United States       Office of Emergency and   Publication 9355.4-05
            Environmental Protection   Remedial Response     PB92-963346
            Agency         Washington, DC 20460   February 1992

            Superfund
<&EPA     Evaluation of Ground-Water
           Extraction Remedies:
           Phase II

           Volume 1
           Summary Report

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                              Publication 9355.4-05
                                  February 1992
EVALUATION OF GROUND-WATER
EXTRACTION REMEDIES: PHASE II
              Volume 1
           Summary Report
   Office of Emergency and Remedial Response
     U. S. Environmental Protection Agency
            Washington, D.C.

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                                             NOTICE

The conclusions outlined in this document are intended solely for technical support to EPA personnel.  They
are not intended, nor can they be relied upon, to create any rights, substantive or procedural, enforceable by
any party in litigation with the  United States.  The Agency reserves  the right to act at variance with these
policies and procedures and to change them at any time without public notice.
                           For additional copies of this report please contact:

                            National Technical Information Service (NTIS)
                                    U.S. Department of Commerce
                                        5285 Port Royal Road
                                       Springfield, VA  22161
                                           (703) 487-4650
                                                 11

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                         INTRODUCTION  TO  VOLUME 1
   This report is the second phase of a study to evaluate the effectivenss of ground-water extraction systems
being used to remediate ground-water contamination at hazardous waste sites.  This report was prepared in the
volumes.   Volume 1: Summary Report, contains an Executive Summary and chapters  which discuss  the
purpose, methodologies,  and conclusion of  the project.  Volume 2:  Case  Studies, contain the individual
analyses of each of the 24 sites associated with this project.
                                             ill

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                            CONTENTS

                                                                  Page

           Executive Summary  	vii

Chapter

   1       Introduction  	1
                Project History	1
                Phase II Methods and Objectives	1
                   Background on the Importance of NAPLs  	2

   2       Overview of Case Studies	3
                Site Background Characteristics	3
                   Length of Historical Record	3
                   Plume Size  	3
                   Contaminants of Concern	6
                   Geologic Environments	6
                Issues Related to System Design	6
                   Remedial Objectives	6
                   Projected Cleanup Time	7
                   Extraction and Monitoring System Sizes  	9
                   Enhancement Technologies  	9
                   System Design Information	10
                Occurrence of NAPLs  	10

   3       Summary of Remedial Progress	13
                Plume Containment	13
                Aquifer Restoration Effectiveness	15
                   Contaminant Mass  Removal	15
                   Contaminant Concentrations	17
                   Plume Area Reduction 	19
                Use and Effectiveness  of Enhancement Technologies .... 19
                   Soil Vapor Extraction  	19
                   Ground-Water Reinjection	20
                   Slurry Wall Containment	20
                   Fracture Enhancement	21
                Update on Site Data Requirements	21
                   Hydrogeologic Information  	21
                   Contaminant Characteristics and Distribution	22
                                 IV

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                CONTENTS
                (Continued)
                                                   Page
Occurrence and Implications of NAPLs	24
       Waste Handling Practices Leading to NAPL
       Contamination 	24
       Identification of NAPL Presence 	24
       Implications of NAPL Presence	26

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                               EXHIBITS






Figure       Name                                                  Page



Figure 2-1    Geographic Distribution of Case-Study Sites  	4



Table 2-1     Site Background Characteristics	5



Table 2-2     Summary of Design-Related Information	8



Table 2-3     Summary of NAPL Occurrence 	12



Table 3-1     Summary of Remedial Effectiveness  	14
                                    VI

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                                 EXECUTIVE SUMMARY
This summary report describes the second phase of
an  evaluation  of  the  current  effectiveness  of
ground-water  extraction   in   remediating
contaminated aquifers at several hazardous waste
sites. This project  involved reviewing data from
existing  extraction  systems and should not be
viewed as a "technology evaluation" in the typical
sense because no attempt was made to select sites
where the extraction systems had been optimized.
Due to the limited number of sites with operating
extraction systems,  selection criteria were limited
to identifying those  sites where extraction systems
had  been in  operation long enough  to generate
initial performance data.

This report does not go beyond describing  the
operation and conclusions associated with  the 24
sites in  the study.   However,  analysis of these
findings  provides part of the basis for identifying
other guidance needs, determining modifications to
our  approach  to ground-water remediation, and
assessing the need for future studies and research.
A data  collection guide, a screening guide  for
assessing  the  likelihood of  DNAPLs,  and a
Directive clarifying EPA's approach  to ground-
water remediation will be developed by EPA over
the next year.

Phase I of the study was  completed in 1989 (U.S.
EPA, 1989). In this second phase, data from 17 of
the original 19 case  studies were updated, and new
case studies were prepared for five additional sites.
Two of the original  case  studies were not updated
because more current site data either had not been
generated or could  not be obtained.  The  second
phase  of   the   study   put   special  emphasis
nonaqueous phase  liquids  (NAPLs),  which can
increase the time frame and complexity of ground-
water remediation.

The  24 case studies (U.S. EPA,  1991) that now
comprise the results  of this evaluation must still be
considered  a very small  database from which to
draw general conclusions.  The   case-study sites
represent a variety  of subsurface contamination
situations,  geologic environments,  and  remedial
approaches.     Records  of  extraction   system
operation vary in length, but  in most cases  are
relatively short compared to the time that may be
required  to complete aquifer remediation (aquifer
remediation is not always the declared remedial
objective).  Because these sites represent some of
the  few sites  where  extraction  systems have
actually been in operation, they  also  represent
some of the  earliest ground-water investigations.
Consequently,   those    investigations   predate
application   of   recent  advances   in   site
characterization methods and approaches.  In most
of the cases,  site data that were obtained for  this
evaluation leave important questions  unanswered.
These are described in more detail in Chapter 3.
Despite  these shortcomings, it is possible to draw
some tentative  conclusions  from  the  results
reported here. Continued monitoring of remedial
progress at these and other ground-water extraction
sites, together with  results  from  other ongoing
research in the field, can be expected  to lead to
more  effective  application  of  ground-water
extraction technology in the future.

             CONCLUSIONS

The  results of the phase n study reinforced the
main conclusions of phase I and led to some
additional  conclusions  concerning  impacts  of
NAPLs  on ground-water remediation.   The first
four  conclusions are the same  conclusions drawn
in the initial  study and are presented here to re-
emphasize these  findings.

Conclusion   1:     Data  collected,  both   site
characterization data prior to system design  and
subsequent operational data, were not sufficient to
fully  assess contaminant movement  or   ground-
water system response to  extraction.

Conclusion 2: In the majority of cases studied (15
of the  24 sites),  the ground water  extraction
systems   were   able    to   achieve  hydraulic
containment  of  the dissolved-phase  contaminant
plume.

Conclusion 3: Extraction systems were often able
to remove  a substantial  mass  of contamination
from the aquifer.

Conclusion 4:   When extraction systems were
started  up,  contaminant concentrations  usually
showed  a rapid initial decrease, but then tended to
level off or  decrease at  a greatly reduced  rate.
                                                vil

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 This may be a result of the type of monitoring
 data collected as much as a reflection of an actual
 phenomenon of ground-water extraction systems.
 For example, it can reflect successful remediation
 as  the  contaminated  zone  shrinks  and  less-
 contaminated ground water  is  puEed  into  the
 extraction system, or poor  placement of ground-
 water monitoring  wells.

 Conclusion 5:  Based on the available information,
 potential NAPL presence was not addressed during
 site investigations at 14 of the 24 sites.  At 5 sites
 they   were   "addressed"   because  they   were
 encountered unexpectedly during the investigation.
 As a  result, it is  difficult  to determine NAPL
 presence conclusively  from available  site  data.
 Because NAPLs  were not  addressed in the  site
 investigation, they also were not addressed in the
 remedial design.   Consequently,  a ground-water
 extraction system may be performing as designed
 (removing  dissolved  phase contaminants)  even
 though it will not achieve the cleanup goals within
 the predicted timeframe.

j Conclusion 6:  At 20 of the 24 sites, chemical data
 collected  during   remedial  operation  exhibited
 trends  consistent  with  the  presence  of  dense
 nonaqueous  phase liquids (DNA'PLsJp However,
t even where  substantial solTand water quality data
 were available, a separate immiscible phase was
 rarely  sampled "or observed.   This is  consistent
 with  DNAPL  behavior;  i.e.,  they  can   move
 preferendSHy^ through very discrete pathways that
 may easily be missed even in thorough sampling
 schemes.  DNAPL was observed at sites where
 contaminant concentrations  in ground water were
 less than 15% of the respective solubilities.

 Conclusion 7:  The importance of treating ground-
 water remediation as an iterative process, requiring
 ongoing  evaluation of system design, remediation
 time  frames,  and data collection  needs,  was
 recognized at all of the sites where remedial action
 was continuing.

           SITE  BACKGROUND
               INFORMATION

 With  the completion  of phase II,  moderately
 detailed case studies of 24 hazardous waste sites
 have   been  produced.   Remedial  performance
 histories range from 1  to  12  years, involving
 contaminant plumes ranging in size from less than
 1  acre to more than 7,000 acres.  In 19 of  cases,
the contaminants of  concern included volatile
organics, usually chlorinated solvents.

Ground-water  remediation  systems installed at
these sites reflected a wide range of intensity of
remedial effort  The number of extraction wells
per site ranged from 1 to 203, and total extraction
rates of  up to 9,200  gallons per  minute  were
reported.  The number of monitoring wells at
individual sites ranged from six to 250.

Ground-water extraction systems at several sites
were   supplemented   by   additional   remedial
technologies.   The most common of these were
ground-water reinjection and soil vapor extraction,
each of which were used at six sites.  Soil vapor
extraction systems  usually  removed  significant
quantities of contaminants, but the effect of this
removal  on reducing aquifer cleanup time could
not be  quantified.  Reinjection  was  sometimes
used more  as a means of ground-water disposal
than to increase the rate of contaminant migration.
Slurry  wall containment was used at three sites;
French   drains,  fracture   enhancement,   and
intermittent pumping were used at one site each.

     REMEDIAL PERFORMANCE

As of  the  conclusion of  this  second  phase
evaluation,  a successful aquifer cleanup has been
reported for only one of the subject sites (Emerson
Electric  in  Altamonte  Springs,  Florida).   An
apparent remedial success was reported in the first
phase  evaluation.   However, remedial success
claims  were based on limited monitoring data, and
may therefore be open  to question.  No new  data
were available for this site during the second phase
evaluation.

Plume containment appeared effective at 15 of the
24 sites.   At  six  other sites, the containment
effectiveness was uncertain because of insufficient
plume  monitoring (chemical  or water level) or
contradictory   site  data.    Plume  containment
appeared incomplete at only three sites.

Fifteen   sites  had  data  on  contaminant  mass
removed by  the  extraction  systems.   Amounts
removed ranged  from  10  pounds to  more  than
203,000  pounds.     Removal  estimates  were
provided   by   the    parties   responsible  for
remediation, or were  calculated   as part  of the
Phase II study.  Information needed to make such
an estimate was unavailable for nine sites.
                                                 Vlll

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In  light  of the  observation  that  contaminant
concentrations frequently appear to stabilize above
the cleanup goals, an effort was made to identify
these levels in the performance  records for each
site.  Based on data availability,  this trend  was
identified in either the influent  to the treatment
system (11 cases), or in individual wells (9 cases).
The identification of stabilization  required some
subjective judgment as to what constituted a stable
concentration  and what  did  not.    Stabilized
concentrations appear to have occurred at 17 sites.
The  apparent   stabilization  of  contaminant
concentrations may be due to a number of factors
not necessarily related to technical limitations of
ground-water  extraction.   These  include  non-
representative   monitoring   techniques,   other
contaminant  sources   not  previously  identified,
inadequate  extraction  network  design,  and/or
inefficient operation of the extraction network.

      OCCURRENCE OF NAPLs

At  nine  case-study sites, parties responsible for
remediation acknowledged the presence of NAPLs.
NAPLs  were observed directly in eight of these
cases, and in the ninth, the determination  was
based on circumstantial  evidence.   For at least
seven of the other 15 sites, NAPLs appeared likely
even though there was no direct confirmation or
mention  of  them in  the  site  reports.    The
likelihood of NAPL  presence at all 24 sites  was
estimated using a rating scale of 1 through 5.
Ratings  were based on indirect evidence such as
high contaminant  concentration in ground  water,
depth of contamination in the aquifer, persistance
of  contaminant  plume during remediation,  and
contaminant source characteristics.

Analyte   concentrations   in   excess   of  the
contaminant  aqueous  phase   solubility  were
reported  for ground-water samples at three sites.
This provides a strong indication of the presence
of NAPLs.  One of these instances occurred  at a
site where the presence of NAPLs has not been
acknowledged.    At  some  sites  where  NAPL
presence  was  acknowledged,   the  maximum
contaminant concentrations reported were less than
15 percent of contaminant solubility.  It is possible
that in some cases, NAPL is being removed by the
ground-water extraction systems without this being
recognized by the system operators.
                                                 IX

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                                           Chapter 1
                                      INTRODUCTION
           PROJECT HISTORY

 In  1989,   EPA's  Office  of  Emergency  and
 Remedial Response (OERR) completed a study of
 19 hazardous waste sites at which ground-water
 extraction  systems were being used to remediate
 aquifer  contamination.     The  study  utilized
 available  site-investigation  documents,  such  as
 remedial investigation  (RI) and feasibility studies
 (FS) reports, and annual or quarterly performance
 monitoring reports that were generally  current
 through late 1988. A project report was issued as
 three  volumes  (U.S.  EPA,  1989):  Volume  1,
 Summary  Report; Volume 2, Case Studies;  and
 Volume 3, General Site Data-Data Base Reports.
 That study and the reports produced comprise the
 first phase of the evaluation.

 In late 1990, OERR initiated a second phase of the
 ground-water  extraction evaluation.   In  it  the
 original case studies were to be updated, and five
 new case-study sites  were to be evaluated with
 special   emphasis   on   the  occurrence   of
 contaminants in the form of NAPLs.

       PHASE II METHODS  AND
               OBJECTIVES

 In general, the second  phase objective was to
 evaluate   the   remedial    effectiveness   of
 ground-water extraction systems that had sufficient
 operational data to allow an initial  assessment of
 system performance.   These evaluations focused
 on  the capability of  the  extraction  systems to
 control and remove  ground-water  contamination.
 Evaluation of subsequent treatment and disposal of
 the extracted ground water is beyond the scope of
 this  evaluation,  except  for instances  where
 treatment   or   disposal   issues   affected  the
 performance of the extraction system.   In  this
 regard, the objectives  of the first and second
 phases of the evaluation are the same.  The second
 phase   updates the original  19 case studies using
 current performance information and provides five
 new case studies.

 Site information updates covering the period from
• late 1988  through  1990 was obtained  from the
  same  regulatory and  responsible-party  contacts
  who  provided  site  data  in  the  first phase.
  Remedial performance information generally was
  received  in  the form of  annual or  quarterly
  monitoring reports.  Commonly, the annual reports
  for the preceding year are compiled and released
  in the first half of the following year.  The timing
  of  these reports caused problems for some  site
  evaluations, because 1990 annual reports were not
  always available. For most sites, performance data
  were obtained through the third or fourth quarter
  (September or December, respectively) of 1990.

  Effort was made to locate  new  case-study sites
  that satisfied the second phase selection criteria:
  Superfund sites  at which  NAPLs were known to
  be  present and at which aquifer remediation  had
  been in progress long enough  to produce initial
  performance data.  These criteria proved difficult
  to  satisfy.  In the  ends five sites were selected,
  four  of which were Superfund sites.   The fifth,
  Occidental  Chemical,  predates  the   Superfund
  legislation and is therefore,  strictly speaking, not
  part  of the  program.    However,  it  is  being
  administered by  the State of California and the
  EPA National Enforcement Investigation Center
  using  procedures   comparable   to   those   of
  Superfund.    The  presence  of  NAPLs  was
  acknowledged at three of the five new case-study
  sites, and NAPLs are quite likely to be present at
t  one of the others.

  The reporting  format used in Phase II is similar to
  that  of the first-phase evaluation.  Background
  information on site history, geology, hydrogeology,
  and waste characteristics is presented first. This is
  followed  by a  description  of the ground-water
  extraction system, remedial  objectives, and some
  of  the pertinent design considerations.  The next
  section presents a review of system performance
  data.   This  review is based  only on  the  site
  information obtained.  This information was not
  always conclusive, and disagreements  regarding
  data  interpretation  has sometimes  been  noted
  among various  parties  involved  in the response
  action. Statements presented in the performance-
  evaluation sections  of the case  studies reflect
  judgements   (by   others)  contained   in   site
  information packages and were not the result of

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this study.  Conclusions drawn in the course of
this evaluation are contained in the "Summary of
Remediation" or the "Summary of NAPL-Related
Issues" sections.

Records for many sites contain no explicit mention
of NAPLs or the  possibility  of their presence.
Nonetheless,  site  data  frequently contain  clues
indicating that NAPLs may be present, and these
data are  discussed for each case study.   In the
"Summary of NAPL-Related Issues" section, the
Phase II authors  of the case studies speculated on
this possibility in light of the evidence hi the site
background  and  performance data.   This  should
not be construed as an  official determination by
EPA concerning  the nature of the  contaminants at
the site.

The format used for case study updates is similar
to that  used in  the original  case  studies,  but
background  issues  are  presented in  less  detail.
The   updates  are  meant  to  be  readable  as
stand-alone  documents,  but to gain  the  fullest
understanding of the sites it is  necessary to read
both the original and the update of the case study.

       BACKGROUND ON THE
       IMPORTANCE OF NAPLs

Phase I of this study identified  several factors that
potentially increase the time frame and complexity
of  ground-water  remediation.    These  factors
include:  hydrogeological factors (e.g., subsurface
heterogeneity, presence of low-permeability zones,
and  presence of  fractures);  contaminant-related
factors (e.g., sorption to soil, presence of NAPLs);
continued leaching from source areas; and  system
design parameters  (e.g.,  pumping rate,  screened
interval, and location of extraction wells).   Phase
II of the study again recognizes the importance of
these factors as  affecting  the  remediation  of
ground water, and focuses on the role of NAPLs
in particular.

NAPLs have become a subject of special interest
for those  involved in ground-water  remediation.
In the early  days  of  the  Superfund  program,
contaminants  present  in   the  subsurface  in
immiscible form  were not necessarily recognized
as  a  special  threat  to  ground-water  quality.
References can frequently be found  in early site
investigation   documents  to  "visible    soil
contamination"   or  "soil  staining,"  but   these
conditions  were not interpreted as evidence  of
NAPLs.

With  increased experience in the  application  of
pump and treat technology there has developed a
greater understanding of factors that may impede
progress in remediation of ground water.  NAPLs
are now frequently identified as a key factor in the
longer-than-anticipated  time  frames for aquifer
restoration.  NAPLs present in the subsurface act
as a residual source of ground-water contamination
that typically takes a very long time to deplete
solely by ground-water extraction. This is because
the   aqueous   solubility   of   NAPL-forming
compounds  is a  limiting  factor;   consequently,
large quantities of ground  water  must be pumped
to  remove  a   significant   quantity   of  the
contaminant. Even so, the solubility of many of
these  compounds  is much higher  (e.g., 5 or 6
orders of magnitude) than their health-based water
quality criteria.

A more  efficient way  to deal  with  NAPL
contamination is to remove the contaminants in the
immiscible  phase  rather  than  in  the dissolved
phase.  To some  extent this is practical for light
nonaqueous phase liquids (LNAPLs), which  are
often found floating on the water table.  However,
the physical behavior of dense nonaqueous phase
liquids (DNAPLs) makes them difficult  to  locate
and  even  more  difficult  to control, given  the
current state of the science.

The  emphasis  on  NAPLs  in  Phase II  of  the
ground-water extraction evaluation is intended to
be more empirical than theoretical.  Several recent
studies   present   theoretical  explanations   and
observations on   the  behavior  of NAPLs  in
fractured and porous media (Feenstra and Cherry,
1988;  Ruling and Weaver, 1991; Mercer  and
Cohen, 1990). The intent in this evaluation was to
utilize   field  data   obtained   during   actual
ground-water remediations to develop a  sense of
the pervasiveness of the problem, and  to illustrate
some  of the  special  features  associated with
NAPLs.

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                                         Chapter  2
                          OVERVIEW OF CASE  STUDIES
          SITE BACKGROUND
          CHARACTERISTICS

The  Phase II study includes 24 case-study sites.
Table 2-1 provides a summary of their background
characteristics.   The  geographic  distribution  is
shown in Figure 2-1.  The majority of the sites, 18
of 24, are east of the Mississippi River.  Although
some consideration  was  given  to  geographic
distribution,  the availability of performance data
for  the  ground-water  extraction  system  was
considered a higher priority in site selection.

LENGTH OF HISTORICAL RECORD

Startup  dates  for  the  ground-water  extraction
systems at the case-study sites range from 1974 to
December 1989.

The  site with the longest record of ground-water
extraction is believed to be the Olin Corporation
facility in Brandenburg, Kentucky.  Because the
process-water supply wells at Olin  have gradually
evolved into a ground-water remediation system, it
is  difficult to pinpoint the date when  their use
became  comparable to  the extraction systems  at
the other case-study sites.  Olin's radial collector
wells have been in operation since the early 1950s,
but it was not until  1974 that their effectiveness in
controlling the  spread of contaminated ground
water was recognized.   In  1984 the wells were
specifically operated as part of a ground-water
remediation system.  Performance  data used here
to evaluate the effectiveness of the system begins
in 1984.

The  IBM-Dayton  site,  which  has the second
longest  record  of extraction  for  ground-water
remediation, began operation  in  1978.   After
6 years  of operation, the system was shut down,
with the expectation that natural processes would
complete the restoration of the aquifer.  Instead,
the contaminant plume began to expand again, and
in October  1990  ground-water extraction was
resumed.

At the  Sylvester/Gilson Road  Superfund  site, a
ground-water extraction and recirculation system
was  put into operation in December 1981.  In
1982, the system was enclosed by a slurry wall.
For several  years the slurry  wall and pumping
system was  used  for containment only,  and  the
extracted ground  water was  reinjected  without
treatment.  In April  1986 a treatment system was
put into operation  to  remediate ground  water
within the  enclosure  to alternate  concentration
limits set forth in the Record of Decision (ROD).

               PLUME  SIZE

Table 2-1 lists the number of aquifers  or aquifer
zones affected at each site and the thickness and
areal extent  of the dissolved phase  plume.  This
information gives  some indication of the relative
magnitudes   of   individual  ground-water
contamination problems.

More than half (14 of 24, or 58%) of the  sites are
listed as multi-aquifer remediation sites.  In some
cases,  the  aquifers  are composed  of different
materials and  have  different  water transmitting
properties  but  are  not hydraulically  separated.
These  may  more  properly  be considered  as
separate aquifer zones.   At  other sites aquifer
materials are similar,  but  there  is  a  significant
hydrologic distinction caused by intervening layers
of   lower   hydraulic   conductivity.      The
distinguishing feature at these sites is that separate
extraction and monitoring  wells are dedicated to
individual  aquifers or aquifer zones.   All these
sites,  therefore, require more  complex extraction
and monitoring systems than might a single-aquifer
site  with  an  otherwise  similar magnitude  of
contamination.

Plume thicknesses listed in Table 2-1 are estimated
maximum thicknesses of the contaminant plume.
The estimate includes the saturated thicknesses of
all aquifer zones and intervening layers  between
zones.  Estimates  range  from  20 feet  for  the
GenRad Corporation site to  365 feet at  Tyson's
Dump.

Plume areas listed  in  Table  2-1  refer to  the
estimated maximum  lateral extent of the plume,

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Ponfers
IBM-San
                                                                                                              Road
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                                                                                               Harris Corp.
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                                                                                           Figure 2-1
                                                                                           GEOGRAPHIC DISTRIBUTION OF
                                                                                           CASE-STUDY SITES
                                                                                           CASE STUDIES SUMMARY
CD

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-------
generally measured before the start of remediation.
Areas range from  less than 1  acre at Site A to
7,600 acres at Ville Mercier.

Area  estimates were made from  concentration
contour maps, where  these were available. At the
Mid-South Wood Products site no plume map was
available, so the estimate was based on the area of
contaminated soil.   The actual plume area is
unknown and  may not  conform to the area of
contaminated soil.  At the Emerson Electric site,
the contaminant plume was never delineated. The
extent of the plume  was roughly estimated as a
circular  area  centered  on   the  contaminated
monitoring well with  a radius equal to  the distance
to the nearest "clean"  monitoring well.

   CONTAMINANTS OF CONCERN

At 20 out of 24 sites, the  primary contaminants
were volatile organic  compounds (VOCs). Where
only a few specific  compounds are  significant,
they are listed by name.  However, at many sites,
the number  of VOCs is too great for individual
listing, and  the generic  abbreviation, VOCs, is
used.  At a few sites, other organic compounds in
addition  to  VOCs   are  important,  and  the
contaminants are listed as "organics."  Many of
these  organic  compounds are  not miscible with
water,  and  therefore have the  potential  to  be
present in the aquifers as a NAPL.

The case studies include two wood-treating sites,
with PAH  compounds,  and two pesticide sites.
Metals were significant  contaminants of concern
only at the Western  Processing site.  The metals
involved  were nickel, cadmium,  zinc, chromium,
arsenic, copper, and  lead.  This site also had a
wide variety of organic contaminants.

     GEOLOGIC  ENVIRONMENTS

Various geologic environments are represented in
the collection of case studies.  The sites with the
simplest  hydrogeologic  conditions  are  Emerson
Electric and Site A.  In both cases, the zones with
known contamination were relatively uniform sand
of marine origin.  It is  interesting  to  note  that
these  two sites appear to have progressed most
rapidly toward aquifer restoration.

The remaining 22 sites had greater hydrogeologic
complexity than the two mentioned above.  Many
of  the  aquifers   are   layered  or   interbedded
combinations of sand, silt, and clay deposited in
alluvial  or  glacial  environments.     Aquifer
restoration using extraction wells is less efficient
in heterogeneous formations than in more uniform
materials.  Ground-water flow toward  extraction
wells  tends   to  take  place  mainly  in  the
higher-conductivity materials.  Low-conductivity
zones, which may contain significant quantities of
contaminants, are largely bypassed.  Difficulties in
remediating heterogeneous aquifers are presented
in the Phase  I report (U.S. EPA,  1989),  and
discussed in greater  conceptual detail by  Keely
(1989).

Nine sites involve contamination of fractured rock
aquifers,   which  are  especially   difficult  to
remediate.   The movement  of  ground water in
fractured rock takes  place mainly in the fractures.
Usually,  the  fracture density is uneven,  which
results in nonuniform,  direction-dependent flow.
Fractured bedrock aquifers are especially difficult
to remediate as shown in several of the case study
sites,  particularly at Black  &  Decker,  Nichols
Engineering,  Mid-South  Wood  Products,  and
Tyson's Dump.

   ISSUES  RELATED  TO SYSTEM
                 DESIGN

Table 2-2 summarizes information used to evaluate
extraction system design for  the case study sites.
This   information  includes   the   number  of
monitoring and extraction  wells and the maximum
rate of extraction, which give an indication of the
level of effort expended to remediate ground water
at each site.

       REMEDIAL OBJECTIVES

The   remedial objectives   generally   have  an
important influence on the design and operation of
the overall  remedial system.   Therefore, it is
important to recognize that the remedial objectives
for the extraction systems may differ for different
sites.

Aquifer restoration is a remedial goal for 17 out of
24 of the sites. Restoration is understood to mean
that  the  concentrations of contaminants   in the
aquifer are  to  be reduced to levels  that  would
allow ground  water to be used as it could have
been  before being  contaminated.   The implicit
assumption is  that, when  these concentrations are
achieved,    no   further   action    aside   from

-------
ground-water   monitoring   will   be   required.
Cleanup goals are usually maximum concentration
levels (MCLs) or other health-based criteria, such
as   10"6  excess   cancer   risk  concentrations.
However,  in some cases, alternative concentration
goals have  been  established  on a site-specific
basis.

At  the Amphenol site,  the  restoration goal is  a
total VOC concentration of less than 5 ppb.  The
General Mills site  cleanup  goal  is  270 ppb for
trichloroethylene (TCE) in the shallow aquifer and
27 ppb  in  the  underlying aquifers.    At  the
Sylvester/Gilson   Road  site,   alternative
concentration  limits for  16 key contaminants,
based on  a  site-specific risk assessment, are the
cleanup goals.

Remedial  goals  at  the Savannah River Site are
similar to that  for aquifer restoration but are
expressed  in terms of reduction  of contaminant
mass.  Specifically, the goal is to  remove 99
percent of the contaminant mass from affected
aquifers in 30 years. Goals  stated in this manner
have proven to be a problem, because efforts to
quantify the mass of contaminants in the aquifers
using sampling data from monitoring wells  have
produced highly variable results. Recent (February
1991) discovery of contaminants  in  NAPL  form
will make  accurate estimation of total contaminant
mass even more difficult.

The  remedial  objective at  seven sites  is  plume
containment.   This means ground-water quality
restoration  is  not  expected   within  the  site
containment area  using  the existing  extraction
system.

At the Verona Well Field site,  two separate, but
related,  remediations  are  in progress.   At the
Thomas Solvent Raymond  Road  (TSRR)  source
area, aquifer restoration is being pursued.  In the
well field  itself, current remedial action includes a
system of blocking wells to contain  the spread of
the plume and protect the remaining unaffected
wells.     It  may  eventually  be   possible  to
discontinue the blocking system if final remedial
actions are successful  in all contaminant  source
areas.

Remedial  objectives   at   the   Fairchild
Semiconductor site  were  changed  from  plume
containment to aquifer restoration  in 1988 when
the remedial action at the  site changed from an
interim  remedial measure  to  a final  remedial
action.

At  the IBM-Dayton site, the  goal  was changed
from aquifer restoration to  plume containment in
response to the determination that contaminants are
present in NAPL form. This change was reported
in Phase I.

Three case-study  sites (Harris,  IBM-Dayton, and
Ponders Corner) have well-head treatment systems.
At Ponders Corner,  the extraction system consists
of two municipal production wells with treatment
for VOCs.  These wells serve both to remediate
the aquifer and as a source of potable water.  At
Harris  and  IBM-Dayton,  separate  ground-water
remediation   systems   have  been  installed   in
contaminant  source  areas   in  addition  to  the
well-head treatment systems that are in operation
at down-gradient production wells.

    PROJECTED CLEANUP TIME

At  several  aquifer restoration  sites,  extraction
system  designers  have  predicted  time frames
required to complete the remediation. For three of
the sites,  the predicted cleanup time has passed.
Our experience with ground-water remediation and
the science involved in projecting remediation time
frames has  progressed significantly since  these
original estimates were made.   These  cleanup
timeframes were underestimated due, in part, to a
lack of knowledge of factors  affecting  ground-
water remediation. Projections made based on the
current  understanding  of  fate  and  transport
processes   and   subsurface  characteristics  are
expected to be more representative.

At  Site  A,  the  cleanup  was  expected to  be
complete in  60 days, but monitoring records show
that concentrations above the remedial goals were
still present at least  2 years  after  the onset  of
pumping.

At Sylvester/Gilson  Road, it was expected that the
alternate  concentration levels  (ACLs)  would be
reached 1.7 years after the ground-water treatment
plant started operating in April 1986.  However,
monitoring  data  show that 7  of  the  16  ACL
compounds are still above the target concentrations
after more than 2 years.   During this time,  the
maximum concentration of one compound

-------
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(toluene) appears to be higher now  than before
ground-water  treatment  began.     Toluene   is
suspected to be present in NAPL form.

Remediation  at  the Emerson Electric site was
judged to be  complete in  June 1987, after 2.5
years of ground-water  extraction.   However, the
original estimates were that the cleanup would take
only  9  months.   It  should  be noted  that the
determination of remedial effectiveness at Emerson
Electric was based on limited monitoring data
(samples mainly from  extraction wells and little
post  remediation monitoring).   This  site was
discussed in greater detail in  Phase I (U.S. EPA,
1989).

At  three other case-study sites, definite cleanup
times have  been  projected  that  have  not yet
expired.  Designers of the ground-water extraction
system at the Amphenol site predicted the aquifer
would be restored to the desired water quality in 5
to 10 years after system startup. This projection
was  based  on  the estimated volume  of the
dissolved contaminant plume  and the assumption
that flushing several complete plume volumes of
ground  water  would  exhaust  the   supply  of
adsorbed  contaminants.    After  approximately
4 years of extraction, it appears that ground-water
contaminant concentrations are being reduced at a
rate that may be consistent with projected cleanup
time.

At  the Fairchild Semiconductor site,  a projection
was made that aquifer restoration goals (achieving
drinking  water standards  in  the  ground water)
would be met in 1994.  This estimate was based
on  observed  water quality  improvement  since
remedial extraction started in 1982.

Designers of the extraction system at the Savannah
River Site  initially expected to achieve aquifer
restoration goals within 30 years of system startup.
In  the six  years of operation, both the system
design and the understanding of the contamination
problem  have changed.  No  new cleanup time
projections   have been made, but  the  system
operators now describe the 30-year timeframe as a
standard for evaluation of remedial progress rather
than a firm objective.
  EXTRACTION AND MONITORING
             SYSTEM  SIZES

Table 2-2  lists  the  number  of monitoring  and
extraction  wells at  each  site, as  well  as  the
maximum  ground-water extraction  rate  for  all
wells.  The number of extraction wells represents
the maximum because, at several of the sites, the
size of the  system has changed over the years.

The Western  Processing  site has  the  largest
number of  extraction wells with 203 well points
installed in rows coupled  to  a common vacuum
header.  Each well point is designed to withdraw
at approximately 1  gpm.

The highest combined pumping for the case study
sites (9,200 gpm for 36 extraction  wells) occurred
at the Fairchild Semiconductor site. The Fairchild
system operated  at this rate for only a short time
in 1983. Since then, the extraction rate has been
steadily cut back in an effort  to balance remedial
effectiveness with the need for water conservation.
Likewise,  at  the  nearby  IBM-San  Jose site,
extraction rates  have been reduced  from 6,000
gpm (30 extraction wells) to less than 1,000 gpm.
The highest sustained extraction rate (6,200 gpm
for 10 extraction wells) is at the Olin Corporation
site, where  the ground water is pumped from wells
and radial collectors next to, and extending under,
the Ohio River.

  ENHANCEMENT TECHNOLOGIES

The term "enhancement technologies" as used here
and in Table 2-2 refers to remedial activities used
to augment or assist ground-water extraction in the
removal  of subsurface  contamination.    These
technologies are not necessarily new or innovative.
Examples include:

    •    Soil vapor extraction can reduce cleanup
        times  by removing residual  contaminant
        sources  in the vadose zone.

    •    Slurry  wall containment can  limit the
        amount  of water  requiring treatment or
        reduce the quantity  of water pumped to
        maintain a containment system.

    •    Re-injection of treated ground water can
        increase hydraulic gradients and saturated
        thickness in the aquifer being remediated,
        and block  plume movement.

-------
    •   Variations on the standard extraction well
        design, such as French drains, enhanced
        fracture zones,   well-point systems, and
        horizontal wells can increase  extraction
        effectiveness.

The most common enhancement technologies were
reinjection  and soil vapor  extraction, which are
used  at  six  sites  each.     At  the  Fairchild
Semiconductor  and  IBM-San  Jose sites,  both
enhancement technologies  are  used.    Treated
ground  water  was  reinjected   at  the   Harris
Corporation  and  Occidental  Chemical  sites.
However,  it is not considered an  enhancement
technology here because it was done solely for
disposal purposes, and the injection was  to deep
aquifers that are not hydraulically connected to the
aquifers being remediated.

The next  most frequently  used enhancement is
slurry wall  containment.   The  Sylvester/Gilson
Road and Western Processing sites are enveloped
by  slurry  walls  that  are not  keyed  into an
underlying  aquitard.  At Fairchild Semiconductor,
the most contaminated portion of the upper two
aquifers is enclosed by a slurry wall keyed into a
continuous  low-permeability layer.

French  drains  are  listed  as  an  enhancement
technology at the  Mid-South Wood Products site.
The extraction system  at this site includes  both
conventional wells  and wells  combined  with
French  drains.    French drains  were  added to
provide  an  improved hydraulic connection to the
fractured rock aquifer.

A  similar  concern  for  improving  hydraulic
communication  in fractured  rock exists  at  the
Black & Decker  site.   Here a single  extraction
well was drilled in an artificially enhanced  fracture
zone that was created using explosives.

Intermittent pumping is listed as an enhancement
at the GenRad site, because the extraction system
is turned  off for three months  every  winter.
However,  this is  done more  to prevent freezing
damage  to  the   system than  to  improve  the
efficiency of contaminant removal.

  SYSTEM DESIGN INFORMATION

The remaining columns of Table 2-2 provide a
checklist of commonly  used analytical techniques
for  the  design  of extraction systems.    Aquifer
testing  is  a basic  method of  determining  the
hydraulic   responsiveness  of  the  aquifer   to
pumping.  It is believed to have been used at all
but four of the sites. (The Ville Mercier site was
not treated in detail in this phase of the study, and
information about the design techniques used there
was not available.)

At  18  sites, some  form  of ground-water flow
modeling  was  used to help select locations and
pumping rates  of extraction wells. In most cases,
numerical  or  semi-analytical  computer  models
were used.

Some form of  travel-time analysis was used for at
least  ten  of the sites.   This analysis basically
consisted of estimating the time it would take for
the distant portion of the plume to be drawn into
an extraction well and was used as part  of  the
process for estimating  restoration  time  frames.
Details of the analysis were usually not explained
in site documents obtained for this study.  In a few
cases,  particle tracking or streamline-generation
techniques were  used to evaluate  the  flow  of
ground water to  extraction wells.  In other cases,
travel-time estimates were based on comparisons
of  the  extraction  well-pumping  rate  to  the
estimated plume  volume.

Numerical contaminant transport modeling appears
to have been used rarely.

Documents  reviewed  for   17  sites,  explicitly
mention  the importance of solute adsorption  to
aquifer  materials.  However, it  was not always
clear how this consideration was used in judging
the potential effectiveness of the extraction system.
In  some  cases,  the  estimated  travel  time  for
contaminants to  reach  the extraction wells from
remote  portions  of  the  plume  was  increased  to
account for adsorptive retardation. In other cases,
the estimate  of total  contaminant mass  was
adjusted to account  for  adsorption.   A  third
common approach was to increase the estimated
number of pore volumes of ground water that
would have  to  be  removed  to  complete  the
remediation.   The  overall  effect  of  all  three
methods is roughly equivalent

      OCCURRENCE OF NAPLs

The occurrence of contaminants as NAPLs at the
case-study sites was  of special interest in Phase  II.
In Phase  I, NAPLs were  identified as residual
                                                10

-------
sources of contamination at the sites where  they
were known or suspected to be present.  However,
conditions associated  with  their  presence  and
reasons for suspecting  it were  not discussed  in
detail.

Table  2-3 gives a summary  of issues associated
with  the  presence  of  NAPLs at the case-study
sites.

At most sites  studied, it was difficult to establish
NAPL  presence  conclusively.   The  exceptions
were  sites where  NAPLs  had  been  directly
observed and reported in monitoring wells or soil
samples.  Even though  NAPLs  are suspected,  to
some extent, at 20 of the 24 sites, they have been
directly observed at only 8.   Certain features  of
NAPL behavior in the subsurface make it possible
for  them to remain undetected by traditional  site-
investigation procedures. This is especially true  of
compounds having a density greater than that  of
water (DNAPLs).   Some of the more  important
aspects of DNAPL  behavior will  be  discussed
briefly in  Chapter 4.

At nine sites,  parties responsible for  remediation
acknowledge  that NAPLs are present.  At  three
others, it  is acknowledged that NAPLs may be
present.   Frequently, however,  site  information
contains  clues indicating  that  NAPLs  may be
present, even  though   this possibility  was  not
mentioned in  site  documents.    This  is  not
surprising  for  older sites, because the  issue  of
NAPLs was   not  emphasized  by  the  scientific
community until the early 1980s, and even now
the concept is  relatively  new.

Table 2-3 includes a column labeled  "Likelihood
of NAPL  Presence (1-5)".  Entries in  this column
give a rough quantification of NAPL likelihood on
a scale of 1 through 5.  An entry of  1 indicate that
the  site  probably does not  have  NAPLs.    A
likelihood of 5 was  assigned  only  when  NAPLs
have   been directly observed   or  the  parties
responsible for site remediation assert that they are
present.  Entries of 2, 3, or 4 provide a range  of
relative likelihoods between these extremes but do
not  have  precise  definitions  in   terms   of
quantitative site data.

Table 2-3 also lists several types of evidence that
were  used to  judge the  relative  likelihood  of
NAPL presence.   The most  conclusive is direct
observation.  Less conclusive, but still suggestive,
clues include the following observations:

    •   High concentrations  in the ground water
        compared to the aqueous solubilities of
        the compounds,

    •   Unusually deep (for DNAPLs) or shallow
        (for LNAPLs) concentration distributions
        that do not  seem to be  attributable to
        other hydrogeologic influences,

    •   Persistence of contamination in spite of
        the remediation efforts,

    •   Source  characteristics  or  methods  of
        waste disposal  that  would be likely to
        result in the presence of NAPLs  in the
        aquifer.

All of these circumstantial clues are relative, being
more or less persuasive depending on the degree to
which they  appear.  Ground-water concentrations
greater than 100 percent of solubility, for instance,
would be  considered very  strong  evidence of
NAPL presence,  whereas concentrations in the
range of  1  to  5  percent give a  questionable
indication.   The relative and cumulative nature of
these clues were considered in assigning likelihood
scores in the range of 1  through 4 in Table 2-3.

To  provide  insight into   the  importance  of
ground-water  concentrations  as an  indicator of
NAPL presence, a  column has been included in
Table 2-3 listing the highest reported concentration
as a percentage of aqueous solubility for each site.
In  several  cases,  concentrations  greater  than
100 percent of aqueous solubility were reported in
ground-water samples.  Although the co-solvent
effect is a possible explanation, this is most likely
to be an indication that the compound was present
in the sample in colloidal-size NAPL droplets.  It
was  considered   strong   evidence   for  NAPL
presence in  the aquifer.

The final  column  in  the  table  lists  the chemical
species for which the relative concentration in the
preceding  column was reported.
                                                 11

-------
to
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-------
                                          Chapter 3
                     SUMMARY OF REMEDIAL PROGRESS
In the first phase of the study,  four conclusions
were reached concerning the remedial performance
of the extraction systems at the sites studied.

1.   The ground-water extraction systems at most
     of the sites studied appeared to be achieving
     hydraulic   containment   of    aqueous
     contaminant plumes,

2.   Most  of   the  extraction  systems  were
     removing,   or   had  removed,  substantial
     quantities of contaminants.

3.   When extraction systems are first turned on,
     contaminant concentrations usually show a
     rapid initial decrease, but then tend to level
     off or decrease at a greatly  reduced rate.

4.   The data collected prior to  system  design
     and  during  operation  were  often   not
     adequate   to   fully   assess  contaminant
     movement and the response of the ground-
     water system to extraction.

The  information obtained in the  second  phase of
the  study   seems to  generally  confirm  these
conclusions.   However,  the collection  of  case
studies  contains  enough   variety to   provide
exceptions  to each  of the  general conclusions.
Table 3-1 gives a concise summary of the major
indicators  of  remediation  effectiveness at  the
case-study sites.

        PLUME CONTAINMENT

As   shown  in  Table 3-1,  containment  of  the
aqueous plume  appeared  to be effective  at 15 of
the  24 sites.   This judgment  was  made  by
comparing  the extent of  known  ground-water
contamination, based on ground-water monitoring,
to the  capture zone  of the extraction  system, as
indicated   by   water-level  measurements  in
monitoring wells and piezometers.

Containment effectiveness is listed as uncertain for
six  sites in  Table 3-1.   In  each  case, this is
because of a lack of enough site data on  which to
base a firm determination.  At the Du Font-Mobile
and General Mills sites, the delineation of capture
zones  was  uncertain,  because  there  were  not
enough piezometers on the downgradient side of
the extraction wells.  At Emerson Electric, Site A,
and Mid-South Wood Products, both the extent of
the ground-water contamination and the hydraulic
effects of the extraction system were unclear. At
Utah Power & Light, the main problem was the
difficulty  in determining the boundary  of  the
contaminant plume in the fractured rock aquifer.

It should be emphasized that both water-level and
water-quality  measurements  are  required  to
demonstrate  that   the  extraction  system   is
effectively containing  the  aqueous contaminant
plume.  Observation of water-quality trends alone
is insufficient.

At three of the case-study sites, the available data
indicated  that  hydraulic  containment  was  not
completely  effective.    These   sites   were  the
Savannah  River Site, Sylvester/Gilson Road, and
Tyson's Dump.

At  the Savannah  River  Site,  the contaminant
plume extends beyond the zone of influence of the
recovery system.   In the Phase  I  report,  it was
noted that the capacity of the recovery system did
not seem to be commensurate with the magnitude
of the contamination problem.   Since  1988,  the
total  pumping  rate  for  the system  has  been
increased from an average of 436 gpm to as much
as 550 gpm.  In  addition, new  extraction  wells
have  been  installed in  areas  that   were  not
previously being remediated. However,  it appears
that there  are still portions of the plume that are
not being captured.  Also, downward migration of
the plume has not been completely reversed.

At  the Sylvester/Gilson Road site, the  extraction
rates apparently  have not been  high enough to
maintain  inward   gradients around the   entire
periphery of the slurry wall that encloses the site.
In addition, observation of vertical gradients within
the enclosed area indicate that contaminants may
be escaping by vertical  migration to  lower aquifer
zones.   In response to these observations, new
extraction   wells   are   to  be   added to  the
ground-water recirculation system inside the slurry
wall.  Also, consideration is being given to
                                                13

-------

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increasing the rate at which treated ground water is
removed from recirculation and discharged outside
the wall.

The interim ground-water extraction system at the
Tyson's Dump site captures most, but not all, of
the solute  plume.   That is all  that  the interim
extraction  system  was  intended  to  do.    An
expanded extraction system designed for complete
hydraulic control of the solute plume  is presently
in the final stages of construction.

Table  3-1  lists  containment  effectiveness  as
uncertain  at six of the case-study sites.   This
judgment was generally reached because of lack of
information  about  either  the   extent  of  the
contaminant plume or the hydrodynamic conditions
generated by the extraction system.

At the Emerson Electric site, it was impossible to
judge  the  containment   effectiveness  of  the
extraction  system,  because  the extent of  the
contaminant  plume  was never  defined  and no
water-level measurements were reported.

Containment effectiveness is listed as uncertain for
the General Mills site, because the site documents
that were obtained for review do  not show enough
water-level measuring points to  support accurate
delineation of the capture  zone.  The extraction
system operators assert that the portions of the
plume  that exceed  the  cleanup  levels are  being
captured.  In the lower of the  two aquifers being
remediated,  however, concentrations in excess of
the  cleanup standards  are  consistently  being
detected  at  monitoring  wells  that appear  to be
outside  the  likely  zone  of  influence  of  the
extraction well.

At Site A, no water-level measurements have been
presented  to  support the  contention  that  the
recovery well has captured the contaminant plume.
The hydraulic design of the extraction  well seems
to  have   been  based  on  the  assumption  of
horizontal radial flow to the well.  There is no
indication that  the  effects  of  vertical flow  or
regional gradients were  considered.   The  only
indication of the actual hydrodynamic performance
of the well is the assertion, appearing  in the early
performance reports, that no drawdown could be
detected in any of the monitoring wells when the
extraction system was turned on.
Table 3-1 lists the containment effectiveness at the
Utah Power & Light site as uncertain, because the
available  site data do  not support an  accurate
delineation of the extent of the contaminant plume
in all  aquifer zones.   Water-level measurement
data indicate that the extraction system's capture
zone does include all  of the monitoring wells
currently reported to be contaminated.

Capture  effectiveness  at  the Mid-South Wood
Products site is listed as uncertain, because the
available  site documentation  does  not  indicate
either the extent of the contaminant plume or the
ground-water flow patterns induced in the aquifer
by the extraction system.

At the Du Pont-Mobile site,  no new information
on  the hydrodynamic effects  of the  extraction
system has been obtained since the first phase of
the  study.    The  potentiometric  surface  map
presented in the first case study appeared to show
that  the contaminant plume was entirely captured.
However,  some  uncertainty   was  cast  on this
conclusion by  some rough,   contaminant mass-
balance calculations, which  indicated  that  only
about half of the contamination approaching the
line  of extraction  wells could be accounted for by
the concentrations and flow rates being extracted.
It is  likely  that  the  discrepancy is  due  to
inaccuracies in estimating the contaminant flux in
the  plume.    But,  it  is   also  possible  that
contaminants are bypassing the extraction wells in
the deeper portions of  the  aquifer  that are not
monitored.

       AQUIFER RESTORATION
            EFFECTIVENESS

  CONTAMINANT  MASS REMOVAL

Table 3-1 lists the available estimates of the initial
contaminant mass and the mass removed to date
for each of the case-study sites. In most cases, no
estimate was available for the initial mass  in place.
Where such estimates were available,  they  have
often been proven wrong.

For  instance, at the Des  Moines TCE  site, the
representatives of the responsible parties  have, in
the  past,   contended  that   the  ground-water
contamination was caused by the former practice
of pouring contaminated sludges on the ground for
dust  control at the rate of 100 to 200 gallons per
                                                 15

-------
year.   Considering the maximum measured TCE
concentration in the sludge and the period of years
over which  this  practice was followed, the total
mass of TCE disposed of can be estimated at 50 to
90 pounds.  Influent concentration records for the
ground-water treatment plant, however, show that
more  than 9,100 pounds of TCE were removed
from  the  aquifer during  the first 9  months  of
operation.  By the  end of  1989, the total mass of
TCE  removed was estimated at  15,860 pounds.
This discrepancy highlights the obvious uncertainty
about the true nature of the contaminant source.

Another  example  is  the  Savannah  River Site,
where the initial estimate of contaminant mass in
place  was  based on  volume integration of  the
contaminant  concentrations   in  the   plume,   as
measured    by   the   extensive   ground-water
monitoring   system.      This   calculation   of
contaminant  mass  in  place  has  been  repeated
regularly at  the Savannah  River Site and used in
conjunction  with estimates  of the  quantity  of
contaminants removed  as  a means of monitoring
the  performance  of   the   extraction  system.
Experience with this procedure has shown that the
quantity  of contamination actually  removed  is
greater than the  estimated change in contaminant
mass  in  the aquifer.   The  recent discovery  of
DNAPL contamination  in the aquifer provides one
explanation for this discrepancy, and highlights the
difficulty of determining what is actually present
in the subsurface.

The estimates given in Table 3-1 for the mass of
contaminants removed by the extraction system are
expected to be more reliable than the estimates of
mass  in place.   In some  cases, the estimates  of
mass   removal  were   made  by  the  parties
responsible for the remediations.  However, most
of the estimates  were made as part of this study,
and were based on treatment plant influent records
presented in the case studies.

The  quantity of contaminant mass  removed is
presented in Table  3-1  as a measure of extraction
system  performance  because  it  represents   an
accomplishment  that   can   be   attributed
unambiguously to the system. In effect, however,
it seems to be a measure more  closely associated
with the magnitude of the problem than with the
degree of remedial success.   The two case-study
sites  that  appear  to  be  closest  to  successful
remediation,  Emerson  Electric  and Site A,  are
among the  three with  the  lowest  estimates of
contaminant mass removed.

CONTAMINANT CONCENTRATIONS

The last seven columns of Table 3-1 deal with the
concentration  of  an indicator compound (or a
composite contamination parameter)  that has been
selected  for  each site  to  serve  the  illustrative
purposes of the table. In many cases, the indicator
compound is also the primary contaminant at the
site,  but this is  not true in every case.   The
indicator compounds were chosen only  for use in
this table and have no official status as indicators
at the sites themselves.

The  maximum  reported  concentration  of  the
indicator compound, as listed in Table 3-1, was
culled from the site records made available for this
study.  In a few cases, a nearly complete record of
site-monitoring data was available, and was used
to identify  the  highest  reported  concentration.
More  often,  the concentration  listed was  the
highest mentioned either in text, tables,  or figures
in a remedial investigation  report  for the  site.
Higher concentrations may have been measured,
but were not reported  in the documents made
available for the case study.

At  three sites-Fairchild  Semiconductor,  Utah
Power   &   Light,   and   Mid-South   Wood
Products—the  maximum  reported  concentration
exceeded the aqueous  solubility  of the indicator
compound.  These  occurrences  were taken as a
strong  indication of the presence of NAPLs.

At  three other  sites-Ville  Mercier,  Occidental
Chemical, and Site A~the  maximum reported
concentration   was   the   initial   recovery
concentration.  For the first two sites, this was
probably because  the information collected for the
case studies  consisted mostly of summary reports.
If  a  complete  data  base  of  ground-water
monitoring  results  had  been available,  higher
concentrations  than   those  reported   for   the
treatment plant influent probably would have been
found.   At  Site  A, however, a  fairly complete
record of site-monitoring data was made available,
and   none   of   the   reported  monitoring-well
concentrations  were  as  high   as the  initial
concentration  reported  in  the  treatment  plant
influent.
                                                16

-------
 At several sites (particularly Utah Power & Light,
 Nichols Engineering,  and  GenRad)  the  initial
 recovery concentrations were very  low.  This is
 simply the  result of the  extraction  wells initially
 not being in  a high concentration portion of the
 plume. In each case, however, the extraction wells
 later  produced  at  higher  concentrations  as
 contaminants  were drawn toward them.

 One of the  general  conclusions drawn in the first
 phase  of  the  study  was that  ground-water
 extraction frequently produces a rapid initial drop
 in concentration and then levels out to relatively
 constant, or slowly  declining, contaminant levels.
 This  leveling out in concentration  reduction can
 result from  a number of factors and can,  in fact,
 reflect progress in cleaning  up  a plume.  Before
 any conclusions can be  drawn from looking at
 concentration  reduction trends, a thorough review
 of extraction  system design  should be performed.
 This  was  not  done  as  part  of this   study;
 consequently,  it is not possible to  determine if the
 plateaus observed and described in  the  following
 paragraphs  reflect a true limitation  or inefficient
 design of the extraction system or  sampling that
 does not represent the full impact of remediation.
 In  most cases,  the latter two occurrences are
 associated   with   dilution   of   contaminant
 concentrations at the monitoring point through one
 of the following mechanisms:

    •   Selective  pumping  of  wells  in  less
        contaminated areas at relatively high flow
        rates.

    •    The  well  is  constructed such that the
        water table  is quickly lowered below the
        contaminated zone.

    •    The outer edge of the  plume is cleaned
        up  and individual monitoring wells reflect
        a   continuing  decline   in   contaminant
        concentrations,  yet  monitoring  samples
        are taken from a point at which  ground
        water  from  all  extraction   wells  is
        combined.

This dilution  of samples with surrounding clean
ground water can mask the fact  that ground-water
is being cleaned up.

Assuming the above design limitations have been
addressed,   the   occurrence  of   a  stabilized
concentration can indicate that the clean  up of the
affected portion  of the aquifer is  limited by  the
kinetics of contaminant desorption or dissolution.
This could be due to  the release of contaminants
from  a  residual  source,   such   as  adsorbed
contaminants or a NAPL.

As shown in  Table 3-1, an attempt was made to
identify such  a  concentration plateau  at  each
case-study site.  This identification was  entirely a
matter of perception, and required  the application
of  subjective  judgment as to what constituted a
stabilized concentration  and  what did  not.   No
precise mathematical or statistical definition of the
stabilized concentration was used.  Where leveling
out of the concentration record  was  noted, it
frequently occurred in only part of the contaminant
plume,   or  in  the  extraction   wells.     The
identification  of  a  stabilized concentration in
Table 3-1 does not  constitute a prediction  that it
will persist for  a very  long time.   In  several
instances in which concentrations seemed to have
stabilized in the first phase case studies, additional
data  gathered  in  the   second  phase  showed
concentration  reductions.   Examples  of this  are
Monitoring Well 1-S at the  Amephenol site and
Extraction Well ERW-8 at Des Moines  TCE (see
Case Studies 1 and 3).

No concentration  plateau could be identified  for
some of the sites.  At the Du Font-Mobile and
Utah  Power  &  Light  sites, the  concentration
records showed too much variability  for plateau
identification.   At the Emerson Electric site,  the
initial high rate of concentration reduction was not
maintained, but the concentrations did continue to
decline  steadily  until  the  cleanup  goals  were
reached.  The concentration  records at Site A
showed a similar pattern,  at least for the selected
indicator compound.  At the Savannah River Site,
the record of concentration in the treatment plant
influent  showed  a  slow, but fairly  continuous,
downward trend with no obvious leveling off.  At
the  Mid-South   Wood  Products  site,    the
performance record was  too  short and  available
data too limited for trends to  be identified.

The initial  effort   at each   site   to  identify  a
concentration  plateau  focused on  the  treatment
plant  influent record  since  this  allowed  the
selection of a single point  for each site.  (This
does  not  mean   that  treatment   plant  influent
concentrations are the best measurement of pump
and treat performance as indicated above.)   In
10 cases, concentration plateaus were found in the
                                                  17

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influent records.  Where plateaus  could not be
found in the  influent records, either because the
records were unavailable or the concentrations did
not level off, records from individual wells were
scrutinized. Several instances of leveling off were
identified  in  monitoring  wells  or  individual
extraction wells, even though concentrations were
not stable for the extraction system as a whole.

Table 3-1 also lists both the approximate time after
the beginning of extraction when the concentration
plateau was reached and the remediation goal for
the indicator  compound, where  applicable.  The
cleanup goals for the  indicator  compounds were
listed here primarily  for  comparison with  the
maximum,   initial   recovery   and   plateau
concentrations.   The  cleanup  goal is listed  as
"N/A"   (not  applicable)  when  the   indicator
compound is  total VOCs or the remedial goal at
the  site  is  containment  rather  than  aquifer
restoration.   For  the  IBM-San Jose site,  the
cleanup goal for  Freon 113  is  different for the
different  aquifers,   and   because  no   point
measurements of concentration are listed, there is
nothing to compare.  At the Western Processing
site, the cleanup goal for TCE is  expected to be an
ACL that is to be specified in a future record of
decision.   For  the  Savannah  River Site,  the
remediation goals have not been specified in terms
of cleanup levels.

      PLUME AREA REDUCTION

Reduction of the area of a contaminated aquifer is
an alternative measure of restoration effectiveness.
Remedial progress is less commonly viewed in this
way,  probably  because this kind  of  evaluation
requires  mapping of  contaminant  concentration
values,  usually  in  the form   of  concentration
isopleths.  One reason such maps  are not more
widely relied on to  evaluate remedial progress is
that their  construction makes use of interpolated
concentrations  between the  monitoring   wells.
Consequently, the maps are partly the result of
interpretation  as  opposed  to  being  a  direct
measurement.   The advantage  of this  format,
however,  is  that  it shows  the  extent to which
aquifer restoration has  been partially achieved.

Plume mapping is  usually  done as part of the
remedial  investigation,  but  is  less  commonly
encountered  in  status reports  for  operating
remedial systems. At nine of the case-study sites,
contaminant plume  maps were available in the
operational data reports and have been presented in
the case studies.  In each of these cases, the maps
demonstrated  that  the  area  of  groundwater
contamination has been reduced for some or all of
the contaminants of concern. The sites for which
plume maps were produced are:

   •    Fairchild Semiconductor
   •    GenRad Corporation
   •    Harris Corporation
   •    IBM-Dayton
   •    IBM-San Jose
   •    Nichols Engineering
   •    Occidental Chemical
   •    Sylvester/Gilson Road
   -    Verona Well Field
   •    Western Processing

Of these sites, Fairchild Semiconductor and IBM-
San  Jose  show  the  most  marked reduction  in
plume size.

   USE  AND EFFECTIVENESS OF
  ENHANCEMENT TECHNOLOGIES

Supplemental  remediation  techniques  that  are
being used in addition  to basic ground-water
extraction  at the case-study sites, and that have the
potential to improve the ground-water remediation,
are referred to here as enhancement technologies.
These  techniques  are  not necessarily new  or
innovative.  Various enhancement technologies,
including  soil  vapor extraction,  reinjection, and
slurry wall containment are being used at  several
sites.  In addition, fracture enhancement was used
at the  Black   &  Decker  site.  Many  other
enhancement technologies are available that were
not used at the case-study sites.

     SOIL VAPOR EXTRACTION

At the  Fairchild  Semiconductor site,  soil vapor
extraction  was begun as a pilot system in October
1988 and  was expanded to full scale  in January
1989.   The system  consists  of 32 vapor wells
installed in  the dewatered  upper aquifer, in the
partially dewatered underlying aquifer, and in the
aquitard layer that separates them. Eight air inlet
wells have also been installed to facilitate vapor
sweeping  in the  deeper  zones.   By  September
1990, after approximately 1 year of operation, the
system had removed 14,700 pounds of VOCs.
                                                18

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contaminants is large, compared to
total of 1,500 pounds recovered in i
A pilot scale  system was tested in five  separate
areas of the IBM-San Jose site in 1990.   Both
LNAPL petroleum hydrocarbons and VOCs  were
successfully recovered.  As a result of the test, a
full-scale vapor extraction system was planned for
the site.

At Ponders Corner, a vapor extraction system was
installed around the contaminant source area in
December   1987.    The  system   consisted  of
10 vertical wells and 3 horizontal vapor extraction
headers.   When the system  was  turned on in
March  1988,  it  recovered  tetrachloroethylene
(PCE) at a rate  much higher than  had  been
foreseen by the  designers of the vapor treatment
system.  Consequently,  the system operated  only
intermittently,  with  interruptions for replacement
of the treatment system's activated carbon. During
the first month of operation, the system removed
360 pounds  of PCE  from the soil.  Operation of
the system was permanently discontinued in April
1988, by which time  it had recovered an estimated
775 pounds  of PCE.  Even though this mass of
                                  the estimated
                                 5 years by the
ground-water extraction  system, it had no obvious
effect on the PCE concentrations pumped by the
extraction wells.

At the Savannah River Site, a pilot scale vapor
extraction  system was tested in 1990. It recovered
a   total   of  approximately   1,500 pounds   of
contaminants in 3 weeks. As a result of the test, a
full-scale system has  been proposed.

A soil vapor extraction  system   has  been  in
operation in the  Thomas Solvent Raymond Road
portion of the  Verona Well Field site since 1987.
It consists of 23 PVC wells of 2-inch and 4-inch
diameter. After approximately 1 year of operation,
the   system   had   removed   an   estimated
45,000 pounds of VOCs from  the  vadose zone.
However, the rate of removal had fallen off to less
than 10 pounds per day, and the soil remediation
goals had not been met.  Several reasons were put
forward by  the system operators to explain  this.
They included many of  the  same effects   that
impede the restoration of aquifers by ground-water
extraction  systems.   For instance, it was pointed
out that VOC  concentrations had been reduced to
low  levels in the soil  vapor so that  continued
pumping resulted in low rates of mass extraction.
The  rate of mass transfer from residual LNAPL
globules  to  the surrounding  soil vapor   had
apparently  been  reduced  because  the  smaller
globules, with their greater ratios of surface area to
volume,   had  been   exhausted.     Also,  the
concentrations of volatile constituents within the
residual  LNAPL  were  reduced,  so  that  they
volatilized at lower rates.  Finally, it was pointed
out that  the  majority  of  the  vapor  flow in the
vadose zone was following preferential flow paths,
a situation that was exacerbated by the desiccation
of the soil in these areas.

   GROUND-WATER REINJECTION

Reinjection  has  been  tried at  several of the
case-study sites.  As reported in the first phase of
the study, reinjection wells were used briefly at the
IBM-Dayton  site  until their effectiveness was
destroyed by clogging.  The new extraction system
at IBM-Dayton uses spray irrigation as a form of
ground-water reinjection primarily to dispose  of
the treated   water  from  the  extraction  wells.
However, the spray field is  upgradient  of the
contaminated portion of the unconfined aquifer and
may also increase the rate  of  groundwater flow
toward the extraction wells.

Reinjection   is   also   being   used  at   the
Sylvester/Gilson   Road  site  and   at  Western
Processing.   In  both  cases,  the reinjection  is
through trenches rather than wells.  Even so,  there
were problems with clogging of the trenches due
to iron precipitation at Sylvester/Gilson Road. The
ground-water treatment system, which came on
line in 1986, includes iron removal, and no further
problems with iron clogging  are expected.  At
Western Processing, there has been no indication
of any problems with the reinjection trenches.

At  Fairchild  Semiconductor,   a   system  of
reinjection  wells  was put  into operation  in
September 1990.  Their installation was preceded
by  pilot  testing,  which  apparently indicated
success.  As  yet, there has been no indication of
the success of the full-scale system.  A system of
reinjection wells  is also planned for the  nearby
IBM-San Jose site.

   SLURRY WALL CONTAINMENT

Slurry  walls are  being used at the  Fairchild
Semiconductor,    Sylvester/Gilson   Road,   and
Western Processing sites.  At Fairchild, the wall
was  constructed  only around  the  most  highly
contaminated portion of the plume to isolate the
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source areas.  It was completed through the two
uppermost aquifers  and keyed into a  continuous
clay layer.   Ground-water extraction  within the
wall has resulted in significant aquifer dewatering,
and  permitted  soil  vapor  extraction  to  be
conducted at depths  below the normal water table.

At Sylvester/Gilson Road, the slurry wall encloses
nearly  the entire contaminant plume, but it is not
keyed  into  a  continuous underlying aquitard.
Consequently, the containment effectiveness of the
wall is highly dependent on maintenance of inward
hydraulic gradients.  It appears that the rate of net
ground-water withdrawal in the enclosed area has
not been high enough to produce inward gradients
everywhere.  Contamination  is also thought to be
escaping by  vertical  flow  into  the  underlying
bedrock in the  interior portion of the site.

The slurry wall at the Western Processing site also
depends heavily on  hydraulic gradient control for
its  effectiveness.    A  fairly  elaborate gradient-
monitoring   system  is  used  to  ensure   that
contamination  does not escape under the  wall.
This system is probably  effective for dissolved
constituents. However, if  DNAPLs were present,
which  has  not been shown to be the case, the
gradients  being  maintained  across   the  wall
probably would not prevent their  migration to
lower aquifer zones.

     FRACTURE ENHANCEMENT

The ground-water extraction system at the Black &
Decker site  uses an artificially created, enhanced
fracture zone  to improve the effectiveness of
extraction.  It is probably due to this zone that the
system  seems   to  provide  effective   plume
containment. DNAPLs have not been shown to be
present at this site. However, if they were present,
the deep fracturing  produced when the enhanced
fracture zone was created might  permit them to
penetrate more deeply into the bedrock than they
would  otherwise have done.

        UPDATE ON SITE  DATA
            REQUIREMENTS

In the summary of the first phase of the study,
considerable attention was  paid to  the types of site
information necessary for the design and operation
of effective ground-water extraction systems.  The
emphasis in that discussion was on the design and
operation  of systems to control  and remediate
plumes of dissolved contaminants.  The new case
studies and updates developed in the second phase
tend to reinforce the observations made in the
original study.    In  addition, with  the  present
emphasis  on NAPLs, some  of  the  information
requirements take on new importance.

It   has   been   observed   that   a   conclusive
determination  of the  presence  or  absence  of
NAPLs is often difficult.  At many  of  the sites
where  circumstantial evidence  suggested  that
NAPLs were likely to be present, no confirmation
in  the  form  of direct observation has  been
forthcoming.     Considering   the   important
implications that  the occurrence of  NAPLs can
have, it is obviously desirable to obtain  the site
data that would be  most helpful in reaching the
correct determination.

In this section, examples will be selected from the
new site information gathered in the second phase
of the study, to illustrate  the importance of various
types of field data with respect to the selection and
design of ground-water remediation systems. The
usefulness of this information in the search for
NAPLs will also be  discussed.

 HYDROGEOLOGIC  INFORMATION

               Stratigraphy

For   design  of  a   successful  ground-water
remediation  system, it is important to know the
number of aquifers involved and  the degree of
hydraulic  interconnection between  them.    At
several of the case-study sites, the ground-water
extraction system was installed in more  than one
aquifer. At  sites like Fairchild Semiconductor and
IBM-San Jose,  the sand and gravel aquifers were
clearly  separated by layers  of  silt and  clay,
although these layers were not always continuous.
At these sites, each of the contaminated aquifers
had its own set of extraction wells, which could be
operated more or  less independently.

The contaminant plume at the Occidental Chemical
site occurs in an upper aquifer that is divided into
three  permeable  zones  with partial  hydraulic
interconnection.   Here,  some of  the  extraction
wells are screened  in more  than one zone, and
pumping from a well hi one zone creates hydraulic
gradients  in other  zones  as well.    Even  so,
distinctions  can be made between the behavior of
                                                20

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the plume in  the  separate zones.   For instance,
incomplete  hydraulic  containment  has  been
observed in the deep zone during certain periods
of high-volume pumping from nearby water-supply
wells.  This can only be distinguished because the
monitoring system has  been designed  to  permit
observations in the individual zones. In contrast,
the monitoring system at the Du Font-Mobile site
has  not  been designed  to distinguish between
zones. As a result, there are persistent questions
about the effectiveness of plume capture.

Stratigraphy may also influence the movement and
detectability  of DNAPLs.    When  downward
moving   DNAPLs   arrive  at  a   layer   of
lower-permeability material, they may be unable to
penetrate them. The nonaqueous liquid may then
pool on top of the low permeability layer and flow
laterally in the direction of dip. If the stratigraphic
information  identifies such a situation,  it may
provide an opportunity to sample the DNAPL and
perhaps even to control its migration.

           Aquifer Properties

An understanding of the hydraulic properties of the
aquifer is very important for the design  of  the
ground-water extraction  system.  An  interesting
example  of  this is the  Western Processing site,
where a system consisting of many low-capacity
shallow wells was used to concentrate the capture
zone  in  the  highly  contaminated shallow soils.
This was done because it was recognized that  the
underlying soils had higher hydraulic conductivity
and would yield large quantities of relatively clean
water to  a system  composed  of  a  few  high-
capacity extraction wells.

In dealing with NAPLs, several other hydrologic
properties of  the  aquifer  materials besides  the
saturated  hydraulic  conductivity  are  important.
These  include  the  porosity and  the  complex
relationships between the degree of saturation,  the
capillary pressure, and the relative permeability for
the wetting and nonwetting fluids.  A consequence
of these additional porous matrix flow properties is
the phenomenon of residual saturation for NAPLs.
This is the degree of saturation below which  the
NAPL is, for practical purposes, immobile.  These
properties can be measured in the laboratory, and
some  analytical   and    numerical   modeling
techniques are available  for using  them to predict
the  behavior  of  NAPLs.    However,   these
techniques  are  not yet  developed  to  the stage
where they are considered reliable for widespread
practical application. More commonly,  grain size
analysis may be used to obtain rough predictions
of the NAPL holding and transmitting capacity of
the soil (Mishra, et al., 1980) (Carsel and Parrish,
1988).

       Potentiometric Gradients

The ability of an extraction system to capture and
remove contaminated ground  water  will depend
partly  on  the  potentiometric  gradients that  it
creates in comparison to the external gradients.  A
simple  manifestation  of  this  relationship  is
illustrated  in  the  case study for the  Nichols
Engineering site. The extraction system designers
for this site have provided graphical depictions of
several   alternative   capture   zone   estimates,
depending  on  the  magnitude of  the regional
gradient.

A  somewhat  less  obvious  illustration  of  the
importance of the regional gradient is provided at
the Sylvester/Gilson Road site. Here, the regional
gradient  has  been   strong  enough  to cause
contaminated ground water to flow out from under
the  slurry  wall  containment system  on   the
downgradient side of the site.  In response to this
problem, it may be necessary to increase the rate
of net  ground-water withdrawal from within  the
area enclosed by the wall.

The application  of horizontal  gradients by  the
ground-water extraction system usually has little
effect on the movement of DNAPLs, which  are
primarily governed  by gravitational forces.   In
some cases,  changes in vertical  gradients may
reinforce or counteract the buoyancy forces and
affect the vertical  movement  of the free phase.
However, this cause and effect relationship would
probably be difficult  to detect, and the present
study provides no examples of it.

             CONTAMINANT
       CHARACTERISTICS AND
             DISTRIBUTION

             Identification of
              Contaminants

An important step in evaluating the likelihood of
NAPLs is the identification of the compounds that
are present at the site and then- potential to persist
                                                21

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in the nonaqueous phase.  Creosote, toluene, and
the  chlorinated ethenes  and  ethanes  are  the
contaminants that were most commonly found as
NAPLs  in this  study.   Other compounds with
higher  aqueous  solubility,  such  as  acetone,
tetrahydrofuran, and 1,4-dioxane, are less likely to
be found as NAPLs.

The  solubilities of the compounds should be kept
in mind when evaluating site data.  At some of the
case study sites, analytical data for ground-water
samples were  reported that indicated  constituent
concentrations higher than the solubility of  the
compounds.  There was usually no indication that
this  had been noticed by the  site investigators.
These  occurrences  should be  interpreted  as a
strong indication of the presence of NAPLs.

Attention should also be paid to the possibility that
several  compounds that  are  miscible  with one
another may be present as a NAPL. This is a very
common at disposal sites for used solvents.  The
properties of a  multicomponent NAPL may be
significantly different from the properties of  the
individual constituent compounds.  One effect is
that  the partitioning of each individual compound
between  the NAPL  and the  ground  water will
reduce the effective  aqueous  solubility for each
compound.

Another effect is that compounds that are  more
dense than water in pure form may be caught up
in a NAPL that floats. For instance, an LNAPL is
present at the Verona Well Field site consisting of
chlorinated  ethenes  and ethanes  mixed  with
benzene, xylene, and toluene.  The proportions of
this  mixture result in a NAPL that floats, even
though  several  of the  compounds  of greatest
concern  would  normally  be   expected  to  form
DNAPLs.   A  similar situation  exists  at    the
Mid-South   Wood   Products   site,   where
pentachlorophenol  (PCP), a  compound  with a
specific gravity of approximately  2.0,  was mixed
with a light carrier oil for use in wood treatment.
The  ground-water monitoring data show extensive
PCP  contamination,   but  do  not mention  the
presence or nature of the carrier oil. Nonetheless,
the extraction system is designed to deal with  the
resulting LNAPL.
    Contaminant Distribution  and
              Concentration

Concentrations  in both  the soil  and the ground
water are important clues to the likelihood of
NAPL presence.    Ground-water concentrations
close  to or greater than  solubility indicate a high
likelihood of NAPLs.  However, as has frequently
been  noted,  concentrations that are  less than 10
percent  of solubility  may also  indicate NAPL
presence (Feenstra and Cherry, 1988; Huling and
Weaver,  1991).   At  the  case  study sites with
acknowledged NAPLs,  the range of maximum
detected ground-water concentrations was from 4.1
percent to over 100 percent of solubility.

Concentrations measured in soil samples may also
be a good indicator of NAPL presence.  High soil
concentrations were noted in the update of the
Verona Well Field case study and interpreted as an
indication  of  NAPL   presence.    When  soil
concentrations  are   interpreted   in  this   way,
allowance must be made for the partitioning of the
contaminant between the adsorbed, dissolved, and
vapor phases  that  are  included  in  the sample
(Feenstra, et al., 1991).

The  vertical   distribution   of   contaminant
concentrations may also be an indicator of NAPLs.
Sampling  from a well  cluster in the  suspected
source area  at the  IBM-Dayton  site showed
contaminant concentrations increasing with depth.
This was one of the  clues used to support the
contention of DNAPL contamination at this  site,
where there has  been no direct observation of
DNAPLs.

       Sorption Characteristics

The  importance  of contaminant  sorption  was
emphasized  in  the  first phase study, both as a
retarding mechanism to  aquifer restoration and as
a form  of residual contaminant source.  These
effects may complicate the determination of NAPL
presence on the basis of resistance to remediation,
because both adsorbed contaminants and NAPLs
can prolong the aquifer-restoration process.

For instance,  at  the  Ponders  Corner  site, the
concentrations in the contaminant  plume have been
relatively  steady over a period of approximately
6 years.   This is  an  indication of a residual
contaminant source, which could be due  to NAPLs
or adsorbed contamination.   If  the soil did not
                                                22

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have high sorption potential, more suspicion would
be directed  to  NAPLs.  However, at Ponders
Comer, much of the contamination is believed to
be adsorbed  to the soil in a heavily contaminated
till layer. This does not rule out NAPLs, but does
tend  to cloud the evidence for them.

            Identification of
         Contaminant Sources

It has already been noted in this summary that a
high  proportion of the known  NAPL sites in the
case  studies were the result of  leakage  from
chemical storage and handling facilities and the
direct disposal of solvents in the ground. Where
these practices are known to have taken place, the
likelihood of NAPLs resulting seems to be high.
                                              23

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                                       Chapter 4
              OCCURRENCE  AND  IMPLICATIONS  OF NAPLS
NAPLs have been directly observed at eight of the
case-study sites and their presence is suspected at
several others.   This chapter  will discuss the
waste-handling  methods  that led to release of
NAPL contamination  at these sites, the signs that
revealed their presence, and their implications for
aquifer remediation.

  WASTE HANDLING  PRACTICES
          LEADING TO  NAPL
          CONTAMINATION

The  following  table  enumerates  the known or
suspected sources of the NAPLs at the nine sites
where they are acknowledged to be present:
In  such  cases,  site  investigation  procedures
intended to detect the presence of NAPLs should
generally be implemented. At  some of the case-
study sites, compounds that, by themselves, would
be expected to sink were found to  be present as
LNAPLs.  At Verona Well Field, for instance,
chlorinated solvents are floating as LNAPLs on the
water table because they are part of a mixture in
which toluene  is  a constituent of  a  DNAPL
dominated   by   the   dense  compound   1,2,3-
trichloropropane.

     IDENTIFICATION OF NAPL
              PRESENCE

Although the presence of NAPLs is acknowledged
at several of the sites, there are several others
IBM-Dayton
IBM-San Jose
Savannah River Site
Utah Power & Light
Verona Well Field
Ville Mercier
Mid-South Wood Products
Tyson's Dump
Western Processing
Suspected leaks or spillage from storage tanks
Suspected DNAPL leaks from storage tanks; known spill of
Shell Sol hydrocarbon
Leakage from liquid waste settling basin
Leakage from underground pipeline
Leakage from buried storage tanks
Dumping in abandoned gravel pit
Leakage from waste storage lagoon
Dumping hi abandoned sand pit
Dumping of liquid wastes
In six of the nine cases listed above, the problem
was caused by  faulty storage or handling  of the
nonaqueous liquids.    This  implies  that  the
problems could have been avoided in two-thirds of
the  cases by   better  design,  operation,  and
monitoring of the storage and handling facilities.
At the other three sites,  the NAPLs  were hi such
cases,  site investigation  procedures   toluene
predominates.   At Tyson's Dump,  on the other
hand, toluene  is  a  constituent of a  DNAPL
dominated   by   the  dense   compound
1,2,3-trichloropropane introduced by dumping of
waste liquids into pits as a means of disposal.
where they are uncertain or are  the subject of
contention.   Because of  their  elusive nature,
especially  for DNAPLs, it  is often  difficult to
prove beyond doubt that they are present; and, it is
even more difficult to prove their absence. Some
of the identifying signs  and clues found at the
case-study sites are discussed below.

          Direct Observation

NAPLs have been observed dkectly at eight of the
sites.   At  Verona  Well Field,  IBM-San  Jose,
Western   Processing, Tyson's Dump,  and the
                                            24

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Savannah River Site, NAPLS  were discovered in
ground-water samples.

In  the  first three cases,  the  contaminants  were
LNAPLs.   LNAPLs are  more  likely  to  be
discovered in this  way  because they are  often
present at greater than residual saturation  at, and
just above,  the  water table.   It is common to
screen monitoring wells across  the water table, and
if the LNAPL saturation of the soil is greater than
the residual saturation, it  can  flow into the  well.
Once the LNAPL has entered the well, it is likely
to be discovered during sampling.

DNAPLs are less likely to appear in ground-water
samples because of their ability to penetrate below
the water table.   By penetrating deeper into the
aquifer, they travel a greater distance through the
porous material and are, therefore, less likely  to be
encountered at greater than  residual  saturation.
Also,  because of their  propensity  for  vertical
movement,  they  are more  likely  to  spread
vertically  than laterally and are  less likely to be
intersected by  a monitoring well.  Furthermore, if
they do  enter a  well, they tend to sink to the
bottom where they  may  escape detection during
sampling. In  spite of these difficulties, DNAPLs
were  found  by  ground-water sampling  at the
Savannah River Site  and Tyson's Dump.

The movement of DNAPLs in the subsurface is
governed  primarily  by gravity and, where  their
downward movement is unobstructed, the depth of
penetration  depends  on   the  residual  holding
capacity of the aquifer materials and the volume
and rate of contaminant release.  In many cases,
the DNAPLs may not move laterally very far from
the original source area. This seems to be the case
at the IBM-Dayton site, where the residual source
area is localized  near the former solvent  storage
tanks.  This situation is expected to facilitate the
control of plume migration.

NAPLs may also be  directly observed staining or
flowing from soil samples, coating the outside of
drill rods (as at Utah Power & Light), or seeping
into  surface  water   bodies  (Mid-South  Wood
Products).

        High Concentrations in
    Ground-Water or Soil Samples

A strong indication that NAPLs may be present is
when   the   ground-water   samples    show
concentrations that are near the aqueous solubility
of the contaminant  At three of the  case-study
sites, ground-water concentrations greater than the
aqueous solubiUty were  reported.  These sites are
Fairchild Semiconductor, Utah Power & Light, and
Mid-South Wood Products. Fairchild is not a site
where  NAPLs have  been  acknowledged, but the
other  two are.   One  possible   explanation for
ground-water concentrations exceeding solubility
would be the co-solvent  effect,  but  this is not
likely  unless  the  concentration  of some  other
constituent is  extremely high.  The most  likely
explanation  is  that  NAPLs  were  present  in
colloidal form in the sample and  were not noticed
visually.    This  can  be  considered a strong
indication that NAPLs  are also present in the
aquifer. It is possible that, in some cases, NAPLs
are being removed with the ground water by the
extraction systems.

The   lack  of   any   measured  ground-water
concentrations close to solubility, however, is not a
good  argument for the  absence  of NAPLs.  At
several of the case-study sites where NAPLs are
acknowledged, the highest reported concentration
of the contaminant  in  question  is considerably
below   aqueous  solubility.      Examples  are:
IBM-Dayton  at 4.1  percent for  PCE, Savannah
River Site at 12 percent for TCE, and Verona Well
Field at 11.3 percent for PCE.  Several factors that
could  account  for  this  observation  include
reduction of effective solubility due to partitioning
of the compound between  water and a mixture of
nonaqueous  solvents, kinetic effects limiting the
rate of dissolution  of  the compound from the
NAPL, dilution by the flow of ground water in the
aquifer, and dilution during the sampling  process.
Because  of these  effects,  concentrations in the
range of 1 to 10 percent of aqueous solubility may
be high enough to lead to  the suspicion of NAPL
presence.

The detection  of high concentrations of potential
NAPL  compounds  in  soil   samples  can  also
indicate that NAPLs are  present.  In this case,
however,  the relationship  between  the measured
concentration and the likelihood of NAPL presence
is not as direct as it is for ground-water samples.
Analytical results  for soil samples indicate the
quantity of contaminant that was present in the
sample in all forms.  This includes the adsorbed
phase,  the vapor phase, dissolved constituents in
the soil  moisture,  and the NAPL phase.   By
invoking  the  assumption  of  linear equilibrium
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partitioning, Feenstra, Mackay, and Cherry (1991)
have  developed a  procedure  for assessing the
meaning of high contaminant concentrations in soil
samples. Using a procedure similar to this, it was
determined  that  high  concentrations  of  PCE
measured at the Thomas Solvent Annex portion of
the Verona  Well Field  site are an indication of
potential DNAPL contamination there.

        Depth of Contamination

Another indicator  of the  possible presence of
DNAPLs is the observation of high concentrations
at  greater  depths  in  the aquifer   than would
otherwise be expected in the absence of a strong
vertical gradient. This is one indicator that led to
the determination  of DNAPL presence at the
IBM-Dayton  site, where DNAPLs have not  been
directly observed.    At  the  Mid-South Wood
Products    site,   high   concentrations   of
pentachlorophenol also  have been  detected in the
deepest monitoring  well,  indicating  that   this
contaminant may have sunk deep into the bedrock
in DNAPL form.

At  the  Sylvester/Gilson  Road  site,  the highest
concentrations of toluene were detected near the
water table,  even  though there is a downward
component   of  ground-water  flow  that   has
transported  other contaminants to greater depth.
This, together with the high toluene concentrations
and  their resistance to  remedial efforts  lends
credence to the possibility that nonaqueous toluene
is present.

      Resistance to Remediation

The main  reason  for   the  determination   that
DNAPLs were present at the IBM-Dayton site was
the persistence of the contaminant plume and the
reappearance  of high  concentrations when  the
extraction system was turned off. It has frequently
been noted that contaminant concentrations tend to
increase when  pumping  is discontinued.   This
effect  is considered to  be an indication of  a
residual source of contaminants  in  the aquifer.
Such a source could be of several kinds.  It could
be due to continued leaching from the vadose zone
or leakage from the disposal area.  It could be due
to the  release  of adsorbed contaminants  from
highly sorptive aquifer materials or to a lessening
of the  hydrodynamic dilution after the extraction
wells  were  turned off.   At the IBM-Dayton site,
these effects were judged not to have the potential
to  explain  the  observed magnitude  of plume
resurgence, and  it was concluded  that DNAPLs
must, therefore, be present.

       IMPLICATIONS  OF NAPL
                PRESENCE

The discovery of NAPLs  at an aquifer restoration
site usually marks a turning point in the course of
the  remediation.    Aquifer  restoration  using
ground-water extraction alone is likely to be a very
slow   process  when   NAPLs   are  present.
Ground-water extraction is an  inefficient method
of removing  NAPL compounds from the aquifer
because,  by  definition,  it  removes   only  the
dissolved constituent. Thus, to remove  the NAPL,
it is necessary to wait for it  to dissolve so that it
can be removed  with the  ground water.  Because
most   NAPL-forming  compounds  have   low
solubility,  large  quantities  of  water  must  be
removed  to  extract  a  small  amount  of  the
contaminant.

In a  few instances,  the  pumping  of  free-phase
DNAPLs from ground-water extraction wells has
been  reported.  Globs of  creosote  have been
produced from extraction  wells at the Utah Power
&  Light  facility.   This  was  an  unexpected
occurrence  that required the  retro-fitting of phase
separation   equipment   in   the  ground-water
treatment process. Phase  separation has also been
provided for at the Mid-South Wood Products site
in  anticipation   of  free-phase  creosote   and
pentachlorophenol recovery from the ground-water
extraction system.

There are several removal technologies that have
been used with success at LNAPL sites.  These
include   soil   vapor  extraction,   free-product
skimming,  and enhanced biodegradation.  Both
vapor extraction  and free-product skimming were
used in the remediation of LNAPLs at the Verona
Well  Field site.   It was estimated that 45,000
pounds of LNAPL constituents were removed by
vapor extraction,  and 1,200 pounds by free-product
skimming.  This  should shorten the time required
for aquifer  restoration,  but  the  ground-water
concentrations are still above cleanup goals  and
further restoration is expected to be slow. Both of
these removal techniques are  also being applied to
the LNAPL Shell Sol spill area at the IBM-San
Jose site.
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Where  DNAPLs  are  concerned,   the  current
established removal technologies  are relatively
ineffective. Many new technologies are currently
being  tested  (e.g.,  use  of  surfactants,  water
flooding, air sparging) but none of them were used
at the case-study sites.

At four of the case-study sites  with acknowledged
DNAPL  contamination,  the  remedial  goal  is
containment of the solute plume rather than aquifer
restoration. This goal is usually feasible when the
DNAPL has   been  located  or there  are strong
indications that it is present, and it is immobile.
Containment  in  the area  where the  DNAPL is
located can  be  combined  with restoration  of
portions of the ground-water plume  that  have
migrated beyond the DNAPL zone.  If the residual
DNAPL source  is  limited to a relatively  small
area, the migration  of the resulting solute plume
may be fairly easy to control. At the IBM-Dayton
site, for example, it is expected that only one
extraction well located near the DNAPL source
area will  eventually be sufficient  to  control the
migration of contaminants.

At several of the case-study sites, there seemed to
be some resistance on the part of the responsible
parties  to  acknowledging   the  existence  of
DNAPLs, even though the evidence for  them is
fairly   strong.     This   resistance   may   be
counter-productive.    Failure  to recognize  the
implications of DNAPL presence can result in a
much  more costly and  less  effective remedial
action   hi  the long run  than  recognizing  the
presence of the DNAPL and determining a more
appropriate remedial strategy. In some cases (as at
IBM-Dayton)  the existence  of a DNAPL source
may only become apparent  after  an effort  at
aquifer remediation.
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*U.S. G.P.O.:1992-311-893;60269

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