The present invention relates generally to an apparatus and method for testing the integrity of landfill liners principally employed in solid waste disposal sites. More particularly, the present invention discloses an apparatus and method for testing the integrity of liners installed in solid waste landfill sites prior to opening the site for waste disposal. Further, the present invention permits periodic testing of landfill liner integrity after the waste disposal site is open, during the time it is being filled and after the waste disposal site is closed.
In the United States alone about 160 million tons of solid waste are generated each year. This translates to approximately 31/2 pounds of refuse per person per day. Landfills currently receive about 80% of all garbage and are rapidly filling up. (See, e.g., 107 U.S. News & World Report, No. 25, pp. 60-61 (Dec. 25, 1989)). The rapid growth of governmental legislation pertaining to management of waste disposal, coupled with the growing public concern about the long and short-term environmental impact of waste disposal facilities, has increased design complexity of waste disposal facilities. Moreover, the rapidly declining availability of landfill solid waste disposal sites is reaching a critical point. New landfill sites will have to be opened, or other less environmentally safe methods of solid waste disposal, e.g., ocean dumping, incineration, etc., will have to be employed. The public's awareness of the waste disposal dilemma has only recently captured broad public attention. With this attention, the public has been and will, increasingly, demand more and safer disposal sites.
Most landfills have an impermeable liner which acts as a leakage barrier between the landfill and the underlying soil. When building a new landfill site, it is customary to prepare an underlayer of compacted sand or clay which serves as a bed for the liner. After installation of the liner, another sand or clay overlayer is provided on top of the liner. The disposed trash is then filled onto the composite layers. The proper function of waste disposal facilities depends upon the integrity of the landfill liner. Generally, liner failure is not detected until the waste leaches into the underlying soil and causes environmental damage.
Under present efforts to prevent leachate from reaching the subsurface soil area underneath the landfill, numerous systems have been developed to test liner integrity:
a) leak prevention through an induced hydraulic gradient between a plurality of liners (See, Mutch, R. D., U.S. Pat. No. 4,335,978, Issued June 22, 1982, Induced Intragradient System for Secure Landfill);
b) collecting leachate and detecting the presence of leachate in a sump (See, Turner, D. M., U.S. Pat. No. 4,810,131, Issued Mar. 7, 1989, Landfill Leachate Collection and Leak Detection Sump System);
c) providing a liquid collection zone at a level beneath the landfill and determining the presence of leachate in the liquid collection zone (See, Bennett, R. J., U.S. Pat. No. 3,505,820, Issued Apr. 14, 1970, Leak Detection for Lined Reservoirs);
d) collecting and treating landfill leachate (See, Lavingne, R. L., et al, U.S. Pat. No. 4,276,164, Issued June 30, 1981, Effluent Treatment System: Leachate, Landfill);
e) detecting loss of gas pressure in a gas pressurized annulus about an underground storage zone (See, Butler, W. J., U.S. Pat. No. 4,474,053, Issued Oct. 10, 1984, Storage or Disposal Cavern Leak Detection and Loss Prevention);
f) applying an external electrically conductive metal foil liner to the impermeable landfill liner, applying an electrical potential to the liner to determine if a leak exists (See, Benard, G. J., et al, U.S. Pat. No. 3,252,155, Issued May 17, 1966, Liquid Receptacle and Method for Preparing Same);
g) providing a tank liner with fluid passageways to conduct fluid entering a tank to a drain pipe; (See, Wagner, R., U.S. Pat. No. 4,787,772, Issued Nov. 29, 1988, Device for Detecting Leaks in Underground Fluid Tanks);
h) using a leak flow rate measuring apparatus, to determine the rate of flow of an impounded liquid through an opening in a geomembrane liner, which employs a pair of spaced voltage measuring sensors which measure voltage across a liquid passage (See, Cooper, John, W., U.S. Pat. No. 4,755,757, Issued July 5, 1988, Fluid Leak Detection System for Determining the Fate of Leakage Through a Geomembrane);
i) disposing an electrically conductive liquid between two contiguous liners, applying an electrical current to the liquid and sweeping the landfill surface with magnetic surfaces for magnetic field variations indicating leakage of the fluid through the lower liner (See, Converse, M. E., et al, U.S. Pat. No. 4,740,757, Issued Apr. 26, 1988, Method and Apparatus for Locating Leaks in a multiple layer Geomembrane Liner);
j) using an electronic directional potential analyzer having a differential voltage detection probe which is moved through a conducting liquid contained within a liner to measure a differential potential between electrodes on the probe relative to positions in the liner (See, Converse, M. E., et al, U.S. Pat. No. 4,725,785, Issued Feb. 2, 1988, Directional Potential Analyzer Method and Apparatus for Detecting and Locating Leaks in Geomembrane Liners);
k) employing a liner having a sheet of electrically insulating material supported by an electrically conductive medium, applying an electrical potential between fluid retained within said liner and the supporting medium and determining whether there is a change in the electrical potential as an electrode is moved about the fluid surface (See, Boryta, D. A., et al, U.S. Pat. No. 4,543,525, Issued Sept. 24, 1985, Method for Determining a Leak in a Pond Liner of Electrically Insulating Sheet Material); or
l) providing a set of channels adjacent to a liner, each of the channels having a plurality of lateral openings into a surrounding casing and a series of connecting tubes connected to the channels to locate leaks in nuclear reactor liners (see, Escherich, K. H., et al, U.S. Pat. No. 4,341,110, Issued Mar. 23, 1982, System for Locating Leaks in the Liner of a Pressure Vessel Equipped with Cooling Tubes; for Nuclear Reactors).
There is a recognized need, therefore, for an apparatus and method for testing the integrity of landfill liners prior to opening of the landfill for refuse disposal and for periodically testing the integrity of landfill liners.