This document discusses physical treatment technologies for soil and groundwater remediation. It begins by describing key physicochemical properties of contaminants and media that physical technologies exploit. It then discusses several common physical technologies: free product recovery removes separate-phase contaminant layers, pump-and-treat extracts contaminated groundwater for above-ground treatment but suffers from contaminant tailing and rebound, and soil vapor extraction removes volatile contaminants from the vadose zone. Free product recovery techniques include skimming systems and lowering the water table. Recovery of dense, sinking contaminants requires enhanced dissolution or mobilization methods.

1. CHAPTER 3
Physical Treatment Technologies
Ravi Damera and Alok Bhandari
REMEDIATION TECHNOLOGIES FOR SOILS
AND GROUNDWATER
American Society of Civil Engineers
1801 Alexander Bell Drive
Reston, Virginia, 20191-4400
Copyright © 2007 by the American Society of Civil Engineers. All Rights Reserved.
ISBN 13: 978-0-7844-0894-0 ISBN 10: 0-7844-0894-7
Manufactured in the United States of America.

2. INTRODUCTION
Physical treatment technologies take advantage of physicochemical
properties of the contaminant and the affected media to remediate soil
and groundwater.
PHYSICOCHEMICAL PROPERTIES
in this context include:
for CONTAMINANT
 density,
 solubility,
 viscosity,
 volatility
for MEDIA (that can be exploited during site remediation)
 physical state (solid, liquid or gas),
 its bulk density,
 moisture content,
 permeability,
 porosity,
 particle size distribution
 ability to conduct heat or electric current
Most conventional physical treatment technologies:
 free product recovery,
 pump and treat,
 soil vapor extraction,
 air sparging,
 groundwater circulation wells,
 multi-phase extraction,
 induced fracturing,
 soil heating

3. 1. FREE PRODUCT RECOVERY
Free product, also known as free phase
contamination, refers to concentrated contaminants
that are not miscible with groundwater and
therefore form a separate layer.
Free phase product recovery is often applied in
combination with other treatment processes such
as soil vapour extraction (SVE), dual phase
extraction, ex-situ treatments and bioremediation. It
is rarely undertaken alone except in the least
sensitive environmental settings. Depending on
physical properties, product can be recovered as a
liquid or vapour and the recovery could be
enhanced by steam injection or surfactant flushing.

4. 1. FREE PRODUCT RECOVERY
Light non-aqueous phase liquids (LNAPL):
these contaminants are less dense than
water and float on the water table surface.
Dense non-aqueous phase liquid (DNAPL): these
contaminants are denser than water and sink to the
bottom of water table and rest on impermeable
surfaces such as clays and bedrock.
There are two types of free product:
Contaminants
Free product recovery is applicable to all chemicals,
common free product contaminants are:
•Light non-aqueous Phase liquids (LNAPL)
•Diesel range organics (DRO)
•Petroleum range organics (PRO)
•Kerosene
•Dense non-aqueous phase liquid (DNAPL)
•Creosote
•Chlorinated solvents
•Coal tars
•Polychlorinated biphenyls (PCBs)

5. The design phase for a free product recovery system is often initiated by seeking
answers to the following questions (EPA 1996a):
• What is the spatial distribution of the free product in the subsurface?
• What is the expected mass of free product in the contaminated zone?
• What mass/volume of the free product is recoverable?
• How quickly/easily can the free product be recovered?
Widely used approaches to recover free product from subsurface contaminant pools
include skimming systems, recovery with water table depression, soil
vapor/groundwater extraction, and dual phase (liquid and vapor) recovery and
separation. The selection of a particular approach is often guided by site conditions,
specific remedial objectives or design constraints. Skimming systems (Figure 3.1) are used
for short-term remedial actions where the free phase is removed from a well or trench
without recovering groundwater. These systems work effectively to remove free product
exits from permeable subsurface zones such as utility bedding or buried underground open
structures. Skimming systems may be passive such as filter canisters or absorbent bailers
or active such as belt skimmers, pneumatic pumps or floaters.

6. Table 3.1 summarizes key properties of the fluid and geologic media that affect subsurface migration and free
product recovery

7. Figure 3.1
Skimming system for
LNAPL free product
recovery includes an
interceptor trench and
a recovery well.

8. Recovery of free phase DNAPLs is complicated by the fact that these
products sink to the bottom of the aquifer. Chemical flooding methods
such as enhanced dissolution and physical mobilization are often
used to flush the free product out of soil pores before recovery using
extraction wells. Enhanced dissolution methods utilize cosolvents or
solubilizing surfactants to increase the solubility of the DNAPL. Physical
mobilization of DNAPL by reducing interfacial tension is accomplished
through mobilizing surfactants or miscible alcohol floods.

9. 2. PUMP-AND-TREAT
Pump-and-treat is the most
widely used remediation
technology. Pump-and-treat has
been used both as a stand-alone
treatment system and in
conjunction with
complementary technologies.
Conventional pump-and-treat
methods focus on the extraction
of contaminated groundwater to
the surface for subsequent
treatment. Such systems have
been used in about 75% of
Superfund clean up actions
where groundwater was
contaminated (NRC, 1994). The
treated groundwater may be re-
injected into the subsurface or
discharged into a receiving

10. PUMP-AND-TREAT
Once groundwater is extracted, a variety of physical, chemical and biological processes can be
used to treat the contaminated water. These processes include adsorption, volatilization,
precipitation, oxidation-reduction, and biotransformation. However, the effective extraction
of contaminated groundwater at the site requires that the contaminant sources be identified,
located, and controlled. Wherever possible, source removal should be implemented to
prevent further contamination. A thorough study of the site should include assessing the type
and extent of contamination and a three-dimensional characterization of the subsurface
including hydraulic conductivity, particle size distribution and the sorption potential of aquifer
material

11. Pump-and-treat systems are severely limited by the extensive contaminant tailing and
rebound problems often associated with the technology. Tailing represents the progressively
slow decline in aqueous contaminant concentration in the extracted water with pumping
duration (Figure 3.4). Tailing of contaminants results in long treatment times. At longer
treatment periods, larger and larger volumes of water have to be extracted to remove the
smaller and smaller concentrations of pollutant. At several sites, pump-and-treat systems
would have to run for hundreds of years before contaminant concentrations have receded
to acceptable cleanup levels.
Contaminant rebound refers to the momentary increase in aqueous contaminant
concentration observed when a well is re-started after a period of no pumping. Rebound is
also known to occur when pumps are restarted after a treatment system appears to have
achieved the cleanup standard. The reasons for tailing and rebound during pump-and-treat
operations often relate to mass-transfer limitations from aquifer surfaces and NAPL pools.
Other factors may include precipitate dissolution in case of inorganic solutes, contaminant
diffusion into low permeability media, and variations in groundwater velocity (EPA 1996b).

12. Figure 3.4 Tailing and rebound behavior typically observed in pump-and-treat
systems (Cohen et al., 1994).

15. REFERENCES:
■ 1. Remediation technologies for soils and groundwater / sponsored by
Remediation Technologies for Soils and Groundwater Task committee of the
Environmental Council, Environmental and Water Resources Institute (EWRI) of
the American Society of Civil Engineers ; edited by Alok Bhandari ... [et al.].
■ 2. How To Effectively Recover Free Product At Leaking Underground Storage
Tank Sites. A Guide For State Regulators, EPA 510-R-96-001, September 1996
■ 3. https://www.vertasefli.co.uk/our-solutions/expertise/free-product-
recovery