Electricity: measuring and testing – For insulation fault of noncircuit elements
Reexamination Certificate
1997-08-25
2001-12-18
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
For insulation fault of noncircuit elements
C324S512000, C324S715000, C324S718000
Reexamination Certificate
active
06331778
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to methods for the detection and location of leaks in containment facilities such as landfills, surface impoundments, storage tanks, or other like structures. This invention relates more specifically to methods for the detection and location of leaks in geomembrane lined containment facilities and the like, using mise-á-la-masse methods for collecting electrical potential data, mathematical inversion methods for characterizing electrical resistivity, and electrical resistivity tomography (ERT) methods. The methods are applicable to detecting and locating leaks in both newly installed and existing geomembrane lined containments and the like.
2. Description of the Related Art
The primary purpose of geomembrane liners, steel liners, and concrete liners utilized in various types of storage facilities is to provide barriers for liquids contained within the facility in order to prevent the leakage of these liquids into the surrounding environment. The detection and location of leaks in such liners is therefore a critical element in preventing environmental problems such as groundwater pollution and the like. Typical examples of such lined facilities include water reservoirs, surface impoundments, steel tanks, concrete tanks, landfills, leach pads, and other types of liquid and semi-liquid containment facilities. The majority of these facilities, especially those that contain groundwater contaminants, are lined with geomembrane liners.
During geomembrane liner installation the liner is inspected for leaks using visual inspection methods, vacuum box methods, air lance methods, spark testing methods, air pressure testing methods, or other types of well known test methods. These conventional test methods are typically limited to the testing of the liner seam areas. The majority of the liner is, therefore, only visually inspected for leaks.
More recently, electrical leak location methods have been used to detect and locate leaks in geomembrane liners. These electrical methods are capable of testing 100% of the liner area that is covered with water or soil. All of these existing test methods, however, including the electrical methods, require access to the interior of the containment facility by field personnel, or the placement of an electrical wire grid system under or on top of the geomembrane during construction. Electrical leak location methods are the only field proven methods that can locate leaks in a geomembrane liner when soil is placed over the liner. However, even the existing electrical methods require the collection of an array of electrical potential data on the surface of the soil using a close spaced survey grid of some type. A test method is therefore needed that can remotely and automatically detect and locate leaks in both new and existing liners without the need for an extensive survey grid.
U.S. Pat. Nos. 4,543,525; 4,719,407; 4725,785; 4,720,669; 7,751,841; 4,751,467; 4,755,757; and 4,740,757, are all directed to various systems and methods for electrically detecting and locating leaks in geomembrane liners. All of these systems, however, require either the extensive sensor grid structure described above, or require direct access by test operators to the interior liquid or sludge contained in the impoundment. Many of the systems described in these earlier patents involve complex and extensive electrical structures that must often be installed during the installation of the liner.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to eliminate the necessity of accessing the interior of a lined containment facility in order to test the containment liner for leaks. This is accomplished by making electrical measurements around the periphery of the liner, under the liner, or within the facility, and using computer software to process the electrical potential and/or electrical resistivity survey data.
Another object of this invention is to eliminate the need for collecting large amounts of electrical potential data in a close spaced grid pattern and to allow reduced amounts of data to be collected using widely spaced monopoles, dipoles, linear dipoles, broadside dipoles, or other electrode configurations.
Another object of this invention is to enable a containment facility to be monitored for leaks from a remote location an on a periodic basis, to warn facility operators of potential problems.
Another object of this invention is to detect and locate leaks at sites that contain material that can not be removed, by making measurements around the periphery, on top of the existing material, or between two liners within the facility.
Another object of this invention is to detect leaks in steel or concrete storage tanks by methods similar to those utilized in geomembrane lined facilities so as to eliminate the need for access to the interior of such containment vessels.
The methods of the present invention utilize electrical potential and electrical resistance measurements within the contents of the containment facility and within the sub-surface outside the facility, to detect and locate the presence of leaks in the lined containment. In most cases, it is assumed that the contents of the facility are electrically isolated from the sub-surface outside the facility by a geomembrane type liner which acts as a barrier to electric current flow. The methods of the present invention are, however, applicable to a containment facility constructed with an electrically conductive shell or barrier.
In a first method of the present invention, the contents of the containment facility are excited to an electrical potential above the surrounding soil. Any location where an electrically conductive liquid can pass through the liner and enter the sub-soil will also pass an electric current. The presence of this current demonstrates a fluid leak in the liner. In the first method, the electrical potential distribution set up in the sub-surface soil and within the contents of the facility due to the current flow through the liner is sensed by measuring the electrical potential at a series of electrodes (either outside the facility, in the soil, or inside the facility) and determining from the electrical potential profile, the location of the electric current flowing through the liner.
In a second method of the present invention, the electrical measurements detect and characterize changes in the electrical resistivity within the sub-surface soil outside of the containment facility. A base-line resistivity image is constructed and is later compared with subsequent resistivity images to detect and locate leak points in the liner. The electrical resistivity profile identifies changes in the sub-surface electrical characteristics brought about by the flow of a conductive liquid through the liner.
Other objects and applications of the methods of the present invention will become apparent from a reading of the following detailed description and the appended claims.
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W. Daiily, A. Ramirez, D. LaBrecque, and W. Barber 1995 (month unavailable) Electrical Resistance Tomography Experiments at the Oregon Graduate Institute;Journal of Applied Geophysics(33, 1995); pp. 227-237.
Thomas J. Yorkey et al. 11/87 “Comparing Reconstruc
Daily William D.
Laine Daren L.
Laine Edwin F.
Brown Glenn W.
Leak Location Services, Inc.
Walker LLP Jackson
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