Section Three
SITE REMEDIATION
B. SOIL REMEDIATION
15    EVALUATION OF IN SITU SOIL FLUSHING TECHNIQUES
FOR HEAVY METALS REMOVAL FROM
CONTAMINATED SOILS
J. C. O'Shaughnessy, Professor
Professor R. A. D'Andrea, Associate Professor
M. R. Canniff, T. J. St Germain, S. Venkataramanappa, and M. J. Macaulay,
Graduate Research Assistants
Department of Civil Engineering
Worcester Polytechnic Institute, Worcester, Massachusetts 01609
BACKGROUND INFORMATION
The constant use of hazardous and toxic materials has created numerous examples of severe
environmental degradation. A result of past and present waste disposal practices, shipping of trade
chemicals, and other intentional misuses of hazardous substances have resulted in the release of these
materials into the environment. The end result is the required remediation of more and more existing
hazardous waste sites. With the enforcement of Land Disposal Restrictions (LDRs) at Superfund
sites, treatment of heavy metal-contaminated soils is required before disposing of the soils at a
disposal facility. In situ soil flushing has been found to be effective at extracting heavy metals from
contaminated soils in laboratory tests and has been selected, through the Record of Decision (ROD),
as a remedial alternative to clean the Lipari Landfill located in New Jersey.
As shown in Table I, the most widespread class of soil contaminant at Superfund sites was found to
be slightly water soluble organics which included aromatics and halogenated hydrocarbons. Based on
research data available on treatment of soils contaminated with slightly water soluble organics, the
most promising countermeasure is a full scale in situ countermeasure operation with water injection
and recovery. Surfactants and/or other chemical countermeasures may be added to increase the
remediation effort.1 If in situ flushing is used, then the implication of this remediation method on
heavy metals must also be understood.
The solubility of heavy metals in soil largely determines their mobility in the environment and,
therefore, the degree of pollution and environmental damage. The solubility depends on soil/solution
pH, soil texture and composition, the amount and type of organic compounds in the soil, soil
moisture content and temperature, and the type and number of other ions present in the soil.2"5 The
major metal removal processes in soil are adsorption, precipitation, biological assimilation and
chelation, although the metal will stay in solution when chelated with a sequestering agent.
Clean, coarse grained soils containing reduced organic matter provide relatively little adsorption
surface and, therefore, are more inclined to let soluble metals pass through with groundwater flow.
Silt and clay sized soil particles and organic soils build up metal concentration by removing metal
from solution and, thus, decrease metal leaching through to groundwater.
The number and type of adsorption sites on a given soil is determined by the soil type and
composition. All ions in solution will compete for these sites and also compete for available ligands
for chelation/complexing. Organic ligands, such as fluvic and humic acid, can impact metals mobility. Precipitation of metals depends on the soil composition which then can provide the necessary
carbonates, hydrous oxides, oxides, phosphates and sulfides that are required to form precipitates.
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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