United States	Hazardous Waste Engineering
Environmental Protection	Research Laboratory
Agency	Cincinnati OH 45268
Research and Development	EPA/600
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and various oil products to produce a
combustible product gas. Steam was ted
through a bed of incandescent coke,
producing a gas containing hydrogen
and carbon monoxide. This gas (blue
gas) then passed through two chambers
containing hot firebrick where oil was
sprayed into the gas and cracked into
gaseous hydrocarbons and tar. Oil gas
cracked oil alone into gaseous
hydrocarbons, tar, and carbon
(lampblack). A variety of oil-based
feedstocks were used in the production
of carbureted water gas and oil gas,
including naphtha, gas oil, fuel oil, and
residuum oils.
In general, all three processes were
employed in all areas of the United
States, but each process became
predominant in specific geographical
areas m the United States. Gas plants
along the West Coast started as coal-
gas plants, switched to CWG, then
converted to oil-gas production. Plants
along the East Coast were generally
CWG, with some coal-gas production.
Coal-gas production was predominant
m the Middle States. The gas purification
processes, byproducts, and wastes from
the gas production varied with each
production method The final report
discusses many aspects of the specific
production methods and associated
byproduct recovery operations ot
individual gas sites. Among the aspects
discussed are: feedstocks, fuel gas
chemical constituents and waste
products.
The final report also presents a much
longer, more detailed historical and
scientific treatment of former sites.
Included are alternative manufacturing
processes, characteristics of early
wastes, which often varied from site-
to-site, and early waste disposal
methods. A comparison of early gas
production processes in the United
States and the United Kingdom reveals
that marketing of byproducts was more
economically feasible in the UK, and that
waste products were easier to haul away
there, than in (he U.S. As a
consequence, U.S. sites contain more
wastes discarded onsite.
In the U.S., after the first natural gas
pipelines were installed in an area
formerly served by manufactured gas,
the natural gas was generally used to
meet baseline demand, and the
manufactured-gas plant was modified to
produce gas for mixing with 1he natural
gas to meet peak demands. As larger
pipelines were installed for natural gas
delivery and better storage methods for
natural gas became available, the need
for a standby gas production facility
evaporated. The manufacturing plants
were generally idle for several years
before thay were decommissioned. The
most frequent reason for
decommissioning the plants was to
remove structures from the site and
reduce the site valuation for tax
purposes The purpose of site
decommissioning was to remove surface
structures from the site. Gas storage
tanks were cut off at ground level, and
the tanks were filled with debris from the
plant site. Underground tanks and
Structures were rarely removed, and
some tanks and tar separators were left
filled with tar or liquid wastes. Many gas
companies still awn the original sites
used for the manufacture of gas, in that it
is generally much cheaper to keep the
site as unused land than it would be to
clean the site for sale.
Investigation and Remediation
of Town Gas Sites
The investigation and remediation of
abandoned town gas sites is a large task,
considering the large number of former
sites that have been discovered and the
even larger number that remain
undiscovered. Contacts made with State
and Federal agencies during Ihe course
of this project indicated that, of the sites
that have been discovered, only a few
have progressed beyond preliminary
assessments, and fewer still have had
remedial actions implemented to address
contamination. Thus.site investigation
activities and remedial action activities in
town gas sites should increase markedly
over the next few years.
As with any uncontrolled site
contaminated with potentially hazardous
chemicals.site investigation activities
should focus on determining threats lo
human health and the environment
posed by the site and on generating the
information necessary to evaluate and
select remedial alternatives. Selection of
remedial alternatives should concentrate
on cost-effective alternatives that
effectively mitigate the threat, with an
emphasis on treatment or destruction
alternatives that eliminate the hazardous
nature of the wastes.
The most commonly occurring and
environmentally significant contaminants
at abandoned town gas sites are
byproduct tars and oils and spent oxide
wastes. Byproduct tars and oils represent
multiple-density contaminants at gas-
works sites. For the purpose of this
discussion, byproduct oils are defined as
liquid hydrocarbon from gas manufacture
with densities less than water; bypror1
tars are defined as liquid hydrocarb^
with densities greater than water. These
substances are of concern
environmentally because of their potential
to contain high concentrations of
carcinogenic compounds, such as PAH's
and nitrogen heterocyclics. From the
standpoint of groundwater contamination,
the byproduct oils are of most concern
because of their higher solubilities and
tendency to float on the watertable.
where soluble components may be
leached out by infiltration. The byproduct
tars are also of concern; however,
because of their potential to flow in
density currents through subsurface
fractures and coarse-grained deposits.
Byproduct tars and oils from gas
manufacture are immiscible fluids and as
such do not readily mix with
groundwater. The flow of immiscible
fluids is more complex than is the flow of
soluble contaminants. An immiscible fluid
that is more dense (e.g., tar) than water
will migrate according to the combined
effects of relative density and the fluid-
fluid and fluid-solid interfacia! pressures.
Because of the density contrast, the fluid
will generally sink within the groundwater
Lighter hydrocarbons, such as byprod"-'
oil, will generally "float" on the w.
table or on the tension-saturated zone
The existence of capillary pressure in a
two-phase flow system means that the
migration of an immiscible fluid is not
entirely dependent on the flow of
groundwater and, as a result, can migrate
in an opposite direction of the dominant
(low system It is not uncommon in spills
of low-density fluids, for example, for
the fluid to migrate "upgradient" of the
groundwater flow system within the
capiilary fringe. The most significant
contaminants in spent oxide wastes are
sulfuric acid, arsenic, and complexed iron
cyanides. These complexed cyanides
occur in the form of ferricferrocyanide.
imparting a blue color to the spent oxide
wastes. Procedures for conducting
hydrogeological investigations of town
gas facilities are not significantly different
from those used (or investigating
uncontrolled chemical and industrial
waste sites The primary difference is
that town gas sites generally lend to be
older, and less background information is
available about past site activities. In
many cases, the present-day site has
been cleared,and little or no evidence of
past site activities is visible at the ground
surface. As a result, research into
historical records often is necessar-
determine the physical layout a..d
operating history of the plant. As with any
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investigation of an industrial site, it is
'remely important to utilize process
information to help determine what
contaminants may be present at the site
and where these materials may be
located.
Most investigations of manufactured-
gas plant sites rely on conventional site
investigation methods that are not
significantly different from contamination
investigations of other industrial sites
These methods include surface water
sampling, shallow soil and groundwater
sampling (from borings and test pits),
and, when necessitated by the results of
these sampling activities, more extensive
groundwater monitoring. In most
instances, these methods appear
adequate for an initial understanding of
the potential for adverse impacts on
human health and the environment.
Other potentially useful (and often
cost-effective) alternative techniques of
investigation, such as geophysics and
soil-gas sampling, have not been
extensively employed at manufactured-
gas sites to date. However, based on
limited use at manufactured-gas sites
and more extensive utilization at
industrial waste sites, these techniques
'iow potential utility for screening sites
optimize sampling and analysis plans.
A discrepancy commonly encountered
in the gasworks site investigations
reviewed by Research Triangle Institute
(RTI) is insufficient information on the
processes that operated at the specific
sites Most site assessments reported
that gas was produced by coal pyrofysis
or carbonization (i.e . retort or coke-
oven gas); most of these sites actually
were carbureted water gas (CWG) plants.
The difference is significant, both in
terms of waste characteristics and
byproduct utilization practices. For
instance, nitrogen and sulfur compounds
are more prevalent in coal carbonization
tars than in tars from CWG processes
Tar emulsions produced by CWG
processes were hard to dewater. As a
result, they were not reused and were
disposed onsite, especially in smaller
plants. Spent oxides from CWG cleanup
processes often do not have the brilliant
blue color often considered a
characteristic of spent oxides because of
the absence of significant levels of
ferricferrocyanides. Historical back-
ground information on the gas industry is
invaluable in planning and conducting
gas plant site investigations because it
<~an provide data on the characteristics
d likely disposition of potential
contaminants at site
Site investigation techniques
employed for hazardous waste site
investigations are generally applicable to
former manufactured-gas sites.
However, some special considerations
should be taken into account when
conducting site investigations in order to
focus the investigations on characteristic
features of these sites. First,
contaminants, especially gasifier tar and
oil, often are contained in below-ground
structures that were covered over and
left when the plant was decommissioned.
Gasworks site investigations initially
should concentrate on identifying these
structures because they often contain
almost pure contaminants. Because such
contaminants are contained, they are
relatively easy to remove, and because
they may be relatively pure, the
materials may be reused as
supplementary fuel or chemical
feedstocks. In addition, it is especially
important to take extreme care not to
damage these structures during site
investigation or remediation because this
could result in the release and spread of
contaminants, complicating and
increasing the expense of cleanup
operations.
Second, it is important to determine
the real extent of contamination on and
off a site as wastes, especially solid
wastes from gas cleanup operations
(e.g., woodchips, spent oxides). Such
wastes were often disposed in areas
adjacent to but not actually on the
original gas plant site In addition, gas
plant siies were usually sited in low-
lying areas (to facilitate gas distribution)
and were adjacent to streams, lakes, or
wetlands. In many cases, waste were
accidentally or deliberately discharged
into these areas; recent releases into
streams, lakes, and rivers have resulted
in site discoveries in many cases. It is
important, therefore.to investigate
wetlands and waterbodies adjacent to
gas plant sites for potential
contamination.
Third, it is important to recognize that
organic contaminants with various
densities commonly occur at gasworks
sites. Multiple-density contaminants can
result in complex contaminant migration
patterns in the subsurface and can
complicate the design and
implementation of site investigation and
groundwater monitoring. The relative
density of potential contaminants should
be known, at least qualitatively, during
the planning stages of site investigation
activities
Fourth, it is important to understand
the variety of methods used to produce
the gas and the resulting variability of
byproducts and waste products. By
knowing the gas production processes
used at a given manufactured-gas site,
it is possible to determine the most
appropriate chemical analyses for
development of the site investigation
plan, thereby resulting in lower
investigation costs. For example, an
assessment plan being developed for a
site that used a coal-carbonization
process should include analysis of
phenolic compounds, nitrogen
heterocyclics, ammonia, and cyanides
The analysis of these substances at
carbureted water-gas and oil-gas
production sites is less important
because they usually were produced in
low amounts in these processes. In
addition, it is important to determine the
potential toxicity and other hazards that
may be associated with gas-plant
wastes (e.g., the carcinogenicity of coal
tar and the tendency of spent oxides to
spontaneously combust) so that adequate
provisions may be made for the health
and safety of onsite workers and the
general public during site investigation
and remediation.
Gasworks sites have certain unique
features that can influence the selection
of remedial alternatives. First, the sites
are old: many were abandoned more
than 50 years ago, and almost all are
more than 30 years old. This age can
affect remediation in several ways It can
result in a low-priority ranking for the
site in terms of cleanup. If the site owner
can demonstrate that there is no history
of contaminant migration and that wastes
currently are remaining onsite. it is
possible that site remediation efforts
could be postponed without damage to
human health or the environment. The
fact that a site has existed for decades
without problems may be taken as
evidence that postponing remediation will
cause no further problems. If cleanup is
postponed, however, groundwater
monitoring should be employed to detect
contaminant release, and measures such
as restricted site access should be taken
to avoid exposure of the public to
contaminants at the site.
On the other hand, the age of these
sites can afford a long period of time for
contaminants to move offsite, thereby
resulting in a significant spreading of
contaminants and an increase in the
volume of material that must be cleaned
up
When gasworks were de-
commissioned, surface structures often
were removed but structures below the
surface usually were left in place. These
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slructures often contain contaminants,
usually tars, oils, or tar/water emulsions.
Because of this, it is important to
determine the locations ol these
slructures during a site investigation and
to consider their locations when planning
site remediation activities. In some
cases, free tars and oils occur in these
structures; such gasification byproducts
may be reused as supplementary boiler
fuel or chemical feedstocks. If reuse is
nol a viable alternative, careful recovery
of the material from the structures results
in a more concentrated waste stream lor
treatment or disposal. If surface
structures are damaged during
remediation efforts, contamination can
spread into surrounding soils, increasing
the expense and complexity of
remediation efforts.
Another feature of gasworks sites that
can affect remediation efforts is the
presence of injection wells that were
used for waste disposal (e.g., for tar
residues and emulsions). At least one
site reviewed in this study. Stroudsburg,
Pennsylvania, may have had one of
these wells. Research by the
Stroudsburg site investigators suggested
that other gasworks m the area may have
used wells for waste disposal. Maps for
the Lowell, Massachusetts, plant showed
a "deep well" on the site. However, it is
not clear whether this well was used for
waste disposal. Additionally, it is
important when reviewing old site maps
not to confuse tar wells, which are
underground structures containing tar,
with injection wells used for disposing of
wastes.
The location and depth of all welts on
a site should be determined during
remedial investigations. These wells may
be reopened and sampled for contami-
nation. Care should be taken during
reopening to prevent them from adding
to the spread of contaminants. If no
contamination is delected, they should
be properly closed and sealed to prevent
them from becoming pathways for
contaminant migration. II contaminated,
they can complicate site remediation
efforts. However, if wastes were pumped
down a well, it may be possible to pump
them back out. This was accomplished at
Stroudsburg, where over 8,000 gallons of
free coal tar was removed from the
subsurface. However, considerable tar
remains bound up in subsurface material
at Stroudsburg; this necessitated
containment (slurry wall) to prevent
migration of contaminants offsite.
Remedial action alternatives for
gasworks sites are similar to those for
other uncontrolled hazardous waste sites.
Containment, removal and disposal, and
treatment all are applicable. Some
containment generally will be required for
all remedial actions to prevent Ihe
release and spread of contaminants,
Slurry walls and caps have been used to
contain gasworks wastes. Removal and
disposal is a simple,but expensive option
that also has been used to clean up
gasworks sites Treatment to stabilize,
detoxify, or destroy gasworks wastes has
not been employed to a great extent, but
it is attractive, because it can destroy a
waste's hazardous nature, enabling safe
disposal of residues in nonhazardous
waste landfills and eliminating future
liability.
The finat report discusses in much
detail the technical and economic
aspects of site investigations conducted
at six former gas manufacturing sites and
one iron oxide disposal site.
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~ U. S. GOVERNMENT PRINTING OFFICE: 1938/543-153/67099
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