Waste disposal landfill

A waste disposal landfill comprises a layer of porous material such as stone or crushed concrete applied over the waste before the final cover. Conduits extend from the layer through the cover to atmosphere and terminate in self-aligning airscoops. Ventilation through the porous layer occurs in response to ambient winds to remove water from the landfill especially that intercepted and temporarily retained by the porous layer and thus inhibit leachate formation.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates generally to waste disposal landfills and is 
particularly concerned with abatement of leachate formation in a waste 
disposal landfill. More specifically, leachate abatement is accomplished 
by a ventilation layer with means to induce airflow through the 
ventilation layer so as to evaporate water which may have intruded into 
the landfill and to remove the water from the landfill. 
There exists substantial concerns about the possibility and potential 
adverse consequences of long-term leachate formation within hazardous 
waste disposal landfills. Indeed, governmental regulations have recently 
mandated positive means for inhibiting formation of and removing leachate 
from hazardous waste disposal landfills during their active lives. For 
example, sloping the bottom liner of the landfill, providing a collection 
drainage blanket and collection pipe, and specific treatment of leachate 
are mandated. 
Notwithstanding stringent requirements for both the bottom liner to 
preclude exfiltration of any residual leachate and providing a highly 
impermeable and properly sloped cover for the landfill, there is still 
concern that some small portion of the local precipitation will find its 
way through the final cover and over a period of time generate appreciable 
leachate which in turn may escape the landfill. If nothing else, slowly 
accumulating leachate could fill and ultimately spill from the landfill 
(so called bathtub effect). 
The currently specified remedy for this is to periodically pump such 
leachate as may accumulate from the collection system for an indefinite 
period of time. This is both expensive and bothersome, and there will be 
the temptation to delay pumping until a "worthwhile" amount of leachate 
has accumulated. This will increase the risk that some of the leachate 
will exfiltrate in an uncontrolled and undefined amount. 
The present invention is directed to providing a new and improved waste 
disposal landfill with a particular improvement in abating leachate 
formation. Through such abatement, the concerns expressed above will be 
substantially lessened, if not entirely eliminated. In addition to its 
objective attributes in minimizing or eliminating leachate formation, the 
invention possesses the advantage of being a purely mechanical system 
comprised of relatively inexpensive, proven, and readily available 
materials and apparatus. Moreover, it can be easily inspected and repaired 
if necessary. It is also redundant and can be modified without the 
necessity of exposing the in situ waste. The system can be installed to 
supplement the final cover of a waste disposal landfill over a wide range 
of suspect or uncontrolled hazardous wastefills thereby to provide assured 
long-term abatement of surface infiltration and consequent leachate 
generation and possible migration from the landfill. 
The invention arises in part through applicant's recognition that at most, 
if not all, current or potentially available landfill sites, certain 
natural conditions or circumstances prevail which can be used to advantage 
in substantially minimizing or entirely eliminating leachate formation. 
Included among these conditions and circumstances are the following: (A) 
generally less than one inch of annual rainfall is likely to infiltrate 
through a proper final cover of a waste disposal landfill; (B) there are 
extended periods of time during which the ambient atmospheric relative 
humidity is below 100%; (C) during a preponderance of the year, the dew 
point temperature of ambient air is well below that of the prevailing 
temperature in the upper portion of the waste landfill (i.e. immediately 
below the final clay cover); and (D) during a preponderance of the year 
there are appreciable natural wind currents. 
Recognizing and utilizing these naturally occurring environmental 
phenomena, applicant has invented a waste disposal landfill in which the 
ambient relatively dry atmospheric air (relative humidity less than 100%) 
is forced by natural wind forces through a porous ventilating layer 
interposed between the top of the waste and the underside of the final 
cover. The ventilating layer will intercept and temporarily retain the 
limited volumes of moisture which may percolate from the overlying cover. 
The concomitant air movement through the layer will tend to evaporate, 
convey and remove any free moisture which it encounters as well as to 
diffuse through and thereby reduce the overall humidity of air which it 
may encounter in the layer. 
In one embodiment of the invention, air enters through intake pipes located 
at the periphery of the covered landfill and exits from one or more 
centrally located exhaust pipes. Both are provided with self-aligning 
airscoops. Intake pipes are provided with self-aligning airscoops to face 
upwind and to provide a partial positive pressure; exhaust pipes with an 
analogous self-aligning airscoop facing downwind to provide a partial 
negative pressure, thereby to facilitate movement of ambient air through 
the ventilating blanket layer. The number and location of pipes are chosen 
to provide adequate ventilation below the entire area of the final cover. 
It is possible to utilize the invention with either a fully enclosed 
landfill (i.e., one having an impervious bottom liner) or a partially 
enclosed landfill (i.e. without impervious bottom). In the latter case, a 
wick and blanket capillary system may be used to provide a blanket portion 
coextensive with the ventilation layer and with a wick portion extending 
through the waste material to a level below that of the prevailing water 
table. The capillary action will be effective to induce a capillary flow 
of any accumulated water upwardly within the landfill to the ventilating 
layer where it is removed in the manner explained above. With the 
partially enclosed landfill being in hydraulic communication with the 
surrounding water table, the capillary action creates a hydraulic gradient 
from the water table toward the interior of the reservoir so as to thereby 
impede the recharge of ground water which is being removed from below the 
waste deposit. The rate is sufficient to maintain the interior free water 
level below that of the surrounding water table and the hydraulic gradient 
thus created inhibits the outward excursion of leachate which might 
otherwise occur. 
Several embodiments of the invention are disclosed herein in order to 
illustrate its principles.

DESCRIPTION OF PREFERRED EMBODIMENT 
FIGS. 1, 2 and 3 illustrate a first embodiment of waste disposal landfill 
10 embodying principles of the present invention. The landfill comprises 
an in-ground reservoir 12. Where the existing soil conditions are such 
that the soil is not effective to contain waste material within the 
reservoir without leaching, an impervious bottom liner 14 of suitable 
material, typically clay or highly impermeable plastic membrane(s), is 
used to line the reservoir. The reservoir is then filled with the waste 
material 16. 
In accordance with prior constructions, the landfill, after having been 
filled with waste material, is then closed, or capped, by a final cover 18 
which is highly impermeable to water and leachate, for example clay. 
Preferably, the landfill cover is shaped with a central crown so that 
natural drainage carries precipitation outwardly beyond the perimeter of 
the reservoir. 
The prior constructions also typically included a collection pipe 22 at the 
bottom of the reservoir for collecting leachate. The collection pipe was 
typically associated with pumping mechanism (not shown) which would pump 
the collected leachate from the reservoir so that outflow and overflow 
would be avoided. This prior construction, however, was susceptible to the 
disadvantages enumerated earlier. 
In accordance with principles of the present invention, a ventilation layer 
24 is included in the construction of the landfill. The ventilation layer 
comprises accessible air passages (i.e., the layer is porous), and 
appreciable surface area to intercept and temporarily hold infiltrating 
moisture. The preferred construction contemplates the use of larger sized 
uniform graded stone or crushed concrete as the material forming the 
layer. The layer is applied after the reservoir has been filled to a 
suitable level with the waste material 16. Crowning remains a preferred 
constructional technique, although it will be recognized that crowning is 
not essential to practice of the principles of the invention in its 
broadest aspect. The ventilation layer has air spaces forming air passages 
throughout, and the size of the stone and/or crushed concrete is selected 
so as to provide approximately 30% to 50% air space of the total overall 
volume occupied by the layer. After the ventilation layer has been formed, 
then the closing cover is applied. In this way, the ventilation layer 
provides subjacent support for the clay cover 18. 
Ventilating airflow is created throughout the ventilation layer by means of 
a ventilation system which in the preferred embodiment comprises a 
plurality of vent pipes, or conduits, communicating the ventilation layer 
to atmosphere. The illustrated embodiment 10 comprises a central 
ventilation conduit 26 and six ventilation conduits 28 at locations around 
the margin of the perimeter. The drawing figure is merely illustrative of 
principles of the invention and is not to any particular scale. Each of 
the ventilation conduits comprises a self-aligning airscoop at its point 
of communication to atmosphere. The airscoops are of conventional design 
capable of freely revolving about the corresponding vertical pipe to face 
either upwind or downwind as will be explained. For central conduit 26, 
the self-aligning airscoop is designated by the reference numeral 30 while 
the reference numeral 32 designates the self-aligning airscoops for the 
outer conduits 28. 
The drawing illustrates the conduits 26, 28 as being vertically disposed. 
The lower ends of the conduits terminate within the ventilation layer, for 
example about halfway through its thickness. 
The self-aligning airscoops are illustrated as 90.degree. elbows having 
openings disposed in generally vertical planes so as to face horizontally. 
The airscoop 30 is configured with a vane 31 so that its opening to 
atmosphere faces downwind while each of the self-aligning airscoops 32 is 
configured with a vane 33 to face upwind. 
This construction results in the creation of pressure differentials in the 
ventilation layer between conduit 26 and conduits 28 giving rise to flow 
in the ventilation layer. Ambient air entering one of the airscoops 32 
around the perimeter is conducted through the corresponding ventilation 
conduit 28 and through a path in the ventilation layer to the central 
conduit 26. This air will at most times have a relative humidity of less 
than 100%. In passing through the ventilation layer, air will tend to pick 
up water vapor present in the ventilation layer and to promote the 
evaporation of any liquid water present especially from the surfaces of 
the ventilating layer or underside of the clay cover. The moisture is 
carried by the air through the central conduit 26 to exhaust to atmosphere 
via the central air scoop 30. 
It can thus be perceived that the invention makes accessible and utilizes 
the induced natural convection flow of ambient air through the ventilation 
layer in response to any direction of ambient wind so that moisture is 
thereby removed from the landfill and a tendancy toward evaporation of 
water is created within the landfill. 
The invention can preclude the need for a collection pipe and pumping 
system to remove accumulated leachate at the bottom. However, the 
invention may be used with or without that or any other additional type of 
system. 
It can be perceived that the invention is advantageous in that it is 
entirely a passive system, constructed from existing readily available and 
inherently durable devices and materials. The stone or crushed concrete 
layer is a readily available material and can be readily applied to cover 
the waste in the reservoir. It maintains suitable air voids for the flow 
of air and will intercept and temporarily retain percolating surface 
moisture and it provides subjacent support for the clay cover. The 
ventilation pipes and self-aligning airscoops are also conventional, 
readily available and relatively inexpensive devices. 
It will also be noted that the ventilation structure is contained entirely 
above the level of the waste material and, hence, inspection and repair, 
if necessary, can be readily accomplished without having to expose the 
waste. Moreover, the system can be added to or subtracted from without 
having to expose the waste. Because it is entirely passive, operating 
through the natural phenomena referred to above, the invention is 
extremely efficient both in construction and in use and it is entirely 
compatible with the surrounding environment. 
During certain times under certain ambient conditions (high relative 
humidity, absence of wind, etc.) the system will be relatively inactive. 
However, prevailing climatological conditions over time will give rise to 
a preponderance of favorable factors adequate to provide a sufficient 
level of average airflow to prevent water which may intrude into the 
landfill from percolating through the waste material to where it may 
collect and escape the enclosure. The exact sizes, locations, etc. and 
numbers of ventilating elements can be determined from engineering 
calculations and/or emperically and with reference to available ambient 
environmental data. Hence, the drawings are illustrated on an arbitrary 
scale and are merely to intend to disclose the principles of the 
invention. Other configurations may also be used to advantage. 
One such configuration is illustrated in FIGS. 4 and 5. Arbitrarily a 
rectangular shape landfill is shown in which a pair of distribution 
conduits 34 and 36, respectively, are shown extending horizontally along 
opposite sides of the facility. These distribution conduits are disposed 
parallel within the ventilating layer and extend lengthwise within the 
ventilating layer throughout their full length. Each contains a series of 
spaced apart apertures 38 which face those of the opposite conduit in the 
installed position. Also in communication with each distribution conduit 
34, 36 is a corresponding communication conduit 40, 42, respectively, 
which extends vertically upwardly from a central region of the 
corresponding distribution conduit 34, 36 to atmosphere. The conduit 
passes through the clay cover 18 and on the exterior portion is provided 
with a self-aligning airscoop 44, 46. The construction of the airscoop 44 
is such as to face upwind while the airscoop 46 is constructed to face 
downwind. The air flow in response to a prevailing wind is such that air 
enters the airscoop 44 passes through the conduit 40 to the distribution 
conduit 34. From there, air passes through the apertures 38 of conduit 34 
into the ventilation layer. It passes across the ventilation layer to 
enter the apertures 38 of distribution conduit 36 and from there passes 
upwardly through conduit 42 to be discharged via airscoop 46. 
FIGS. 6 and 7 illustrate yet another configuration in which multiple 
vertical conduits 40 are associated with each distribution conduit 34 and 
multiple conduits 42 which each distribution conduit 36. The pattern is 
such that the conduits 42 are offset from the conduits 40 in the direction 
lengthwise of the conduits 34, 36. The pattern of FIG. 6 illustrates a 
landfill containing a repeat pattern of ventilating layer constructions. 
The repeat patterns are separated by a clay cutoff 50. Once again, the 
scale is entirely arbitrary in the drawings since they are intended to 
illustrate general principles of the invention. Moreover, the number of 
repeat patterns is also arbitrary. 
The other details of the construction and operation of the FIGS. 6 and 7 
configuration correspond to details described in connection with the 
configuration of FIGS. 4 and 5. 
FIG. 8 illustrates a further embodiment of landfill 60 which differs from 
the first embodiment of FIGS. 1-3 in that instead of the reservoir being 
fully lined by an impervious bottom liner, it comprises a circumferential 
vertical barrier 62 within which the waste material is contained. In this 
embodiment, the waste material may extend downwardly to a level 64 which 
is below that of the prevailing ground water table level 66. As such, the 
reservoir is only partially enclosed and is in hydraulic subterranean 
communication with the existing water table. In this embodiment, means are 
provided to impede recharging by the existing aquifier of the water 
removed from the waste reservoir such that an inward hydraulic gradient is 
consistently maintained which is effective to prevent outward excursion of 
contaminated waters which may have been in contact with the waste (i.e. 
leachate). 
The means for doing this is illustrated by itself in FIG. 9 and comprises a 
capillary blanket and wick construction. The blanket portion 68 is 
disposed at the ventilating layer. The wicks 70 extend from the blanket 
downwardly through the waste to a level below that of the water table 66. 
This structure creates by capillary action an upward movement of water 
through the waste which gives rise to the inward hydraulic gradient 
referred to above. The upward flow of moisture is promoted through the 
operation of the ventilation layer in the manner described above for the 
preceding embodiments. The blanket and wick structure may be any suitable 
material such as synthetic fiber mat and strips. Once again, the details 
of construction will depend upon the various parameters existing at the 
site and can be calculated on the basis of engineering computations and/or 
empirically determined. 
While a preferred embodiment has been disclosed, it will be appreciated 
that principles of the invention are applicable to other embodiments.