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Product Abstract

Electrokinetic Removal of Coal Tar Constituents From Contaminated Soils

Product ID:TR-103320
Date Published:01-Mar-1994
File size:7.30 MB
Sector Name:Environment
Document Type:Technical Report
FileType:Adobe PDF (.pdf)
Price:No Charge

This Product is publicly available.

Abstract
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 50  Manufactured Gas Plant Site Management
Keywords
  • Coal Tar
  • Contamination
  • Decontamination
  • Soils
  • Surfactants
Report
TR-103320
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