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Laboratory studies on soil cores collected from a former manufactured
gas plant (MGP) site demonstrated that electrokinetic processes can
facilitate the transport and removal of coal tar constituents from
contaminated soils. Further development of the method is required to
determine if electrokinetics can be used on a field scale to provide a
reliable method for in situ remediation of MGP sites.

Background

Soils contaminated with coal tar at former manufactured gas plant sites
present a major remediation challenge to the electric utility industry.
Currently, more than 1500 former MGP sites exist in the United States,
each containing from 1000-50,000 gallons of free tar and oil. Many of
these sites are located in urban areas. Excavation and removal of the
coal-tar contaminated soils is expensive and often impossible due to
development on and around the sites. Electrokinetic migration
represents an emerging technology for in situ removal of contaminants
from soils. Electrokinetics refers to the movement of water, ions, and
charged particles relative to one another under the action of an
applied direct current electric field. Contaminants transported to an
electrode are subsequently removed from the soil via a collection
system. This tailored collaboration project on electrokinetics was
cosponsored by Illinois Power Company and EPRI.

Objective

To investigate use of electrokinetics to facilitate the transport of
coal tar compounds in soils; to examine enhanced transport using
surfactants as solubilizing agents to increase the level of
decontamination.

Approach

Investigators conducted long-term electrokinetic tests on soil cores
collected from a former MGP site, enhancing some tests by injecting
solubilizing agents (surfactants) into the soil. They subjected samples
to varying levels of water flow, depending on the physical properties
of the soil, for a period of three to four weeks. During each test,
they monitored the systems for voltage, current, and in-flow and
out-flow of liquid through the soil. After each test, they analyzed
soil specimens for polynuclear aromatic hydrocarbon (PAH) concentration
profiles and pH profiles to assess the extent of the PAH transport and
removal.

Results

The results of the study indicate that coal tar constituents do undergo
electrokinetic transport under laboratory conditions. The primary mode
of transport was electro-osmosis (water transport). The average removal
rate for 16 targeted PAH compounds ranged from 44-70% of the original
PAH mass in the soil samples. Naphthalene proved the most consistently
transported compound, while chrysene experienced the lowest removal
rate. No consistent and significant correlation appeared between the
transport rate and molecular weight of the PAH compounds. However,
coarse-grained soils exhibited greater transport of PAHs than
fine-grained soils. Injection of an anionic surfactant at the cathode
significantly enhanced transport, yielding removal percentages of about
90% of the PAH mass at the cathode.

EPRI Perspective

Utilities will spend billions of dollars on remediation of former MGP
sites over the next few decades. Under the Environmental Behavior of
Organic Substances (EBOS) research project, EPRI is developing methods
for site assessment and remediation to provide utilities with a range
of options for selecting the most cost-effective approach for a
specific site. Electrokinetic transport offers a new technology that
has shown promise for in situ remediation of soils contaminated with
heavy metals and some organic compounds, with possible application at
some MGP sites. Related EBOS research includes development of field
assessment techniques for MGP sites (EPRI reports EN-7319, TR-101060),
characterization of coal tars (TR-102184), and development of the MGP
Remediation Options Assessment Model (ROAM; report TR-103202).

Program

Program 50Manufactured Gas Plant Site Management

Keywords

Decontamination

Soils

Contamination

Surfactants

Coal Tar

Report

TR-103320

Note

For further information about EPRI, call the EPRI Customer Assistance Center at (800) 313-3774 or email askepri@epri.com

Laboratory studies on soil cores collected from a former manufactured
gas plant (MGP) site demonstrated that electrokinetic processes can
facilitate the transport and removal of coal tar constituents from
contaminated soils. Further development of the method is required to
determine if electrokinetics can be used on a field scale to provide a
reliable method for in situ remediation of MGP sites.

Background

Soils contaminated with coal tar at former manufactured gas plant sites
present a major remediation challenge to the electric utility industry.
Currently, more than 1500 former MGP sites exist in the United States,
each containing from 1000-50,000 gallons of free tar and oil. Many of
these sites are located in urban areas. Excavation and removal of the
coal-tar contaminated soils is expensive and often impossible due to
development on and around the sites. Electrokinetic migration
represents an emerging technology for in situ removal of contaminants
from soils. Electrokinetics refers to the movement of water, ions, and
charged particles relative to one another under the action of an
applied direct current electric field. Contaminants transported to an
electrode are subsequently removed from the soil via a collection
system. This tailored collaboration project on electrokinetics was
cosponsored by Illinois Power Company and EPRI.

Objective

To investigate use of electrokinetics to facilitate the transport of
coal tar compounds in soils; to examine enhanced transport using
surfactants as solubilizing agents to increase the level of
decontamination.

Approach

Investigators conducted long-term electrokinetic tests on soil cores
collected from a former MGP site, enhancing some tests by injecting
solubilizing agents (surfactants) into the soil. They subjected samples
to varying levels of water flow, depending on the physical properties
of the soil, for a period of three to four weeks. During each test,
they monitored the systems for voltage, current, and in-flow and
out-flow of liquid through the soil. After each test, they analyzed
soil specimens for polynuclear aromatic hydrocarbon (PAH) concentration
profiles and pH profiles to assess the extent of the PAH transport and
removal.

Results

The results of the study indicate that coal tar constituents do undergo
electrokinetic transport under laboratory conditions. The primary mode
of transport was electro-osmosis (water transport). The average removal
rate for 16 targeted PAH compounds ranged from 44-70% of the original
PAH mass in the soil samples. Naphthalene proved the most consistently
transported compound, while chrysene experienced the lowest removal
rate. No consistent and significant correlation appeared between the
transport rate and molecular weight of the PAH compounds. However,
coarse-grained soils exhibited greater transport of PAHs than
fine-grained soils. Injection of an anionic surfactant at the cathode
significantly enhanced transport, yielding removal percentages of about
90% of the PAH mass at the cathode.

EPRI Perspective

Utilities will spend billions of dollars on remediation of former MGP
sites over the next few decades. Under the Environmental Behavior of
Organic Substances (EBOS) research project, EPRI is developing methods
for site assessment and remediation to provide utilities with a range
of options for selecting the most cost-effective approach for a
specific site. Electrokinetic transport offers a new technology that
has shown promise for in situ remediation of soils contaminated with
heavy metals and some organic compounds, with possible application at
some MGP sites. Related EBOS research includes development of field
assessment techniques for MGP sites (EPRI reports EN-7319, TR-101060),
characterization of coal tars (TR-102184), and development of the MGP
Remediation Options Assessment Model (ROAM; report TR-103202).

Program

Program 50Manufactured Gas Plant Site Management

Keywords

Decontamination

Soils

Contamination

Surfactants

Coal Tar

Report

TR-103320

Note

For further information about EPRI, call the EPRI Customer Assistance Center at (800) 313-3774 or email askepri@epri.com