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Chapter 5

	


	





	

This chapter describes technologies for treating former MGP residues. These

technologies have either been proven successful and cost effective or are new

and promising for use at former MGP sites. The technologies described

below destroy or encapsulate MGP residuals in the vadose zone, reducing or

eliminating the threat that chemicals from these materials will reach groundwater

or human populations and thus limiting or reducing the responsible party’s

liability. (This is in contrast to past methods of disposal that often involved

sending wastes to landfills where the responsible parties continue to bear longterm responsibility for the waste’s environmental and health effects.)

The technologies discussed in this chapter are summarized in the following table.

Although each technology is discussed independently, multiple treatment

technologies may be applied at a site to address the various chemical components.

For example, soil vapor extraction (SVE) may be applied at a former MGP site to

remediate the volatile components of the MGP residues concurrent with or prior to

in situ stabilization (which will treat the heavier, less mobile chemical

compounds). Multiple technologies applied concurrently or sequentially are often

referred to as treatment trains, and are often formed to address an overall site

remediation.

The costs provided in this section are based on limited data and are dynamic.

Many variables will affect the cost of a remediation technology as applied to a

specific site or set of sites. The cost information provided herein reflects an orderof-magnitude guide to cost, and is provided on an informational basis.

This document does not address the treatment of NAPLs or MGP contaminants in

groundwater. These issues may be addressed in a future volume of this document.

However, remediation at a site should address all the site’s contaminants,

including those present in both soil and groundwater.

	


	


The following sections contain specific information pertaining to each of the

technologies for treating residuals and contaminated soil from former MGP sites.
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Source Material Treatment Technologies

Name Description Benefits Limitations Approximate

Cost *

Co-Burning Combustion of MGP residues with

coal in utility boilers and cementkilns.

• Recycles wastes• Destroys organic contaminants• Cost effective

• Long-term impacts on boiler efficiency,maintenance, and operation is unknown

$44-$309/ton

Thermal Treatment Processes

Ex Situ Thermal Desorption Desorption and/or destruction of

organic contaminants in excavatedsoil by heating.

• Demonstrated PAH and organiccontaminant reduction• Moveable units available for onsitetreatment

• Hazardous levels of contaminants may notbe accepted at offsite facilities• Wet or saturated media requires dewateringprior to treatment• Soil with high organic content is unsuitablefor treatment• Air emissions control may be required

$100-$200/ton

In Situ Thermal ProcessesDynamic Underground Stripping(DUS)

Injection of steam into subsurfacecontaminants to volatilize andmobilize contaminants.

• Minimal disruption to site operations• Removes contaminants under existingstructures• Works well under wide range of soiltypes

• Utility costs may be high• Sufficient contaminant mass may not beremoved during treatment

$110/cy

In Situ Thermal Desorption (ISTD) Soil heating via in-well heater or

electrodes to vaporize/volatilizefluids and contaminants.

• Minimal disruption to site operations• Removes contaminants under existingstructures• Works well under wide range of soiltypes

• Utility costs may be high• Works best in unsaturated conditions

$120-$300/cy

Contained Recovery of OilyWastes (CROW)

Hot water flushing/displacementand extraction of subsurfacecontaminants.

• Minimal disruption to site operations• Removes contaminants under existingstructures• Works well under wide range of soiltypes

• Utility costs may be high• Sufficient contaminant mass may not beremoved during treatment

N/A
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Source Material Treatment Technologies, continued

Name Description Benefits Limitations Approximate

Cost *

Asphalt Batching

Cold-Mix Asphalt Batching Encapsulation of contaminant by

blending residues, wet aggregateand asphalt emulsion at ambienttemperature.

• Reuses materials• Immobilizes PAHs• Viable treatment technology for coal tars

• Curing times can be affected by temperature• Not viable for fine-grained materials (e.g., clays)• Physical properties of final product not alwaysappropriate for traffic reuse

$40-$70/ton

Hot-Mix Asphalt Batching Encapsulation of contaminant by

blending residues, wet aggregateand asphalt emulsion at hightemperature.

• Reuses materials• Immobilizes PAHs• Viable treatment technology for coal tars

• Curing times can be affected by temperature• Not viable for fine-grained materials (e.g., clays)• Physical properties of final product not alwaysappropriate for traffic reuse

$40-$70/ton

Bioremediation/ Chemically Enhanced BioremediationEx Situ BioremediationLandfarming Destruction of organic compounds

in contaminated soil bymicroorganisms. Treatment occurson lined beds during contaminatedsoil tilling and irrigation.

• Shorter treatment periods than in situbioremediation alternatives• Reduces contaminant concentrations

• Not effective for higher molecular-weighthydrocarbons• May be slower than alternative treatmenttechnologies

$75/cy exclusive oflab and pilot studies

Biopiles Destruction of organic compounds

in contaminated soil bymicroorganisms. Treatment occursthrough soil amendment andstockpiling.

• Shorter treatment periods than in situbioremediation alternatives• Reduces contaminant concentrations

• Not effective for higher molecular-weighthydrocarbons• May be slower than alternative treatmenttechnologies

$100-$200/cyexclusive of lab andpilot studies

Bioreactor Destruction of organic compounds

in contaminated soil bymicroorganisms. Treatment occursin an enclosed reactor vessel.

• Shorter treatment periods than in situbioremediation alternatives• Reduces contaminant concentrations

• Not effective for higher molecular-weighthydrocarbons• May be slower than alternative treatmenttechnologies

$216/cy exclusive oflab and pilot studies

In Situ Bioremediation/Bioventing

Destruction of organic compoundsin subsurface contaminated soil bymicroorganisms.

• Generally inexpensive• Minimal disruption of existing operations• Removes contaminants from underexisting structures

• Verification of destruction is sometimes difficult• Not effective for higher molecular-weighthydrocarbons• Treatment uniformity uncertain because ofsubsurface variables

$10-$70/cy exclusiveof lab and pilotstudies
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Source Material Treatment Technologies, continued

Name Description Benefits Limitations Approximate

Cost *

Containment Containment or capping of

contaminated soil to prevent orsignificantly reduce contaminantmigration and to prevent human andanimal exposure.

• Quick installation• Does not require soil excavation• Prevents vertical infiltration of water• Prevents human and animal exposure

• Contains wastes; does not reduce contaminantconcentration• Requires operation and maintenance program• Typically requires institutional controls (e.g.,deed restriction)

$45,000-$170,000/ac

Stabilization/Solidification

In Situ S/S Encapsulation of contaminant by in

situ blending with chemical bindersto immobilize contaminant ofconcern.

• Immobilizes contaminants• Neutralizes soil• Improves bearing capacity or shearstrength of treated area

• Possible leaching of volatile or mobilecontaminants• Creation of concrete-like material in subsurface• Effective in situ mixing may be difficult

$40-$60/cy inshallow applications,exclusive of lab andpilot studies

Ex Situ S/S Encapsulation of contaminants in

excavated soil by blending withchemical binders to immobilizecontaminant of concern.

• Immobilizes contaminants • Performance dependent upon chemical

composition of wastes• Long-term immobilization of contaminant maybe affected by environmental conditions

$100/ton exclusiveof lab and pilotstudies

Soil Washing Physical/chemical process for

scrubbing soils ex situ to removecontaminants.

• High degree of certainty regardingtreatment performance

• Material handling possibly expensive• Effectiveness limited by complex wastemixtures and high humic content

$170/ton

Soil Vapor Extraction Extraction of air from subsurface to

remove volatile compounds fromvadose zone soils.

• Removes contaminant from underexisting structures• Promotes in situ biodegradation• Well established treatment technology• Minimal disruption to site operations

• Not effective for low-volatility compounds• May not be effective in areas with water tablesshallower than 5 to 10 feet bgs or in fine-grainsoils• Limited effectiveness on pools of contaminants

$2-$450/cy

* Approximate costs do not include cost of excavation, transportation, material handling, etc.
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Co-burning is the process by which MGP residues such as coal tar and tarcontaminated soils are combusted along with coal in utility boilers. Developed by

the Edison Electric Institute’s (EEI) subcommittee for MGP sites with technical

support from the Electric Power Research Institute (EPRI), this technology blends

remediation waste recovered during site excavation with coal so as to render it

nonhazardous for co-burning in utility boilers. EPRI also developed a sampling

approach that is consistent with EPA test methods for characterizing soils and

wastes and for developing blending ratios for treating soils. This strategy is

intended to ensure that only nonhazardous MGP wastes are co-burned in utility

boilers, and allows utilities to burn this waste without entering the RCRA

hazardous waste permit program or paying the high cost of commercial

incineration (EPRI, 1995).

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Utilities have co-burned MGP site wastes in a variety of utility boilers, including

stokers, cyclones, and those fired by pulverized coal. Preparation consists of

screening waste to remove oversized material and rendering the material

nonhazardous under RCRA if necessary (GRI, 1996). MGP materials are typically

blended with coal feedstock in the range of 5 to 10 percent coal or wastes. Coburning increases the amount of ash requiring management. For example, a 10

percent co-burning mixture doubles the amount of ash generated by a boiler (GRI,

1996).

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As of 1996, co-burning was used as part of full-scale remediation at five MGP sites;

four other demonstration tests have been completed (GRI, 1996). Media that have

been treated include coal tars, purifier box wastes, and contaminated soils. Coburning is currently offered as a commercial service by one utility in the northeast

United States. The cost of co-burning in a case study in Rochester, New York,

ranged from $44 to $142 per ton for soil and from $134 to $309 per ton for tars.

The utility company currently offering co-burning charges a tipping fee of

approximately $90 per ton to incorporate the MGP site residuals into its boiler

feed, but this cost does not include any preprocessing, transportation, or analytical

work necessary for disposal (GRI, 1996).

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 Reuses/recycles waste into a usable product

 Has demonstrated technical feasibility to destroy organic contaminants

 Allows utilities to expedite flexible, cost-effective remediation at MGP sites

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 Long-term impact of co-burning on boiler efficiency, maintenance, and

operation is unknown
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Rochester Gas and Electric (RG&E) with the assistance of EPRI, the Gas Research

Institute (GRI) and the New York Gas Group evaluated co-burning for use at their

plant. RG&E operates an 80-megawatt, tangentially fired, pulverized coal unit

built in 1959 by Combustion Engineering. It is located on the same site as the

former West Station MGP. Residues in the form of “neat” coal tar and soil with

major amounts of rock, brick, coke, concrete, and other demolition debris remain

at the West Station site. The soil contains from 40,000 to 70,000 ppm of PAHs.

Although preprocessing was needed to remove large rocks and other debris, the

tar and soil were easily blended with coal to make two distinct fuel products. One

fuel product contained 4 percent tar, and the other contained 5 percent soil, with

the balance in both cases made up of coal.

The test burn program contained a series of inspection and evaluation protocols

directed at monitoring the effects of these mixed fuels on the boiler and ancillary

systems. In a program that lasted approximately 12 weeks (4 weeks of which were

dedicated to actual co-burning), the boiler performed without significant

performance losses, PAH removal efficiency exceeded 99 percent, electrostatic

precipitator performance was unchanged, and emissions appeared unaffected (air

emissions were actually significantly reduced for certain parameters).

Two factors that arose in this demonstration could greatly affect the feasibility and

cost of co-burning. The first factor is that the state environmental agency required

ash leachate to meet drinking water standards before it would grant RG&E

permission to reuse the ash. Because drinking water standards are set below the

method detection limit for many parameters, the ash could not meet these

standards, and the state denied permission to reuse it. If not resolved, this

prohibition on reuse will add more than $50 per ton to the cost of the residues to

be treated. (One bottom ash sample also showed PAH concentrations of 800 ppb,

attributed to spillover from the mill reject system.) The second factor that affects

co-burning is the potential physical damage to a boiler using this technology. Mill

abrasion was measured during the test and one measurement indicated a rate of

wear about eight times that from processing ordinary coal. If this measurement

and test are representative, maintenance costs of co-burning could increase

proportionally.

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Kevin L. Hylton, Rochester Gas and Electric Corporation, (716) 546-2700

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Co-burning of MGP residues was demonstrated in a pulverized-coal, tangentially

fired utility boiler at the Duke Power Company in South Carolina. The

remediation site was the Broad Street MGP in Greenville, where a 1.2-acre,

carbureted water gas plant operated from 1875 until 1951. The co-burn facility was

Duke Power Company’s Lee Steam Station, located in Pelzer, South Carolina. The

MGP residues were co-burned in unit No. 3, which has a capacity of 175 MW and

was constructed in 1956.
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The project’s remediation goals were to prepare the site for future sale as an

industrial/commercial property. A cleanup level of 200 ppm total PAHs was

required. The matrix treated consisted of soil impacted with MGP residues. Prior

to co-burning, soil was screened to 1⁄2 inch and then blended with coal at a

maximum rate of 5 percent. Plant operations preferred a 2 percent blend.

This was a full-scale operation. The plant had a permit for 19,000 tons of soil per

year, but the actual amount treated was estimated at 3,000 tons per year. Before

treatment, total PAH concentrations in site soils ranged up to 1,600 ppm. After

treatment, BTEX and PAH concentrations were below the detection limit in all

bottom ash and fly ash samples. Stack gas concentrations were the same as when

co-burning was not taking place. The project is now complete, with 3,000 tons of

material treated and managed; a destruction and removal efficiency (DRE) of 100

percent was obtained. No additional co-burns of MGP residues are planned at this

time.

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Ralph Roberts, Duke Power Company, (704) 875-5536, rcrobert@duke-energy.com 

Lori Murtaugh, South Carolina Department of Health and Environmental Control,

(803) 734-4668

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Illinois Power and Illinova Resource Recovery, Inc. operate a commercial waste

management facility at Illinois Power’s Baldwin Power Station. The program is

designed to co-burn MGP remediation wastes from the utility industry. These

wastes are blended with coal and burned in the Baldwin Power Station’s two

cyclone boilers. 

Power Station Description

The Baldwin Power Station is located outside the village of Baldwin, Illinois,

approximately one hour southeast of St. Louis, Missouri. The area is primarily

rural agricultural property. 

Two 600-megawatt cyclone boilers are utilized to co-burn remediation wastes. The

cyclone units are especially suited to burning these wastes due to the fact that

materials can be fed at up to a one-inch size, without the need of pulverization to

200 mesh as is required in some coal-fired power plants. In addition, 90 percent of

the ash generated from cyclone boilers is in the form of a vitrified, inert slag

material. All this slag is sold commercially as sandblast grit and roofing shingle

aggregate. Both power station boilers are base-load units, meaning that they

operate 24 hours per day, 7 days per week at full-load. This allows co-burning to

be conducted on a steady basis and maximizes the capacity of the program. The

Baldwin units are equipped with electrostatic precipitators and continuous

emission monitors. The units are fueled with Illinois Basin coal.

Waste Management Facility

A dedicated waste management facility has been constructed at the Baldwin

Power Station specifically designed to receive, store, and process remediation

wastes. All waste storage and processing activities are conducted in a 30,000
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square foot water-tight concrete and steel containment pad. The containment pad

can store 8,000 cubic yards of contaminated soil. Baldwin is allowed to load waste

at a rate of 5 percent of the coal loaded daily. This corresponds to approximately

450 tons per day capacity. Baldwin has demonstrated a 300-ton-per-day sustained

rate capacity. The practical annual capacity is currently about 100,000 tons per

year. The waste materials are delivered by dump trailer and off-loaded directly

into the containment pad. The materials are then crushed, screened, and blended

with coal to produce a final product that is homogenous, less than two inches in

size, and free of metal, plastic and other unprocessable debris. Rock, gravel, and

masonry are accepted and crushed with the other materials and burned in the

boilers. The processed material is delivered to the power plant coal conveyors

using an enclosed conveyor system.

Environmental Permits

The Baldwin facility is fully permitted by the Illinois Environmental Protection

Agency as a commercial waste treatment and storage facility. Solid waste permits

limit types and quantities of acceptable waste, and define the management

practices, documentation and inspection requirements, and quality control

procedures. Water discharge permits require collection, treatment, and analysis of

runoff water prior to discharge to the environment. Air permits limit the amount

of dust generated and the emissions from the boiler stacks. The Illinois

Environmental Protection Agency has been very supportive of the program as a

safe and effective means of permanently eliminating the hazards and liabilities

associated with these wastes, which previously were disposed of in landfills

almost exclusively. Three USEPA Regions have approved the operation for receipt

of coal tar and petroleum contaminated soil and debris for federal Superfund sites.

Operating History

A test burn in March of 1994 convinced Illinois Power that the power plant

systems could handle the contaminated soils effectively with acceptable impacts to

boiler operations and efficiencies. The costs, however, indicated that the process

would not be cost effective for only Illinois Power’s quantities of waste. It was

determined that a commercial operation could be supported by the quantities of

waste market, thereby providing the economies of scale required to make the

project feasible.

Since the initiation of operations in June of 1996, over 135,000 tons of waste have

been accepted and treated at Baldwin. Materials have been received from as far as

1,200 miles away. Baldwin has been an integral contributor to the remediation of

over 40 contaminated sites for more than 20 customers.






Thermal desorption is a treatment technology in which organic chemical

constituents contained within a contaminated soil matrix volatilize as a result of

heating. The volatilized constituents are then extracted from nonvolatile materials,

such as soil, and treated prior to release. Thermal desorption can be grouped into

in situ and ex situ practices. Both technologies are described below.
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Full-scale thermal desorption has been successfully used to remediate soils

containing MGP wastes (e.g., lampblack, coal tar) since the early 1980s, achieving

concentration reductions of more than 98 percent for TPHs, BTEX compounds,

PAHs, and cyanide. Thermal desorption has been used in many non-MGP

applications, and is a common remediation technology for MGP sites. The

technology can be applied on site with a mobile unit or at an off-site facility. Below

is a photograph of a thermal desorption unit.

Thermal desorption uses temperatures ranging from 400°F to 1,200°F to desorb

chemicals from the soil. Soil is fed into a material dryer where heated air causes

chemicals to volatilize. In general, temperatures between 200° F and 900°F are

required to desorb VOCs and many PAH compounds. Higher temperatures (up to

1,200°F) are required to desorb high-molecular-weight PAHs (Barr, 1996). After

chemicals in the offgas are treated, the cleaned air is vented to the atmosphere.

The dry, hot soil is then discharged to a pug mixer where water is introduced to

reduce dust and lower the soil temperature. The quenched soil is discharged and

transported to a stockpile. Each day’s production volume of soil is held separately

while residual concentrations are determined. The treated soil is then returned to

the excavation, transported to an off-site facility for disposal, or reused at a

different location. A typical thermal desorption unit can treat approximately 8 to

45 tons per hour, depending on soil conditions (e.g., water content, waste

concentrations, etc.) and the size of the dryer unit used.

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The thermal desorber’s operational characteristics depend on soil type and

properties, contaminant type and concentrations, moisture content, organic

material content, pH, compound volatility, and temperature and residence time

during drying. This technology may require a pilot test demonstration. Blending is

recommended to reduce variations in organic concentrations.
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Full-scale systems have achieved a DRE of 99 percent when treating contaminated

soils from MGP sites at temperatures of 750°F to 850°F with residence times of

approximately 10 minutes (GRI, 1996). A summary of costs from six remediation

efforts conducted to date in California (see the table below) shows on-site

treatment costs ranging from approximately $110 to $130 per ton for 16,000 and

9,000 tons of soil, respectively, and offsite treatment costs ranging from

approximately $100 to $200 per ton for 11,000 and 1,000 tons of soil, respectively.

All estimates include costs for general contracting, confirmation sampling,

construction management, permits, and transportation for offsite treatment (GRI,

1996). Recent projects suggest the potential for even more favorable pricing.

Summary of Total Project Costs for Thermal Desorption

at six California Former MGP Sites

(Cost/Ton ($)) Santa

Barbara

Dinuba Covina Inglewood Orange Visalia

Thermal Treatment $52 $49 $45 $38 $44 $32

Transportation -- -- $18 $19 $20 $30

General Contractor $42 $25 $31 $35 $62 $24

Confirmation Sampling $10 $4 $7 $5 $19 $2

Construction

Management

$30 $21 $17 $11 $45 $7

Miscellaneous Costs

(Agency oversight, air

permitting)

$14 $4 $8 $8 $13 $3

Adjusted Total Cost $131 $106 $120 $115 $202 $96

Total Cost $178 $140 $130 $133 $202 $96

Total Project Costs $1,556,974 $2,257,630 $906,735 $666,416 $212,384 $1,055,950

Tons Soil Excavated 8,745 16,120 7,000 5,024 1,050 10,775

Source: Southern California Gas Company

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 Demonstrated PAH reduction to less than 1 mg/kg under optimal conditions

 80 to 99 percent removal of carcinogenic PAHs

 90 to 99.7 percent removal of total PAHs (Barr Engineering, 1996)

 Production rates of 8 to 15 tons per hour for small units and 25 to 45 tons per

hour for large units
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 Very wet or saturated media must be dewatered prior to treatment

 Soil with high organic content (peat) is unsuitable

 Air emissions of chlorinated compounds, sulfur, etc. may need to be abated

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The Huron MGP site is a 3-acre parcel that once housed a process plant for the

production of carburetor water gas. Site geology consists of a surficial fill unit

underlain by a clayey lacustrine deposit and a glacial till unit. Depth to bedrock

beneath the site is approximately 100 feet. The glacial till unit acts as a barrier to

the vertical migration of MGP residuals.

The requirements under which the ex situ thermal desorption project was

conducted were negotiated with the state regulatory agency. These included

excavation criteria, a treatment performance criterion, and an operating permit for

thermal treatment. Field demonstration activities consisted of excavating and

staging soils containing MGP residuals, preparing the staged soils, treating the

prepared soils, backfilling and compacting the treated soils, and managing

wastewater.

The Huron MGP site used a low-temperature thermal desorption (LTTD) system, a

two-stage counter-flow direct-fired rotary desorber capable of heating

contaminated soils to 1,200 °F. The system is equipped with an oxidizer that can

operate at 1,800 °F. Field demonstration costs included mobilization/

demobilization, material excavation and handling, thermal treatment, soil and

water analyses, utilities, backfilling and compaction, dewatering and wastewater

management, and project oversight. The total cost of the project was $3,819,000.

Approximately 47,000 tons of soil containing total PAH concentrations ranging

from 84 to 3,733 mg/kg were treated to below the treatment performance criterion

of 43 mg/kg for the sum of cPAHs, at a cost of $82 per ton.

Conclusions from the Huron MGP site field project are summarized as follows:

 The thermal desorption system achieved removal/destruction rates of greater

than 79 percent to greater than 99 percent for cPAH compounds, and greater

than 89 percent to 99.7 percent for total PAH compounds.

 The system showed good operating stability; critical operating parameters,

shown below, were relatively constant:

- Feed rate of 20 to 31 tons per hour with an average rate of 26 tons per hour

- Desorber temperature of 1,050 °F to 1,200 °F with a residence time of 18 

minutes

- Oxidizer temperature of 1,741 °F to 1,773 °F with a residence time of 2 to 2.5 

seconds
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 Stack emissions, which were in compliance with the operating permit

requirements, were as follows:

Opacity <20 percent

Sulfur Dioxide 2.4 pounds per million Btu of heat input

Oxides of Nitrogen 10.7 pounds per hour

Total Hydrocarbons 0.07 pounds carbon per hour

Naphthalene <926 micrograms per second

 Soil type and moisture content affected total cost. Had the clay and moisture

content of the site soils been lower, soil preparation time would have been

shorter, and unit treatment costs would have been lower.

 Inclement weather significantly affected project costs. Approximately 20 days

out of a 6-month period were lost to rain delays. The rain delays increased soil

preparation time and costs associated with dewatering, wastewater

management, and project oversight.

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Ed Highland, Northwest Public Service Co., (605) 353-7510

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A two-stage thermal desorption unit was installed on the Waterloo, Iowa, former

MGP site. The treatment used natural gas as a fuel. In the first stage of the twostage desorber, the soil was mixed in a rotating drum and heated to approximately

300 °F to 500 °F by a 40-million-Btu-per-hour burner. In the second stage, the soil

was further heated to between 1,100 °F and 1,200 °F by three additional 6-millionBtu-per-hour burners. The first stage was used to drive off moisture and the more

volatile hydrocarbons; the second stage desorbed the contaminants from the soil.

All heating conducted by the two-stage desorber was direct fired and oriented

counter to soil flow. The vapors from the desorption stage were passed through an

oxidizer (secondary burner) and heated to between 1,750 °F and 1,800 °F to destroy

hydrocarbon contaminants. The desorber unit used at the Waterloo site was

specifically modified for treatment of coal tar compounds and operated at a higher

temperature in the high-temperature stage of the two-stage desorber than some

thermal desorption units. This was necessary to desorb higher-molecular-weight

coal tar compounds. The desorber used at the Waterloo site was capable of

thermally treating soil at a rate of 25 to 40 tons per hour, depending upon the

concentration of contaminants, and soil type and moisture content. During the

trial burn conducted at the site, soil was treated at a rate of 31.6 tons per hour.

The minimum space required for setup and operation of the Waterloo desorber

unit was approximately 140 feet by 120 feet, not including space for storage of soils

prior to and after treatment. The thermal desorption unit and all auxiliary

equipment were transported to and from the temporary locations with 14 tractor
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trailers. It took approximately 7 days to complete setup of the equipment and an

additional 5 days for startup and fine tuning of the equipment in preparation for

trial burn or routine treatment of soils. Natural gas (or propane), electricity, and

water were required to operate the system. In addition, water was required for

rehydration of the treated soil and other cooling operations.

The remediation goal for the project was to treat the soil to less than 5 mg/kg total

PAHs. Routine sampling of treated soil showed concentrations well below 5

mg/kg. A total of 83 samples of treated soil (one sample for every 300 tons of soil)

had an average concentration of 0.59 mg/kg total PAHs. The media treated

included clay, sand, and silt.

A trial burn of coal tar materials was conducted to determine the DRE for the

organic contaminants in the excavated coal tar materials. A grab sample of soil

was collected for every 100 tons of treated soil, composited with two other 100-ton

representative samples, and analyzed for PAHs. Routine thermal treatment of soil

began as soon as the Iowa DNR and USEPA approved the results of the DRE

testing. The treated soil could not be backfilled, however, until laboratory analysis

was received and the results were shown to be below the treatment criterion of

less than 5 mg/kg total PAHs.

The specific operating conditions observed during the trial burn were used as the

operating criteria for the remainder of the soil to be treated. Continuous

monitoring included waste feed rate, system treatment temperatures, carbon

monoxide concentration in stack gas, and other parameters. Of the 83 samples of

treated soil that were collected and analyzed throughout the project, three lots of

300 tons each did not pass. These values were not included in the average above

because the soil was blended with other soil and retreated.

The following table shows the amount of soil excavated and treated for each of the

four sites:

Site Tons of Soil Treated

Hampton 3,651

Charles City 2,138

Independence 4,734

Waterloo 14,167

Total 24,690

Treated soils from all sites were used to backfill an earlier excavation on the

Waterloo site. All contaminated oversized debris was crushed and thermally

treated. Some exceptionally large debris, such as foundations, was decontaminated

in place and left in the excavation. All scrap steel was cleaned and sent to a

recycler. As a result, nearly all of the materials removed were thermally desorbed
&KDSWHU 

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5-14

or recycled. Very little material, primarily wood debris and tree roots, was taken to

the local landfill. The total cost of the project was $2 million. This cost includes

preparing the thermal desorption site and installing utilities, excavating all the

sites, hauling excavated material from Hampton, Charles City, and Independence

to Waterloo, backfilling, and labor to place the fill; it also includes the thermal

desorption services, with the cost of fuel. The average cost per ton of soil treated

was calculated for the project and is shown in the table below.

Item Average Cost per Ton* ($)

Excavation 4.83

Thermal Treatment 47.87

Transportation 12.53

Backfill 4.83

Miscellaneous* 8.62

Total 78.62

*This includes the cost of analytical and engineering services, air monitoring, etc.

&RQWDFWV

Sam Nelson, MidAmerican Energy Company, (712) 277-7851

Dan Klimek, MidAmerican Energy Company, (712) 277-7930

Johanshir Golchin , Iowa Department of Natural Resources, (515) 281-8925

Jim Colbert, USEPA Region VII, (913) 551-7489

0DVRQ &LW\ ,RZD )RUPHU 0*3 6LWH

Thermal desorption was used at a site in Mason City, Iowa, owned by Interstate

Power Company. The property had been used for production of natural gas from

coal in the late 1900s and had become contaminated with a variety of heavily

weathered PAHs and cPAHs. From April to October 1996, approximately 22,000

tons of soil were thermally treated at temperatures of up to 1,200 °F. A process rate

of 32 tons per hour was achieved. 

The soil that was treated contained concentrations of PAHs in excess of 3,000

mg/kg, and in many areas, soft, agglomerated, heavy oil was present.

Pretreatment of excavated soils included shredding, crushing, screening, and

blending to avoid exceeding the process capacity of the thermal desorption

system. Also, a significant amount of brick, concrete, wood, and steel pipe

required specialized material handling and processing. The brick and concrete

were crushed and blended with more heavily contaminated soil before thermal

treatment; the steel and wood were separated and sent off for recycling.
&KDSWHU 

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Six test runs were performed during a comprehensive demonstration testing

program. The average results of these test runs showed that concentrations of total

and cPAHs in the treated soil were reduced from 804 mg/kg and 95 mg/kg,

respectively, to less than 3.3 mg/kg and less than 1.22 mg/kg, respectively. A DRE

of greater than 99.99 percent was demonstrated for all combined PAH compounds.

Stack gas was sampled and analyzed for all combined PAH compounds. Sulfur

dioxide, nitrogen oxide, carbon monoxide, and PAH emissions were in accordance

with the USEPA and Iowa DNR protocol.

&RQWDFWV

Bruce Greer, Alliant Energy, (608) 252-3948

Johanshir Golchin, Iowa Department of Natural Resources, (515) 281-8925

Diane Engeman, USEPA Region VII, (913) 551-7746

 ,Q 6LWX 7KHUPDO 3URFHVVHV

In situ thermal processes are treatment processes designed to increase the

mobilization of contaminants via volatilization and viscosity reduction. The

addition of heat to the subsurface by radio frequency, electrical resistance, or

steam increases the removal of organic compounds particularly in low

permeability formations. Heat also increases volatility (and hence removal) of

compounds that are not readily extractable using conventional SVE (e.g., heavy

oils). Three in situ thermal processes are reviewed in this section: Dynamic

Underground Stripping (DUS), In Situ Thermal Desorption (ISTD), and Contained

Recovery of Oily Waste (CROWTM).

 '\QDPLF 8QGHUJURXQG 6WULSSLQJ '86

7HFKQRORJ\ 'HVFULSWLRQ

Lawrence Livermore National Laboratory and the School of Engineering at the

University of California, Berkeley (UC Berkeley), developed DUS in the early

1990s. The area to be cleaned using DUS is ringed with wells for injecting steam.

Extraction wells in the central area are used to vacuum out vaporized

contaminants. To ensure that thick layers of less permeable soils are heated

sufficiently, electrode assemblies may be sunk into the ground and heated, which

forces trapped liquids to vaporize and move to the steam zone for removal by

vacuum extraction. These combined processes achieve a hot, dry, treatment zone

surrounded by cool, damp, untreated areas. Steam injection and heating cycles are

repeated as long as underground imaging shows that cool (untreated) areas

remain (Newmark, 1998).

2SHUDWLRQDO &RQVLGHUDWLRQV

The capacity of DUS treatment systems is limited only by the size of the

installation. DUS generally does not require material handling or pretreatment

prior to application at a site. Electrical heating may be applied to less-permeable

contaminated clay layers in situ to help release contaminants prior to steam

injection. DUS requires both subsurface and aboveground equipment.

Aboveground equipment includes a steam generation plant, electrical heating
&KDSWHU 

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equipment, and treatment systems for recovering free product and contaminants

from the separate liquid and vapor streams collected from the extraction wells.

Because the aqueous and gaseous streams are in intimate contact with the free

product, they will typically be saturated with dissolved or vaporized free product

components following their passage through the oil/gas/water separators.

The DUS treatment system consumes significant quantities of electricity, water,

and, for some applications, natural gas. Operation difficulties that may be

encountered during DUS include biofouling (especially from microorganisms

destroyed by steaming), scaling and deposits on sensors, clogging from fines

brought to the surface, and difficulties in maintaining the cycling, pressurevarying, and high-temperature technology. Further refinement is also required for

system design and operating and monitoring techniques.

The DUS technology is labor intensive, requiring significant field expertise to

implement. It is best applied to sites with contaminants above and below the water

table and complex sites that are difficult to clean up.

$SSOLFDWLRQV DQG &RVW

Although the initial capital outlay for DUS is higher than for pump-and-treat

systems, DUS could save money in the long run because it is completed much

more quickly. Most of the equipment, such as boilers for generating steam, can be

rented. Initial expenditures include installing the heating wells and operating the

system intensively for a short period of time. Because the technology is short term,

long-term operation and maintenance costs are reduced or eliminated. In a 1993

field trial of DUS at Lawrence Livermore National Laboratory, the technology cost

about $110 per cubic yard of soil treated (Newmark, 1998).

%HQHILWV

 Will work in a wide range of soil types

 Works in both saturated and unsaturated conditions

 Treatment possible in areas where traditional excavation and removal are

impossible

 Minimal disruption to nearby industrial operations or surrounding

neighborhoods; no digging and hauling of contaminated materials eliminates

exposure to toxic fumes and dust

 Will work close to or under existing structures, including buildings and

roadways

/LPLWDWLRQV

 Although DUS removes considerable mass and may improve groundwater

quality, there is currently limited experience regarding the ability of DUS to

achieve maximum contaminant levels (MCLs) and thus alleviate the need for

pump-and-treat.
&KDSWHU 

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&DVH 6WXG\

9LVDOLD 3ROH\DUG &DOLIRUQLD

The Southern California Edison Visalia Poleyard site was used for 80 years to treat

utility poles with both creosote and pentachlorophenol (PCP). Creosote contains

PAHs similar to those found in MGP wastes. This 4-acre site was one of the first to

be listed on the National Priorities List. The sediments underlying the poleyard are

alluvial fan deposits, and the site currently contains DNAPL contamination in

three distinct water-bearing zones. There are several shallow aquifers from about

35 to 75 feet bgs, and an intermediate aquifer from about 75 to 100 feet bgs. The

most sensitive groundwater resource is found in the deep aquifer below about 120

feet. The thermal remediation system was designed to remove contaminants from

the intermediate and shallow aquifers without disturbing the deep aquifer.

DUS was selected for the Visalia poleyard. An array of 11 injection wells was

installed encircling the contaminant source area. Although each injection point

had two injection pipes, screened in either the shallow or the intermediate aquifer,

only the 11 pipes completed in the lower unit were used for injection from 80 to

100 feet bgs. Three additional extraction wells were placed in the central area to

supplement existing extraction wells. No supplemental electrical heating was

performed; the entire site was heated using steam alone. Steam was generated

utilizing commercially available oil field steam generators (Struthers type). Steam

was injected at pressures up to 150 psi, routinely at pressures less than 100 psi.

Vacuum pressures of approximately 0.5 atmospheres (atm) were applied in a

steady mode.

Ancillary equipment included cooling equipment for the extracted water and

vapor, two stages of free product separation (including dissolved air flotation),

and final filtration of the pumped water by activated carbon. Approximately 16

percent of the contaminant was destroyed in place, yielding carbon dioxide. Both

vapor and water streams were continuously monitored for hydrocarbon and

carbon dioxide content.

In addition to thermocouples, an innovative geophysical technique was employed

to monitor movement of steam and progress of heating. Electrical resistance

tomography is an imaging method like CAT scanning that provides near-real-time

images of underground processes between pairs of monitoring wells. Baseline

measurements are used to characterize a site and predict steam pathways. Soil

electric properties vary with temperature, soil type, and fluid saturation. During

treatment at Visalia, daily resistivity readings provided a picture of the progress of

the steam front and heated zones. Monitoring the progress of the heating fronts

ensured that all soil was treated. Temperature measurements made in monitoring

wells revealed details of the complex heating phenomena in individual soil layers.

As of August 1998, the DUS process recovered approximately 110,000 gallons of

free product a rate of about 46,000 pounds per week. In addition, approximately

29,400 pounds of hydrocarbon were burned in the boilers; 17,500 pounds of

dissolved hydrocarbon were collected in the activated carbon filtrator; and, based

on removed carbon dioxide, an estimated 45,500 pounds were destroyed in situ.
&KDSWHU 

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Contaminant concentrations in recovered groundwater continue to decline.

Southern California Edison will treat the liquid free product onsite and may use it

as a lubricant. Current estimates are that the project will be completed in 1 to 2

years, with an additional 4 years of monitoring. This is in contrast to the 20 or

more years expected for pump-and-treat remediation.

With DUS, contaminants are vaporized and recovered at the surface.

Approximately 50 percent of the cost of cleanups is associated with treating

recovered groundwater and disposing of contaminants. The addition of hydrous

pyrolysis oxidation (HPO) to the basic DUS technology could save additional

costs. HPO involves injection of steam and air to aerate a heated oxygenated zone.

When injection is halted, the steam condenses and contaminated groundwater

returns to the heated zone. The groundwater mixes with the condensed steam and

oxygen, destroying dissolved contaminants. As noted above, HPO is estimated to

be responsible for a portion of the contaminant treatment at the Visalia site. To

evaluate the progress of in situ chemical destruction, field methods were

developed to sample and analyze hot water for contaminants, oxygen,

intermediate products, and reaction products.

Laboratory testing on the Visalia suite of contaminants showed that both PCP and

the range of PAH compounds present are readily destroyed by HPO’s in situ

oxidation process. Isotopic testing during remediation showed that the carbon

dioxide being recovered in the vapor stream was coming from oxidation of

creosote. This process is expected to aid in bringing groundwater concentrations to

regulatory standards.

&RQWDFWV

Roger D. Aines, Lawrence Livermore National Laboratory, (925) 423-7184

Robin Newmark, Lawrence Livermore National Laboratory, (925) 423-7184

Kent Udell, UC Berkeley, (510) 642-2928

Craig Eaker, Southern California Edison, (626) 302-8531

 ,Q 6LWX 7KHUPDO 'HVRUSWLRQ ,67'

7HFKQRORJ\ 'HVFULSWLRQ

ISTD consists of a system or array of surface and/or in-well heaters or electrodes

combined with vacuum wells to heat contaminated soils and extract the resulting

vaporized/volatilized fluids and contaminants. Vapors produced through the soil

heating process are treated in surface facilities to remove residual contaminants.

According to the ISTD vendor, up to 99 percent of contaminants are destroyed.

ISTD involves the placement of Thermal Blankets (over areas of surface

contamination to a depth of approximately 18 inches) or Thermal Wells (which can

be drilled in areas of deep contamination) in the area to be treated. Both the

blankets and the wells use electricity to heat soil to the boiling temperatures of

contaminants. The contaminant vapors are then extracted and further processed

through a flameless thermal oxidizer and activated charcoal filter. Water and

carbon dioxide are released to the atmosphere during treatment. 
&KDSWHU 

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5-19

2SHUDWLRQDO &RQVLGHUDWLRQV

A staging area near the contaminated site and accessibility to a local power grid

are required for the placement of ISTD process and control trailers. Limitations of

the ISTD process are primarily related to the amount of moisture in the soil. Too

much water (e.g., groundwater recharge) requires either dewatering or installing

of a barrier to halt groundwater recharge as the soil is heated. There is minimal

impact to surrounding neighborhoods during ISTD treatment because the process

is confined to the site, and there is no direct handling of contaminated soils.

Minimal dust and noise are generated during treatment. A schematic ISTD setup is

shown below.

A limited number of applications have been conducted to date; therefore, other

operational considerations that may affect the application of this technology at

former MGP sites are not known. Additional unknown factors include how the

technology will handle tarry waste material and underground subsurface

structures (e.g., former gas holders) at former MGP sites, and the depth of soil to

which this technology can practicably be applied. 
&KDSWHU 

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5-20

$SSOLFDWLRQV DQG &RVW

ISTD can be applied to shallow contamination (to a depth of 18 inches below

grade) through the use of Thermal Blankets and to deeper contamination through

the use of Thermal Wells. The technology is capable of treating a wide variety of

volatile and semivolatile organic contaminants including PCBs, chlorinated

solvents, pesticides, and petroleum wastes. The system is designed to control

emissions through use of a flameless oxidizer and activated carbon absorber.

Soil treatment by TerraTherm Company’s ISTD at the Missouri Electric Works

(MEW) Superfund site in Cape Girardeau, Missouri, cost $120 to $200 per cubic

yard of soil. Sites with special water-handling requirements, custom well or

blanket configurations, or other size restrictions may cost up to $300 per cubic

yard.

%HQHILWV

 Will work in a wide range of soil types

 Treatment possible in areas where traditional excavation and removal are

impossible

 Minimal disruption to nearby industrial operations or surrounding

neighborhoods; no digging and hauling of contaminated materials eliminates

exposure to toxic fumes and dust

 Will work close to or under existing structures, including buildings and

roadways

 Demonstrated ability to recover PCBs with residual soil concentrations well

below 2 ppm

/LPLWDWLRQV

 ISTD has not been applied in full-scale at an MGP site to date, nor has it been

applied to MGP wastes (e.g., PAHs, tars)

 Unclear whether sufficient contaminant mass can be recovered to alter

groundwater quality

 Utility costs associated with heating may be high

&DVH 6WXGLHV

0DUH ,VODQG 1DYDO 6KLS\DUG &DOLIRUQLD

A demonstration of ISTD was performed at the Mare Island Naval Shipyard in

California from October through November 1997. Soil samples at Mare Island’s

former electrical shop site were contaminated with PCB Aroclors 1254 and 1260,

with average pretreatment concentrations of 54 ppm and maximum concentrations

of 2,300 ppm. The most stringent USEPA requirement for residual PCB

concentrations is 2 ppm following treatment. 

The Mare Island demonstration was conducted as a collaboration between the U.S.

Navy, the Bay Area Defense Conversion Action Team, TerraTherm (a subsidiary

of Shell Technology Ventures, Inc.), and RT Environmental Services, who acted as
&KDSWHU 

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5-21

general contractor. Agencies participating included the USEPA, California EPA,

and the Bay Area Air Quality Management District. A draft Toxic Substance

Control Act (TSCA) permit was issued by USEPA. California EPA worked closely

with TerraTherm to streamline the permit process and expedite approvals with the

California DTSC and the Bay Area Air Quality Management District while still

providing strong regulatory oversight.

The test site was chosen to demonstrate the effectiveness of ISTD near an existing

large structure without damaging it. Both Thermal Blankets (two 8-foot by 20-foot

units) and Thermal Wells (12 wells containing heating elements drilled to a depth

of 14 feet) were used during the demonstration. The soil was heated to the boiling

point of the PCBs (approximately 600 °F); heated vapors were extracted through a

vacuum collection system utilizing a flameless ceramic oxidizer and an activated

charcoal filter. Resulting vapor releases to the atmosphere contained primarily

carbon dioxide and water. Both aspects of the demonstration were completed in a

total of 44 days. All post-treatment samples exhibited nondetectable PCB

concentrations (less than 0.033 ppm).

&RQWDFW

Rich G. Hansen, TerraTherm, (281) 544-2020

&DSH *LUDUGHDX 0LVVRXUL

A field demonstration of ISTD was completed at the Missouri Electric Works

Superfund site in Cape Girardeau, Missouri, from April 21 to June 1, 1997. This

demonstration removed high-concentration PCB contamination from clay soils

using 12 heater/vacuum wells installed in multiple triangular arrays with 5-foot

well spacing to a depth of 12 feet. Surface heating pads were placed at the center of

each triangle to assist in heating near-surface soils between the wells. A vacuum

frame structure was constructed around the well area to insulate the surface and

provide a seal. Steel sheets were fitted together and welded to the heater wells. A

16-inch-thick layer of vermiculite insulation was placed over the steel plates to

reduce heat losses and insulate the surface-piping manifold embedded in the

vermiculite (TerraTherm, 1997). 

During remediation, electric resistance heating and vacuum were applied to the

wells for 42 days. Approximately 500 watts per foot were initially injected into the

clay soil at heater temperatures of 1,600 °F. Later in the process as the soil dried,

about 350 watts per foot could be injected. The thermal wells were connected to a

single manifold, which delivered the desorbed and partially treated vapors to a

thermal oxidizer unit. Stack sampling was performed to monitor for by-products

(e.g., hydrogen chloride) and to measure DRE of PCBs. 

Soil temperatures were monitored throughout the experiment, and soil samples

were taken with a split-spoon sampler fitted with 6-inch brass coring sleeves to

verify the removal of contaminants. Temperatures above 1,000 °F were achieved in

the interwell regions, and PCB concentrations in the treated area were reduced

from a maximum of approximately 20,000 ppm to nondetect (< 33 ppb) after

treatment by EPA Method 8080. The system DRE for PCBs was 99.98 percent

(TerraTherm, 1997).
&KDSWHU 

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&RQWDFWV

Ms. Paulette France-Isetts, USEPA Region VII, 726 Minnesota Avenue, Kansas

City, KS 66101, (913) 551-7701

Mr. Donald Van Dyke, Missouri Department of Natural Resources, P.O. Box 176,

Jefferson City, MO 65102, (573) 751-3176

Mr. Rich G. Hansen, TerraTherm, (281) 544-2020

 &RQWDLQHG 5HFRYHU\ RI 2LO\ :DVWH &52:

7HFKQRORJ\ 'HVFULSWLRQ

The CROWTM process was developed by the Western Research Institute (WRI) in

the 1970s as a hot-water flushing technology to aid in extraction of oil from sands

and deep shale deposits. During the 1980s, the concept of hot water flushing was

revisited as a remedial technology. Hot-water displacement is used to move

accumulated oily wastes and water to production wells for aboveground

treatment. Hot water is injected through wells and in groundwater to dislodge

contaminants from the soil matrix. The mobilized wastes are then displaced

toward pumping wells by the hot water. 

With the CROWTM process, subsurface accumulations of oily wastes are reduced by

reducing NAPL concentrations to residual saturation. Controlled heating of the

subsurface reverses the downward penetration of NAPL. The buoyant oily wastes

are displaced to production wells by sweeping the subsurface with hot water.

NAPL flotation and vapor emissions are controlled by maintaining both

temperature and concentration gradients in the injection water near the ground

surface.

2SHUDWLRQDO &RQVLGHUDWLRQV

CROWTM requires both subsurface injection and extraction wells and an

aboveground treatment train. No pretreatment of soils is required for CROWTM

operation.

$SSOLFDWLRQV DQG &RVW

The CROWTM process has been demonstrated to treat PAHs, coal tars,

pentachlorophenol, creosote, and petroleum by-products.

%HQHILWV

 Will work in a wide range of soil types

 Applicable in both saturated and unsaturated conditions

 Treatment possible in areas where traditional excavation and removal are

impossible

 Minimal disruption to nearby industrial operations or surrounding

neighborhoods; no digging and hauling of contaminated materials eliminates

exposure to toxic fumes and dust

 Will work close to or under existing structures, including buildings and

roadways
&KDSWHU 

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5-23

/LPLWDWLRQV

 Ability to control injected steam in the subsurface has been questioned

 Unclear whether sufficient contaminant mass can be recovered to alter

groundwater quality

&DVH 6WXG\

6WURXGVEXUJ 3HQQV\OYDQLD

The Brodhead Creek MGP Site is an NPL site located in Stroudsburg,

Pennsylvania. The site occupies a flood plain area of approximately 12 acres at the

confluence of Brodhead Creek and McMichael Creek. The enhanced recovery

technology CROWTM was utilized to mobilize and extract free coal tar from the

subsurface at the site. The ROD specified that 60 percent of the free coal tar be

removed from the subsurface at the site. Because of sampling difficulties and the

heterogeneity of the subsurface, the tar volume was not quantified although it was

estimated to be several thousand gallons. Without a reliable starting figure,

removal of 60 percent was impossible to document.

However, based on treatability results, the enhanced recovery process was

expected to recover more than 80 percent of the free tar present. For this reason,

EPA allowed a performance standard to be written that the enhanced recovery

process would operated until the increase in cumulative recovery of coal tar

dropped to 0.5 percent or less per pore volume of water flushed through the

formation.

The affected soils at the site were 30 feet bgs, below the water table. The soils were

a sand/gravel mixture residing above a silty sand confining layer. The sand and

gravel soils did not allow for representative sampling of the subsurface to

determine chemical characterization although free DNAPL was observed in wells

in this portion of the site at depths from inches to several feet.

At the Brodhead Creek site, six injection wells were installed near the edges of the

tar deposit. Two production wells were installed near the center of the tar deposit.

Water and tar were pumped from the production wells at approximately 40

gallons per minute (gpm), which produced a drawdown within the wells and

induced a gradient from the injection points to the production points. The induced

gradient contained the heat within the target zone and prevented mobilized

contaminants from being released into the surrounding aquifer. Once the

tar/water mixture was pumped to the surface, tar and water were separated. The

tar was then stored in the gravity settling tanks and an oil storage tank until being

trucked off site for disposal. Approximately 33 gpm of separated water was

recycled through the water heater and injected into the six injection wells. The

remaining 7 gpm was pumped to a granular activated carbon fluidized bed reactor

where the organic constituents were biologically degraded. The treated water was

then pumped through four carbon adsorption units prior to discharge to Brodhead

Creek.

Because of sampling difficulties in the gravelly matrix and because of

heterogeneity of the subsurface soils, no pre- and post-remediation samples were

obtained that were representative of the subsurface. CROWTM was operated at the
&KDSWHU 

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5-24

site for one year. During that time, the CROWTM process swept approximately

5,000 to 6,000 cubic yards of soil in the subsurface to recover more than 1,500

gallons of DNAPL. Remediation at the site has been completed, and the

equipment has been dismantled and removed. The final Remedial Action Report

has been accepted by USEPA Region III.

&RQWDFWV

Mr. James F. Villaume, Pennsylvania Power & Light Company, (610) 774-5094

Dr. Thomas D. Hayes, Gas Research Institute, (773) 399-8325

Mr. John Banks, USEPA Region III, (215) 566-3214


 	

Asphalt batching is a widely demonstrated technology for reuse of

petroleum-contaminated soils. During asphalt batching, contaminated soils are

mixed with asphalt, aggregate, and other emulsions to create a product for use in

paving and backfilling. Asphalt batching can be a cold-mix or hot-mix process;

both are described below.

 &ROG0L[ $VSKDOW %DWFKLQJ

7HFKQRORJ\ 'HVFULSWLRQ

Cold-mix asphalt batching has been successfully used to immobilize and reuse

MGP-contaminated soils and residues. Asphalt batching is essentially an ex situ

stabilization process that binds contaminated soil and tarry residues into the

matrix of an asphalt product. Residues are mixed with wet aggregate and asphalt

emulsion at ambient temperature. The product is used as paving. 

In the cold-mix asphalt batch process, wet aggregate material and an asphalt

emulsion are mixed and left at ambient temperature. The cold-mix batch product

is then cured or allowed to set undisturbed for a specific period that depends on

its ingredients. This curing process can begin either before or after the pavement

has been placed and compacted. 

The asphalt batching process is generally performed in several steps:

 Excavation and stockpiling of materials

 Material preprocessing (typically screening and/or crushing material to the

desired size)

 Stabilization with asphalt emulsion reagent

 Curing in a stockpile

 Using material for paving 

The final product is a material that can be used as a sub-base for paving in areas of

heavy vehicular traffic or possibly as surface paving in areas of light traffic.

Additional grading and paving or excavation are often required around the

treated material to accommodate its height.
&KDSWHU 

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Cold-mix asphalt batch products are typically produced either at a central plant

location or are mixed in place. The choice between producing them at a central

plant pavement or mixing in place must consider the intended use of the product

and the logistics and economics of staging an onsite treatment versus transporting

to an offsite facility (EPRI, 1997). A photograph of asphalt plant operations is

shown below.

2SHUDWLRQDO &RQVLGHUDWLRQV

This technology requires a treatability study to test leachability and engineering

properties of the treated material. The mix design is dependent on the

performance requirements of the finished product and the nature of the soil being

treated. Clayey soils are generally not appropriate for cold-mix asphalt batching

because a high clay content will reduce the strength of asphalt concrete. However,

soils with high clay or loam content can be mixed with high-grade aggregate to

produce a material used in lower-performance applications such as parking lots or

driveways. Similarly, the percentage of fine grains in contaminated soil should be

less than 20 percent passing the No. 200 sieve because excessively fine-grained

particles could lead to both an increase in the required asphalt content and

performance problems such as cracking and instability.

$SSOLFDWLRQV DQG &RVW

Before processing soil for cold-mix asphalt batching, an asphalt batching

contractor typically examines the physical and chemical characteristics of the soil

to determine whether it can be incorporated into a usable-quality pavement. For

offsite asphalt batching, the preacceptance criteria for using soil that contains tar

are plant specific and designed to meet certain chemical and physical thresholds.

None of the preacceptance criteria require that the chemistry of the MGP tar be

examined to see how closely it resembles that of asphalt (EPRI, 1997). The
&KDSWHU 

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5-26

analytical requirements of the batch plant may include EPA-certified analyses for

VOCs and SVOCs, petroleum hydrocarbons, pesticides, herbicides, and metals.

Because there have been few full-scale applications of cold-mix asphalt batching,

cost information is limited. In California, vendor quotations range from $40 to $50

per ton for onsite cold asphalt batching and $60 to $70 per ton for offsite batching

(transportation included).

%HQHILWV

 Material reused rather than disposed of offsite

 Effective in immobilizing PAHs

/LPLWDWLRQV

 Curing times can be long, particularly in cold weather

 Limits on acceptable percentage of fine-grained material

 Few examples of long-term durability of the product

&DVH 6WXGLHV

0RQWHUH\ )RUPHU 0*3 6LWH

From 1900 to 1947, an MGP in Monterey, California, provided gas to canneries in

the immediate area. This former MGP site was subsequently sold to the City of

Monterey, which planned construction of a gymnasium and pool complex. Site

investigations indicated that MGP wastes were present in the form of an oxidized

mixture of crude oil and bunker fuel to depths of 20 feet below grade. Soil at the

site consisted of sandy silt to clay material with a moisture content ranging from 6

to 22 percent.

Contaminated soil excavated from the former MGP site was blended into an

asphalt product at a rate of 300 tons per hour using onsite portable mixing

equipment. The treated material was then trucked to a second location, also

owned by the city of Monterey. The treated material was used in place of 3⁄4-inch

Class II aggregate base in a new construction project. A 2-inch lift of dense hot mix

was applied as a wearing surface over the treated material.

&RQWDFW

Robert Doss, Pacific Gas and Electric Company, (415) 973-7601

6DOW /DNH &LW\ )RUPHU 0*3 6LWH

From 1872 to 1908, the American Barrel NPL site in Salt Lake City, Utah, was used

as a coal gas manufacturing plant with an oil gas plant for meeting peak demands.

The plant had one holder, one tar well pump, six tar wells, and two coal tar stills.

From approximately 1920 to 1950, creosote operations were conducted at the site.

From 1955 to 1987, the site was leased to a barrel refurbisher, American Barrel,

who stored approximately 50,000 barrels on the property. The surface soils

contained high levels of PAHs, phenolic compounds, heavy metals and other

organic residues associated with the barrel storage activities. Subsurface soils had

high levels of PAHs and phenolic compounds. 
&KDSWHU 

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5-27

USEPA and state agency regulatory managers felt that recycling the material was

superior to landfilling or thermal desorption. Salt Lake City is a Clean Air Act

nonattainment area; therefore at the time of the remediation, the air quality

division of the state would not allow thermal desorption in the valley. Cold-mix

asphalt batching was selected over hot-mix asphalt batching for the proposed

remedial technology because the regulators felt that the hot mix was simply

another form of thermal desorption. USEPA and the state required that the asphalt

produced be used for roads and not for parks and schools. 

Approximately 20,700 tons of soil and debris were removed from the site. About

12 tons of this material were determined to be hazardous (e.g., wood from the tar

wells) and shipped to an incinerator. About 1,300 tons of the material were

nonhazardous but were not acceptable for asphalt batching (e.g., contained metal

and other debris). These were shipped to a landfill. The remaining 19,400 tons of

material were incorporated into cold-mix asphalt, including bricks and concrete

from the gas holder, tars from the holder and tar wells, and contaminated surface

and subsurface soils. This produced 194,966 tons of cold-mix asphalt. The gravel

pits in the Salt Lake City area are very low in fines, and the contaminated soil had

a high percentage of fine-grained material, so the asphalt with the contaminated

soil was of higher quality than could be produced with local gravel. The original

estimates for blending the contaminated soil into asphalt were 10 percent

contaminated soil, 7 percent oil, and 83 percent aggregate. The contaminated soil

had enough tar and oils in it to replace 40 percent of the oil needed to produce the

cold-mix product.

The first batch of asphalt produced with 7 percent oil was not of good quality and

had to be removed and mixed with additional aggregate. The final batches of

asphalt contained 4 percent oil, 10 percent contaminated soil, and 86 percent

aggregate and were of very high quality. All the resulting asphalt product was

donated to counties and cities. The county and city that ultimately used the

product asked the contractor if the mix could be made as a regular product

because of its superior performance in Utah’s cycles of cold and hot weather.

&RQWDFW

Jeff Tucker, Pacific Corp, (801) 220-2989

 +DUERU 3RLQW 6WXG\ 8WLFD 1HZ <RUN

In August 1993, Niagara Mohawk Power Corporation (NMPC) and United Retek

Corporation jointly performed a field demonstration of cold-mix asphalt batching

of soils at the Harbor Point site located in Utica, New York. Four 100-ton pilot

batches of soil were processed into pavements; three of the batches included MGP

soils containing tar; the fourth was a control sample of aggregate that met the

grading requirements of cold-batch pavements. The following evaluations were

then conducted:

 Leachability and permeability testing to determine how well hazardous

constituents were immobilized

 Marshall stability tests to determine the structural applicability of the finished

product
&KDSWHU 

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5-28

 Road tests to evaluate how the fines content and constituents of the MGP soils

affected the product’s environmental acceptability

 Evaluation of the extent of contaminant migration from the installed product

as measured by a stormwater runoff test

 Additional nondestructive deflection road tests to further evaluate structural

performance 

General conclusions of the testing indicated that the incorporation of MGP tarcontaining soils in cold-batch asphalt pavements reduced the leachability of the tar

constituents associated with these soils (EPRI, 1997). The data showed that the

more water-soluble compounds, such as benzene and naphthalene, would

continue to leach from these pavements after 21 days of curing. Further research to

establish the curing time to decrease leaching needs to be conducted. During the

study, unconsolidated material curing durations of the pavements was 2 weeks;

however, depending on the site-specific tar composition, curing durations may

need to be extended to ensure benzene and naphthalene concentrations in leachate

are minimized. 

MGP asphalt products appear to be slightly lower in strength than PCS asphalt

while still meeting the minimum requirements specified by the Asphalt Institute.

The durability of MGP asphalt was inferior to the control asphalt in the Harbor

Point study, as evidenced by the development of some potholes in the test road

sections (EPRI, 1997).

&DOLIRUQLD )RUPHU 0*3 6LWH

A cold-mix asphalt batching study was performed for a California utility to assess

the potential for treating tar-containing soils from MGPs in standard cold-batch

pavements. Chemical data consisting of total and extractable PAHs were

evaluated to determine how successful the batching was in immobilizing

contaminants. Several structural parameters were also evaluated to determine the

engineering properties of the pavement created by the batching process.

The results of the study indicated that some lighter-weight PAH compounds

leached from the pavement. However, the study also concluded that, had

additional leaching tests been conducted on the asphalt products after longer

curing periods, improvement in chemical immobilization might have been

observed. Further investigation into the relationship between curing times and

chemical immobilization was recommended (EPRI, 1997). Engineering data also

indicated that as the MGP soil percentage was increased, engineering properties

deteriorated, most notably for durability parameters such as moisture loss.

Nonetheless, the pavements generated through the cold-mix asphalt batching

process were strong enough for general use (all batches exceeded the minimum

Marshall stability value of 2,200 Newtons) even though their moisture content was

higher than is generally accepted for cold-batch pavements (EPRI, 1997).
&KDSWHU 

7HFKQRORJLHV IRU 6RXUFH 0DWHULDO 7UHDWPHQW

5-29

 WR  +DUERU 3RLQW 6WXG\ 8WLFD 1HZ <RUN

Niagara Mohawk Power Company conducted a joint hot- and cold-mix asphalt

batching study in 1995 and 1996 at its Harbor Point facility. As part of this study,

tar-containing soils from MGP sites were thermally desorbed before cold-mix

batching. The desorption step was necessary because of acceptance criteria

established by New York State Department of Environmental Conservation

(NYSDEC). Approximately 100 tons of previously excavated MGP soils were

mixed and designated for use in the project; these consisted of 30 percent coal tar

soils, 30 percent water gas tar soils, 30 percent processed construction spoils, and

10 percent tar emulsion soils (EPRI, 1997).

Following thermal desorption, two cold-mix designs were used. The first cold-mix

design was for a bituminous stabilized base course; the second was a dense graded

mix. Desorbed material was supplemented with clean aggregate: 56 percent

desorbed soil for cold-mix No. 1 and 40 percent desorbed soil for cold-mix No. 2.

The cold-mix products were prepared offsite by combining the desorbed material

and clean aggregate in a pugmill with a predetermined addition of asphalt

emulsion.

Two areas were selected for test panels using the cold-mix asphalt. Panel A

consisted of a composite design of a 3-inch-thick layer of bituminous stabilized

base course overlain with a 3-inch-thick layer of hot-mix top course. Panel B

consisted of adjoining 3-inch-thick sections of the two cold-mix products. After the

panels were placed, they were subjected to qualitative and quantitative

evaluations. Visual inspections were made over six months. The cold-mix products

improved over that period, consistent with previous observations that cold-mix

asphalt batch products require longer curing times. A quantitative analysis which

consisted of in-place density and deflection testing was also conducted. Based on

the results of these tests, the study concluded that the test panels performed

satisfactorily for a variety of applications, especially for roads subjected to light

and moderate traffic.

 +RW0L[ $VSKDOW %DWFKLQJ

7HFKQRORJ\ 'HVFULSWLRQ

Pilot projects have used hot-mix asphalt batching to immobilize and reuse MGPcontaminated soils and residues. Hot-mix asphalt batching is an ex situ

stabilization process that blends contaminated soil and tarry residues with

aggregate and asphalt emulsion to create a hot asphalt product. The high

processing temperatures of hot asphalt batching volatilize lighter weight

compounds found in MGP wastes (e.g., benzene) and promote formation of a

homogenous blend of aggregate and asphalt cement. Materials treated via hot-mix

asphalt batch are used in paving surfaces. 

The hot-mix asphalt batching process is generally performed onsite or offsite in

several steps:

 Excavation and stockpiling of materials
&KDSWHU 

7HFKQRORJLHV IRU 6RXUFH 0DWHULDO 7UHDWPHQW

5-30

 Material preprocessing (typically screening and/or crushing material to the

desired size)

 Heating and drying aggregate material prior to mixing

 Stabilization of dried material with asphalt emulsion reagents

 Compacting the finished product at temperatures well above ambient

 Using treated material for paving

The final product is a material that can be used as a sub-base for paving in areas of

heavy vehicular traffic.

2SHUDWLRQDO &RQVLGHUDWLRQV

Hot-mix asphalt batching requires a treatability study to test leachability and

engineering properties of the treated materials. The mix design is dependent on

Marshall and Hveem testing of the performance requirements of the finished

product and on the nature of the material being treated. Clayey soils are generally

not appropriate because a high clay content will reduce the strength of asphalt

concrete. However, soils with high clay or loam content can be mixed with highgrade aggregate to produce a material used in lower-performance applications

such as parking lots or driveways. Similarly, the percentage of fine grains in the

contaminated soil should be less than 20 percent passing the No. 200 sieve because

excessively fine-grained particles could lead to both an increase in the required

asphalt content and performance problems such as cracking and instability.

$SSOLFDWLRQV DQG &RVW

Prior to processing soil for hot-mix asphalt batching, an asphalt batching

contractor typically examines the soil’s physical and chemical characteristics to
&KDSWHU 

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5-31

determine whether it can be incorporated into a pavement of usable quality. For

offsite asphalt batching, different plants have different preacceptance criteria

regarding use of soil that contains tar; these criteria establish certain chemical and

physical thresholds. None of the preacceptance criteria require that the chemistry

of the MGP tar be examined to see how closely it resembles that of asphalt (EPRI,

1997). The analytical requirements of a plant may include EPA-certified analyses

for VOCs, SVOCs, petroleum hydrocarbons, pesticides, herbicides, and metals.

Because there have been few full-scale applications of this technology, cost

information is limited. In California, vendor quotations have ranged from $60 to

$70 per ton for offsite asphalt batching (transportation included).

%HQHILWV

 Material reused rather than disposed of offsite

 Effective in immobilizing PAHs and volatilizing VOCs

 One of the few viable technologies available for MGP tars

/LPLWDWLRQV

 Potential for leaching of contaminant from the asphalt product

 Potential for release of volatile contaminants

 Potential for objectionable odors

 Excavation treatment primarily limited to gravelly soils and sands

 For offsite asphalt batching, possible difficulty in identifying a local facility

technically prepared and permitted to process MGP waste

 Few examples of long-term durability of the product

&DVH 6WXGLHV

:LVFRQVLQ 3RZHU 	 /LJKW

EPRI, in cooperation with Wisconsin Power & Light, performed a limited study on

the chemical and physical properties of hot-batched asphalt pavements that

incorporate tar-containing soils from MGPs. The aggregate blend produced for hot

batching consisted of 25 percent tar-containing soils, 20 percent clean sand, 40

percent bottom ash with 9/16-inch diameter, and 15 percent bottom ash with 3/32-

inch diameter. The tar-containing soils used in this study had total PAH

concentrations as high as 690 mg/kg. The only TCLP metal detected in a

pretreatment extract was barium. This constituent actually increased in extract

concentration after treatment. The average reduction in contaminants was 88

percent. TCLP extract concentrations were reduced to below the practical

quantitation limit (PQL) for all of the metals and all VOCs except benzene,

toluene, and naphthalene, which were reduced but still detected in the low parts

per billion range (EPRI, 1997).
&KDSWHU 

7HFKQRORJLHV IRU 6RXUFH 0DWHULDO 7UHDWPHQW

5-32

+DUERU 3RLQW 6WXG\ 8WLFD 1HZ <RUN

Niagara Mohawk Power Company conducted a joint hot- and cold-mix asphalt

batching study in 1995 and 1996 at its Harbor Point facility. In this study, tarcontaining soils from an MGP were thermally desorbed prior to hot-mix batching.

The desorption step was necessary because of the acceptance criteria set by the

state regulatory agency. Approximately 100 tons of previously excavated MGP

soils were mixed and designated for use in the project; these consisted of 30

percent coal tar soils, 30 percent water gas tar soils, 30 percent processed

construction spoils, and 10 percent tar emulsion soils (EPRI, 1997).

Following thermal desorption, two hot-mix designs were used. The first hot-mix

design was for a top course, and the second hot-mix design was for a modified

bituminous plant mix. Desorbed material was supplemented with clean aggregate:

30 percent desorbed soil for hot-mix No. 1, and 40 percent desorbed soil for hotmix No. 2. The hot-mix products were prepared at an offsite batch mix plant, with

hot asphalt and the desorbed material-aggregate blended in a pugmill. These

products were then conveyed to the site in trucks. Temperature loss during

transport of the hot mix was approximately 25°F, which was within acceptable

limits.

Three areas were selected for test panels using the hot-mix asphalt. Panel A

consisted of a composite design of a 3-inch layer of bituminous stabilized base

course overlain with a 3-inch thick layer of hot-mix top course (hot-mix design No.

1). Panel C consisted of adjoining 3-inch sections of the two hot-mix products.

After the panels were placed, they were subjected to qualitative and quantitative

evaluations. Visual inspections were made over 6 months. A quantitative analysis

was also conducted which consisted of in-place density and deflection testing.

Based on the results of these tests, the study concluded that the test panels

performed satisfactorily for a variety of applications, especially for roads subjected

to light and moderate traffic.

!	
		"	#$	
		

 ([ 6LWX %LRUHPHGLDWLRQ

Bioremediation generally refers to the breakdown of organic compounds

(contaminants) by microorganisms. This degradation can occur in the presence of

oxygen (aerobic) or in the absence of oxygen (anaerobic). Bioremediation

techniques create a favorable environment for microorganisms to use

contaminants as a food and energy source. Ex situ bioremediation processes treat

soil above grade using conventional soil management practices to enhance

degradation of contaminant. Generally, some combination of oxygen, nutrients,

and moisture are provided and pH is controlled. Bioaugmentation may be used, in

which microorganisms adapted for degradation of specific contaminants are

applied (USEPA, 1998).

Although not all organic compounds are amenable to biodegradation,

bioremediation techniques have been successfully used to remediate soils and

sludges contaminated by petroleum hydrocarbons, solvents, pesticides, wood
&KDSWHU 

7HFKQRORJLHV IRU 6RXUFH 0DWHULDO 7UHDWPHQW

5-33

preservatives, and other organic chemicals. The rate and extent to which

microorganisms degrade these contaminants is influenced by the specific

contaminants present, soil type, oxygen supply, moisture content, nutrient supply,

pH, and temperature. Other factors that influence the rate and extent of

degradation include the availability of contaminant(s) to the microorganisms, the

concentration of the contaminants (e.g., high concentrations may be toxic to the

microorganisms), and the presence of other substances toxic to the

microorganisms, (e.g., mercury), or inhibitors to the metabolism of the

contaminant (USEPA, 1998).

For MGP applications, biological treatment is generally most effective on BTEX

and 2- and 3-ring PAH compounds, with treatment efficiency declining for 4-, 5-,

and 6-ring PAH compounds because of their reduced solubility and availability to

microorganisms. 

A common observation with bioremediation is that eventually the degradation

rate reaches a plateau and it is difficult to reduce concentrations further in a

practical manner. Residual PAHs after bioremediation, though detectable and

often above regulatory standards, may have little or no significant effect on the

environment. The leaching potential from residual PAHs in soils and direct

contact toxicity from these residuals are the subject of ongoing research.

The most commonly used ex situ biological technologies include landfarming,

biopiles (composting), and slurry phase biological treatment. Each of these is

described below.

 /DQGIDUPLQJ

7HFKQRORJ\ 'HVFULSWLRQ

Landfarming (also called land treatment) involves placing contaminated soil in

lined beds and periodically turning it over or tilling it to aerate the waste. The soil

is irrigated, and nutrients are added as needed to optimize growing conditions.

Land farming requires excavation and placement of contaminated soils onto

prepared beds or liners to control leaching of contaminants. Contaminated soil is

then treated in lifts that are up to 18 inches thick. After the desired treatment is

achieved, the lift is removed and a new lift is constructed. It is advantageous to

remove only the top of the remediated lift and then to construct the new lift by

adding more contaminated media to the remaining material and mixing. This

strategy inoculates the freshly added material with an actively degrading

microbial culture and can reduce treatment times (USEPA, 1998).

2SHUDWLRQDO &RQVLGHUDWLRQV

Soil conditions are controlled for ex situ bioremediation to optimize the rate of

contaminant degradation. Conditions normally controlled include:

 Moisture content (for biopiles and landfarming; solids content for slurry

treatment)

 Aeration 
&KDSWHU 

7HFKQRORJLHV IRU 6RXUFH 0DWHULDO 7UHDWPHQW

5-34

 pH

 Nutrients

 Other amendments (e.g., bulking agents)

Although a contaminant might have been shown to be biodegradable in the

laboratory or at another site, its rate and extent of degradation in each particular

location and specific soil condition depend on many factors. To determine whether

bioremediation is an appropriate and effective remedial treatment for the

contaminated soil at a particular site, it is necessary to characterize the

contamination, soil, and site, and to evaluate the biodegradation potential of the

contaminants. A preliminary treatability study for all ex situ bioremediation

methods should identify: 

 Amendment mixtures that best promote microbial activity

 Percent reduction and lowest achievable concentration limit of contaminant

 Potential degradation rate

Landfarming requires a large amount of space and is dependent on environmental

conditions affecting biological degradation of contaminants (e.g., temperature and

rainfall). VOC emissions and dust control are also important considerations,

especially during tilling and other material handling operations. Waste

constituents may be subject to “land-ban” regulation and thus may not be eligible

for treatment by landfarming. 

$SSOLFDWLRQV DQG &RVW

Ex situ bioremediation methods have been used to treat petroleum hydrocarbons,

VOCs, and PAHs. As a rule of thumb, the higher the molecular weight (and the

more rings a PAH has), the slower the degradation rate. Landfarming is very

simple from a technology point of view.

Costs for treatment include approximately $75 per cubic yard for the prepared

bed. Studies conducted prior to treatment can range from $25,000 to $50,000 for

laboratory studies, and $100,000 to $500,000 for pilot tests or field demonstrations. 

%HQHILWV

 Ex situ’s main advantage is that it generally requires shorter time periods than

in situ treatment, and there is more certainty about the uniformity of treatment

because soil can be homogenized, screened, and continuously mixed

 Ex situ treatment is favored over in situ biological techniques for

heterogeneous soils, low-permeability soils, areas where underlying

groundwater would be difficult to capture, or when faster treatment times are

required

 Bioremediation reduces the source of contamination

/LPLWDWLRQV

 None of the ex situ biological treatment options can completely remove organic

contaminants
&KDSWHU 

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5-35

 All ex situ treatment requires excavation of soils, with associated costs and

engineering for equipment, permits, and material handling/worker exposure

considerations

&DVH 6WXG\

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MidAmerican Energy has used the Institute of Gas Technologies (IGT) MGP-REM,

a chemically enhanced bioremediation process, for a full-scale remediation of its

MGP site near Des Moines, Iowa. This was the first full-scale use of the MGP-REM

chemical/biological treatment process for coal-tar contaminated soils in a solidphase application (landfarming). The process combines the two complementary

remedial techniques of chemical oxidation and biological treatment. The MGPREM process uses the addition of Fenton’s reagent (H2O2 plus Fe2+) to produce

hydroxyl radicals that start a chain reaction with the organic contaminants. These

contaminants, specifically PAHs, are transformed into products that are more

readily degraded by microorganisms; the ultimate products of the process are

carbon dioxide, water, and biomass (Srivastava, 1996).

The Vandalia Road site is a former landfill that contains residues from a former

MGP related to the Capital Gas Light Company site located in Des Moines. This

site operated from 1876 to 1957. The Vandalia Road MGP site was selected for a

full-scale test of the MGP-REM technology because of a number of site attributes:

 The site is located on property that is currently owned by MidAmerican. 

 The site is located in a rural area, even though it is within the city limits of the

City of Pleasant Hill.

 The site is surrounded by company-owned farmland that could be used to

construct an adjacent treatment facility (Kelley, 1997).

After laboratory treatability studies were completed at the IGT laboratory facilities

in Des Plaines, Illinois, and the data indicated that the contaminated media at the

Vandalia Road MGP site were amenable to the MGP-REM process, the full-scale

treatment facility was constructed in the fall of 1996 and the spring of 1997. The

soil treatment portion of the facility was 100 feet by 300 feet, bermed and lined

with high-density polyethylene (HDPE). The two 12-inch lifts each had a capacity

of 1,000 cubic yards. Overall capacity for a given treatment phase was 2,000 cubic

yards. At the end of the first treatment phase, treated soil was removed from the

facility and used for backfill in the former excavation. Adjacent facility structures

included a water retention basin for runon and runoff control, an automatic

sprinkler system, a decontamination/soil processing pad and a field laboratory.

The total cost of the treatment facility and associated structures was approximately

$360,000 (Kelley, 1997). Additional phases of treatment may be required to

complete the site remediation.

In 1997, contaminated soil was excavated from the former landfill and placed in

the treatment facility. All of the soil that was excavated from the former landfill

was located below the groundwater level, so a dewatering area was constructed

adjacent to the excavation to assist in reducing the water content of the excavated
&KDSWHU 

7HFKQRORJLHV IRU 6RXUFH 0DWHULDO 7UHDWPHQW

5-36

media prior to loading into the land treatment unit (LTU). Once sufficiently

dewatered to allow handling, the material was hauled to the adjacent treatment

facility and placed in the LTU (Kelley, 1997). A small bulldozer was used to spread

the materials across the facility to a consistent depth of 12 inches. Originally,

excavated material was to be processed through a screening plant to remove

oversize debris; however, the material, even after dewatering, was too wet to pass

through the screening plant. Because the landfill appeared to consist of coal tar

materials placed there in liquid form, the debris typically found at an MGP site

(brick, concrete, timbers, etc.) was not present, which reduced the need for

screening.

The routine operations for the biological portion of the process consisted of

aeration of the soil, addition of nutrients, and maintenance of the proper moisture

content. All of the equipment used for operation of the treatment facility was

standard agricultural equipment, such as field cultivators, rototillers, subsoilers,

and a two-bottom plow. The two-bottom plow was necessary to turn over the

entire lift of soil placed in the facility, for proper aeration. The plow was necessary

because the lower 4 to 6 inches of soil were so compacted by loading in the LTU

that the soil could not be turned over using a tiller or field cultivator. A critical

parameter for biological degradation is the moisture content of the media treated;

moisture content needs to be between 40 and 80 percent of field-holding capacity.

An irrigation system was installed to automate the soil moisture adjustments.

During the first year of operation, too much water, in the form of heavy rain,

affected the facility’s operations. This made aeration difficult and may have caused

a lack of oxygen, which may have inhibited biological degradation.

Chemical enhancement was also used in this bioremediation treatment process.

IGT’s MGP-REM chemical treatment process consisted of three steps. First, the soil

pH was adjusted to approximately 5.0. Next, ferrous sulfate was added to the soil

and mixed by rototilling. Third, hydrogen peroxide was added to the process

resulting in a combination of direct oxidation and hydroxylation of the 4-, 5-, and

6-ring PAH compounds. Both of these chemical reactions (oxidation and

hydroxylation) generally increase the solubility of the PAH compounds and, as a

result, improve their biological availability to the bacteria (Kelley, 1997). The

chemicals were added to the plot using commercially available agricultural

equipment modified for this project.

During the first year of operation of the biological treatment phase, total PAH

reduction was 51 percent. Chemical treatment reduced total PAHs by an

additional 20 percent. In addition, the reduction of 4- to 6-ring compounds was

increased twofold. Overall, the MGP-REM process used at the Vandalia Road

MGP site reduced total PAHs by 70 percent. Based upon current cost estimates for

continued operation of the facility, MidAmerican expects to save approximately

$1.2 million using this technology as compared to co-burning the soil in its power

plant facility near Sioux City, Iowa (Kelley, 1997).
&KDSWHU 

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5-37

 %LRSLOHV

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Biopile treatment is a variation of composting in which excavated soils are usually

mixed with soil amendments and placed in piles on a treatment area. Biopiles

often include leachate collection systems and some form of aeration. In most cases,

indigenous microorganisms are used. Soil amendments may include nutrients,

moisture, or bulking agents such as wood chips.

Moisture, heat, nutrients, oxygen, and pH can be controlled to enhance

biodegradation. The treatment area will generally be contained with an

impermeable liner to minimize the risk of contaminants leaching into

uncontaminated soil. Biopiles often have a buried distribution system that passes

air through the soil either by vacuum or by positive pressure. As an alternative to

forced aeration, biopiles may also be turned regularly. Biopiles can be covered

with plastic to control runoff, evaporation, and volatilization (USEPA, 1998). Heat

can be generated in the piles, potentially providing for higher degradation rates

and winter operation.

2SHUDWLRQDO &RQVLGHUDWLRQV

Soil conditions are controlled for ex situ bioremediation to optimize the rate of

contaminant degradation. Conditions normally controlled include:

 Moisture content (for biopiles and landfarming; solids content for slurry

treatment)

 Aeration 

 pH

 Nutrients

 Other amendments (e.g., bulking agents)

Although a contaminant might have been shown to be biodegradable in the

laboratory or at another site, its rate and extent of degradation in each particular

location and under specific soil conditions depend on many factors. To determine

whether bioremediation via biopiles is an appropriate and effective remedial

treatment for contaminated soil at a particular site, it is necessary to characterize

the contamination, soil, and site, and to evaluate the biodegradation potential of

the contaminants. A preliminary treatability study for all ex situ bioremediation

methods should identify: 

 Amendment mixtures that best promote microbial activity

 Percent reduction and lowest achievable concentration limit of contaminant

 Potential degradation rate

For biopiles, batches of the same size may require longer retention times than in

slurry-phase processes. Static treatment processes may result in less uniform

treatment than processes that involve periodic mixing, which is difficult for

biopiles. Windrow composting is an alternative that overcomes that problem.
&KDSWHU 

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5-38

$SSOLFDWLRQV DQG &RVW

Ex situ bioremediation methods have been used to treat petroleum hydrocarbons,

VOCs, and PAHs. As a rule of thumb, the higher the molecular weight (and the

more rings a PAH has), the slower the degradation rate. Biopiles are a little more

complex technologically than landfarming. The associated costs of this method

reflect the increased complexity. Costs for biopiles may run $100 to $200 per cubic

yard, exclusive of laboratory and pilot studies. Laboratory studies may cost

between $25,000 and $50,000. Pilot tests or field demonstrations may cost $100,000

to $500,000.

%HQHILWV

 Ex situ treatment’s main advantage is that it generally requires shorter time

periods than in situ treatment, and there is more certainty about the uniformity

of treatment because soil can be homogenized, screened, and continuously

mixed

 Ex situ treatment is favored over in situ biological techniques for

heterogeneous soils, low-permeability soils, areas where underlying

groundwater would be difficult to capture, or when faster treatment times are

required

 Bioremediation reduces the source of contamination

/LPLWDWLRQV

 None of the ex situ biological treatment options can completely remove organic

contaminants

 All ex situ treatment requires excavation of soils, with associated costs and

engineering for equipment, permits, and material handling/worker exposure

considerations

&DVH 6WXG\

1DY\ 1DWLRQDO 7HVW 6LWH

A demonstration of biopile technology was performed to investigate and optimize

methods of pretreatment, construction, operation, and performance monitoring.

Soil contaminated with petroleum hydrocarbons was treated in 500-cubic-yard

biopiles at Port Hueneme, California, following a treatability study that was

conducted to predict biopile performance and to identify optimum nutrient rates.

Two biopiles with the appropriate dimensions of 52 feet by 52 feet by 8 feet were

constructed on a liner, with an aeration system consisting of slotted PVC piping

and a positive displacement blower. An irrigation system was also included. The

piles were covered with polyethylene, and a carbon emission control system was

installed (Chaconas, 1997). The demonstration was conducted in two phases from

1994 to 1996. In the first phase, soils consisted of brown silty sand with a trace of

clay (35 percent passing a No. 200 sieve), contaminated primarily with diesel fuel.

The second phase of the test used soils that consisted of brown clayey silt (52

percent passing a No. 200 sieve), contaminated with a combination of diesel fuel

and heavier fuel oils. In both phases, the petroleum hydrocarbons were found to

be significantly weathered (degraded), as evidenced by the absence of normal
&KDSWHU 

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5-39

alkanes. In the second phase of the test, contaminated soils were pulverized with

the hammer mill prior to placement in the biopile; in the first phase soils were

directly placed in the pile.

Moisture and temperature probes, field respirometry testing, and innovative

laboratory techniques to track degradation of various hydrocarbon classes were

employed to monitor performance. Nondestructive field measurements of

biological respirometry (oxygen uptake), moisture content, and temperature

proved successful in monitoring the operation of the biopiles (Chaconas, 1997).

During the first phase, the technology removed 88 percent (reduction from an

average of 1,990 mg/kg to 232 mg/kg) of petroleum hydrocarbons in the diesel

range during 51 weeks. During 47 weeks of operation, the second phase achieved

an 88 percent reduction in the diesel range, from an average of 4,769 mg/kg to 592

mg/kg, and a 71 percent reduction in the motor oil range, from an average

concentration of 5,638 mg/kg to 1,617 mg/kg (Chaconas, 1997). In each phase, the

largest reductions occurred during the first 4 weeks of biopile operations, and

TEPH degradation rates slowed dramatically after 6 to 8 weeks of operation. This

“plateauing” of concentrations is consistent with result of other studies in the

literature for this technology. The hammer mill step in the second phase appears to

have been successful because comparable results were obtained although the

pulverized soil contained more clay. Degradation rates calculated from

respirometry testing data correlated well with TEPH degradation observed in

laboratory analyses.

 %LRUHDFWRUV

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Slurry-phase biological treatment involves controlled treatment of excavated soil

in a bioreactor. Excavated soil is first physically processed to separate gravel, sand,

and debris, and the soil is then mixed with water to a predetermined concentration

dependent upon the concentration of the contaminants, the rate of biodegradation,

and the physical nature of the soils. Typically, a slurry contains from 10 to 50

percent solids by weight.

The solids are maintained in suspension in a reactor vessel and mixed with

nutrients and oxygen. Microorganisms may be added if a suitable population is

not present. When biodegradation is complete, the soil slurry is dewatered using

clarifiers, pressure filters, vacuum filters, sand drying beds, centrifuges or other

dewatering devices.

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Soil conditions are controlled for ex situ bioremediation to optimize the rate of

contaminant degradation. Conditions normally controlled include:

 Solids content (for slurry treatment, moisture content for biopiles and

landfarming)

 Aeration 
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 pH

 Nutrients

 Other amendments (e.g., bulking agents)

Although a contaminant might have been shown to be biodegradable in the

laboratory or at another site, its rate and extent of degradation in each particular

location and under specific soil conditions depend on many factors. To determine

whether bioremediation is an appropriate and effective remedial treatment for the

contaminated soil at a particular site, it is necessary to characterize the

contamination, soil, and site, and to evaluate the biodegradation potential of the

contaminants. A preliminary treatability study for all ex situ bioremediation

methods should identify: 

 Amendment mixtures that best promote microbial activity

 Percent reduction and lowest achievable concentration limit of contaminant

 Potential degradation rate

For bioreactors, sizing of materials prior to putting them into the reactor can be

difficult and expensive. Nonhomogeneous and clayey soils can create serious

materials handling problems. Dewatering of treated soil fines can be expensive,

and finding an acceptable method for disposing of nonrecycled wastewaters is

required.

$SSOLFDWLRQV DQG &RVW

Ex situ bioremediation methods have been used to treat petroleum hydrocarbons,

VOCs, and PAHs. As a rule of thumb, the higher the molecular weight (and the

more rings a PAH has), the slower the degradation rate. Bioreactors are the most

complex of the ex situ processes. The associated costs of this method reflect its

complexity. However, bioreactors provide the highest level of treatment attainable

for ex situ bioremediation of soils because they provide optimal conditions (e.g.,

mixing, temperature, pH). Costs for bioreactors run approximately $216 per cubic

yard, exclusive of laboratory and pilot studies. Laboratory studies may cost

between $25,000 and $50,000. Pilot studies or field demonstrations may run

between $100,000 and $500,000.

%HQHILWV

 Ex situ treatment’s main advantage is that it generally requires shorter time

periods than in situ treatment, and there is more certainty about the uniformity

of treatment because soil can be homogenized, screened, and continuously

mixed

 Ex situ treatment is favored over in situ biological techniques for

heterogeneous soils, low-permeability soils, areas where underlying

groundwater would be difficult to capture, or when faster treatment times are

required

 Bioremediation reduces the source of contamination
&KDSWHU 

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5-41

/LPLWDWLRQV

 None of the ex situ biological treatment options can completely remove organic

contaminants

 All ex situ treatment requires excavation of soils, with associated costs and

engineering for equipment, permits, and material handling/worker exposure

considerations

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A field-scale pilot test of bioslurry treatment was performed in 1995 at the Niagara

Mohawk Power Corporation (NMPC) Remediation Research Facility in Utica,

New York. Sediment was dredged from Utica Harbor and placed in two 10,000-

gallon capacity slurry bioreactors where it was mixed by single top-mounted

mixers, aerated by blowers, and treated for 68 days. 

Grain size analysis of the sediments dredged from the harbor indicated that the

material was approximately 34 percent sand, 52 percent silt, and 14 percent clay.

The target slurry density for the pilot test was 20 percent by weight, and a working

slurry volume of 7,300 gallons was used in each tank. Prior to treatment, the

sediments exhibited a hydrocarbon odor and sheen. Initial concentrations of BTEX

and PAHs were 86 and 651 mg/kg, respectively. Oil and grease analysis showed a

concentration of 1.4 percent (dry weight), and total organic carbon was measured

at 5.8 percent (dry weight).

Following bioslurry treatment, the sediments did not exhibit the hydrocarbon odor

or sheen that had been observed when the material was dredged. No detectable

BTEX was present in the sediments, and the total PAH concentration was

measured at 203 mg/kg. The overall DRE for PAHs was 69 percent, ranging from

a DRE of 89 percent for 3-ring PAHs to a DRE of 0 percent for 6-ring PAHs. The

majority of PAH degradation was achieved within the first 21 to 35 days of

treatment. The oil and grease concentration was measured following treatment at

0.31 percent, a reduction of 78 percent.

The sediments were tested before and after treatment using a 14-day earthworm

test. Prior to treatment, only 24 percent of the test organisms survived using

undiluted dewatered sediment; after treatment, 94 percent of the organisms

survived. Decanted wastewater post treatment was found to be toxic to fish, in

part because of residual nutrient concentrations from the treatment process. These

results indicate that management of residual nutrients in the wastewater effluent

will be required as part of full-scale bioslurry treatment.

The potential for leaching BTEX and PAHs before and after bioslurry treatment

was measured using the EPA synthetic precipitation leaching procedure test

(SPLP). Following treatment, no BTEX or PAHs were found in the SPLP extract

above the detection limit.

This remedial technology demonstration confirmed that bioslurry treatment of

aquatic sediments can be performed at a field scale. Although bioreactor treatment

of the sediments did not achieve the removal efficiency typical of more aggressive
&KDSWHU 

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5-42

methods such as incineration or thermal desorption, this demonstration suggests

that, after bioslurry treatment, sediments may be placed in aquatic or terrestrial

environments. Using risk-based treatment criteria for such placement may be an

environmentally acceptable option for biologically treated sediments.

&RQWDFWV

Jean-Pierre Moreau, Niagara Mohawk Power Corporation, 300 Erie Boulevard,

West, Syracuse, NY 13322, (315) 428-6808

Dr. Thomas D. Hayes, Gas Research Institute, 8600 West Bryn Mawr Avenue,

Chicago, IL 60631, (312) 399-8325

James B. Harrington, P.E., New York State Department of Environmental

Conservation, 50 Wolf Road, Albany, NY, (518) 457-0337

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Bioremediation generally refers to the breakdown of organic compounds

(contaminants) by microorganisms. This degradation can occur in the presence of

oxygen (aerobic) or in the absence of oxygen (anaerobic). Bioremediation

technologies stimulate the growth of microorganisms and their use of

contaminants as a food and energy source. Biodegradation processes are enhanced

by creating a favorable environment for microorganisms through the introduction

of some combination of oxygen (aerobic), nutrients and moisture, and by

controlling the temperature and pH of the soil or groundwater environment.

Bioaugmentation is another bioremediation technology in which microorganisms

adapted for the degradation of specific contaminants are added to enhance the

biodegradation process (USEPA, 1998). Bioventing is a third bioremediation

technology. It uses conventional soil vapor extraction (SVE) equipment to

introduce oxygen to indigenous soil microorganisms.

Although not all organic compounds are amenable to biodegradation,

bioremediation has been successfully used to clean up soils and sludges

contaminated by petroleum hydrocarbons, solvents, pesticides, wood

preservatives, and other organic chemicals. Aerobic biodegradation is the primary

mechanism for in situ biotreatment of petroleum hydrocarbons and PAHs in soil.

The rate at which microorganisms degrade contaminants is influenced by the

concentrations of contaminants present, the degree of contact between the

microorganisms and the contaminants, the oxygen supply, moisture, temperature,

pH, and nutrient supply in the soil or water to be treated (USEPA, 1998). In situ

biological treatment technologies are sensitive to certain soil parameters. For

example, the presence of clay or humic materials in soil can cause variations in

biological treatment process performance. For MGP sites, biological treatment of

PAHs is generally most effective on BTEX and 2- and 3-ring PAH compounds;

treatment efficiency declines for 4-, 5-, and 6-ring PAH compounds because of

their reduced solubility and availability to microorganisms.

Of the available in situ biological treatment technologies, bioventing has been the

most frequently demonstrated. As previously mentioned, this technology

stimulates the in situ biodegradation of aerobically degradable compounds in soil
&KDSWHU 

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by providing oxygen to existing indigenous soil microorganisms. Bioventing uses

conventional SVE equipment to stimulate biodegradation by providing oxygen to

indigenous soil microorganisms. However, bioventing uses low air-flow rates to

provide just enough oxygen to sustain microbial activity while minimizing

contaminant volatilization (GRI, 1996), which is the opposite of the high air-flow

rates used in treatment by SVE. Bioventing systems may either use a vacuum

approach to draw air and oxygen into the contaminated subsurface area or a

positive pressure system to inject air into the contaminated subsurface through

wells. Extraction wells may be used at the perimeter of the treatment zone to

control vapors. Bioventing is a medium- to long-term technology applicable only

to soils in the vadose zone, and cleanup times range from a few months to several

years (USEPA, 1998).

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Soil characteristics that affect microbial activity (and therefore biodegradation

rates) include pH, moisture, presence of nutrients, (e.g., nitrogen and phosphorus),

and temperature. The optimal pH range is 6 to 8 for microbial activity although

microbial respiration has been observed at sites that have soils outside this range.

Optimum soil moisture is very soil-specific. For bioventing, too much moisture can

reduce the air permeability of the soil and decrease its oxygen transfer capability.

Too little moisture inhibits microbial activity. A sufficient population of

microorganisms needs to be present to attain reasonable degradation rates.

$SSOLFDWLRQV DQG &RVW

In situ bioremediation is typically useful for treating the portion of MGP residues

containing lower molecular-weight hydrocarbons (e.g., volatile and semi-volatile

portions of coal tar.) Bioventing and in situ bioremediation techniques have been

successfully used to treat soils contaminated by petroleum hydrocarbons,

nonchlorinated solvents, pesticides, wood preservatives, and other organic

chemicals. For example, the U.S. Air Force Bioventing Initiative is demonstrating

that this technology is effective under widely varying site conditions. As of 1996,

data have been collected from 125 sites (Leesch and Hinchee, 1996). Regulatory

acceptance of bioventing has been obtained in 35 states and in all 10 USEPA

Regions (Leesch and Hinchee, 1996). 

The time required to remediate a site using bioventing or in situ bioremediation is

highly dependent upon the specific soil and chemical properties of the

contaminated media. Costs for operating a bioventing system typically are $10 to

$70 per cubic meter of soil ($10 to $60 per cubic yard; AFCEE, 1994). Factors that

affect the cost of bioventing include contaminant type and concentration, soil

permeability, injection well spacing and number, pumping rate, and off-gas

treatment. Bioremediation costs vary considerably depending on the volume of

soil to be treated, specific soil and chemical properties of the contaminated media,

and site-specific requirements for bioremediation enhancements or nutrients. The

technology does not have high capital or operation and maintenance costs because

it does not require expensive equipment and relatively few personnel are involved

in the operation and periodic maintenance of the bioventing system.
&KDSWHU 

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%HQHILWV

 Cost savings achieved by avoiding excavation and transportation of soil

 Generally inexpensive

 Contaminants partially destroyed

 “Low tech” and relatively easy to implement.

 Minimal disruption of current operations at sites

 Bioventing demonstrated highly effective for treating lighter-weight petroleum

hydrocarbons (e.g., gasoline)

/LPLWDWLRQV

 Generally more time required than for ex situ processes 

 Verification that contaminants have been destroyed sometimes difficult

 Treatment uniformity uncertain because of variability in soil characteristics

and contaminant distribution

 Not demonstrated effective for higher-molecular-weight petroleum

hydrocarbons or PAHs

 Bioventing performance reduced by shallow groundwater table, saturated soil

lenses, or low-permeability soils; low soil moisture content may limit

bioventing effectiveness.

 Monitoring of offgases at soil surface possibly required for bioventing; possible

vapors buildup in basements within the radius of influence of air injection

wells can be alleviated by extracting air near any facility of concern

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A demonstration of bioventing was conducted at the Reilly Tar and Chemical

Corporation site in St. Louis Park, Minnesota. This site formerly housed a coal tar

refinery and wood-preserving facility at which creosote in mineral oil served as

the primary preservative. The facility operated from 1917 until 1979. A pilot-scale

bioventing demonstration began in November 1992 to determine whether the

technology was effective for PAHs.

The pilot-scale bioventing system consisted of a single-vent well with 12 tri-level 

soil-gas monitoring points. The vent well was screened from 5 to 15 feet below

grade and was placed in the center of a 50-foot by 50-foot treatment area that was

selected based on depressed oxygen concentrations measured during an initial soil

gas survey (Alleman, 1995). The soil-gas monitoring points were placed radially

outward at 10, 20, and 30 feet from the vent well in four directions towards the

corners of the plot. The probes were set at 4, 6, and 8 feet below grade. A control

area was established approximately 150 feet to the northwest of the treatment area.

Soil samples were collected from both the treatment and control areas to quantify

PAH concentrations prior to bioventing. Respiration measurements were made to
&KDSWHU 

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5-45

estimate PAH biodegradation as a means of monitoring the progress of the

bioventing. In situ respiration tests were conducted every 3 months to measure

oxygen utilization rates and calculate biodegradation rates (Alleman, 1995).

Bioventing at the tar site achieved a greater than 10 percent reduction per year in

total PAHs during the first two years of the study. Respiration measurements

indicated that 13.4 percent and 17.3 percent degradation of total PAH content was

possible during the first and second year, respectively. Although not all of the

respiration can be attributed conclusively to PAH metabolism, strong correlations

were found between the PAH concentration and biodegradation rates (Alleman,

1995).

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Bioventing was selected to treat petroleum-contaminated soils at Loring AFB in

Maine. Sixteen bioventing systems were installed and all continue to operate.

These systems cover approximately 17.6 acres and are treating a combined total of

more than 500,000 cubic yards of fuel-contaminated soil. The major contaminants

being treated by bioventing are TPHs, benzene, toluene, and xylene. The cleanup

goal for TPHs is 870 mg/kg, based on risk to human health. Cleanup criteria for

benzene, toluene, and xylene are based on soil leaching potential.

Operational difficulties have been encountered because of soil heterogeneity, high

or perched groundwater, and inability to collect soil-gas samples. Oxygen

utilization rates from more than 40 respiration tests range from 0.01 to 7.5 percent

per hour, with the site median being 0.63 percent per hour (Underhill, 1997).

	

7HFKQRORJ\ 'HVFULSWLRQ

Containment methods are used to prevent or significantly reduce migration of

contaminants in soils or groundwater and to prevent human and animal exposure

to contaminants. Containment is generally necessary whenever contaminated

materials are to be buried or left in place at a site. In general, containment is

chosen when extensive subsurface contamination at a site precludes excavation

and removal of wastes because of potential health hazards, prohibitive costs, or

lack of adequate treatment technologies (USEPA, 1998).

Containment or site capping can be implemented in various forms. The technology

can be as simple as an asphalt or concrete cap or as elaborate as RCRA Subtitle C

or Subtitle D engineered landfill cap. The goals of cap design are to prevent

rainwater infiltration through impacted soils, prevent soil vapors from rising to

the surface, and provide a barrier between animal and plant life and the

underlying contaminated media. The final design of a cap depends on the

structural and performance requirements of the particular area. The cap should be

designed to facilitate water collection into drains and to minimize ponding. Cap

maintenance consists of inspection for and repair of cracks.
&KDSWHU 

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Cap design is site-specific and depends on the intended or existing use of the

former MGP site. The most effective single-layer caps are composed of concrete or

bituminous asphalt. These materials are used to form a barrier between the waste

and the surface environment. All covers should be designed to prevent the

“bathtub” effect, which occurs when a more permeable cover is placed over a less

permeable bottom liner or natural subsoil. When this occurs rainfall infiltrates the

cover and ponds on the less permeable underlying material, thereby “filling up”

the bathtub (USEPA, 1998).

Landfill caps are generally complex and can range from a one-layer system of

vegetated soil to a complex multi-layer system of soils and geosynthetics. The

most critical components of a landfill cap are the barrier layer and the drainage

layer. The barrier layer can be low-permeability soil (clay) and/or geosynthetic

clay liners (GCLs). The low-permeability material diverts water and prevents its

passage into the underlying waste. The higher permeability materials placed atop

the barrier layer carry away water to prevent percolation through the cap. Soils

used as barrier materials are generally clays compacted to a hydraulic conductivity

no greater than 1 x 10-6 cm/sec. Compacted soil barriers are generally installed in

6-inch minimum lifts to achieve a thickness of 2 feet or more (USEPA, 1998).

2SHUDWLRQDO &RQVLGHUDWLRQV

Aspects to be considered in cap design include the existing and future uses of the

facility, the leaching potential of the waste materials, and the location of the waste

relative to the groundwater table. Other considerations include the ease of

relocating existing facility operations during construction activities.

Site capping mitigates migration, but does not lessen toxicity, mobility, or volume

of hazardous wastes. Caps are most effective where most of the underlying waste

is above the water table. A cap, by itself, can prevent only the vertical entry and

migration of precipitation into and through waste, not the horizontal flow of

groundwater through the waste. In many cases, caps are used in conjunction with

vertical cutoff walls to minimize horizontal flow and migration. The effective life

of the cap can be extended by long-term inspection and maintenance. Vegetation

must be eliminated from the cap area because roots may penetrate deeply.

Precautions must be taken to assure that the integrity of the cap is not

compromised by surface activities. 

Laboratory tests are needed to ensure that the materials being considered for cap

components are suitable. Testing includes grain size analysis, Atterberg limits, and

compaction characteristics (USEPA, 1998). The key engineering soil properties that

must be defined are shear strength and hydraulic conductivity. Shear strength

may be determined with the unconfined compression test, direct shear test, or

triaxial compression test. Hydraulic conductivity of soils may be measured in the

laboratory by the constant or falling head permeability test. Laboratory tests are

also needed to ensure that geosynthetic materials will meet cap requirements

(USEPA, 1998).
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Quality assurance for cap construction is the most critical factor in containment;

USEPA has generated a technical guidance document on this subject; this technical

guidance should be consulted during design and construction. 

$SSOLFDWLRQV DQG &RVW

Containment approaches vary from repaving existing blacktop to installing a

single- or double-layer concrete cap to installing a full-blown RCRA landfill cap.

In between these extremes are double-layer concrete caps and non-RCRA Subtitle

D landfill caps.

A RCRA Subtitle C multi-layered landfill cap is a baseline design that is suggested

for RCRA hazardous waste applications. This cap generally consists of an upper

vegetative (topsoil) layer, a drainage layer, and a low-permeability layer made of a

synthetic liner over 2 feet of compacted clay. Compacted clay liners are effective if

they retain a certain moisture content and are susceptible to cracking if the clay

material dries out. Therefore, other cap designs are usually considered for arid

environments.

RCRA Subtitle D requirements are for nonhazardous municipal solid waste

landfills. The design of a landfill cover for a RCRA Subtitle D facility is generally a

function of the bottom liner system or natural subsoils present. The cover must

meet the following specifications (USEPA, 1998):

 The material must have a permeability no greater than 1 x 10 -5 cm/s or

equivalent permeability of any bottom liner or natural subsoils present,

whichever is less.

 Generally the infiltration layer must contain at least 45 cm of earthen material.

 The erosion control layer must be at least 15 cm of earthen material capable of

sustaining native plant growth.

 Concrete is somewhat less susceptible to cracking and is more durable than

asphalt (engineered or standard) as a capping material.

The costs of single-layer concrete and asphalt caps are dependent upon the cost of

the material and local labor costs. Approximate per-acre construction costs for

concrete caps are $140,000; for asphalt caps and multi-layer, $170,000; for soil caps,

$45,000. Each type of cap involves some operations and maintenance costs. Costs

per acre per year are estimated as follows: concrete caps, $2,000; asphalt caps,

$4,000; multi-layer and soil caps, $20. Additional cost information can be found in

the Hazardous, Toxic, and Radioactive Wastes Historical Cost Analysis System

developed by Environmental Historical Cost Committee of Interagency Cost

Estimation Group.

%HQHILWV

 Requires only short installation times 

 Unlike ex situ soil treatment, does not require excavation of soils and thus

avoids some of the associated disadvantages (increased costs from engineering

design of equipment, permits, waste handling)
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 Generally less expensive than other technologies

 Minimizes potential worker exposure onsite at an operating facility

 Prevents vertical infiltration of water into wastes and subsequent vertical

migration of contaminants

 Creates a land surface that can support vegetation and/or be used for other

purposes

/LPLWDWLRQV

 Generally contains wastes, does not address future liability at site

 Requires periodic inspections for settlement, ponding of liquids, erosion, and

naturally occurring invasion by deep-rooted vegetation

 Usually requires groundwater monitoring for verification of containment

 Typically requires deed restrictions or other institutional controls

 Typically requires long-term operation and maintenance programs 

&DVH 6WXG\

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The Jackson, Michigan, site housed an MGP that operated from 1887 until 1947

and was demolished during the 1950s. The current land uses at the site include a

residential apartment complex, city park, and elementary school playground. The

remedy selected for a portion of the site was a cap consisting of an impermeable

HDPE membrane covered with 3 feet of soil for frost protection. The cap was

designed and constructed according to Michigan’s requirements for an

impermeable cap at a hazardous waste landfill. 

The remedial goals for the cap were to: eliminate a potential direct human contact

hazard posed by PAHs present in subsurface soils and fill materials at

concentrations in excess of Michigan’s residential criteria; and limit the leaching of

PAHs to groundwater to less than Michigan’s health-based drinking water criteria.

The matrix covered by the cap is a mixture of topsoil, sandy subsurface soils, and

fill materials consisting of slag, wood, coal, and brick. A concrete slab foundation

for a former gas holder is also present below ground. The area covered by the cap

is approximately 2 acres. A cap was chosen because removal of the wastes would

have resulted in greater human exposure.

Total PAH concentrations in the subsurface soils and fill materials range up to

9,000 mg/kg. The cap is not expected to affect the concentration of PAHs.

However, the cap will control exposure by eliminating a direct human contact

pathway at the site. The cap is also expected to serve as a source control by

eliminating potential source of PAH loading to groundwater.

The volume of subsurface soils and fill materials impacted by PAHs and covered

by the cap is estimated to be approximately 10,000 cubic yards. The Michigan

Department of Environmental Quality approved the cap as an interim remedial
&KDSWHU 

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5-49

action (pending completion of the remedial investigation on other portions of the

site) in May 1995. Construction of the cap was completed in August 1995.

&RQWDFW

G.L. Kelterborn, (517) 788-2484, fax (517) 788-1064

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In situ solidification/stabilization (S/S) is a remediation technology that can be

used for MGP-related soil contamination. In-place cutoff walls are constructed,

and soils and residues are treated in situ to depths of 30 feet or more. In situ S/S

involves mixing soil with chemical binders such as cement, bentonite, additives,

and proprietary chemicals that immobilize contaminants of concern (e.g., PAHs).

One method of in situ S/S uses a series of overlapping, large-diameter stabilized

soil columns. A crane-mounted drill attachment turns a single-shaft, largediameter auger head consisting of two or more cutting edges and mixing blades.

As the auger head is advanced into the soil, grout is pumped through a hollow

drill shaft and injected into the soil at the pilot bit. Cement, bentonite, additives,

and proprietary chemicals may also be mixed into the grout. The cutting edges

and mixing blades blend the soil and grout with a shearing motion. When the

design depth is reached, the auger head is raised to expose the mixing blade at the

surface and then advanced again to the bottom. Once the shaft is completed,

another column is drilled using a specified pattern of overlapping columns; what

is left behind is a series of interlinked columns.

The following is a schematic diagram showing the mixing augers.
&KDSWHU 

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5-50

A second method of in situ S/S requires the MGP wastes to be stabilized in

shallow soil (approximately the upper 2 feet). In this scenario, admixtures

containing Portland cement, bentonite, and other chemicals are placed directly on

the ground surface. Tillers and sheepsfoot rollers are used to mix and compact the

soil.

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The success of S/S methods depends on soil type and properties, contaminant

type and concentrations, moisture content, organic content, density, permeability,

unconfined compressive strength, leachability, pH, and particle size. A treatability

study is recommended for this technology to create a mix that minimizes leaching

and has appropriate strength characteristics. The creation of concrete-like material

in the subsurface may severely limit access to utilities, which may need to be

permanently rerouted. The machinery used for in situ S/S via mixing augers is

approximately the same size as a large drilling rig; low overhead lines may limit

the use of this technology.

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Inorganic constituents have traditionally been the target contaminant group for in

situ S/S. The technology has limited effectiveness against SVOCs and no expected

effectiveness against VOCs. It has been applied to MGP sites for PAH treatment.

Costs for cement-based S/S techniques vary widely according to materials or

reagents used and their availability, project size, and the chemical nature of the

contaminants. In situ mixing/auger techniques average $40 to $60 per cubic yard

in shallow applications.

%HQHILWV

 Immobilizes contaminants

 Neutralizes soil

 Improves bearing capacity or shear strength of treated area

 Leaves treated area, if reinforced, able to withstand differential soil and

hydrostatic loading

/LPLWDWLRQV

 Possible leaching of volatile or mobile constituents

 Creation of concrete-like material in the subsurface (may severely limit access

to utilities, which may need to be permanently rerouted)

 Possible significant increase in volume of mixture (up to double the original

volume)

 Reagent delivery and effective mixing more difficult than in ex situ

applications

&DVH 6WXGLHV

&ROXPEXV *HRUJLD )RUPHU 0*3 6LWH

A full-scale demonstration of in situ S/S for MGP contamination was performed in

Columbus, Georgia, where an estimated 94,000 cubic yards of soil at a town gas
&KDSWHU 

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5-51

site were stabilized (Geo-Con, 1993). The 4-acre site is located in the central

business district of Columbus and is bounded to the west by the Chattahoochee

River. Contaminated soils extended over a 15-foot interval beneath 10 to 20 feet of

miscellaneous fill. Depth to groundwater was approximately 20 feet bgs, and the

10-foot saturated zone was underlain by bedrock.

In situ treatment was accomplished by mixing/drilling a Type I Portland Cement

slurry with the soil to an approximate depth of 35 feet using an 8-foot-diameter

auger. A containment wall was installed adjacent to the river; the remainder of the

site was stabilized by advancing augers at approximately 1,800 overlapping

locations. 

Prior to treatment, contamination of the MGP-affected soils was as high as 300

mg/kg of VOCs, 2,400 mg/kg of PAHs, and 5,500 mg/kg of petroleum

hydrocarbons. The performance criteria for the concrete mixtures were:

 Ultimate Compressive Strength (UCS) of 60 psi within 28 days

 Permeability of no more than 1x10 -6 cm/s for the containment wall and no

more than 1x10 -5cm/s for the remainder of the site

 PAH concentration in TCLP leachate not to exceed 10 mg/L

UCS testing was conducted on all samples, and permeability and leach testing was

performed on 10 percent of the samples obtained from approximately 300

randomly selected shafts of freshly stabilized soils. Any shafts that did not comply

with the performance criteria had to be reprocessed. After the soils were stabilized,

the area was covered with an HDPE liner and backfilled soil and then converted

into a park and walkway.

&RQWDFWV

Darahyl Dennis, Georgia Power Company, Atlanta, GA 30302, (404) 526-7064

Harold F. Reheis, Georgia Department of Natural Resources, Atlanta, GA 30334,

(404) 656-4713

0DQLWRZRF :LVFRQVLQ )RUPHU 0*3 6LWH

The Wisconsin Fuel & Light site is a former MGP facility located along the

Manitowoc River in Manitowoc, Wisconsin. The site had been filled with

uncontrolled material, including debris and other material typically used behind

sea walls. Portions of the foundations from the previous coal gasification

structures also remained. The underlying soils at this site were contaminated with

coal tars; these were stabilized using a reagent mixture of activated carbon,

cement, fly ash, and organophilic clays.

The S/S treatment of impacted soil was accomplished by simultaneous injection

and mixing of cement-based grout using 4- and 7-foot-diameter tools. This created

a series of overlapping, vertically oriented columns of stabilized soil. The rotary

and vertical movement of the boring/mixing tool was designed to assure effective

mixing. In 1994 alone, a total volume of 6,859 cubic yards of soil was stabilized
&KDSWHU 

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5-52

with 209 soil columns. Overall, approximately 15,000 cubic yards of soil were

treated during a 2-year period to an average depth of 32 feet. 

A minimum UCS of 120 psi and a permeability of 1.8 x 10 -7 cm/s were achieved

through the stabilization process, and the stabilized material also passed ASTM

D559 and D560 durability tests. Verification soil samples were extracted using a

modified Static Leaching Method. Of 16 extracts, only one contained a PAH

(naphthalene at a concentration of 16 μg/L), and no other SVOCs were detected

above the Minimum Detection Limit. Four extracts contained a VOC, methylene

chloride, but because this compound also showed up in an apparatus blank and is

not a normal constituent of coal tar, it is thought that this was a laboratory

contaminant.

&RQWDFW

Ted Vallis, Wisconsin Fuel & Light, Manitowoc, Wisconsin, (414) 683-2538

 ([ 6LWX 6WDELOL]DWLRQ6ROLGLILFDWLRQ 66

7HFKQRORJ\ 'HVFULSWLRQ

Stabilization/solidification (S/S) uses physical and chemical means to reduce the

mobility of hazardous substances and contaminants. Unlike other remedial

technologies, S/S seeks to trap or immobilize contaminants, instead of removing

them. The term S/S has been used synonymously with other terms, including

immobilization, encapsulation, and fixation (GRI, 1996). Specific definitions have

been assigned to each of these terms by USEPA and others to differentiate among

them. For the purposes of this document, all of these technologies will be referred

to as S/S.

Ex situ S/S was originally developed for inorganic wastes. Although this

technology has limited applicability to organics and cyanides, it may be useful at

MGP sites for management of purifier box wastes, gas-holder tank sludge, and

soils contaminated with organic compounds (GRI, 1996). Contaminants are

physically bound or enclosed within a stabilized mass (solidification), or chemical

reactions are introduced between the stabilizing agent and contaminants to reduce

their mobility (stabilization). 

Ex situ S/S is one method by which soil containing MGP wastes can be stabilized

and replaced. The technology typically involves mixing the soil with chemical

binders that solidify and/or immobilize the chemicals of concern. Pugmills are

often used to perform mixing, although stockpiles may be mixed by mechanical

means. Following S/S, treated materials may be replaced in their excavation,

recompacted, and allowed to cure. Leachability testing is typically performed to

verify contaminant immobilization.

There are many variations of the S/S technology using different processes and/or

stabilizing agents such as Pozzolan/Portland cement, bitumen, and emulsified

asphalt. The technology has been applied to soils, sludges, lagoons, and

radioactive waste. The use of MGP soils in the production of asphalt is discussed
&KDSWHU 

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5-53

in Section 5.2.3. The discussion in this section will focus on the use of

Pozzolan/Portland Cement with MGP soils.

Pozzolan/Portland cement consists primarily of silicates from Pozzolanic-based

materials like fly ash, kiln dust, pumice, or blast furnace slag as well as cementbased materials. These materials react chemically with water to form a solid matrix

that improves the strength of the matrix in which waste is found and minimizes

the likelihood of contaminant leaching. They also raise the pH of the water, which

may help precipitate and immobilize some heavy metals. Pozzolanic and cementbased binding agents are typically appropriate for inorganic contaminants. The

effectiveness of this binding agent with organic contaminants varies (USEPA,

1998).

2SHUDWLRQDO &RQVLGHUDWLRQV

A key design consideration is the identification of a stabilizing agent that is

compatible with the waste at a site and that yields a treated product that contains

no free liquids, meets a minimum compressive strength, and does not leach

contaminants (GRI, 1996). Lab- and pilot-scale studies are required to identify the

type and quantity of agent for each application. Physical and chemical

characterization of the soil are also required to select suitable mixing materials.

The effectiveness of ex situ S/S depends primarily on effective mixing. If large

materials (greater than 3/8 inch) are present, they must be excluded by screening.

These materials can be used in the S/S process if they are crushed and screened.

Mixing time should be sufficient to produce a homogeneous mix. This parameter

has a great impact on project duration and treatment cost (GRI, 1996).

Soil parameters that must be determined for ex situ S/S include particle size,

Atterberg limits, moisture content, metal concentrations, sulfate content, organic

content, and density. Post-treatment parameters that require monitoring and

testing include permeability, unconfined compressive strength, leachability,

microstructure analysis, and physical and chemical durability (USEPA, 1998). Soil

particle size is an important factor as fine particles may delay setting and curing

times and can surround larger particles, causing weakened bonds in S/S processes

(USEPA, 1998). Soil homogeneity and isotropy also affect S/S. Larger particles,

such as coarse gravel or cobbles, may not be suitable for the S/S technology. 

A consideration in the use of the technology at MGP sites is the presence of oil and

grease. Oil and grease coat soil particles, which tends to weaken the bond between

soil and cement in cement-based solidification (USEPA, 1998).

$SSOLFDWLRQV DQG &RVW

Ex situ S/S may be used to treat soils from MGP sites. It is a viable option when

soil contaminants are primarily metals (as with purifier box wastes). Full-scale S/S

of free-phase hydrocarbons and contaminated soils from MGP sites has been

performed, but there is little documentation of the result of these demonstrations

(GRI, 1996).

Cost of ex situ S/S depends on the costs of mobilization/demobilization of

personnel and equipment, excavation, equipment, startup, supplies and
&KDSWHU 

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5-54

consumables, labor, utilities, and analytical requirements. Ex situ S/S processes

are among the most accepted remediation technologies. Comparing representative

overall costs from more than a dozen vendors gives an approximate cost of under

$110 per metric ton ($100 per ton), including excavation (USEPA, 1998).

%HQHILWV

 Has been widely used to immobilize inorganic chemicals; several vendors

claim that their proprietary additives can make organics amenable to

stabilization

/LPLWDWLRQV

 Performance of S/S process is dependent upon the chemical composition of the

wastes

 Long-term immobilization of contaminants possibly affected by environmental

conditions 

 Certain wastes incompatible with certain S/S processes; treatability studies

generally required

 VOCs are generally not immobilized by the stabilization process

 Long-term effectiveness not demonstrated for many contaminant/process

combinations

 Volumetric increase in amount of material

&DVH 6WXG\

'X4XRLQ )RUPHU 0*3 6LWH

Remedial activities were conducted under the Illinois Site Remediation Program at

an 8-acre former MGP site owned by Ameren CIPS in DuQuoin, Illinois. The

remedial work, funded jointly by Ameren CIPS, Commonwealth Edison, and

Nicor Gas, was conducted during the first half of 1997.

Tar and purifier waste was excavated from a lagoon approximately 59,650 square

feet in area. A total of 4,290 tons of tar and tar-contaminated soil was generated

during the excavation of impacted material at the site. This material was

manifested as a hazardous waste and transported to a RCRA Subtitle C landfill.

The area identified as the lagoon excavation was stabilized by incorporating

calciment bottom ash at a ratio of 7 parts ash to 10 parts soil into the bottom two

feet of impacted clay subgrade. The stabilized clay was then placed back in 6-inch

lifts and compacted with a D-6 bulldozer and sheepsfoot roller. 

Soils from other areas of the site, identified as posing a risk greater that 10 -6 to

industrial workers (hot-spot soils), were excavated, stabilized with calciment

bottom ash (at a one-to-ten ratio) and placed on top of the lagoon subgrade. The

material was placed in 6-inch lifts and compacted with the use of the D-6

bulldozer and sheepsfoot roller. Approximately 4,611 cubic yards of stabilized

material were used as backfill in the lagoon area. Confirmation sampling
&KDSWHU 

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5-55

performed in the area of excavation and stabilization activities indicated that the

remediation activities were successful.

Backfill obtained from an offsite commercial source was used to cover the

stabilized material in the lagoon area. The backfill was compacted in place, graded

to promote drainage of precipitation, and seeded with prairie grass.

The site is zoned commercial/industrial and will be used for these purposes in the

future. Because stabilized impacted soils are present beneath the 1-foot surface

cover, certain procedures and precautions will be followed to maintain this layer.

&RQWDFWV

Don Richardson, Ameren CIPS, (314) 554-4867

Peter McCauley, Com Ed, (312) 394-4470

Stan Komperta, Illinois Environmental Protection Agency, (217) 782-5504

*	+
	

7HFKQRORJ\ 'HVFULSWLRQ

Soil washing is a physical/chemical process for scrubbing soils ex situ to remove

contaminants.

The process removes contaminants from soils in one of two ways (USEPA, 1998):

by dissolving or suspending them in the wash solution (which can be sustained by

chemical manipulation of pH for a period of time); or by concentrating them into a

smaller volume of soil through particle size separation, gravity separation, and

attrition scrubbing (similar to techniques used in sand and gravel operations).

Soil washing is considered a media transfer technology because contamination is

not destroyed but merely transferred from solid- to liquid-phase media. The

contaminated water generated from soil washing is treated with the technologies

suitable for the contaminants. Soil washing is potentially applicable to soils

contaminated with a wide variety of heavy metals, radionuclides, and organic

contaminants. Application of the process is not widespread in the United States.

This technology has been more widely applied in Europe.

The concept of reducing soil contamination through the use of particle size

separation is based on the finding that most organic and inorganic contaminants

tend to bind, either chemically or physically, to clay, silt, and organic soil particles

(USEPA, 1998). Silt and clay attach to sand and gravel particles by physical

processes, primarily compaction and adhesion. Washing separates the fine (small)

clay and silt particles from coarser sand and gravel soil particles thus

concentrating contaminants into a smaller volume of soil that can then be

managed (treated further or disposed of at a landfill). Gravity separation is

effective for removing high- or low-specific-gravity particles such as heavy-metalcontaining compounds. Attrition scrubbing removes adherent contaminant films

from coarser particles. It can also increase the fines in soils. The clean soil can be

returned to the site for reuse.
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Complex mixtures of contaminants in soil (such as a mixture of metals, nonvolatile

organics, and semivolatile organic compounds) and heterogeneous contaminant

compositions throughout a soil mixture make it difficult to formulate a single

washing solution that will consistently and reliably remove the different types of

contaminants. Soil washing is typically not recommended for these types of sites.

2SHUDWLRQDO &RQVLGHUDWLRQV

Soil type is an important factor for soil washing. In general, coarse, unconsolidated

materials, such as sands and fine gravels, are easiest to treat. Soil washing may not

be effective where the soil is composed of large percentages of silt and clay

because of the difficulty of separating the adsorbed contaminants from fine

particles and from wash fluids (USEPA, 1998).

High soil moisture content may cause excavation, material handling, and material

transport problems (USEPA, 1998).

The pH of the waste being treated may affect soil washing; high pH in soil

normally lowers the mobility of inorganics in soil (USEPA, 1998).

High humic content will bind the soil, decreasing the mobility of organics and

thus the threat to groundwater; however, high humic content can inhibit soil

washing as a result of strong adsorption of the contaminant by the organic

material (USEPA, 1998).

A complete bench-scale treatability study is typically required before using soil

washing as a remedial solution. Like any ex situ soil treatment, this technology

requires space for soil processing and materials handling.

$SSOLFDWLRQV DQG &RVW

This technology is suitable for treating soils and sediment contaminated with

organics such as PCBs, creosote, fuel residues, and heavy petroleum; heavy metals

sucah as cadmium, chromium, lead, arsenic, copper, cyanides, mercury, nickel,

and zinc; and radionuclides. The technology can recover metals and can clean a

wide range of organic and inorganic contaminants from coarse-grained soils.

At the present time, soil washing is used extensively in Europe but has had limited

use in the United States. Between 1986 and 1989, the technology was one of the

selected source control remedies at eight Superfund sites. The average cost for use

of this technology, including excavation, is approximately $170 per ton, depending

on site-specific conditions and the target waste quantity and concentration. 

%HQHILWV

 Offered by multiple vendors

 High degree of certainty regarding treatment performance

/LPLWDWLRQV

 Material handling possibly expensive and time consuming, especially for large

amounts 
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5-57

 Applicability and effectiveness of the process limited by: 

- Complex waste mixtures (e.g., metals with organics) which make 

formulating washing fluid difficult 

- High humic content in soil, which may require pretreatment 

 Washwater requiring treatment at demobilization

 Additional treatment steps that may be required to address hazardous levels of

washing solvent remaining in the treated residuals

 Difficultly removing organics adsorbed onto clay-size particles

&DVH 6WXGLHV

)RUPHU %DVIRUG *DVZRUNV 1RWWLQJKDP 8.

A large-scale UK soil washing project is being conducted at the former Basford

gasworks site in Nottingham. The 7.8-hectare (ha) site is owned by BG plc, the UK

gas supply infrastructure group. The cleanup is valued at $7.5 million (Haznews,

1998).

Soil washing commenced in August 1997, and was scheduled to be completed in

July 1998 after processing approximately 72,000 cubic meters of contaminated

material. The soil washing was performed by Linatex/Heijmans, a joint-venture

between UK and Dutch firms, using a plant with a nominal process rate of 50

tonnes per hour.

The Basford site is underlain by a drinking water aquifer, with no subsurface

geological barrier to prevent off-site migration of contaminants. The soil

conditions at the site made it a suitable candidate for evaluating the costeffectiveness of soil washing; information which would be useful in evaluating

this technology for other contaminated MGP sites. Basford began operating in

1854 and was the principal gas supply for the City of Nottingham. The site also

provided by-products such as coke, sulphuric acid, and ammonium sulphate

fertilizer until gas production stopped in 1972 (Haznews, 1998).

During the site characterization, 350 test pits were dug on a 10 meter grid,

producing 2,500 samples for analytical testing. This detailed investigation allowed

a more accurate identification of waste types, volume, and location. A model was

subsequently developed to optimize the treatment technology and estimate the

amount of materials that could be recycled. For example, 26,000 cubic meters of

clean ash and clinker are being recovered for use in steel and building block

production (Haznews, 1998).

Approximately 91,000 cubic meters of contaminated material was identified. Of

this, about 15,000 cubic meters has been classified as untreatable (along with tar

and asbestos wastes) and was sent to an off-site disposal location. The remainder

of the wastes are being processed through the soil washing plant.

In the soil washing process, excavated material is crushed and screened to 100 mm

and magnetically separated. The remaining material is wetted and then passed to
&KDSWHU 

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5-58

a 2-mm vibrating screen where it is disaggregated with high-pressure water. The >

2 mm gravel fraction goes to a counter-current washer and is eventually drained

and discharged for reuse as onsite fill. The gravel washwater and a smaller slurry

fraction is split between two hydrocyclones which separates the material into a 63

μm to 2 mm sand fraction and a < 63 μm slurry (Haznews, 1998). The sand is

processed in a dense medium separator from which clean sand is dewatered and

then discharged to a collection bay. The fines fraction slurry is treated in a

thickener tank where flocculants may be added to improve the treatment process.

This tank produces sludge with 20 to 40 percent dry matter which is pumped to a

continuous filter press. The resulting contaminated filter cake is sent to a landfill

for disposal.

Light materials, such as coke, wood fragments, and plastics, are separated out

during the washing process and also sent to the landfill with the contaminated

fines (Haznews, 1998).

According to BG’s property division, the use of soil washing has resulted in a

remediation period that is 60 to 70 percent longer than the conventional clean-up

approach of excavation of contaminated material and landfill disposal. However

the advantages of soil washing include the reduced need for imported clean fill,

and a large reduction in transportation during the site work. Overall, the cost of

the project is comparable to a “dig and haul” approach (Haznews, 1998).

6,7( 3URJUDP 'HPRQVWUDWLRQ 7RURQWR 2QWDULR

Soil washing was accepted into the Superfund Innovative Technology Evaluation

(SITE) Demonstration Program in the winter of 1991. It was demonstrated in

Toronto, Ontario, Canada, in April 1992 as part of the Toronto Harbour

Commission soil recycling process. 

The soil washing process begins when an attrition soil wash plant removes

relatively uncontaminated coarse soil fractions using mineral processing

equipment; contaminants are concentrated in a fine slurry that is routed for further

treatment. The wash process includes a trommel washer to remove clean gravel,

hydrocyclones to separate the contaminated fines, an attrition scrubber to free

fines from sand particles, and a density separator to remove coal and peat from the

sand fraction. If only inorganic contaminants are present, the slurry is treated in an

inorganic chelator unit. This process uses an acid leach to free inorganic

contaminant from the fine slurry and then removes the metal using solid

chelating-agent pellets in a patented countercurrent contactor. The metals are

recovered by electrowinning from the chelation agent regenerating liquid. Organic

removal is accomplished by first chemically pretreating the slurry from the wash

plant or metal removal process. Next, biological treatment is applied in upflow

slurry reactors using bacteria that have developed naturally in the soils. The

treated soil is dewatered using hydrocyclones and returned to the site from which

it was excavated. 

The technology is designed to reduce organic and inorganic contaminants in soils.

The process train approach is most useful when sites have been contaminated as a
&KDSWHU 

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5-59

result of multiple uses over a period of time. Typical sites where the process train

might be used include refinery and petroleum storage facilities, former metal

processing and metal recycling sites, and manufactured gas and coal or coke

processing and storage sites. The process is less suited to soils with high inorganic

constituents that are inherent to the mineralogy. 

Results of the demonstration described above have been published in the

Demonstration Bulletin (EPA/520/MR-92/015), the Applications Analysis Report

(EPA/540/AR-93/517), the Technology Evaluation Report (EPA/540/R-93/517),

and the Technology Demonstration Summary (EPA/540/SR-93/517). These

reports are available from USEPA. 

The demonstration results showed that soil washing produced clean coarse soil

fractions and concentrated the contaminants in the fine slurry. The chemical

treatment process and biological slurry reactors, when operated on a batch basis

with a nominal 35-day retention time, achieved at least a 90 percent reduction in

simple PAH compounds such as naphthalene, but did not meet the approximately

75 percent reduction in benzo(a)pyrene required to achieve the cleanup criteria. 

The biological process discharge did not meet the cleanup criteria for oil and

grease; the washing process removed almost no oil and grease. The hydrocyclone

dewatering device did not achieve significant dewatering. Final process slurries

were returned to the excavation site in liquid form.

The metals removal process achieved a removal efficiency of approximately 70

percent for toxic heavy metals such as copper, lead, mercury, and nickel.

The metals removal process equipment and chelating agent were fouled by free oil

and grease, forcing sampling to end prematurely. Biological treatment or physical

separation of oil and grease will be required to avoid such fouling. 

&RQWDFW

Teri Richardson, USEPA Project Manager, National Risk Management Research

Laboratory, 26 West Martin Luther King Drive, Cincinnati, OH 45268, (513) 569-

7949, fax (513) 569-7105

6,7( 3URJUDP 'HPRQVWUDWLRQ 6DJLQDZ 0LFKLJDQ

A field demonstration of Bergmann, Inc.’s soil washing technology was conducted

in May 1992 at the Saginaw Bay Confined Disposal Facility in Saginaw, Michigan.

The Applications Analysis Report (EPA/540/AR-92/075) and the Demonstration

Bulletin (EPA/540/MR-92/075) are available from USEPA. 

Demonstration results indicate that the soil- and sediment-washing system can

effectively isolate and concentrate PCB contamination into organic fractions and

fines. Levels of metals contamination were also beneficially altered. The

effectiveness of soil and sediment washing on inorganic compounds equaled or

exceeded its performance for PCB contamination.
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During a 5-day test in May 1992, the Bergmann soil and sediment washing system

experienced no downtime, operating for 8 hours per day to treat dredged

sediments from the Saginaw River. 

The demonstration provided the following results:

 Approximately 71 percent of the particles smaller than 45 μm in the input

sediment were apportioned to the enriched fines stream. 

 Fewer than 20 percent of the particles smaller than 45 μm in the input sediment

were apportioned to the coarse clean fraction of soil.

The distributions of the concentrations of PCBs in the input and output streams

were as follows:

 Input sediment = 1.6 mg/kg

 Output coarse clean fraction = 0.20 mg/kg

 Output humic materials = 11 mg/kg

 Output enriched fines = 4.4 mg/kg 

Heavy metals were concentrated in the same manner as the PCBs. The coarse clean

sand consisted of approximately 82 percent of the input sediment. 

&RQWDFWV

Mr. Jack Hubbard, USEPA Project Manager, National Risk Management Research

Laboratory, 26 West Martin Luther King Drive, Cincinnati, OH 45268, (513) 569-

7507, fax (513) 569-7620

Mr. George Jones, Bergmann, A Division of Linatex, Inc., 1550 Airport Road,

Gallatin, TN, 37066-3739, (615) 230-2217, fax (615) 452-5525

6,7( 3URJUDP 'HPRQVWUDWLRQ 1HZ %ULJKWRQ 0LQQHVRWD

The BioTrol Soil Washing System is a patented, water-based volume reduction

process used to treat excavated soil. The system may be applied to contaminants

concentrated in the fine-sized soil fraction (silt, clay, and soil organic matter) or in

the coarse soil fraction (sand and gravel). 

In the first part of the process, debris is removed from the soil. The soil is then

mixed with water and subjected to various unit operations common to the mineral

processing industry. The equipment used in these operations can include mixing

trommels, pugmills, vibrating screens, froth flotation cells, attrition scrubbing

machines, hydrocyclones, screw classifiers, and various dewatering apparatus. 

The core of the process is a multistage, countercurrent, intensive scrubbing circuit

with interstage classification. The scrubbing action disintegrates soil aggregates,

freeing contaminated fine particles from coarser material. In addition, surficial

contamination is removed from the coarse fraction by the abrasive scouring action

of the particles themselves. Contaminants may also be solubilized as dictated by

solubility characteristics or partition coefficients. 
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5-61

Contaminated residual products can be treated by other methods. Process water is

normally recycled after biological or physical treatment. Contaminated fines may

be disposed of offsite, incinerated, stabilized, or biologically treated. 

This system was developed initially to clean soils contaminated with wood

preservative wastes, such as PAHs and PCP. The system may also apply to soils

contaminated with petroleum hydrocarbons, pesticides, PCBs, various industrial

chemicals, and metals. 

The BioTrol Soil Washing System was accepted into the SITE Demonstration

Program in 1989 and demonstrated between September and October 1989 at the

MacGillis and Gibbs Superfund site in New Brighton, Minnesota. A pilot unit with

a treatment capacity of 500 pounds per hour operated 24 hours per day during the

demonstration. Feed for the first phase of the demonstration (2 days) consisted of

soil contaminated with 130 ppm PCP and 247 ppm total PAHs; feed for the second

phase (7 days) consisted of soil containing 680 ppm PCP and 404 ppm total PAHs.

Contaminated process water was treated biologically in a fixed-film reactor and

then recycled. A portion of the contaminated soil fines was treated biologically in a

three-stage, pilot-scale EIMCO Biolift reactor system supplied by the EIMCO

Process Equipment Company. The Applications Analysis Report (EPA/540/AR91/003) and the Technology Evaluation Report Volume I (EPA/540/5-91/003a)

and Volume II (EPA/540/5-91/003b and EPA/540/5-91/003c) are available from

EPA. 

Key findings from the BioTrol demonstration are summarized below:

 Feed soil (dry weight basis) was successfully separated into 83 percent washed

soil, 10 percent woody residues, and 7 percent fines. The washed soil retained

about 10 percent of the feed soil contamination; 90 percent of this

contamination was contained in the woody residues, fines, and process wastes.

 The multistage scrubbing circuit removed up to 89 percent PCP and 88 percent

total PAHs, based on the difference between concentration levels in the

contaminated (wet) feed soil and the washed soil. 

 The scrubbing circuit degraded up to 94 percent PCP in process water. PAH

removal could not be determined because of low influent concentrations.

&RQWDFW

Dennis Chilcote, BioTrol, 10300 Valley View Road, Suite 107, Eden Prairie, MN

55344-3456, (612) 942-8032, fax (612) 942-8526

,	- 
$.
	(-$)

SVE is mechanically similar to bioventing (Section 5.2.4.2), but is operated at a

higher flow rate to achieve volatile compound removal in addition to oxygen

replenishment. SVE uses an electric- or gasoline-powered blower system

connected to wells via manifolds. Air treatment, whether through a separate

system (such as activated carbon or catalytic oxidation) or as part of a gasoline-
&KDSWHU 

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5-62

powered system, is usually the most expensive single component of an SVE project

and may represent as much as 50 percent of the overall cost.

Performance of an SVE system is monitored using measurements at the blower

system and at piezometers (small-diameter wells or soil gas sample points)

installed in the zone being treated. Flow measurements at the blower or at

individual wells can be used to help calculate removal rates. Vapor samples from

piezometers, wells, or at the blower discharge can be analyzed in the field or by a

laboratory, and the results can be used to estimate the rate of subsurface

decontamination and the rate of volatile compound removal. Vapor samples from

the discharge of the air treatment system are usually required to test system

performance and to verify permit requirements. Final evaluation of SVE

performance can be assessed by collecting soil vapor samples from piezometers

and/or soil samples from the treated zone.

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The suitability of SVE for MGP sites will depend on the site-specific requirements

for volatile compound removal or prevention of volatile compound migration as a

remediation objective. The site also needs to have a water table depth at least 10

feet and a subsurface profile that allows air to flow through the zone to be treated.

This profile criterion is met if the soil is coarse- or fine-grained but not saturated

and if the organic compound mass is infiltrated into the soil, rather than collected

in a subsurface pool (which would be impermeable to air flow).

The design feasibility of SVE is typically proven through a field pilot test. The test

typically consists of pumping a single well that is screened in the center of the

zone to be treated. Piezometers are placed throughout and near the margins of the

zone to be treated. The purposes of this test are to:

 Size the blower by assessing how much air can be pumped from a well.

 Size the air treatment system by determining what initial concentrations might 

 be expected.

 Observe the subsurface flow pattern throughout the zone of treatment.

If the piezometers indicate the pilot test well did not produce an adequate

subsurface flow pattern, the full-scale design could call for additional wells, a new

well with a deeper screened interval, or sealing to eliminate surface leakage.

Shallow sites may be more effectively treated using horizontal wells in trenches.

Most SVE systems operate for 1 to 3 years. During this time, the air treatment

system requires periodic maintenance or changeout, a condensate tank requires

emptying (especially in cold weather), and samples and measurements need to be

collected and reported. At the site, the aboveground portion of the system usually

takes up one or two parking spaces and almost always requires 115V or 220V

electrical power. Natural gas is sometimes required (if catalytic oxidation is

selected as the air treatment option). The blower itself may be a source of excessive

noise if silencers (upstream and downstream) or soundproof containment are not

provided or if the blower is undersized and working near its maximum output.

The underground portion of the system is typically accessed through well vaults,
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and the manifold lines connecting the wells to the blower system are often buried

in frequently accessed areas.

Sites with relatively shallow water tables or with wells screened near the water

table can experience excessive water accumulation and blockage of air flow if too

much vacuum is applied to the system. Most systems can be operated safely under

these conditions by managing the applied vacuum (in feet of water column) to be

less than one half the distance from the water table to the top of the well screen. 

Granular activated carbon is often selected as the air treatment alternative because

of its minimal power requirements, its availability, and its acceptability to

regulators. It is often the least expensive, on a unit basis, for sites with relatively

low vapor concentrations. Carbon operates at highest efficiency when

temperatures are lower than 120(F; however, most SVE design manuals fail to

provide guidance on temperature management of the blower discharge to the

carbon vessels. Excessive heat may be a concern at sites with high ambient

temperature, such as in the south or southwestern United States, and/or where

relatively high vacuums are required because of fine-grained soil conditions. In

these situations, carbon may still be cost effective if used in conjunction with a

condenser or a heat exchanger.

$SSOLFDWLRQV DQG &RVW

SVE has been used as a remediation process of choice at thousands of

underground storage tank leak sites. Applications at MGP sites are not as

widespread; however, SVE can be used to treat soils at sites contaminated with

some SVOCs (such as naphthalene).

SVE can be applied with little disturbance to existing facilities and operations. The

technology can be used at sites where areas of contamination are large and deep or

when the contamination is present beneath a building. The system may be

modified depending on additional analytical and subsurface characterization data

and/or changing site conditions (RIMS, 1998).

The components of SVE systems are commonly available off the shelf, and the

necessary wells can be installed by any qualified local engineering firm.

Aboveground installations typically include:

 Vacuum pumps and/or blowers and associated controls

 Pressure gauges and flow meters at wellheads and pumps

 Control valves to adjust air flow

 An air-liquid separator (for removing moisture from the extracted gases)

 Vapor treatment unit(s)

More complex SVE systems may incorporate trenches, horizontal wells, forced air

injection wells, passive air inlet wells, low permeability or impermeable surface

seals, or multiple level vapor extraction wells in single boreholes. In addition,

sophisticated systems are available to monitor moisture, contaminant levels, and

temperature (RIMS, 1998).
&KDSWHU 

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5-64

The efficiency of SVE can be enhanced through the use of formation fracturing,

pulsed pumping, or horizontal extraction wells. These enhancements can increase

the soil permeability or the efficiency of mass removal or allow access to

previously inaccessible areas of contaminated soil (e.g., below the water table, in

less permeable formations) (RIMS, 1998).

Treatment costs for sites using SVE depend on various conditions such as site size,

extent of contamination, regulatory requirements for permits, other site-specific

and chemical-specific conditions, and site cleanup criteria. Therefore, cost can only

be estimated on a case-by-case basis. To provide an indication of the range in SVE

project costs, the treatment of 185,000 cubic yards of soil at one site cost $2 per

cubic yard while, at another site where 650 cubic yards required treatment, the

cost was $450 per cubic yard. These values represent treating the soil rather than

cost per pound of contaminant treated. The major part of the total process cost

associated with SVE is usually the operating expenses for labor, maintenance, and

monitoring (RIMS, 1998).

%HQHILWV

 Treats in situ, volatile compounds in soil, including areas beneath structures, at

lower cost than excavation

 Accomplishes both volatile compound removal and oxygen replenishment,

and promotes in situ biodegradation for compounds that may not be removed

 Can be implemented with relatively little disruption to ongoing operations

 Focuses on volatile compounds, including benzene and naphthalene; therefore

treats the most mobile of the organic compounds beneath an MGP site, which

makes it an effective risk-reduction approach

 Has well-established design and feasibility evaluations

/LPLWDWLRQV

 Not effective at sites where remediation goals include concentration reduction

of low-volatility compounds (which are frequently important for MGP site

restoration)

 Difficult to successfully implement where the water table is shallower than 5 to

10 feet below grade, or where the soil is fine-grained (clayey) and nearly

saturated

 Limited effectiveness on volatile compounds trapped in a liquid mass or pool

of subsurface organic compounds (air will not flow through liquids; volatile

compounds trapped in liquids will only be removed through diffusion, which

is too slow to be cost effective)

&DVH 6WXG\

%HDOH $)% 0DU\VYLOOH &DOLIRUQLD

Numerous SVE systems were installed using granular activated carbon with no air

temperature management. Upon start up, breakthrough of the carbon occurred

within three days. Systems were retrofitted with a converted truck radiator 
&KDSWHU 

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5-65

installed downstream of the blower. Air was produced at ten degrees above

ambient for carbon treatment; and carbon efficiency increased three-fold 

(CH2M HILL, 1998; Nelline Scheuer).

&RQWDFWV

Ms. Carol Goudette, 9 CES/CEVR, 6601 “B” Street, Beale AFB, CA 95903

Ms. Cori Condon, RWGCB, Assistant Engineering Geologist, 3443 Routies Road,

Sacramento, CA 95827
&KDSWHU 

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5-66
6-1

Chapter 6



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&KDSWHU 

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&KDSWHU 

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7-1

Chapter 7

	

		

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7-2