Thermal Treatment And Non-Thermal Technologies
For Remediation Of MGP (Manufactured Gas Plant) Sites

Thomas F. McGowan,
TMTS Associates, Inc.
399 Pavillion Street
Atlanta, GA 30315

Bruce A. Greer
RMT, Inc.

Mike Lawless
Draper Aden Associates

Presented at HMCRI Superfund XVI,
Washington, DC
November 6-8, 1995


More than 1,500 MGP (manufactured gas plant) sites exist throughout the U.S.  Many are contaminated with coal tar from coal-fueled gas works which produced "town gas" from the mid-1800s through the 1950s (1, 2).  Virtually all old U.S. cities have such sites.  Most are in downtown areas, as they were installed for central distribution of manufactured gas.

While a few sites are CERCLA/Superfund, most are not.  However, the contaminants and methods used for remediation are similar to those used for Superfund clean-ups of coal tar contamination from wood-treating and coke oven facilities.

Clean-up of sites is triggered by regulatory pressure, property transfers and re-development as well as releases to the environment -- in particular, via groundwater migration.  Due to utility de-regulation, site clean-ups may also be triggered by sale of a utility or of a specific utility site to other utilities.

Utilities have used two approaches in dealing with their MGP sites.  The first is ·do nothing and hope for the best.·  History suggests that sooner or later, these sites become a bigger problem via a release, citizen lawsuit or regulatory/public service commission intervention.  The second, far better approach is to define the problem now and make plans for waste treatment or immobilization.

This paper describes recent experience with high capacity/low cost thermal desorption process for this waste and reviews non-thermal technology, such as bio-treatment, capping, recycling, and dig and haul.  Cost data is provided for all technologies, and a case study for thermal treatment is also presented.


MGP coal tars are a byproduct of coal gasification.  Figure 1 (3) shows a cross-section of a typical gas works for production of "carbureted" water gas.  The coal tar primarily resulted from cooling and scrubbing of the gas stream prior to sending it to the gas holder (a floating head tank) and the distribution mains.  It was also periodically removed while rodding the gas mains and cleaning residue from the gas holders.  While much was sold (used for many processes prior to the widespread availability of petroleum products) to industrial markets, contamination still occurred from plant operations, leaks and demolition.  In fact, when many sites were shut down, coal tar on site was simply buried with other debris.  Other wastes exist, such as wood chips and iron compounds used to purify gas and to remove sulfur from the gas stream.  However, this article focuses on the coal tar, the predominant contaminant.

Why is coal tar an environmental problem?  Many of its constituents are known to be carcinogenic and mutagenic, based on animal and bacterial studies, while others are suspected carcinogens.  They can end up in groundwater, rivers or wells and enter drinking water supplies.  While coal tar constituents vary with the source, degree of distillation and history, principal compounds are acenaphthene, anthracene, fluorene, fluoranthene, naphthalene, phenanthrene and pyrene, accounting for about 64% of coal tar (4).

How toxic are coal tars to humans?  Dermal and inhalation exposure of the workers in the coal tar wood-treating industry shows no strong or consistent health effect.  Occasional skin cancers (4) have been noted in human case reports; however, these are in small numbers and leave open the question of causality.  Coal tars are still used medicinally in dandruff shampoos and in treatment of psoriasis.

Must MGP sites be remediated?  For some that are not near active wells or surface water and where contamination is light, a case can be made to leave the site undisturbed. To do so requires a risk assessment, knowledge of principles of natural attenuation, modeling of contaminant migration and cooperative regulators.  For sites with significant contaminant release, removal or isolation of concentrated source material is a wise course of action.


Thermal Treatment

Heating the soil is the key to removing organic contaminants.  Based on RMT's experience, coal tars and other high-boiling-point organics can be removed at soil temperatures above 750 F.  At 900 F with appropriate residence time, virtually all organics are removed to below the 1 ppm level.  The soil matrix is a major factor in setting the required temperature.  Sand and gravel release organics easily and have low moisture content.  Clays have higher moisture content and the organics may bind tightly to clay particles.  Heat may be transferred directly to the soil (as in direct-fired rotary desorbers) or indirectly (via externally-heated retorts or paddle dryers).  Both low-temperature (below 1,000 F) and high-temperature systems exist.  Due to the higher cost and current de-emphasis by EPA, high-temperature incineration systems are not covered in this paper.  More on these, and EPA's "Draft Combustion Strategy" which affects them, can be found in Reference 5.

Which is the best type of thermal processor to use?  In general, the authors believe that a desorber/oxidizer using a co-current direct-fired desorber is the best choice for MGP coal tars of <4% concentration.  Its slightly higher capital and operating cost (when compared to counter-current desorbers) is more than offset by reliability and simplicity.  It also avoids design defects of counter-current desorbers (e.g., condensation of tars in the baghouse and coal tar in baghouse fines), and high cost and off-site disposal of residues from desorber/condensers.

The desorber/oxidizers do well on soil <4% organic by weight (about 800 Btu/lb) if suitably equipped per NFPA requirements.  The desorber/condensers may have an economic edge for soils of higher organic concentration.  Good candidates are soils with stable organics which are non-reactive and do not decompose at the temperatures encountered in the processing system.  The desorber/condensers are the obvious choice for sites where EPA has ruled out use of direct-fired desorbers.

Rotary Desorbers -- These are the most common type.  They are direct-fired, rotating flighted drums, similar to industrial dryers.  Processed soil temperatures up to 800 F are achieved at moderate equipment cost.  Soil temperatures of 1,000 F are possible with higher-cost alloy drums.  If the desorber is co-current, it is followed by cyclones, an oxidizer (also called an SCC or secondary combustion chamber), a dry bottom quench tower, baghouse, ID fan and scrubber (if required for SO2 removal).  If the desorber is counter-current, it is followed by a baghouse, ID fan, oxidizer and scrubber if required for SO2 removal.  In both co- and counter-current designs, a quench and activated carbon adsorber can be used to capture the vapors.  RMT favors use of an external furnace on direct-fired desorbers (both co- and counter-current) to keep the flame from direct contact with soil, thereby precluding quenching of the flame.  A process flow diagram for a desorber/oxidizer is found in Figure 2.  A desorber/condenser block diagram is shown in Figure 3.

Retorts and Paddle Dryers -- Retorts are a heat-resistant rotary high-alloy shell with external gas or electric heat.  They have been used for many years in the mineral industry.  Normal design temperatures for processed soil are 800-1,000 F.  Paddle dryers and hollow flight augers with hot oil or molten salts pumped through the shafts and jackets are also used.  Both retort and paddle dryer/auger technologies reduce or prevent oxidation of the organics due to low oxygen levels in the desorber.  Maximum practical soil temperatures are 700 F for hot-oil-heated systems and 1,000 F for molten salt heat transfer fluids.  Retorts and paddle dryers are usually followed by condensers and activated carbon adsorbers to remove the organics desorbed in the upstream process.

Infrared Belt -- This is a mesh belt-type furnace using electrically heated "glow bars" over the soil on the belt to drive off organic vapors.  The furnace can be equipped with an oxidizer and an air pollution control system.  Alternately, the organic vapor can be condensed and adsorbed.

Commercial Low-Temperature Systems

Examples of commercially-available equipment in use are Williams Environmental Services' 25 tph TPU-01 desorber/scrubber plus activated carbon adsorber, and their 20 tph TPU-02 and 30 tph TPU-03 desorber/oxidizers (6); Four Seasons Environmental Services· 40 tph co-current rotary desorber/oxidizer system; ENSCI's 40 tph co-current rotary desorber/oxidizer system; OHM/CWM's 5 tph X*TRAX desorber/condenser and 35 tph LT*X desorber/oxidizer (7); Weston's 7.5 tph LT3 desorber/condenser (8); and Westinghouse/Haztech 8 tph infrared desorber/condenser (9).  Many other systems exist for UST (petroleum-contaminated soils) which could be used for MGP soils.  However, most are counter-current designs and will likely have problems with condensation of coal tars in their baghouses.

Cost for Thermal Treatment

Costs for thermal treatment of soil may be categorized by the level of contamination present and use of on-site or off-site facilities.  Table 1 shows some typical "chute-to-chute" soil decontamination costs, for a project of greater than 30,000 tons.  When excavation and engineering are added, costs may double.  Excavation and solids handling have been problematic in many MGP pilot projects.  They need not be if the remedial design engineers are experienced and the right equipment is utilized by the remedial action contractor.

The selection of the proper thermal equipment is predicated more on the concentration and boiling point of the contaminant than its toxicity.  The largest transportable desorber/oxidizer systems have capacities of up to 45 tph, and are used on jobs of 10,000 tons and above.  Off-site treatment is available from a few firms that process contaminated soil at their own sites.  One example is Southeastern Soil Recovery, Inc.

Table 1
Typical Cost of Thermal Treatment for MGP Soil
"Chute-to-Chute" Costs for 30,000-ton Project
Type of Waste  Cost, $/Ton
Off-site treatment, low-temp desorber/oxidizer, <4% organic $60
On-site treatment, low-temp desorber/oxidizer, <4% organic $75
On-site treatment, high-temp incinerator, <4% organic  $150
On-site desorber/condenser, <2,000 Btu/lb $200+
Off-site incineration, <1,200 Btu/lb  $1,000

Bio Treatment

Some of the wastes and by-products of MGP sites can be degraded by biological processes over time.  Several factors affect the efficiency of the in situ biodegradation, including soil hydraulic conductivity, depth of groundwater, infiltration rates, soil temperature, soil aeration and the low solubility and bio-availability of PAHs.  Although it has been demonstrated that various PAHs can be degraded, the rate of removal for constituents of concern is limited.  Available data and pilot tests in soil-water-tar matrices point to a threshold soil concentration of PAH below which biodegradation becomes either very slow or ceases (10).  It is difficult to generalize about costs due to site-specific design.

Bench-scale study has demonstrated that slurry-phase chemical/biological treatment can effectively treat MGP soil impacted with PAHs to meet regulatory requirements.  Treatment would include excavation, soil screening, slurry preparation, slurry treatment and slurry de-watering.  Handling of soils, with the exception of sand and gravel, after slurry treatment is not without problems.  The wet material will be well above the moisture content corresponding to maximum Proctor density.  Hence, handling and compaction for use as engineered fill are problematic.  Preliminary cost estimates for the treatment of approximately 10,000 cubic yards of soil ranged from $220 to $230 per cubic yard (11).

Capping and Slurry Walls (Containment)

The containment of affected soil material does not provide source reduction, but does limit future migration of contaminants into the environment.  Options include construction of clay/membrane ($2.50-3.50/sf) or clay cover ($1.60-2.50/sf), and the placement of clean fill, asphalt, including base course ($1.90-2.80/sf), or concrete, including gravel base ($2.50-3.50/sf).  These costs can be translated into $/cu yard units when the depth of the contaminated layer is known.  Each alternative must also be considered in light of the planned future development of the site.  With current "Brownfield" initiatives, containment may be an appropriate solution for some sites.

Containment of groundwater can be accomplished through the use of slurry walls ($18-25/sf) or grout curtains.  These are effective at restricting groundwater if they can be keyed into a low-permeability strata.  Effective hydraulic containment also requires water contained behind the slurry wall to be removed and disposed on a continuous basis.  Costs are site-specific and the groundwater removal and treatment systems, when required, are a permanent installation.


Stabilization is similar to capping and slurry walls as it attempts to prevent the spread of contaminants.  Reagents, such as fly ash and Portland cement, are mixed with the soil to reduce permeability.  While this technique has been used widely for metals, its use with organics is more problematic and it is clearly not appropriate for high concentration MGP coal tars.  Cost varies with the "add rate" of reagent and depth of mixing, but is typically $50-$120/cu yd of soil.

Sheet Piling

Sheet piling may be used in conjunction with stabilization.  This was done at a Columbus, GA site, where deep-earth auger mixing of stabilization reagents was performed adjacent to a river.  Sheet piling may also be used alone or in conjunction with capping or slurry walls for control of water flow, or to mechanically stabilize soil.

Excavation and Hauling

Removal of near-surface, unsaturated impacted soil is possible using conventional excavation equipment.  In the case of small sites with limited contamination, dig and haul (excavation and landfilling) may be the simplest solution.  However, finding a landfill to accept the waste is becoming more of a problem due to potential liability for leaching of organics.  Phase IV of the Landban and other regulations may restrict landfilling.  Even if a landfill accepts the waste, no environmental manager wants to have to "take it back" at a later date should problems arise.

Although costs vary, the removal of materials contained in former structures (gas holders, tar holders, tar wells) is practical and provides for source removal.  The removal of deep saturated soil would require extensive construction and de-watering.  In addition, shoring of the excavation or the over-excavation of large volumes would require removal of impacted material.  Removal of material below the water table may not be worthwhile because contact and off-site release is unlikely.  Cost for near-surface routine removal of soil and moderate trucking distances (100 miles) is in the range of $20-25/cu yd.

While effective, off-site treatment or disposal (via desorbers, incinerators, chemical fixation or landfilling) of large volumes of excavated material can involve substantial costs.  Costs are highly variable, from $50/ton for lightly-contaminated soil treated with a desorber or deposited in a Subtitle D landfill, to $2,000 per cubic yard for high-temperature incineration of highly-contaminated material.  In addition, no single treatment technology is effective due to the heterogeneity of site materials (i.e., the presence of tar, soil, bulk debris and fill material).


Limited work has been done in reclaiming coal tars (by Allied Signal) for re-use in wood treating or other current applications.  Their ES&S division has recycled coal tars from MGP plants in the northeast (12) as well as K001 waste from coal tar wood-treating sites.  Cost for processing pumpable tars (FOB their plant) is $0.15-0.20/lb ($300-400/ton).  Small amounts of low-concentration soils can be treated in their RCRA permitted incinerator, at a cost of approximately $1,000/ton.

Burning of contaminated soil in utility boilers can be considered recycling in that the fuel value is reclaimed in the combustion process.  Pilot projects with selected utility boilers were successful in feeding and burning coal/coal tar soil blends.  Specific blending and handling issues must be addressed due to the range of boiler designs (e.g., cyclone burners, corner-fired furnaces, older grate-fired equipment).  Blending material and ratios are determined during pilot-scale testing to insure proper combustion during full-scale operation.  The higher ash content (typically 10% for coal vs. 90% for MGP soil) results in significantly higher bottom and fly ash production.  Costs from pilot projects for co-burning contaminated soils are highly variable.  Values of $44-142/ton (13), $65/ton (14) and $75/ton (15) have resulted from recent projects.

MGP waste has also been recycled in cement and light-weight aggregate kilns, in asphalt production and in brick-making.  In these applications, the soil becomes part of the product.  The fate of the coal tars is more problematic.  If the waste is fed to a counter-current kiln or other process where coal tar vapors do not pass through an appropriately hot oxidizing atmosphere, they may be vaporized and exit the stack as vapor or become adsorbed on particulate such as baghouse fines, rather than being fully oxidized and destroyed.

MGP waste can, of course, be destroyed in commercial hazardous waste rotary kiln incinerators.  Costs, however, are prohibitive unless quantities are exceedingly small.

A cost summary for typical thermal and non-thermal technology is presented in Table 2, based on MGP waste and hydrocarbon waste projects.

Table 2
Typical Cost of Treatment for MGP Waste
Type of Treatment  Cost,*
$/Cu Yd
Capping and slurry walls** $8
Stabilization $80
Excavation and landfilling  $100
Thermal treatment via desorber/oxidizer $115
Recycling, via utility boiler $120
Bio-treatment  $225
Recycling, recovery of pumpable tars $350

*To convert to cost per ton for soils, divide by 1.5; for tars, by 1.  Costs vary with concentration, soil properties, hydrology of site and depth of contamination.
**Based on clay/membrane cap and 10' deep contamination layer.


Clean-ups are primarily triggered by groundwater issues or property transfers.  EPA's groundwater limits (based on drinking water standards) for selected PAH compounds are presented in Table 3.

Table 3
Federal Drinking Water Standards for Coal Tar PAH Compounds (mg/L)
Polynuclear Aromatic Hydrocarbons  
Cyanide (free)
Xylenes (total)
-- = Not published    
bold = Promulgated           
( ) = Proposed              

MCL = Max. Contam. Level
SMCL = Secondary MCL


 Responsible parties must comply with an increasingly complex spectrum of environmental regulations.  Three major programs require compliance and address both the investigation and the remediation of releases of hazardous substances and hazardous wastes into the environment.  Even if a site is not governed by RCRA or Superfund, remediation frequently follows similar guidelines.

 The three programs are:

  • The corrective action program of the Resource Conservation and Recovery Act of 1976 (RCRA) as amended by the Hazardous and Solid Waste Amendments of 1984 (HSWA)
  • The remedial response program of the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA), as amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA)
  • The Clean Air Act (CAA) and state air regulations

Several currently pending reform initiatives under RCRA are likely to affect the remediation of MGP sites.  All have the potential to increase the regulatory burdens associated with clean-ups.  They are also likely to increase cost and delay clean-up work.  These initiatives are the Hazardous Waste Identification Rule (HWIR) for contaminated media, the MGP Presumptive Remedies Guidance and the Listing Petition.  Under a worst-case scenario, MGP coal tar could be regulated in the future as a listed hazardous waste (16).  In addition, Phase IV of the Landban Regulations, expected in late 1996, could require pre-treatment of MGP coal tar soils prior to landfilling.

Thermal Treatment Regulations

 MGP sites are (with few exceptions) non-RCRA and non-CERCLA.  The waste is not from current operation and is not "listed" in CFR Part 261.  Thus, thermal treatment of MGP via desorber/oxidizers is normally performed under state air permits governing PM and VOC emissions.  These regulations are simpler and cheaper to comply with than those governing Superfund/RCRA wastes covered by CFR 264.340 RCRA regulations for hazardous waste incinerators.

With a state air permit or permit guidelines, the major issues are particulate limits (virtually always at or less than 0.08 gr/dscf, in some states below 0.03 gr/dscf) and organic vapors.  The organic vapors may be subjected to a mass limit (e.g., 20 lb/hr).  However, in some states, a dispersion model using risk factors for major coal tar constituents is required.  In this case, a tall stack (above 75') for desorber/oxidizers aids in obtaining favorable values for operating limits.

For organics, a DRE (destruction and removal efficiency) test of coal tar (or its constituents) may be required.  DRE is defined as 100 x ((weight in - weight out)/weight in) of the organic.  The "weight in" is that of the organic compound or family of compounds in the feed soil and its corresponding weight out the stack.  A typical state DRE requirement would be 99% for coal tars.

DRE-based regulations emphasized the "D" for destruction, while for desorber/condensers, the goal is the "R" for removal, and the organics are not destroyed but rather condensed.  Hence, there are some logic problems in using DRE as a yardstick for desorber/condensers.  Stack emissions limits may be based on NAAQS or OSHA ambient levels (with safety factors used) using dispersion models to back-calculate allowable emissions.  In addition to organics, emissions of the 10 BIF (boiler and industrial furnace) metals may be a concern.  With low-temp desorbers, however, only low-boiling-point metals (mercury, lead and cadmium) are a concern as a stack emission.

When burning soil in utility coal boilers, the current facility air permits are normally sufficient.  This is appropriate, as coal tars are part of the volatile content of the coal they currently burn, and furnace temperatures are high, insuring good destruction.  Stack particulate tests are occasionally required to verify that higher ash does not result in excessive stack particulate emissions.

Potential for Future Innovation

RMT has a patent application on a process to desorb MGP coal tars in conjunction with utility boiler operation.  In this proprietary process, coal tars essentially free of ash are injected into a coal-fired utility boiler furnace.  Since the boiler is large compared to the desorber capacity, and since the vaporized coal tars are similar to the volatiles in the primary coal, no new permits should be required.  This system addresses boiler operator concerns about using their boilers for "waste disposal," as it removes most of the particulate which can cause boiler tube fouling and erosion.  It also preserves the integrity of the normal coal feed and prep system.  Finally, the cost for this process is also lower than that projected by many coal/soil mixture pilot tests in utility boilers or from conventional desorber/oxidizers.


Envirotech Mid-Atlantic (later merged with ENSCI Environmental) purchased a thermal desorber/oxidizer in 1990.  The 40 tph system was placed in service for desorption of petroleum soils, and later for MGP coal tar soils.  RMT provided engineering assistance for specification of the systems and for permitting for both types of contaminants.

The system was built by Astec, Inc., Chattanooga, TN.  It is composed of a co-current, 7' diameter x 30' long, rotary direct-fired desorber with external furnace, dual cyclones for dust removal, an oxidizer, dry bottom quench tower, baghouse, ID fan and stack, control system and feed and processed soil handling systems.  Total burner capacity (desorber plus oxidizer) is 84 MM Btu/hr.  It is trailer-mounted, relocatable and can be set up at a new site in less than two weeks.

When not in service at other sites, the desorber/ oxidizer was located at a company-owned landfill.  It was taken to Fredericksburg, VA, where it was co-sited with an asphalt producer.  A storage building (Butler type) was constructed to house contaminated soil at the site.

The Virginia state air permit was amended to allow operation on MGP coal tars. The permit does not allow operation on hazardous waste, such as coal tars from RCRA regulated coal tar creosote wood-treating sites.  The state MGP permit limit was 2% by weight coal tars.

The Niagara Mohawk utility company contracted with Envirotech Mid-Atlantic for MGP soil decontamination.  The soil was a sandy silt with a trace of clay.  Details of the project are summarized in Table 4.

Table 4
MGP Coal Tar
Soil Decontamination
by Envirotech Mid-Atlantic
Soil processing start/end dates 8/8/91 - 11/26/91
Soil processed 11,540 tons
Maximum raw soil TPH concentration (via 418.1/IR) 5,500 ppm
Processed soil TPH concentration <10 ppm
Maximum raw soil, coal tar PAH concentration 150 ppm
Processed soil coal tar PAH concentration <1.65 ppm
Processed soil temperature 740 F
Oxidizer temperature 1,400 - 1,600 F
Maximum permitted treatment cap. on MGP coal tars 720 tpd (30 tph)

Light and uniformly contaminated soils were processed smoothly.  Some loads of soil had heterogeneous lumps of coal tar and were re-run to insure that processed soil passed the required process soil limits on PAH compounds.  The processed soil was recycled and used for asphalt paving material.

Niagara Mohawk MGP Project Costs

 The base price was $48/ton FOB the facility in Virginia.  This was a "chute-to-chute" price and did not include excavation or transportation.  Pricing was multi-tiered, with a premium paid for soils associated with higher operating costs (as shown below).  The average price was $52/ton.

TPH > 10,000, ppm < 20,000 ppm: +$5/ton
Moisutre > 18% but < 25% +$10/ton
Moisture > 25% but < 30% +$15/ton


MGP coal tars represent an environmental problem at multiple sites.  Remedial action is required for property transfer, and when a release occurs; it should be considered before such events occur to preclude future liability.  Remedial technology spans a wide range.  Thermal treatment and removals are two methods which are fast and thorough.  Others, like pump-and-treat, take more time and may leave residual contamination.  Finally, capping a site can contain the contaminants and reduce the likelihood of release, but restricts future use of the property.

Clearly, the best path for utilities is to define the MGP problem now, keep in touch with regulators, make plans for remediation and keep firm control of their sites.


1.  Radian Corp., Survey of Town Gas and By-Product Production and Locations in the U.S., for U.S. EPA, PB85-173813, February 1985.

2.  Handbook on Manufactured Gas Plant Sites, Utility Solid Waste Activities Group, Superfund Committee, Environmental Research & Technology, Inc. and Koppers Company, Inc., ERT Project No. P-D215, September 1984.

3.  Haslam, R.T., Russell, R.P., Fuels and Their Combustion, McGraw Hill, 1926.

4.  Creosote, Special Review Document 2/3, U.S. EPA, Office of Pesticides and Toxic Substances, PB 87-17885 1, August 1984.

5.  McGowan, T.F., Santoleri, J.J. and Spratt, B.M., A Comparison of Low- and High-Temperature Thermal Desorption For Superfund Sites, HMCRI Superfund XV, Washington, DC, December 1994.

6.  Personal communication with Brett Burgess, Williams Environmental Systems, August 1994.

7.  Rust/CWM LT*X low-temperature thermal desorption sales literature, #RRS SOQ1, and personal communication with Phil Crincoli, Rust Corp., August, 1994.

8.  Nielson, R.K., and Cosmos, M.G., Low-temperature Thermal Treatment (LT3) of VOCs from Soil, AIChE Summer National Meeting, Denver, CO, August, 1988.

9.  Personal communication with John O'Brien, Westinghouse/Haztech, regarding desorber systems, August, 1994.

10.  Luthy, R.G., et. al., Remediating Tar-Contaminated Soils at MGP Sites, Vol. 28, No. 6, pp. 226-276, Environmental Science and Technology, 1994.

11.  Srivastava, V.J., et. al., MGP Soil Remediation in a Slurry Phase:  A Pilot-scale Test, IGT 6th International Symposium on Gas, Oil and Environmental Bio-technology, Colorado Springs, CO, 1993.

12.  Personal communication with Brett DeFeo, Allied Signal, ES&S, May, 1995, and three-page Superfund Site Remediation Done at Lowest Cost and in Record Time, undated publication.

13.  Hylton, K., Co-burning of MGP Site Residuals in Utility Boilers: A Case Study from New York, Management of Manufactured Gas Plant Sites Conference, Chicago, IL, June, 1995.

14.  Helmers, D.A., Co-burning of MGP Site Residuals in Utility Boilers:  A Case Study from Indiana, Management of Manufactured Gas Plant Sites Conference, 6/7-9/95, Chicago, IL)

15.  Witts, W., Co-burning of MGP Site Residuals in Utility Boilers:  A Case Study from Illinois, Management of Manufactured Gas Plant Sites Conference, Chicago, IL, June, 1995.

16.  Wiessman, W.R., Regulatory Issues and Trends:  Fundamental Changes in Regulatory Policy to Streamline Site Remediation, or Much Ado About Nothing?, Management of Manufactured Gas Plant Sites Conference, Chicago, IL, June, 1995.



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