9    DNAPL REMOVAL - IS IT POSSIBLE?
Michael J. Elliott, Environmental Manager
Materials & Controls Group
Texas Instruments Incorporated
Attleboro, Massachusetts 02703
James O'Shaughnessey, Professor
Department of Civil Engineering
Worcester Polytechnic Institute
Worcester, Massachusetts 01609
Paul Mathisen, Professor
Department of Civil Engineering
Worcester Polytechnic Institute
Worcester, Massachusetts 01609
INTRODUCTION
One of the greatest challenges in the field of environmental engineering today involves the
presence of Dense Non-Aqueous Phase Liquid (DNAPL) contamination in the subsurface soils
and groundwater at many industrial sites. DNAPL contamination includes a broad range of hy-
drodynamically immiscible organic compounds that exhibit densities greater than that of water.
Because of the particular behavior of DNAPL in the subsurface, and its potential toxicity to
human receptors at extremely low concentrations, it has proved to be a troublesome, persistent
contaminant whose removal to safe levels eludes currently available technologies in most cases.1
Traditional pump and treat strategies that have been almost universally applied at many contaminated sites have demonstrated limited effectiveness, at best, toward achieving the desired remediation outcome. While pump and treat still serves an important role in managing subsurface
contamination, in light of the physical realities, its application at DNAPL sites will have to
change from one of direct mass removal and environmental restoration to one of long-term containment and control to prevent exposure of potentially sensitive receptors to such contaminants.
UBIQUITOUS NATURE OF CHLORINATED ALIPHATIC HYDROCARBONS
AT CONTAMINATED INDUSTRIAL SITES.
In its haste to introduce the new family of "wonder" solvents, society, and in particular the industrial engineering community, failed to recognize the long-term potential toxicological effects
of these chemicals and the adverse environmental impact that might ensue from their mismanagement. It is common to hear anecdotes about how solvents were loosely managed in the so-
called "old-days." The sensitivity and awareness of the potential hazards of solvent usage didn't
really exist until just the last 10 to 15 years. While solvent management has dramatically improved with increased knowledge of their potential hazards, enough time had passed to cause the
occurrence of thousands of numerous contaminated industrial sites in the USA alone, some of
which are listed by the Environmental Protection Agency (EPA) on the National Priority List
pursuant to the Comprehensive Emergency Response, Compensation and Liability Act (CERCLA a.k.a. "Superfund"). In fact, some EPA publications have listed solvents such as TCE as
one of the most commonly identified chemical contaminants at Superfund sites.2
51st Purdue Industrial Waste Conference Proceedings, 1996, Ann Arbor Press. Ine., Chelsea, Michigan 48118.
Printed in U.S.A.