

In various embodiments, System 100 may include contaminant concentration sensors and hydraulic pressure sensors 85. In various embodiments, sensors 85 may include, but are not limited to, water pressure sensors, water conductivity sensors, temperature sensors, dissolved oxygen sensors, oxidation-reduction potential (ORP) sensors, turbidity sensors, total dissolved solids (TDS) sensors, pH sensors, and water velocity sensors. In alternative embodiments, levels of contaminants, leaking argon and nitrogen, and other analytes in collected samples are analyzed by gas chromatography, gas chromatography-mass spectrometry (GC-MS), a photoionization detector (PID), a flame ionization detector (FID), or another analyzer. In various embodiments, sensors 85 are located at the level of the potentiometric head or surface, which is the elevation to which water in a system would rise without physical obstacles or constraints. In other embodiments, sensors 85 may be located in isolated test zone 20 and upper test zone 22.

In still other embodiments, contaminant concentration and hydraulic pressure sensors 85 may transmit data to computer processor 60. In the exemplary embodiment shown, computer processor 60 is a computer processor configured to run back diffusion calculations. In the exemplary embodiment shown, computer processor 60 analyzes data extracted from gas and liquid samples to monitor and model back-diffusion, forward-diffusion, volatilization, and degradation processes. User inputs for computer processor 60 may include but are not limited to: source location and timestamp of each sample, and central isolated test zone volume.

In the exemplary embodiment shown, sparged contaminant conduit 70 is operatively coupled with conformable barriers 10a and 10b and allows the positioning of barriers 10a and 10b at the desired depth in borehole 99. Sparged contaminant conduit 70 is a hollow stand pipe with a top, open end located above the water level of borehole 99 to allow gas to escape from borehole 99 and a bottom, open end located below barrier 10a to facilitate lowering and raising gas sampling containers 30a and water sampling containers 40a into and out of borehole 99 and central isolated test zone 20 to collect samples. The end of sparged contaminant conduit 70 located below barrier 10b is sealed so as not to interact with water from lower test zone 26.

In the exemplary embodiment shown, sparged contaminant conduit 70 is a PVC pipe or riser that connects to sample collection interface 80. In the exemplary embodiment shown, sample collection interface 80 is a 1″-1.5″ diameter pipe that passes through the inflatable component of barriers 10a and 10b. All or a portion of sample collection interface 80 in the interval between the lower surface of barrier 10a and the upper surface of barrier 10b is perforated section 24, which allows exchange and migration of liquids and gases between sparged contaminant conduit 70 and central isolated test zone 20.

In one exemplary embodiment, upper conformable barrier 10a and lower conformable barrier 10b are devices known in the art referred to as packers. Packers are inflatable devices known in the art which each have an inflatable component to create a hydraulic seal in borehole 99.

In various embodiments, System 100 may include redundant barriers. In various embodiments, upper conformable barrier 10a and lower conformable barrier 10b may be comprised of multiple layers or structures to create a stronger hydraulic seal. In alternative embodiments, barriers 10a and 10b may be other components that can conform to borehole 99 to create a hydraulic seal. Barriers 10a and 10b may also deform or deflate to be removed from borehole 99 after testing for reuse in another borehole.

In the exemplary embodiment shown, sample collection interface 80 connects upper conformable barrier 10a and lower conformable barrier 10b. Sample collection interface 80 and perforated section 24 allow the use of any means known in the art for collection and retrieval of gas and liquid samples from central isolated test zone 20.

In the exemplary embodiment shown, samples are collected in gas sampling containers 30a through 30i and water sampling containers 40a through 40g. In various embodiments, gas sampling containers 30a through 30i are passive vapor samplers (PVS) made of polyethylene material that contains contaminant-free inert gas or air before being lowered into borehole 99. In various embodiments, water sampling containers 40a through 40g are passive diffusion bags (PDB) made of polyethylene material that contains contaminant-free deoxygenated, deionized water before being lowered into borehole 99. In still other embodiments, water in sampling containers 40a through 40g is deoxygenated to prevent the increase of bacterial growth and bacterial biofilm generation, which can interfere with sampling.

In the exemplary embodiment shown, at least one gas sampling container 30a and one water sampling container 40a is lowered into central isolated test zone 20 through sparged contaminant conduit 70.

At least one of gas sampling containers 30 and one of water sampling containers 40 is lowered into sparged contaminant conduit 70, above barrier 10a. In alternative embodiments, at least one of gas sampling containers 30e through 30g and one of water sampling containers 40e through 40g is lowered into borehole 99, outside of sparged contaminant conduit 70 (into upper test zone 22). In alternative embodiments, the time interval between sampler deployment and sampler retrieval/sample collection may be customized based on chemical-specific properties of contaminants of interest, material properties of samplers, or other factors. In alternative embodiments, a sample is collected from the lower test zone through tubing attached to a dedicated deployed bladder pump or similar pump installed below barrier 10b.

In the exemplary embodiment shown, sparging conduit 50 is operatively coupled with barrier 10a. In alternative embodiments, sparging conduit 50 is lowered through sparged contaminant conduit 70 and gas contaminants exit through sparged contaminant conduit 70.

In alternative embodiments, instead of sparging after creating a hydraulic seal, the contaminant level is reduced by pumping the water from central isolated test zone 20 to a can or drum at the ground surface and replacing it with uncontaminated water, which is deoxygenated, deionized water. In various embodiments, a peristaltic pump or bailer is used to pump the water through ¼″ Teflon tubing and a carbon filter to remove contaminants.

In the exemplary embodiment shown, perforated section 24 is a perforation or aperture corresponding to a portion of the length of sample collection interface 80. In the embodiment shown, the lengths of sample collection interface 80 and perforated section 24 can be customized to be longer or shorter. Lower test zone 26 is a zone within the open borehole in borehole 99 located below barrier 10b and upper test zone 22 is a zone within the open borehole in borehole 99 located above barrier 10a. In alternative embodiments, sample collection interface 80 with a perforated or perforated section 24 may be a prescribed length of commercially-available well screen constructed from PVC, stainless steel, or other material.

In the exemplary embodiment shown, sample retrieval lines 32, 42 and 52 are operatively coupled with gas sampling containers 30a through 30i and water sampling containers 40a through 40g, to lower and raise the sampling containers into and out of borehole 99 for sample collection.

In the exemplary embodiment shown, System 100 allows back-diffusion testing in wells or boreholes with a diameter of at least 6 inches, at depths of several hundred feet or less. Typical ambient groundwater temperatures and pressures are assumed.

In various embodiments, System 100 allows the measurement of contaminant mass in unfractured rock and leaking through miniscule cracks in the rock known as microcracks.

In various embodiments, diffusion rates calculated by System 100 for a specific groundwater site will decrease after each remediation attempt at that site and can be used to measure the effectiveness of a clean-up effort. Diffusion rates calculated at a site can also influence decision-making about the best remediation technique to use at that site.

FIG. 3 illustrates exemplary method 200 for testing rock back-diffusion in a low permeability zone.

Method 200 is a method for assessing contaminant mass and concentrations utilizing existing boreholes. Various embodiments of Method 200 may be performed at well-field sites with wells or boreholes that have been exposed to natural and manmade contamination.

In various embodiments, Method 200 allows for a quick assessment of the mass and concentration of contaminants which have diffused into the bedrock or other solid or porous substances. In various embodiments, Method 200 allows for measuring the flow of liquid through microcracks (microflow), which is not easily detectable by other methods.

In the exemplary embodiment shown, Method 200 isolates a central test zone without fractures in the bedrock and utilizes gas and liquid samples and analyses to monitor the rate of back diffusion in each zone.

Step 1 is the optional step of categorizing borehole in the bedrock for subsequent testing. See FIG. 4 for exemplary categories of bedrock. Step 1 may include the step of collecting a series of water samples in a vertical profile. Analysis of this sample will provide information about the baseline contaminant concentration in the borehole water before testing.

Step 2 is the step of selecting and isolating a test zone. In various embodiments, specialized straddle packers isolate the test zone. The central isolated test zone is known as a negligible flow zone because it is hydraulically isolated by straddle packers and water is not able to easily move into or out of the central test zone.

Step 3 is the optional step of testing the integrity of the hydraulic seal by performing directional pumping from below and above the central isolated test zone.

Step 4 is the optional step of testing the integrity of the hydraulic seal by using a tracer system.

Step 5 is the step of collecting a water sample from the central isolated test zone and from above and below the central isolated test zone. Analyzing this sample will provide information about the baseline contaminant concentration in the borehole water before testing.

Step 6 is the step of modifying the water content of the test zone.

In one exemplary embodiment, an air sparger reduces or eliminates the contaminants in the water in the test zone. In one exemplary embodiment, the air sparger is comprised of sparging conduit 50 and a pressurized air source. In various embodiments, the air sparger is any sparger known in the art.

In an alternative embodiment, the water in the test zone is replaced by clean, deoxygenated water.

Step 7 is the step of collecting a water sample from the central isolated test zone. Analysis of this sample will demonstrate whether the water was successfully cleaned and flushed of contaminants through the sparging process.

Step 8 is the step of inducing both backward and forward diffusion into the rock matrix. This is the step of allowing contaminants from surrounding rock and crevices to diffuse into water in the central isolated test zone. Backward diffusion is the movement of contaminants from the bedrock into the water contained in the borehole and central isolated test zone and forward diffusion is the movement of argon or other gases introduced via sparging from the water into the adjacent bedrock and passive vapor and water samplers.

Step 9 is the step of sampling the test zone at timed intervals to provide information on matrix back diffusion and other important processes.

In the exemplary embodiment shown, this step includes extracting samples from an array of passive diffusion bags (PDB), comprised of water-filled sampling containers, and passive vapor samplers (PVS), comprised of gas-filled sampling containers, which allows the monitoring of back diffusion, forward diffusion, volatilization, and degradation processes.

Step 10 is the step of displaying results. This step may include plotting the results on a chart or graph with time displayed on the x-axis and measured concentrations displayed on the y-axis.

Step 11 is the step of calculating rock matrix diffusion coefficients by modeling trends and patterns in collected data.

Method 200 may be used in a preexisting or newly drilled borehole without requiring extensive sample preparation, rock crushing equipment, or elaborate on-site analytical testing equipment and methods. Method 200 may be performed by one or more workers without the need for heavy duty winches or other mechanical means.

In various embodiments, Method 200 includes the step of using sensors to measure water pressure and other water characteristics, and analyzing the results to detect microflow and the presence of microfractures in the bedrock.

FIG. 4 illustrates hydraulic and chemical zone classifications for open-boreholes.

In the exemplary embodiment shown, zones can have one of three hydraulic classifications. Water can flow into a zone (active inflow), out of a zone (active outflow), or a zone can have no significant flow of water into or out of the zone (no flow/inactive). Zones can also have one of three chemical classifications. A zone can have no significant change in chemical concentration over time (static/no change in concentration), an increase in concentration over time, or a decrease in concentration over time.

In the exemplary embodiment shown, samples from the following zones, Active-Influx chemical, Inactive Chemical diffusion, and Inactive-Potential unidentified zones, are the most useful for calculating an accurate back-diffusion rate coefficient.

Claims

1. A low permeability rock matrix back diffusion testing system comprised of:

an upper conformable barrier and a lower conformable barrier which form an upper seal and a lower seal when in contact with the inner surface of a borehole;

wherein said upper seal and said lower seal form a plurality of test zones comprised of a lower test zone, a central isolated test zone and an upper test zone wherein each of said test zones has measurable chemical concentration values and hydraulic pressure values;

at least one lower test zone water line coupled with a lower test zone pump to enable the extraction of water from said lower test zone;

an air sparging conduit operatively coupled with a pressurized air source to expel contaminants from said central isolated test zone, wherein said air sparging conduit passes through said upper conformable barrier; and

a sparged contaminant conduit which passes though said upper barrier and said lower barrier to conduct sparged contaminants from said central isolated test zone.

2. The system of claim 1 which includes a test zone air line which conducts air to said lower test zone pump, which conducts water through said lower test zone water line and enables testing to obtain the hydraulic pressure values of said lower test zone independently from said central isolated test zone.

3. The system of claim 1 which includes a component for adjusting said hydraulic pressure values of said lower test zone while said hydraulic pressure values of said central isolated test zone remain constant.

4. The system of claim 1 which further includes an upper test zone water line and a central isolated test zone water line to conduct water independently from said upper test zone and said central isolated test zone.

5. The system of claim 1 which further includes chemical concentration sensors which independently measure said chemical concentration values of said upper test zone, said central isolated test zone and said lower test zone.

6. The system of claim 5 wherein said chemical concentration sensors are selected from a group consisting of water pressure sensors, water conductivity sensors, temperature sensors, dissolved oxygen sensors, oxidation-reduction potential sensors, turbidity sensors, total dissolved solids sensors, pH sensors, and water velocity sensors.

7. The system of claim 1 which further includes hydraulic pressure sensors which independently measure the hydraulic pressure values of said upper test zone, said central isolated test zone and said lower test zone.

8. The system of claim 1, wherein said upper conformable barrier and said lower conformable barrier are comprised of inflatable structures containing a gas.

9. The system of claim 8 wherein said inflatable structures are filled with a combination of gas and fluid.

10. The system of claim 1, wherein said upper conformable barrier and said lower conformable barrier are comprised of conformable material which conforms to the inner surface of a borehole to form a seal.

11. The system of claim 10, wherein said upper conformable barrier and said lower conformable barrier are comprised of a material which are disposable after a single testing session.

12. The system of claim 1, wherein said central isolated test zone includes a quantity of a detectible substance which indicates the presence of a leak in one or more of said upper and lower seals formed by said upper and said lower conformable barriers.

13. The system of claim 1 which further includes more than one of said upper conformable barriers and more than one of said lower conformable barriers.

14. The system of claim 1 which further includes a computer processing component which receives said chemical concentration values from said central isolated test zone.

15. The system of claim 14 which further includes a computer processing component which associates a time stamp with each of said chemical concentration values.

16. The system of claim 14 which further includes a computer processing component for performing a rock matrix diffusion calculation which calculates the change in said chemical concentration values over time for a given borehole radius.

17. A method for measuring back diffusion, comprised of the steps of:

placing a lower conformable barrier and an upper conformable barrier within a borehole to create a seal;

forming a central isolated test zone within a space between said lower conformable barrier and said upper conformable barrier containing a quantity of isolated fluid;

obtaining a first chemical concentration value associated with a first time;

sparging pressurized air into said central isolated test zone;

obtaining a second chemical concentration value associated with a second time; and

calculating the difference between said first contaminant concentration measurement and said second contaminant concentration measurement.

18. The method of claim 17 which further includes the step of adjusting lower test zone hydraulic pressure values while hydraulic pressure values of said central isolated test zone remain constant.

19. The method of claim 17 which further includes the step of performing a rock matrix diffusion calculation which calculates the change in said first and second chemical concentration values over time for a given borehole radius.

20. The method of claim 17 which further includes the step of monitoring for the presence of a detectible substance which indicates the presence of a leak in one or more of said upper and lower seals formed by said upper and said lower conformable barriers.