Corey L.J. Fischer
Robert D. Schmitter
Eliesh O'Neil Lane
Technical Outreach Services of Communities Program
South & Southwest Center
Georgia Institute of Technology
Atlanta, Georgia
November 1999
Introduction Top of page
Manufactured gas plants (MGP) are former coal gasification plants. Coal
gasification is a process for converting coal partially or completely to
combustible gases (Clark). In turn, after purification, these gases can be used
as fuels or as raw materials for other processes (Clark).
Background Top of page
It is reported that London and Westminister Chartered Gas, Light and Coke Company
built the first manufactured gas plant in 1812, although the first record of
experimental manufactured gas production from coal dates back to seventh century
England (Srivastava, 1997). In the United States the first uses of manufactured
gas for the purposes of lighting appear to have been in Philadelphia in 1796 and
in Richmond in 1803 (Mon, 1995). North America's first manufactured gas plants
were built in Baltimore (1816), Boston (1822), and New York (1825) (Srivastava,
1997). During the latter half of the 19th century the manufactured gas industry
expanded in the urban industrial areas of the country (Mon, 1995). At the turn of
the century almost every good-sized city had its own manufactured gas plant (Mon,
1995). From approximately the 1850s to the early 1950s, MGP sites were the
primary source of energy for lighting and heating (Ackerman et al). It is
estimated that at the peak of the industry in the 1920s and 1930s, there were
more than 10,000 MGPs in operation throughout North America and Europe (Ackerman
et al). However, the growing availability of low-cost natural gas delivered by a
network of pipelines between the 1940s and 1960s lead to its substitution and
replacement of gases derived at MGP sites (Srivastava, 1997; Larsen, 1997; GZA,
1998b). After natural gas was introduced via the pipeline, manufactured gas was
only used to supplement natural gas in periods of high demand such as extremely
cold weather (Mon, 1995).
After plants were closed, they were often demolished, and the property sold
(Murarka, 1995). While many former MGPs were demolished long before the advent of
environmental regulations, many old plants are still structurally intact today
(Ackerman et al). In fact, the majority of properties where larger gas holders
were built have been converted to "modern" facilities that are part of the
capital assets of the American gas electric utility industry (Neuhauser, 1995).
Therefore, the liabilities associated with the former MGP operations are now the
responsibility of viable companies. The American people are only just now
beginning to understand the extent and magnitude of the legacy left behind by the
MGP process (Murarka, 1995). There may be as many as 2,500 such site that, while
originally owned by the corporate predecessors of today's gas distribution
companies, are now part of modern electric and gas utilities (Murarka, 1995).
These sites range from half an acre to over 100 acres in size and could cost
between $25-75 billion of the next thirty years to clean up or contain (Murarka,
1995). Liabilities for individual utility companies vary according to the size of
their former MGP operations. For instance, Niagara Mohawk Power Corporation,
which represents less than two percent of the total American MGP sites, estimates
their environmental liability at more than $200 million spread over 24 cities and
towns in upstate New York (Neuhauser, 1995).
In light of the present environmental awareness, the former MGPs have been
gaining attention from regulators as sources of onsite and offsite soil,
sediment, surface water and groundwater contamination. In addition, former MGP
sites represent a vast amount of unused land. The federal brownfields initiative
encourages investigation, remediation, and redevelopment of abandoned, unused or
under-developed property. The redevelopment of these sites for reuse can help
utilities become more competitive under the current deregulation business climate
(Ackerman et al). However, prior to redevelopment of former MGPs, the site must
be investigated to delineate onsite and potential offsite environmental impacts.
The impacts then must be quantified in order to determine the most advantageous
remediation technology on a site-by-site basis. After remediation is completed to
appropriate cleanup levels, redevelopment can occur.
Because MGPs are a problem nationwide, there have been extensive investigations
to determine what waste materials are typically found at the sites, as well as
research performed to decide which remediation technologies can be utilized to
cleanup the various contaminated matrices. Although the wastes at MGP sites are
generally described, there are a number of factors affecting the volume,
characteristics, and toxicity of the wastes generated, such as the type of gas
manufacturing process used, the raw materials used in the manufacturing process,
the feedstock used in the manufacturing process, and the former disposal
practices for the by-products (Larsen, 1997; GZA, 1998b).
Gas Manufacturing Processes Top of page
In the United States manufactured gas was produced mainly by three major
processes: coal carbonization, carburetted water gas, and oil gas (GZA, 1998b;
Mon, 1995). The majority of the process steps described below reference Mon's
History of the Manufactured Gas Business in the United States unless otherwise
noted.
Coal Carbonization Process Top of page
The coal carbonization process, also known as coal gas, was used exclusively from
1816 to 1875 until the carburetted gas process was developed. Coal gas was
normally produced by the distillation of bituminous coal in air/oxygen deficient
containers called retorts. This process could be better defined as the
decomposition of coal into volatile products by the action of heat in the absence
of air or oxygen. The retorts used for the distillation of coal are made of clay
and usually have an oval or D form and are arranged in a furnace as a bench and
heated by coke. The coal is charged into the retorts at fixed intervals.
During heating, about two-fifths of the coal's weight is converted into products
that are vapors at the temperature of the retorts, and the remaining three-fifths
is left in the retorts as a porous mass known as coke. After the volatile matter
has been driven off, the coke is drawn from the retorts and quenched with water,
and is either stored for sale or used for heating the bench.
Vertical pipes that rise from one end and are connected to the hydraulic main
placed horizontally above the bench remove the vapors given off in the retorts.
In the hydraulic main some of the vapors are condensed into liquids. These
liquids are partially water and partially tar; the gas leaving the hydraulic main
still contains large amounts of condensable materials.
From the hydraulic main, the gas passes through a condenser. This is usually of
such form that the gas passes through a long series of pipes that are either
exposed to the air or surrounded by water, where the temperature of the gas is
greatly reduced. By this cooling, more water and tars are condensed and removed.
Next to the condenser or, in some gas works, between the gas condenser and the
hydraulic main, there is an exhauster. The purpose of the exhauster is to relieve
the pressure on the retorts. The friction of the gas in the pipes and various
parts of the purifying apparatus where the gas is forced to pass through water
and layers of solid materials causes this pressure. The exhauster draws the gas
from the retorts and forces it through the rest of the train.
The gas, now freed from most of the liquid impurities, still contains ammonia and
gaseous sulfur compounds which must be removed before the gas is commercially
acceptable. The removal of ammonia is easily accomplished by washing the gas with
water. The water, after it has absorbed the ammonia, combined with the water
product from the hydraulic main, is then known as ammonia liquor. When property
treated, ammonia is recovered from this liquor.
Two substances were commonly used to remove sulfur compounds: moist lime or moist
iron oxide. These are arranged in iron vessels, called purifiers, through which
the gas is forced. The hydrogen sulfide is then absorbed by (reacts with) the
purifying materials.
From the purifiers, the gas passes to the station meter where it is measured and
is then sent to the gas storage holder. From the holder, the gas is sent through
the street mains to the customers. This method produced a coal gas that had a low
thermal content per unit volume of gas, approximately 100-150 Btu/cubic foot
(Clark; Srivastava, 1997).
Carburetted Water Gas Process Top of page
In 1873 in Pennsylvania, Professor L. Lowe invented the carburetted water gas
process that consists of spraying oil into water gas (blue gas) in a hot vessel
to increase the caloric value of the blue gas. The method utilized a cyclic
steam-air process that produced a gas with a thermal content of approximately
300-350 Btu/cubic foot (Clark). This "water gas" was mainly comprised of carbon
monoxide and hydrogen (Clark). The invention of this process and the abundant
supply of gas oil from the petroleum industry soon made carburetted water gas the
most important manufactured gas in the United States in its time.
The process is an intermittent one, consisting of alternate 'blows' or blasting
periods, and 'runs' or gas making periods. The typical carburetted water gas
generating equipment consists of three brick-lined, cylindrical, steel wheels -
the generator, the carburetor and the superheater.
The generator has a blast connection, top and bottom steam inlets, a fuel bed
(typically coke or anthracite) and bottom and top off-take pipes. The top of the
carburetor is connected to the gas off-take from the generator and provisions are
made for the introduction of enriching oil at the top of the carburetor. At the
top of the superheater there is a stack valve and a gas connection to the wash
box.
Alternate blows heat the apparatus and alternate runs make gas. During the blow a
producer gas high in carbon dioxide is formed in the generator by passing air
through an incandescent mass of coke or anthracite. This gas is burned by
secondary air. The hot products of combustion heat the checkerbrick of the
carburetor and superheater and then pass form the top of the superheater to the
stack.
During the run, water gas is made in the generator and then passes into the top
of the carburetor where oil is sprayed. This mixture passes down through the
carburetor and up through the superheater. In their pass through the hot
checkerbrick, the oil vapors are thermally cracked and fixed into gases. The
carburetted water gas, a mixture of blue and oil gas, passes from the top of the
superheater through a water sealed wash box where the gas is initially cooled and
some of the heavy tars are condensed and removed.
After the wash box, the gas passes through condensers where it is normally cooled
to ambient temperature. The condensers cause water vapor and tars to condense
into a light tar that is then removed from the condensers. The condensers that
transformed heat from the gas to the air were the first type employed for cooling
the gas. Water cooled condensers were basically of the shell and tube
construction type with cooling water passing through the tubes and gas flowing
through the shell.
Direct contact with water was also used to cool and scrub the gas. The gas heats
the water and the circulating water removes the condensed vapor and tars. The
direct cooling of the gas is usually accomplished in a counter-current packed
scrubber to increase the contact surface between the gas and the water.
The gas then passes into the relief holder. The function of the relief holder is
to provide a continuous gas supply to the exhauster and smooth the intermittent
gas making runs of the gas making process. From the relief holder the gas is
forced by the exhauster through the rest of the purification equipment, the
station meter, and into the storage holder.
From the removal of tar mist from the gas, three types of scrubbing apparatus may
have been used: 1) the 'wire drawing' or friction for the separation of fine
particles of tar in which the friction generated by the gas passing through fine
orifices, the impact of the particles on the surface opposite to the orifices,
and the sudden change in velocity of the gas, cause the separation of the tar
particles; 2) the shaving scrubber which removes the tar mist by adsorption of
the fine particles on the surface of shavings through which the gas is passed;
and 3) the modern direct current electrical precipitation of suspended particles
from gases invented by Cottrell in 1912-1913.
Tar extractors were used in large plants. For example, by 1926 Cottrell's
electrical precipitation technique had been installed in ten plants in the United
States with capacities of over 6 million cubic feet of gas per precipitator per
day.
Naphthalene scrubbers were also used in larger plants to remove naphthalene that
was one of the main causes of trouble in the distribution system. After the
naphthalene scrubbers, the gas was forced through a series of boxes filled with
lime or a mixture of iron oxide and wood shavings to remove the hydrogen sulfide
from the gas.
Large plants with capacities of over 20 million cubic feet per day may have used
liquid purification systems to remove the bulk of the hydrogen sulfide after
which the gas was passed through a dry (iron oxide) purification system.
After the hydrogen sulfide removal the gas was metered in the station meters and
sent to the storage holders for its eventual distribution through the
distribution gas mains to the customers. In the United States, the last
carburetted water gas plant closed its doors in the early 1970s (Neuhauser,
1995).
Oil Gas Process Top of page
By adding oil to the reactor in the oil gas method, the thermal content of the
gas was increased to 500-550 Btu/cu ft thereby generating more heat. The oil gas
process became the standard for gas distributed to residences and industry
(Clark). The first patent to manufacture oil gas was obtained by L. Lowe in 1889
and the first large gas plant for the production of oil gas was built in Oakland,
California in 1902.
The oil gas process consists of the thermocracking of oil in a steam atmosphere.
The generating equipment is similar to that used for carburetted water gas; the
generator was replaced by a vaporizer similar to the carburetor, filled with
checkerbrick and equipped with oil spray; the carburetor was replaced by a
vaporizer followed by the superheater as in the carburetted water gas process.
The vaporizers and superheater are interconnected at their bases.
The process is cyclical and consists of blows and runs. During the blow, oil is
burned in the vaporizers and the products of combustion heat the checkerbrick of
the vaporizers and superheater and then pass from the top of the superheater to
the stack. During the run, oil is sprayed in the vaporizers in the absence of air
and presence of steam. In their passage through the hot checkerbrick the oil
vapors are thermally cracked and fixed into gases. During the run the stack valve
is closed and the oil gas passes to the washbox. The rest of the oil gas process
is essentially the same as the carburetted water gas process.
In its day, manufactured gas provided a source of energy that was far more
efficient and cleaner than coal. Initially manufactured gas was used extensively
in the lighting of streets for example, thereby making a significant contribution
to the public in the area of safety. Later, manufactured gas replaced coal and
wood for heating and cooking purposes. Indeed, manufactured gas made a number of
positive contributions to society until the 1950s when its use was largely
replaced by natural gas.
Waste Products Top of page
By-products of the gas manufacturing process that cannot be recycled, sold, or
given away are considered waste products. Many times the wastes were simply
covered over with dirt or buried where contaminants could leach into the
surrounding sediments, soil, surface water or groundwater. The volume, toxicity,
and specific chemical make-up of the waste vary depending upon raw material
inputs and processing. In addition to the environmental issues derived from the
disposal of wastes generated during processing, historical spills or leaks
occurring during gas generation, purification and storage also created
environmental concerns. The waste products or spills can cause contaminated
soils, sediments, and surface and groundwater at or near the manufacturing
facility (GZA, 1998b).
In general the waste products found at former MGPs are tars; oils; inorganic
spent oxides (ferrocyanide); benzene, toluene, ethylbenzene, and xylene (BTEX);
volatile organic compounds (VOCs); semi-volatile organic compounds (SVOCs);
phenolics; polynuclear aromatic hydrocarbons (PAHs); cyanides; thiocyanates;
metals (arsenic, chromium, copper, lead, nickel, and zinc); ammoniates; nitrates;
sludges; ash; ammonia; lime wastes; and sulfates/sulfides (Hatheway and Johnson;
Larsen, 1997; Srivastava, 1997; GZA, 1998b).
The PAHs and VOCs are found in the coal tar left over from the gasification
process (EPA). Coal tar is a by-product of all former MGP sites. Coal tar is a
dense, non-aqueous phase liquid (DNAPL) which, when released into an aquifer, can
migrate downward until a low-permeability layer is encountered. Therefore, pools
of coal tar can be encountered at the bottom of an aquifer, becoming a continuous
source of groundwater contamination. The toxicity of MGP coal tars and residues
is not well understood as little data exists in the literature (Murarka, 1995).
Cyanides are typically found in the cyanide salts left in the iron oxide waste
produced when the gas was purified (EPA). The presence of oils, which are light
non-aqueous phase liquids (LNAPLs), and tars, which are DNAPLs, creates a dual
concern at MGP sites -- the possibility of having a floating product on the water
table and a sinking product that can penetrate the entire depth of an aquifer
(Larsen, 1997).
The Institute of Gas Technology categorizes wastes from former MGP sites into six
major categories (Srivastava, 1997):
- Pumpable liquids (free tars and oils)/source material
- Organic waste or tar/oil-contaminated waters
- Organic waste or tar-contaminated soils and sediments
- Non-pumpable tars and sludges
- Purifier box (or spent oxide) wastes
- Demolition debris
In addition, the contaminants of concern (COC) at MGP sites can be divided into
five chemical types: inorganics, metals, volatile aromatics, phenolics, and PAHs.
The organic contaminated or PAH containing soils represent the largest waste type
at most MGP sites (Srivastava, 1997).
Investigation of Former MGP Sites Top of page
It is estimated that from 1880 to 1950, gas plants produced approximately 15
trillion cubic feet of gas and approximately 11 billion gallons of tar as a
by-product (Srivastava, 1997). The result was thousands of contaminated acres of
land and millions of gallons of impacted water. When owners/operators and
regulators began to realize that these natural assets were valuable and could be
restored, it was necessary to identify what type of contamination was there,
where it was located, and how bad it was. In order to complete this type of
assessment it is necessary to use the appropriate site investigation techniques
to address MGP-type wastes (VOCs, SVOCs, PAHs, metals, tars, oils, etc.). Below
is a summary of site investigation techniques that can be instituted during the
investigation and characterization of a former MGP site.
Buried Objects Top of page
Ground penetrating radar (GPR) is a technology that emits pulses of
electromagnetic energy (radio waves) into the subsurface and measuring waves that
are scattered back at the surface. By evaluating the reflection and refraction of
the waves by the subsurface materials, areas or layers of different composition
can be identified. GPR techniques can be used to locate buried objects, map
shallow groundwater surfaces, or map various geologic formations.
Electromagnetic (EM) Induction is a geophysical technology used to induce a
magnetic field beneath the earth's surface, which in turn causes a secondary
magnetic field to form around nearby objects that have conductive properties,
such as ferrous and nonferrous metals. The secondary magnetic field is then used
to detect and measure buried debris.
Infrared Monitor (IM) is a device used to monitor the heat signature of an object
and therefore detect buried objects in soil.
Seismic Reflection and Refraction are technologies used to examine the subsurface
features of soil and bedrock. Seismic techniques can produce geophysical profiles
as well as locate buried debris, channels, or other subsurface anomalies.
Geophysical Profiles Top of page
Seismic Reflection and Refraction technologies were previously described.
Direct Push Sampling is a technique in which a sampling tube is hydraulic pushed
or driven into the subsurface collecting material as it advances. The sampling
tubes are usually 2 or 4 feet in length and can provide a continuous sample of
the subsurface material. By visually analyzing the material within the sampling
tubes an environmental specialist or geologist can derive a subsurface
geophysical profile consistent with the depth from which the samples were
collected. Direct push sampling can only occur in unconsolidated sediments where
bedrock is not present. Direct push sampling cannot penetrate bedrock.
Soil Screening Top of page
Flame Ionization Detector (FID) measures the change of signal as a hydrogen-air
flame ionizes analytes. A FID can be used alone to give a total reading of
ionized contaminants in parts per million (ppm). When used in this setting, the
FID is a screening tool for soil contamination. It can provide a general idea
whether soil is slightly or grossly impacted based on the total ppm reading.
However, note that there is not a direct relationship between the contaminant
levels identified with a FID and those obtained during laboratory analysis of the
soil. In addition, when a FID is used alone the contaminant is unknown because it
cannot identify the individual contaminants causing the ionization. Because a FID
can detect phenols, phthalates, PAHs, VOCs, and petroleum hydrocarbons, the ppm
reading could be any one of these individual contaminants or a combination of
them. A FID can also be used in conjunction with a gas chromatograph to identify
and quantify the individual constituents causing the soil contamination.
Photoionization Detector (PID), similar to a FID, measures the change of signal
as analytes are ionized by an ultraviolet lamp. It can be used alone to give a
general idea of levels of soil contamination, but cannot identify the individual
constituents that are present. The PID can detect VOCs and petroleum
hydrocarbons. A PID can also be used in conjunction with a gas chromatograph to
identify and quantify the individual constituents causing the soil contamination.
Soil Sampling Top of page
Direct Push sampling is a technique in which a sampling tube is hydraulic pushed
or hammered into the subsurface collecting material as it advances. The sampling
tubes are usually 2 or 4 feet in length and can provide a continuous sample of
the subsurface material. The environmental specialist or geologist will log the
type of material (i.e. clay, course sand, etc.) collected at each sampling
interval and collect a representative sample from the material for laboratory
analysis. The volume of soil and the sampling jars needed will depend on the
laboratory analysis to be completed. The type of laboratory analysis conducted is
contingent on the suspected type of contaminants. Direct push sampling can occur
only in unconsolidated sediments where bedrock is not present. This technique can
be used when sampling for any constituent (VOCs, SVOCs, PCBs, PAHs, etc.).
Drilling techniques can be utilized not only to collect soil samples but to
install groundwater wells as well. The method of drilling employed depends on the
subsurface material and the expected depth to groundwater.
Soil Gas Survey consists of gaseous elements and compounds that occur in small
spaces between particles of the earth and soil. Such gases can move through or
leave the soil or rock, depending on changes in pressure. During a soil gas
survey a small hole (less than 1-inch diameter) is advanced in the soil to a
desired depth. A small tube from the PID or FID is placed into the hole so the
soil gas can travel up the tube to the ionization device. After ionization, the
gas enters into a portable gas chromatograph (GC) that identifies and quantifies
the individual organic compounds on the basis of molecular weight, characteristic
fragmentation patterns, and retention times. The results of a soil gas survey
give a general quantification and location of the constituents of soil
contamination at the site. Soil gas surveys are applicable when the suspected
contaminants are VOCs and SVOCs.
Immunoassay Test Kits are an innovative technology used to measure
compound-specific reactions to individual compounds or classes of compounds. The
reactions are used to detect and quantify contaminants. In-field portable test
kits using this method are available for the following compounds or groups of
compounds: benzene, toluene, ethylbenzene, and xylene (BTEX), PCPs, PCBs, PAHs,
pesticides, explosives, and metals. In order to use immunoassay testing
effectively, one must know or have a strong suspicion what contaminant is in the
soil, as well as where it is. Colorimetric Kits are another in-field soil testing
method. Colorimetric refers to chemical reaction-based indicators that are used
to produce compound reactions to individual compounds, or classes of compounds.
The reactions, such as visible color changes or other easily noted indications,
are used to detect and quantify contaminants. In order to use colorimetric kits
effectively as a testing method, one must know or have a strong suspicion what
contaminant is in the soil, as well as where it is. Colorimetric kits can be used
to analyze for organic and explosive contaminants.
Laser-Induced Fluorescence/Cone Penetrometry is a field screening method that
couples a fiber optic-based chemical sensor system to a cone penetrometer mounted
on a truck. It is most effectively used when petroleum contamination is present.
X-ray Fluorescence (XRF) analyzer is a self-contained, field-portable instrument,
consisting of an energy dispersive x-ray source, a detector, and a data
processing system that detects and quantifies individual metals or groups of
metals.
Groundwater Sampling Top of page
Direct Push sampling is a technique in which a sampling tube is hydraulic pushed
or advanced into the subsurface coring a hole. After the hole reaches the
groundwater table, a groundwater sampling tube is dropped down to collect a
sample. The volume of groundwater and the sampling jars needed will depend on the
laboratory analysis to be completed. The type of laboratory analysis conducted is
contingent on the suspected type of contaminants. Direct push sampling can only
be used when the groundwater table is in the unconsolidated sediments because it
cannot penetrate bedrock. This technique can be used when sampling for any
constituent (VOCs, SVOCs, PCBs, PAHs, etc.).
Drilling techniques can be utilized not only to collect soil samples but to
install groundwater wells as well. The method of drilling employed depends on the
subsurface material and the expected depth to groundwater.
Immunoassay Test Kits were previously described in the soil section.
Colormetric Kits were previously described in the soil section.
Laser-Induced Fluorescence/Cone Penetrometry was previously described in the soil
section.
Remediation of Former MGP Sites Top of page
Only after a site is fully characterized can an effective remediation project
begin. However, prior to initiating the remediation, a remediation technology or
technologies must be selected. In addition to considering site specific features
such as geology or contaminant properties, a project manager must also consider
social and political factors including but not limited to the regulatory
environment, risks to the surrounding population and environment, the time frame
for cleanup, liability issues, and the projected future use of the land.
MGP sites represent a large remediation challenge because of their complexity.
Brown et al. from Groundwater Technology, Inc. summarize the challenges as
follows (Brown et al, 1995):
1. The base contaminant, coal tar, is composed of a complex mixture of PAHs which
as a class of compounds, generally have low volatility, low solubility, and low
biodegradability and are, therefore, difficult to treat.
2. The mixture of PAHs present in the coal tar is highly variable so that
technologies that work at one site may not work at another site. The variability
in coal tar composition is a function of the type of coal used and of the type of
gasification process employed.
3. There is a wide range in the depositional history and levels of the coal tars
even within one site.
The lack of remediation technology has been a problem for many years, but there
is an increasing number and variety of technologies and approaches available for
the remediation of MGP sites (Brown et al, 1995). Brown et al. group these into
four main categories: thermal processes, desorbtion processes, biological
processes, and chemical oxidation processes (1995).
However, in order to successfully utilize any remediation technology, the degree
of contamination and the level of treatment (or cleanliness) must be considered.
There are three levels of treatment that technologies can achieve. The first is
gross reduction where high levels of contamination are reduced so that the
residuals do not continue to pose an immediate or acute health and safety threat
to the surrounding population. The second level of treatment is to control the
continued migration of the contaminants by reducing soil concentrations to a
low-leachable level. The final level of treatment is to 'clean', where a specific
standard for soil and/or groundwater is met. Many times this specific standard is
based on the future potential risk the contamination will pose at the site. This
risk-based approach considers contaminants, exposure pathways, site design, and
end-use. The matrix below adapted from Ackerman et al., generalizes the key
remediation criteria and the associated cleanup/reuse factor.
| Key Criteria | Distinctive Cleanup/Reuse Factor |
| Real Estate Market Intelligence and Redevelopment Analysis |
- Wide-variety in landmass (1-to-100+acres).
- Often adjacent to or nearby municipally significant, viable sites.
- Many sites border large water bodies.
- Proven cleanup/restoration case studies exist.
- Conceivable reuses vary: industrial, office, retail, municipal, recreational, residential, and marine-related uses, or some such mix.
|
| Identifiable Trails of Site Responsibility and Ownership |
- Frequently owned by utilities via precedent companies.
- Utilities maintain ownership; sometimes reuse such sites themselves.
- Records of past uses and tenants usually recoverable.
- Potentially responsible parties (PRPs) often identifiable.
|
| Location of Leverage for Opportunity Bartering |
- Some of socioeconomic significance; urban-centralized.
- Often near rivers, streams, and other surface water bodies.
- May enjoy (or be subject to) high visibility.
- Big sites can attract high-ticket end users.
- Smaller sites often trigger social value.
|
| Existing Infrastructure |
- Often near major transportation amenities.
- Electricity, natural gas pipelines, and public sewage system: many.
- Near other businesses, hospitals, and schools: typically.
- Local demographics can prejudge reuse options.
|
| Structural Similarities and Distinguishing Characteristics |
- Usually insignificant architectural appeal; some are unique.
- MGPs often already dilapidated, demolished, or destroyed.
- Power plants need decontamination, demolition, and renovation.
- Some building material has significant recycling value.
|
| Property Tax Impacts |
- Usually insignificant architectural appeal; some are unique.
- MGPs often already dilapidated, demolished, or destroyed.
- Power plants need decontamination, demolition, and renovation.
- Some building material has significant recycling value.
|
| Property Tax Impacts |
- Taxes usually paid by utilities via site ownership.
- Devalued property conditions generate lower than potential tax revenue.
- Often zoned for near-term property tax exemptions/incentives for new-use investors.
- Reuse can have profound long-term property tax increases.
|
| Available Funding Mechanisms and Magnets |
- Costs can be recovered by utilities through several channels.
- Varied funding mechanisms may be available: public/private.
- Some sites are targets for economic redevelopment funding alliances.
- Low-interest, revolving funds sometimes available.
- Partnering with municipalities helps identify other funding.
- Financial management groups may purchase/redevelop these sites.
- End uses can stimulate utility's vested interest.
|
| Nature and Extent of Environmental Contamination |
- Asbestos from roofing and pipe lagging; lead paint from gas holder structures; coal tar residuals-NAPLs, PAHs; cyanide composites from purifier waste; structural, chemical, and petroleum products and wastes; mercury-containing equipment. (Asphalt, earth, electrical
fixtures, masonry, rubble, metal, and plastics often can be recycled and offset remediation costs. MGP residuals can be used for recycling or co-burning processes.)
|
| Liability Management Strategies |
- Agreements with state: covenants-not-to-sue.
- Comfort letter from EPA regions helps manage liability.
- Quantify re-opener possibilities.
- Seller/buyer/lease concurrence issues.
- Insurance available to protect investment.
|
| Regulatory Process |
- State-led; sometimes federal involvement/lead.
- Cleanup often conducted through consent orders.
- Cleanup standards depend on future intended use.
|
Remediation Strategy Top of page
The first goal of a cleanup strategy should be to remediate the hot spots or
source(s) in order to prevent additional releases to the environment. The source
may be pumpable hydrocarbons, contaminated soil, or USTs. After the source(s) are
removed, the remediation goal should be to intercept any contamination that
potentially may migrate offsite. This step could be as easy as removal of stacked
drums near the property boundary or more complicated such as interception of
groundwater flow by pumping and treating onsite. The last step in the cleanup
strategy would be treatment of any contaminated soils or sediments. The treatment
may be completed offsite after excavation or onsite (in-situ) depending on site
conditions, contaminant properties, and time and budgetary constraints.
Remediation Technology Selection Factors Top of page
The recent developments through funding from various agencies and utilities have
resulted in the availability of several remediation technologies that can be
applied at MGP sites. However, the selection of techniques generally depends upon
many factors that include technical, socioeconomic, regulatory, risk, liability,
as well as financial (Srivastava, 1997). The factors for selecting an appropriate
remediation technology or technologies will depend on the following factors
(Srivastava, 1997):
- Waste and Waste Matrix
- Toxic or non-toxic waste
- Waste type
- Waste concentration
- Soil type and co-contaminants
- Current Risks
- Treatment End Point
- Risk-based remediation
- End point concentration based remediation
- Natural Attenuation
- Waste Matrix Location
- Excavated
- In place
- Below or above the groundwater
- Plume location
- Availability of Land for Remediation
- Future Land Use and Proximity to Residential and Industrial Areas
- Regulatory Environment and/or Legal Issues
- Time and Schedule for Remediation
- Maturity of Technology, Effectiveness, and Treatment Costs
- Financing and Financial Factors
Remediation Alternatives Top of page
Risk-based management practices are gaining momentum because they not only
eliminate the risk and associated liabilities, but also offer significant cost
savings (Srivastava, 1997). However, it must be noted that end land use and
potential future land uses must be addressed when completing a risk-based
cleanup. For instance, if the potential use for the land in the future is
commercial, commercial risk-based standards will be the cleanup objective during
remediation. There must be controls, such as a deed restriction, that do not
allow the property to be redeveloped in the future to a higher risk use (i.e.
residential).
As stated previously, The Institute of Gas Technology categorizes wastes from
former MGP sites into six major categories (Srivastava, 1997):
- Pumpable liquids (free tars and oils)/source material
- Organic waste or tar/oil-contaminated waters
- Organic waste or tar-contaminated soils and sediments
- Non-pumpable tars and sludges
- Purifier box (or spent oxide) wastes
- Demolition debris
The remediation of the first three categories of wastes is discussed below.
Remediation of Pumpable Liquids (free tars and oils) and Source Material Top of page
Solvent extraction is an innovative treatment technology that uses a solvent to
separate or remove hazardous organic contaminants from oily-type wastes, soils,
sludges, and sediments. The technology does not destroy contaminants, but
concentrates them so they can be recycled or destroyed more easily by another
technology. Solvent extraction has been shown to be effective in treating
sediments, sludges, and soils that contain primarily organic contaminants, such
as PCBs, VOCs, halogenated organic compounds, and petroleum wastes. Such
contaminants typically are generated from metal degreasing, printed circuit board
cleaning, gasoline, and wood preserving processes. Solvent extraction is a
transportable technology that can be brought to the site.
Surfactant flushing is an innovative treatment technology used to treat
contaminated groundwater. Surfactant flushing of NAPLs increases the solubility
and mobility of the contaminants in water so that the NAPLs can be biodegraded
more easily in an aquifer or recovered for treatment aboveground.
Remediation of Organic Waste or Tar/Oil-Contaminated Waters Top of page
Bioremediation refers to treatment processes that use microorganisms (usually
naturally occurring) such as bacteria, yeast, or fungi to break down hazardous
substances into less toxic or nontoxic substances. Bioremediation can be used to
clean up contaminated soil and water. In-situ bioremediation treats the
contaminated soil or groundwater in the location in which it is found. For
ex-situ bioremediation processes, contaminated soil must be excavated or
groundwater pumped before they can be treated.
Air sparging involves injecting air or oxygen into the aquifer to flush volatile
contaminants out of the groundwater as the air or oxygen bubbles up through the
groundwater. The volatilized contaminants are typically captured by a vapor
extraction system that requires additional treatment upon removal. The system
works as an in-situ air stripper.
A treatment wall is a structure installed underground to treat contaminated
groundwater found at hazardous waste sites. Treatment walls, also called passive
treatment walls, are put in place by constructing a giant trench across the flow
path of contaminated groundwater and filling the trench with one of a variety of
materials carefully selected for the ability to clean up specific types of
contaminants. As the contaminated groundwater passes through the treatment wall,
the contaminants are trapped by the treatment wall or transformed into harmless
substances that flow out of the wall. The major advantage of using treatment
walls is that they are passive systems that treat the contaminants in place so
the property can be put to productive use while it is being cleaned up. Treatment
walls are useful at some sites contaminated with chlorinated solvents, metals, or
radioactive contaminants.
Groundwater is extracted using a system of wells and pumps, placed in a vessel
and then treated by UV oxidation. Extraction and treatment by UV oxidation is
best utilized for water contaminated by VOCs and SVOCs.
Groundwater is extracted using a system of wells and pumps and then pumped into
an activated carbon treatment system. The system causes the contaminants to
adhere to the carbon surface, thereby creating "clean" water effluent.
Groundwater is extracted using a system of wells and pumps. The groundwater then
flows into an air stripping system that removes or "strips" VOCs from
contaminated groundwater or surface water as air is forced through the water,
causing the compounds to evaporate. The separated groundwater is then treated
using activated carbon. As the contaminated water flows through an activated
carbon system, the contaminants adhere to the carbon surface allowing the "clean"
water to pass out of the system. Groundwater is extracted using a system of wells
and pumps and then discharged into a sanitary sewer system. The sanitary sewer
discharges into the publicly owned treatment works (POTW) that will be
responsible for the treatment.
Surfactant flushing is an innovative treatment technology used to treat
contaminated groundwater. Surfactant flushing of NAPLs increases the solubility
and mobility of the contaminants in water so that the NAPLs can be biodegraded
more easily in an aquifer or recovered for treatment aboveground.
Remediation of Organic Waste or Tar-Contaminated Soils and Sediments Top of page
Soil Vapor Extraction (SVE) physically separates contaminants from soil in a
vapor form by exerting a vacuum through the soil formation. Soil vapor extraction
removes VOCs and some SVOCs from soil beneath the ground surface.
Bioremediation refers to treatment processes that use microorganisms (usually
naturally occurring) such as bacteria, yeast, or fungi to break down hazardous
substances into less toxic or nontoxic substances. Bioremediation of soil is
typically in-situ but can also be applied ex-situ. In-situ bioremediation treats
the contaminated soil in the location in which it is found. For ex-situ
bioremediation processes, contaminated soil must be excavated or groundwater
pumped before they can be treated.
Bioventing is an in-situ remediation technology that combines soil vapor
extraction methods with bioremediation. It uses vapor extraction wells that
induce airflow in the subsurface through air injection or through the use of a
vacuum. Bioventing can be effective in remediating releases of petroleum
products, such as gasoline, jet fuels, kerosene, and diesel fuel.
Impacted soil is excavated using heavy machinery and stockpiled for treatment. If
state and federal regulations allow, an area of the site can be designed for
onsite aeration of contaminants. Aeration is the process of air coming into
contact with the soil and contaminant(s) in an effort to volatilize the
contaminants. Volatilization is the process of transfer of a chemical from the
aqueous or liquid phase to the gas phase. Solubility, molecular weight, and vapor
pressure of the liquid and the nature of the gas-liquid affect the rate of
volatilization. This treatment process works best on light (low molecular weight)
contaminants, such as VOCs and some SVOCs.
Impacted soil is excavated using heavy machinery and stockpiled for treatment.
The treatment system can either be onsite or offsite. Low temperature thermal
desorption (LTTD) is a physical separation process in which wastes are heated to
between 90o C and 320o C to volatilize contaminants and water but not oxidize them.
The carrier gas or vacuum system transports the volatized water and organics to a
gas treatment system. The decontaminated soil is considered clean and can support
microbiological growth. LTTD works best for VOC, SVOC and petroleum contaminated
soil.
Impacted soil is excavated using heavy machinery and stockpiled for treatment.
The high temperature thermal desorption (HTTD) system can either be onsite or
offsite. HTTD is a physical process in which wastes are heated to between 320o C
and 560o C to volatilize contaminants and water but not oxidize them. The carrier
gas or vacuum system transports the volatized water and organics to a gas
treatment system. The decontaminated soil is considered clean and can support
microbiological growth. Because HTTD heats the wastes to a higher temperature,
it is especially used for treatment of SVOCs which are harder to volatilize but
can also be used for VOCs.
Impacted soil is excavated from the ground using heavy machinery and is then
stockpiled for treatment. The incineration system can either be onsite or
offsite. Incineration uses high temperatures (870o C to 1200o C) to volatilize and
combust halogenated and other refractory organics, such as VOCs and SVOCS, in
hazardous wastes.
Soil washing> is an innovative treatment technology that uses liquids (usually
water, sometimes combined with chemical additives) and a mechanical process to
scrub soils, remove hazardous contaminants, and concentrate the contaminants into
a smaller volume. The technology is used to treat a wide range of contaminants,
such as metals, gasoline, fuel oils, and pesticides. Soil washing is a relatively
low-cost alternative for separating waste and minimizing volume as necessary to
facilitate subsequent treatment. It is often used in combination with other
treatment technologies. The technology can be brought to the site, thereby
eliminating the need to transport hazardous wastes.
Solvent extraction is an innovative treatment technology that uses a solvent to
separate or remove hazardous organic contaminants from oily-type wastes, soils,
sludges, and sediments. The technology does not destroy contaminants, but
concentrates them so they can be recycled or destroyed more easily by another
technology. Solvent extraction has been shown to be effective in treating
sediments, sludges, and soils that contain primarily organic contaminants, such
as PCBs, VOCs, halogenated organic compounds, and petroleum wastes. Solvent
extraction is a transportable technology that can be brought to the site.
In-situ soil flushing is an innovative treatment technology that floods
contaminated soils beneath the ground surface with a solution that moves the
contaminants to an area from which they can be removed. The technology requires
the drilling of injection and extraction wells on site and reduces the need for
excavation, handling, or transportation of hazardous substances. Contaminants
considered for treatment by in-situ soil flushing include heavy metals (such as
lead, copper, and zinc), halogenated organic compounds, aromatics, and PCBs.
Ex-Situ versus In-Situ Remediation Top of page
In addition to dividing clean-up technologies into classifications according to
waste material, they can be further separated depending on whether an in-situ or
ex-situ treatment is desired. An in-situ remediation technology treats the waste
material in-place. An example is using soil vapor extraction (SVE) to clean-up
shallow soil contaminated with VOCs. An ex-situ remediation technology removes
the waste from its location and then treats it. Excavating and then thermally
treating soil contaminated with PAHs is an example of an ex-situ remediation
technology. The physical and chemical characteristics of the waste material will
partially dictate whether an in-situ or ex-situ remediation method is even
technically feasible. For instance, in-situ treatment of soil contaminated with
PAHs is technically challenging and would, therefore, be better remediated
through ex-situ technologies. The remediation technologies described above are
broken down into in-situ and ex-situ categories for further explanation.
EX-SITU
- Excavation and aeration of soil
- Excavation and LTTD of soil
- Excavation and HTTD of soil
- Excavation and incineration of soil
- Soil washing of soil
- Excavation and aeration of soil
- Hydraulic barriers through well or trench installation with pumping and treatment of groundwater
- Groundwater extraction and UV oxidation treatment for groundwater or surface waters
- Groundwater extraction and treatment via carbon adsorption
- Groundwater extraction and air-stripping followed by carbon adsorption
- Groundwater extraction and disposal at a POTW
IN-SITU
- SVE for Soil
- Bioremediation of Soil
- Bioremediation of Groundwater
- Bioventing of Groundwater
- Treatment Walls for Impacted Groundwater
Technologies for the Future Top of page
Because former MGP sites are prevalent throughout the United States and represent
a large area of land, new technologies must be developed and field-tested to
demonstrate their technical feasibility. Innovative, cooperative strategies need
to be forged with regulatory communities involved to assure that incentives,
rather than deterrents, exist for site owners.
An example of this type of joint venture centers on the disposal of hazardous
materials. The American utility industry and regulators have negotiated a
strategy where voluntary clean-ups at MGP sites are encouraged by allowing the
blending of hazardous materials with fuel (i.e. coal) to render them
non-hazardous for co-burning in utility boilers (Murarka, 1995). Research is
currently underway using utility boilers to co-burn tars with contaminated media.
Initial results indicate that with low feed rates (between 3 to 5% of remediation
wastes with the remainder coal), that this is a viable option (Murarka, 1995).
The environmental legacy left behind by manufactured gas plants represents some
of the worst contamination of land in the nation. However, opportunities exist to
demonstrate and refine new assessment and remediation technologies that can
assist in expediting cleanup processes that can place these contaminated sites
back into productive use for communities across the country.
References Top of page
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