Multi-layer waste containment barrier

An apparatus for constructing an underground containment barrier for containing an in-situ portion of earth. The apparatus includes an excavating device for simultaneously (i) excavating earthen material from beside the in-situ portion of earth without removing the in-situ portion and thereby forming an open side trench defined by opposing earthen sidewalls, and (ii) excavating earthen material from beneath the in-situ portion of earth without removing the in-situ portion and thereby forming a generally horizontal underground trench beneath the in-situ portion defined by opposing earthen sidewalls. The apparatus further includes a barrier-forming device attached to the excavating device for simultaneously forming a side barrier within the open trench and a generally horizontal, multi-layer barrier within the generally horizontal trench. The multi-layer barrier includes at least a first layer and a second layer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a device and method for building 
an underground barrier. More particularly, this invention is directed to 
constructing a containment barrier underneath and around a hazardous waste 
site or municipal landfill. 
2. Background Art 
It is often necessary to form a containment barrier around a hazardous 
waste site to stop or prevent the migration of contaminants into the 
nearby soil and water tables. The containment barrier must prevent the 
migration of contaminants both horizontally and vertically away from the 
waste site. Therefore, a properly constructed containment barrier may be 
compared to a huge bathtub, with the hazardous waste contained within four 
side walls and a generally horizontal floor. 
A present method is to physically remove the hazardous waste and haul it to 
a permitted storage facility. However, such method is costly, impractical, 
and dangerous. Digging up sites with buried drums, radioactive dusts, or 
other airborne wastes may actually release the contaminants, spreading 
them into the atmosphere and through the soil. 
In response, researchers at Halliburton Nus Environmental Corp. have 
developed an apparatus and method to place a containment barrier around a 
hazardous waste site, as shown in International Publication Nos. WO 
94/19547 and WO 93/00483. The Halliburton system uses a row of high 
pressure jets to shoot a slurry into the soil surrounding a hazardous 
waste site, somewhat liquefying the surrounding soil. The slurry cuts a 
path through the soil as it intermixes with the liquefied soil. Gravity 
and/or mechanical means pull the row of high pressure jets through the mix 
of liquefied soil and slurry. The liquified soil and slurry then harden 
into a protective barrier. 
Although the Halliburton system has promise for some applications, it has 
several shortcomings that limit its use. First, the use of hydraulic jets 
may introduce liquids that can further spread contaminants. Second, 
because the system uses the same slurry for both cutting and mixing, in 
many applications there may be an imbalance between the amount of slurry 
needed for cutting and the amount of slurry needed for hardening the soil. 
Third, the hydraulic jets may only work in sandy or soft soils and may not 
work in rocky or hard soils. 
Fourth, in the Halliburton system, the slurry is not controlled as it is 
deposited. Since the slurry mixes with the liquefied soil, the strength of 
the barrier depends on the soil composition encountered. Too little slurry 
may be deposited where the soil is easily cut. Excess slurry may be 
deposited where the soil is difficult to cut. Weak spots will form in the 
containment barrier if the soil contains air cavities or mixed pockesuch 
weak spots is unpredictable. Those using the Halliburton system have no 
way of knowing when and where such weak spots will be. 
OBJECTS AND SUMMARY OF THE INVENTION 
An object of the invention is to provide a means for building a multi-layer 
containment barrier for a hazardous waste site. 
Another object of the invention, in accordance with one aspect thereof, is 
to provide a means for building a horizontal containment barrier under a 
hazardous waste site without disturbing any buried waste. 
A further object of the invention is to provide a less expensive and 
simpler means for building a containment barrier for a hazardous waste 
site. 
An additional object of the invention, in accordance with one aspect 
thereof, is to provide a means for simultaneously building the sides and 
the horizontal floor of a containment barrier. 
A further object of the invention is to provide a containment barrier 
having enhanced, reinforced strength. 
An even further object of the invention is to provide a containment barrier 
capable of resisting radiation and other waste pit contaminants. 
Still another object of the invention, in accordance with one aspect 
thereof, is to provide a containment barrier capable of chemically 
immobilizing contaminants and inhibiting movement of said contaminants 
through the barrier by chemical means. 
The above objects and others not specifically recited are realized in a 
specific illustrative embodiment of an apparatus for constructing an 
underground containment barrier for containing an in-situ portion of 
earth. The apparatus includes an excavating device for simultaneously (i) 
excavating earthen material from beside the in-situ portion of earth 
without removing the in-situ portion and thereby forming an open side 
trench defined by opposing earthen sidewalls, and (ii) excavating earthen 
material from beneath the in-situ portion of earth without removing the 
in-situ portion and thereby forming a generally horizontal underground 
trench beneath the in-situ portion defined by opposing earthen sidewalls. 
The apparatus further includes a barrier-forming device attached to the 
excavating device for simultaneously forming a side barrier within the 
open trench and a generally horizontal, multi-layer barrier within the 
generally horizontal trench. The multi-layer barrier includes at least a 
first layer and a second layer. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be apparent from the 
description, or may be learned by the practice of the invention without 
undue experimentation. The objects and advantages of the invention may be 
realized and obtained by means of the instruments and combinations 
particularly pointed out in the appended claims.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS 
For the purposes of promoting an understanding of the principles in 
accordance with the invention, reference will now be made to the 
embodiments illustrated in the drawings and specific language will be used 
to describe the same. It will nevertheless be understood that no 
limitation of the scope of the invention is thereby intended. Any 
alterations and further modifications of the illustrated apparatus, and 
any additional applications of the principles of the invention as 
illustrated herein, which would normally occur to one skilled in the 
relevant art and possessed of this disclosure, are to be considered within 
the scope of the invention claimed. 
Applicants have discovered that hazardous waste can be contained more 
effectively by encapsulating the waste site with a large container, 
preferably made from a material having emplacement and curing properties 
the same as, or similar to, fluidic or flowable grout or other 
cementitious material, without moving or disturbing the waste. 
Conventional methods of removing the waste to some other site, or forming 
a containment barrier by intermixing grout with the native soil 
surrounding the waste, are less effective in minimizing the risks 
associated with disturbing the waste and failing to seal the waste 
properly. Applicants' method subsists in actually forming a containment 
barrier beneath and around the waste site to encapsulate the waste with 
independently-formed barrier walls, without moving or even disturbing the 
waste, and preferably without using the native surrounding soil as part of 
the barrier-forming material. 
The further concepts of the present invention include a preferred method 
for containing an in-situ waste site disposed within earthen material, 
said method comprising the steps of: 
(a) excavating a generally horizontal trench beneath the in-situ waste site 
substantially without disturbing said in-situ waste site and thereby 
forming a generally horizontal underground trench defined by opposing 
earthen sidewalls; 
(b) forming a generally horizontal barrier within the horizontal trench, 
preferably as the horizontal underground trench is excavated; more 
specifically, an excavation device is advanced underground beneath the 
waste site and as excavated material is removed to form a section of the 
trench and delivered upwardly to the surface, curable barrier material is 
injected to replace the soil--a barrier-forming injection apparatus 
follows the underground excavation device such that underground soil is 
incrementally removed and replaced with the barrier-forming material until 
a continuous horizontal underground barrier of sufficient length is 
formed; 
(c) excavating side trenches continuously surrounding the entire in-situ 
waste site such that said side trenches are disposed in communication with 
the horizontal trench; 
(d) forming interconnected side barriers within the side trenches such that 
said side barriers continuously surround the waste site and form a 
continuous upper perimeter; 
(e) interconnecting the side barriers with the horizontal barrier such that 
said horizontal and side barriers cooperatively form a one-piece unitary 
barrier enclosure. 
The method described above may be further augmented by: 
(f) forming an upper barrier cover over the waste site and interconnecting 
said barrier cover with the side barriers, said upper barrier cover being 
of a size sufficient to span all opposing side barrier portions, and 
(g) securing said upper barrier cover along the continuous upper perimeter 
of the side barriers to thereby encapsulate the waste site. 
Referring now to FIG. 1, a waste site 11 contains drums 13 filled with 
hazardous waste, both on the surface 15 and buried deep under the ground 
17. Contaminants 19, leaking from the drums 13, threaten to migrate into a 
water table 12 or to otherwise contaminate the environment. 
As shown in FIGS. 2-4, the invention provides a way to build a containment 
barrier 21 (200 in FIG. 4). The invention places a floor or horizontal 
barrier 29 (or multi-layer floor 29a as in FIG. 4) without digging up the 
drums 13 or otherwise disturbing the contaminated soil of the waste cite 
11. Side barriers 23 (206 in FIG. 4) of the containment barrier 21 may be 
made using conventional methods and may be interconnected to the 
horizontal barrier 29 (29a in FIG. 4). However, in one embodiment of this 
invention, the floor 29 and the sides 23 are built simultaneously. 
The waste site 11 may be completely encapsulated by forming an upper 
barrier cover. Referring now to FIG. 3, an upper barrier cover 26 is shown 
in phantom line and is interconnected with the side barriers 23 and the 
front and rear barriers 25 and 27 (shown in FIG. 2, with the front barrier 
25 shown in phantom line). 
Referring now to FIG. 6, there is shown schematically a barrier placement 
machine 220, adapted to form a generally horizontal, multi-layer barrier 
228 within a generally horizontal trench 222, said multi-layer barrier 228 
having at least a first layer 202 and a second layer 204. However, the 
concept of the barrier placement machine 220 may of course be utilized to 
form a single-layer underground barrier as well, such as barrier 29 in 
FIGS. 2-3. 
The conceptual workings of the barrier placement machine 220 contemplate 
advancing a main frame support structure 102 along the surface 34 by 
advancing means 104. The support structure 102 carries soil cutter and 
grout injector assembly 333 which is placed initially in the bottom of a 
suitably sized beginning trench 246. As the advancing means 104 advances 
the support structure 102 horizontally in the direction of arrow B, the 
soil cutter and grout injector assembly 333 is also advanced in that same 
direction and proceeds to excavate a horizontal underground trench 940 and 
construct therein the horizontal barrier 228. The soil cutter and grout 
injector assembly 333 operate to excavate earthen material 985 from 
beneath the in-situ portion of earth 216 without removing said in-situ 
portion. 
For example, the soil cutter and discharge device 31,33 may include cutting 
teeth 31 (or any suitable soil cutter) and soil removing cups 33 (not 
detailed in the drawings, but indicated schematically in FIG. 6 and 
therefore understandable to one of ordinary skill in the relevant art), 
for removing the excavated soil 985 as described above. A soil conveyor 
933 carries excavated soil upwardly, in any manner and structure known to 
those of ordinary skill in the relevant art, and discharges the soil 985 
above ground where it lies conveniently accessible for testing if desired. 
As an incremental section of underground soil is excavated and removed, 
grout or other curable barrier material is injected in the soil's place by 
an injector means to form the underground horizontal barrier, such as 
barrier 228 (FIG. 6, multi-layer) or barrier 29 (FIGS. 2-3, single layer). 
Unlike the Halliburton system discussed above in The Background Art 
section, the barrier placement machine 220 includes a soil cutter and 
discharge device 31,33 which is separate from a grout injection system 
224. Therefore, only the grout needed for the containment barrier is 
introduced into the soil. There is less disturbance of the soil and the 
present invention introduces no excess liquid that may further spread 
contaminants. Further, different grout compositions may be used as needed 
to contain different contaminants present in the waste site. 
However, this invention further includes an embodiment where the soil is 
not removed but mixed directly with the grout. The removing cups 33 could 
be detached so the broken up soil remains in the void 41 created by the 
cutting teeth 31, and the broken soil is then pressure grouted such that 
the barrier 29 (FIG. 2) is formed as a continuous barrier of earth and 
grout. 
In addition to grout, this assembly may dispense any material that 
initially flows as a slurry into an open space, yet over time cures into a 
solid mass having generally the shape of the open space. The material may 
include any cementitious material, latex polymer cement, bentonite clay 
slurry, hot wax (such as paraffin wax), hot asphalt, hot polyethylene, 
gelled water, any organic epoxy or any other suitable compound. 
Additionally, the grout itself may contain additional radiation shielding 
components or biological and chemical neutralizing components. 
The concept of forming the single underground layer 29 as shown in FIG. 2 
is augmentable to allow two or more layers of different materials to be 
placed simultaneously. In reference to FIG. 6, a stack of two injection 
chambers can be used to dispense two different barrier-forming materials 
within the void as the barrier placement machine 220 advances. Thus, a 
layer of material other than grout may be added at the same time as the 
grout layer, or two non-grout layers may be formed, or any suitable layer 
combination. A possible containment barrier produced by this invention 
would include a cementitious layer and one or more preferably plastic 
layers. The cementitious layer would provide the strength and support 
while the plastic would add leak protection, especially if cracks develop 
in the cementitious layer. 
FIG. 3 shows a cross-section view of the contained hazardous waste site 11. 
Grout side walls 23 and a grout floor 125 enclose the hazardous waste pit 
11, along with the upper barrier cover 26. The machine 220 (FIG. 6) 
includes a pair of side-trench excavators disposed on the frame 102, one 
of which is shown as item 91 in FIG. 6 with the understanding that a 
similar or identical side-trench excavator is located adjacent the one 
shown. 
The side-trench excavator 91 includes a continuous revolving soil cutter 
and conveyor, in accordance with any method or structural apparatus known 
to those having ordinary skill in the relevant art, for cutting in the 
direction of arrow B and therefore into soil 227 and removing the soil 
upwardly onto a trench excavator conveyor 991 to produce side trench 226. 
Grouting machinery, including a sidewall traveling pan 953 and sidewall 
consolidator 955, are used to form the side barriers (23 in FIGS. 2-3, 206 
and 214 in FIGS. 4-5). The soil excavated to form the side trench 226 is 
replaced as soil 984 in a back fill against the newly formed side barrier. 
Referring now more particularly to FIGS. 4-7, a key aspect in accordance 
with the principles of the present invention is shown therein. Applicants 
have found that utilizing a multi-layer barrier provides several distinct 
advantages, including enhanced inhibition of seepage from the contained 
waste, and increased structural capacity of the barrier. 
In FIG. 4 is shown a double layer containment barrier, designated generally 
at 200. The barrier 200 includes a first layer 202, and a second layer 204 
disposed atop the first layer 202. Side portions 206 of the barrier 200 
are shown in double, multi-layer construction, but may alternatively be 
embodied in a single layer construction. 
In FIG. 5 is shown a triple layer containment barrier, designated generally 
at 210. The barrier 210 includes the same first layer 202 and second layer 
204 as in FIG. 4, as well as a third layer 212 sandwiched between the 
first and second layers 202 and 204. Side portions 214 of the barrier 210 
are shown in triple, multi-layer construction, but may alternatively be 
embodied in a single layer construction. 
The first, second and third layers 202, 204 and 212 may comprise any 
suitable material for the intended purpose of containing the buried waste 
pit 11. For example, any or all of the layers 202, 204 and 212 may 
comprise grout or some other cementitious material, or alternatively sand 
or clay. Further, one or more of the layers, preferably the third or 
middle layer 212, may comprise a homogenous, non-reinforced layer. 
Preferably at least one of the layers is formed from an at least partially 
synthetic material. For example, the third layer 212 may comprise a 
high-performance polyethylene membrane, or a fiber reinforced composite 
layer, or a Teflon(tm) mesh, or any other suitable mesh material. The 
third layer 212 is preferably thinner than either of the first or second 
layers 202 and 204. 
The principles of the present invention extend to cover any apparatus or 
method capable of constructing a multi-layer barrier around an in-situ 
portion of earth, such as in-situ portion 216 that contains the buried 
waste pit 11. Referring now to FIG. 6, there is shown a barrier placement 
machine 220. For example, the machine 220 includes the operator's cab 97, 
the cutting chain and grout injector assembly 333 including cutter teeth 
31 and discharge paddles 33, the grout receiving conveyor 959, the 
sidewall traveling pan 953, the sidewall consolidator 955, a side trench 
excavator 91, soil conveyor 933, and advancing means 104 for moving the 
entire machine 220. The machine 220 is depicted in FIG. 6 in schematic 
form, and may include all other components necessary 79 for its operation, 
as understood by those of ordinary skill in the relevant field. For 
example, the grout may be pumped through pipes (not shown) extending from 
the barrier placement machine 220, through the side trench 226, to the 
cutting chain and grout injector assembly 333, as is understood by those 
of ordinary skill in the relevant field. 
As the barrier placement machine 220 moves forward, a trench excavator 91 
digs a side trench shown in phantom line at 226. The trench excavator 91 
carries the excavated soil 984 up out of the ground and dumps it on the 
trench excavator conveyor 991, which carries the soil backwardly along the 
machine 220. Grout or other suitable barrier forming material is then 
placed within the side trench 226 by the sidewall traveling pan 953 and 
the sidewall consolidator 955, along with any other necessary grout 
injecting devices known to those of ordinary skill, to form the side 
barrier (shown as a multi-layer barrier 206 and 214 in FIGS. 4-5, but may 
also comprise a single-layer barrier). The trench excavator conveyor 991 
dumps the soil 984 behind the barrier placement machine 220, refilling the 
side trench 226. Simultaneously, the cutting chain and grout injector 
assembly 333 and soil conveyor 933 operate to excavate earthen material 
985 from beneath the in-situ portion of earth 216 without removing said 
in-situ portion, and discharges the soil 985 above ground as shown in FIG. 
6 where it lies conveniently accessible for testing if desired. 
The machine 220 thus includes excavating means 91, 31, 33, 933 and 991 for 
simultaneously (i) excavating earthen material 984 from beside the in-situ 
portion of earth 216 without removing said in-situ portion 216 and thereby 
forming an open side trench 226 defined by opposing earthen sidewalls, and 
(ii) excavating earthen material 985 from beneath said in-situ portion of 
earth 216 without removing said in-situ portion 216 and thereby forming a 
generally horizontal underground trench 222 beneath said in-situ portion 
16 defined by opposing earthen sidewalls. 
The machine 220 further includes a barrier-forming means 953, 955 and 224 
attached to the excavating means 31, 33 and 91 for simultaneously forming 
a side barrier 206 (as in FIG. 4) within the open trench 226 and a 
generally horizontal, multi-layer barrier 228 within the generally 
horizontal trench 222, said multi-layer barrier 228 having at least a 
first layer 202 and a second layer 204. Regarding the side barrier 206 (as 
in FIG. 4), the sidewall travel pan 953 lowers grout into the side trench 
226 with a sidewall consolidator 955 where the grout is shaped into an 
upwardly extending, preferably vertical wall. 
Regarding the horizontal, multi-layer barrier 228, the means 224 of the 
machine 220 constitutes a horizontal barrier forming means for forming at 
least a portion of the second layer 204 simultaneously with forming at 
least a portion of the first layer 202. More specifically, the horizontal 
barrier forming means 224 includes: a first injector means 232 for 
injecting a first material for forming the first layer 202 in the 
horizontal trench 222; a means for placing an intermediate shield 234 over 
the material for the first layer 202; a second injector means 236 for 
injecting a second material for forming the second layer 204 onto the 
intermediate shield 234; and a frame means 238 to which the intermediate 
shield 234 is attached for removing the intermediate shield 234 from 
between the first and second material forming the first and second layers 
202 and 204. Since the frame means 238 is coupled to the structure 102, 
the attached shield 234 is moved between the first and second layers 202 
and 204 as the machine 220 advances. The intermediate shield 234 is 
disposed between the first and second injection means 232 and 236 and, as 
an extension of the frame 238, is advanced horizontally between the first 
and second layers 202 and 204 as they are formed, as the advancing means 
104 advances the machine 220. As indicated above, grout may be pumped 
through pipes extending from the barrier placement machine 220, through 
the side trench 226, to the horizontal barrier forming means 224, and to 
the first and second injector means 232 and 236, as is understood by those 
of ordinary skill in the relevant field. 
Since the horizontal excavating means 31, 33 and the first and second 
injector means 232 and 236 are advanced along the underground horizontal 
trench 222, the advancing means 104 and the frame support structure 102 
cooperate as advancing means for simultaneously advancing the excavating 
means and the barrier-forming means such that at least a portion 31, 33 of 
the excavating means and at least a portion 232, 236 of the 
barrier-forming means are advanced beneath the in-situ portion of earth 
216. 
It is to be understood that the machine 220 may be utilized to form a 
two-layer horizontal barrier as illustrated in FIG. 4, or a three-layer 
horizontal barrier as illustrated in FIG. 5, for example. The machine 220 
may include a stack of injector means of any desired number, two being 
shown in FIG. 6 as items 232 and 236. If, alternatively, four injector 
means were disposed in a stacked arrangement, then a four-layer horizontal 
barrier could be thereby formed by simply injecting a clay slurry, grout, 
or other material to form each layer. Alternatively, a stack of three 
injector means, with two layers from a roll of material disposed between 
each injector means in the same or similar manner as depicted by the roll 
244, could be used to form a five-layer horizontal barrier. 
With respect to the two-layer barrier 200 as in FIG. 4, a roll of 
pre-formed barrier material (item 244 in FIG. 6, or item 250 in FIG. 7) 
would not be used. The first and second layers 202 and 204 would be formed 
simultaneously, and material for the second layer 204 would preferably be 
dispensed from the second injection means 236 directly on top of the 
intermediate shield 234, to prevent any intermixing between the first and 
second layers 202 and 204 during their initial cure cycles. Accordingly, 
the intermediate shield 234 is preferably sufficiently long in a lateral 
dimension A, and is advanced in a direction B at a sufficiently slow rate, 
such that the first and second layers 202 and 204 are cured to a degree 
sufficient to prevent intermixing therebetween when the shield 234 moves 
to permit contact between said first and second layers 202 and 204. These 
same principles and procedures may be used to form three-layer, 
four-layer, or five-layer horizontal barriers, or any other number of 
layers. 
Alternatively, users might prefer to induce some degree of interaction 
between the first and second layers 202 and 204. The rate of movement of 
the shield 234 may be sufficiently fast, and its length in the dimension A 
might be sufficiently short, to permit contact between the layers 202 and 
204 in an uncured state sufficient to allow a chemical reaction at an 
interface 205 (shown in FIG. 4) between those layers, perhaps to produce a 
chemical bond at the interface. The barrier forming materials for 
constructing the layers 202 and 204 may be selected to react at the 
interface 205 in a manner to produce a chemically different material than 
the initial material used in the layers 202 and 204. 
The first and second injector means 232 and 236 are contained within first 
and second chambers 240 and 242, respectively. The intermediate shield 234 
thus operates as a carrying member coupled to the chambers 240 and 242. 
The third, middle layer 212 begins as a dispensable, pre-formed roll 244 
of barrier material that resides in a suitably sized trench 246. The roll 
244 of barrier material includes a first end 248. Any suitable attaching 
means known to those of ordinary skill in the art may be used for 
attaching the first end 248 of the roll 244 of barrier material to the 
intermediate shield 234, such that barrier material is withdrawn from the 
dispensable roll 244 as the machine 220 advances. In such manner the roll 
of material 244, which might comprise a high performance material such as 
polyethylene or any suitable material, is pulled between the first and 
second layers 202 and 204 as the machine 220 advances. In this embodiment, 
the barrier material of the roll 244 preferably has sufficient strength to 
be pulled between the first and second layers 202 and 204 without 
substantial tearing. 
An alternative embodiment is depicted in FIG. 7. A dispensing means 250 
comprises a pre-formed roll of barrier material rotatably disposed between 
the horizontal digging means 31, 33 and the chambers 240, 242. The second 
injector means 236 is positioned to inject the second layer 204 on top of 
an intermediate shield 234a such that said shield 234 separates the second 
layer 204 and the pre-formed layer 212 as said second layer 204 and said 
pre-formed layer 212 are being respectively injected and dispensed. The 
intermediate shield 234a thereby operates as a retaining plate. 
In the embodiment of FIG. 7, the pre-formed roll 250 must of course be 
small enough to fit within the horizontal barrier forming means 224a. 
Since the length of many waste pits exceeds 100 feet, the internally 
placed roll 250 would probably not contain a sufficient length of 
material, and would be periodically replaced with additional rolls of 
material to complete the third, middle layer 212. The roll 250 could be 
removed and replaced through the side trench 226. 
If desired, a sensing means (now shown) may be disposed on the barrier 
material of the rolls 244 and 250 for sensing hazardous materials, for 
example. In this manner, any desired sensing means can be deployed between 
the first and second layers 202 and 204 by being incorporated into the 
barrier material forming the roll 244 or the roll 250. 
The trench excavator 91 and horizontal digging means 31, 33 are preferably 
configured and arranged for forming the side trench 226 such that it is 
disposed in communication with the horizontal trench 222. Additional 
digging means known in the art are used to dig the initial, beginning 
trench 246 and a final trench (not shown) located on the opposite side of 
the in-situ portion of earth 216 as the beginning trench 246. As such, the 
invention comprises means for forming a pair of side trenches adjacent the 
in-situ portion of earth 216 such that said side trenches are disposed in 
communication with the horizontal trench 222. 
Any suitable means for forming a side barrier in the trench 246 and in the 
oppositely located final trench (not shown) may be utilized. As such, the 
invention includes means for forming side barriers (including barrier 206 
in FIG. 4 or 214 in FIG. 5, as well as side barrier in the trench 246 and 
the oppositely positioned final trench) within the plurality of side 
trenches and interconnecting the side barriers (206 or 214) with the 
horizontal, multi-layer barrier 228 such that said horizontal and side 
barriers cooperatively form a one-piece unitary barrier enclosure. 
Most preferably, the interconnected side trenches continuously surround the 
in-situ portion of earth 216, such that the interconnected side barriers 
continuously surround the in-situ portion of earth 216 and form an upper 
perimeter 252 (FIG. 4) or 252a (FIG. 5). 
Applicants note than any of the apparatus or method described herein and 
shown in any of the FIGS. 1-7 may be optionally incorporated into a single 
layer barrier forming machine, as an adaptation of the multi-layer barrier 
forming machine 220 of FIG. 6. 
In accordance with the above, a preferred method for constructing an 
underground containment barrier for containing an in-situ portion of earth 
216 comprises the steps of: 
(a) excavating a generally horizontal trench 222 beneath the in-situ 
portion of earth 216 substantially without disturbing said in-situ portion 
216 and thereby forming a generally horizontal underground trench 222 
beneath said in-situ portion 216 defined by opposing earthen sidewalls; 
and 
(b) forming a generally horizontal, multi-layer barrier 228 within the 
horizontal trench 222 comprising a first layer 202 and a second layer 204 
disposed above said first layer. 
The above description contemplates a physical containment of contaminants 
and waste by simply encapsulating them with a barrier, the barrier being 
preferably impermeable. A further aspect of the invention subsists in a 
chemical containment of the contaminants, preferably through use of a 
permeable barrier. 
For example, the layers 202 and 204 of the multilayer barrier 29a in FIG. 4 
could be made of a permeable material. At least one of the layers contains 
therein chemical means for (i) chemically immobilizing contaminants 
disposed in the in-situ portion of earth and (ii) inhibiting movement of 
said contaminants through said at least one of the layers. Contaminants 
such as radio nuclides, metals and organic materials could be contained in 
this manner. 
It is contemplated that the chemical means could either comprise a property 
of the material of the layer, such as might be accomplished by forming the 
layer from bentonite, hematite, or apatite, or the chemical means could 
comprise an additive to the layer, such as a zeolite, or a clay additive 
of bentonite, hematite or apatite. The layers could also comprise any 
other suitable crystalline inorganic material. 
Such materials, and other known to those of ordinary skill in the art, may 
operate to permit ground water movement through the layer but chemically 
immobilize certain contaminants in the manner of a sieve, through 
precipitation, ion exchange, or adsorption. The permeable layer would, for 
example, form a chemical bond with certain contaminants and thereby 
inhibit the release of said contaminants into the environment. The 
contaminants become immobilized within the barrier itself. 
A multi-layer barrier may thus be constructed such that only some, or all, 
of the layers include a chemical means for immobilizing the contaminants 
in the soil. Different materials for the layers (or in the alternative 
different chemical additives) may be used for the different layers, such 
that certain layers will immobilize some contaminants but not others. For 
example, the chemical means of the first layer may be capable of 
immobilizing a first contaminant but not a second, third or fourth 
contaminant, and the chemical means of the second layer may be capable of 
immobilizing a second contaminant but not the first, third or fourth 
contaminant, and the chemical means of the third layer may be capable of 
immobilizing a third contaminant but not the first, second or fourth 
contaminant, and the chemical means of the fourth layer may be capable of 
immobilizing a fourth contaminant but not the first, second or third 
contaminant. 
Alternatively to chemical containment device, the invention may instead 
comprise permeable layers designed to contain therein degrading means for 
chemically degrading contaminants disposed in the in-situ portion of 
earth. The degrading means may comprise an iron-based media capable of 
chemically reducing the contaminants to non-toxic components, or any other 
suitable agent for reactively destroying contaminants. 
It is to be understood that the chemical containment features contemplated 
above (such as through precipitation, ion exchange, or adsorption), and 
the chemical degradation features, could possibly be included in 
combination with impermeable layers as well, to provide a physical 
containment as well as a chemical containment. 
Thus, multiple layers can be designed to address containment of different 
classes of contaminants of concern. The barrier layers could be composed 
of either soils, clays, crystalline inorganics or other material (or a 
combination of these) that will react with the contaminants to either 
immobilize (through precipitation, ion exchange or adsorption) or destroy 
(chemically decompose) and prevent or mitigate the releases of 
contaminants to the environment to an acceptable level. Additives (such as 
zeolite, bentonite, other chemical reagents) to a layer of the underground 
horizontal barrier could enhance the capability of the barrier to 
immobilize or destroy contaminants that begin migrating through the 
permeable barrier. 
A further aspect of the invention contemplates a self-healing layer, which 
could repair itself of fractures produced by earthquakes or other forces. 
For example, at least one of the layers of the multi-layer barrier may 
comprise a self-healing layer having sufficient flexibility and softness 
to reform and reseal fractured portions of itself back together. 
The invention of FIGS. 6-7 may further comprise cutting means for simply 
cutting earthen material from beneath the in-situ portion of earth 216 
without removing said in-situ portion 216 and thereby forming a loosened 
section of soil beneath the in-situ portion. The soil cutter and discharge 
device 31,33 would simply be modified to not include any soil removing 
cups 33 (not detailed in the drawings, but indicated schematically in FIG. 
6 and therefore understandable to one of ordinary skill in the relevant 
art), and one of the first and second injector means 232 and 236 would 
simply inject uncured slurry into the loosened soil to thereby cause the 
slurry and loosened soil to intermix and cure to form at least one of the 
layers of the multi-layer barrier 228. The cutter 31 would simply cut up 
the soil without removing it. In the alternative, the soil cutter and 
discharge device 31,33 could simply be designed to remove only part of the 
loosened soil, thereby permitting the injected slurry to intermix with the 
remaining loosened soild to fill the void from the removed soil and cure 
to form a generally horizontal barrier. 
For example and by illustration only, the slurry could be injected under 
sufficient pressure to cause intermixing between the soil and the slurry. 
The term "slurry" as used herein shall refer broadly to any suitable 
aqueous material which is sufficiently curable to form a rigid and hard 
barrier. 
It is to be understood that the inventive combinations described herein are 
applicable to a wide variety of uses. The inventive concepts of excavating 
surrounding trenches around an in-situ waste site without removing the 
waste site, and forming barriers within the trenches without relying on 
the native soil to form the barrier material, are broadly applicable. 
These concepts may be used in building construction, canal construction, 
leach mining and tunnel construction, in various applicable ways 
understandable to those of ordinary skill in the art. The concepts herein 
may also be used as a secondary containment system to surround an existing 
containment structure such as an underground tank. They could further be 
used to create a subjacent reinforcing barrier beneath a building 
foundation, or to repair a leaking pond or channel or to contain 
environmental spills, munitions, or unexploded ordinance. The installation 
and reinforcement of pipe may also be served by the invention combinations 
described herein. A containment well barrier could also be formed with the 
concepts of the present disclosure. The phrase "in-situ" as used herein 
shall be broadly construed to refer to objects or cumulations of objects 
which remain situated in their original position. The adjective "earthen", 
as used herein in phrases such as "earthen material" or "earthen 
sidewalls", shall be construed broadly herein to refer to anything 
composed at least partially of earth, including, but not limited to, soil, 
rock, gravel, clay, dirt, sand and the like. As such, the phrase "in-situ 
portion of earth" as used herein shall be construed broadly to include 
waste dumps as well as undisturbed earth. 
The term "contain" as used herein shall be construed broadly to include the 
concept of any degree of containment or structural impedance, and shall 
therefore not be limited in meaning to the concept of complete 
encapsulation. For example, a single, unattached horizontal layer disposed 
beneath a waste site which prevents, or at least inhibits seepage from the 
waste site, can be described as providing containment to the waste site. 
In that sense, such a horizontal layer does indeed contain the waste site. 
The phrase "generally horizontally" as used herein shall be construed 
broadly to refer to a direct horizontal direction as well as an at least 
partial horizontal direction. For example, an underground layer that 
extends laterally but also at some degree of downward incline may be 
described as extending generally horizontally, provided the downward 
inclined portion defines an angle with horizontal of less than 45.degree.. 
It is also to be understood that the above-described arrangements are only 
illustrative of the application of the principles of the present 
invention. Numerous modifications and alternative arrangements may be 
devised by those skilled in the art without departing from the spirit and 
scope of the present invention and the appended claims are intended to 
cover such modifications and arrangements.