Section Three
SITE REMEDIATION
B. SOIL REMEDIATION
11    EVALUATION OF SOIL WASHING FOR REMEDIATING
LEAD CONTAMINATED SOILS
William H. Young, Graduate Student
Mark E. Buck, Graduate Student
John E. Van Benschoten, Assistant Professor
Mark R. Matsumoto, Associate Professor
Department of Civil Engineering
State University of New York at Buffalo
Buffalo, New York 14260-4300
INTRODUCTION
Soil washing is a physical/chemical treatment process in which excavated soil is treated first by
physical separation and then washed with chemical extractants to remove contaminants. Physical
separation involves screening followed by density/gravity separation techniques. Mechanical screens
and hydrocyclones are used to separate the soil into different size fractions. The bulk oversize
material which may consist of clean or slightly contaminated cobbles and stones undergoes a water
rinse before being returned to the site as fill. The silt and clay fraction typically contains the highest
concentration of contaminants and is treated by stabilization/solidification techniques to immobilize
contaminants before landfilling. The remaining fine and coarse sands may be treated further by
density/gravity separation processes to isolate high density aggregates and metal fragments. Contaminant soil washing is achieved by mixing the pretreated fine and coarse sands with an extractant
solution. Extractants vary depending on the contaminant type and binding characteristics. Common
extractants include water, acids, bases, surfactants, solvents, chelating agents, and reducing agents.
After chemical treatment, the washed soil is rinsed with water to remove residual contaminants and
returned to the site. The washing extractant may be recycled or discharged following precipitation and
clarification to remove metals and GAC to remove organic contaminants.
Although soil washing techniques have been widely used in Europe, the first soil washing operation
in the United States was completed in October, 1992 at the King of Prussia Technical Corporation site
in New Jersey. Soil washing also has been selected for remediation at 23 Superfund sites including
eight wood preserving sites (PAHs, PCP, and metals), one Pb battery recycling site, three pesticide
sites, one site containing VOCs and metals, and two sites containing metals only. The majority of
these 23 full-scale soil washing projects were in the process of planning, design, or installation by the
end of 1993.'
In this study, an evaluation of soil washing for remediating Pb contaminated soils was performed.
Bench-scale experiments were used to evaluate the efficacy of various soil washing extraction agents
and operating conditions for removing Pb from the contaminated soils. The objectives of the study
were to 1) evaluate the efficacy of soil washing to remove Pb from seven contaminated soils, 2)
examine operational factors affecting soil washing performance including pH, mass liquid-to-solid
(L/S) ratio, temperature, mineral acids, chelating agents, and reductants, and 3) identify correlations
between contaminant characteristics and soil washing performance.
METHODS
Pb contaminated soils from industrial sites across the U.S. were received for testing after initial
preparation by Hazen Research, Inc. (HRI) of Golden, Colorado. Initial preparation included various
49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.