United States
 Environmental Protection
 Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
 Research and Development
EPA/600/SR-93/022   April 1993
  Project  Summary
 DNAPL  Site  Evaluation
 Robert M. Cohen and James W. Mercer
   Dense  nonaqueous-phase  liquids
 (DNAPLs), especially chlorinated sol-
 vents, are among the  most prevalent
 subsurface contaminants identified in
 ground-water supplies and at waste dis-
 posal sites. There are several site-char-
 acterization issues specific to  DNAPL
 sites including (a) the risk of inducing
 DNAPL migration by drilling, pumping
 or other field activities; (b) the use of
 special sampling and  measurement
 methods  to assess  DNAPL presence
 and migration potential; and (c) devel-
 opment of a cost-effective character-
 ization strategy that accounts for
 DNAPL chemical  transport processes,
 the risk of inducing DNAPL movement
 during field work,  and the data required
 to select and implement a realistic rem-
 edy. This  manual  provides information
 to address these issues and describes
 and evaluates  activities that can  be
 used to determine the presence, fate,
 and transport  of subsurface DNAPL
 contamination.  The manual discusses
 the scope of the  DNAPL problem, the
 properties of DNAPLs and subsurface
 media affecting DNAPL transport and
 fate,  objectives  and  strategies for
 DNAPL site characterization, invasive
 and non-invasive methods of site  char-
 acterization, and laboratory methods for
 characterizing fluid and media proper-
 ties. The  manual  concludes  with sev-
 eral case histories illustrating problems
 specific to DNAPL  sites and priority
 research needs for improving DNAPL
 site characterization.
  This Project Summary was developed
 by EPA's Robert S. Kerr Environmental
 Research  Laboratory, Ada, OK, to an-
 nounce key findings of the research
 project that is  fully  documented in a
 separate report of the same title (see
 Project Report ordering information at
 the back).

 Introduction
  Dense  nonaqueous  phase  liquids
 (DNAPLs), such as some chlorinated sol-
vents, creosote-based  wood-treating oils,
coal tar wastes, and pesticides, are  im-
miscible fluids with a density greater than
water. As a result of widespread produc-
tion, transportation, utilization, and disposal
of hazardous  DNAPLs, particularly since
1940, there are numerous DNAPL con-
tamination sites in North America and Eu-
rope. The potential  for serious long-term
contamination of groundwater by  some
DNAPL  chemicals at many sites is high
due to their toxicity, limited solubility (but
much higher than  drinking water  limits),
and significant migration potential in soil
gas, groundwater,  and/or as  a separate
phase (Figure 1). DNAPL chemicals,  es-
pecially  chlorinated  solvents,  are among
the most prevalent ground-water contami-
nants identified in ground-water supplies
and at waste disposal sites.
  The subsurface movement of DNAPL is
controlled substantially by the nature  of
the release, the  DNAPL density, interfa-
cial tension, and viscosity, porous media
capillary properties, and, usually to a lesser
extent,  hydraulic forces. Below the water
table, non-wetting DNAPL migrates pref-
erentially through  permeable pathways
such as soil and rock fractures, root holes,
and sand layers that provide relatively little
capillary resistance to flow. Visual detec-
tion of  DNAPL in soil  and ground-water
samples may be difficult where the DNAPL
is transparent, present in low saturation,
or distributed heterogeneously. These fac-
tors confound characterization of the move-
ment and distribution of DNAPL even  at
sites with relatively homogenous soil and
a known, uniform DNAPL source. The dif-
ficulty  of site  characterization is further
compounded by  fractured bedrock, het-
erogeneous  strata, multiple DNAPL mix-
tures and releases, etc.
  Obtaining  a detailed delineation of sub-
surface DNAPL,  therefore, can be very
costly and may be impractical using con-
ventional site investigation  techniques.
Furthermore, the risk of causing DNAPL
migration by drilling or other actions may
be substantial  and should be  considered
prior to commencing field work. Although
DNAPL can  greatly complicate site char-
                                                     Printed on Recycled Paper

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           Dissolved
          Contaminant
            Plumes
Figure 1.   DNA PL chemicals are distributed in several phases: dissolved in groundwater, adsorbed to
         soils, volatilized in soil gas, and as residual and mobile immiscible fluids (modified from
         Huling and Weaver, 1991;WCGR, 1991).
acterization, failure to adequately define
its presence, fate, and transport can re-
sult in misguided investigation and  re-
medial efforts.  Large savings   and
environmental benefits can  be realized
by conducting studies and implementing
remedies  in a cost-effective  manner.
Cost-effective  DNAPL site management
requires an understanding of DNAPL prop-
erties and  migration processes, and of the
methods available to investigate and in-
terpret the transport and fate of DNAPL in
the subsurface.
  Lighter-than-water  NAPLs (LNAPLs)
which  do  not sink through the saturated
zone,  such  as petroleum  products, are
also present and cause ground-water con-
tamination at  numerous sites.  Although
many  of the same  principles  and  con-
cerns apply  at both  LNAPL and DNAPL
sites,  LNAPL site characterization  is not
specifically addressed in this document.

Objectives
  This manual is designed to guide inves-
tigators involved in the planning and imple-
mentation  of characterization studies  at
sites suspected of having subsurface con-
tamination by  DNAPLs.  Specifically, the
document  is intended to
      Summarize the  current  state  of
      knowledge  for  characterizing
      DNAPL-contaminated sites;
      Develop a framework for planning
      and implementing DNAPL site char-
      acterization activities;
      Provide a detailed discussion of the
      types of data,  tools, and methods
      that can be used to identify,  char-
      acterize, and monitor DNAPL sites,
      and an analysis of their utility, limi-
      tations, risks, availability, and cost;
      Identify and illustrate methods, in-
      cluding the development of concep-
      tual models, to interpret contaminant
      fate and transport at DNAPL sites
      based on the data collected;
      Assess  new and developing site
      characterization methodologies that
      may be valuable and identify addi-
      tional research needs; and,
      Review the scope  of the  DNAPL
      contamination problem, the proper-
      ties of DNAPLs and media, and
      DNAPL transport processes to pro-
      vide context  for  understanding
      DNAPL site characterization.
  The  primary goal  of this manual is  to
help site managers minimize the risks and
maximize the cost-effectiveness of site in-
vestigation/remediation by providing the
best information available to describe and
evaluate  activities that can be used  to
determine the presence, fate,  and trans-
port of subsurface DNAPL contamination.
Outlook
  Remedial  activities at a contaminated
site need to account for the possible pres-
ence of DNAPL. If remediation  is imple-
mented at a DNAPL  site, yet does  not
consider the DNAPL, the remedy will  un-
derestimate the time and effort required to
achieve remediation goals. Thus, adequate
site characterization is required to under-
stand contaminant behavior and to make
remedial decisions.
  There is no practical cookbook approach
to DNAPL site  investigation or data analy-
sis. Each site presents variations of con-
taminant transport conditions and issues.
Although there are  no  certain answers to
many of the DNAPL  site  evaluation  is-
sues, this manual provides a framework
for their evaluation.

Conclusions and
Recommendations
  As awareness of DNAPL contamination
increased in  the 1980s, research was con-
ducted to better understand the  behavior
of DNAPL in the subsurface.  Much of this
research was an expansion of the investi-
gations performed  by Schwille  (1988).
DNAPL research is  currently focusing on
remediation  (National Center for Ground
Water  Research, 1992). Throughout this
progression of  DNAPL research,  relatively
little effort has been expended on devel-
oping new site characterization tools  or
methods for  DNAPL sites.
  What has  generally occurred at DNAPL
sites is  that  tools and  techniques utilized
at contamination  sites in  general have
been applied with varying degrees of suc-
cess. Additionally,  some new tools and
methods have been developed  and oth-
ers  have been adapted to better satisfy
the  requirements of a DNAPL site investi-
gation.  Site characterization strategies
have also evolved to more closely match
the  special concerns and risks posed by
DNAPL presence.
  Despite substantial progress, additional
research on  DNAPL site characterization
tools and methods is warranted utilizing a
variety of venues:  laboratories, controlled
field sites with  emplaced DNAPL, and  un-
controlled  contamination sites. Additional
research and  technology transfer efforts
should focus on
  1.  Well drilling techniques to demon-
      strate the isolation of DNAPL zones
      through  the use  of double-cased
      wells  or other techniques;
  2.  Well and boring abandonment tech-
      niques to demonstrate the efficacy
      of different grouting mixtures and

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    methods to prevent preferential ver-
    tical fluid migration;
3.   The utility of surface and borehole
    geophysical methods to better char-
    acterize DNAPL presence and dis-
    tribution, and stratigraphic controls
    on DNAPL movement;
4.   The utility of soil gas surveying to
    better characterize NAPL presence
    and related chemical migration;
5.   Methods to determine in-situ NAPL
    saturation (e.g., borehole geophys-
    ics,  simple quantitative sample
    analysis);
6.   Techniques to determine field-scale
    constitutive relationships between
    saturation, capillary pressure, and
    relative permeability;
7.   Practical field or laboratory tech-
    niques to delineate mobile DNAPL
    from DNAPL in stratigraphic traps
    from DNAPL at residual  saturation;
8.   Additional cost-effective methods to
    determine NAPL presence, compo-
    sition, and properties;
9.   Techniques to  better  define  site
    stratigraphy, heterogeneity,  and
    fracture distributions;
10. The long-term capacity of capillary
    barriers (e.g., clayey soil  layers) to
    prevent DNAPL movement, includ-
    ing methods for determining barrier
    continuity  and time-dependent as-
    pects of DNAPL-mineral  structure
    and wettability interactions;
11. Identifying the limited characteriza-
    tion  efforts  required to determine
    and  implement  appropriate  reme-
    dial measures at  DNAPL contami-
    nation sites;
12. Further  optimization of character-
    ization  strategies given  different
    source, hydrogeologic, risk and rem-
    edy considerations;  and,
13. Refinement of pilot test designs, pro-
    tocols, and monitoring requirements
    to determine the  feasibility and/or
    technical  impracticali'.,    f alterna-
    tive remedial measure.-,
References
  Huling, S.G. and  J.W. Weaver,  1991.
      Dense nonaqueous phase liquids,
      USEPA Ground  Water  Issue  Pa-
      per, EPA/540/4-91/002, 21 pp.
  National Center for Ground Water  Re-
      search,  1992. Extended abstracts,
      Proceedings of the Subsurface Res-
      toration Third Internationa! Confer-
      ence  on  Ground Water Quality
      Research, Rice  University, Hous-
      ton, Texas, 343 pp.
  Schwille,  F., 1988. Dense Chlorinated
      Solvents in Porous and Fractured
      Media, Lewis Publishers, Chelsea,
      Michigan,  146 pp.
  WCGR, 1991. Dense, Immiscible Phase
      Liquid Contaminants (DNAPLs) in
      Porous  and  Fractured  Media, A
      Short Course, DNAPL Short Course
      notes,  October  7-10,  Kitchner
      Ontario, Canada,  Waterloo Center
      for Groundwater Research, Univer-
      sity of Waterloo.

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  Robert M. Cohen and James W. Mercer are with GeoTrans, Inc., Sterling, VA20166.
  John E. Matthews is the EPA Project Officer (see below).
  The complete report, entitled "DNAPL Site Evaluation," (Order No. PB93-150217;
    Cost: $44.50, subject to change), will be available only from:
          National Technical Information Service
          5285 Port Royal Road
          Springfield, VA 22161
          Telephone: 703-487-4650
  The EPA Project Officer can be contacted at:
          Robert S. Kerr Environmental Research Laboratory
          U.S. Environmental Protection Agency
          Ada, OK 74820
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268

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