Process for regenerating spent solvent

A process for regenerating a solvent from a waste extract after use in a remediation process includes monitoring the water content and the amount of organic contaminants in the extract. If the water content in the extract is above a predetermined threshold value, the extract is distilled to yield the solvent therefrom for reuse in the remediation process. If the water content is below the threshold value but the amount of organic contaminants is above a predetermined limit, the extract is also distilled to yield the solvent therefrom for reuse. If the water content and amount of organic contaminants are both below their respective predetermined parameters, the extract is filtered through a molecular sieve to yield the solvent therefrom. The yield solvent is then collected from the distillation and filtering processes, and the regenerated solvent is then reused in the remediation process.

FIELD OF THE INVENTION 
This invention relates in general to extraction processes and in particular 
to a purification process for solvents. More specifically, this invention 
relates to a novel low cost method of removing organic contaminants from 
an organic solvent stream using a molecular sieve/molecular absorber so 
that the organic solvent can be reused in a solvent extraction process or 
other process requiring solvent regeneration and the contaminants are 
concentrated for disposal. 
BACKGROUND OF THE INVENTION 
Heretofore, solvent extraction systems for removing organic contaminants 
from soil, sediment, sludges and debris have used distillation systems to 
purify the organic solvent process fluids. The organic solvents used in 
these systems are typically volatile, while the contaminants in the 
solvents are semi-volatile to non-volatile. During the distillation 
process, the volatile solvents are removed from the distillation column, 
and the semi-volatile and non-volatile contaminants are concentrated as 
still bottoms. The volatile solvent is condensed after leaving the 
distillation column and is reused in the system to extract more 
contaminants from soil. The still bottoms with the concentrated 
contaminants are removed and are typically shipped off-site for 
destruction at an approved facility. 
The solvents used in these systems to dissolve the organic contaminants 
vary widely. They are selected for their ability to dissolve the 
contaminant of interest, usually have lower toxicity than the contaminant, 
and can be separated from the target contaminant by distillation. Because 
of the energy usage in distilling and condensing the solvent, compounds 
with low latent heat values are selected in order to minimize energy 
usage. 
The contaminants collected by these systems include Polychlorinated 
Biphenyls (PCBs), chlorinated dioxins, chlorinated furans, chlorinated 
pesticides, chlorinated herbicides, wood preservatives, and other organic 
compounds. Nonvolatile compounds are most often processed by solvent 
extraction systems as these contaminants have no low cost remedial 
alternatives. 
The distillation process has been successful in separation of contaminants 
from the solvent streams, and solvent extraction processes have been used 
to clean United States superfund sites and other contaminated sites 
throughout the world. Distillation systems, do, however, have several 
serious problems. 
Distillation systems use large amounts of energy to volatilize the solvent, 
and also large amounts of energy to condense the solvent. Because of the 
heat involved, and the fact that many of the solvents used in solvent 
extraction systems are flammable, safeguarding the system to operate in an 
explosive proof manner is a large expense. The capital cost of 
distillation systems is also expensive. A full scale solvent extraction 
system may have a $1,000,000 distillation system. Due to the large capital 
expense, the size of the systems can not be altered to fit the individual 
site size, rather, sites have to be found that are in the size range of 
the distillation unit. 
Distillation systems also require continuous monitoring, which drives the 
instrumentation and labor costs upwards. 
Because of the high capital costs, energy costs, and labor costs associated 
with distillation units, solvent extraction companies have focused on 
large superfund type sites. Sites smaller than 10,000 tons have usually 
not been addressed by solvent extraction systems. Current solvent 
extraction methods using distillation have need for improved solvent 
purification systems that will lower capital costs, energy costs, and 
labor costs so that small and large contaminated sites can be processed 
with this technology. 
SUMMARY AND OBJECTS OF THE INVENTION 
In view of the foregoing limitations and shortcomings of prior art devices 
as well as other disadvantages not specifically mentioned above, it is 
apparent that a need exists in the art for a low cost and highly effective 
method or removing organic contaminants from the solvent in solvent 
extraction systems. 
It is therefore an object of this invention to fulfill that need by 
providing a process for removing organic contaminants from solvent that is 
cost effective, safe to operate, has low capital costs, low energy 
consumption, and low labor costs to operate. 
Another object of this invention is a process that can be quickly adapted 
to the size of the site to be processed, instead finding sites to fit the 
distillation capacity. 
A further object of this invention is a process that can be used to 
pre-concentrate an organic waste stream so that the distillation capacity 
of any system can be inexpensively increased. 
A further object of this invention is a process that is easy to transport 
and set-up. 
A further object of this invention is a process that requires little 
training to operate. 
A further object of this invention is a process that can be used to 
separate contaminants with boiling points close to that of the extracting 
solvent. 
A further object of this invention is a process which can allow blending of 
solvents with similar or non-similar boiling points and vapor pressures, 
allowing a wider variety of extraction fluids. 
A further object of this invention is a process that is not affected by the 
water content of the solvent, as water is a natural component of soil. 
A further object of this invention is a process that is safer to operate 
than systems with distillation. 
A further object of this invention is a process that creates a safer 
concentrate of contaminants for shipping. 
A further object of this invention is a process which uses no heat in the 
solvent/contaminant separation process, as heat can cause other unwanted 
components to form. 
A further object of this invention is a process in which the equipment 
necessary can be delivered without long fabrication delays. 
It is another object of the present invention to provide a cost effective 
method for regenerating spent solvents which relies on alternatively 
selecting distillation or filtration as the means for withdrawing 
contaminants from a soil remediation extract. More specifically, by first 
determining whether water content levels are high or low in the extract, 
and by then selectively determining whether contaminant levels are high or 
low in the extract, only the high water level and high contaminant level 
extracts need to be processed by the more expensive distillation methods. 
These objects and other objects not specifically mentioned above are 
accomplished in accordance with preferred embodiments of the present 
invention by the use of selected solvents with molecular sieve/molecular 
absorbent materials for removing organic contaminants from the solvents.

DESCRIPTION OF INVENTION 
FIG. 1 is a schematic representation of using a molecular sieve/molecular 
absorbent 3 to separate clean solvent from contaminants within the solvent 
for solvent extraction systems. Because of molecular size or shape, some 
compounds 1 will migrate through a molecular sieve/molecular absorber, 
while other compounds 2 will be trapped in constriction areas in pore 
throats 4 or along various surfaces. If the compounds that can migrate 
through a molecular sieve/molecular absorber are selected as the carrier 
solvent for contaminant compounds that do not migrate as well through the 
molecular sieve/molecular absorber, then a separation of carrier solvent 
from contaminants will occur when the contaminated solvent is moved in one 
direction through the molecular sieve/ molecular absorber. 
In current practice, many of the contaminant compounds that are within the 
solvent to be regenerated have molecular weights far in excess of the 
carrying solvents. Contaminants that can be easily removed from compatible 
solvent streams with the molecular sieve/molecular absorber include but 
are not limited to Polychlorinated Biphenyls (PCBs), chlorinated 
pesticides such as Aldrin, BHC, Chlordane, DDD, DDE, DDT, Dieldrin, 
Endosulfan, Endrin, Endrin aldehyde, Heptachlor, Heptachlor epoxide, 
Lindane, Methoxychlor, and Toxaphene, chlorinated herbicides such as 
2,4-D, 2,4,5-T, and agent orange, wood preservatives such as 
pentachlorophenol, creosote, and other phenols, chlorinated dioxins, 
chlorinated furans, and coal gasification plant contaminants such as 
polycyclic aromatic hydrocarbons (PAHs). 
Solvents that can migrate through molecular sieves/molecular absorbers, and 
thus be used as carrier solvents include but are not limited to 
Acetaldehyde, Acetic Acid, Acetone, Acetonitrile, Acetylene, Acrolein, 
Amines, Ammonia, Butadiene, Butane, n-Butane, tert-Butyl Alcohol, 
Butylene, Carbon dioxide, Carbon monoxide, Dichloromonofluoromethane 
(Freon 21), Dimethyl sulfide, Ethane, Ether, Ethyl alcohol, Ethyl 
Chloride, Ethyl formate, Ethyl mercaptan, Ethylene, Ethylene oxide, 
Formaldehyde, Formic Acid, Freon 11 5, Hexane, Hexene, Hexyne, Isopropyl 
alcohol, Methane, Methyl acetate, Methyl alcohol, Methyl bromide, Methyl 
chloride, Methyl ether, Methyl formate, Methyl mercaptan, Nitromethane, 
Pentane, Pentylene, Pentyne, Phosgene, Propionaldehyde, Propane, 
Triethylamine, and Vinyl Chloride. 
Molecular sieves/molecular absorbers that can be used include but are not 
limited to activated granular carbon (AGC), zeolites, peat moss and other 
biomasses, and synthetic plastic molecular sieves. 
FIG. 2 is a schematic representation of a second preferred embodiment of 
the present invention. The contaminated solvent within the contaminated 
solvent holding vessel 13 is pumped into the molecular sieve/molecular 
absorbent vessel 28 where it flows through the molecular sieve/molecular 
absorbent 3. Clean solvent will pass out of the molecular sieve/molecular 
absorbent 3 and can be reused in the system. After a period of time, which 
is variable dependent upon the incoming contaminant types and 
concentration levels, the molecular sieve/molecular absorbent is flushed 
with clean solvent in the opposite direction of normal flow. This 
dislodges contaminant in great volumes 5 which is back flushed into a back 
flush holding vessel 6. The heavily contaminated concentrate can be 
disposed of directly, or can be further processed by distillation for 
additional waste volume reduction. This procedure adds additional life to 
the molecular sieve/molecular absorber, and can greatly reduce the amount 
of distillation volume necessary for system processing. 
FIG. 3 is a schematic representation of a solvent extraction system using a 
third preferred embodiment of the present invention. At highly 
contaminated sites, a distillation system is used to remove the 
contaminant from the solvent in the first few cycles of the solvent 
through the extraction vessel. After initial contamination has dropped, 
then the contaminated solvent is cleaned by a molecular sieve/molecular 
absorbed 28. The use of distillation initially followed by the use of the 
molecular sieve/molecular absorbent is called a split system, and results 
in significant economic savings over the use of distillation alone. High 
contaminant concentrations can be first treated with distillation, then 
the low contaminant concentrations can be treated with the molecular 
sieve/molecular absorbent. The split system configuration is the second 
alternative embodiment of the present invention. 
In full explanation of the diagram, starting with a pile of excavated 
soil/sediment/debris 14, the soil is moved by any earth moving technique 
including but not limited to front end loaders, augers, conveyor belts, 
and backhoes into the extraction chamber 26. The extraction chamber can be 
any size or shape of vessel that will contain the solvent without reacting 
with the solvent. Examples of extraction chambers include but are not 
limited to fiberglass, high density plastics, stainless steel and concrete 
vessels which can be used for many organic solvents and surfactants, while 
fiberglass, glass, and stainless steel can be used for many acid and base 
solvents. The vessels can be above ground, or in ground, transportable or 
fixed. The extraction chamber will use a removable top cover impermeable 
and nonreactive to the solvent vapors if these vapors cause a threat to 
human health or the environment. Examples of these covers include but are 
not limited to plastic sheets, stainless steel lids, glass lids, 
fiberglass lids, and flexible rubber sheets. If the removable to piece is 
used, a vent in the piece allows air or alternately, non-flammable gasses, 
to enter and exit the extraction chamber. The air to and from the 
extraction chamber passes through a porous and permeable vapor collection 
media 22 to stop vapors from escaping to the atmosphere. Examples of the 
porous and permeable vapor collection media include but are not limited to 
water bubblers, activated carbon, and molecular sieve/molecular 
absorbents. 
The removable top piece 27 is attached to the extraction chamber 26 at the 
top seating area 28. This sealing area can be but is not limited to rubber 
gaskets, bolt down mechanisms, shock cords or soft putty. Within the 
Extraction Chamber 26 the bottom is lined with a highly porous and 
permeable media 25 that will support the filter 24 and will serve as a 
collection area for leachate. Examples of highly porous and permeable 
media 25 include but are not limited to pebbles, marbles, plastic beads, 
and plastic netting. The filter 24 can be a solid sheet or layers of 
sheets covering the highly porous and permeable media 25. The filter 
should be compatible with the contaminants in the soils, sediments, and 
debris and also compatible with the solvent selected. The filter should 
also allow the free movement of fluids and vapors, but should retard fine 
particles. Examples of the filter 24 include but are not limited to 
reinforced filter paper, non-woven geotextiles, and fine netting. Above 
the filter 24 a fine sand 23 holds the filter in place, serves to collect 
formation fines that are mobilized during the leaching, and prevents 
premature loading of the filter 24. The contaminated soil, sediment, and 
debris to be leached is placed directly on the clean fine sand. 
After leaching, the cleaned soil, sediments, and debris is removed from the 
extraction chamber with standard earth moving equipment for either reuse 
at the site, transportation offset, or for further treatment 19. 
Contaminated solvent from the leaching process is removed from the highly 
porous and permeable media 25 by either gravity drainage or by pump 
through rigid or flexible pipes to a settling vessel or filter station 10. 
This settling vessel or filter station removes any suspended solids from 
the contaminated leachate that may have come from the extraction chamber. 
Examples of settling vessels or filter stations include but are not 
limited to tower clarifiers, flocculation tanks, sand filters, bag 
filters, and cartridge filters. Collected fines from the settling vessel 
or filter stations can be returned periodically to the top of the soils, 
sediments, and debris in the extraction chamber by any method including 
but not limited to hand carrying, augers and belts. 
Contaminated solvent from the settling vessel or filter station 10 is 
gravity fed or pumped to the contaminated solvent holding vessel 13. This 
vessel should be compatible with both the collected contaminant and the 
solvent selected for use at the site. 
The collected contaminant is placed in vessels 17 for disposal or further 
processing. The clean solvent is either gravity fed or pumped through 
rigid for flexible pipe to the clean solvent holding vessel 21. The clean 
solvent holding vessel should be constructed of materials compatible with 
the solvent selected. The clean solvent from this vessel is then gravity 
fed or pumped to the extraction chamber 26. 
Referring now to FIG. 4, a method in accordance with the present invention 
is shown as a logic flow chart and is generally designated 30. To begin, 
as indicated by box 32, the contaminated solvent extract which has been 
generated during the remediation process is collected. Typically, the 
remediated material is contaminated soil (box 34) and the extract contains 
organic contaminants and water which have been removed from the remediated 
material and are dissolved in the extract. Next, as indicated by box 36 in 
FIG. 4, the water content of the contaminated extract is monitored. In the 
preferred embodiment of the invention, the water content of the 
contaminated extract is monitored by a hydrometer (not shown) of a type 
well known in the pertinent art. The extract's water content is then 
compared to a predetermined threshold value, as shown by decision box 38. 
It is typical that the water content of the extract will initially be in a 
range of between zero and eighty percent water by weight of contaminated 
extract. Accordingly, the predetermined threshold value for water content 
can be chosen from this range by the operator and, preferably, will be 
approximately fifty percent (50%) by weight of the extract. 
As indicated by the decision block 38 in FIG. 4, if the percentage of water 
in the contaminated extract is greater than the threshold value (e.g. 
50%), the contaminated extract is deemed to be a high water level extract. 
If the percentage of water in the extract is less than the threshold 
value, however, then the extract is a low water level extract. For low 
water level extracts, the amount of organic contaminants is then measured 
as indicated by box 42 in FIG. 4. Preferably, the measurement indicated by 
box 42 is done by a gas chromatograph (not shown) in a manner well known 
by the skilled artisan. It is to be appreciated by the skilled artisan, 
however, that a gas chromatograph can measure any one or a combination of 
organic contaminants such as those listed above in the discussion of FIG. 
1. It will most likely happen, however, that most of the contaminants 
present of concern will be PCBs, chlorinated pesticides, and other 
chlorinated hydrocarbon contaminants. 
Once the amount of organic contaminants in the low water level extract has 
been determined, the amount is compared to a predetermined limit, as 
indicated by decision box 44. As shown, this predetermined limit should be 
somewhere around one hundred parts per million (100 ppm) of organic 
contaminants. It is to be appreciated by the skilled artisan, however, 
that the predetermined limit is dependent on the organic contaminants that 
are to be monitored. 
In accordance with the decision box 44 shown in FIG. 4, if the amount of 
organic contaminants in the low water extract is greater than the 
predetermined limit, the low water extract is reclassified and is 
thereafter considered a high contaminant extract. On the other hand, if 
the amount of organic contaminants in the low water level extract is less 
than the predetermined limit indicated in decision box 44, the extract is 
deemed to be a low contaminant extract. 
By considering block 40 in combination with the decision blocks 38 and 44, 
it will be seen that both the high water level extract and the high 
contaminant level extract are the be distilled (block 40). A low 
contaminant level extract, however, is to be filtered (block 46). In 
either case, the regenerated solvent which results from distillation 
(block 40) or filtration (block 46) is collected for further use (block 
48). One use for the collected solvent will be for futher remediation 
projects. It may, however, be necessary that the regenerated solvent be 
diverted to repeat the regeneration process of the present invention for 
further purification. This diversion of regenerated solvent is indicated 
by the dotted line between box 48 and box 36 in FIG. 4. 
Although many different filters can be used, the filtering step of the 
method of the present invention is preferably accomplished using a 
molecular sieve. When a molecular sieve is used, the lighter molecular 
weight solvent and water can pass through the sieve, but the sieve traps 
the heavier molecular weight contaminants (See FIG. 1). In the preferred 
embodiment of the invention, the molecular sieve is made of a material of 
activated granular carbon (AGC). Alternatively, a zeolite or peat moss 
material can be used for the sieve or synthetic filter sheeting, such as 
nylon, Teflon, and polypropolene. In any case, for the molecular sieve to 
properly accomplish the filtering step indicated by box 46, a large 
difference in the molecular weights of the solvent the molecular weight of 
the primary organic contaminants is desired. For example, and in the 
preferred embodiment of the invention, isopropyl alcohol with a molecular 
weight of substantially sixty grams per mole (60 g/mole) is used to filter 
PCB's and other chlorinated hydrocarbons which have a minimum molecular 
weight of two hundred and twenty-five grams per mole (225 g/mole). With 
this order of magnitude of difference between the molecular weights of the 
the respective solvent and contaminant, the sieve can be very effective at 
removing the contaminants. 
SUMMARY, RAMIFICATIONS, AND SCOPE 
Accordingly, the reader will see that the use of the molecular 
sieve/molecular absorbent for removing organic contaminants from the 
solvent can be successfully implemented for solvent extraction systems. 
This system will decrease the overall capital costs of solvent extraction 
systems, allowing this remedial technology to be used more economically. 
Further advantages include: 
Molecular sieve/molecular absorbents can reduce contaminant levels in the 
solvent to very low levels. This makes the solvent more effective as a 
removal agent, especially when removing very low concentrations of 
contaminants. In tests performed by the US EPA Superfund Innovative 
Technology Evaluation (SITE) program with the author, Isopropyl Alcohol 
was used as the extraction solvent to remove PCBs from soil and debris. 
The contaminated solvent contained up to 5,000,000 parts per billion (ppb) 
Aroclor 1260 (a type of PCB). After one pass through a Activated Granular 
Carbon (AGC) filter drum (the molecular sieve/molecular absorbent used in 
this case), the PCB content of the solvent was below the detection limit 
of the test, 1 ppb. This is a reduction of 99.99998 percent. 
The use of Activated Granular Carbon (AGC) as a molecular sieve/molecular 
absorbent has been used for the separation of organic contaminants from 
water successfully, and this technology is widely available in a variety 
of containers. AGC has not been used to separate solvents other than water 
from other organics prior to the use by the Author. Certain compounds are 
"transparent" to AGC, and these can be used as extraction solvents for the 
solvent extraction system. These extraction solvents include alcohols, low 
molecular weight (less than 50) and/or high polar compounds such as, but 
not limited to the following: Acetaldehyde, Acetic Acid, Acetone, 
Acetonitrile, Acetylene, Acrolein, Amines, Ammonia, Butadiene, Butane, 
n-Butane, tert-Butyl Alcohol, Butylene, Carbon dioxide, Carbon monoxide, 
Dichloromonofluoromethane (Freon 21), Dimethyl sulfide, Ethane, Ether, 
Ethyl alcohol, Ethyl Chloride, Ethyl formate, Ethyl mercaptan, Ethylene, 
Ethylene oxide, Formaldehyde, Formic Acid, Freon 11 5, Hexane, Hexene, 
Hexyne, isopropyl alcohol, Methane, Methyl acetate, Methyl alcohol, Methyl 
bromide, Methyl chloride, Methyl ether, Methyl formate, Methyl mercaptan, 
Nitromethane, Pentane, Pentylene, Pentyne, Phosgene, Propionaldehyde, 
Propane, Triethylamine, Vinyl Chloride. 
Previous solvent extraction systems have relied upon distillation, so the 
solvents had to be very volatile in order to work effectively. 
Additionally, the solvents had be fairly pure in order to achieve 
consistent separation from the contaminants. Mixed solvents needed to have 
similar boiling points and vapor pressures. The use of a molecular 
sieve/molecular absorbent will allow mixing of various solvents with 
different boiling points and different vapor pressures, as the dynamics of 
the molecular sieve/molecular absorbent are not strictly dependent upon 
vapor pressure and boiling points. 
Water, a natural component of soil, is not stopped by the GAC molecular 
sieve/molecular absorbent, and can be cleaned of organic contaminants 
along with the extraction solvent. The water in previous solvent 
extraction systems was typically disposed of with the distillation 
bottoms. This water disposal is very expensive, and is not necessary when 
using a molecular sieve/molecular absorbent. 
The flow dynamics of GAC and other molecular sieve/molecular absorbents 
have been researched to reduce channeling and to determine the maximum 
flow rates of each container configuration. This technical information can 
be applied to use in solvent extraction without the need for extensive 
research and development of the flow dynamics of each commercially 
available system. 
The range of molecular sieve/molecular absorbent sizes available on the 
market offer the opportunity to match the solvent extraction system to be 
used with the size and contaminant make-up of the site to be processed. A 
small site can use 55-gallon drum filters, while a larger site may require 
several 2,000 pound filter systems. The capital costs of a 55 gallon drum 
are approximately $500.00, and can process a maximum of 10 gallons 
contaminated solvent per minute (600 gallons per hour). An equivalent 
distillation system would cost approximately $500,000.00, or 1000 times as 
much as the molecular sieve/molecular absorbent. Due to the high cost of 
distillation systems, once a system is constructed, it is rarely upsized 
or downsized to accommodate a site sizing requirement. 
Split systems which use distillation and molecular sieve/molecular 
absorbents can process very high contaminant levels to very low levels at 
much lower costs than distillation systems alone. Initially, distillation 
is used to remove the high contaminant levels from the solvent, which is 
usually seen in the first few extractions of the soil. The molecular 
sieve/molecular absorber is then used to process the lower contaminant 
solvents, which are seen in successive extractions of the soil after the 
initial flush of higher contamination. During the time the molecular sieve 
is being used, the distillation system can be working upon the next batch 
of highly contaminated solvent, thus increasing the output of the system, 
while not increasing the size of the expensive distillation facility. 
Distillation facilities use heat to separate the contaminants from the 
carrier solvent. With this heat in combination with oxygen, there exists 
the possibility that unwanted new compounds can be formed. The molecular 
sieve/molecular absorber uses no heat for separation. 
Many of the solvents used in solvent extraction processes are flammable. 
The use of molecular sieves/molecular absorbers is much safer than using a 
heat driven process such as distillation. 
The concentrated contaminants within a molecular sieve are within a solid 
matrix, that if spilled will result to less injury to human health and the 
environment. 
Molecular sieves are smaller than distillation systems with equal 
capacities, so shipment and transport of these systems is less expensive. 
Molecular sieves/molecular absorbers require little to no maintenance, 
thus reducing overall costs. 
Molecular sieves/molecular absorbers can be operated by persons with little 
training, thus reducing labor costs. 
The availability of molecular sieves/molecular absorbers is such that there 
is near 24 hour availability. Distillation systems are special order 
items, and require long lead times for availability. 
Using molecular sieves with compressed gasses or gasses near their critical 
point can alleviate the need for decompression and subsequent 
recompression of the gasses, resulting in lower operating costs. 
Molecular sieves/molecular absorbers can be used to concentrate 
contaminants that have boiling and vapor pressures similar to the carrier 
solvent, resulting in increased operating efficiency and cleaner solvent 
streams than distillation facilities. 
Molecular sieves/molecular absorbers can be used to concentrate low 
contaminant streams into higher contaminant streams by filtration and 
capture of the contaminants, and then back flushing the molecular 
sieve/molecular absorber into the distillation facility to further 
concentrate the contaminant stream. This is a waste volume reduction step, 
and also reduces greatly the distillation Capacity needed for solvent 
extraction systems. 
In another aspect of the present invention, a method for regenerating spent 
solvent involves the measurement of water content levels and contaminant 
levels in the spent solvent. Once obtained, these measurements are used to 
determine whether the spent solvent is to be processed by distillation or 
filtration. In the practice of the method of the present invention, the 
spent solvent (extract) is first monitored, or measured, for its water 
content level. Depending on whether the content level is above or below a 
predetermined threshold value (e.g. approximately 50%) the extract will be 
classified respectively as either a high water level extract or a low 
water level extract. For a low water level extract, further classification 
is required according to its contaminant level. Specifically, depending on 
whether the contaminant level in the low water level extract is above or 
below a predetermined value (e.g. 100 ppm) the extract will be 
reclassified respectively as either a high contaminant level extract or a 
low contaminant level extract. In accordance with the present invention, 
both the high water level extracts and the high contaminant level extracts 
will be processed by distillation. On the other hand, the low contaminant 
level extracts will be regenerated by a relatively less expensive 
filtration process. In either case, the regenerated solvent is collected 
and either used for future remediation projects, or recycled and then used 
for future remediation projects. 
Although the description above contains many specificities, these should 
not be construed as limited the scope of the invention but as merely 
providing illustrations of some of the presently preferred embodiments of 
this invention. For example, instead of activated granular carbon, a 
zeolite sieve could be used, or a synthetic sieve could be used. 
Thus the scope of the invention should be determined by the appended claims 
and their legal equivalents, rather than by the examples given.