CA2053539A1 - Structure for waste containment - Google Patents

Abstract

A B S T R A C T

A method and structure is described for containment of waste or contaminated material where the waste body is completely contained within a sealed impermeable membrane envelope encased within a concrete structure. Inspection and repair of the structure is enabled by a series of access tunnels running through the structure under the waste body.
Overlying the waste body is a self-supporting parabolic arch which enables buildings to be constructed over the structure. Noxious gas build-up within the waste body can be removed by venting to the exterior. Leakage from the waste body may be collected for analysis at various points of the structure.

Description

DESCRIPTION OF THE PRIOR ART

This invention relates to a method and structure for containment of waste or contaminated material.
There is a global problem regarding disposal of waste material. Increased production of industrial and household waste materials has not been met with corresponding advances in the technology associated with storage and disposal of wa~te material.
Frequently waste material is transported from the community where it is generated to a landfill site. Waste materials are deposited onto the site until such time as the site is full. The site may be then covered with clean fill, top soil laid, and the land used for recreational purposes.
No roads or buildings may be constructed over top of a landfill site due to its instability.
Additionally, contaminants from the waste material will pervade the surrounding soil and the ground water, resulting in widespread contamination and toxicity. A~
landfill sites, test wells are installed around the perimeters of the site and samples of the ground water are taken on a regular basis. Detection of contaminants in samples indicates that the landfill site is leaking contaminants into the ground water below the site. Further, erosion of the surface landfill allows surface water from rain to mix with the contaminated waste body below the ~ ' ~;~9 :

surface landfill, thereby creating more severe problems in terms of leaka~e of contaminants from the land~ill site.
Several proposals have been made to deal with the waste or contaminatPd waste.
U.S. Patent 4,6~7,954 discloses a basemented waste landfill site designed to carry heavy loads far long periods of time. The floor structure cvnsists of individual supporting elements o~ upwardly convex or concave forms, separated by seams from one another. The support: elements are arranged in a regular pat~ern in which zones are formed.
The upper surfaces of the support elements slop towards the feet which rest on piers. Such zones enable the gathering and drainage of seepage.
U.S. Patent 4,375,930 discloses a permanent disposal vault for containers containing chemical hazardous waste materials. The containers are distributed on the base surface of the vault separated from one another. The space between the deposited containers is filled with cementitious substance and the containers are then covered with a slab of cementitious substance. Each individual container is thereby isolated within a structural skeleton of the cementitious substance. Multiple tiers o~ containers may be accumulated in this fashion and then completely encapsula~ed within a permanent disposal vault. The vaul~ is further provided with an outlet conduit connected to a sump for monitoring any liquid accumulations from the encapsulated vault.

~:C~5~9 ; U.S. Patant 4,844,840 discloses a structure for hazardous waste containment wherein primary waste containers are placed in pre-fabricated canisters and sealed with a curable fluid sealant. The canisters are then stacked in an interlocking manner to form a stable integrated structure.
The containers are not permanently attached to one another so that individual containers are able to shift relative to one another in response to earth movement such as earthquakes.
The structure is placed over an impermeable bed used to collect leacha~e emanating from the waste canisters. The structure is covered with a la~er of clay, a layer of gravel and uncompacted fill which is then landscaped.
The prior art waste landfill sites or waste of disposal vaults only addresg the current problem of disposal of the contaminated waste or landfill. They do not address the long term problem of what to do with the site after it has been filled to capacity.

OBJECTS OF_INVENTION
The disadvantages associated with the prior art may be overcome by providing a self supporting structure which completely encapsulates the waste and which enables the construction of roads, buildings or recreational structures over the top of the site without interference with the encapsulated waste body.
It is a further objec~ of this invention to provide a '- , ~ ' :' . ~ ' ' Z(~ 9 concrete parabolic arch overlying the waste to prevent surface water ~rom mixing with the encapsulated wast body and to prevent external interference ~y animals and humans.
It is a further object of this invention to provide a structure having a basemented floor for supporting the waste body and for permitting access beneath the waste body to effect repairs.

SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided a waste containment structure which completely encapsulates the waste material, enabling the land above the structure to be developed and built upon. The structure consists generally of a graded foundation divided into sloping fields bordered by side walls and end walls. Arched support elements are erected upon the foundation, creating a network of tunnels for supporting a waste body. A graded surface is prepared overtop of the arched support elements and divided into zones corresponding to the sloping fields of the foundation. A first impermeable membrane overlies the graded surface and underlies the waste body. A second impermeable membrane overlies the waste body and is sealed with the first impermeable membrane to completely encapsulate the waste body. A parabolic arch extends from one side wall to the othex side wall over the encapsulated waste body, enclosing the was~e body. Venting is provided through the 2~

membrane and the arch to the ext~rior through the top of the structure to remove noxious gases produced by the waste body for analysis and treatment as requirecl.
In operation, any fluid leak~ng from the waste body will be collected in the upper zones and drained through to the corresponding field in the foundat:ion. The fluid will be collected at a collection basin centrally located in each field, and will then be analyzed and diverted via valved pipes to be treated.
The arch is self-supporting, thereby enabling structures to be constructed over top of the containment structure.

DESCRIPTION OF THE DRA~INGS
In drawings which illustrate embodiments of the invention, Fig. 1 is a front elevational view of the preferred embodiment of the waste containment structure illustrated in section, Fig. 2 is a perspective view, partly in section, of the waste containment structure of Figure 1, Fig. 3 is a plan view, partly in section, of the waste containment structure of Figure 1, Fig. 4 is a front eleYational view o~ the side wall of the embodiment of Figure 1, Fig. 5 is a perspective view o~ a modular form unit of the - .

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2Ir ~ ? ~ e~9 embodiment of Figure 1, Fig. 6 is a plan view of a plurality of modular form units arranged in an array of the emhodiment of Figure 1, Fig. 7 is an obl~que exploded view o~ thP basemented structure and the field arrangement of the embodiment Figure 1, Fig. 8 is a cross-sectional view of the embodimen~ of Figure l through the expansion join~ between each field, Fig. 9 is a cross-sectional view of the embodiment of Figure 1 through the high points between each field where no expansion joints are required.

DETAILED DESCRIPTION OF TH~ PREFERRED EMBODIMEN~
With reference to Figures 1 and 2, the general arrangement of the waste containment s~ructure 1 is illustrated. ~enerally, waste containment structure comprises foundation 10 extending from side wall to side wall 12 and from end wall to end wall 14. Overlying foundation 10 are modular form units 16 which are placed in an array forming a series o~ tunnels. Over top of the modular form unit 16 is poured a concrete waste floor 18. The waste floor is covered with a lower impermeable membrane 20 extending over the entire surface of the waste floor 18. A concrete covering 22 is placed over top of the lower permeable membrane, presenting a surface which the was~e body 24 may be deposited thereover~ Overlying the waste body 24 and in -sealing engagement with the lower impermeable membrane 20 is upper impermeable memb~ane 26. The top of the waste body 24 is covered with a concrete parabolic arch 28. A sealant 30 covers the parabolic arch 28. Landfill 32 may be deposited over top of the structure ~or landscaping or the construction of buildings 34. Vents 36 which extend through the landfill and into the waste body may also be installed.
Governments have passed regulations regarding the safe disposal of waste. These regulations must be consulted before a waste site is selected and construction commenced.
However, for the purposes of this invention, any open space which can be excavated is suitable. Abandoned gravel pits or other sites of open pit mining would be particularly suited for this invention. Abandoned gravel pits are particularly well suited for this invention as large scale excavation has already been completed.
Once the site is selected, foundation 10 is prepared.
The foundation 10 is graded level and then compa~ted using known methods. The area to be graded and compacted corresponds to the selected dimensions overall of the structuxe 1. In the preferred embodiment, of the waste structure 1 is rectangular in plan view. However, any number of shapes may be utilised for the waste structuxe. Further, a~ illustrated in figure 3, several like structures may be constructed side by side or end to end using common walls 12 and 14 to increase the capaci~y of the waste site.

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2~ 19 With reference to Figure 7, the foundation 10 is divided up into a number of zones 38, 40, 42 and 44. The number of zones depends on the dimensions of the waste containment structure 1. Each zone is identical and constructed in a similar manner.
The foundation 10 is providec~ with a gravel layer 46 which is further compacted and leva~led. Installed in gravel layer 46 is a series of pipes 48 which run substantially parallel to the side walls 12. At the centre of each zone 38, 40, 42 and 44 is a catch basin 50. Catch basin 50 extends below the surface of the lower level of the gravel layer 46.
Flexible pipes 48 extend from catch basin 50 of one zone to the catch basin o~ the next adjacent longitudinally extending zone. For example catch basin of zone 38 is joined to the catch basin of zone 42 and similarly the catch basin of zone 40 is joined by pipe 48 to the catch basin of zone 44. Pipe 48 drains to a water treatment plant for treating the liquids which accumulate in catch basin and drained through pipes 48 for the safe disposal thereof. The drainage system also provides a means for draining water from the site during the construation process.
; A poured concrete floor 49 is constructed in zones 38, 40, 42 an~ 44, each zone sloping downwardly from the outer perimeter thereof to the centre where catch basin 50 is located. Each zone 38, 40, 42 and 44 is constructed using ~r~?~

reinforced concrete. Between each adjacent zone, a compressible and expandable material 80 is inserted between the concrete floors 49 of adjacent zones to keep the ioint sealed.
5Any time after the preparation of the compacted gravel layer 46 has been completed, side walls 12 and end walls 14 may be constructed. The ~imensions of the side walls 12 and end walls 14 depend on th~ dimensions of the waste containment structure 1 and the anticipated loading o~
10any structures 34 to be built over ~op of the waste containment s~ructure 1. The dimensions of the side walls 12 and end walls 14 are dictated by local building codes such as the National Building Code in Canada. A structural engineer could easily calculate the requisite dimension~ for specific 15loading requirements.
As illustrated in figure 4, the preferred cross-sectional shape of side wall 12 and end walls 14 has a rectangular base portion ex~ending substantially perpendicular to the level surface of foundation 10 and a 20triangular top portion for joining with the roof as described hereinafter.
A modular form unit 16 is placed on floor 49, as illustrated in Figure 5. In plan view, modular form unit 16 is substantially square. Each corner of the modular unit has 25a corner r moved defining surface 52 such that when like modular units 16 are adjacent to one another in an array as .~ , ~ .

2 ~? ~9 illustrated in Figure 6 a pillar s~ructure 54 is defined.
The upper surface 56 of modular fo~n unit 16 has a curved surface which merges with leg surface 52. Each side wall of the modular unit 16 is provided with an archway 58 such that when like units are placed side by side in array there is defined a series of tunnels forming a grid ~elow upper surface 56.
As illustrated in figure 6, the first modular form unit 16 is placed directly over top of catch basin 50 with like units placed side by side to form an array. Between the units 16 at each corner thereof, a form for pillar structure 54 is established.
A drain pipe 60 extends through the upper surface 56 of the modular unit at the vertex thereof. Drain pipe 60 drains into the catch basin 50.
Modular unit 16 can be fabricated from a precast reinforced concrete. They may either be precast and manufactured away from the site and then delivered upon completion and when necessary, or cast on site.
Once the modular ~mits have been placed side-by-side and completely filled a zone the waste floor 18 may then be prepared. The surface of the waste floor 18 is sloped in a similar fashion and degree as founda~ion 10. ~t the lower most point of ~loor 18 is drainpipe 60.
Waste floor 18 is constructed by reinforced cast in place concrete which is p~ured over top o~ the modular forms 16 and filling the pillars 54, presenting an upper field 62 which corresponds in size to zone 38.
Adjacent fields have corresponding fields 64, 66 and 68, which correspond in size and location. Adjacent fields are joined in a similar fashion as ~etween zones, namely, a compressible and expandable material 84 is inserted between waste floor 18 of adjacent fields to keep the joint sealedO
The joint is then covered with a formed steel p].ate 86 to cover the joint~ Between the plate 86 and waste floor 1~, a sealing material 88 available under the trade-mark Bentonite is injected to seal the joint.
Floor 49 and waste floor 1~ of each field and zone respectively have been described as being a single poured concrete unit and ha~ing corresponding ~oints therebetween.
However, floor 49 and waste floor 18 may be constructed using several sections and therefore would have corresponding joints. Figure 9 illustrates such a joint. Extending between adjacent sections of floor 49 and waste floor 18 are the reinforcing steel rods 90 with cross reinforcements extending substantially perpendicular to rods 90. Lower tie strip 92 is poured after floor 49 of adjacent zones is poured. This will permi~ sufficient time to permit floor 18 to shrink to its finished size. Similarly upper tie strip 94 is poured after waste ~loor 18 is poured to reduce the effects of shrinkage of the concrete.
The total number of zones and fields depends on their :

s?~3 respective area. However, the entire area being bounded by side walls 12 and end walls 1~ must be completely covered.
Each field is covered with a lower impermeable membrane ~0. The impermeable membrane is preferably made from a polyvinylchloride (PVC) ma~terial of a thickness suitable to prevent liquids from passing therethrvugh. Each adjoining field is covered with an impermeable membrane and is sealed at its respec~ive edges to the membrane of the adjoining field. Heat sealing the membrane is suitable however, other methods may be used of sealing the impermeable membrane.
Where the field abuts with side wall 12 or end wall 14, and impermeable membrane layer covers the wall 70 of side wall 12 or end wall 14 upwardly ~rom the lower membrane 20. The side wall covering is joined with the lower membrane 20 using conventional sealing methods.
A thin layer of concrete is poured over top of the lower membrane 20 to form a waste floor 22, which extends over the entire area defined by the side walls 12 and end walls 1~, leaving openings for drainpipes 60 to communicate with the waste body 24. The waste floor 22 reduces the risk of the lower membrane 20 ~rom being damaged during the period of depositing the waste on the site.
The landfill site is now ready for receiving the contaminated waste or land~ill to form waste body 24. Trucks loaded with landfill, waste or contaminated waste may drive d ~:3 over the waste floor 22 for deposit of the waste where desired.
The waste or landfill is deposited o~er top of the waste floor 22 such that the greatest height of the landfill will be at the mid-point between the end walls 14. The waste is deposited commencing at one end of the waste floor 18.
The upper surface of the waste body 24 is graded to a parabolic shape as viewed in cross-section.

The mid-point height of the upper surface of the waste body increases parabolically in longitudinal cross-section until a maximum height is obtained. The mid-point height increases gradually until it reaches a maximum desired height. As the landfill site continues further longitudinally from the end wall 14 the mid-point height is maintained at the maximum until a point where the mid-point height may ~e gradually decreased as the same rate as increased of the first part of the landfill site~ The upper surface of the completed waste body 24 is substantially Z0 uniorm in cross-section both in the longitudinal and cross-sectional directions.
As the top of the landfill site is prepared and graded to the requisite parabolic arch, the landfill may be covered with an upper impermea~l~ membrane 26. The upper permeable membrane is sealed with the lower impermeable membrane 20 where i~ extends upwardly along the wall 70 and ' ' .

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At approximately 150 ft. intervals, a vent 36 is installed at the apex of the parabolic arch. The vent extands from the waste body through the upper impermeable membrane and through the parabolic arch 28 and continues to extend upwardly to the desired level.
Once the waste body is completely covered the upper membran~ is sealed with the lower membrane. The construction of the parabolic arch commences at one end and prugresses along the length of the site until it joins and seals at the end wall o~ the structure. once the waste body is completely encapsulated, uncontaminated landfill may then be deposited over top of the parabolic arch and landscaped as desired.
The upper surface of the waste body 24 acts as a lower form for a parabolic arch 28 to be constructed thereon.
A reinforced concrete parabolic arch 28 is poured over top of the upper impermeable membrane 26 which extends from the vertex 78 of side wall 12 to the vertex on the opposite side wall 12. As the concrete cures, it becomes a self-supporting structure o~erlying the waste body 24. The parabolic arch 28 is then coated with an impermeable sealant 30. The thickness of the parabolic arch 28 depends on the distancP between side walls 12 and endwalls 14 and the anticipated loading overtop of the arch 28.
The parabolic arch is completely self supp~arting.
Further, ~he parabolic arch is capable of supporting not only ~t-,~,'?~3 th0 loading of the uncontaminated landfill but also small structures in buildings which may ~e used for recreational, housing or other commercial purpose~;. For instance, golf courses can be constructed with a club house built on the site. Other numerous possibilities for the upper surface is unlimited.
In operation, the waste body is completely encapsulated within the membrane 20 and 26. Theoretically, the membrane maintains the waste including any gases generated by the waste or any liquid within the waste to be contained within the membrane 20 and 26. However, known technology does not provide a material which is compl~tely impermeable to all substances. Therefore it is possible that leachates may escape from the membrane and pass into the adjoining s~ruc~ure. Electronic sensors installed throughout the structure may be used to de~ect the presence of toxic or contaminated waste which escape from the waste body 24.
If some leachate does pass through the impermeable membrane, the leachate ought to follow the path of least resistance. The designed water flow is that the leachate will flow downwardly along concrete surface 72 and down the inclination of such surface towards the drainpipe 60. The leachate will flow down the drainpipe 60 and into catch basin 50. Pipes 48 are provided with valves to regulate the flow from catch basins 50.
If the leachate does not follow this path and finds ~J?.-~3 another path down through the modular unit level, the leachate will ~hen fall on to the surface of each zone 38, 40, 42 and 44. The water will then flow downwardly towards the catch basin 50.
Catch basin 50 is regular~y monitored by taking samples of the leachate uncovered in each catch basin 50. If the liquid in the catch basin is analyzed to be contaminated or toxic, the liquid transpor~ed by pipes 4~ to the location where the leachate may be decontaminated and disposed safely.
10 If the leachate is analyzed to be not toxic or contaminated, it is then drained in the normal course.
Similarly, vents 36 are used to allow gasses which are generated by the wa~te body to be exhausted. The exhaust is sampled to determine whether the exhaust is contaminated 15 or toxic. If it is determined to be safe then the gas is exhausted to the atmosphere. If not, the exhaust is pumped to a holding tank where it may be transported for decontamination.
The invention has been described in some detail by 20 way of illustration and example for ~le purpose of clarity.
However, certain changes and modifications could be made without departing from the spirit and scope of the invention.

Claims (8)

1. A structure for the containment of a waste body and for supporting dynamic and static loads thereover, comprising:
a foundation having a graded and compacted sub-grade under a concrete base surface;
reinforced concrete side and end walls extending about the perimeter of said foundation, said walls adapted for receiving a parabolic arch and supporting said loads;
a plurality of concrete arched support elements mounted on said base surface arranged in an array providing a series of tunnels over the base surface and providing access beneath said waste body;
a waste floor constructed on said plurality of support elements, said waste floor being divided into a plurality of collecting fields for channelling leachate emanating from said waste body to a catch basin;
a first impermeable membrane overlying said waste floor for receiving waste to form said waste body;
a second impermeable membrane overlying said waste body and sealingly engaging said first impermeable membrane for encapsulating said waste body;
said reinforced concrete parabolic arch extending across from side wall to side wall and from end wall to end wall to cover said waste body, said arch adapted for supporting said loads thereover; and means for transporting leachates from said catch basin for analysis and disposal.

2. A structure as claimed in claim 1 wherein said waste floor is a reinforced poured concrete layer poured over said plurality of support elements.

3. A structure as claimed in claim 2 wherein said plurality of collecting fields comprises a surface having a central point and a perimeter wherein said surface slopes downwardly from the perimeter to the central point.

4. A structure as claimed in claim 3 wherein said catch basin is constructed in said base surface and connected with a drain pipe located at said central point of said collecting field for receiving leachates and connected to a flexible pipe for transferring said leachates for disposal and decontamination.

5. A structure as claimed in claim 4 wherein said means for detecting leachates includes electronic sensors installed throughout said structure.

6. A structure as claimed in claim 5 wherein said means for collecting leachates includes a plurality of vents through said parabolic arch for discharging gases.

7. A structure as claimed in claim 6 wherein said structure further includes a layer of concrete poured over said first impermeable membrane providing a surface whereover trucks carrying the waste may drive preventing damage to said first membrane.

8. A structure as claimed in claim 7 wherein said base surface is divided into a plurality of collecting zones for receiving leachate from said waste body, said collecting zones corresponding in size and shape with said plurality of collecting fields.