DNAPL Site Evaluation


                                       3-150217
                                   February 1993

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                                             NOTICE


      The information in this document has been funded wholly Or in part by the United States Environmental
Protection Agency under contract 68-C8-0038 to Dynamac Corporation;  This report has been subjected to the
Agency's peer and administrative review and has been approved for publication as an EPA document. Mention
of trade names or commercial products docs not constitute endorsement or recommendation for use.

      All research  projects making conclusions or recommendations based  on environmentally related
measurements and funded by the Environmental Protection Agency are required to participate in the Agency
Quality Assurance Program, This project did not involve environmentally related measurements and did not
involve a Quality Assurance Project Plan.

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                                                  Ill
                                           FOREWORD


      EPA is charged by Congress to protect the Nation's land, air and water systems.  Under a mandate of
national environmental laws focused on air and water quality, solid waste management and the control of u>xit-
substances, pesticides, noise and radiation, the Agency strives to formulate and implement actions which lead to
a compatible balance between human activities and the ability of natural systems to support and nurture life.

      The  Robert  S,  Kerr Environmental Research Laboratory  is  the  Agency's center of expertise  fur
investigation of  ihe  soil and  subsurface environment.   Personnel  at the  laboratory are responsible  for
management of research programs to: (a) determine the fate, transport and transformation rates of pollutants in
the soil, the unsaturated and the saturated /«nes of the subsurface environment; (b) define the processes to be
used in characterizing the  soil and subsurface environment as a receptor of pollutants; (c) develop techniques for
predicting  the effect of  pollutants on ground  water, soil, and indigenous organisms;  and {dj define and
demonstrate the applicability and limitations of using natural processes,  indigenous  to soil and subsurface
environment, for the protection of this resource.

      Dense Noniqueous £hase Liquids (DNAPLs), such as some chlorinated solvents,  wood preservative
wastes, coal tar wastes, and pesticides, are immiscible fluids with densities greater than water.  As a result of
widespread production, transportation, utilization, and disposal of hazardous DNAPLs, particularly since 1940.
there are numerous DNAPL contamination sites in  the United States,  The potential for serious long-term
contamination of groundwater by DNAPL chemicals is high at many sites due to  their toxicity,  limited
solubility  {but  much higher than  drinking water limits), and significant migration  potential in'soil gas,
groundwaier. and/or as a separate phase.

      The goal of the EPA's Subsurface Cleanup and Mobilization Processes (SCAMP) research program is to
improve the effectiveness of remedial activities at sites with subsurface contamination from DNAPLs   This
report was prepared as part  of the SCAMP research program and is designed to guide and assist investigators
involved in the planning, implementation, and evaluation of DNAPL  site characterization studies.
                                              Clinton W. Hall
                                              Director
                                              Robert S, Kerr Environmental Research Laboratory

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IV
CONTENTS
Disclaimer ii
Foreword iii
List of Tables ix
iii
Ackowledgements
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CONTENTS

5.3.3 What thickness DNAPL must accumulate on the capillary fringe to cause
DNAPL to enter the saturated zone? 5-13
5.3.4 Will a finer-grained layer beneath the contamination zone act as a
capillary barrier to continued downward migration of DNAPL? What minimum
DNAPL column or body height is required to enter a particular capillary
barrier beneath the water table? 5-16
5.3.5 If DNAPL is perched above a finer-grained capillary barrier layer, what
size fracture or macropore will permit continued downward migration into
(or through) the capillary barrier? 5-16
5.3.6 What saturation must be attained at the base of a host medium for DNAPL to
enter an underlying finer-grained capillary barrier? 5-16
5.3.7 What upward hydraulic gradient will be required to prevent continued
downward migration of DNAPL? 5-20
5.3.8 What upslope hydraulic gradient will be required to prevent continued
downslope movement of DNAPL along the base of a dipping fracture or the
base of a comer layer underlain by a dipping finer layer? 5-24
5.3.9 What will be the stable DNAPL pool length that can exist above a sloping
capillary barrier or sloping fracture below the water table? 5-24
5.3.10 What will be the stable DNAPL height and area after spreading above an
impenetrable flat-lying capillary barrier? 5-24
5.3.11 What is the volume of DNAPL contained below the water table within porous
or fractured media? 5.-24
5.3.12 How do fluid viscosity and density affect the velocity and distance of
DNAPL migration? 5-27
5.3.13 What hydraulic gradient will be required to initiate the lateral movement
of a DNAPL pool or globule? 5.-27
5.3.14 How long does DNAPL in the saturated zone take to dissolve completely? 5-32
5.3.15 Given a DNAPL source of dissolved groundwater contamination, how do you
determine the movement of a dissolved plume? 5-32
5.3.16 Given a DNAPL source of vapor contamination in the vadose zone, how do you determine the
movement of the vapor plume? 5-34
5.3.17 What will be the composition of a dissolved plume associated with a DNAPL
source? 5r34
5.3.18 What is the equivalent mass/volume of DNAPL contained within a dissolved
groundwater plume? 5-36
5.3.19 What is the relationship between concentrations in soil gas and
groundwater? 5^40
5.3.20 Given a DNAPL source in the vadose zone, how can you evaluate the movement
of a vapor plume? What are the conditions that favor vapor transport away
from a DNAPL source in the vadose zone that would allow soil-gas monitorying 5-40
5.4 Numerical simulation of Immiscible Fluid Flow 5-44
5.4.1 Mass Balance Equations 5-46
5.4.2 Immiscible Flow Equations 5-46
5.4.3 Compositional Equations 5-46
5.4.4 Constitutive Relations 5-47
5.4.5 Model Utility 5-47
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VI

CONTENTS

Chapter 6 DNAPL Site Characterization Objectives/Strategies 6-1
6.1 Difficulties and Concerns 6-1
6.2 Objectives and Strategies 6-3
6.2.1 Regulatory Framework 6-3
6.2.2 Source Characterization 6-4
6.2.3 Mobile DNAPL Delineation 6-4
6.2.4 Nature and Extent of Contamination 6-4
6.2.5 Risk Assessment 6-5
6.2.6 Remedy Assessment 6-5

Chapter 7 DNAPL Site Identification and Investigation Implications 7-1
7.1 HistoricalSiteUse 7-1
7.2 Site Characterization Data 7-1
7.2.1 Visual Determination of DNAPL Presence 7-1
7.2.2 Inferring DNAPL Presence Based on Chemical Analyses 7-1
7.2.3 Suspecting DNAPL Presence Based on Anomalous Conditions 7-8
7.3 Implications for Site Assessment 7-8

Chapter 8 Noninvasive Characterization Methods 8-1
8.1 Surface Geophysics 8-1
8.1.1 Surface Geophysical Methods and Costs 8:1
8.1.2 Surface Geophysical Survey Applications 8-5
8.1.2.1 Assessing Geologic Conditions 8:5
8.1.2.2 Detecting Buried Wastes and Utilities 8-5
8.1.2.3 Detecting Conductive Contaminant Plumes 8-12
8.1.2 .4 Detecting DNAPL Contamination 8-12
8.2 Soil Gas Analysis 8-12
8.2.1 Soil Gas Transport andDetection Factors 8-12
8.2.2 Soil Gas Sampling Methods 8-17
8.2.3 Soil Gas Analytical Methods 8-21
8.2.4 Use of Soil Gas Analysis atDNAPL Sites 8-24
8.3 Aerial Photograph Interpretation 8-31
8.3.1 Photointerpretation of Site Conditions 8.-31
8.3.2 Fracture Trace Analysis 8-31

Chapter 9 Invasive Methods 9-1
9.1 Utility of Invasive Techniques 9-1
9.2 Risks and Risk-Mitigation Strategies 9-1
9.3 Sampling Unconsolidated Media 9-4
9.3.1 Excavations (Test Pits and Trenches) 9-4
9.3.2 Drilling Methods 9-7
9.3.3 Sampling and Examination Methods 9-7
9.4 Rock Sampling 9-14
9.5 Well Construction 9-22
9.6 Well Measurements of Fluid Thickness and Elevation 9-29
9.6.1 Inteface Probes 9-29
9.6.2 Hydrocarbon-Detection Paste 9-31
9.6.3 Transparent Bailers 9-31
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Vll
CONTENTS

9.6.4 Other Methods 9-31
9.7 Well Fluid Sampling 9-33
9.8 Assessing DNAPL Mobility 9-33
9.9 Borehole Geophysical Methods 9-33
9.10 Identification of DNAPL in Soil and Water Samples 9-38
9.10.1 Visual Detection of NAPL in Soil and Water 9-38
9.10.2 Indirect Detection of NAPL Presence 9-45
9.10.2.1 Effective solubility 9-45
9.10.2.2 Assessing NAPL Presence in Soil Based on Partitioning Theory 9-46
9.11 Integrated Data Analysis 9-46

Chapter 10 Laboratory Measurements: Methods and Costs 10-1
10.1 DNAPL Composition 10-1
10.1.1 Infrared(IR) Spectrometry 10-1
10.1.2Chromatography 10-7
10.1.2.1 Gas Chromatography/Mass Spectrometsy (GC/MS) 10-7
10.1 .2.2 High Performance Liquid Chromatography with
Mass Spectrome~(HPLC/MS) 10-9
10.2 Saturation 10-9
10.3 Density (Secific Gravity) 10-11
10.3.1 Displacement Methtod for Solids 10-11
10.3.2 Density of Liquids by Westphal Balance Method 10-12
10.3.3 Density of Liquids by Densitometer 10-12
10.3.4 Spcific Gravity Using a Hydrometer 10-12
10.3.5 Density of Liquids by Mass Detemination 10-12
10.3.6 Certified Laboratory Determinations 10-12
10.4 Viscosity 10-12
10.4.1 Falling Ball Method 10-12
10.4.2 Falling Needle Method 10-16
10.4.3 Rotating Disc Viscometer 10-16
10.4.4 Viscosity Cups 10-16
10.4.5 Certified Laboratory Analyses for Viscosity 10-16
10.5 interfacial Tension 10-16
10.5.1 Surface Tension Determination by Capillary Rise 10-16
10.5.2duNouyRingTensiometerMethod 10-16
10.6 wettability 10-19
10.6.1 Contact Angle Method 10-19
10.6.2 Amott Method 10-19
10.6.3 Amott-Harvey Relative Displacement Index 10-21
10.6.4 United States Bureau of Mines (USBM) wettability Index 10-21
10.6.5 Modified USBM wettability Index 10-21
10.6.6 Other Methods 10-21
10.7 Capillary Pressure Versus Saturation 10-21
10.7.1 Cylinder Methods for Unconsolidated Media 10-24
10.7.2 Porous Diaphragm Method (Welge Restored State Method) 10-24
10.7.3 Mercury Injection Method 10-24
10.7.4 Centifuge Method 10-27
10.7.5 Dynamic Method Using Hassler's Principle 10-27
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CONTENTS

10.8 Relative Permeability Versus Saturation 10-30
10.8.1 Steady State Relative Permeability Methods 10-30
10.8.2 Unsteady Relative Permeability Methods 10-30
10.9 Threshold Entry Pressure 10-30
lO.lOResidual Saturation 10-30
10.11 DNAPL Dissolution 10-31

Chapter 11 Case Studies 11-1
11.1 IBMDayton. Site. South Brunswick. N. J 11-1
11.1.1 BriefHistory 11-1
11.1.2 Site Characterization 11-1
11.1.3 Effects of DNAPL Presence 11-6
11.2 UP&L Site. Idaho Falls. Idaho 11-6
11.2.1 Br'efHistory 11-11
11.2.2 Site Characterization 11-11
11.2.3 Effects of DNAPL Presence 11-11
11.3 Hooker Chemical Company DNAPL Sites, Niagara Falls 11-15
11.3.1 Love Canal Landfill 11-15
11.3.2102nd Street Landfill 11-24
11.3.3 Hyde Park Landfill 11-28
11.3.4 S-Area Landfill 11 -33
11.4 Summary 1.1-33

Chapter 12 ResearchNeeds 12-1

Chapter 13 References 13-1

Appendix A: DNAPL Chemical Data

Appendix B: Parameters and Conversion Factors

Appendix C: Glossary
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LIST OF TABLES

Table 2-1. Contamination site investigation guidance documents.

Table 3-1. DNAPL types: sources, use, properties, contamination, and references.

Table 3-2. U.S. production of selected DNAPL chemicals in Ibs (U.S. International Trade Commission data).

Table 3-3. Frequency of detection of most common organic contaminants at hazardous waste sites (USEPA,
10/17/91; and Plumb and Pitchford, 1985).

Table 3-4. Production, physical property, and RCRA groundwater action level data for selected DNAPL
chemical.

Table 3-5. American Wood-Preservers' Association standards for creosote and coal tar products.

Table 3-6. Creosote production in the United States in 1972 by plant.

Table 3-7. Composition of creosote and coal tar, solubility of pure coal tar compounds, proposed RCRA
groundwater action levels, and prevalence in groundwater at wood-treating sites.

Table 3-8. Creosote and coal tar wood preserving sites on the Superfund list (modified from USEPA, 1989).

Table 3-9. Approximate molecular composition (%) and selected physical properties of Aroclor PCBs (from
Moore and Walker, 1991; Monsanto, 1988; and Montgomery and Welkom, 1990).

Table 4-1. Results of contact angle experiments conducted using DNAPLs by Arthur D. Little, Inc., 1981
(from Mercer and Cohen, 1990).

Table 4-2. Relationships between capillary pressure, gravity, and hydraulic forces useful for estimating
conditions of DNAPL movement (from Kueper and McWhorter, 1991; WCGR, 1991; and Mercer
and Cohen, 1990).

Table 4-3. Threshold entry (displacement) pressures in sediments with various grain sizes based on a (n cos
n ) value of 25 dynes/cm (0.025 N/m) Equation 4-5 (Hubbert, 1953).

Table 4-4. Laboratory and field residual saturation data for the vadose zone.

Table 4-5. Laboratory and field residual saturation data for the saturated zone.

Table 4-6. Vapor concentration and total gas density data for selected DNAPLs at 25°C (from Falta et al.,
1989).

Table 5-1. Conceptual models of DNAPL transport processes (reprinted with permission from ACS, 1992).

Table 5-2. Parameters and values used to calculate the relative order of transport velocity for TCA, TCE, and
MC in Chapter 5.3.15 (reprinted with permission from ACS, 1992).

Table 5-3. Equivalent DNAPL mass associated with some relatively well-documented organic contaminant
plumes in sand-gravel aquifers (modified from Mackay and Cherry, 1989).
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LIST OF TABLES
Table 5-4. Volumes of TCE required to produce a range of TCE concentrations in 884,000 ft3 of aquifer
assuming porosity = 0.3 and K^ = 0.126.

Table 5-5. Parameter values for assessment of TCE diffusion and nomenclature used in Chapter 5.3.20.

Table 6-1. Remedial options potentially applicable to DNAPL Contamination sites (modified from USEPA,
1992).

Table 7-1. Industries and industrial processes using DNAPLs and some DNAPL chemicals (modified from
Newell and Ross, 1992).

Table 7-2. Sources and types of site history information.

Table 7-3. Industrial site areas frequently associated with contamination.

Table 7-5. Characteristics of extensive field programs that can help indicate the absence of DNAPL (modified
from Newell and Ross, 1992).

Table 7-6. Implications of DNAPL presence on site assessment activities (see Figure 7-1) (modified from
Newell and Ross, 1992).

Table 8-1. Summary of various surface geophysical survey methods (modified from Benson, 1991; Gretsky et
al., 1990; O'Brien and Gere, 1988).

Table 8-2. Surface geophysics equipment rental, equipment purchase, and contract surveying estimated prices
in 1992 dollars not including mobilization or shipping fees.

Table 8-3. Applications of selected surface geophysical survey methods (modified from Benson, 1988).

Table 8-4. Surface geophysical methods for evaluating natural hydrogeologic conditions (modified from
Benson, 1991).

Table 8-5. Surface geophysical methods for locating and mapping buried wastes and utilities (modified from
Benson, 1991).

Table 8-6. Surface geophysical methods for mapping conductive contaminant plumes (modified from Benson,
1991).

Table 8-7. Surface geophysical methods for evaluating DNAPL site contaminations.

Table 8-8. Typical analytes and products detectable by soil gas surveys (modified from Tillman et al., 1990a).
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LIST OF TABLES

Table 8-9. Advantages and limitations of several soil gas analytical methods (modified from McDevitt et al,
1987).

Table 8-10. Conceptual models (longitudinal sections) of soil gas and groundwater contamination resulting
from NAPL releases (modified from Rivett and Cherry, 1991).

Table 8-11. Sources of aerial photographs and related information.

Table 9-1. Drilling and excavation costs in April, 1987 dollars (from GRI, 1987).

Table 9-2. Information to be considered for inclusion in a drill or test pit log (modified from USEPA, 1987;
Alleretal, 1989).

Table 9-3. Drilling methods, applications, and limitations (modified from Aller et al., 1989; GRI, 1987;
Rehm et al., 1985; USEPA, 1987).

Table 9-4. Borehole and well annulus grout types and considerations (modified from Aller et al., 1989; Edil et
al., 1992).

Table 9-5. Soil sampler descriptions, advantages, and limitations (modified from Acker, 1974; Rehm et al.,
1985; Alleretal., 1989).

Table 9-6. Comparison of trichloroethene (TCE) concentrations determined after storing soil samples in jars
containing air versus methanol; showing apparent volatilization loss of TCE from soil placed in
jars containing air (from WCGR, 1991).

Table 9-7. Advantages and disadvantages of some common well casing materials (modified from Driscoll,
1986; GeoTrans, 1989; and Nielsen and Schalla, 1991).

Table 9-8. Comparison of measured LNAPL thicknesses using water-detection paste, a clear bottom-loading
bailer, and an interface probe (from Sanders, 1984).

Table 9-9. Utility and limitations of borehole geophysical methods for site characterization (modified from
Benson, 1991; Rehm et al., 1985; Keys and MacCary, 1971).

Table 9-10. Summary of Test Results (Note: A = NAPL presence apparent based on visual examination; B =
NAPL presence suspected based on visual examination; and C = no visual evidence of NAPL
presence).

Table 9-11. Example effective solubility calculations (using Equations 9-3 and 9-4) for a mixture of liquids
with an unidentified fraction (DNAPL A) and a mixture of liquid and solid chemicals (DNAPL B).

Table 10-1. Analytical methods to determine chemical composition.

Table 10-2. Approximate relationship between wettability, contact angle, and the USBM and Amott
wettability indexes (from Anderson, 1986).

Table 10-3. TCLP regulatory levels for metals and organic compounds (Federal Register - March 29, 1990).
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Xll

LIST OF TABLES

Table 11-1. Chemical analysis of a creosote sample taken from a borehole drilled into bedrock at the UP&L
Site (from USEPA, 1989). All values in mg/L unless otherwise noted.

Table 11-2. Estimated quantities and types of buried wastes at the Love Canal, Hyde Park, S-Area, and 102nd
Street Landfills (Interagency Task Force, 1979).

Table 11-3. Chemical analyses of DNAPL sampled from the 102nd Street, S-Area, Love Canal, and Hyde Park
Landfills in Niagara Falls, New York (from OCC/Olin, 1990; Conestoga-Rovers and Associates,
1988a; Herman, 1989; and Shifrm, 1986).

Table 11-4. DNAPL distribution and properties in wells completed directly into the Love Canal landfill
(modified from Pinder et al, 1990).

Table A-l. Selected data on DNAPL chemicals (refer to explanation in Appendix A).

Table B-l. Listing of selected parameters, symbols, and dimensions.

Table B-2. Length Conversion Factors (multiply by factor to convert row unit to column unit),

Table B-3. Area Conversion Factors (multiply by factor to convert row unit to column unit).

Table B-4. Volume Conversion Factors (multiply by factor to convert row unit to column unit).

Table B-5. Mass Conversion Factors (multiply by factor to convert row unit to column unit).

Table B-6. Time Conversion Factors (multiply by factor to convert row unit to column unit.

Table B-7. Density Conversion Factors (multiply by factor to convert row unit to column unit).

Table B-8. Velocity Conversion Factors (multiply by factor to convert row unit to column unit).

Table B-9. Force Conversion Factors (multiply by factor to convert row unit to column unit).

Table B-10. Pressure Conversion Factors (multiply by factor to convert row unit to column unit).
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Xlll

LIST OF FIGURES

Figure 2-1. DNAPL chemicals are distributed in several phases: dissolved in groundwater, adsorbed to soils,
volatilized in soil gas, and as residual and mobile immiscible fluids (modified from Huling and
Weaver, 1991; WCGR, 1991).

Figure 2-2. DNAPL site characterization flow chart.

Figure 3-1. Specific gravity versus absolute viscosity for some DNAPLs. DNAPL mobility increases with
increasing density :viscosity ratios.

Figure 3-2. U.S. production of selected DNAPLs in millions of Ibs per year between 1920 and 1990.

Figure 3-3. Uses of selected chlorinated solvent in the U.S. circa 1986 (data from Chemical marketing Report
and U.S. International Trade Commission).

Figure 3-4. Location of wood treating plant in the United States (modified from McGinnis, 1989).

Figure 3-5. Pattern of U.S. PCB production and use between 1965 and 1977 (modified with permission from
ACS, 1983).

Figure 4-1. Various immiscible fluid distributions - Dark NAPL (Soltrol) and water in a homogeneous
micromodel after (a) the displacement of water by NAPL and then (b) the displacement of NAPL
by water (with NAPL at residual saturation). A more complex blob in the micromodel is shown
in (c). In (d), a pore body is filled with the dark non-wetting phase fluid; and is separated from the
wetting phase by a light intermediate wetting fluid.. The distribution of (dark) tetrachloroethene
(PCE) retained in large pore spaces between moist glass beads after being dripped in from above is
shown in (e). In (f), PCE infiltrating into water-saturated glass beads pooled in coarse beads
overlying finer beads and PCE fingers extend into the underlying finer bead layer. Figures (a) to
(d) are from Wilson et al. (1990); Figures (e) and (f) are from Schwille (1988).

Figure 4-2. Contact angle (measured into water) relations in (a) DNAPL-wet and (b) water-wet saturated
systems (modified from Wilson et al., 1990). Most saturated media are preferentially wet by water
(see Chapter 4.3).

Figure 4-3. Capillarity is exemplified by the pressure difference between the wetting fluid (water) and the non-
wetting fluid (air) at the interface within a tube that causes the wetting fluid to rise above the level
of the free surface (from Wilson et al., 1990); where Pnw is the pressure in the non-wetting phase
and Pw is the pressure in the wetting phase, Pa is atmospheric pressure.

Figure 4-4. Observed infiltration of tetrachloroethene into water-saturated parallel-plate cell containing
heterogeneous sand lenses after (a) 34 s, (b) 126 s, (c) 184 s, (d) 220 s, (e) 225 s, and (f) 313 s
(from Kueper and Find, 1991 a). Sands are: 1 is #16 Silica sand (k = 5.04E-10 m2,Pd = 3.77 cm
water); 2 is #25 Ottawa sand (k = 2.05 E-10 m2, pd = 4.43 cm water); 3 is #50 Ottawa sand (k =
5.26E-11 m2;pd = 13.5 cm water); and 4 is #70 Silica sand (k = 8.19E-12 m2;pd = 33.1 cm
water).

Figure 4-5. Capillary pressure as a function of liquid interfacial tension and contact angle (CA) (from Mercer
and Cohen, 1990).
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XIV

LIST OF FIGURES

Figure 4-6. Tetrachlomethene-water drainage Pc(sw) curves determined for seven sands of varying hydraulic
conductivity (from Kueper and Frind, 1991b).

Figure 4-7. (a) Unsealed and (b) scaled Pc(sw) relations for air-water, air-benzyl alcohol, and benzyl alcohol-
water fluid pairs in the same porous medium (from Parker, 1989).

Figure 4-8. Tetrachloroethene-water drainage Pc(sw) curves (shown in Figure 4-6) for seven sands of varying
hydraulic conductivity scaled using Equation 4-6 (from Kueper and Frind, 1991b).

Figure 4-9. (a) Hysteresis in two-fluid Pc(sw) relations whereby changes in capillary pressure depend on
whether the medium is undergoing imbibition (wetting) or drainage of the wetting fluid; in (b), the
main drainage and imbibition curves determined for a tetrachloroethene and water in #70 silica sand
are shown (from Kueper and McWhorter, 1991). Note the STO is the irreducible wetting fluid
content; smw is the nonwetting fluid residual saturation; sw is the wetting fluid saturation; and snw
is the nonwetting fluid saturation.

Figure 4-10. Sketches illustrating capillary trapping mechanisms: (a) snap-off and (b) by-passing (modified
from Chatzis et al, 1983; from Wilson et al, 1990).

Figure 4-11. (a) Water-NAPL relative permeability (modified from Schwille, 1988); (b) ternary diagram
showing the relative permeability of NAPL as a function of phase saturations (from Faust, 1985).

Figure 4-12 (a) Development of fingering and (b) advanced stages of fingering in Hele-Shaw cell models (from
Kueper and Frind, 1988).

Figure 5-1. (a) Spherical DNAPL globule at rest in a pore space within water saturated media; (b) a
nonspherical DNAPL globule at rest halfway through an underlying pore throat because the
downward gravity force is balanced by the upward capillary force; (c) centered within the pore
throat with equal capillary force from above and below, the DNAPL globule will sink through the
pore throat due to the gravity force; and, (d) if the DNAPL globule is primarily through the pore
throat, then the capillary and gravity forces will both push the globule downward (modified from
Arthur D. Little, Inc., 1982). Note that arrows represent the magnitude of capillary forces.

Figure 5-2. The effect of pore size and associated capillary pressure on DNAPL body height (modified from
Arthur D. Little, Inc., 1982).

Figure 5-3. The overall mapped outline and plan views of PCE migration from (a) an instantaneous release,
and (b) a drip release of 1.6 gallons of PCE which penetrated 2.0 and 3.2 m into the Borden sand,
respectively (reprinted with permission from ACS, 1992).

Figure 5-4. DNAPL volume retained in the vadose zone as a function of residual saturation, Sr, effective
porosity, n, and contamination zone volume.

Figure 5-5. Critical DNAPL height required to penetrate the capillary fringe as a function of pore radius given
a DNAPL density of 1300 kg/m3, an interfacial tension of 0.040 N/m, and a contact angle of 35
degrees.
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XV

LIST OF FIGURES

Figure 5-6. Critical DNAPL height required to penetrate a capillary barrier beneath the water table as a
function of pore radius given a DNAPL density of 1300 kg/m3, an interfacial tension of 0.040
N/m, and a contact angle of 35 degrees.

Figure 5-7. Sensitivity of critical DNAPL height to DNAPL density below the water table.

Figure 5-8. Pressure profiles in a fracture network for DNAPL at hydrostatic equilibrium (from Kueper and
McWhorter, 1991).

Figure 5-9. Comparison of Pc(sw) curves to determine the DNAPL saturation required in an overlying coarser
layer to enter an underlying finer liner.

Figure 5-10. Neglecting the capillary pressure gradient, the upward vertical hydraulic gradient required to prevent
DNAPL sinking in the saturated zone is a function of DNAPL density.

Figure 5-11. Considering both the density and capillary pressure gradients, the upward vertical hydraulic gradient
required to prevent DNAPL sinking through a capillary barrier is a function of DNAPL density and
the capillary pressure difference between the base of the overlying coarser layer and the threshold
entry pressure of the underlying finer layer.

Figure 5-12. Neglecting the capillary pressure gradient, the upslope hydraulic gradient required to arrest DNAPL
movement downslope along an inclined capillary barrier is a function of DNAPL density and
capillary barrier dip.

Figure 5-13. The stable DNAPL pool length above an inclined capillary barrier is a function of DNAPL density
and capillary barrier dip.

Figure 5-14. Fracture porosity equations for the slides, matches, and cubes fracture models where a is the
fracture spacing and b is the fracture aperture.

Figure 5-15. Fracture porosity is a function of fracture spacing and aperture.

Figure 5-16. The hydraulic gradient required to initiate lateral movement of a DNAPL pool or globule is
directly proportional to the threshold entry pressure of the host medium and inversely proportional
to pool length.

Figure 5-17. Hydraulic gradient, J, necessary to initiate DNAPL blob mobilization (at Nc*), in soils of various
permeabilities, for DNAPL s of various interfacial tensions, o. The upper curve represents the
gradient necessary for complete removal of all hydrocarbons (Nc*), with o = 10 dynes/cm (from
Mercer and Cohen, 1990; after Wilson and Conrad, 1984).

Figure 5-18. Dissolution time versus average interstitial groundwater velocity for four different TCE pool
lengths (reprinted with permission from ACS, 1992).
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XVI

LIST OF FIGURES

Figure 5-19. Measured and predicted dissolution characteristics for a mixture of chlorobenzenes: 37%
chlorobenzene, 49% 1,2,4-trichlorobenzene, 6.8% 1,2,3,5-tetrachlorobenzene, 3.4%
pentachlorobenzene, and 3.4% hexachlorobenzene (from Mackay et al, 1991). The water/CB
(chlorobenzene) volume ratio, Q, is the volume of water to which the chlorobenzene mixture was
exposed divided by the initial volume of chlorobenzene mixture.

Figure 5-20. Radial vapor diffusion after 1, 10, and 30 years from a 1.0 m radius DNAPL source for a vapor
retardation factor of 1.8 and diffusion coefficient of (a) 1.6xlO-6m2/sec, (b) 3.2xlO6m2/sec, and
(c) 4.8x10-6 m2sec.

Figure 5-21. Radial vapor diffusion after 1,10, and 30 years from a 1.0 m radius DNAPL source for a diffusion
coefficient of 3.2X1O6 m2/sec and vapor retardation factors of (a) 1, (b) 10, and (c) 100.

Figure 6-1. DNAPL site characterization flow chart.

Figure 7-1. DNAPL occurrence decision chart and DNAPL site assessment implications Matrix (modified from
Newell and Ross, 1992).

Figure 8-1. Comparison of station and continuous surface EM conductivity measurements made along the
same transect using an EM-34 with a 10 m coil spacing (from Benson, 1991). The electrical
conductivity peaks are due to fractures in gypsum bedrock.

Figure 8-2. Examples of stratigraphic interpretations using surface geophysical surveys: (a) ground-
penetrating radar (from Benson et al., 1982); (b) delineating of a bedrock channel by seismic
reflection (from Benson, 1991); (c) relationship of EM conductivity data and a sand/gravel channel
(from Hoekstra and Hoekstra, 1991); and (d) electrical resistivity profile of karst terrain (from
Hoekstra and Hoekstra, 1991).

Figure 8-3. Examples of geophysical survey measurements over buried wastes (from Benson et al., 1982
Technos, 1980): (a) a gradiometer magnetometer survey over metal drums buried in a trench
measuring approximately 20 ft by 100 ft by 6 ft deep; (b) a metal detector survey of the same
trench; (c) a ground-penetrating radar image showing three buried drums and (d) shallow EM
conductivity survey data at the Love Canal landfill showing the presence of large concentrations of
conductive materials and buried iron objects (i.e., drums) associated with chemical waste disposal
areas at each end of the landfill.

Figure 8-4. Examples of conductive plume detection using: (a) shallow and (b) deep electrical resistivity
surveys at an approximately 1 square mile landfill with values given in ohm-feet; and (c) a
continuous EM conductivity survey showing a large inorganic plume (center rear) (from Benson,
1991).

Figure 8-5. Soil gas concentration profiles under various field conditions (reprinted with permission ACS,
1988).

Figure 8-6. solubility vapor pressure, and Henry's Law Constants for selected DNAPLs (refer to Appendix
A).

Figure 8-7. Flowchart for conducting a soil-gas survey.
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XV11
LIST OF FIGURES
Figure 8-8. Soil gas probe sampling apparatus: (a) close-up view of syringe sampling through evacuation
tube; and (b) hollow soil gas probe with sampling adapter (from Thompson and Marrin, 1987).

Figure 8-9. Passive soil gas sampling apparatus (from Kerfoot and Barrows, 1987).

Figure 8-10. Correlations between halogenated solvent concentrations in shallow soil gas sampled between 3
and 8 ft below ground and underlying groundwater (a) chloroform along a transect perpendicular
to the direction of groundwater flow at an industrial site in Nevada (reprinted with permission from
ACS, 1987); and, (b) 1,1,2-trichlorotnfluoroethane (Freon 113) at an industrial site in California
(from Thompson and Marrin, 1987).

Figure 8-11. Aerial extent of soil gas and groundwater contamination derived from TCE emplaced below the
water table (Site A) and in the vadose zone (Site B) (from Rivett and Cherry, 1991). All values in
ug/L. Refer to Rivett and Cherry (1991) for details.

Figure 8-12. Longitudinal profiles showing the extent of soil gas and groundwater contamination parallel to the
direction of flow and through the source areas derived from TCE emplaced (a) below the water table
(Site A) and (b) in the vadose zone (Site B) (from Rivett and Cherry, 1991). All values in ug/L.
Refer to Rivett and Cherry (1991) for details.

Figure 8-13. Selected waste disposal features identified at a manufacturing site using aerial photographs taken
between 1965 and 1966.

Figure 8-14. Relationship between fracture traces and zones of subsurface fracture concentration (from Lattman
andParizek, 1964).

Figure 8-15. Preferential migration of contaminants in fracture zones can bypass a detection monitoring system
(fromUSEPA, 1980).

Figure 9-1. Defined areas at a DNAPL site (from USEPA, 1992).

Figure 9-2. Schematic diagrams of several boring methods: (a) screw and bucket augers, (b) solid stem auger,
(c) hollow-stem auger, (d) cone penetrometer test probe, (e) mud rotary, and (f) air rotary with a
casing driver (reprinted with permission, EPRI, 1985).

Figure 9-3. Schematic diagrams of a (a) split-spoon sampler, (b) thin-wall open-tube sampler, and (c) thin-wall
piston sampler used to obtain undisturbed soil samples; and of a (d) double-tube core barrel used to
obtain rock core (modified from Aller et al, 1989).

Figure 9-4. The drilling sequence for coring, hydraulic testing, and grouting through the Lockport Dolomite
utilized at the Occidental Chemical Corporation S-Area DNAPL site in Niagara Falls, New York
(from Conestoga-Rovers and Associates, 1986).

Figure 9-5. Overburden casing installation procedure utilized prior to drilling into the Lockport Dolomite at
the Occidental Chemical Corporation S-Area DNAPL site in Niagara Falls, New York (from
Conestoga-Rovers and Associates, 1986).
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xvm

LIST OF FIGURES

Figure 9-6. Typical packer/pump assembly used for bedrock characterization at the Occidental Chemical
Corporation S-Area DNAPL site in Niagara Falls, New York (from Conestoga-Rovers and
Associates, 1986).

Figure 9-7. Results of the Lockport Dolomite characterization program at the S-Area DNAPL site reflect
heterogeneous subsurface conditions (from Conestoga Rovers and Associates, 1988a). The non-S-
Area DNAPL detected at depth in Well OW207-87 has different chemical and physical properties
than S-Area DNAPL, and is believed to derived from another portion of the Occidental Chemical
Corporation plant site (Conestoga-Rovers and Associates, 1988a).

Figure 9-8. The measured thickness of DNAPL in a well may exceed the DNAPL pool thickness by the length
of the well below the barrier layer surface (after Huling and Weaver, 1991).

Figure 9-9. The measured DNAPL thickness in a well may be less than the DNAPL pool thickness by the
distance separating the well bottom from the capillary barrier layer upon which DNAPL pools.

Figure 9-10. DNAPL elevation and thickness measurements in a well are likely to be misleading where the well
is screened across a capillary barrier with perched DNAPL.

Figure 9-11. DNAPL that enters a coarse sandpack may sink to the bottom of the sandpack rather than flow
through the well screen and thereby, possibly escape detection.

Figure 9-12. DNAPL that enters a well from above may flow out of the base of the well screen and into the
underlying sandpack (or formation).

Figure 9-13. Sandpacks should be coarser than the surrounding media to ensure that the sandpack is not a
capillary barrier to DNAPL movement.

Figure 9-14. Purging groundwater from a well that is screened in a DNAPL pool will result in DNAPL
upcoming in the well (after Huling and Weaver, 1991).

Figure 9-15. The elevation of DNAPL in a well may exceed that in the adjacent formation by a length
equivalent to the DNAPL-water capillary fringe height where the top of the DNAPL pool is
undergoing drainage (invasion by DNAPL) (after WCGR, 1991).

Figure 9-16. Schematic diagram of borehole geophysical well logging equipment (from Keys and MacCary,
1976).

Figure 9-17. Examples of borehole geophysical logs: (a) six idealized logs (from Campbell and Lehr, 1984);
(b) a gamma log of unconsolidated sediments near Dayton, Ohio (form Norris, 1972); and (c) an
idealized electrical log (from Guyod, 1972).

Figure 9-18. Sequence of NAPL detection procedures utilized by Cohen et al.,(1992).

Figure 9-19. Summary of NAPL detection method results (from Cohen et al, 1992).
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XIX

LIST OF FIGURES

Figure 9-20. OVA concentrations plotted as a function of NAPL type and saturation (from Cohen et al, 1992).
OVA measurements shown as 1000 ppm are actually > 1000 ppm. Dissolved contaminant
samples are treated at 0% NAPL saturation samples.

Figure 9-21. Relationship between measured concentration of TCE in soil (Ct) and the calculated apparent
equilibrium concentration of TCE in pore water (Casw) based on: K^ = 126, bulk density (Pb) =
1.86 g/cm3; water-filled porosity (nw) = 0.30 air-filled porosity (na) = 0 and three different values
of organic carbon content (f^) (from Feenstra et al., 1991 ). NAPL presence can be inferred if
Casw exceeds the TCE effective solubility

Figure 10-1. Use of a separator funnel to separate immiscible liquids (modified from Shugar and Ballinger,
1990).

Figure 10-2. Flow chart for analysis of complex mixtures (from Devinny et al., 1990).

Figure 10-3. Schematic of a gas chromatography (modified from Shugar and Ballinger, 1990).

Figure 10-4. Modified Dean-Stark apparatus for extracting NAPL from soil or rock sample (modified from
Amyxetal, 1960).

Figure 10-5. Schematic of a Westphal balance (modified from Shugar and Ballinger, 1990).

Figure 10-6. Use of a glass hydrometer for specific gravity determination (of a DNAPL with a specific gravity
of approximately 1.13 at the sample temperature).

Figure 10-7. Schematic of a falling ball viscometer. Viscosity is measured by determining how long it takes a
glass or stainless steel ball to descend between the reference lines through a liquid sample.

Figure 10-8. Use of a viscosity cup to determine kinematic viscosity. Liquid viscosity is determined by
measuring how long it takes for liquid to drain from a small hole at the bottom of a viscosity cup.

Figure 10-9. Determination of surface tension by measuring capillary rise and contact angle (modified from
Shugar and Ballinger, 1990).

Figure 10-10. Use of a contact angle cell and photographic equipment for determination of wettability. A small
DNAPL drop is aged on a flat porous medium surface under water.

Figure 10-11. USBM wettability measurement showing (a) water-wet, (b) NAPL-wet, and (c) neutral conditions
(reprinted with permission from Society of Petroleum Engineers, 1969).

Figure 10-12. Schematic of a P^SW) test cell (modified from Kueper et al., 1989).

Figure 10-13. Schematic of the Welge porous diaphragm PC(SW) device (modified from Bear, 1972; and, Welge
and Bruce, 1947).
Figure 10-14. Schematic of a centrifuge tube with graduated burette for determining PC(SW) relations (modified
from Amyx et al., 1960; and Slobod et al., 1951).
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LIST OF FIGURES

Figure 10-15. A schematic of Hassler's apparatus used for PC(SW) and relative permeability measurements
(modified from Bear, 1972; and Osoba et al, 1951).

Figure 11-1. Dayton facility location map showing public water supply well SB 11 (from Robertson, 1992).

Figure 11-2. TCA distribution in the Old Bridge aquifer in January 1978-March 1979 associated with three
facilities near SB 11 (from Roux and Althoff, 1980).

Figure 11-3. TCA distribution in the Old Bridge aquifer in January 1985 associated with IBM facilities (Plant A
in Figure 9.2) (from Robertson, 1992).

Figure 11-4. TCA distribution in the Old Bridge aquifer in June 1989 (from Robertson, 1992).

Figure 11-5. Structure and extent map of Woodbridge clay (from U.S. EPA, 1989).

Figure 11-6. History of TCA ad PCE variations in extraction well GW32, six-month average concentrations in
ppb (from U.S. EPA, 1989).

Figure 11-7. History of TCA and PCE variations in extraction well GW168B, six-month average
concentrations in ppb (from U.S. EPA, 1989).

Figure 11-8. History of TCA and PCE variations in extraction well GW25, six-month average concentrations
in ppb (from U.S. EPA, 1989).

Figure 11-9. Locations of the Utah Power and Light Pole Yard site in Idaho Falls, Idaho (from USEPA, 1989).

Figure 11-10. East-west geologic cross section across a portion of the Utah Power and Light Pole Yard site
(modified from USEPA, 1989).

Figure 11-11. Locations of waste disposal sites in Niagara Falls, including the Love Canal, 102nd Street, Hyde
Park, and S-Area landfills (from Cohen et al., 1987).

Figure 11-12. A schematic geologic cross-section through the Love Canal landfill (from Cohen et al., 1987).

Figure 11-13. Example boring and laboratory log of soils sampled adjacent to the Love Canal landfill (from
New York State Department of Health, 1980).

Figure 11-14. Locations of well completed directly into the Love Canal landfill. The original canal excavation
is shaded, and is enclosed by an outer line designating the approximate landfill limits.

Figure 11-15. Areal distribution of DNAPL and chemical observations at Love Canal (north half to the left;
south half to the right).

Figure 11-16. South-North geologic cross section through the 102nd Street Landfill (from OCC/Olin, 1980).

Figure 11-17. Suspected NAPL disposal areas at the 102nd Street Landfill (from OCC/Olin, 1990).
Figure 11-18. Approximate horizontal extent of DNAPL in fill and alluvium at the 102nd Street Landfill (from
OCC/Olin, 1990).
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XXI
Figure 11-19. Typical conceptual DNAPL distribution along a cross-section at the 102nd Street Landfill (from
OCC/Olm, 1990).

Figure 11 -20. The surface of the silty clay and glacial till capillary barrier layers appear to form a stratigraphic
trap beneath the south-central portion of the site (from OCC/Olin, 1990).

Figure 11-21. Boundaries of dissolved chemical and DNAPL plumes emanating from the Hyde Park Landfill
(from Cohen et al, 1987).

Figure 11-22. Proximity of the City of Niagara Falls Water Treatment Plant water-supply intake tunnels to the
S-Area Landfill (from Cohen et al., 1987).
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XX11

ACKNOWLEDGEMENTS

Several associates at GeoTrans, Inc. helped to prepare this document. Robin Parker authored much of
Chapter 10. Anthony Bryda contributed to Chapter 9. Barry Lester performed the analytical modeling of soil gas
transport described in Chapter 5.3.20. Tim Rogers helped research historic chemical production discussed in
Chapter 3. James Mitchell and Brenda Cole prepared many of the figures contained herein. We are also indebted
to Steve Schmelling, Chuck Newell, and Tom Sale for their reviews, and to the many investigators whose work
forms the basis of this report.
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1 EXECUTIVE SUMMARY

The potential for serious long-term contamination of
groundwater by DNAPL chemicals is high at many sites
due to their toxicity, limited solubility (but much higher
than drinking water standards), and significant migration
potential in soil gas groundwater, and/or as a separate
phase liquid. DNAPL chemicals, particularly, chlorinated
solvents, are among the most prevalent contaminants
identified in groundwater supplies and at contamination
sites.

Remedial activities at a contaminated site need to
account for the possible presence of DNAPL. If
remediation is implemented at a DNAPL site, yet does
not consider the DNAPL, the remedy will underestimate
the time and effort required to achieve remediation goals.
Thus, adequate site characterization is required to
understand contaminant behavior and to make remedial
decisions.

Based on the information presented, the main findings of
this document include the following.

(1) The major types of DNAPLs are halogenated
solvents, coal tar and creosote, PCB oils, and
miscellaneous or mixed DNAPLs. Of these types,
the most extensive subsurface contamination is
associated with halogenated (primarily chlorinated)
solvents due to their widespread use and properties
(high density, low viscosity, significant solubility
and high toxicity).

(2) The physical and chemical properties of subsurface
DNAPLs can vary considerably from that of pure
DNAPL compounds due to: the presence of
complex chemical mixtures; the effects of in-situ
weathering and, the fact that much DNAPL waste
consists of off-specification materials, production
process residues, and spent materials.

(3) DNAPL chemicals migrate in the subsurface as
volatiles in soil gas, dissolved in groundwater, and
as a mobile, separate phase liquid. This migration
is governed by transport principles and the
following chemical and media specific properties:
saturation, interfacial tension, wettability, capillary
pressure, residual saturation, relative permeability,
solubility vapor pressure, volatilization, density, and
viscosity.

(4) DNAPL chemical migration is controlled by the
interaction of these properties and principles with
site-specific hydrogeologic and DNAPL release
conditions. Based on this information, a conceptual
model may be developed concerning the behavior of
DNAPL in the subsurface. Various quantitative
methods can be employed to examine DNAPL
chemical transport within the framework provided
by a site conceptual model. Conceptual models are
used to guide site characterization and remedial
activities.

(5) Subsurface DNAPL is acted upon by three distinct
forces due to: (1) gravity (sometimes referred to as
buoyancy), (2) capillary pressure, and (3)
hydrodynamic pressure (also known as the hydraulic
or viscous force). Each force may have a different
principal direction of pressure and the subsurface
movement of immiscible fluid is determined by the
resolution of these forces.

(6) Gravity promotes the downward migration of
DNAPL. The fluid pressure exerted at the base of
a DNAPL body due to gravity is proportional to the
DNAPL body height, the density difference between
DNAPL and water in the saturated zone, and the
absolute DNAPL density in the vadose zone.

(7) Capillary pressure resists the migration of
nonwetting DNAPL from larger to smaller openings
in water-saturated porous media. It is directly
proportional to the interfacial liquid tension and the
cosine of the DNAPL contact angle, and is inversely
proportional to pore radius. Fine-grained layers
with small pore radii, therefore, can act as capillary
barriers to DNAPL migration. Alternatively,
fractures, root holes, and coarse-grained strata with
relatively large openings provide preferential
pathways for nonwetting DNAPL migration.
Capillary pressure effects cause lateral spreading of
DNAPL above capillary barriers and also act to
immobilize DNAPL at residual saturation and in
stratigraphic traps. This trapped DNAPL is a long-
term source of groundwater contamination and
thereby hinders attempts to restore groundwater
quality.

(8) The hydrodynamic force due to hydraulic gradient
can promote or resist DNAPL migration and is
usually minor compared to gravity and capillary
pressures. The control on DNAPL movement
exerted by the hydrodynamic force increases with:
(a) decreasing gravitational pressure due to reduced
DNAPL density and thickness; (b) decreasing
capillary pressure due to the presence of coarse
media, low interfacial tension, and a relatively high
contact angle; and (c) increasing hydraulic gradient.
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1-2
Mobile DNAPL can migrate along capillary barriers
(such as bedding planes) in a direction opposite to
the hydraulic gradient. This complicates site
characterization.

(9) DNAPL presence and transport potential at
contamination sites needs to be characterized
because: (a) the behavior of subsurface DNAPL
cannot be adequately defined by investigating
miscible contaminant transport due to differences in
properties and principles that govern DNAPL and
solute transport, (b) DNAPL can persist for
decades or centuries as a significant source of
groundwater and soil vapor contamination; and (c)
without adequate precautions or understanding of
DNAPL presence and behavior, site
characterization activities may result in expansion of
the DNAPL contamination and increased remedial
costs.

(10) Specific objectives of DNAPL site evaluation may
include: (a) estimation of the quantities and types
of DNAPLs released and present in the subsurface,
(b) delineation of DNAPL release source areas; (c)
determination of the subsurface DNAPL zone; (d)
determination of site stratigraphy; (e) determination
of immiscible fluid properties; (f) determination of
fluid-media properties; and (g) determination of the
nature, extent, migration rate, and fate of
contaminants. The overall objectives of DNAPL
site evaluation are to facilitate adequate
assessments of site risks and remedies, and to
minimize the potential for inducing unwanted
DNAPL migration during remedial activities.

(11) Delineation of subsurface geologic conditions is
critical to site evaluation because DNAPL
movement can be largely controlled by the capillary
properties of subsurface media. It is particularly
important to determine, if practicable, the spatial
distribution of fine-grained capillary barriers and
preferential DNAPL pathways (e.g., fractures and
coarse-grained strata).

(12) Site characterization should be a continuous,
iterative process, whereby each phase of
investigation and remediation is used to refine the
conceptual model of the site.
(13) During the initial phase, a conceptual model of
chemical presence, transport, and fate is formulated
based on available site information and an
understanding of the processes that control chemical
distribution. The potential presence of DNAPL at
a site should be considered in the initial phase of
site characterization planning. Determining
DNAPL presence should be a high priority at the
onset of site investigation to guide the selection of
site characterization methods. Knowledge or
suspicion of DNAPL presence requires that special
precautions be taken during field work to minimize
the potential for inducing unwanted DNAPL
migration.

(14) Assessment of the potential for DNAPL
contamination based on historical site use
information involves careful examination of: (a)
land use since site development; (b) business
operations and processes; (c) types and volumes of
chemicals used and generated; and, (d) the storage,
handling, transport, distribution, dispersal, and
disposal of these chemicals and operation residues.
Pertinent information can be obtained from
corporate records, government records, historical
society documents, interviews with key personnel,
and historic aerial photographs.

(15) DNAPL presence can also be: (a) determined
directly by visual examination of subsurface samples;
(b) inferred by interpretation of chemical analyses of
subsurface samples; and/or (c) suspected based on
interpretation of anomalous chemical distribution
and hydrogeologic data. However, due to limited
and complex distributions of DNAPL at some sites,
its occurrence may be difficult to detect, leading to
inadequate site assessments and remedial designs.

(16) Under ideal conditions, DNAPL presence can be
identified by direct visual examination of soil, rock,
and fluid samples. Direct visual detection may be
difficult, however, where DNAPL is colorless,
present in low saturation, or distributed
heterogeneously. Direct visual detection can be
enhanced by the use of hydrophobic dye to colorize
NAPL in water and soil samples during a shake test,
ultraviolet fluorescence analysis (for fluorescent
DNAPLs), and/or centrifugation to separate fluid
phases. For volatile NAPLs, analysis of organic
vapors emitted from soil samples can be used to
screen samples for further examination.

(17) Indirect methods for assessing the presence of
DNAPL in the subsurface rely on comparing
-------
measured chemical concentrations to effective
solubility limits for groundwater and to calculated
equilibrium partitioning concentrations for soil and
groundwater. Where present as a separate phase,
DNAPL compounds are generally detected at
<10% of their aqueous solubility limit in
groundwater due to the effects of non-uniform
groundwater flow, variable DNAPL distribution, the
mixing of groundwater in a well, and the reduced
effective solubility of individual compounds in a
multi-liquid NAPL mixture. Typically, dissolved
contaminant concentrations > 1% of the aqueous
solubility are highly suggestive of NAPL presence.
Concentrations less than 1% of the solubility limit,
however, are not necessarily indicative of NAPL
absence. In soil, contaminant concentrations in the
percent range are generally indicative of NAPL
presence. However, NAPL may also be present at
much lower concentrations. The presence of
subsurface DNAPL can also be inferred from
anomalous contaminant distributions, such as
higher dissolved concentrations with depth beneath
a shallow release area or higher concentrations
upgradient hydraulically from a release area.

(18) Noninvasive methods can often be used during the
early phases of field work to optimize the cost-
effectiveness of a DNAPL site characterization
program. Specifically, surface geophysical surveys,
soil gas analysis, and air photointerpretation can
facilitate characterization of contaminant source
areas, geologic controls on contaminant movement
(e.g., stratigraphy and utilities), and the extent of
subsurface contamination. Conceptual model
refinements derived using these methods reduce the
risk of spreading contaminants during subsequent
invasive field work.

(19) The value of surface geophysics at most DNAPL
sites will be to aid characterization of waste
disposal areas, stratigraphic conditions, and
potential routes of contaminant migration. The use
of surface geophysical surveys for direct detection of
NAPL is currently limited by a lack of: (a)
demonstrable methods, (b) documented successes,
and (c) environmental geophysicists trained in these
techniques.

(20) Soil gas analysis can be an effective screening tool
for detecting volatile organic compounds in the
vadose zone. Consideration should be given to its
use during the early phases of site investigation to
assist delineation of volatile DNAPL in the vadose
zone, contaminant source areas, contaminated
shallow groundwater, and contaminated soil gas;
and, thereby, guide subsequent invasive field work.

(21) Aerial photographs should be acquired during the
initial phases of site characterization study to
facilitate analysis of waste disposal practices and
locations, drainage patterns, geologic conditions,
signs of vegetative stress, and other factors relevant
to contamination site assessment. Additionally,
aerial photograph fracture trace analysis should be
considered at sites where bedrock contamination is
a concern.

(22) Following development of the site conceptual model
based on available information and noninvasive field
methods, invasive techniques will generally be
required to advance site characterization and enable
the conduct of risk and remedy assessments.
Various means of subsurface exploration are utilized
to directly observe and measure subsurface materials
and conditions. Generally, these invasive activities
include: (a) drilling and test pit excavation to
characterize subsurface solids and liquids, and (b)
monitor well installation to sample fluids, and to
conduct fluid level surveys, hydraulic tests, and
borehole geophysical surveys.

(23) Invasive methods will generally be used to: (a)
delineate DNAPL source (entry) areas; (b) define
the stratigraphic, lithologic, structural, and/or
hydraulic controls on the movement and distribution
of DNAPL contaminated groundwater, and
contaminated soil gas; (c) characterize fluid and
fluid-media properties that affect DNAPL migration
and the feasibility of alternative remedies; (d)
estimate or determine the nature and extent of
contamination, and the rates and directions of
contaminant transport; (e) evaluate exposure
pathways; and, (!) design monitoring and remedial
systems.

(24) The risk of enlarging the zone of chemical
contamination by use of invasive methods is an
important consideration that must be evaluated
during site characterization. Drilling, well
installation, and pumping activities typically present
the greatest risk of promoting DNAPL migration
during site investigation. Precautions should be
taken to minimize these risks. DNAPL transport
caused by characterization activities may (a)
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1-4
heighten the risk to receptors; (b) increase the
difficulty and cost of remediation and (c) generate
misleading data, leading to the development of a
flawed conceptual model, and flawed assessments of
risk and remedy.

(25) Drilling methods have a high potential for
promoting downward DNAPL migration. For
example, DNAPL trapped in structural or
stratigraphic lows can be mobilized by site
characterization activities (e.g., drilling through a
DNAPL pool). To minimize drilling risks, DNAPL
investigators should: (a) avoid unnecessary drilling
within the DNAPL zone; (b) minimize the time
during which a boring is open; (c) minimize the
length of hole which is open at any time; (d) use
telescoped casing drilling techniques to isolate
shallow contaminated zones from deeper zones; (e)
utilize knowledge of site stratigraphy and chemical
distribution, and carefully examine subsurface
materials brought to the surface as drilling
proceeds, to avoid drilling through a barrier layer
beneath DNAPL; (f) consider using a dense drilling
mud to prevent DNAPL from sinking down the
borehole during drilling and, (g) select optimum
well materials and grouting methods based on
consideration of site-specific chemical compatibility.

(26) Monitor wells are installed to characterize
immiscible fluid distributions, flow directions and
rates, groundwater quality, and media hydraulic
properties. Pertinent data are acquired by
conducting fluid thickness and elevation surveys,
hydraulic tests, and borehole geophysical surveys.
The locations and design of monitor wells are
selected based on consideration of the site
conceptual model and specific data collection
objectives. Inadequate well design can increase the
potential for causing vertical DNAPL migration and
misinterpretation of fluid elevation and thickness
measurements.

(27) As knowledge of the site increases and becomes
more complex the conceptual model may take the
form of either a numerical or analytical model.
Data collection continues until the conceptual
model is proven sufficiently.

(28) At some sites, it will be very difficult and/or
impractical to determine the subsurface DNAPL
distribution and DNAPL transport pathways in a
detailed manner. Subsurface characterization is
particularly complicated by the presence of
heterogeneous strata, fractured media, and complex
DNAPL releases. The significant of incomplete
site characterization should be analyzed during the
conduct of risk and remedy assessments.

(29) During implementation of a remedy, the subsurface
system is stressed. This provides an opportunity to
monitor and not only learn about the effectiveness
of the remediation, but to learn more about the
subsurface. Therefore, remediation (especially pilot
studies) should be considered part of site
characterization, yielding data that may allow
improvements to be made in the conduct of the
remediation effort.

(30) Site characterization, data analysis, and conceptual
model refinement are iterative activities which
should satisfy the characterization objectives needed
to facilitate risk and remedy assessments. As
emphasized throughout this manual, site
characterization includes both data collection and
data interpretation. For sites involving DNAPL
challenges are presented to both activities, but
perhaps data interpretation is most challenging. For
that reason, in addition to site characterization
techniques, data interpretation should be
emphasized during all phases of site
characterization.

There is no practical cookbook approach to DNAPL site
investigation or data analysis. Each site presents
variations of contaminant transport conditions and issues.
Although there are no certain answers to many of the
DNAPL site evaluation issues, this manual provides a
framework for their evaluation.
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2 INTRODUCTION

Dense nonaqueous j>hase liquids (DNAPLs), such as
some chlorinated solvents, creosote based wood-treating
oils, coal tar wastes, and pesticides, are immiscible fluids
with a density greater than water. As a result of
widespread production, transportation, utilization, and
disposal of hazardous DNAPLs, particularly since 1940,
there are numerous DNAPL contamination sites in North
America and Europe. The potential for serious long-term
contamination of groundwater by some DNAPL chemicals
at many sites is high due to their toxicity, limited
solubility (but much higher than drinking water limits),
and significant migration potential in soil gas,
groundwater, and/or as a separate phase (Figure 2-1).
DNAPL chemicals, especially chlorinated solvents, are
among the most prevalent groundwater contaminants
identified in groundwater supplies and at waste disposal
sites.

The subsurface movement of DNAPL is controlled
substantially by the nature of the release, the DNAPL
density, interfacial tension, and viscosity, porous media
capillary properties, and, usually to a lesser extent,
hydraulic forces. Below the water table, non-wetting
DNAPL migrates preferentially through permeable
pathways such as soil and rock fractures, root holes, and
sand layers that provide relatively little capillary
resistance to flow. Visual detection of DNAPL in soil
and groundwater samples may be difficult where the
DNAPL is transparent, present in low saturation, or
distributed heterogeneously. These factors confound
characterization of the movement and distribution of
DNAPL even at sites with relatively homogeneous soil and
a known, uniform DNAPL source. The difficulty of site
characterization is further compounded by fractured
bedrock heterogeneous strata, multiple DNAPL mixtures
and releases, etc.

Obtaining a detailed delineation of subsurface DNAPL,
therefore, can be very costly and may be impractical using
conventional site investigation techniques. Furthermore,
the risk of causing DNAPL migration by drilling or other
actions may be substantial and should be considered prior
to commencing fieldwork. Although DNAPL can greatly
complicate site characterization, failure to adequately
define its presence, fate, and transport can result in
misguided investigation and remedial efforts. Large
savings and environmental benefits can be realized by
conducting studies and implementing remedies in a cost-
effective reamer. Cost-effective DNAPL site
management requires an understanding of DNAPL
properties and migration processes, and of the methods
available to investigate and interpret the transport and
fate of DNAPL in the subsurface.

Lighter-than-water NAPLs (LNAPLs) which do not sink
through the saturated zone, such as petroleum products,
are also present and cause groundwater contamination at
numerous sites. Although many of the same principles
and concerns apply at both LNAPL and DNAPL sites,
LNAPL site characterization is not specifically addressed
in this document.
2.1 MANUAL OBJECTIVES

This manual is designed to guide investigators involved in
the planning and implementation of characterization
studies at sites suspected of having subsurface
contamination by DNAPLs. Specifically, the document is
intended to:

• Summarize the current state of knowledge for
characterizing DNAPL-contaminated sites;

• Develop a framework for planning and implementing
DNAPL site characterization activities;

• Provide a detailed discussion of the types of data, tools,
and methods that can be used to identify, characterize,
and monitor DNAPL sites, and an analysis of their
utility, limitations, risks, availability, and cost;

• Identify and illustrate methods, including the
development of conceptual models, to interpret
contaminant fate and transport at DNAPL sites based
on the data collected;

• Assess new and developing site characterization
methodologies that may be valuable and identify
additional research needs; and,

• Review the scope of the DNAPL contamination
problem, the properties of DNAPLs and media, and
DNAPL transport processes to provide context for
understanding DNAPL site characterization.

The primary goal of this manual is to help site managers
minimize the risks and maximize the cost-effectiveness of
site investigation/remediation by providing the best
information available to describe and evaluate activities
that can be used to determine the presence, fate, and
transport of subsurface DNAPL contamination.
-------
2-2
DNAPL
Entry Area
/DNAPL
X Gaseous Vapors
Dissolved
Contaminant
Plumes
»~.
Figure 2-1. DNAPL chemicals are distributed in several phases: dissolved in groundwater, adsorbed
to soils, volatilized in soil gas, and as residual and mobile immiscible fluids (modified
from Huling and Weaver, 1991; WCGR, 1991).
-------
2.2 DERIVATION OF MANUAL

DNAPL contamination has been identified by USEPA at
numerous hazardous waste sites and is suspected to exist
at many others. Growing recognition of the significance
of DNAPL contamination has prompted the USEPA's
Robert S. Kerr Environmental Research Laboratory to
sponsor research and technology transfer concerning
DNAPL issues. Pertinent DNAPL documents published
recently by the Kerr Laboratory include: Laboratory
Investigation of Residual Liquid Organics from Spills,
Leaks, and the Disposal of Hazardous Wastes in
Groundwater (EPA/600/6-90/004), Dense Nonaqueous
Phase Liquids — Ground Water Issue Paper (EPA/540/4-
91-002), Dense Nonaqueous Phase Liquids — A Workshop
Summary, Dallas Texas, April 17-18, 1991 (EPA/600/R-
92/030) and Estimating Potential for Occurrence of DNAPL
at Superfund Sites (EPA Quick Reference Fact Sheet,
8/91).

An objective of the DNAPL Workshop Meeting held in
Dallas, Texas during April 1991 was to develop a
document covering DNAPL fundamentals, site
characterization, remedial alternatives, and promising
topics for further investigation. Although the document
that evolved from the Workshop summarizes the main
observations and conclusions of participants regarding
DNAPL site investigation and remediation concerns, it is
not a detailed site characterization manual.
2.3 DNAPL SITE INVESTIGATION ISSUES

Numerous site characterization guidance documents have
been developed by USEPA and others during the past
decade (Table 2-1). Few of these manuals focus on
characterization issues specific to DNAPL sites. The
primary additional investigation concerns at DNAPL sites
relate to: (a) the risk of inducing DNAPL migration by
drilling, pumping, or other field activitities (b) the use of
special sampling and measurement methods to assess
DNAPL presence and migration potential; and, (c)
development of a cost-effective characterization strategy
that accounts for DNAPL chemical transport processes,
the risk of inducing DNAPL movement during field work,
and the data required to select and implement a realistic
remedy.

The potential presence of DNAPL at a contamination site
dictates consideration of the following issues/questions
during scoping, conduct, and interpretation of a site
characterization study.

• What questions should be asked prior to initiating a
field investigation to determine if a site is a potential
DNAPL site? What do preexisting site data indicate
regarding the presence and distribution of DNAPL?

• If DNAPL contamination is possible, how should the
site be sampled? What should the goal of sampling be
and how does this affect the sampling strategy?

• What are the risks of sampling and what technical
considerations should be made in order to balance
those risks against the risks of not sampling? How do
these risks and technical considerations vary with
different geologic environments and DNAPLs?

• Given some knowledge of the type of DNAPL presence
and site hydrogeology, can a preliminary conceptual
model of DNAPL chemical migration be formulated?
If so, how can the site investigation be optimized based
on the development of a conceptual model?

• How do we determine where to place and install
monitor wells? What materials should be used for well
construction and other equipment which contacts
DNAPL?

• Is it possible to isolate zones of DNAPL contamination
through use of telescoped well construction (e.g.
double-cased wells) or other techniques?

• What methods are available for characterizing DNAPL
sites? How accessible, reliable, and costly are the
various methods?

• How should noninvasive techniques, such as soil gas
analysis and surface geophysical surveys, be used to
characterize DNAPL sites?

• How can the extent, volume, and mobility of subsurface
DNAPL be estimated?

• What data are necessary to facilitate evaluation of
alternative remedial options at DNAPL sites? What
data are necessary to conduct risk assessments? What
data are necessary to meet regulatory requirements?

Although there are no certain answers to many of these
questions, this manual provides a framework for their
evaluation.
-------
2-4
Table 2-1. Contamination Site Investigation Guidance Documents.
AASHTO, 1988. Manual on subsurface investigations, American Association of State Highway and Transportation Officials, 391 pp.
Aller, L., T.W. Bennett, G. Hackett, R.J. Petty, J.H. Lehr,H. Sedoris, D.M. Nielsen, and J.E. Denne, 1989. Handbook of Suggested
Practices for the Design and Installation of Ground-Water Monitoring Wells, USEPA-600/4-89/034, National Water Well
Association, Dublin, Ohio, 398 pp.
American Petroleum Institute, 1989. A guide to the assessment and remediation of underground petroleum releases, API Publication
1628, Washington, D.C., 81 pp.
Barcelona, M.J., J.P. Gibb, J.A. Helfrich, and E.E. Garske, 1985. Practical guide for ground-water sampling, USEPA/600/2-85-104, 169
PP.
Barcelona, M.J., J.P. Gibb, and R.A. Miller. 1983. A guide to the selection of materials for monitoring well construction and ground-
water sampling, Illinois State Water Survey Contract Report 327 to USEPA R.S. Kerr Environmental Research Laboratory, EPA
Contract CR-809966-01, 78 pp.
Barcelona, M.J., J.F. Keely, W.A. Pettyjohn, and A. Wehrmann. 1987. Handbook ground water, USEP A/625/6-87/016, 212 pp.
Berg, E.L., 1982. Handbook for sampling and sample preservation of water and wastewater, USEP A/600/4-82-029.
Claasen, H.C., 1982. Guidelines and techniques for obtaining water samples that accurately represent the water chemistry of an aquifer,
USGS Open-File Report 82-1024, 49 pp.
dePastrovich, T. L., Y. Baradat, R. Barthell, A. Chiarelli, and D.R. Fussell, 1979. Protection of groundwater from oil pollution,
CONCAWE (Conservation of Clean Air and Water Europe). The Hague, 61 pp.
Devitt, D.A., R.B. Evans, W.A. Jury, and T.H. Starks, 1987. Soil gas sensing for detection and mapping of volatile organics, USEPA/
600/8-87/036, 266 pp.
Dunlap, W.J., J.F. McNabb, M.R. Scalf, and R.L. Cosby, 1977. Sampling for organic chemicals and microorganisms in the subsurface,
USEPA/600/2-77/176 (NTIS PB272679).
Electric Power Research Institute, 1985. Preliminary results on chemical changes in groundwater samples due to sampling devices,
EPRIEA-4118 Interim Report, Palo Alto, California.
Electric Power Research Institute, 1989. Techniques to develop data for hydrogeochemical models. EPRI EN-6637, Palo Alto,
California.
Fenn, D., E. Cocozza, J. Isbister, O. Braids, B. Yard, and P. Roux, 1977. Procedures manual for ground water monitoring at solid waste
disposal facilities, USEPA SW-611, 269 pp.
Ford, P.J., D.J. Turina, and D.E. Seely, 1984. Characterization of hazardous waste sites — A methods manual, Volume 11 Available
sampling methods, USEPA-600/4-84-076 (NTIS PB85-521596).
Fussell, D.R., H. Godjen, P. Hayward. R.H. Lilie, A. Marco, and C. Panisi, 1981. Revised inland oil spill clean-up manual, CONCAWE
(Conservation of Clean Air and Water -Europe), The Hague, Report No. 7/81, 150pp.
Gas Research Institute, 1987. Management of manufactured gas plant sites, GRI-87/0260, Chicago, Illinois.
GeoTrans, Inc., 1983. RCRA permit writer's manual ground-water protection, USEPA Contract No. 68-01-6464,263 pp.
GeoTrans, Inc., 1989. Groundwater monitoring manual for the electric utility industry, Edison Electric Institute. Washington, D.C.
Klute, A., cd., 1986. Methods of Soil Analysis, Soil Science Society of America. Inc., Madison, WI, 1188 pp.
Mercer, J.W., D.C. Skipp, and D. Giffin, 1990. Basics of pump-and-treat ground-water remediation technology, USEPA-600/8-90/003.
Nielsen, D.M. (ed.). 1991. Practical Handbook of Ground Water Monitoring, Lewis Publishers. Chelsea, Michigan, 717 pp.
NJ Department of Environmental Protection, 1988. Field sampling procedures manual, Hazardous Waste Program, NJDEP, Trenton,
New Jersey.
Rehm, B.W., T.R. Stolzenburg, and D.G. Nichols, 1985. Field measurement methods for hydrogeologic investigations: A critical
review of the literature, Electric Power Research Institute Report EPRI EA-4301, Palo Alto, California.
Sara, M.N., 1989. Site assessment manual, Waste Management of North America, Inc., Oak Brook, Illinois.
Scalf, M.R., J.F. McNabb, W.J. Dunlap, R.L. Cosby, and J.S. Fryberger, 1981. Manual of Ground-Water Quality Sampling Procedures,
National Water Well Association, Worthington, Ohio, 93 pp.
Simmons, M. S., 1991. Hazardous Waste Measurements, Lewis Publishers. Chelsea, Michigan, 315 pp.
Sisk, S.W., 1981. NEIC manual for groundwater/subsurface investigations at hazardous waste sites, USEPA-330/9-81-002 (NTIS PB82-
1 03755).
Skridulis. J., 1984. Comparison of guidelines for monitoring well design, installation and sampling practices. NUS Cooperation Report
to USEPA, Contract No. 68-01-6699.
Summers, K. V., and S.A. Gherini, 1987. Sampling guidelines for groundwater quality, Electric Power Research Institute report EPRI
EA-4952, Palo Alto, California.
USEPA, 1986. RCRA ground-water monitoring technical enforcement guidance document, OSWER-9550.1.
USEPA, 1987. A compendium of Superfund field operations methods, USEPA/540/P-87/001.
USEPA, 1987. Handbook - Ground Water, EPA/625/6-87/016, 212 pp.
USEPA, 1988. Guidance for conducting remedial investigations and feasibility studies under CERCLA, USEPA/540/G-89/004.
USEPA, 1988. Field screening methods catalog - User's guide, USEPA/540/2-88/005.
USEPA, 1989. Interim final RCRA facility investigation (RFI) guidance, USEPA/530/SW-89/031.
USEPA, 1991. Seminar publication - Site characterization of subsurface remediation, EPA/625/4-91/026, 259 pp.
USGS, 1977. National handbook of recommended methods for water-data acquisition.
Wilson, L.G., 1980. Monitoring in the vadose zone: A review of technical elements and methods. USEPA-600/7-80-134. 168 pp.
-------
2-5
2.4 DNAPL SITE INVESTIGATION PRACTICE

Remedial investigations were conducted at numerous
DNAPL sites in the United States during the 1980s
pursuant to requirements of the Comprehensive
Environmental Response, Compensation, and Liability
Act (CERCLA) and the Resource Conservation and
Recovery Act (RCRA). Unfortunately, dissemination of
procedures and strategies for DNAPL site investigation
has been slow. This is due to prior limited recognition of
the DNAPL problem and the fact that many DNAPL
sites are the subject of litigation which has stifled
publication of investigation results.

Within the past few years, however, recognition of the
significance of DNAPL contamination has grown
considerably. This is evidenced by and due to events
which include publication of an English translation of
Friedrich Schwille's DNAPL experiments entitled Dense
Chlorinated Solvents in Porous and Fractured Media in
1988, increasing focus on DNAPL issues during the
annual conference on Petroleum Hydrocarbons and
Organic Chemicals in Ground Water sponsored by the
National Ground Water Association and the American
Petroleum Institute, presentation of DNAPL
contamination short courses by the Waterloo Centre for
Groundwater Research, organization of the Conference on
Subsurface Contamination by Immiscible Fluids by the
International Association of Hydrologists in Calgary
during April 1990, and increased attention given to
DNAPL issues by USEPA and technical journals (such as
Ground Water, Ground Water Monitoring Review, Water
Resources Research, and the Journal of Contaminant
Hydrology).
surface geophysical techniques) in Chapter 8, invasive
methods (i.e., test pits and drilling) in Chapter 9, and
laboratory methods for characterizing fluid and media
properties in Chapter 10. Several case histories
illustrating investigation findings and problems specific to
DNAPL sites are provided in Chapter 11. Priority
research needs are discussed briefly in Chapter 12; and
references for the entire document are listed in Chapter
13. Chemical properties of DNAPL chemicals, a listing
of parameters and conversion factors, and a glossary of
terms related to DNAPL site contamination are given in
Appendices A, B, and C, respectively. The Executive
Summary (Chapter 1) outlines the main findings of this
document.
2.5 MANUAL ORGANIZATION

The organization of this document is outlined in the
DNAPL site characterization flow chart given in Figure
2-2. Discussions of the scope of the DNAPL
contamination problem (Chapter 3), the properties of
DNAPLs and media (Chapter 4), and DNAPL transport
processes (Chapter 5) are provided as a foundation for
understanding DNAPL site characterization methods and
strategies. Objectives and strategies of DNAPL site
characterization are described in Chapter 6. The
identification of DNAPL sites based on historic
information and preexisting data is addressed in Chapter
7. This is followed by an examination of noninvasive
characterization methods (i.e., soil gas analysis and
-------
NOTE:

Characterization should be conducted in a
phased, evolutionary manner starting with.
review of available data. Early field work
should focus on areas beyond the DNAPL
zone and use noninvasive methods in the
DNAPL zone. Each characterization
activity should be designed to test the
conceptual model in a manner that will
increase the capacity to perform risk
and remedy analysts.

To limit the potential for promoting
contaminant migration, avoid' (I) conducting
unecessary field work: (2) drilling through
capillary barriers beneath DNAPL; (3) pumping
from beneath DNAPL zones; and, (4) using
invasive characterization or remediation
methods without due consideration for the
potential consequences.
REVIEW EXISTING DATA
(CHAPTER 7)
Industry type and processes used
Documented use or disposal of DNAPL
Available site, local, or regional
investigation reports
Corporate/client records
Government records
University, library, historical society records
Interviews with key personnel
Aerial photographs
UNDERSTANDING OF THE DNAPL PROBLEM,
DNAPL AND MEDIA PROPERTIES, AND
TRANSPORT PROCESSES
(CHAPTERS 3, 4, & 5)
| DEVELOP INITIAL CONCEPTUAL MODEL \4-

1
SITE CHARACTERIZATION ACTIVITIES
NONINVASIVE METHODS
(CHAPTER 8)

Surface geophysics
Soil gas analysis
INVASIVE METHODS
(CHAPTER 9)
Test pits
Borings
Wells
Hydraulic tests
LABORATORY METHODS
(CHAPTER 10)
T
T
ESTIMATE
QUANTITIES
OF DNAPL
RELEASED
AND IN
SUBSURFACE

Historical data
Field data
T
DELINEATE

DNAPL

SOURCE

AREAS

EXAMINE
SUSPECT AREAS

ROOT drains and sumps
Catch basins
Pits, ponds, lagoons
Other disposal areas
Septic tanks
Leach fields
French drains
Sewers
Process tanks
Wastewater tanks
USTs
Aboveground tanks
Chemical storage areas
Chemical transfer areas
Pipelines
Waste storage areas
Loading dock areas
Work areas
Discolored soils
Stressed vegetation
Disturbed earth
Disturbed low-lying areas
DETERMINE
DNAPL
ZONE

Delineate
mobile
DNAPL
Estimate
saturations
Delineate
residual
DNAPL
DETERMINE
STRATIGRAPHY
Stratigrophic taps
Co pillory barriers
(presence and slope)
Preferential pathways
T
DETERMINE

FLUID
PROPERTIES

Density
Viscosity
Interracial tension
Solubility
Sorptive properties
Vopor transport properties
Chemical composition
Cosolvency and reactivity
T
1
DETERMINE
MEDIA
PROPERTIES
Intrinsic
permeabilities
Porosities
Organic carbon
content
Heterogeneities
MORE DATA IS NEEDED
REFINE THE CONCEPTUAL MODEL
-j RISK ASSESSMENT
-{REMEDY ASSESSMENT
TREATABIUTY AND
PILOT STUDIES
SITE REMEDIATION
AND LONG-TERM
MONITORING
DETERMINE THE

NATURE, EXTENT,

MIGRATION RATE,

AND FATE OF
CONTAMINANTS

NATURE AND EXTENT
DNAPL
Aqueous phase
groundwater contamination
Adsorbed soil and
rock contamination
Soil gas
contamination
Surface water
and sediment
contamination

MIGRATION RATE
DNAPL
Aqueous phase chemicals
Flow directions
and velocities

FATE
DNAPL dissolution
DNAPL volatilization
DNAPL immobilization
Adsorption and
degradation of
aqueous and vapor
phase contaminants
to

ON
Figure 2-2. DNAPL site characterization flow chart.
-------
3 DNAPL TYPES AND SCOPE OF PROBLEM
3.1 INTRODUCTION

The potential for widespread contamination of
groundwater by DNAPLs is substantial because of the
extensive production, transport, utilization, and disposal
of large volumes of DNAPL chemicals during the 20th
Century. Some DNAPL wastes are older, such as coal tar
generated as early as the 1820s at manufactured gas sites
in the eastern U.S. There are literally thousands of sites
in North America where DNAPLs may have been
released to the subsurface in varying quantities (NRC,
1990, p.24). At some of these sites, tons of DNAPL were
released over time and DNAPL presence is obvious in
subsurface materials. At most sites, however, the limited
volume of DNAPL present hinders direct identification
even though it is sufficient to provide a source for
significant groundwater contamination. As a result,
DNAPL chemicals are frequently detected at
contamination sites even where DNAPL presence has not
been determined.

The most prevalent DNAPL types are outlined in Table
3-1 with summary information on DNAPL density,
viscosity, production, and usage, and selected
contamination site references. The major DNAPL types
include: halogenated solvents, coal tar and creosote, PCB
oils, and miscellaneous or mixed DNAPLs. Of these
types, the most extensive subsurface contamination is
associated with halogenated (primarily chlorinated)
solvents, either alone or within mixed DNAPL sites, due
to their widespread use and properties (high density, low
viscosity, significant solubility, and high toxicity). As
shown in Figure 3-1, pure chlorinated solvents are
generally much more mobile than creosote/coal tar and
PCB oil mixtures due to their relatively high
density:viscosity ratios.

Although the physical properties of pure DNAPL
chemicals are well-defined, the physical properties of
subsurface DNAPLs can vary considerably from that of
the pure DNAPL compounds due to:

• the presence of complex chemical mixtures,

• the effects of in-situ weathering (dissolution,
volatilization, and degradation of the less persistent
DNAPL fractions), and,
• the fact that much DNAPL waste consists of off-
specification materials, production process residues,
and spent materials.

Physical and chemical properties of numerous DNAPL
chemicals are provided in Appendix A.
3.2 HALOGENATED SOLVENTS

Halogenated solvents, particularly chlorinated
hydrocarbons, and brominated and fluorinated
hydrocarbons to a much lesser extent, are DNAPL
chemicals encountered at contamination sites. These
halocarbons are producd by replacing one or more
hydrogen atoms with chlorine (or another halogen) in
petrochemical precursors such as methane, ethane,
ethene, propane, and benzene. Many bromocarbons and
fluorocarbons are manufactured by reacting chlorinate
hydrocarbon intermediates (such as chloroform or carbon
tetrachloride) with bromine and fluorine compounds,
respectively. DNAPL halocarbons at ambient
environmental conditions include: chlorination products
of methane (methylene chloride, chloroform, carbon
tetrachloride), ethane (1,1-dichloroethane, 1,2-
dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-
tetrachloroethane), ethene (1,1-dichloroethene, 1,2-
dichloroethene isomers, trichloroethene,
tetrachloroethene), propane (1,2-dichloropropane, 1,3-
dichloropropene isomers), and benzene (chlorobenzene,
1,2-dichlorobenzene, 1,4-dichlorobenzene); fluorination
products of methane and ethane such as 1,1,2-
trichlorofluormethane (Freon-11 and 1,1,2-
trichlorotrifluorethane (Freon-113); and, bromination
products of methane (bromochloromethane,
dibromochloromethane, dibromodifluoromethane,
bromoform), ethane (bromoethane, 1,1,2,2-
tetrabromoethane), ethene (ethylene dibromide), and
propane (l,2-dibromo-3-chloropropane).

Although most chlorinated solvents were first synthesized
during the 1800s, large-scale production generally began
around the middle of the 1900s primarily for use as
solvents and chemical intermediates. Annual production
rates at five-year intervals between 1920 and 1990 for
selected chlorinated solvents and other DNAPL chemicals
are shown in Table 3-2 and Figure 3-2. An estimated 29
billion Ibs of chlorinated hydrocarbons were produced in
the U.S. during 1990 (U.S. International Trade
Commission, 1991). The uses of six common chlorinate
solvents are illustrated in Figure 3-3.
Fluorocarbons were discovered in the search for improved
refrigerants by General Motors in 1930. In the U. S.,
-------
Table 3-1. DNAPL Types: Sources, Use, Properties, Contamination, and References.
DNAPL Type, Derivation, Specific Gravity
and Absolute Viscosity
Uses and Contamination
Sources
Selected Statistics on Extent of DNAPL
Production, Usage, and Contamination
Selected References
Halogauued Hydrocarbon Solvents
(such as dichloroethene, trichloroethene,
tetrachloroethane, dichloroethane, trichloroethane,
mctbylene chloride, chloroform, carbon tctrachloride,
bromoform, clhylene dibromide, chlorobenzene, and
chlorotoluene)

Halogenated hydrocarbon solvents are produced by
replacing one or more hydrogen atoms with chlorine
(or another halogen) in petrochemical precursors such
as methane, ethylene, and benzene.

Specific gravities at 20° C. of the pure halogenated
solvents listed above range from approximately 1.08
(chlorotoluene) to 2.89 (bromoform).

Absolute viscosities at 20° C of the pure compounds
listed above range from approximately 0.36 cp (1,1-
dichloroethene) to 2.04 cp (bromoform).
Chemical manufacturing
Solvent manufacturing, reprocessing,
and/or packaging
Vapor degreasing operations
Commercial dry cleaning operations
Electronic equipment manufacturing
Dry plasma etching of semiconductor
chips
Computer parts and manufacturing
Metal parts/products manufacturing
Aircraft and automotive manufacturing,
maintenance and repair operations
Machine shops and metal works
Tool-and-dic plants
Musical instrument manufacturing
Photographic film manufacturing and
processing
Dye and paint manufacturing
Pharmaceutical manufacturing
Plastics manufacturing
Flame retardant materials
manufacturing
Refrigerants manufacturing
Military equipment manufacturing and
maintenance
Printing presses and publishing
operations
Septic tank cleaners
Textile processing, dying, and finishing
operations
Solvent and carrier fluid formulations
in rubber coatings, solvent soaps,
printing inks, adhesives and glues,
sealants, polishes, lubricants, and
silicones
Insecticide and herbicide production
Waste disposal sites
Halogenated (particularly chlorinated) solvents have been
widely used in manufacturing and cleaning industries since
about the 1940s. Production and use of these solvents has
generally proliferated with time, but demand for some
solvents has diminished due to environmental, cost, and/or
other factors. U.S. production estimates for selected
chlorinated solvents in 1990 include: 484,000,000 Ibs of
chloroform; 461,000,000 Ibs of methylene chloride;
802,000,000 Ibs of 1,1,1-trichIoroethane; 372,000,000 Ibs of
tetrachloroethene; and 237,000,000 Ibs of chlorobenzene (U.S.
International Trade Commission, 1991). An estimated
620,400,000 Ibs of waste solvents were produced by
degreasing operations in 1974.

Halogenated solvents are among the contaminants most
frequently detected at subsurface contamination sites. They
are associated with waste disposal and chemical releases from
numerous industries and operations. Due to their extensive
release, high density, low viscosity, and toxic nature,
chlorinated solvents present the most severe DNAPL
contamination problem.
Chlorinated solvent contamination at the
Gloucester Landfill in Ottawa, Ontario
(Jackson et al., 1985;, Jackson and
Patterson, 1989; Jackson et al., 1990; and
LeSage et al., 1990)

Solvent contamination at the IBM Dayton
facility in South Brunswick, N J. (Althoff et
al., 1981; CH2M-Hill, 1989; Stipp, 1991)

Solvent contamination of fractured shale at
Oak Ridge, Tennessee (Kueper et al., 1991)

VOC contamination at the General Mills
site in Minneapolis, Minnesota (CH2M-HUI,
1989)

Chlorinated solvent contamination of
production wells in Birmingham, U.K.
(Rivett et al., 1990)

Release of 1,2-dichloroethane due to a train
derailment in British Columbia (Dakin and
Holmes, 1987)

Other References:
Begor et al. (1989), CH2M-HJ11 (1989),
Feenstra and Cherry (1988), Mackay and
Cherry (1989), Holmes and Cambell (1990),
Robertson (1992), Schaumburg (1990)
-------
Table 3-1. DNAPL Types: Sources, Use, Properties, Contamination, and References.
DNAPL Type, Derivation, Specific Gravity
and Absolute Viscosity
Uses and Contamination
Sources
Selected Statistics on Extent of DNAPL
Production, Usage, and Contamination
Selected References
Coal Tar and Creosote

Derived from the destructive distillation of coal in coke
ovens and retorts, coal tar is composed of thousands of
hydrocarbons dominated by PAHs (porycyclic aromatic
hydrocarbons with a substantial content of naphthalene
compounds) that are mixed with lesser amounts of tar
acids such as phenol and cresol; N-, S-, and O-
heterocyclic aromatic compounds; and <5% BTEX
(benzene, toluene, ethylbenzene, and xylenes).

Creosote consists of various coal tar distillates
(primarily the 200-400° C fractions) blended to meet
product standards. It is estimated to contain
approximately 85% PAHs, 10% phenolic compounds,
and 5% N-, S-, and O- heterocyclics. For wood-
treatment applications, creosote may be applied
undiluted or mixed with coal tar or a petroleum oil
(such as diesel fuel) in ratios that range from 80:20 to
50:50, creosote:carrier.

The specific gravity of creosote is typically between 1.01
and 1.05, but ranges up to 1.14 in certain blends. The
specific gravity of coal tar ranges between 1.01 and
1.18. The viscosity of creosote and coal tar is generally
much greater than that of water, typically in the range
of 10 to 70 cp.
Wood treating plants
Coal tar distillation plants
Steel industry coking operations
Manufactured gas (coal gasification)
plants
Roofing tars
Road tars
There are an estimated 700 active and abandoned wood-
treatment plants in the U.S. In 1978,188 of 631 wood-
treatment plants in the U.S., operating predominantly along
the eastern seaboard, in the southeast, and in the Pacific
northwest, were reported using creosote and/or coal tar
(McGinnis, 1989).

Manufactured gas plants produced "town" gas for lighting and
heating primarily between 1850 and 1950. More than 900
coal gasification plants were operational in the U.S. in 1920
(Rhodes, 1979).

There were 64 coal tar producers and 24 coal tar distillation
plants producing creosote in the U.S. in 1972 (USDA, 1980).
In 1986, an estimated 1000 million Ibs of creosote were
utilized by 415-550 creosoting operations in the U.S. (Mueller
et al., 1989). In 1990, an estimated 596 million liters of crude
coal tar and 297 million liters of creosote oil were produced
in the U.S. (U.S. International Trade Commission, 1991).

Large quantities of DNAPL were released at some wood
treatment and manufactured gas plant sites due to the
longterm use and/or generation of large quantities of coal tar
and creosote chemicals and the waste disposal practices at
these sites. DNAPL contamination at wood treatment sites
derives from leaking tanks and pipelines, dripping treated
lumber, leaking holding ponds, etc. In 1988, approximately 40
creosote/coal tar wood treatment sites were on the National
Priority List of CERCLA sites (USEPA, 1988).
Union Pacific Railroad Tie Plant in
Laramie, Wyoming (Sale and Pkmtek, 1988;
Sale et al., 1988; and Sate et al., 1989)

Abandoned creosote waste site in Conroe,
Texas (Bedient et al., 1984)

American Creosote Works site in
Pensacola, Florida (Troutman et at., 1984;
Mattraw and Franks, 1984; Goerlitz et al.,
1985; USOS, 1985; and, Franks, 1987)

Reilly Tar site in St. Louis Park, Minnesota
(Erlich et al., 1982; and, Hull and
Schoenberg, 1984)

Manufactured gas plant site in Stroudsburg,
Pennsylvania (Villaume et al., 1983; and,
Villaume, 1985)

Manufactured gas plant site in Waltingford,
Connecticut (Conway et al., 1985; and,
Quinn et al., 1985)

Other references:
Austin (1984), Baechler and MacFarlane
(1990), Belangcr et al. (1990), Edison
Electric Institute (1984), Feenstra and
Cherry (1990), Ghiorse et al. (1990), GRI
(1987), Konasewich et al. (1990), Litherland
and Anderson (1990), McGinnis et al.
(1991), Mueller et al. (1989), Murarka
(1990), Raven and Beck (1990), Rosenfeld
and Plumb (1991), USDA (1980), USEPA
(1989d), Villaume (1984)
-------
Table 3-1. DNAPL Types: Sources, Use, Properties, Contamination, and References.
DNAPL Type, Derivation, Specific Gravity
and Absolute Viscosity
Uses and Contamination
Sources
Selected Statistics on Extent of DNAPL
Production, Usage, and Contamination
Selected References
PCBs (and mixtures of PCBs and organic solvents such
as chlorinated benzenes and mineral oil)

PCBs (Potychlorinaled Biphenyls) are extremely stable,
nonflammable, dense, and viscous liquids that have
been primarily used as insulators in electrical
transformers and capacitors. They are formed by
substituting chlorine atoms for hydrogen atoms on a
biphenyl (double benzene ring) molecule. Commercial
PCBs are a series of technical mixtures, consisting of
many isomers and compounds. Monsanto Chemical
Co. sold PCBs using the trade name Aroclor*. Each
Aroclor is identified by a four-digit number such as
1254. The first two digits, 12, indicate the twelve
carbons in the biphenyl double ring. The last two digits
indicate the weight percent of chlorine in the PCB
product mix. Aroclor 1016 which contains
approximately 41% chlorine by weight, however, was
not named using this convention.

Specific gravities at 25° C. and viscosities at 38° C. of
several PCBs are:
PCB Sp.G. Viscosity
Aroclor 1221 1.18 12 cp
Aroclor 1232 1.27 37 cp
Aroclor 1016 1.37 55 cp
Aroclor 1242 1.38 63 cp
Aroclor 1248 1.44 150 cp
Aroclor 1254 1.53 1900 cp
Aroclor 1260 1.62 sticky resin

Note that physical properties of PCB products are
modified by mixture with chlorobenzenes, mineral oil,
or other solvents.
Transformer/capacitor oil production,
reprocessing, and disposal facilities

Between 1929 and 1971, PCBs were
sold for use as dielectric fluids in
electrical transformers and capacitors,
in oil-filled switches, electromagnets,
voltage regulators, heat transfer media,
fire retardants, hydraulic fluids on
machines that handled hot metals to
reduce fire hazards, lubricants, cutting
oils, plasticizers, wax extenders,
carbonless copy paper, paints, inks,
adhesives, vacuum pumps, gas-
transmission turbines, and dedusting
agents.

In 1972, Monsanto restricted sales of
PCBs to applications involving only
closed electrical systems (transformers,
capacitors, and electromagnets).
In the U.S., the only large producer of PCBs was Monsanto
Chemical Co., which sold them between 1929 and 1977 under
the Aroclor trademark. PCB production peaked in 1970
when more than 85 million Ibs were produced in the U.S. by
Monsanto of which 57% was Aroclor 1242 (HEW, 1972).
Due to environmental concerns, Monsanto ceased production
of Aroclor 1260 in 1971; restricted the sale of other PCBs to
totally enclosed systems (electrical transformers, capacitors,
and electromagnets) in 1972; and, ceased all production and
sale of PCBs in 1977. In 1979, USEPA issued final rules
under the 1976 Toxic Substances Control Act restricting the
manufacture, processing, use, and distribution of PCBs to
specifically exempted and authorized activities.

In 1977, it was estimated that of the 1.25 billion Ibs of PCBs
sold in the U.S. since 1929, 750 million Ibs (60%) were still in
use, 290 million Ibs (23%) were in landfill and dumps, 150
million Ibs (12%) had been otherwise released to the
environment, and only 55 million Ibs (5%) had been
destroyed by incineration or degraded in the environment
(Lavigne, 1990). The 1242,1254, and 1260 Aroclors
comprise approximately 80% of the PCBs produced in the
U.S. by Monsanto.

Approximately 200,000 transformers containing askarel (a
generic name for PCB fluid) were in use in the U.S. Half of
these were estimated to be still in service in 1990 (Derks,
1990).

Approximately 17% of CERCLA sites involve PCB
contamination (Haley et al., 1990). The potential for DNAPL
migration is greatest at sites where PCBs were produced,
reprocessed, and/or disposed in quantity.
Transformer oil contamination site in
Regina, Saskatchewan (Roberts et al., 1982;
Schwartz et al., 1982; and, Anderson and
Pankow, 1986; Atwater, 1984)

Contamination at a PCB storage and
transfer station in Smithville, Ontario
(Feenstra, 1989; Mclehvain et al, 1989)

Other references:
Addison (1983), Alford-Stevens (1986),
Derks (1990), Feenstra (1989), Griffin and
Chian (1980), HEW (1972), Hutzinger et
al. (1974), Lavigne (1990), Mclelwain et al.
(1989), Miller (1982), Moein et al. (1976),
Monsanto (undated), Monsanto (1988),
Moore and Walker (1991), NRCC (1980),
USEPA (1983), USEPA (1990c), Wagner
(1991)
DNAPL mixtures and uncommon DNAPLs including
pesticides and herbicides
Chemical industry facilities
Waste handling, reprocessing, and
disposal sites
Many industrial waste disposal sites contain complex DNAPLs
mixtures derived from off-specification materials and process
residues.
Chlorinated organic chemical contamination
at hazardous waste sites in Niagara Falls,
N.Y. (Cohen et al, 1987; Faust et al, 1990;
and, Finder et al, 1990)

Motco CERCLA site in LaMarque, Texas
(Connor et al, 1989; and, Newell et al,
1991)
-------
1.7
1.6
1.5
1 1.44

o
CJ
c_> i a
CD •*-•-'

00
1.2
1.1

Tetrachloroethene
--T
Caroon i etracnioride r

H
1,1

tt~
•
mm
1,2-Dichloropropane

I
,2-Trichloroethane

Methylene Chloride

f
\
1-Dichloroethene

•

I
1-Dichloroethane

Ls-^
L Chloroform
|

f
Trlchloroethene

]

1 ,1 ,2,2-Tetrachloroethane

r i
1,1,1-Trichloroethane II

T
..
Chlorobenzene

L
1,

,
•

H 1.2-Dichlorobenzene

2-Dlchloroethane

I
1
PCB Aroclor 1221

I Water
T

I 1 1 1 1 — 1 — TTT 1 1 | 1 1 — | | | I
Note: All values at 20-25 deg. C. except for
PCB viscosities which are at 38 deg. C
(see Appendix A).

PCB Aroclor 1242
i*

)B Aroclor 101 (

PCBAroclor1232

1 1

III!

•m

•

PCB Aroclor 1254

BArocloM248

! Typical range o
creosote and
coal tar

—

-
-

0
10

Absolute Viscosity (cp)
100
1000
Figure 3-1. Specific gravity versus absolute viscosity for some DNAPLs. DNAPL mobility increases with increasing densityrviscosity
ratios.
-------
Table 3*2. U.S. Production of Selected DNAPL Chemicals In libs (U.S. International Trade; Commission data, no entry means no data available).
Chemical
Compound
Aniline
o-Anisidine
Benzyl chloride
Bromoethane
Carbon disulfide
Carbon tetrachloride
Chlorobenzene
Chloroform
Chloropicrin
1 ,2-Dibromo-3-chloro-
propane
Dibutyl phthalate
1 ,2-Dichlorobenzene
1,2-Dichloroelhane
1 ,2-Dichloropropane
Dicthyl phthalate
Dimethyl phthalate
Ethylene dibromide
Methylene chloride
Nitrobenzene
2-Nitrotoluene
Parathion
Tetrachloroethene
1,2,4-Trichlorobenzene
1 , 1 ,1 -Trichloroethane
1 , 1 ,2-Trichlorofluoro-
methane
1920
3.92E+07

1.25E+06

483E+06

5.32E+07
2.17E+06

1925
1.33E+07

5.73E+05

8.69E+06

3.13E-I-07
3.34E+06

1939
2.64E+07

3.92E+07

1935
3.26E-I-07

5.58E+07

1.92E+06

2.90E+06

4.82E+07

1940
5.57E+07

2.38E+06

1.01E+08

3.08E+06

5.85E+06

6.91E+07
1.10E+01

1945
8.72E+07

4.03E+05
3.55E+08
1.93E+08
2.38E+08
9.22E+06

4.S7E+07
1.18E+07

9.70E+06
1.88E+07

1.16E+08

1950
9.80E+07

1.04E+07

4.26E-t-08
2.17E+08
3.83E+08
2.03E+07

1.98E+07
1.74E+07
3.05E+08

1.61E+07
3.77E+06

3.'97E+07
3.'»7E+07

1955
1.32E+08

1.22E+07
9.22E+06
5.66E+08
Z87E+08
4.36E+08
4.04E+07

2.39E+07
2.56E-I-07
5.10E+08

1.58E+07
3.95E+06

7.40E+07
1.76E+08

5.17E+06
1.78E+08
1.52E+07

1960
1.20E+08
l.:JOE+06
2.1L4E+07
1.27E+07
5.23E+08
3.72E+08
6.05E+08
7.(>4E+07

3.08E+06
l.f$9E+07
2.47E+07
1.27E+09

1.68E+07
3.39E+06

1.13E+08
1.62E+08

7.43E+06
2.09E+08

7.24E+07
1965
1.96E+08
1.59E+06
6.20E+07
1.43E+07
7.S7E+08
5.94E+08
5.46E+08
1.53E+08

3.43E+06
2.00E+07
4.11E+07
2.46E+09
6.11E+07
1.80E+07
4.41E+06

2.11E+08
2.80E+08

1.66E+07
4.29E+08

1.70E+08
1970
3.?*E+08
1.85E+06
7.31E+07
2.1IOE+07
7.21E+08
1.01E+09
4.85E+08
2.40E+08

2.:»E+07
6.62E+07
7.46E+09

Z06E+07
8.12E+06
2.S>7E+08
4.:3E+08
5.4«E+08

1.53E+07
7.07E+08
9.2ME+06
3.(*E+08
2.1WE+08
1975
4.07E+08

3JSOE+07
4.79E+08
9.I36E+08
3.Q6E+08
2.62E+08
5.70E+06

l.:23E+07
5.47E+07
7.'»8E+09
8.42E+07
UTE-t-07
6.77E+06
2.75E-I-08
4.'S>7E+08
4.14E+08

6.79E+08

4.59E+08
2.70E+08
1980
6.59E+08

3.77E+08
7.10E+08
Z83E+08
3.53E+08
5.42E+06

1.23E-I-07
5.47E+07
1.11E+07
7.70E+07
2.09E+07
7.04E+06

5.64E+08
6.12E+08

7.65E+08

6.92E+08
1J8E+08
1985
7.16E408

6.46E+08

2.75E+06
1.09E+07

2.17E+07

1.21E+10

1.72E+07
7.65E+06

4.67E+08
9.13E+06

6.78E+08

8.69E+08
1.76E+08
1990
9.88E+08

4.13E+08
2J7E+08
4.84E+08

1.74E+07
4.87E+07
1.38E+10

1.25E+07

4.61E+08

3.72E+08

8.02E+08
1.34E+08
OJ

ON
-------
3-7
U.S. Production of Selected DNAPLs
1920-1990
Millions of Ibs
Aniline
Carbon Tetrachloride
Chlorobenzene
^ Chloroform
1,2-Dichlorobenzene
1920 1930 1940 1950 1960 1970
Year
1980 1990
1000
800 -
600 -
400 -
200 -
1920
Millions of Ibs
Dibutyl Phthalate
Dimethyl Phthalate
-*- Melhylene Chloride
Nitrobenzene
Tetrachloroethene
Freon 11
1930
1940
1950
1960
1970
1980
1990
Year
Ref: US International Trade Commission
Figure 3-2. U.S. production of selected DNAPLs in millions of Ibs per year between 1920 and 1990.
-------
3-8
Use in
diphenyl oxide
and diphenylphenol
production
15%
Solvent for
pesticides formulations,
diisocyanate manufacture
and decreasing auto
parts 37%
Nitrochlorobenzene
manufacture
Chlorobenzene
(US Production: 237,000,000 Ibs in 1990)
Miscellaneous
Export
Manufacture of chlorodifluoromethane
(70% for refrigerant use, 30% for fluoropolymers)
90%
Chloroform
(US Production: 484,000,000 Ibs in 1990)
Miscellaneous
(polyurethane foam
blowing, metal decreasing
electronic components
degreasing, adhesive
production, etc.)
50%
Industrial
metal
cleaning
(10%)
Exports
Chemical
intermediate
(primarily for
manufacture of
FluorocarbonF-113)
Dry cleaning and
textile processing
53%
Methylene Chloride
(US Production: 461,000,000 Ibs in 1990)
Tetrachloroethene
(US Production: 372,000,000 Ibs in 1990)
Electronics
6%
Coatings
Chemical 2%
intermediate
4% I Miscellaneous
Cold cleaning of metal
parts, electronic components
precision instruments,
fabrics, etc.
4!%
Vapor degreasing
operations
22%
Vapor degreasing of
fabricated metal parts
80%
1,1,1-Trichloroethane
(US Production: 802,000,000 Ibs in 1990)
Trichloroethene
(US Production: est. 170,000,000 Ibs in 1986)
Figure 3-3. Uses of selected cholrinated solvents in the U.S. circa 1986 (data from Chemical Marketing Reporter and
U.S. International Trade Commission).
-------
3-9
fluorocarbon refrigerants have been produced primarily by
duPont under the trade name Freon. In 1990,
approximately 918 million Ibs of fluorinated hydrocarbons
were produced in the U.S. (U.S. International Trade
Commission, 1991). Of the 793 million Ibs of
fluorocarbons produced in 1980: 46% were used as
refrigerants, 20% as foam blowing agents, 16% as
solvents, 7% as fluoropolymers (such as teflon), and < 1%
as aerosol propellants (Austin, 1984). Prior to 1974,
when concerns arose regarding atmospheric ozone
depletion, aerosol propellants were the main end use
(52%) of fluorocarbons.

In 1980, approximately 60% of domestic bromine output
was used to manufacture ethylene dibromide (EDB) for
use in engine fuel antiknock fluids to prevent lead oxide
deposition (Austin, 1984). Use of EDB for this purpose,
however, has diminished with the phaseout of leaded
gasoline. Brominated hydrocarbon DNAPLs are used as
fire retardants and fire extinguishing agents, and in a
variety of other products.

Chlorinated solvents are frequently detected in
groundwater supplies and at disposal sites. For example,
as shown in Table 3-3, chlorinated solvents account for
ten of the twenty organic contaminants detected most
frequently at contamination sites. The halogenated
solvents present an extremely high contamination
potential due to their extensive production and use,
relatively high mobility as a separate phase (high
density:viscosity ratio), significant solubility and high
toxicity. This is reflected in the physical properties,
production, and drinking water standards data for several
Common halogenated solvents provided in Table 3-4.

Subsurface contamination derived from halogenated
solvents are associated with industries that produce
and/or use these DNAPLs and waste disposal sites. Their
subsurface presence is caused by leakage from tanks,
pipelines, drums, and other containers; spillage during
filling operations; and intentional discharge to landfills,
pits, ponds, sewers, etc. Halogenated solvents are
frequently present in mixed DNAPL sites.
3.3 COAL TAR AND CREOSOTE

Coal tar and creosote are complex chemical mixture
DNAPLs derived from the destructive distillation of coal
in coke ovens and retorts. These oily DNAPLs are
generally translucent brown to black, and are
characterized by specific gravities that range between 1.01
and 1.20, viscosities much higher than water (typically 10
to 70 cp), and the distinctive odor of naphthalene (moth
balls).

Historically, coal tar has been produced by coal tar
distillation plants and as a byproduct of manufactured gas
plant and steel industry coking operations. Manufactured
gas plants began producing illuminating or "town" gas for
lighting and heating, and by-products for chemical
production, in several eastern cities circa 1820. More
than 900 gasification plants were operational in the U.S.
by 1920 (Rhodes, 1979). Substantial manufactured gas
production continued until about 1950 when natural gas
became widely available via pipeline. Currently,
approximately 98% of coal-tar produced in the U.S. is a
by-product of blast furnace coke production (Austin,
1984). In 1990, U.S. production of crude coal tar was 158
million gallons (U.S. International Trade Commission,
1991).

During the coking process, coal is heated to between 450"
and 900° C for approximately 16 hours and transformed
to coke and vapors by pyrolysis. The evolved coal vapors
are then condensed to produce water and approximately
8 to 9 gallons of liquid tar per ton of coal upon cooling.
With a specific gravity of between about 1.15 and 1.20,
coal tar sinks and is separated for processing. This coal
tar is then distilled fractionally to yield approximately
(1) 5% light oil (up to 200° C), (2) 17% chemical or
middle oil (200°-25O°C), (3) 7% heavy oil (250°-300°C),
(4) 9% anthracene oil (300°-350°C), and (5) 62% pitch
(Edison Electric Institute, 1984).

Creosote consists of various coal tar distillates (primarily
the 200°C to 400°C fraction) which are blended to meet
American Wood-Preservers'Association (AWPA) product
standards. These creosote blends are then used alone or
diluted with coal tar, petroleum, or, to a very limited
extent, pentachlorophenol. Existing AWPA product
specifications and physical properties are given in Table
3-5. As shown, the specific gravity of creosote products
without petroleum oil ranges from 1.07 to 1.13 (at 38° C
to 15.5° C for water). Dilution with petroleum reduces
the specific gravity of creosote-petroleum solutions to
approximately 1.01 to 1.05.

Commercial utilization of creosote/coal tar for pressure
treating lumber in the United States commenced circa
1870 with construction of a plant in Mississippi (USDA,
1980). Numerous pressure-treating plants were
constructed between 1870 and 1925 to meet the growing
demand for treated railroad cross-ties and bridge timbers.
-------
3-10
Table 3-3. Frequency of Detection of Most Common Organic Contaminants at Hazardous Waste Sites
(TJSEPA, 10/17/91; and Plumb and Pitchford 1985).
RANKING
BASED ON
NUMBER OF
SITES AT
WHICH
ORGANIC
CONTAMINANT
WAS DETECTED
IN ANY MEDIUM
(USEPA, t(V17/»l)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
23
40
ORGANIC
CONTAMINANT
Toluene
Trichloroethene
Methylene Chloride
Benzene
Tetrachloroethene
Ethylbenzene
1,U-
Trichloroethane
Chloroform
Xylenes
bis(2ethylhexyl)
phthalate
Acetone
1,1-Dichloroethane
Phenol
trans-1,2-
Dichloroethene
Napthalene
1,1-Dichloroethene
1,2-Dichloroethane
Vinyl Chloride
2-Butanone
Chlorobenzene
Dibutyl Phthalate
Chloroethane
DNAPL
CHEMICAL?
No
Yes
Yes
No
Yes
No
Yes
Yes
No
No
No
Yes
No
Yes
No
Yes
Yes
No
No
Yes
Yes
No
PERCENTAGE
OF 130G SITES
AT WHICH
CONTAMINANT
WAS
DETECTED IN
ANY MEDIUM
(USEPA,
1W17/M)
60.5
57.3
54.7
53.2
51.8
47.5
47.1
45.4
44.3
41.8
40.0
39.7
39.4
38.4
35.5
33.2
32.7
32.1
31.8
31.4
30.3
18.1
RANKING BASED
ON NUMBER OF
SITES AT WHICH
ORGANIC
CONTAMINANT
WAS DETECTED
IN
GROUNDWATER
(PLUMB AND
mCHFORD,
1985)
2
1
3
7
4
11
9
10
-
6
20
5
14
8
18
13
12
15
-
16
17
19
PERCENTAGE
OF 183 SITES AT
WHICH
CONTAMINANT
WAS DETECTED
IN
GROUNDWATER
(PLUMB AND
* PITCHFORD,
19*5)
31.15
34.43
31.15
27.32
31.15
25.14
26.78
25.14
-
28.42
12.02
28.42
19.13
27.32
12.57
20.22
21.31
16.39
-
16.39
15.30
12.57
-------
3-11

Table 3-4. Production, physical property, and RCRA groundwater action level data for selected DNAPL
chemical.
DNAPL
Carbon tetrachloride
Chlorobenzene
Chloroform
1,2-Dichloroethane
Methylene chloride
Tetrachloroethene
1,1,1-
Trichloroethane
Trichloroethene
1,1,2-Trichloro-
fluoromethane
Water
U.S.
ProducUon
(U»s/yr)
4.13E+08
2.37E+08
4.84E+08
1.38E+10
4.61E+08
3.72E+08
8.02E+08
1.65E+08
L34E+08

Specific
Gravity
1.594
1.106
1.483
1.235
1.327
1.623
1.339
1.464
1,487
1.00
Absolute
Viscosity
(q>)
0.97
0.80
0.58
0.80
0.43
0.89
0.83
0.57
0.42
1.12
Solubility
(mg/L)
800
500
8000
8690
20,000
150
1360
1100
1100

Safe Drinking
Water Act
Maximum
Concentration
Limits (MCLs)
-------
3-12
Table 3-5. American Wood-Preservers' Association standards for creosote and coal tar products.
SPECIFICATIONS
% Water by volume
% Matter insoluble in xylene by weigh!
% Coke residue by weight
Specific gravity at 38° C compared to water
at 15,5° C Whole Creosote
Fraction 235-315° C
Fraction 315-355° C
DistSlatJon - The distillate % by weight on
A water-free basis shall be within the
following limits: Up to 210° C
Up to 235° C
Up to 315° C
Up to 355° C

% Water by volume
% Matter insoluble in xylene by weight
% Coke residue by weight
Specific gravity at 38° C compared to water
at 15.5° C: Whole Creosote
Fraction 235-315° C
Fraction. 315-355° C
Distillation - The distillate % by weight on
a water-free basis shall be within the
following limits: Up to 210° C
Up to 235° C
Up to 315° C
Up to 355° C
NEW MATERIAL
Not less than
Not more
than
OLD MATERIAL
Not less than
Not more
than
P1IP13-91 STANDARD FOR COAL TAR CREOSOTE FOR
LAND, FRESHWATER, AND COASTAL WATER USE
~
-
-
1.08
1.025
1.085
32
52
15
3.5
9.0
1.13
5
25
-
-
-
1.08
1.025
1.085
32
52
3.0
4.5
10.0
1.13
5
25
P2-90 STANDARD FOR CREOSOTE SOLUTIONS
-
-
-
1.08
1.025
1.085
32
52
15
3.5
9.0
1.13
5
25
-
-
-
1.08
1.025
1.085
32
52
3.0
4.5
10.0
1.13
5
25
Notes:
1. The products must be derived entirely from the carbonization of bituminous coal.
2. Creosote-petroleum oil solutions shall consist solely of specified proportions of coal tar creosote
which meets AWPA Standard PI and of petroleum oil which meets AWPA Standard P4. No
creosote-petroleum oil solution shall contain less than 50% by volume of such creosote or more
than 50% by volume of such petroleum oil.
3. The P4-86 Standard for petroleum oil for blending with creosote specifies that petroleum oil for
blending with creosote have a specific gravity at 60°F/60°F not less than 0.%; not more than 1%
water and sediment; a flash point not less than 175° F; and a kinematic viscosity between 4.2 and
10.2 cSt at 210° F.
-------
3-13
The industry continued to expand thereafter due to the
demand for treated poles by developing utility companies.
Prior to the introduction of pentachlorophenol-petroleum
mixtures for wood preservation in the 1930s, creosote/coal
tar was the only potent wood preservative available.

According to U.S. International Trade Commission
records, the production of creosote oil in the United
States has decreased from 145 million gallons in 1953 to
63 million gallons in 1990. Although creosote has lost
market share since the 1950s to inorganic arsenical and
pentachlorophenol preservatives, it remains the dominant
wood preservative in the U. S., particularly for treating
railroad cross-ties, switch ties, and pilings.

Creosote solutions were used at approximately 188 of 631
wood-treating plants operating in the U.S. during 1978
(USDA, 1980). Most of these plants are located in the
east/southeast and west/northwest wood-growing belts as
shown in Figure 3-4. Creosote and coal tar are supplied
to wood-treating operations by coal tar distillation plants.
In 1972, there were 24 coal tar distillation plants
producing creosote in the U.S. (Table 3-6).

During 1976, of an estimated 1.18 billion Ibs of creosote
and coal tar used to treat approximately 47% of all
commercially preserved wood in the U. S.: 415 million Ibs
(35%) were used as straight creosote 626 million Ibs
(53%) were used in creosote/coal tar solutions (averaging
63% creosote and 37% coal tar); 137 million Ibs (12%)
were used in creosote-petroleum solutions typically with
50 to 70% creosote; and 2 million Ibs (<0.2%) were used
in creosote-pentachlorophenol solutions (USDA, 1980).
Creosote-petroleum mixtures are utilized primarily in the
Central and Western U.S. for treating railroad ties.

In addition to wood-preservation, coal tar is used for
road, roofing, and water-proofing solutions. Considerable
use of coal tar is also made for fuels.

Creosote and coal tar are complex mixtures containing
more than 250 individual compounds. Creosote is
estimated to contain 85% polycyclic aromatic
hydrocarbons (PAHs), 10% phenolic compounds, and 5%
N-, S-, and O- heterocyclic compounds. The composition
of creosote and coal tar are quite similar, although coal
tar generally includes a light oil component (<5% of the
total) consisting of monocyclic aromatic compounds such
as benzene, toluene, ethylbenzene, and xylene (BTEX).
Chemical composition data for coal tar and creosote are
given in Table 3-7.
Creosote and coal tar contamination of the subsurface are
associated with wood-treating plants (Figure 3-4), former
manufactured gas plants, coal tar distillation plants, and
steel industry coking plants. In 1988, there were 55
wood-preserving contamination sites on the National
Priority List of CERCLA sites. Creosote and/or coal tar
are a source of groundwater and soil contamination at
approximately forty of these sites (Table 3-8).

Prior to the 1970s, liquid wastes (including creosote and
coal tar) from wood-treating plants were typically
discharged to ponds, sumps, and/or streams. Many plants
had small (1 to 4 acres) unlined ponds to trap the
DNAPL wastes as effluent discharged to streams or
public water treatment facilities (McGinnis, 1989). As a
result, many wood-treating sites have large volumes of
DNAPL-contaminated soils in the vicinity of former
discharge ponds. Soil contamination at wood-treating
plants is also prevalent in the wood treating, track, and
storage areas due to preservative drippage from wood as
it is being moved and stored, and around preservative
tanks and pipelines due to spillage and leaks. Consistent
with the composition of creosote and coal tar, PAHs (in
addition to BTEX compounds) are common contaminants
detected in groundwater at wood-treating sites (Rosenfeld
and Plumb, 1991).

Before development of the coal tar distillation industry in
about 1887, most coal tar derived from manufactured gas
plants was apparently disposed at or near the plant site
(Villaume et al., 1983). Due to their long period of
operation and voluminous coal tar generation, substantial
DNAPL contamination is associated with many former
manufactured gas plants. GRI (1987) recently reviewed
available site investigation reports for 33 former
manufactured gas plants. Heavily contaminated soils or
sludges were found at and near coal tar ponds, coal tar
holding tanks, pipeline and tank spill and leak sites, and,
in DNAPL stratigraphic traps.

DNAPLs similar to coal tar and creosote were produced
by manufactured gas plants that used crude oil rather
than coal. Additionally, refinery (petroleum) coke units
process heavy end hydrocarbon to produce coke and
Bunker C oil with a typical density of 1.01 g/cm3.
3.4 POLYCHLORINATED BIPHENYLS (PCBs)

PCBS are extremely stable, nonflammable, dense, and
viscous liquids that are formed by substituting chlorine
atoms for hydrogen atoms on a biphenyl (double benzene
-------
Figure 3-4. Locations of wood-treating plants in the United States (modified from McGinnis, 1989).
-------
3-15

Table 3-6. Creosote production in the United States in 1972 by plant*.
Plant
Allied Chemicals Corporation
Detroit, Michigan
Ensely, Alabama
fronton, Ohio
Koppers Companv. Inc.
Cicero (Chicago), Dlinois
Follansbee, West Virginia
Fonlana, California
Houston, Texas
Portland, Oregon
Kearny (Seaboard), New Jersey
St. Paul, Minnesota
Swedeland, Pennsylvania
Woodward, Alabama
Youngstown, Ohio
Reillv Tar and Chemical Corp.
Cleveland, Ohio
Granite City, Illinois
fronton, (Provo), Utah
Lone Star, Texas
Chattanooga, Tennessee
USS Chemicals
Clairton, Pennsylvania
Fairfield, Alabama
Gary, Indiana
The Western Tar Products Corp.
Memphis, Tennessee
Terre Haute, Indiana
Witco Chemical Corporation
Point Comfort, Texas
TOTAL ANNUAL PRODUCTION
(1972)
Estimated
Plant Capacity
(million Ibs/yr)
100-200
100-200
100-200
100-200
100-200
200-300
10-20
10-20
10-20
10-20
10-20
100-200
100-200
10-20
10-20
10-20
10-20
10-20
100-300
100-200
100-200
10-20
10-20
10-20

Estimated
Annual Production
(million Ibs)
250-350
350-450
50-100
250-350
20-40
10-20
1,150
•USDA (1980)
-------
Table 3-7. Composition of creosote and coal tar, solubility of pure coal tar compounds, proposed RCRA groundwater action levels, and prevalence in
groundwater at wood-treating sites.
CKtiOSOlt/COAL TAK
FRACTION and
Compounds
VOLATILE AROMATICS
Benzene
Ethylbenzene
Toluene
Xylene
Styrene
ACID EXTRACTABLES
Phenol
Cresols
Pentachlorophenol
Xylenols
2,4-Dimethylphenol
2,3,5 -Trimethylphenol
BASE/NEUTRALS
Naphthalene
Methylnaphthalenes
Dimethylnaphthalenes
Biphenyl
Acenaphthene
Fluorene
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Chrysene
CREOSOTE
1-Comaiercial creosote (USEPA, 1990d)
2-U.S. creosote (USDA, 1980)
3=German creosote (USDA, 1980}
4-Creosote (Mueller et at, 1989)
(Note: Relative weigh! percent* of dominant
compounds in each fraction given for creosote no.
4.)
1234

17.0%
10.0%

1.9%
7.8%
6.0%
19.4%
2.5%
11.8%
8.4%
4.2%

3.0%
2.1%

0.8%
9.0%
10.0%
21.0%
2.0%
10.0%
8.5%
3.0%

7.3%
4.2%

4.1%
9.6%
12.6%

6.8%
5.0%
2.8%

10%
20
30
10
35

5
85%
13
21
8
8
4
8
13
13
4
2
2
COAL TAR
1 - Coal tar (ORI, 1987)
6 - British coal tar (USDA.1980)
7 » U.S. coal tar (USDA, 1980)
567
5%
0.1%

0.2%
1.0%

5%
0.7%
1.1%

0.2%

28%
10.9%
2.4%
3.3%

1.3%
1.6%
4.0%
1.1%

0.25%
0.02%
0.22%
0.19%
0.04%

0.57%
0.10%

0.48%

8.9%
2.0%

0.96%
0.88%
6.30%
1.00%

0.12%
0.02%
0.25%
0.14%
0.02%

0.61%
0.97%

0.36%

8.8%
1.9%

1.06%
0.84%
2.66%
0.75%

Aqueous
Solubility of Pure
Compound
(mg/L)
(Montgomery and
Welkom, 1990;
and Mueller et al,
1989)

1780
152
515
200
300

82,000
24,000
20
5000

32
25
2
7
3
2
1
0.07
0.3
0.1
0.002
RCRA
Groundwater
Action
Levels
Proposed
7/5/91
(mg/L)

0.005
0.7
2
10
0.005

20
2
0.2

0.02

0.1

2
0.002
0.002

1
1
0.0002
% Detects in
GW Samples
from 5
Wood-
treating Sites
(Roscnfeid
and Plumb,
1991)

22%
19%
20%
18%

12%

13%

35%
27%

38%
34%
29%
21%
22%
22%
13%
Average
Concentration lit
Groundwater
Samples at S
Wood-treating Sites
(mg/L)
(RoKitfetd and
Plumb, 1991)

0.033
0.039
0.048
0.094

1.537

1.219

3.312
0.563

0.805
0.661
1.825
0.425
1.025
0.666
0.249
O-S
-------
Table 3-7. Composition of creosote and coal tar, solubility of pure coal tar compounds, proposed RCRA groundwater action levels, and prevalence in
groundwater at wood-treating sites.
CREOSOTE/COAL TAR
FRACTION ami
Compounds
Anthraquinonc
2,3-Benzo[b]fluorene
Methylanthracene
Bcnzo[a]pyrene
Diphenyldimethylnaphth.
Diphenyloxide
N,S,O-HETEROCYCLICS
Quinoline
Isoquinoline
Carbazole
2,4-Dimethylpyndine
Benzo[b]thiophene
Dibenzothiophene
Dibenzofuran
PITCH
TOTAL
CREOSOTE
^Commercial craxote (USEPA, 199W)
2*>U.S. creosote (USDA, 1980)
3- German creosote (USDA, 1980}
4*Creo80te (Mueller et al, 1969)
(Note; Relative weight percents of dominant
compounds in each fraction given for creosote no.
<*->
1234

5.1%

94.1%

4.0%

2.0%

75.4%

3.2%
3.4%

59.3%
1
1
1
1

5%
10
10
10
10
10
10
10

COAL TAR
1 » Coal tar (OKI, 1987}
6 ** British coal tar (USDA.1980)
7 - VS. coal tar (USDA, 1980)
567

1.1%

62%
91%

1.5%

1.33%

59.8%
84.5%

0.60%

63.5%
82.6%
Aqueous
Solubility of Pure
Compound
0»»8/L)
(Montgomery and
Welkom, 1990;
and Mueller et al.,
1989)

0.002
0.04
0.003

6700
4500
1

130
2
10

RCRA
Groundwater
Action
Levels
Proposed
75/91
(mg/L}

0.00005

0.0002

% Detects to
GW Sample*
from 5
Wood-
treating Sites
(RoseafeM
and Plumb,
1991)

28%

Average
Concentration in
Groundwater
Sample* at 5
Wood-treating Sites
(mg/L)
(RoaenfeJd and
Plumb, 1991)

0.057

0.332

-------
3-18
Table 3-8. Creosote and coal tar wood preserving sites on the Superfund list (modified from USEPA, 1989d).
SITE
Hocomonoo Pond
Southern Maryland Wood Treating
L-A. dark & Sons
Atlantic Wood Industries, Inc.
Remold), Inc. (VA Wood Preserving Division)
American Creosote, Pensacola Pit
Brown Wood Preserving
American Creosote, Jackson Plant
Cape Fear Wood Preserving
Koppers Co., Inc. Florence Plant
Reilry Tar, St. Louis Park Plant
Reilry Tar & Chemical, Dover Plant
MacGillis & Gibbs/Bell Lumber
Boise-Cascade-Onan/Medtronics
Burlington Northern (Brainerd)
Joslyn Manufacturing & Supply Co.
Moss-American (Kerr-McGee Oil Co.)
Galesburg/Koppers Co.
Mid-South Wood Products
Texarkana Wood Preserving Co.
United Creosoting Co.
Bayou Bonfouca
Midland Products
Koppers Co., Inc., Texarkana Plant
South Cavalcade Street
North Cavalcade Street
Arkwood
Baxter/Union Pacific Tie Treating
Broderick Wood Products
Montana Pole and Treating
Idaho Pole Co.
Burlington Northern, Somers Plant
Libby Groundwater (Champion International)
Koppers Co., Inc., Oroville Plant
Southern California Edison (Visalla)
J.H. Baxter
Marley Cooling Tower Co.
Wyckoft Co./Eagle Harbor
American Crossarm & Conduit Co.
LOCATION
Westborough, MA
Hollywood, MD
Spotsytvania City, VA
Portsmouth, VA
Richmond, VA
Pensacola, FL
Live Oak, FL
Jackson, TN
Fayettevilte, NC
Florence, SC
St. Louis Park, MN
Dover, OH
New Brighton, MN
Fridley, MN
Brainerd/Baxter, MN
Brooklyn Center, MN
Milwaukee, WI
Galesburg, IL
Mena, AR
Texarkana, TX
Conroe, TX
Slidell, LA
Ola/Birta, AR
Texarkana, TX
Houston, TX
Houston, TX
Omaha, AR
Laramie, WY
Denver, CO
Butte, MT
Bozeman, MT
Somers, MT
Libby, MT
Oroville, CA
Visalla, CA
Weed, CA
Stocktom, CA
Bainbridge Island, WA
Chehalis, WA
CONTAMINATED MEDIA
GW, SW, SO
GW, SW, SO
GW, SW, SO
SO, GW?, SW?
GW, SW, SO
GW, SO
SO
GW, SW, SO
GW, SW, SO
GW, SW, SO
GW, SO
GW, SO
GW, SO
GW, SO
GW, SO
GW, SO
GW, SW, SO
GW, SO, SW?
GW, SO
GW,SO
GW, SO
GW, SW, SO
GW, SO
GW, SO
GW, SO
GW, SO
GW, SO
GW, SW, SO
GW, SO
GW, SO, SO
GW, SW, SO
GW, SW, SO
GW, SW, SO
GW, SW, SO
GW, SO
GW, SW, SO
GW, SO
GW, SO, SD
SO
Notes: GW = Groundwater, SW = Surface water or lagoon, SO = Soil or lagoon sediments, SD = River sediments
-------
3-19
ring) molecule. In the U. S., the only large producer of
PCBs was Monsanto Chemical Co., which sold them
between 1929 and 1977 under the Aroclor trademark for
use primarily as dielectric fluids in electrical transformers
and capacitors. PCBs were also sold for use in oil-filled
switches, electromagnets, voltage regulators, heat transfer
media, fire retardants, hydraulic fluids, lubricants,
plasticizers, carbonless copy paper, dedusting agents, etc.
(Table 3-1).

Production of PCBs peaked in 1970 when more than 85
million Ibs were produced in the U.S. by Monsanto
(HEW, 1972). Due to environmental concerns, Monsanto
ceased production of Aroclor 1260 in 1971; restricted the
sale of other PCBs to totally enclosed applications
(transformers, capacitors, and electromagnets) in 1972;
and, ceased all production and sale of PCBs in 1977. In
1979, USEPA issued final rules under the 1976 Toxic
Substances Control Act restricting the manufacture,
processing, use, and distribution of PCBs to specifically
exempted and authorized activities. The pattern of PCB
production and use in the U.S. between 1%5 and 1977 is
illustrated in Figure 3-5.

Commercial PCBs are a series of technical mixtures,
consisting of many isomers and compounds. Each
Aroclor is identified by a four-digit number such as 1254.
The first two digits, 12, indicate the twelve carbons in the
biphenyl double ring. The last two digits indicate the
weight percent chlorine in the PCB mixture, such as 54%
chlorine in Aroclor 1254. Aroclor 1016, which contains
approximately 41% chlorine, however, was not named
using this convention. Properties and approximate
molecular compositions of the Aroclor formulations are
given in Table 3-9. As shown, the Aroclors become more
dense and viscous and less soluble with increasing
chlorine content. The lower chlorinated formulations
(Aroclors 1016 to 1248) are colorless mobile oils.
Aroclor 1254 is a viscous yellow liquid, and Aroclor 1260
is a black sticky resin.

Aroclors 1242, 1254, and 1260 comprise approximately
80% of the PCBs produced by Monsanto (Feenstra,
1989); and Aroclor 1254 accounted for an estimated 57%
of the more than 85 million Ibs of PCBs manufactured by
Monsanto during peak production in 1970 (HEW, 1972).

PCBs were frequently mixed with carrier fluids prior to
use. For example, PCBs were typically diluted with O to
70% carrier fluid, usually chlorobenzenes or mineral oil,
in askarel. Askarel is a generic name for fire-resistant
dielectric fluids that were used in about 97% of the
estimated 200,000 electrical transformers put in use prior
to 1979 in the U.S. (Derks, 1990; Wagner, 1991;
Monsanto, 1988). Askarel transformers containing 3 to
3000 gallons of PCB oil are generally employed in
hazardous locations where flammability is a concern
(Wagner, 1991). The mix of Aroclor and carrier fluid
type and content, therefore, determines the physical
properties of the PCB fluid, including its density,
viscosity, solubility and volatility. Some petroleum oil -
PCB mixtures form LNAPLs.

In 1977, it was estimated that of the 1.25 billion Ibs of
PCBs sold in the U.S. since 1929,750 million Ibs (60%)
were still in use, 290 million Ibs (23%) were in landfills
and dumps, 150 million Ibs (12%) had been otherwise
released to the environment, and only 55 million Ibs (5%)
had been destroyed by incineration or degraded in the
environment (Lavigne, 1990). An estimated 100,000
electrical transformers containing askarel were estimated
to be still in service as of 1990 (Derks, 1990).

Approximately 15% of CERCLA sites involve PCB
contamination (Haley et al, 1990 and, USEPA, 1990c).
Due to their widespread use and persistence, PCBs are
often detected in the environment at very low
concentrations. The potential for DNAPL migration is
greatest at sites where PCBs were produced, utilized in
manufacturing processes, stored, reprocessed, and/or
disposed in quantity. The extent of PCB contamination
as a DNAPL problem is unclear.
3.5 MISCELLANEOUS AND MIXED DNAPL SITES

Miscellaneous DNAPLs refer to dense, immiscible fluids
that are not categorized as halogenated solvents, coal tar,
creosote, or PCBs. These include some herbicides and
pesticides, phthalate plasticizers, and various exotic
compounds (Appendix A).

Mixed DNAPL sites refer to landfills, lagoons, chemical
waste handling or reprocessing sites, and other facilities
where various organic chemicals were released to the
environment and DNAPL mixtures are present. Many
mixed DNAPL sites derive from the disposal of off-
specification products and process residues in landfills
and lagoons by chemical manufacturers. Typically, these
mixed DNAPL sites include a significant component of
chlorinated solvents.
-------
3-20
O
O
O
m

O
-i_>

0)
O
05
cd
m
o
TOTAL U.S
PCBs
U.S. TRANSFORMER
CAPACITOR
I- PCBs
h U.S. CAPACITOR
PCBs
10
1965
1970
1975
1980
Year

Figure 3-5. Pattern of U.S. PCB production and use between 1965 and 1977 (modified with permission from
ACS, 1983).
-------
3-21
Table 3-9. Approximate molecular composition (%) and selected physical properties of Aroclor PCBs (from
Moore and Walker, 1991; Monsanto 1988 and Montgomery and Welkom, 1990).
Co^bSitttii AND
PROPERTIES
Biphenyl
Monochlorobiphenyl
Dichlorobiphenyl
Trichlorobiphenyl
Tetrachlorobiphenyl
Pentachlorobiphenyl
Hexachlorobiphenyl
Heptachlorobiphenyl
Octachlorobiphenyl
Specific Gravity (@ 25/15.5° C)
Absolute Viscosity (cp @ 38° C)
solubility (|ig/L@25°C)
Vapor Pressure (mm @ 25° C)
LogK^
AROCLOR
1221
11.0
51.0
32.0
4.0
2.0
0.5
—
~
~
1.18
5
200
0.0067
2.8
1232
6.0
26.0
29.0
24.0
15.0
0.5
--
-
-
1.27
8
-
0.0046
3.2
1016
Tr
1.0
20.0
57.0
21.0
1.0
Tr
—
~
1.37
20
240
0.0004
4.4
1242
--
1.0
17.0
40.0
32.0
10.0
0.5
—
-
1.38
24
240
0.0004
4.1
1248
--
..
1.0
23.0
50.0
20.0
1.0
—
-
1.41
70
54
0.0004
6.1
1254
~
--
-
--
16.0
60.0
23.0
1.0
—
1.50
700
12
0.00008
6.5
1260
-
-
-
—
--
12.0
46.0
36.0
6.0
1.56
resin
2.7
0.00004
6.9
Tr = trace (< 0.01%)
-------
-------
4 PROPERTIES OF FLUID AND MEDIA

DNAPL chemicals in the subsurface migrate as volatiles
in soil gas, dissolved in groundwater, and as a mobile,
separate phase. This migration is governed by several
factors and principles, some of which differ from those
controlling miscible contaminant transport. In this
chapter, which is adapted from Mercer and Cohen (1990),
properties of fluid and media associated with DNAPL
flow are described. The influence of these properties on
DNAPL transport at contamination sites is examined
further in Chapter 5 and methods to measure fluid and
media properties are documented in Chapter 10.
4.1 SATURATION

The saturation of a fluid is the volume fraction of the
total void volume occupied by that fluid. Saturations
range from zero to one and the saturations of all fluids
sum to one. Saturation is important because it is used to
define the volumetric distribution of DNAPL, and
because other properties, such as relative permeability
and capillary pressure, are functions of saturation.

Photographs showing variable NAPL distribution and
saturation states observed during laboratory experiments
are presented by Schwille (1988) and Wilson et al. (1990).
In the saturated zone, nonwetting DNAPL flows
selectively through the coarser, more permeable portions
of heterogeneous media, averting the finer-grained zones
which provide greater capillary resistance to entry. As a
result, mobile DNAPL is present as globules (blobs)
connected along fractures, macropores, and the larger
pore openings. Water occupies the smaller pores and
tends to be retained as a film between the nonwetting
NAPL globules and media solids. At residual saturation,
DNAPL occurs as disconnected singlet and multi-pore
globules within the larger pore spaces. The fluid
distribution is more complex in the vadose zone where
NAPL migration occurs by displacing soil gas and
sometimes water from pore throats and bodies. A variety
of saturation states for different subsurface conditions are
illustrated in Figure 4-1.

Measuring saturation presents a costly sampling and
analysis problem. Numerous samples will generally be
needed to assess the distribution of subsurface DNAPL;
and sampling, sample preservation, and analytical
methods must be carefully selected and implemented to
produce reliable results. Ferrand et al. (1989) present a
dual-gamma ("'Cs-^'Am) technique for laboratory
determination of three-fluid saturation profiles in porous
media. They provide porosity and saturation profiles for
sands containing air, water, and trichloroethene or
tetrachloroethene. Gary et al. (1991) demonstrated a
procedure to extract NAPL from soil by shaking a soil-
water suspension with a strip of hydrophobic, porous
polyethylene in a glass jar for several hours. Estimates of
NAPL content were determined by weighing the strips
before and after the extraction procedure. Saturation can
also be estimated gravimetrically in conjunction with
various organic solvent extraction techniques and
specialize distillations (Gary et al., 1989a, b), some of
which are described in Chapter 10. Chemical analyses
can be made to estimate total contaminant concentration
and NAPL saturation. Finally, drilling and sampling,
pumping tests, and borehole geophysical logging can be
used to facilitate field estimates of saturation. These
estimates are qualitative, subject to considerable error
and uncertainty, and the methods used are largely
undocumented.
4.2 INTERFACIAU TENSION

The characteristics of DNAPL movement are largely
derived from interfacial tensions which exist at the
interface between immiscible fluids (NAPL, air, and
water), interfacial tension is related directly to the
capillary pressure across a water-NAPL interface and is a
factor controlling wettability. Liquid interfacial tension
develops due to the difference between the greater mutual
attraction of like molecules within each fluid and the
lesser attraction of dissimilar molecules across the
immiscible fluid interface (Schowalter, 1979). This
unbalanced force draws molecules along the interface
inward, resulting in a tendency for contraction of the
fluid-fluid interface to attain a minimum interfacial area
(Wilson et al., 1990). interfacial tension has been likened
to a contractile skin on the NAPL surface which resists
stretching of the interfacial surface (WCGR, 1991). The
fluid on the concave side of the interface is at higher
pressure than the fluid across the interface and the
pressure difference is proportional to the degree of
interface curvature. As a result of interfacial tension,
nonwetting DNAPLs tend to form globules in water and
water-saturated media.

The interfacial tension between a liquid and its own vapor
is called surface tension. The value of the liquid
interfacial tension is always less than the greater of the
surface tensions for the pure liquids. This results from
the mutual attraction of unlike molecules at the
immiscible liquid interface.
-------
4-2
(a)
(b)
(c)
(d)
(e)
(f)
Figure 4-1. Various immiscible fluid distributions — Dark NAPL (Soltrol) and water in a homogeneous micromodel after (a) the displacement
of water by NAPL and then (b) the displacement of NAPL by water (with NAPL at residual saturation). A more complex blob in
the micromedel is shown in (c). In (d), a pore body is filled with the dark non-wetting phase fluid; and is separated from the
wetting phase by a light intermediate wetting fluid. The distribution of (dark) tetrachlorcethene (PCE) retained in large pore
spaces between moist glass beads after being dripped in from above is shown in (e). In (f), PCE infiltrating into water-saturated
glass beads pooled in coarse beads overlying finer beads and PCE fingers extend into the underlying finer bead layer. Figures (a)
to (d) are from Wilson et al. (1990); Figures (e) and (f) are from Schwille (1988).
-------
Interfacial tension is measured in units of energy per unit
area (or force per unit length) typically using the capillary
rise or Du Nouy tensiometer methods (Chapter 10). It
decreases with increasing temperature (approximately 0.1
dynes/cm/°F for crude oil-water systems) and may be
affected by pH, surface-active agents, and gas in solution
(Schowalter, 1979). interfacial tensions range from zero,
for completely miscible liquids, to 72 dynes/cm, the
surface tension of water at 25°C (Lyman et al., 1982).
Values of interfacial and surface tensions for DNAPL
chemicals, however, generally range between 15 and 50
dynes/cm as shown in Appendix A.
4.3 WETTABILITY

wettability refers to the preferential spreading of one
fluid over solid surfaces in a two-fluid system; it depends
on interfacial tension. Whereas the wetting fluid (usually
water in a DNAPL-water system) will tend to coat solid
surfaces and occupy smaller openings in porous media,
the nonwetting fluid will tend to be constricted to the
larger openings (i.e., fractures and relatively large pore
bodies). Anderson (1986a, 1986b, 1986c, 1987a, 1987b,
and 1987c) prepared an extensive literature review on
wettability, its measurement, and effects on relative
permeability, capillary pressure, residual NAPL
saturation, and enhanced NAPL recovery.

The simplest measure of wettability is the contact angle
at the fluid-solid interface (Figure 4-2). In a DNAPL-
water system, if the adhesive forces between the water and
solid phases exceed the cohesive forces within the water
as well as the adhesive forces between the DNAPL and
solid phases, then the solid-water contact angle, ,
measured into the water (in degrees) will be acute
indicating that water, rather than DNAPL preferentially
wets the medium (Wilson et al., 1990). The porous
medium is considered water-wet if 4> is less than
approximately 70°, NAPL-wet if <£ is greater than 110°,
and neutral if is between 70° and 110° (Anderson,
1986a). Contact angle measurements should be
interpreted as qualitative indicators of wettability because
they do not account for media heterogeneity, roughness,
and pore geometry (Huling and Weaver, 1991; Wilson et
al., 1990). Methods for measuring contact angles and the
bulk wettability of soil and rock samples are described in
Chapter 10 and by Honarpour et al. (1986), Gould
(1964), Anderson (1986b), and Wilson et al. (1990).
wettability relations in immiscible fluid systems are
affected by several factors including media mineralogy,
water chemistry, NAPL chemistry, the presence of organic
matter or surfactants, and media saturation history. With
the exceptions of organic matter (such as coal, humus,
and peat), graphite, sulfur, talc and talc-like silicates, and
many sulfides, most natural porous media are strongly
water-wet if not contaminated by NAPL (Anderson,
1986a). Although water is typically the wetting fluid in
NAPL-water systems and has been considered a perfect
wetting agent in certain petroleum reservoirs (Berg, 1975;
Corey, 1986; Schowalter, 1979; Smith, 1966), other
researchers have documented that petroleum reservoirs,
particularly dolomite and limestone, may be partially or
preferentially wet by oil (Nutting, 1934; Benner and
Bartell, 1941; Treiber et al., 1972 Salathiel, 1973; Leach
et al., 1962 Craig, 1971; Anderson, 1986a).

NAPL wetting usually increases due to adsorption and/or
deposition on mineral surfaces of organic matter and
surfactants derived from NAPL or water (Honarpour et
al., 1986; Thomas, 1982; Treiber et al., 1972; JBF
Scientific Corp, 1981; Schowalter, 1979). For example,
Villaume et al. (1983) reported that coal tar at a former
manufactured gas plant site in Pennsylvania preferentially
wet quartz surfaces, possibly as a result of the presence of
surfactants in the coal tar. NAPL wetting has been
shown to increase with aging during contact angle studies
(Craig, 1971; JBF Scientific Corp., 1981), presumably due
to mineral surface chemistry modifications resulting from
NAPL presence. Equilibrium contact angle
measurements for NAPLs containing surfactants may
require aging samples for hundreds or thousands of hours
(Anderson, 1986b). Another factor to consider is that a
hysteresis effect is frequently observed during contact
angle studies in which the contact angle is less when
NAPL advances over an initially water-saturated medium
than when NAPL is reading from a NAPL-contaminated
medium (Villaume, 1985).

Given the heterogeneous nature of subsurface media and
the factors that influence wettability, some investigators
have concluded that the wetting of porous media by
NAPL can be heterogeneous, or fractional, rather than
uniform (Honarpour et al., 1986; Anderson, 1986a).
Unfortunately, few wettability studies have been
conducted on DNAPLs. Results of contact angle
experiments using several DNAPLs and various substrates
are provided in Table 4-1 (Arthur D. Little, Inc., 1981).
Except for mercury, liquids (NAPL or water), rather than
air, preferentially wet solid surfaces in the vadose zone.
-------
4-4
fluid-fluid
interface
(a) contact 4_ 0 > 110°: DNAPL WET
fluid—fluid interface
(b) contact 4-0 < 70°: WATER WET
Figure 4-2. Contact angle (measured into water) relations in (a) DNAPL-wet and (b) water-wet
saturated systems (modified from Wilson et al, 1990). Most saturated media are
preferentially wet by water (see Chapter 4.3).
-------
4-5
Table 4-1. Results of contact angle experiments conducted using DNAPLs by Arthur D. Little Inc., 1981
(from Mercer and Cohen 1990).
DNAPL
Tetrachloroethene
Tetrachloroethene
1,2,4-Trichlorobenzene
1,2,4-Trichlorobenzene
Hexachlorobutadiene
Hexachlorocyclopentadiene
2,6-Dichlorotoluene
4-Chlorobenzotrifluoride
Carbon Tetrachloride
Chlorobenzene
Chloroform
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL
Tetrachloroethene
Tetrachloroethene
Tetrachloroethene
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL
S-Area DNAPL with solvents
Substrate
clay
clay
clay
clay
clay
clay
clay
clay
clay
clay
clay
clay
clay
clay
fine sand and silt
clayey till (30-40% clay)
Ottawa fine to coarse
sand
Ottawa fine to coarse
sand
Lockport Dolomite
Lockport Dolomite
Lockport Dolomite
Lockport Dolomite
NAPL-contaminated
fine sand
soils with vegetative
matter
paper
wood
cotton cloth
stainless steel
clay
clay
Medium
APL
air
APL
air
water
water
water
water
water
water
water
APL
water
air
water
water
water
water
water
air
water
air
APL
water
water
water
water
water
water (SA)
water
Contact Angle (")
23-48
153-168
28-38
153
32-48
32-41
30-38
30-52
27-31
27-34
29-31
21-54
20-37
170-171
30-40
20-37
33-50
33-45
16-21
171
16-19
164-169
45-105
50-122
31
34-37
31-33
131-154
25-54
15-45
Notes: Adsorbed S-Area (OCC Chemical Corporation site in Niagara Falls, NY) chemicals were
detected on some of the clay samples. APL refers to aqueous phase liquids (water containing
dissolved chemicals). S-Area DNAPL is composed primarily of tetrachlorobenzene,
trichlorobenzenes, tetrachloroethene, hexachlorocyclopentadiene, and octachlorocyclopentene.
SA refers to surface-active agents (Tide* and Alconox*) which were added to the water.
-------
4-6
4.4 CAPILLARY PRESSURE

Capillary pressure causes porous media to draw in the
wetting fluid and repel the nonwetting fluid (Bear, 1972).
This is due to the dominant adhesive force between the
wetting fluid and media solid surfaces. As a result of
contact angle, a meniscus exists at the interface between
two immiscible fluids in a pore with a radius of curvature
that is proportional to the pore radius (Wilson et al,
1990). The pressure drop across this curved interface is
known as capillary pressure which is equal to the
difference between the nonwetting fluid pressure and the
wetting fluid pressure (Figure 4-3). For a water-NAPL
system with water being the wetting phase, capillary
pressure, P0 is defined as:
(4-1)
where PN is the NAPL pressure and Pw is the water
pressure.

Capillary pressure is a function of interfacial tension, u,
contact angle, , and pore size (Bear, 1979):
Pc = (2 a cos ) I r
(4-2)
where r is the radius of the water-filled pore resisting
NAPL entry and a is the interfacial tension between
NAPL and water with the subscripts dropped. Consistent
sets of units for these and other parameters are given in
Appendix B. Equation 4-2 is valid only for immiscible
fluid interfaces that form subsections of a sphere.
Capillary pressure increases as r and decrease and as a
increases.

The capillary pressure that must be overcome for a
nonwetting NAPL to enter the largest pores (which offer
the least capillary pressure resistance) in a water-
saturated medium is known as the threshold or
displacement entry pressure. Because capillary forces can
restrict the migration of NAPL into water-saturated
media, fine-grained layers with small r can be capillary
barriers. That is, before NAPL can penetrate a water-
saturated porous medium, the NAPL pressure head must
exceed the resistance of the capillary forces (e.g., Schwille,
1988). The thickness or height of a NAPL column
required to develop sufficient NAPL pressure head to
exceed capillary force resistance is known as the critical
NAPL thickness (or height), z,,.

Capillary pressure effects explains much of the
distribution and behavior of subsurface DNAPL (see
Chapter 5). DNAPL penetration of the vadose zone is
influenced by the distribution of water content and pore
openings; and enhanced by dry conditions and inclined,
relatively permeable pathways such as those provided by
fractured, root holes, and dipping bedding plane
laminations. Upon reaching the capillary fringe above the
water table, sinking DNAPL will tend to be obstructed
and spread laterally until sufficient DNAPL thickness has
accumulated to exceed the threshold entry pressure at the
capillary fringe (Schwille, 1988; Cary et al., 1989b; de
Pastrovich et al., 1979, and Wilson et al., 1990).
Similarly, in the saturated zone, DNAPL will tend to
spread laterally over fine-grained capillary barriers and
sink through fractures and coarser media where possible
as depicted in Figure 4-4 (Kueper and Frind, 199la;
Kueper and McWhorter, 1991; Schwille, 1988).
Laboratory experiments and contamination site findings
clearly demonstrate that even small-scale differences in
pore size distributions can control the path of DNAPL
migration.

Several relationships between the different forces
affecting DNAPL migration (gravity, capillary pressure,
and hydraulic gradients) for a variety of assumed
conditions are given in Table 4-2. The equations in Table
4-2 approximate capillary pressure because they do not
strictly account for the complicated pore geometries and
distributions in natural porous media. Nevertheless, these
equations provide a means to examine the conditions of
subsurface DNAPL movement. Example applications of
several of these relationships are provided in Chapter 5.3.
Equations for estimating threshold entry pressures and
critical DNAPL heights which must be exceeded for
DNAPL penetration of water-saturated media are
introduced below.

The threshold entry pressure can be estimated as an
equivalent head of water by
hc = (2 a cos <£) / (r Pw g)
(4-3)
where h,. is the capillary rise of the wetting fluid (water),
pw is the density of water, and, g is acceleration due to
gravity, for conditions of hydrostatic equilibrium where
water above, within, and below the DNAPL body is
connected hydraulically and there exists zero capillary
pressure at the top of the DNAPL body. This latter
condition will be present when the top of the DNAPL
body was last under imbibition conditions such as where
residual DNAPL is trapped at the trailing edge of sinking
DNAPL body (Kueper and McWhorter, 1991). Similarly,
the critical DNAPL thickness, z,,, required for DNAPL
-------
4-7
air
the non-wetting fluid

Pa
free surface >
>i"{v t?" ''I^' - ' '
^
/ ;
-
-, ,
'
P - P
* nw ~ * a
P
-------
SOURCE
* J *
3
3
SOURCE
SOURCE
Figure 4-4. Observed infiltration of tetrachloroethene into water-saturated parallel-plate cell
containing heterogeneous sand lenses after (a) 34 s, (b) 126 s, (d) 184 s, (d) 220 s,
(e) 225 s, and (f) 313 s (from Kueper and Frind, 1991 a). Sands are: 1 is #16
Silica sand (k = 5.04E-10 m2, Pd = 3.77 cm water); 2 is #25 Ottawa sand (k =
2. 05E-10 m2, Pd = 4.43 cm water); 3 is #50 Ottawa sand (k = 5.26E-11 m2; Pd =
13.5cm water); and4is#70 Silica sand (k = 8.19E-12 mt;?i = 33.1 cm water).
-------
4-9
Table 4-2. Relationships between capillary pressure gravity, and hydraulic forces useful for estimating conditions
of DNAPL movement (from Kueper and McWhorter, 1991; WCGR 1991; and Mercer and Cohen,
1990).
Condition
(a) Capillary pressure exerted on the surface of a nonwetting NAPL sphere
(b) Capillary pressure exerted on the surface of NAPL in a fracture plane where b
is the fracture aperture
Equation
Pc = PNAPL-Pw=(2<'CoS*)/r
PC = PNAPL - PW = (2*«**) / b
Hydrostatic Condtions
(c) Critical height of DNAPL required for downward entry of DNAPL through the
capillary fringe (the top of the saturated zone)
(d) Critical height of DNAPL required for downward entry of DNAPL into the.
water-saturated base of a lagoon where DNAPL is pooled beneath water, or, below
the water table, for entry of DNAPL into a layer with smaller pore openings
(assuming top of DNAPL body last existed under imbibition conditions)
(e) Critical height of DNAPL required for entry of DNAPL into a water-saturated
fracture at the base of a lagoon where DNAPL is pooled beneath water or, below
the water table, for entry of DNAPL into a water-saturated fracture having an
aperture, b, smaller than the host medium pore radii; or, below the water table, for
entry of DNAPL into a water-saturated fracture segment having an aperture smaller
than that of the overlying heat fracture segment
(assuming top of DNAPL body fast existed under imbibition conditions)
(f) Critical height of DNAPL required below the water table, for entry of DNAPL
into a layer with smaller pore openings where the top of the DNAPL body is under
drainage conditions
(g) The stable DNAPL pool length, L,,, that can exist below the water table
following initial DNAPL migration where $ is the dip angle of the base of the host
medium and Lj is measured parallel to the host medium base slope
(h) The stable DNAPL pool length, L,,, within a fracture that can exist below the
water table following initial DNAPL migration where 6 is the dip angle of the
fracture, b is the maximum fracture aperture at the leading edge of the DNAPL
pool, and L,, is measured parallel to the fracture slope
Hydrodynamic Conditions
(i) Neglecting capillary pressure effects, the critical upward hydraulic gradient, i,.,
required across a DNAPL body of height za to prevent downward DNAPL
migration in a uniform porous medium
(j) Neglecting capillary pressure effects, the minimum hydraulic head difference
between the bottom and top of a DNAPL body of height z,, to prevent downward
DNAPL migration in a uniform porous medium
(k) Neglecting capillary pressure effects, the critical hydraulic gradient, i,., required
to prevent the downward movement of DNAPL along the top of a dipping (angle =
9) capillary barrier (i.e., in sloping fractures, bedding planes, or within a sloping
coarse layer above a fine grained layer) with ic measured parallel to the slope
(1) The critical horizontal hydraulic gradient, ic, which must exist across a DNAPL
pool of length L beneath the water table to overcome capillary resistance and
mobilize DNAPL in the pool (to calculate ic for a pool of DNAPL in a horizontal
fracture, replace r with the fracture aperture, b)
(m) The critical upward hydraulic gradient, ic, requited to arrest the downward
m igration of DNAPL through an aquitard of thickness, AZ, where A?C is the
capillary pressure of DNAPL pooled at the top of the aquitard minus the threshold
entry (displacement) pressure of the aquitard
zn = (2«»s*)/(rgpn)
z,, = (2ocos*) / [rgn - Pw)J
z,, = (2oco«4) / [bg(/>n pv)]
*n = [PcCBneJ-PcCcowvo] / [8w)l
Lj, = (2) 1 [1&(pa - pv) sin 0]
Ln = (2n-pw)sine]

ic = Ah/AZn = (pn - pv) 1 pv
Ah = ic AZ,, = ZntPn -Pw) /Pw
ic = [„ - PW)//JW] + [dV&W*z)]
-------
4-10
penetration into water-saturated pores with radii, r, can
be estimated by

z,, = (2 a cos -A) / [r g (Pn - P.)] (4-4)

where pn is the DNAPL density.

Equation 4-3 is solved for a range of a, <£, and r values in
Figure 4-5. The critical DNAPL thickness, z,,, can be
estimated using Equation 4-4, or variations thereof, for
several conditions, including where

• DNAPL is pooled beneath water above the water-
saturated base of a waste lagoon (Table 4-2d),

• sinking DNAPL encounters the top of the saturated
zone (Table 4-2c),

• below the water table, sinking DNAPL encounters a
layer with smaller pore openings (Table 4-2d),

• below the water table, sinking DNAPL accumulates in
a porous medium above a fractured medium having
fractures apertures that are smaller than the overlying
medium pore radii (Table 4-2e), or,

• DNAPL sinking through fractures encounters fractures
with smaller apertures (Table 4-2e).

For the case of DNAPL entry to the saturated zone
(Table 4-2c), the effective density difference in Equation
4-4 equals pn (because p.^ « 0). For fractured media
(Table 4-2e), hc and z,, can be estimated by substituting a
fracture aperture value, b, for r in Equations 4-3 and 4-4,
respectively. In actuality, the fracture openings are
irregular and the entry pressure will generally be
intermediate between those calculated using the fracture
aperture and radius (Kueper and McWhorter, 1991). The
effects of capillary pressure on DNAPL movement in
fractured media are further discussed by Kueper and
McWhorter (1991).

If the top of a DNAPL body is under drainage conditions
(DNAPL is invading the overlying water), then the
capillary pressure at the top of the DNAPL column will
equal the threshold entry pressure of the host medium
(Kueper and McWhorter, 1991). As a result, capillary
pressure is exerted above and below the DNAPL body
and the z,, value required for downward DNAPL
penetration of a finer layer from an overlying coarser
layer can be estimated by
[Pd(fi«) - Pd<=a*«)] / [g (Pn - P.)]
(4-5)
as given in Table 4-2f where Pd is the threshold entry
pressure (Kueper and McWhorter, 1991).

Under hydrostatic renditions, the potential for DNAPL
penetration of progressively finer pore openings increases
proportionally to the overlying DNAPL column thickness
and the DNAPL-water density difference. Once DNAPL
enters a vertical fracture, it will readily invade finer and
finer fractures with depth due to the increase in DNAPL
column height with fracture depth.

Where DNAPL encounters a coarser underlying medium,
capillary pressure will work to squeeze the DNAPL into
the larger openings. This effect can be demonstrated by
upward rather than downward DNAPL movement after
placing DNAPL (for example, at sn = 0.80 and s, = 0.20)
in a silt layer beneath a very coarse sand with a much
lower DNAPL saturation. Capillary pressure will cause
a portion of the DNAPL in the silt to rise into the
coarser medium against the force of gravity. Therefore,
unless exhausted by residual saturation or prevented by
hydraulic pressure, downward DNAPL movement will
occur readily in homogeneous media or from finer to
coarser layers.

In natural media, pore spaces are extremely complex and
irregular, and their geometry cannot be described
analytically (Bear, 1972). Due to their variability, the
threshold entry pressure for each pore will be different.
Macropore (e.g., fractures and worm tubes) radii can
sometimes be measured directly. The effective mean pore
radius in a porous medium will typically be much smaller
than the mean grain radius. Several researchers have
developed equations that can be used to estimate mean
effective pore radius. Based on laboratory data, Hubbert
(1953) defined capillary pressure and pore radius, r, in
terms of mean grain diameter, d, such that
d/8
(4-6)
and used this relationship to estimate threshold entry
(displacement) pressures in sediments with various grain
sizes for an oil-water system as given in Table 4-3.

Leverett (1941) and others have suggested a semi-
empirical method to evaluate the relationship between
capillary pressure and medium properties in which mean
pore radius, r, can be estimated as
r « (k/n)°
(4-7)
-------
1000
100
10
Liquid Interfacial Tension = 15 Dynes/Cm
He (cm water)
Liquid Interfacial Tension = 30 Dynes/Cm
He (cm water)
Contact Angles:
CA • 0 degrees
CA • 40 degrees
— CA • 60 degrees
CA • 80 degrees
0.1
0.001
0.01 0.1
Pore Radius (mm)
Contact Angles:
CA • 0 degrees
CA - 40 degrees
— CA • 60 degrees
CA • 80 degrees
0.01 0.1
Pore Radius (mm)
1000
100
10
Liquid Interfacial Tension = 45 Dynes/Cm
He (cm water)
Liquid Interfacial Tension = 60 Dynes/Cm
Contact Angles:
CA - 0 degrees
• • •• CA - 40 degrees
--- CA • 60 degrees
CA • 80 degrees
He (cm water)
1000 £
100 E
0.01 0.1
Pore Radius (mm)
Contact Angles:
CA • 0 degrees
• -•• CA • 40 degrees
— CA • 60 degrees
CA - 80 degrees
1 0.001
0.01 0.1
Pore Radius (mm)
Figure 4-5. Capillary pressure as a function of liquid interfacial tension and contact angle (CA) (from Mercer and Cohen, 1990).
-------
4-12
Table 4-3. Threshold entry (displacement) pressures in sediments with various grain sizes
baaed on a (a cos ^) value of 25 dynes/cm (0.025 N/m) and Equation 4-5
(Hubbert, 1953).
Medium
Clay
Silt
Sand
Coarse Sand
Mean Grain Size
Diameter (nun)
< 0.0039
0.0039 - 0.063
0.063 - 2.0
2.0 - 4.0
Threshold Entry
Capillary
Pressure (Pa)
> 100,000
6300 - 100,000
200-6300
100-200
Equivalent
Capillary
Rise of
Water (cot)
>1000
65-1000
2.1-65
1.0 - 2.1
Equivalent
Capillary Rise
of Water (ft)
>33
2.1 - 33
0.06 - 2.1
0.03 - 0.06
-------
4-13
where k and n are the intrinsic permeability and porosity
of the medium, respectively (Bear, 1972).

The threshold entry pressure must be measured to obtain
more accurate data. This is typically done using a
laboratory test cell to determine the height of DNAPL
required to initiate drainage from a water-saturated soil
or rock sample during measurement of the capillary
pressure-saturation, P^s,), relationship. Methods for
measuring threshold entry pressure and Pc^) relations
are described in Chapter 10.

Equation 4-2 implies that the wetting phase will be
progressively displaced from larger-to-smaller pores by
the nonwetting phase with increases in nonwetting NAPL
pressure head and that the P^s,) relationship is driven by
pore size distribution and fluid interfacial tensions
(Parker, 1989). Laboratory experiments demonstrate that
capillary pressure can be represented as a function of
saturation (e.g., Thomas, 1982). Tetrachloroethene-water
drainage capillary pressure-saturation curves determined
for seven sands of varying hydraulic conductivity are
plotted in Figure 4-6 (Kueper and Frind, 1991b). As
shown, the capillary pressure curve is typically L-shaped
with a low threshold entry pressure for coarser-grained,
higher permeability materials and a higher threshold entry
pressure for finer-grained, lower permeability materials.
DNAPL saturation increases with capillary pressure
because higher capillary pressures are required to displace
water from incrementally smaller pore openings.
If the P^s,) curve has been determined for a particular
DNAPL and soil at a contamination site, then the
potential for DNAPL to invade a finer underlying layer
can be assesed by: (1) determining the saturation of soil
samples taken immediately above the finer layer; (2)
estimating the corresponding capillary pressure using the
P^sJ curve; and (3) comparing this capillary pressure to
an estimated or measured value of threshold entry
pressure (Pd) for the finer layer (Kueper and McWhorter,
1991). In less permeable host media, lower DNAPL
saturations will be required to exceed the threshold entry
pressure requirement of an underlying capillary barrier
(Figure 4-6).
To facilitate modeling analyses, laboratory
measurements are often fitted by nonlinear regression
using an empirical parametric model such as the Brooks-
Corey (1964) and van Genuchten (1980) models (see also
Luckner et al., 1989; Parker, 1989). For example, the
Brooks-Corey Pc(sw) relationship is
where se - (s, - ^/(l -s")' s», is the water saturation, $„
is the residual water saturation, P,j is the threshold entry
pressure of the medium corresponding to nonwetting
phase entry, and X is a pore-size distribution index.
Based on the assumptions of Leverett (1941), three-phase
system behavior may also be predicted (Parker, 1989;
Parker et al., 1987).
Different immiscible fluid pairs produce different P^
curves in the same medium. Lenhard and Parker (1987b)
measured P^s,,) relations for several NAPLs (i.e.,
benzene, o-xylene, p-cymene, and benzyl alcohol) in a
sandy porous medium. As part of this study, they
evaluated a scaling procedure (Parker et al., 1987) applied
to PX^) relations of two-phase air-water, air-NAPL and
NAPL-water porous media systems. Relatively good fits
were obtained by matching the experimental data to
multifluid versions of the Brooks-Corey (1964) and van
Genuchten (1980) retention functions. Lenhard and
Parker (1987b) concluded that PcCsJ curves for any two-
phase fluid system in a porous medium can be predicted
by scaling the Pc(s») relationship for a single two-phase
system based on interfacial tension data as suggested by
several prior investigators and illustrated in Figure 4-7.
The capillary pressure, P^, measured for a particular
NAPL,, saturation, and soil can be scaled using liquid
interfacial tension measurements to estimate the capillary
pressure, P^ for NAPLb for the same saturation and soil
using the relation:
(4-9)
where the subscripts a, b, and w refer to NAPL,, NAPL,,,
and water, respectively (WCGR, 1991).

Similarly, Pc(sw) relations can be scaled for curves
generated using different soils (Leverett, 1941; Kueper
and Frind, 199 Ib) by
PCD =
(4-10)
where, for a specific saturation, P,^ is a dimensionless
capillary pressure, P,., is the capillary pressure in the
NAPL,-water-medium, system, a, is the interfacial liquid
tension between NAPL, and water, k, is the permeability
of medium,, n, is the porosity of medium,, subscript b
refers to the NAPLb-water-medium,, system and
parameters, and, a is an exponent fitted by scaling the
P^sJ data for different NAPL-soil system samples.
Kueper and Frind (1991b) used Equation 4-10 to scale
-------
4-14
K=1.21E-02on/s
K=9.10E-03on/s
K=7.38E-03 on/s
K=5.84E-03 cm/s
x xK=5.81E-03 can/s
K=5.44E-03 cm/s
K=4.30E-03 cm/s
WflTER SflTURflTION
Figure 4-6. Tetrachloroethene-water drainage Pc(sw) curves determined for seven sands of
varying hydraulic conductivity (from Kueper and Frind, 1991b).
-------
160
o MR-WATER

A AIR-OIL

OIL-WATER
16O
O. 0 O. 2 0.4 O. 6 O. 8 l.O

WETTING PHASE SATURATION
E
0
D
<
LJ
I
a:
<
_i
_i
•— i
0.
<
U

D
UJ
_l
<
U
120 -
80 -
4O -
<"o
O. O O. 2 O. 4 0.6 O. 8 1.0

WETTING PHASE SATURATION
Figure 4-7. (a) Unsealed and (b) scaled P^s,) relations for air-water, air-benzyl alcohol, and benzyl alcohol-water fluid pairs in
the same porous medium (from Parker, 1989).
-------
4-16
the data that define the seven Pc(s,,) curves shown in
Figure 4-6. The scaled data are plotted with a best-fit
Brooks-Corey curve in Figure 4-8. The validity of
Equation 4-10 is based on the similarity of pore-size
distributions in the scaled media (Brooks and Corey,
1966).

Actual ?„($») relations are more complicated than
portrayed in the monotonic curves shown in Figures 4-6
and 4-7 (Lenhard, 1992; Parker, 1989). Changes in
capillary pressure with saturation depend on whether the
medium is undergoing wetting (imbibition) or drainage of
the wetting fluid (Figure 4-9). This capillary hysteresis
results from nonwetting fluid entrapment and differences
in contact angles during wetting and draining that cause
different drying and wetting curves to be followed
depending on the prior imbibition-drainage history.
During drainage, the larger pores drain the wetting fluid
quickly while the smaller pores drain slowly, if at all. As
a result of this capillary retention, capillary pressure
corresponds to higher saturations on the drainage curve.
During wetting, the smaller pores are filled first and the
larger pores are least likely to fill with the wetting fluid,
thereby leading to a lower capillary pressure curve with
saturation. Significant errors can occur by overlooking
these hysteretic effects during the simulation of some
immiscible flow problems (Lenhard, 1992). Hysteresis is
typically ignored, however, during simulation studies
because its significant is considered minor compared to
uncertainties associated with other parameter estimates
(Parker, 1989).

specific methods to determine entry pressure
requirements and capillary pressure-saturation
relationships are described in Chapter 10. These
measurements provide minimum entry pressure values
and average capillary pressure-saturation curves for the
samples tested. Utilization of laboratory tests on small
samples for interpretation of field-scale phenomena poses
a scale problem that requires careful consideration of site
conditions, sample size, and sample numbers.
4.5 RESIDUAL SATURATION

During migration, a significant portion of NAPL is
retained in porous media, thereby depleting and
eventually exhausting the mobile NAPL body. Below the
water table, residual saturation (sr) of NAPL is the
saturation ('VNApJVvMt) at which NAPL is immobilized
(trapped) by capillary forces as discontinuous ganglia
under ambient groundwater flow conditions. In the
vadose zone, however, residual NAPL may be more or
leas continuous depending on the extent to which NAPL
films develop between the water and gas phases and
thereby interconnect isolated NAPL blobs (Wilson et al.,
1990). The physics of oil entrapment and development of
methods to minimize sr by enhanced oil recovery are of
great importance to the petroleum industry (Mohanty et
al., 1987; Morrow et al., 1988; Chatzis et al., 1988; Wang,
1988; Anderson, 1987c; Chatzis et al., 1983; Melrose and
Brandner, 1974; McCaffery and Batycky, 1983). Similarly,
sr has important consequences in the migration and
remediation of subsurface DNAPL Results of a major
laboratory investigation of the forces affecting NAPL
migration and sr were recently reported by Wilson et al.
(1990).

Residual saturation results from capillary forces and
depends on several factors, including (1) the media pore
size distribution (i.e., soil structure, heterogeneity, and
grain size distribution), (2) wettability, (3) fluid viscosity
ratio and density ratio, (4) interfacial tension, (5)
gravity/buoyancy forces, and (6) hydraulic gradients.
Residual saturation for the wetting fluid is conceptually
different from that for the nonwetting fluid. The
nonwetting fluid is discontinuous at s,, whereas the
wetting fluid is not.

In the vadose zone, NAPL is retained as films, wetting
pendular rings, wedges surrounding aqueous pendular
rings, and as nonwetting blobs in pore throats and bodies
in the presence of water (Wilson et al., 1990; Gary et al.,
1989b). NAPL will spread as a film between the water
and gas phases given a positive spreading coefficient:

V — ( -4- \ (d. 1 1 *\

where £ is the spreading coefficient and a^, amn and am
are the interfacial tensions for air-water, NAPL-water,
and air-NAPA, respectively (Wilson et al., 1990).
Halogenated solvent DNAPLs typically have negative
spreading coefficients and will not spread as films in the
vadose zone due to their internal cohesion (Wilson et al.,
1990).

The capacity of the vadose zone to trap NAPL is
sometimes measured and reported as the volumetric
retention capacity
R = 1000 sr n
(4-12)
where R is liters of residual NAPL per cubic meter of
media and n is porosity (de Pastrovich et al., 1979;
-------
4-17
0.00
0.00
0.25 0.50
WRTER SRTURRTION
0.75
1.00
Figure 4-8. Tetrachloroethene-water drainage Pc(sw) curves (shown in Figure 4-6) for seven
sands of varying hydraulic conductivity scaled using Equation 4-6 (from Kueper
and Frind, 1991b).
-------
100%
'nw
srnw
I
MAIN DRAINAGE
I
'rw
SCANNING
MAIN
IMBIBITION
I
THRESHOLD
ENTRY
PRESSURE
0
>w
100%
LEGEND

O DRAINAGE CONDITIONS
A IMBIBITION CONDITIONS
DISPLACEMENT
PRESSURE
20 40 60 80

% WATER SATURATION
100
(a)
Figure 4-9. (a) Hysteresis in two-fluid Pc(s.) relations whereby changes in capillary pressure depend on whether the medium is
undergoing imbibition (wetting) or drainage of the wetting fluid; in (b), the main drainage and imbibition curves
determined for a tetrachloroethene and water in #70 silica sand are shown (from Kueper and McWhorter, 1991). Note
that s,, is the irreducible wetting fluid content; s^ is the nonwetting fluid residual saturation; s. is the wetting fluid
saturation; and &„, is the nonwetting fluid saturation.
-------
4-19
Schwille, 1988; Wilson and Conrad, 1984). Residual
saturation measurements for a variety of NAPLs and
media compiled in Table 4-4 indicate that sr values
typically range from 0.10 to 0.20 in the vadose zone. In
general, sr and retention capacity values in the vadose
zone increase with decreasing intrinsic permeability,
effective porosity, and moisture content (Hoag and
Marley, 1986; Fussel et al, 1981; Schwille, 1988;
Anderson, 1988).

Residual saturation values in the saturated zone generally
exceed those in the vadose zone because: (1) the fluid
density ratio (NAPL:air versus NAPL:vater above and
below the water table, respectively) favors greater
drainage in the vadose zone; (2) as the nonwetting fluid
in most saturated media, NAPL is trapped in the larger
pores; and, (3) as the wetting fluid (with respect to air) in
the vadose zone, NAPL tends to spread into adjacent
pores and leave a lower residual content behind, a process
that is inhibited in the saturated zone where NAPL is
usually the nonwetting fluid (Anderson, 1988). Values of
sr in saturated media generally range from 0.10 to 0.50
(Table 4-5).

Based on laboratory determinations using various NAPLs
and saturated soils, Wilson et al. (1990) found that sr
could not be reliably predicted from soil texture because
very minor textural differences, such as the inclusion of
trace silt or clay in sand, and the presence of
heterogeneities may significantly affect sr values. They
also reported, for a given NAPL release volume, that: (1)
sr values in fractures and macropores tend to be less than
in homogeneous porous material (see also Schwille,
1988), but can be expected to extend over a larger portion
of the aquifer; and (2) sr values in heterogeneous media
containing discontinuous coarse lenses tend to be greater
than in homogeneous media, but can be expected to
extend over a smaller portion of the aquifer. Similarly,
column experiments performed by Powers et al. (1992)
entrapped larger volumes of NAPL in graded sand than
in uniform sand with the same mean grain size.

On the pore scale, residual NAPL below the water table
is immobilized by the snap-off and bypassing mechanisms
illustrated in Figure 4-10 (Chatzis et al., 1983). Snap-off
occurs in high aspect ratio pores where the pore body is
much larger than the pore throat, resulting in single
droplets or blobs of residual NAPL (Figure 4-10a).
Powers et al. (1992) observed that NAPL entrapped in
coarse, uniform sand was distributed primarily as
spherical, singlet blobs that were larger than singlets
entrapped in finer, uniform sand; and that a much greater
fraction of NAPL is entrapped in large, multi-pore blobs
in graded sand. Bypassing is prevalent when wetting fluid
flow disconnects the nonwetting fluid, causing NAPL
ganglia to be trapped in clusters of large pores
surrounded by smaller pores (Figure 4-1 Ob). As a result
of these mechanisms, sr tends to increase with increasing
pore aspect ratios and pore size heterogeneity (Chatzis et
al., 1983 Powers et al., 1992), and with decreasing
porosity, probably due to reduced pore connectivity and
a decrease in mobile nonwetting fluid in smaller pore
throats (Wilson and Conrad, 1984). Residual saturation
is reduced in near-neutral wettability media because the
capillary trapping forces are minimized (Anderson,
1987c).

As with saturation in general, determination of field-scale
values of sr presents a considerable sampling problem, in
large part, due to the heterogeneity of NAPL
distributions and natural media. Higher sr values will
generally be found in the pathways of preferential NAPL
transport. A sampling volume on the order of the scale
of variability in capillary and permeability properties must
be utilized to obtain a true space-averaged measure of
residual NAPL saturation (Poulsen and Kueper, 1992).
This can be accomplished by analysis of large bulk
samples (which may lead to a misinterpretation of NAPL
absence if NAPL presence is sparse) or of many small
samples (some of which will not contain NAPL).

To determine the potential sr for a particular porous
medium, Wilson et al. (1990) recommend that site-
specific sr measurements be made using an ideal fluid
(such as soltrol or decane) having a sufficient density
difference with water, low solubility low volatility, and
low toxicity rather than the site-specific NAPL (except if
some unusual wetting behavior or NAPL-dependent
interaction between phases is expected). Under low
capillary number and Bond number conditions (see
Glossary for definitions), they found sr values to be
relatively insensitive to fluid properties (Wilson et al.,
1990).

A residual source may contaminate groundwater for
decades because drinking water standards for many
NAPLs are orders of magnitude less than their solubility
limits. Water can be contaminated by direct dissolution
of residual NAPL and/or by contact with soil gas
containing DNAPL volatiles from a residual source in the
vadose zone. Combined with practical limitations on
residual NAPL recovery (Wilson and Conrad, 1984), the
consequences of NAPL dissolution may necessitate
perpetual hydraulic containment at some contamination
-------
4-20

Table 4-4. Laboratory and field residual saturation data for the vadose zone.
Residual Fluid
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Gasoline
Gasoline
Gasoline
Gasoline
Gasoline
Middle distillates
Middle distillates
Middle distillates
Middle distillates
Middle distillates
Fuel oils
Fuel oils
Fuel oils
Fuel oils
Fuel oils
Light oil and gasoline
Diesel and light fuel oil
Lube and heavy fuel oil
Medium
sand
loamy sand
sandy loam
loam
silt loam
silt
sandy clay loam
clay loam
silty clay loam
sandy clay
silty clay
clayey soil
coarse gravel
coarse sand and gravel
medium to coarse sand
fine to medium sand
silt to fine sand
coarse gravel
coarse sand and gravel
medium to coarse sand
fine to medium sand
silt to fine sand
coarse gravel
coarse sand and gravel
medium to coarse sand
fine to medium sand
silt to fine sand
soil
soil
soil
Residual Saturation (sr) or
retention factor (R to IM*>
sr = 0.10
sr = 0.14
sr = 0.16
sr = 0.18
sr = 0.17
sr = 0.07
sr = 0.26
sr = 0.23
sr = 0.19
sr = 0.26
sr = 0.19
sr = 0.18
R = 2.5
R = 4.0
R = 7.5
R = 12.5
R = 20
R = 5.0
R = 8.0
R= 15
R = 25
R = 40
R = 10
R = 16
R = 30
R = 50
R = 80
sr = 0.18
sr = 0.15
sr = 0.20
Ref.
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
3
3
-------
4-21
Table 4-4. Laboratory and field residual saturation data for the vadose zone.
Residual Fluid
Gasoline
Gasoline
Gasoline
Gasoline
Mineral oil
Mineral oil
Mineral oil
Mineral oil
Mineral oil
Mineral oil
Mineral oil
Mineral oil
Mineral oil
Paraffin oil
Paraffin oil
Paraffin oil
DNAPL
Tetrachloroethene
Trichloroethene
Trichloroethene
Trichloroethene
Trichloroethene
Soltrol-130
Tetrachloroethene
Medium
coarse sand
medium sand
fine sand
well graded fine-coarse sand
Ottawa sand (dm=0.5mm) [NA]
Ottawa sand (dm-0.35 mm) [NA]
Ottawa sand (dm=0.25 mm) [NA]
Ottawa sand (dm=0.18 mm) [NA]
glacial till [NA]
glacial till
alluvium [NA]
alluvium
loess [NA]
coarse sand
fine sediments
Ottawa sands
sandy soils
fracture with 0.2 mm aperture
medium sand
fine sand
fine sand
loamy sand
well-sorted, medium-grained,
aeolian sand
fine to medium beach sand
Residual Saturation (sj or
retention toctor (R in Urn*)
sr = 0.15-0.19
sr = 0.12-0.27
sr = 0.19-0.60
sr = 0.46-0.59
sr = 0.110
Sr m 0.140
Sr m 0.172
sr = 0.235
sr = 0.15-0.28
sr = 0.12-0.21
sr = 0.19
sr = 0.19
sr = 0.49-0.52
sr = 0.12
sr = 0.52
sr = 0.11-0.23
sr = >0.01-0.10
R = >3-30
R = 0.05 L/m2
sr = 0.20
sr = 0.19
sr = 0.15-0.20
sr = 0.08
sr = 5.5-12.2
sr ave. = 9.1
sr = 0.002-0.20
Ref.
4
4
4
4
5
5
5
5
5
5
5
5
5
6
6
6
7
8
7
9
9
9
10
11
12
Notes: NA refers to a NAPL-Air unsaturated system (no water); References: 1 = Carsel and Parrish
(1988), 2 = Fussell et al. (1981), 3 = API (1980), 4 = Hoag and Marley (1986), 5 =
Pfannkuch (1983), 6 = Convery (1979), 7 = Schwille (1988), 8 = Feenstra and Cherry (1988),
9 = Lin et al. (1982), 10 = Gary et al. (1989a), 11 = Wilson et al. (1990), 12 = Poulson and
Kueper (1992).
-------
4-22

Table 4-5. Laboratory and field residual saturation data for the saturated zone.
Residual Fluid
Mineral oil
Crude oil
Crude oil
Crude oil
Styrene monomer
Benzene
Benzyl alcohol
p-Cymene
o-Xylene
1,1,1-Trichloroethane
Tetrachloroethene
Kerosene
Gasoline
n-Decane
p-Xylene
Tetrachloroethene
Soltrol
Soltrol
Soltrol
Coal tar
Coal tar
Medium
sandstone
sandstone
sandstone
petroleum reservoirs
sandstone
sand (92% sand, 5% silt, 3% clay)
sand (92% sand, 5% silt, 3% clay)
sand (92% sand, 5% silt, 3% clay)
sand (92% sand, 5% silt, 3% clay)
coarse Ottawa sand
coarse Ottawa sand
medium aeolian sand
medium aeolian sand
medium aeolian sand
medium aeolian sand
medium aeolian sand
medium aeolian sand
clean coarse fluvial sand
clean medium beach sand
siltstone
sandstone
Residual Saturation (sjl or
retention factor (R in L/m*)
sr = 0.35-0.43
sr = 0.16-0.47
sr = 0.26-0.43
sr = 0.25-0.50
sr = 0.11-0.38
sr = 0.24
sr = 0.26
sr = 0.16
sr = 0.19
sr = 0.15-0.40
sr = 0.15-0.25
sr = 0.23-0.29
sr = 0.27-0.31
sr = 0.25-0.29
sr = 0. 20-0.27
sr = 0.26-0.29
sr = 0.22-0.37
sr = 0.16
sr = 0.18
sr = 0.01-0.03
sr = 0.17-0.24
Ref.
1
1
2
3
3
4
4
4
4
5
5
6
6
6
6
6
6
6
6
7
7
Notes: References: 1 = Rathmell et al. (1973), 2 = Wang (1988), 3 = Chatzis et al. (1988), 4 =
Lenhard and Parker (1987b), 5 = Anderson (1988) ,6 = Wilson et al. (1990), 7 = Confidential
site.
-------
4-23
a. high aspect ratio pores (snap-off):
pore
body
wetting
fluid
non-wetting
fluid
pore
throat
pore
throat
pore
throat
b. low aspect ratio pores (no snap-off):
wetting
fluid
non-wetting
fluid
(a)
a) no trapping :
stage 1
stage 2
b) trapping via by-passing :
stage 3
note that due to the
configuration of the
downstream node,
a stable interface is
not formed here.
stage 4
stage 1
stage 2
stage 3
STABLE
c) snap-off at top, by-passing below
stage 1
stage 2
stage 3
stage 4
STABLE
Figure 4-10.
(b)

Sketches illustrating capillary trapping mechanisms: (a) snap-off and (b) by-
passing (modified from Chatzis et al, 1983; from Wilson et al, 1990).
-------
4-24
sites (Mackay and Cherry, 1989 and Cohen et al., 1987).
Unless residual NAPL is replenished by continued
contaminant releases or unusual hydraulic conditions, it
will tend to be slowly diminished by dissolution,
volatilization, and, perhaps, biodegradation. At some
sites, remediation may involve partial mobilization of sr
by increasing the prevailing hydraulic gradient or reducing
interfacial tension.
4.6 RELATIVE PERMEABILITY

When more than one fluid exists in a porous medium, the
fluids compete for pore space. The result is that the
mobility is diminished for each fluid. This diminution can
be quantified by multiplying the intrinsic permeability by
a dimensionless ratio, known as relative permeability.
Relative permeability is the ratio of the effective
permeability of a fluid at a fixed saturation to the
intrinsic permeability; as such, it varies with saturation
from zero to one.

Relative permeability relationships are required for
numerical simulation of immiscible flow problems. Like
capillary pressure, relative permeability can be
represented as a function of saturation and also can
display hysteresis. Due to difficulties associated with
laboratory and field measurement of relative permeability,
alternative theoretical approaches are utilized to estimate
this function from the more easily measured Pc(s,,) data
(Luckner et al., 1989; Parker, 1989; Mualem, 1976).
Laboratory data on two-phase relative permeability are
typically expressed in terms of phase saturation to a
power (n) between 2 and 4 (Faust et al., 1989). For
example, Frick (1962) suggested the following relations
for unconsolidated sands:
= (1 - Se)
(4-13)

(4-14)
where se = (s, - s^)/(l - s^), s. is the water saturation,
and v is the residual water saturation. An example of
relative permeability curves for a water-NAPL system is
shown in Figure 4-lla. General features of these curves
include the following: (1) the relative permeabilities
rarely sum to 1 when both phases are present; (2) kn, is
typically greater than kw at the same saturation for each
respective phase; (3) both k,,, and k, go to zero at a finite
(residual) saturation; and (4) hysteresis is more
prominent for the nonwetting phase than the wetting
phase (Demond and Roberts, 1987). Similar curves are
obtained for air-NAPL systems.

Unfortunately, relative permeability data are generally
unavailable for DNAPLs found at contamination sites.
Lin et al. (1982), however, made laboratory measurements
of pressure-saturation relations for water-air and
trichloroethene (TCE)-air systems in homogeneous sand
columns. These data were converted to two-fluid
saturation-relative permeability data by Abriola (1983)
using Mualem's theory (1976). Other pressure-saturation
data for tetrachloroethene are provided in Kueper and
Frind (1991b) (see Figure 4-6). Reviews of two- and
three-phase relative permeability data, measurement
methods, and governing factors are presented by
Honarpour et al. (1986), Saraf and McCaffery (1982), and
Demond and Roberts (1987). Several measurement
methods are described in Chapter 10.

Three-phase relative permeabilities are required to
describe the simultaneous movement of NAPL, water, and
air at a point. The functional dependence of relative
permeabilities is derived experimentally (Corey et al.,
1956; Snell, 1962). However, given the exceptional
difficulty and expense of measurement, actual site-specific
data and the functional form of three-phase relative
permeability are generally not available, particularly for
DNAPLs. As a result, theoretical models have been
devised to estimate three-phase relative permeability
(Stone, 1970; Stone, 1973; Dietrich and Bonder, 1976;
Payers and Matthews, 1984; Parker et al., 1987; Delshad
and Pope, 1989). For example, Stone (1973) proposed a
model to characterize three-fluid relative permeabilities
using data for two-fluid relative permeabilities. With this
method, relative permeability data for NAPL are acquired
in both water-NAPL and air-NAPL systems. The relative
permeability of NAPL in the three-fluid system is then
calculated as:
* + *«)
(4-15)
where k^* is the relative permeability of NAPL at the
residual saturation of water in the water-NAPL system;
k^ is the relative permeability of NAPL in the water-
NAPL system (a function of water saturation); and k^, is
the relative permeability of NAPL in the air-NAPL
system (a function of air saturation). This equation can
be used to construct a ternary diagram, as given in Figure
4-1 lb.
-------
(b)
Sfl=1
100%
DQ
<
Q_
UJ
0
0
00%
WATER CONTENT
DNAPL CONTENT
o
DNAPL WATER
100%
0
Sa - AIR SATURATION
Sw - WATER SATURATION
Sn = NONAQUEOUS PHASE
SATURATION
Figure 4-11. (a) Water-NAPL relative permeability (modified from Schwille, 1988); (b) ternary diagram showng the relative
permeability of NAPL as a function of phase saturations (from Faust, 1985).
-------
4-26
DelShad and Pope (1989) recently assessd seven different
three-phase relative permeability models by comparing
predicted permeabilities with three sets of experimental
data. They found variable and limited agreement between
the different models and data sets. Similarly, laboratory
relative permeability data often compares poorly with
petroleum reservoir production data (Faust et al, 1989).
Observations of the control exerted by formation
heterogeneity on DNAPL and water flow at
contamination sites suggest that relative permeability
relations should be based on field-scale data which, in
some cases, will tend to be less strongly nonlinear than
the laboratory-scale functions (Faust et al., 1989).
4.7 SOLUBILITY

Aqueous solubility refers to the maximum concentration
of a chemical that will dissolve in pure water at a
particular temperature. Results of laboratory dissolution
experiments (Anderson, 1988; Schwille, 1988) show that
chemical concentrations approximately equal to aqueous
solubility values are obtained in water flowing at 10-100
cm/d through NAPL-contaminated sands. It is widely
reported (e.g., Mackay et al., 1985), however, that organic
compounds are commonly found in groundwater at
concentrations less than ten percent of NAPL solubility
limits, even where NAPL is known or suspected to be
present.

The discrepancy between field and laboratory
measurements is probably caused by heterogeneous field
conditions, such as non-uniform groundwater flow,
complex NAPL distribution, and mixing of stratified
groundwater in a well, and to a lesser extent, NAPL-to-
water mass transfer limitations (Feenstra and Cherry,
1988; Mackay et al., 1985; Powers et al., 1991). Various
studies suggest that dissolution may be rate limited when
NAPL is present as large complex ganglia, groundwater
velocities are high, NAPL saturations are low, and/or the
mass fraction of soluble species in a NAPL mixture is low
(Powers et al., 1992). For halogenated solvents in
particular, these chemical and hydrodynamic processes
promote the creation of large plumes of groundwater with
low chemical concentrations that, however, may greatly
exceed drinking water standards (Tables 3-4 and 3-8).
Another factor to consider is that dissolved chemical
concentrations will also be less than aqueous solubilities
reported for pure chemicals where the NAPL is
composed of multiple chemicals. For this case, the
effective aqueous solubility of a particular component of
the multi-liquid NAPL can be approximated by
multiplying the mole fraction of the chemical in the
NAPL by its pure form aqueous solubility (Banerjee,
1984; Feenstra et al., 1991; Mackay et al., 1991). Details
related to this calculation are presented in Worksheet 7-1.
Alternatively, the effective solubility of individual
components of a complex NAPL can be determined
experimentally (Zalidis et al., 1991; Mackay et al., 1991;
Chapter 10).

As identified in Appendix A DNAPLs vary widely in
their aqueous solubility (Appendix A). Solubilities may
be obtained from literature, measured experimentally, or
estimated using empirical relationships developed
between solubility and other chemical properties such as
partition coefficients and molecular structure. For
example, Lyman et al. (1982) and Kenaga and Goring
(1980) present many regression equations that correlate
aqueous solubility with K^ (octanol/water) and K,,,.
(organic carbon/water) partition coefficients for various
chemical groups. K^ and K^ data for NAPLs are given
in Appendix A. Nirmalakhandan and Speece (1988)
developed a predictive equation for aqueous solubility
based on correlations between molecular structure and
solubility of 200 environmentally relevant chemicals.
Organic concentrations in water can also be estimated
from an equilibrium relationship based on Raoult's Law
and Henry's Law (Corapcioglu and Baehr, 1987). For
most DNAPL chemicals of interest, multiple aqueous
solubilities are reported in the literature (Montgomery
and Welkom, 1990; Montgomery, 1991; Lucius et al.,
1990; Verschueren, 1983).

Factors affecting solubility include temperature,
cosolvents, salinity, and dissolved organic matter.
Although the aqueous solubility of most organic
chemicals rises with temperature, the direction and
magnitude of this relationship is variable (Lyman et al.,
1982). Similarly, the effect of cosolvents (multiple
organic compounds) on chemical solubility depends on
the specific mix of compounds and concentrations. Based
on laboratory data and modeling, Rao et al. (1991),
however, conclude that solubility enhancement for most
organic chemicals will be minor (< 20%) unless cosolvent
concentrations exceed 2% by volume in pore water.
Banerjee (1984) and Groves (1988) describe methods to
predict the solubilities of organic chemical mixtures in
water based on activity coefficient equations. The
aqueous solubility of organic chemicals generally declines
with increasing salinity (Rossi and Thomas, 1981 and
Eganhouse and Calder, 1973). Dissolved organic matter,
such as naturally occurring humic and fulvic acids are
known to enhance the solubility of hydrophobic organic
-------
4-27
compounds in water (Chiou et al, 1986; Lyman et al,
1982).

Subsurface NAPL trapped as ganglia at residual
saturation and contained in pools, such as DNAPL
trapped in depressions along the top of a capillary
barrier, are long-term sources of groundwater
contamination. Factors influencing NAPL dissolution
and eventual depletion include the effective aqueous
solubility of NAPL components, groundwater velocity,
NAPL-water contact area, and the molecular diffusivity of
the NAPL chemicals in water (Feenstra and Cherry, 1988;
Anderson, 1988; Hunt et al., 1988a; Schwille, 1988;
Anderson et al., 1992a, b; Pfannkuch, 1984; Miller et al.,
1990; Mackay et al., 1991). Pfannkuch (1984) reviewed
the literature related to the mass exchange of petroleum
hydrocarbons to groundwater. Laboratory studies of
LNAPL transfer to water were done by the Working
Group (1970), Hoffmann (1969, 1970), Zilliox et al.
(1973, 1974), van der Waarden et al. (1971), Fned et al.
(1979), Zalidis et al. (1991), and Miller et al. (1990).
Schwille (1988), Hunt et al. (1988a), Anderson (1988),
and Mackay et al. (1991) conducted experiments to
analyze the transfer of DNAPL chemicals into
groundwater. Recently, Anderson et al. (1992a, b)
evaluated the dissolution of DNAPL from a well-defined
residual source and from DNAPL fingers and pools.

Experimental data show that mass exchange coefficients
generally (1) increase with groundwater velocity, except
at low velocities where the exchange rate is controlled by
molecular diffusion; (2) increase with NAPL saturation;
(3) increase with the effective aqueous solubility of the
NAPL component; and, (4) decrease with time as NAPL
ages (Pfannkuch, 1984; Miller et al., 1990 Mackay et al.,
1991; Zalidis et al., 1991; Zilliox et al., 1978). The
dissolution process can be rejuvenated, however, by
varying hydraulic conditions (i.e., changing groundwater
flow directions or rates).

The mass exchange rate (mjl), or strength of the
dissolved contaminant source, can be expressed as the
product of the mass exchange coefficient (m^L2A) and
some measure of the contact area (L2). The contact area
of a given mass of residual NAPL ganglia and fingers is
more difficult to estimate, but much greater, than that of
an equivalent mass of pooled NAPL. Laboratory
experiments and theoretical analyses indicate that
dissolution of residual NAPL fingers and ganglia will
result in groundwater concentrations that are near
saturation (Anderson et al., 1992a). These concentrations
will then be subject to the dispersion and dilution
processes noted in the second paragraph of this section.
Similar experimental and mathematical analyses, however,
suggest that dissolution of NAPL pools is mass-transfer
limited (Schwille, 1988; Anderson et al., 1992b; Johnson
and Pankow, 1992). Consequently, dissolution of residual
NAPL fingers and ganglia produces higher chemical
concentrations in groundwater and depletes the NAPL
source more quickly than dissolution of a NAPL pool of
equivalent mass. At many sites, DNAPL pools will
provide a source of groundwater contamination long after
residual fingers and ganglia have dissolved completely.

Many contamination site DNAPLs are composed of
multiple chemicals with varying individual solubilities. At
these sites, preferential and sequential loss of the
relatively soluble and volatile NAPL components leaves
behind a less soluble residue (Senn and Johnson, 1987;
Mackay et al., 1991). This weathering causes the ratios of
chemicals in the NAPL and dissolved plume to change
with time and space. Based on a theoretical analysis of
dissolution kinetics and equilibria of sparingly soluble
NAPL components and experimental results, Mackay et
al. (1991) present equations to estimate: (1) the
equilibrium concentrations of dissolved NAPL chemicals
in contact with a NAPL of defined composition, (2)
changes in the aqueous and NAPL phase chemical
concentrations with time due to NAPL depletion by
dissolution, and (3) the water flow volume (or time) for
a defined depletion of a component within the NAPL
mass.

Similarly, relationships have been developed to estimate
dissolved chemical concentrations in groundwater and the
time required to deplete residual or pooled single-
component NAPL sources (Hunt et al., 1988a; Anderson,
1988; Anderson et al., 1992a, b; Azbel, 1981). These
models are primarily useful as a conceptual tool to assess
the long-term contamination potential associated with
subsurface NAPL. For example, the time needed to
completely dissolve a NAPL source given an existing or
induced interstitial groundwater velocity, Vj, can be
estimated as
t = m /
(4-16)
where m is the NAPL mass, ne is the effective porosity, A
is the cross-sectional area containing NAPL through
which groundwater flow exits with a dissolved NAPL
chemical concentration, C^ The actual dissolution will
generally slow with time due to aging and reduction of
NAPL-water contact area (Powers et al., 1991).
Considering limits to solubility and groundwater
-------
4-28
velocities, it is obvious that dissolution is an ineffective
removal process for significant quantities of many NAPLs

4.8 VOLATILIZATION

Volatilization refers to mass transfer from liquid and soil
to the gaseous phase. Thus, chemicals in the soil gas may
be derived from the presence of NAPL dissolved
chemicals, or adsorbed chemicals. Chemical properties
affecting volatilization include vapor pressure and
aqueous solubility (Appendix A). Other factors
influencing volatilization rate are: concentration in soil,
soil moisture content, soil air movement sorptive and
diffusive characteristics of the soil, soil temperature, and
bulk properties of the soil such as organic-carbon content,
porosity, density, and clay content (Lyman et al., 1982).

Volatile organic compounds (VOCs) in soil gas can: (1)
migrate and ultimately condense, (2) sorb onto soil
particles, (3) dissolve in groundwater, (4) degrade, and/or
(5) escape to the atmosphere. Volatilization of
flammable organic chemicals in soil can create a fire or
explosion hazard if vapors accumulate in combustible
concentrations in the presence of an ignition source
(Fussell et al., 1981).

The partitioning of volatile chemicals in the vadose zone
between the solid, gas, aqueous, and NAPL phases
depends on the volatility and solubility of the VOC, the
soil moisture content, and the type and amount of soil
solids present (Silka and Jordan, 1993). For example,
based on experiments with kerosene, Acher et al. (1989)
found that adsorption of vapor decreased with increasing
soil moisture content. Zytner et al. (1989) observed
greater tetrachloroethene (PCE) adsorption to soil with
higher organic carbon content resulting in a reduced
volatilization rate for both aqueous and pure PCE.
Conversely, increasing soil air movement and/or soil
temperature elevates the volatilization rate.
Volatilization losses from subsurface NAPL are expected
where NAPL is close to the ground surface or in dry
pervious sandy soils, or where NAPL has a very high
vapor pressure (Feenstra and Cherry, 1988).

Estimating volatilization from soil involves (1) estimating
the organic partitioning between water and air, and
NAPL and air; and (2) estimating the vapor transport
from the soil. Henry's Law and Raoult's Law are used to
determine the partitioning between water and air, and
between NAPL and air, respectively. Vapor transport in
the soil is usually described by the diffusion equation and
several models have been developed where the main
transport mechanism is macroscopic diffusion (e.g.,
Lyman et al., 1982; Baehr, 1987). More complex models
are also available (e.g., Jury et al., 1990; Falta et al., 1989;
Sleep and Sykes, 1989; Brusseau, 1991).

Because a chemical can volatilize from a dissolved state
and/or from NAPL, both conditions need be considered
to characterize the total amount of chemical that is
volatilized. Local equilibrium is typically assumed
between the air and other fluids. Henry's Law relates the
concentration of a dissolved chemical in water to the
partial pressure of the chemical in gas:
P — KHCW
(4-17)
where P is the partial pressure of the chemical in the gas
phase (atm), Qy is the concentration of the chemical in
water (mole/m3), and KH is Henry's Law constant (atm
m3/mole). Henry's Law is valid for sparingly soluble, non-
electrolytes where the gas phase is considered ideal
(Noggle, 1985). Henry's Law constants for DNAPL
compounds are given in Appendix A. The tendency of a
chemical to volatilize increases with an increase in
Henry's Law constant.

Raoult's Law can be used to quantify the ideal reference
state for the equilibrium between a NAPL solution and
air (Corapcioglu and Baehr, 1987). Raoult's Law relates
the ideal vapor pressure and relative concentration of a
chemical in solution to its vapor pressure over the NAPL
solution:
XAP
•ArA
(4-18)
where PA is the vapor pressure of chemical A over the
NAPL solution, XA is the mole fraction of chemical A in
the NAPL solution, and PA° is the vapor pressure of the
pure chemical A.

Volatilization represents a source to subsurface vapor
transport. Recent studies have examined soil gas
advection due to gas pressure and gas density gradients
(Sleep and Sykes, 1989; Falta et al., 1989; Mendoza and
Frind, 1990a, b; Mendoza and McAlary, 1990). Density-
driven gas flow can be an important transport mechanism
in the vadose zone that may result in contamination of
the underlying groundwater and significant depletion of
residual NAPL. Density-driven gas flow is a function of
the gas-phase permeability, the gas-phase retardation
inefficient, and the total gas density which depends on
the NAPL molecular weight and saturated vapor pressure
-------
4-29
(Falta et al., 1989). Saturated vapor concentrations and
total gas densities calculated for some common NAPLs
using the ideal gas law and Dalton's law of partial
pressures, respectively, are given in Table 4-6. Density-
driven gas flow will likely be significant where the total
gas density exceeds the ambient gas density by more than
ten percent and the gas phase permeability exceeds 1 X
lO^'m2 in homogeneous media (i.e., coarse sands and
gravel) (Falta et al., 1989; Mendoza and Frind, 1990a, b).
Dense gas emanating from NAPL in the vadose zone will
typically sink to the water table where it and gas that has
volatilized from the saturated zone will spread outward,
The pattern of soil gas migration will be strongly
influenced by subsurface heterogeneities. Soil gas
transport is also discussd in Chapter 5.3 and 8.2.
4.9 DENSITY

Density refers to the mass per unit volume of a substance.
It is often presented as specific gravity, the ratio of a
substance's density to that of some standard substance,
usually water. Density varies as a function of several
parameters, most notably temperature. Halogenated
hydrocarbons generally are more dense than water, and
density increases with the degree of halogenation.
According to Mackay et al. (1985), density differences of
about 1% influence fluid flow in the subsurface. Density
differences as small as 0.1% have been demonstrated to
cause contaminated water to sink in physical model
aquifers over several weeks (Schmelling, 1992). The
densities of most DNAPLs range between 1.01 and 1.65
(1 to 65% greater than water) as shown in Figure 3-1 and
Appendix A. Several simple methods for measuring
NAPL density are described in Chapter 10.
viscosity divided by fluid density is referred to as
kinematic viscosity. At sites with multiple DNAPL types,
therefore, more distant separate phase migration is
usually associated with the less viscous liquids.
Subsurface NAPL viscosity can change with time, typically
becoming thicker as the more volatile, thinner
components evaporate and dissolve from the NAPL mass.
Absolute viscosity data for selected NAPLs are provided
in Appendix A, and measurement methods are described
in Chapter 10.

The NAPL-water viscosity ratio is part of a term used in
the petroleum industry known as the mobility ratio. In a
water flood, the mobility ratio is defined as the mobility
of the displacing fluid (relative permeability/viscosity for
water) divided by the mobility of the displaced fluid
(relative permeability/viscosity for NAPL). Mobility
ratios greater than one favor the flow of water whereas
those less than one favor the flow and recovery of NAPL.

During immiscible fluid displacement in a porous
medium, the interface between the two fluids may become
unstable. Known as viscous fingering, this instability
typically arises when a less viscous fluid moves into a
more viscous fluid (Chouke et al., 1959; Homsy, 1987).
This phenomenon causes fingers of the driving fluid to
penetrate the displaced fluid (Figure 4-12). Where
viscous fingering begins is also influenced by
heterogeneities. These factors are discussed by Kueper
and Frind (1988). As a result of viscous fingering, NAPL
may not occupy the complete cross-sectional area through
which it moves, thus permitting water to flow through
and increase dissolution. Additionally, for a given NAPL
volume, viscous fingering will promote deeper NAPL
penetration than would occur in its absence.
4.10 VISCOSITY

Viscosity is the internal friction derived from molecular
cohesion within a fluid that causes it to resist flow.
Following a release, a low viscosity (thin) NAPL will
migrate more rapidly in the subsurface than a high
viscosity (thick) NAPL assuming all other factors
(including interfacial tension effects) are equal. This is
because hydraulic conductivity, K, is inversely related to
absolute (or dynamic) fluid viscosity, /i, by
K =
(4-19)
where k is the intrinsic permeability, g is the acceleration
due to gravity, and p is the fluid density. Absolute
-------
4-30
Table 4-6. Vapor concentration and total gas density data for selected DNAPLs at 25°C (from Falta et al.
1989).
Chemical
Trichloroethene
Chloroform
Tetrachloroethene
1,1,1 -Trichloroethane
Methylene Chloride
1,2-Dichloroethene
1,2-Dichloroe thane
Chlorobenzene
1 , 1 -Dichloroethane
Tetrachloromethane
Air at 1 atm, 25°C
Molecular
Weight, M
g/mole
131.4
119.4
165.8
133.4
84.9
96.9
99.0
112.6
99.0
153.8
28.6
Vapor Pressure
kPa(@25"C)
9.9
25.6
2.5
16.5
58.4
43.5
10.9
1.6
30.1
15.1
(101.3)
Saturated
Vapor
Concentration
(kg/in*)
0.52
1.23
0.17
0.89
2.00
1.70
0.44
0.07
1.20
0.94

Total Gas
Density kg/in5
1.58
2.11
1.31
1.87
2.50
2.37
1.48
1.23
2.03
1.93
1.17
-------
4-31
(a)
(b)
Figure 4-12. (a) Development of fingering and (b) advanced stages of fingering in Hele-Shaw
cell models (from Kueper and Frind, 1988).
-------
-------
5 DNAPL TRANSPORT: PROCESSES, CON-
CEPTUAL MODELS, AND ASSESSMENT

The properties of fluid and media, and principles of
transport, described in Chapter 4 govern the subsurface
migration of DNAPL chemicals. At field-scale, migration
processes and patterns are controlled by the interaction
of these properties and principles with the porous media
distribution, hydraulic conditions, and the nature of the
DNAPL release. DNAPL migration processes are
described briefly in Chapter 5.1. Laboratory and field
experiments, modeling studies, and site investigations
conducted primarily since 1975 have led to the
development of conceptual models of DNAPL chemical
transport under varied field conditions. These models are
presented and their utility is described in Chapter 5.2.
Several quantitative methods for examining site
conditions within the context of these conceptual models
are discussed in Chapter 5.3. Finally, numerical
simulation of immiscible flow problems is briefly
addressed in Chapter 5.4.
5.1 OVERVIEW OF DNAPL MIGRATION PROCESSES

DNAPL migration in the subsurface is influenced by
(Feenstra and Cherry, 1988): (1) volume of DNAPL
released; (2) area of infiltration; (3) time duration of
release; (4) properties of the DNAPL; (5) properties of
the media; and (6) subsurface flow conditions. Once a
DNAPL release occurs, transport mechanisms include (1)
overland flow; (2) immiscible subsurface flow; (3)
dissolution and solute transport; and (4) volatilization
and vapor transport.
5.1.1 Gravity, Capillary Pressure and Hydrodynamic
Forces

Subsurface DNAPL is acted upon by three distinct forces:
(1) pressure due to gravity (sometimes referral to as
buoyancy or hydrostatic pressure), (2) capillary pressure,
and (3) hydrodynamic pressure (also known as the
hydraulic or viscous force). Each force may have a
different principal direction of action and the subsurface
movement of DNAPL is determined by the interaction of
these forces.

The various forces acting on a given mass of DNAPL
impart potential energy. The magnitude of this potential
energy can be characterized using hydraulic head,
pressure, or hydraulic potential. Hydraulic head is a
potential function, the potential energy per unit weight of
the fluid. Pressure describes the energy on a per unit
volume basis, whereas hydraulic potential is the energy
per unit mass. All of these are scalar quantities, that is,
they are characterized by magnitude only. The rate of
change of hydraulic head, pressure, or hydraulic potential
with distance is known as the gradient of these quantities,
respectively. Gradients of hydraulic head, pressure, or
hydraulic potential are used to determine DNAPL
movement. In the following discussion, the three forces
acting on DNAPL are discussed in terms of head,
pressure, and their gradients.

Gravity forces promote the downward migration of
DNAPL. The fluid pressure exerted at the base of a
DNAPL body due to gravity, Pp is proportional to the
density difference between DNAPL and water (pn-pw)
in the saturated zone (to account for the buoyancy effect
of water), the absolute DNAPL density in the vadose
zone, and the DNAPL body height, z,,, such that
pg =
g(pn - Pw) (saturated zone) (5 -la)
and
= ZH § Pa (vadose zone)
(5-lb)
where g is the acceleration due to gravity (9.807 m/s2).
When using British units (e.g., Ibs, ft), g must be dropped
because weight equals mass multiplied by g. For example,
the Pg acting at the base of a 0.5-m thick pool of
tetrachloroethene below the water table is

Pg = 0.5 m * 9.807 m/s2 * (1620 kg/m3 - 1000 kg/m3)

Pg = 3040 kg/m*s2 = 3040 Pa.
This pressure (Pg) can be converted to an equivalent
pressure head of water,

hg = Zng(Pn - Pw)/(gPw) (5-2)

hg = 0.5 m * [(620 kg/m3) / 1000 kg/m3] = 0.31 m.

Additionally, the hydraulic gradient due to gravity, ip can
be calculated as
lg = (Pn - P*)/P»
(5-3)
which equals 0.620 for tetrachloroethene in water. The
gravity force that drives DNAPL flow is greater in the
vadose zone where the density difference equals the
DNAPL density than in the saturated zone and increases
with depth within a DNAPL body.
-------
5-2
As described in Chapter 4.4, capillary pressure resists the
migration of nonwetting DNAPL from larger to smaller
pore openings in water-saturated porous media. Capillary
pressure effects can be illustrated by considering a
hydrostatic system where DNAPL movement is affected
only by gravitational and capillary forces. The following
discussion of capillary pressure effects in a hydrostatic
system is adapted from Arthur D. Little, Inc. (1982).

The radius of a spherical DNAPL globule at rest in a
pore body approximates that of the pore (Figure 5-la).
For this case, capillary pressure will be exerted uniformly
on the DNAPL globule such that
Pc = 2 a cos I r
(5-4)
where o is the interfacial tension between DNAPL and
water, <£ is the contact angle, and r is the pore radius.

If the DNAPL globule is halfway through the underlying
pore throat (Figure 5-lb), then the capillary pressure
acting on the globule bottom will exceed that acting on
its upper surface. The resulting upward capillary pressure
gradient is given by
i , = [(2ocos<£/rt) - (2ocos^/rp)] /
- l/rp)
(5-5)

(5-6)

(5-7)
where i,.,, is the capillary pressure gradient, Ptt and P^, are
the capillary pressures exerted on the nonwetting fluid in
the pore throat and pore body respectively, r, is the pore
throat radius, rp is the pore body radius, and 2^ is the
height of the DNAPL globule.

If the DNAPL globule is centered within the pore throat
(5-lc), then pore radii (and capillary pressures) at the
upper and lower ends are equal, and the globule can sink
in response to the gravity gradient.

Finally, if the DNAPL globule is significantly through the
pore throat (Figure 5-Id), then a downward capillary
pressure gradient will exist, and both gravity and capillary
pressure will push the globule down into the pore body.

DNAPL migration can occur in a hydrostatic system,
therefore, where the downward gravitational pressure or
gradient exceeds the resisting capillary pressure or
gradient:
Pw)]
[(pn . pw)/pw]
or
5 - 8
(5.9)
The gravity and capillary pressures and gradients are
equal where DNAPL is at rest in a hydrostatic system.

In the field, the capillary pressure exerted downward on
top of a continuous DNAPL body will equal: (1) the
threshold entry pressure of the host medium if there is no
DNAPL above the DNAPL body, or (2) zero if the top of
the DNAPL body was last under imbibition conditions
and is overlain by residual saturation (see Figure 4-9).

The critical height of DNAPL, z,,, in a host medium
required to overcome capillary resistance and penetrate
an underlying finer water-saturated medium is given by
z, = [(2ocos40 (l/r
rraer
/ [g(Pn - p.)] (5-10)
where there is no DNAPL above the DNAPL body
(Kueper and McWhorter, 1991). If the top of the
DNAPL body has last been under imbibition conditions
and is overlain by residual DNAPL that was trapped at
the trailing edge of a sinking DNAPL body, then

z,, = (2m»s^/rfiner) / [g(Pn - Pw)] (5-11)

and rrmer refers to pore radii at the top of the underlying
finer medium (Kueper and McWhorter, 1991). For
example, given this condition, the upward Pc resisting
entry of a PCE column from coarse sand to an underlying
silt layer where a = 0.044 N/m (44 dynes/cm), = 35°,
and the silt layer r = 0.008 mm, can be estimated using
Equation 5-4 as

Pc = [2*0.044 N/m "(cos 35)] / 0.000008 m = 9011 Pa.

Disregarding hydraulic gradients, this capillary pressure is
sufficient, below the water table, to halt the downward
movement of a PCE body with a thickness as great as
1.48 m (based on Equation 5-11).

The significance of pore size variation and DNAPL height
is depicted in Figure 5-2. DNAPL globule A is retained
in the pore space because the gravitational force,
although sufficient to distort the globule bottom, is offset
by the upward capillary pressure gradient. Due to its
greater height and gravity force, DNAPL globule B will
migrate downward to the underlying finer layer, unless it
-------
(a)
Figure 5-1. (a) Spherical DNAPL globule at rest in a pore space within water saturated media; (b) a
nonspherical DNAPL globule at rest halfway through an underlying pore throat because the
downward gravity force is balanced by the upward capillary force; (c) centered within the
pore throat with equal capillary force from above and below, the DNAPL globule will sink
through the pore throat due to the gravity force; and, (d) if the DNAPL globule is primarily
through the pore throat, then the capillary and gravity forces will both push the globule
downward (modified from Arthur D. Little, Inc., 1982). Note that arrows represent the
magnitude of capillary forces.
-------
5-4
Figure 5-2. The effect of pore size and associated capillary pressure on DNAPL body height (modified
from Arthur D. Little, Inc., 1982).
-------
5-5
becomes exhausted by residual saturation. DNAPL
globule C also has the same height and gravity force as
globule B, but it has been immobilized by the increased
capillary pressure gradient caused by the underlying finer
layer. Lastly, DNAPL globule D, with sufficient height to
exceed the resisting upward capillary pressure gradient, is
migrating downward into the underlying finer media.

The hydrodynamic force due to hydraulic gradient can
promote or resist DNAPL migration and is usually minor
compared to gravity and capillary pressures. The control
on DNAPL movement exerted by the hydrodynamic force
rises with: (1) decreased gravitational pressure due to
reduced DNAPL density and thickness, (2) decreased
capillary pressure due to the presence of coarse media,
low interfacial tension, and a relatively high contact angle;
and (3) increasing hydraulic gradient.

Neglecting capillary pressure effects, the upward hydraulic
gradient, ib, and head difference, Ah, necessary to prevent
downward DNAPL migration due to gravity are given by
ih = (Pn - Pw) / P*

and

Ah = z,,(pn - pw) / p.
(5-12)
(5-13)
Hydraulic gradients and head differences required to
overcome capillary and/or gravity forces are further
discussed in Chapter 5.3 and can be calculated using
equations given in Table 4-2.

DNAPL migration will occur if and where the sum of the
driving forces (gravity and possibly hydrodynamic effects)
exceed the restricting forces (capillary pressure and
possibly hydrodynamic effects). The pattern of DNAPL
migration will be greatly influenced by the capillary
properties and distribution of heterogeneous subsurface
media.
5.1.2 DNAPL Migration Patterns

Descriptions of DNAPL transport processes are provided
by Schwille (1988), Wilson et al. (1990), Mercer and
Cohen (1990), Huling and Weaver (1991), USEPA
(1992), Feenstra and Cherry (1988), and others. Key
aspects of subsurface DNAPL flow phenomena are
highlighted below and illustrated in Chapter 5.2.
5.1.2.1 DNAPL in the Vadose Zone

When released to the subsurface, gravity causes DNAPL
to migrate downward through the vadose zone as a
distinct liquid. This vertical migration is typically
accompanied by lateral spreading due to the effects of
capillary forces (Schwille, 1988) and medium spatial
variability (e.g., layering). Even small differences in soil
water content and grain size, such as those associated
with bedding plane textural variations, can provide
sufficient capillary resistance contrast to cause lateral
DNAPL spreading in the vadose zone. Alternatively,
downward movement will be enhanced, and lateral
spreading limited, by dry conditions and the presence of
transmissive vertical pathways for DNAPL transport (i.e,
root holes, fractures, uniform coarse-grained materials,
and bedding planes with high-angle dip).

As it sinks through the vadose zone, a significant portion
of DNAPL is trapped in the porous media at residual
saturation due to interfacial tension effects as described
in Chapter 4. This entrapment depletes and, given a
sufficiently small release or thick vadose zone, may
exhaust the mobile DNAPL body above the water table.
Residual saturation values measured for NAPLs in
variably-saturated soils typically range from 0.05 to 0.20
(Table 4-4), but may be much less if averaged spatially
over a zone where DNAPL has moved through only a
fraction of the sampled volume (Poulsen and Kueper,
1992).

For a given DNAPL release volume, the depth of
infiltration will be influenced by the area over which the
release occurs and the release rate. Two experimental
releases of 1.6 gallons of tetrachloroethene (PCE) into
the vadose zone of a slightly stratified sand aquifer are
described by Poulsen and Kueper (1992). The extent of
PCE penetration resulting from each release was carefully
mapped during excavation of the infiltration area as
shown in Figure 5-3. PCE spilled instantaneously onto
bare ground through a 1.1 ft2 steel cylinder migrated to a
depth of 7 ft (Figure 5-3a). A second release of 1.6
gallons was made by slowly dripping PCE on 0.16 in2 of
ground surface over 100 minutes. PCE from this drip
release infiltrated to the water table at a depth of 10.8 ft
(Figure 5-3b), 3.8 ft deeper than PCE penetration from
the instantaneous spill. This difference was attributed to:
(1) the smaller infiltration area utilized for the drip
release; and, (2) a higher residual PCE content at shallow
depth when pending from the spill release increased the
gravity force and induced PCE movement into a higher
-------
5-6
centimetres
0 60 IPO 180 240
(a)
cen-tlnetres
0 60 120 180 240
Figure 5-3. The overall mapped outline and plan views of PCE migration from (a) an instantaneous release,
and (b) a drip release of 1.6 gallons of PCE which penetrated 2.0 and 3.2 m into the Borden sand,
respectively (reprinted with permission from ACS, 1992).
-------
5-7
proportion of shallow sand laminations (Poulsen and
Kueper, 1992).

PCE from each release was distributed very
heterogeneously as stringers at the millimeter scale due to
the influence of sand bedding stratification. DNAPL
flowed selectively along coarser-grained layers and did not
enter finer-grained layers. The influence of very small-
scale stratification and associated capillary effects on
DNAPL infiltration was greatest for the drip release
where the gravity force was less due to the absence of
PCE pending. Residual PCE saturations of the
laminations containing DNAPL were in the range of 0.02
to 0.20. The results of Poulsen and Kueper (1992) suggest
that small DNAPL releases on the order of only a few
gallons have the potential to penetrate to depths of many
feet below ground surface within hours or days.

DNAPL is retained at residual saturation as films, wetting
pendular rings, wedges surrounding aqueous pendular
rings, and as nonwetting blobs and ganglia in the presence
of water within the vadose zone (Chapter 4.5). This
residual DNAPL will dissolve slowly into infiltrating
precipitation and will be a long-term source for
groundwater contamination (Chapter 4.7). That is, each
recharge event (infiltration of water that reaches the
water table) will transport contaminants to the water
table. Thus, DNAPL immobilized within the vadose zone
can result in multiple repeated incidents of dissolved
contaminant releases to groundwater.

In addition, some of DNAPL will volatilize and form a
vapor extending beyond the separate phase liquid
(Chapters 4.8 and 5.3). These vapors can condense on
soil water and the water table, also causing additional
groundwater contamination. Most dense organic solvents
have high vapor pressures and, where DNAPL exists in
the vadose zone, a plume of solvent vapor develops in the
soil air surrounding the DNAPL source. Modeling
studies indicate that contaminated vapors can diffuse tens
of yards or more from a DNAPL source in the vadose
zone within a period of weeks to months (Mendoza and
McAlary, 1990; Mendoza and Frind, 1990a, 1990b).
Where high vapor pressure compounds with relative
vapor densities significantly greater than air are present
in high permeability media (i.e., coarse sand and gravel),
dense vapors can sink by advection through the vadose
zone to the water table and then dissolve in groundwater
(Falta et al., 1989). Field experiments involving
trichloroethene (TCE) vapor transport in a sand
formation confirm the modeling study findings noted
above (Hughes et al., 1990). These experiments show
that significant groundwater plumes may form over a
period of weeks from solvent vapor sources in a thin (less
than 10 ft thick) vadose zone. Vapor transport can cause
shallow groundwater contamination in directions opposite
to groundwater and/or DNAPL flow. The resulting
groundwater contamination plumes can have high
dissolved chemical concentrations, but tend to be very
thin in vertical extent and occur close to the water table.

In summary, only a small volume of DNAPL is required
to penetrate most vadose zones. Although stratigraphic
layering will cause some lateral migration, penetration
through the vadose zone can be fairly rapid (on the order
of days). Residual DNAPL above the water table will
provide a continuing source of groundwater
contamination via vapor transport and dissolution
processes.
5.1.2.2 DNAPL in the Saturated Zone

Upon encountering the capillary fringe, DNAPL will tend
to spread laterally and accumulate until the gravitational
pressure developed at the base of the accrued DNAPL
exceeds the threshold entry pressure of the underlying
water-saturated medium. When this occurs, DNAPL will
displace water and continue its migration under pressure
and gravity forces. Preferential spreading will occur
where DNAPL encounters relatively permeable layers,
fractures, or other pathways that present less capillary
resistance to entry than underlying less permeable strata.

Given sufficient volume, DNAPL will typically migrate
downward until it reaches a barrier layer upon which it
may continue to flow laterally under pressure and gravity
forces. Transport of DNAPL upon a capillary barrier,
therefore, will be governed in large part by the barrier
layer slope. DNAPL may be immobilized as a reservoir
of continuous immiscible fluid if the capillary barrier
forms a bowl-shaped stratigraphic trap. Multiple DNAPL
reservoirs of varying dimensions may develop in
stratigraphic traps at sites with abundant DNAPL and
complex stratigraphy. Given sufficient accumulation,
DNAPL will overflow discontinuous traps.

In the absence of a stratigraphic trap, mobile DNAPL will
continue to migrate over the surface of the barrier layer.
If the barrier layer slopes in a direction that varies from
that of the hydraulic gradient, DNAPL will move in a
different direction than groundwater flow and solute
transport (unless the hydraulic force is sufficient to
control the DNAPL flow direction, which is unusual).
-------
5-3
Determining the slope and location of low permeability
layers, therefore, can be critical to evaluating DNAPL
migration potential.

Many fine-grained layers are inadequate capillary barriers
to DNAPL migration due to the presence of preferential
pathways which allow spreading DNAPL to sink into
lower formations. For example, as DNAPL spreads above
a fine-grained layer, it may encounter and enter fractures,
root holes, stratigraphic windows, burrow holes,
inadequately sealed wells or borings, etc. DNAPL
migration may occur through hairline fractures that are as
small as 10 microns in diameter. As noted in Chapter
4.4, the potential for DNAPL penetration of progressively
finer pore openings increases proportionally to the
overlying DNAPL column thickness and the DNAPL-
water density difference. Fracture networks are
commonly associated with relatively shallow stiff clayey
soils and nearly all bedrock formations.

As a result of these processes, DNAPL will be present in
the saturated zone as pools and disconnected globules
and ganglia within relatively coarse pathways that are
bounded by fine-grained capillary barriers. A finite
DNAPL source will eventually be immobilized by residual
saturation and/or in stratigraphic traps. Mobile and
immobile DNAPL in the saturated zone will dissolve in
flowing groundwater as described in Chapter 4.7 and
thereby act as a long-term source of groundwater
contamination.
5.2 CONCEPTUAL MODELS

The development and utilization of conceptual models to
explain geologic processes and environments has long
been the province of geoscientists. Contamination site
investigators routinely formulate conceptual models of
chemical migration to guide characterization and clean-up
efforts. Although site conditions, DNAPL properties, and
release characteristics are variable, these parameters
generally conform to certain types of hydrogeologic
environments and releases.

Conceptual model development involves integrating
knowledge of site conditions, physical principles that
govern fluid flow and chemical transport, and past
experiences with similar problems. Field activities are
nearly always guided by some degree of site
conceptualization. Typically, conceptual models are
refined to conform with new information as it becomes
available.
Most of the fundamental physical processes affecting the
subsurface migration of DNAPL chemicals were examined
by Freiderich Schwille in laboratory experiments
conducted in Germany between 1977 and 1984 (Schwille,
1988). Based on his experiments using saturated,
variably-saturated, fractured, and porous media Schwille
developed several conceptual models to illustrate DNAPL
flow, vapor transport of volatilized DNAPL chemicals,
and groundwater transport of dissolved DNAPL
chemicals. Others, most notably researchers at the
Waterloo Centre for Groundwater Research (WCGR,
1991), have further developed and refined these DNAPL
conceptual models. Several DNAPL conceptual model
illustrations are provided in Table 5-1.

DNAPL conceptual models are utilized to assess:

• site characterization priorities,

• the utility of alternative subsurface characterization
methods,

• site data,

• the potential for separate phase DNAPL migration,

• the potential for vapor transport of DNAPL chemicals,

• the potential for dissolution of DNAPL chemicals and
dissolved chemical transport,

• chemical distributions associated with these transport
mechanisms,

• cross-contamination risks associated with
characterization and remedial activities, and,

• the potential effectiveness of alternative remedial
actions.

Several quantitative methods are presented to examine
various site characterization issues within the context of
these conceptual models in following section. In Chapter
6, field investigation objectives and activities are discussed
within the framework provided by these models.
5.3 HYPOTHESIS TESTING USING QUANTITATIVE
METHODS

Based on the properties of fluid and media and transport
processes described in Chapters 4 and 5.1, and the
-------
5-9
Table 5-1. Conceptual models of DNAPL transport processes (modified with permission from ACS, 1992).
CASE
ILLUSTRATION
Case 1: DNAPL Release to Vadose Zone
Only

After release on or near the surface,
DNAPL moves vertically downward under
the force of gravity and soil capillarity.
Because only a small amount of DNAPL
was released, all of the mobile DNAPL is
eventually trapped in pores and fractures
in the vadose zone. Infiltration through
the DNAPL zone leaches soluble organic
constituents from the residual DNAPL
and transports them to the water table,
thereby producing a dissolved organic
contaminant plume in the aquifer.
Migration of gaseous vapors by diffusion
and density flow also act as a source of
dissolved organics to groundwater.
Contaminated vapors are leached by
infiltration which recharges the water
table and sink to contact the saturated
zone.
DNAPL
Residual
Saturation of
: DNAPL in
Vadose Zone
Infiltration, Leaching
and Mobile DNAPL
Vapors
Ground Water
— Flow
Dissolved Contaminant
Plume From DNAPL
Dissolved Contaminant Plume Residual Saturation
I torn DNAPL Soil Vapor
ffrom Newell and Ross, 1992; modified from WCGR,
Infiltration

1 \ \ \ \ \ Ml
/' Sorption from
' Soil Moisture ^— •„ —»- , .
Density Flow —- -+- .~~~
-J, ( J —( CoojHory Fnn9«,.j

, f 1 F
Dissolution into
Groundwoler •
Groundwater Flow
(from Mendoza and Frind, 1990)
Case 2: DNAPL Release to the Vadose
and Saturated Zones

If enough DNAPL is released at or near
the surface, it can migrate through the
vadose zone, overcome the capillary
resistance provided by water-saturated
pores at the capillary fringe, and sink into
the saturated zone because it is denser
than water. DNAPL migration will
continue until the mobile DNAPL is
trapped at residual saturation by capillary
mechanisms and/or in pools above
stratigraphic traps. Groundwater flowing
past the trapped DNAPL leaches soluble
components from the DNAPL, thereby
creating a dissolved contaminant plume
downgradient from the DNAPL zone. As
with Case 1, water infiltrating from the
source zone also carries dissolved
chemicals to the aquifer and contributes
further to the dissolved plume.
AIR OB WATER
FILLED PORE SPACE
TOP OF
CAPILLARY FRINGE

WATER TABLE
LATERAL FLOW AND
POOLING ALONG LOW
PERMEABILITY LAYER
(from Kueper and Frind, 1991)
-------
5-10
Table 5-1. Conceptual models of DNAPL transport processes (modified with permission from ACS, 1992).
CASE
ILLUSTRATION
Focus: DNAPL spreading on the
capillary fringe

As demonstrated during experiments in
porous and fractured media (Schwille,
1988), DNAPL penetration is resisted by
the capillary fringe which results in
lateral spreading.
Top Of
Capillary Fringe
Water Table
Focus: Effect of Layering on DNAPL
penetration, residual saturation,
and dissolved chemical
migration

Within the saturated zone, lateral
spreading of DNAPL is promoted just
above finer layers and generally increases
with decreasing permeability and grain
size. DNAPL saturation typically
increases at the base of coarser layers
overlying finer layers. The rate of
dissolved chemical migration with
groundwater increases with layer
permeability.
(modified from Schwille, 1988)
Residual DNAPL
DNAPL
Dissolved
Plume
(modified from Schwille, 1988)
Case 3: DNAPL Pools and Effect of
Low-Permeability Capillary
Barriers

Mobile DNAPL will continue to sink
downward until it is trapped at residual
saturation (Cases 1 and 2) or until low-
permeability stratigraphic units are
encountered which create capillary
barriers upon which DNAPL pools. In
this figure, a perched DNAPL pool fills
up and then spills over the lip of the low-
permeability lens. The spill-over point
(or points) can be some distance away
from the original source, greatly
complicating the process of tracking the
DNAPL migration. Also see Figure 4-4.
Dissolved
Contaminant
Plume
(from Newell and Ross, 1992)
-------
5-11
Table 5-1. Conceptual models of DNAPL transport processes (modified with permission from ACS, 1992).
CASE
ILLUSTRATION
Case 4: Composite Site

In this case, mobile DNAPL migrates
downward through the vadose zone,
producing a dissolved chemical plume in
the upper aquifer. Although a DNAPL
pool is formed on the fractured clay unit,
the fractures are large enough to permit
vertical migration downward to the
deeper aquifer (also see Case 5).
DNAPL pools in a surface depression in
the underlying capillary barrier and a
second dissolved chemical plume is
formed.
Dissolved
Contaminant
Plumes
Residual DNAPL
"*
DNAPL Pool
(from Newell and Ross, 1992)
7/77///////////////////
Clay
Case 5: Fractured Rock or Fractured
Clay System

DNAPL introduced into a fractured rock
or fractured clay system follows a
complex pathway based on the
distribution of fractures in the original
matrix. The number, density, size, and
direction of the fractures often cannot be
determined due to the heterogeneity of
the fractured system and the lack of
economical formation characterization
technologies. Relatively small volumes of
DNAPL can penetrate deeply into
fractured systems due to the low
retention capacity of the fractures and the
ability of some DNAPLs to migrate
through very small (<20 microns)
fractures. Many clayey units act as
fractured media with preferential
pathways for vertical and horizontal
DNAPL migration.

Focus: DNAPL dissolution, dissolved
chemical migration, and matrix
diffusion in fractured media

DNAPL contained in fractures will
dissolve and be transported through the
fracture network with groundwater, and
will also diffuse into and sorb onto the
porous inter-fracture matrix. Residual
saturation and adsorbed chemicals both
provide long-term sources for
groundwater contamination.
DNAPL RELEASE
JLi
GROUNOWATER
FLOW
DNAPL POOLING
\ DISSOLVED
PLUME
GROUNDWATER
LOWER "* FLOW
AQUIFER
(from Kueper and McWhorter, 1992)
Diffused
into and sorted
onto rock matrix
(from Mackay and Cherry, 1989)
-------
5-12
conceptual models provided in Table 5-1, it is apparent
that several fate and transport issues are common to
many DNAPL sites. Posed as questions, these issues
include the following:

• How much DNAPL is required to sink through the
vadose zone (Chapter 5.3.1)?

• How long will it take DNAPL released at or near the
ground surface to sink to the water table (Chapter
5.3.2)?

• What thickness of DNAPL must accumulate on the
capillary fringe to cause DNAPL to enter the saturated
zone (Chapter 5.3.3)?

• Will a finer-grained layer beneath the contamination
zone act as a capillary barrier to continued downward
migration of DNAPL? What minimum DNAPL
column or body height is required to enter a particular
capillary barrier beneath the water table (Chapter
5.3.4)?

• If DNAPL is perched above a finer-grained capillary
barrier layer, what size fracture or macropore will
permit continued downward migration into (or
through) the capillary barrier (Chapter 5.3.5)?

• What DNAPL saturation at the base of the host
medium must be attained for DNAPL to enter the
underlying finer-grained capillary barrier (Chapter
5.3.6)?

• What upward hydraulic gradient will be required to
prevent continued downward migration of DNAPL
(Chapter 5.3.7)?

• What upslope hydraulic gradient will be required to
prevent continued downslope movement of DNAPL
along the base of a dipping fracture or the base of a
coarser layer underlain by a dipping finer layer
(Chapter 5.3.8)?

• What will be the stable DNAPL pool length that can
exist above a sloping capillary barrier or sloping
fracture below the water table (Chapter 5.3.9)?

• What will be the stable DNAPL height and area after
spreading above an impenetrable flat-lying capillary
barrier (Chapter 5.3.10)?
• What is the volume of DNAPL contained below the
water table within porous or fractured media (Chapter
5.3.11)?

• How will fluid viscosity and density affect the velocity
and distance of DNAPL migration (Chapter 5.3.12)?

• What hydraulic gradient will be required to initiate the
lateral movement of a DNAPL pool or globule
(Chapter 5.3.13)?

• How long does DNAPL in the saturated zone take to
dissolve completely (Chapter 5.3.14)?

• Given a DNAPL source of dissolved groundwater
contamination, how do you determine the movement
of dissolved chemical plumes (Chapter 5.3.15)?

• Given a DNAPL source of vapor contamination in the
vadose zone, how do you determine the relative
movement of the vapor plume (Chapter 5.3.16)?

• How can the chemical composition of a dissolved
plume associated with a DNAPL source be estimated
(Chapter 5.3.17)?

• What is the equivalent mass/volume of DNAPL
contained within a dissolved groundwater plume
(Chapter 5.3.18)?

• What is the relationship between concentrations in soil
gas and groundwater (Chapter 5.3.19)?

• Given a DNAPL source in the vadose zone, how do
you determine the movement of a vapor plume? What
are the conditions that favor vapor transport away
from a DNAPL source in the vadose zone that would
allow soil-gas monitoring (Chapter 5.3.20)?

Relatively simple quantitative methods that can be used
to test hypotheses regarding these issues, in particular, by
making bounding type calculations, are described by
example below.
5.3.1 How much DNAPL is required to sink through the
vadose zone?

The capacity of the vadose zone to trap DNAPL can be
calculated as
VnR = R Vmm = 1000 sr n V.. (5-14)
-------
5-13
or
where: V^ is the liters of DNAPL retained in a volume
of media measured in cubic meters, V^ Vn is the volume
of DNAPL retained in a volume of media, VB (any
consistent units); R is the volumetric retention capacity
in liters of residual DNAPL per cubic meter of media; sr
is residual Saturation and n is porosity. Measured values
of R and sr for variably-saturated media are given in
Table 4-4. Equation 5-15 is solved for a range of $„ n,
and Vm values in Figure 5-4.

For example, how much DNAPL would have to be
released over aim2 area to reach a water table 15 m
below ground surface? If we assume a residual saturation
of 0.1, a porosity of 0.3, and no lateral spreading as the
DNAPL sinks, then only 0.45 m3 of DNAPL would be
required to penetrate 15 m to the water table. For a
given DNAPL release volume, the depth of penetration
will increase with decreases in n, &„ lateral spreading, and
mass loss due to processes such as volatilization and
dissolution. The presence of macropores and fractures
may facilitate deep penetration of small DNAPL volumes.
Although lateral spreading caused by stratified media will
generally slow DNAPL penetration in the vadose zone,
this calculation demonstrates that leaks on the order of
tens of gallons can reach the water table.
5.3.2 How long will it take DNAPL released at or near
the ground surface to sink to the water table?

The rate of DNAPL infiltration in the subsurface may be
extremely rapid. For example, in laboratory experiments,
Schwille (1988) observed tetrachloroethene to sink
through 2 ft of variably saturated coarse sand in 10
minutes and through 3 ft of saturated coarse sand in 60
minutes. At this rate of penetration (with no lateral
diversion), for example, it would take a DNAPL such as
PCE approximately 5 hours to penetrate 60 ft of coarse
sand in the vadose zone. The actual penetration time will
most likely be greater because of soil heterogeneities and
will vary with soil conditions and DNAPL properties (i.e.,
density and viscosity). However, this calculation shows
that for a sufficient volume, DNAPL can reach a
relatively deep water table in days to weeks, as opposed
to years.
5.3.3 What thickness of DNAPL must accumulate on the
capillary fringe to cause DNAPL to enter the
saturated zone?

As illustrated in Table 5-1 (Case 2), upon reaching the
capillary fringe above the water table, sinking DNAPL
will tend to be obstructed and spread laterally until a
sufficient DNAPL thickness has accumulated to exceed
the threshold entry pressure at the capillary fringe.
DNAPL entry will typically occur through the largest
pore connections beneath the area of accumulation. At
some sites, DNAPL entry will be facilitated by
heterogeneous wetting characteristics of the medium (e.g.,
a portion of sediment containing a high organic matter
content conducive to DNAPL entry see Chapter 4.3)
and/or enhanced DNAPL wetting of solid surfaces due to
the presence of surfactant contaminants. The critical
height, z,,, of DNAPL required for downward entry of
DNAPL through the capillary fringe can be estimated by
(rgpn)
(5-16)
where a is the interfacial tension between the DNAPL
and water, $ is the wetting contact angle, r is the pore
radius, g is gravitational acceleration, and pn is the
density of DNAPL.

Given a = 0.040 N/m, = 35°, and, pn = 1300 kg/m3,
Equation 5-16 is solved for pore radii from 0.0001 to 1
mm in Figure 5-5. The DNAPL thickness, z,,, required to
enter the saturated zone varies significantly with pore
size, but is relatively insensitive to interfacial tension
(which typically varies within a factor of about 3, between
0.015 and 0.50), DNAPL density (which typically varies
within a factor of < 2, from 1.01 to 1.70), and contact
angle (unless 0 is > 60°). As shown, substantial DNAPL
thicknesses must accumulate above the capillary fringe to
penetrate water-saturated clay and silt pores (i.e.,
approximately >20 m and 0.8-20 m of DNAPL,
respectively). Subsurface samples from the top of the
saturated zone should be examined carefully for DNAPL
presence at suspected DNAPL sites. In the absence of
macropores or solid surfaces that are not strongly water-
wet, silt and clay layers can prevent DNAPL from
penetrating the water table. Typically, however, shallow
fine-grained materials contain fractures and other
macropores.
-------
5-14
lOOOOOOg
IOOOOOE
'j§ 10000=
Q.
<
Z
Q
"5
c
_o
"c5
O
1000E
100=
i i i i ill ii i in inn 1—i i i inn 1—i Minn 1—i i M MM 1—n~
10 100 1000 10000 100000 1000000
Volume of Soil/Rock with Residual DNAPL
(Cubic Feet)
Figure 5-4. DNAPL volume retained in the vadose zone as a function of residual saturation, sr
effective porosity, n, and contamination zone volume.
-------
5-15
x
g
LLJ
I
Q

W
o
LU
IT
TIXC

10-

nni-

\
\
^

CRITICAL DNAPL HEIGHT REQUIRED TO PENETRATE THE CAPILLARY FRINGE

""-

I !

\
\
^

X
"X

:
|

|
I

Plotted line is based on a DNAPL density
of 1300 kg/cum (1.3 g/cc), an inlerfacial
tension of 0.040 N/m (40 dynes/cm), and
contact angle of 35 degrees.
\
\
^V

\,
"S

T\
"X.
\

•x,
"S

1E-04
Clay Pores
1E-03 1E-02

PORE RADIUS or FRACTURE APERTURE (mm)
Silt Pores
Sand Pores
1E-01 1E+00

Note: Particle pore radii

estimated by dividing

particle diameters by 8.
Figure 5-5. Critical DNAPL height required to penetrate the capillary fringe as a function of pore

radius given a DNAPL density of 1300 kg/m3, an interfacial tension of 0.040 N/m, and a

contact angle of 35 degrees.
-------
5-16
5.3.4 Will a finer-grained layer beneath the
contamination zone act as a capillary barrier to
continued downward migration of DNAPL? What
minimum DNAPL column or body height is
required to enter a particular capillary barrier
beneath the water table?

The thickness of continuous DNAPL required to
penetrate a finer-grained capillary barrier below the water
table exceeds that needed to enter the saturated zone
within a similar unit due to the reduced density difference
between DNAPL and water compared to DNAPL and air.
As explained in Chapter 5.1, the critical height of
DNAPL, z,,, required to penetrate an underlying finer
layer below the water table will depend on the saturation
and direction (drainage or imbibition) of the Pc(sw) curve
being followed at the top of the DNAPL column.

Below the water table, for cases where residual DNAPL
is above the continuous DNAPL body, and the hydraulic
gradient is much less than the DNAPL-water gravity
gradient, z,, can be estimated by
z,, = (2ocos<£) / [rfinerg(Pn - p.)]
(5-17)
where rfiner refers to pore radii in the underlying capillary
barrier. Where there is no DNAPL above the DNAPL
body, then

z. = [(Zocoafl (l/rfmer - 1/r^)] / [g(pn - P.)] (5-18)

where r,,^ is the pore radii in the host medium.

Equation 5-17 is solved for a = 0.040 N/m, (ft = 35°, pn
= 1300 kg/m3, and r from 0.001 to 10 mm in Figure 5-6.
As shown, substantial DNAPL thicknesses may be
required to penetrate clay, silt, and fine sand pores.
Below the water table, z,, is sensitive to DNAPL density,
due to the reduced density-difference between immiscible
fluids within the saturated zone, in addition to pore
radius (and contact angle if+ > 60). This is illustrated
in Figure 5-7. Relatively dense DNAPLs, such as highly
chlorinated solvents, therefore, have a greater vertical
migration potential than less dense DNAPLs such as
creosote and coal tar (Figure 3-2). The influence of
vertical hydraulic gradients on the migration of DNAPL
into capillary barriers is discussed in Chapter 5.3.7.
5.3.5 If DNAPL is perched above a finer-grained
capillary barrier layer, what size fracture or
macropore will permit continued downward
migration into (or through) the capillary barrier?

Neglecting hydraulic gradients, the critical DNAPL
thickness, z,,, required for entry into a fracture with an
aperture, b, can be estimated as
z, -
(bgpn)
at the top of the zone of saturation, and as
[bg(pn - pw)]
(5-19)
(5-20)
where residual DNAPL overlies the continuous DNAPL
body within the saturated zone. To calculate z,, above a
fracture where there is no residual DNAPL over the
DNAPL column, substitute b for r in Equation 5-18.
Values of z,, calculated using Equations 5-19 and 5-20 for
a range of apertures sizes given pn = 1300 kg/m3, a =
0.040 N/m, and = 35° at the top of and within the
saturated zone are graphed in Figures 5-5 and 5-6,
respectively. Due to the irregular geometry of fractures,
the actual DNAPL thickness required to enter a
particular fracture will likely be intermediate between that
calculated using the fracture radius, r, or aperture, b.

If the thickness of a DNAPL body that is perched atop a
capillary barrier is known from boring data, then the
maximum aperture which will resist DNAPL entry can be
calculated by rearranging Equations 5-19 and 5-20.

Once DNAPL enters a vertical fracture, it will readily
enter finer and finer fractures with depth due to the
increase in DNAPL column height with depth. At
hydrostatic equilibrium, the increased gravity force with
depth is countered by increased capillary resistance
provided by the corresponding fracture apertures which
prevent DNAPL entry (Figure 5-8).
5.3.6 What saturation must be attained at the base of a
host medium for DNAPL to enter an underlying
finer-grained capillary barrier?

Several methods are available to determine or estimate
whether or not DNAPL has or will penetrate a capillary
barrier. Direct sampling of water and solids within and
below the capillary barrier can be conducted, but may
pose a significant risk of causing chemical migration. If
the thickness of a DNAPL body, %„, at the base of the
-------
5-17
g
LU
x
Q
Ul
K
CO

m-i-

^d
CRITICAL DNAPL HEIGHT BELOW THE W
AN UNDERLYING FINER-GRAINED CAPIL
TOP OF THE DNAPL BODY WAS LAST Uf
*N

"^c1

ATER TABLE REQUIRED TO PENETRATE
LARY BARRIER ASSUMING THAT THE
gDER IMBIBITION CONDITIONS

Plotted line is based on a DNAPL density
of 1300 kg/cu.m (1.3 g/cc), an interfacial
tension of 0.040 N/m (40 dynes/cm), and a
contact angle of 35 degrees.

•%

v s

1E-03
Silt Pores
1E-02 1E-01
PORE RADIUS or FRACTURE APERTURE (mm)

Sand Pores
1E+00
1E+01
Note: Particle pore radii
estimated by dividing
particle diameters by 8.
Figure 5-6. Critical DNAPL height required to penetrate a capillary barrier beneath the water table as
a function of pore radius given a DNAPL density of 1300 kg/m3, an interfacial tension of
0.040 N/m, and a contact angle of 35 degrees.
-------
5-18
i
LJJ
I
CO

O
LU
tr

1ft-
9-
8-
7-
6_
5-

2-
1 -
0.
1

\
\
\
^

1 1 1 1
05 1
SE

\
\
\

INSITIVITY OF CRITICAL DNAPL HEIGHT, Zn, TO DNAPL DENS
BELOW THE WATER TABLE

\
^

Plotted line is based on a threshol
(displacement) pressure of 6553 F
(developed by an interfacial tensic
0.040 N/m ,a contact angle of 35 d
and a pore radius of 0.01 mm).

fill I 1 1 1 1 1 1 1 I 1 1 1
1 1.15 1.2 1.25 1

"-^^

— !

—

d entry
>a
>nof
egrees,

—

— —

till 1 1 1 1 1 I 1 I fill 1 1 I 1 1 1 1 I
3 1.35 1.4 1.45 1.5 1.55 1
DNAPL DENSITY (g/cc)
ITY

• ~

1 — -
1 1 1 I 1 1 I 1
6 1.65 1.7
Figure 5-7. Sensitivity of critical DNAPL height to DNAPL density below the water table.
-------
5-19
DEPTH
,DNAPL POOL
-WATER
DNAPL
CAPILLARY
PRESSURE
ENTRY PRESSURE
AT 'B'
0
PRESSURE
Figure 5-8. Pressure profiles in a fracture network for DNAPL at hydrostatic equilibrium (from
Kueper and McWhorter, 1991).
-------
5-20
host medium can be determined, then the capillary
pressure at this point can be estimated (by assuming
hydrostatic equilibrium) as
PC » g Zn (pn - Pw)
(5-21)
and inferences can be made regarding the likelihood that
DNAPL has or will enter the barrier layer based on
estimates of the threshold entry pressure of the capillary
barrier.

A third approach is to: (1) determine the DNAPL
saturation in samples of the host medium taken from just
above the capillary barrier; (2) estimate the associated
capillary pressure, P,., above the barrier layer based on a
measured or estimated Pc(sw) curve for the host medium,
and, then (3) compare the inferred Pc to a threshold entry
pressure, Pd, measured or estimated for pores or fractures
in the underlying capillary barrier. If the Pc at the base
of the host medium exceeds the barrier layer Pd, then
DNAPL probably has or will penetrate the finer-grained
underlying layer. Such a comparison utilizing PcCsJ
curves for a sand layer overlying a silt layer is given in
Figure 5-9.

5.3.7 What upward hydraulic gradient will be required
to prevent continued downward migration of
DNAPL?

As described in Chapter 5.1, the three driving forces that
act concurrently on subsurface DNAPL are the gravity
gradient, the capillary pressure gradient, and the hydraulic
gradient. Groundwater flow driven by upward vertical
hydraulic gradients will prevent or slow the downward
movement of DNAPL. Shallow recovery wells and drains,
and/or deeper injection wells, can be used to create or
increase upward vertical hydraulic gradients, particularly
across an aquitard that separate two aquifers. This
hydraulic barrier concept has been likened to using an
upward-blowing fan to suspend a ping-pong ball in air.
It was apparently first considered to contain sinking
DNAPL at the S-Area Landfill in Niagara Falls, New
York (Guswa, 1985; Cohen et al, 1987), and, more
recently, has been evaluated for containment of DNAPL
beneath disposal basins (Hedgecoxe and Stevens, 1991)
and within fractured media (Kueper and McWhorter,
1991).
difference, Ah, needed to prevent DNAPL from sinking
vertically downward due to gravity are given by

ih = (Pn - P.) / P. (5-22)

and

Ah = za(pa - pw) / pw (5-23)

where z^ is the thickness of the DNAPL body.

The hydraulic gradient required to halt DNAPL sinking
due to gravity increases linearly with DNAPL density as
shown in Figure 5-10. As a result, vertical containment
of low density DNAPLs such as coal tar and creosote is
generally much more feasible than for denser DNAPLs
such as highly chlorinated solvents.

In addition to the density gradient, capillary pressure will
influence whether or not DNAPL will migrate vertically
into and through a finer-grained layer. Considering both
the density and capillary pressure gradients in a simple
one-dimensional system, the steady-state upward vertical
hydraulic gradient required to prevent DNAPL sinking
through a capillary barrier is given by

ih = Ah/L = [(Pn-pw)/pw] + [(Pc-Pd)/(pwgL)] (5-24)

where Pc is the capillary pressure at the base of the
DNAPL pool overlying the capillary barrier, Pd is the
threshold entry pressure of the capillary barrier, and L is
the thickness of the capillary barrier. Pc at the base of
the DNAPL pool can be estimated using Equation 5-21
or based on measurement of DNAPL saturation at this
interface as described in Chapter 5.3.6 if the P^sJ curve
is known.

Equation 5-24 is illustrated and solved in Figure 5-11. A
negative ih value is the downward hydraulic gradient that
must be exceeded to overcome capillary pressure and
cause downward DNAPL migration through the capillary
barrier. As shown, the capillary pressure gradient (the
second term on the right side of Equation 5-24) is
inversely proportional to aquitard thickness, L. Vertical
hydraulic gradients required to prevent DNAPL sinking
through a capillary barrier, therefore, decrease as the
thickness of the barrier layer increases.
Neglecting the capillary pressure gradient, the upward
hydraulic gradient, ih, and associated hydraulic head
-------
5-21
10000
(0
(A
(0
0.69
to penetrate the underlying sift layer.
0.4 0.5 0.6
Water Saturation
0.7 0.8 0.9 1.0
Figure 5-9. Comparison of P^s,,) curves to determine the DNAPL saturation required in an overlying
coarser layer to enter an underlying finer liner.
-------
5-22
0.70
0.00
1.00
1.10 1.20 1.30 1.40

DNAPL Density (g/cc)
1.50
1.60
1.70
Figure 5-10. Neglecting the capillary pressure gradient, the upward vertical hydraulic gradient required
to prevent DNAPL sinking in the saturated zone is a function of DNAPL density.
-------
Aquifer
Aquifer
Fine — grained
capillary barrier
(aquitard)
I
•O
UPWARD VERTICAL HYDRAULIC GRADIENT
REQUIRED TO MALT ONAPL SINKING IN
A 1*1 THICK CAPILLARY BARRIER
-0.5i >
-1.0
1.2 13 1.4 1.5
DNAPL Density (kg/cubic meter)
1.0

0.9
UPWARD VERTICAL HYDRAULIC GRADIENT
REQUIRED TO HALT DNAPL SINKING IN
A 5-M THICK CAPILLARY BARRIER
1.1
1.2 1.3 U 1.5 l.(
DNAPL Density (kg/cubic meter)
Pe did.. .10000 Pi
-e-
Pcd».--SOOOP«
1.7
UPWARD VERTICAL HYDRAULIC GRADIENT
REQUIRED TO HALT ONAPL SINKING IN
A 10-M THICK CAPILLARY BARRIES
1.2 1.3 L4 1.5
DNAPL Density (kg/cubic meter)
Figure 5-11. Considering both the density and capillary pressure gradients, the upward vertical hydraulic gradient required to prevent DNAPL
sinking through a capillary barrier is a function of DNAPL density and the capillary pressure difference between the base of the
overlying coarser layer and the threshold entry pressure of the underlying finer layer.
-------
5-24
5.3.8 What upslope hydraulic gradient will be required
to prevent continued downslope movement of
DNAPL along the base of a dipping fracture or the
base of a coarser layer underlain by a dipping
finer layer?

The hydraulic gradient needed to halt DNAPL movement
may be greatly reduced if DNAPL is sinking along an
inclined plane (i.e., a bedding plane, joint, or sloping fine-
grained layer). For this case, neglecting the capillary
pressure gradient, the hydraulic gradient measured
parallel to the inclined plane needed to arrest DNAPL
movement and the associated hydraulic head difference
are given by

ih = [(Pn - Pw) sin 8] / pw (5-25)

and

Ah = [(Pn - Pw) zn sin 6] / Pw (5-26)

where 6 is the inclined plane dip angle in degrees and z,,
is the length of the DNAPL body measured parallel to
the inclined plane. For example, the requisite upslope
hydraulic gradient measured along an inclined plane
surface with a dip of 15° to arrest the downward flow of
DNAPL with a density of 1.18 is 0.047. The diminution
of upslope hydraulic gradient required to prevent
downslope DNAPL movement is shown as a function of
density gradient and slope as shown in Figure 5-12.
Measured vertically, however, the required hydraulic
gradient is still equal to the density gradient.
5.3.9 What will be the stable DNAPL pool length that
can exist above a sloping capillary barrier or
sloping fracture below the water table?

At hydrostatic equilibrium, the stable pool length, L,
measured parallel to a capillary barrier or fracture with a
dip angle of 6 in degrees can be estimated as
L = Pd / [(pn - Pw) g sin
(5-27)
where Pd is the threshold entry pressure of the host
medium or fracture (WCGR, 1991). This scenario is
illustrated and Equation 5-27 is solved for a range of
DNAPL density and capillary barrier dip angles in Figure
5-13. As shown, the stable DNAPL pool length increases
with DNAPL density and dip angle.
5.3.10 What will be the stable DNAPL height and area
after spreading above an impenetrable flat-lying
capillary barrier?

DNAPL will mound and spread along an impenetrable
capillary barrier below the water table until the threshold
entry pressure of the host medium resists further
spreading. If the capillary barrier is flat-lying, the stable
height of the DNAPL pool can be estimated by
z,, =
(5-28)
For a given volume, Vn, of DNAPL released, the
maximum area, A,,,, of DNAPL spreading above the
impenetrable capillary barrier can be estimated by (1)
subtracting an estimate of the DNAPL volume, Vp
retained at residual saturation (and, if applicable, in
stratigraphic traps) above the stable DNAPL pool from
the volume of DNAPL released; and then, (2) dividing
the remaining DNAPL volume by the stable DNAPL
pool height and by an estimate of DNAPL residual
saturation, srt in the saturated zone
A. < (Vn - Vr) / (z, sr)
(5-29)
The actual area of spreading will likely be less than the
calculated value of A,,, because the DNAPL saturation in
the pool will exceed the sr value. Given a homogeneous
host medium and neglecting hydraulic forces, DNAPL can
be expected to spread out radially from a source mound.
In heterogeneous media, however, the pattern of the
DNAPL spreading is typically very irregular and difficult
to define.

5.3.11 What is the volume of DNAPL contained below
the water table within porous or fractured media?

This question is similar to that posed in Chapter 5.3.1 for
the vadose zone, and Equation 5-15 applies, except that
the DNAPL saturation may exceed residual saturation.
Residual saturation data for the saturated zone are
provided in Table 4-5. In general, more DNAPL is
immobilized in the saturated zone than in the vadose
zone (Chapter 4.5). Using the same example as that in
Chapter 5.3.1, but with a DNAPL residual saturation of
0.3, then 93 gallons of DNAPL would be trapped in a
volume of 4 ft X 4 ft X 35 ft. This is three times that
trapped in an equivalent volume of vadose zone (given
the assumed values of residual saturation).

In fractured media, DNAPL presence may be largely
confined to fractures. To estimate the volume of DNAPL.
-------
5-25
0.7-
0.6--
UPSLOPE HYDRAULIC GRADIENT MEASURED
PARALLEL TO AN INCLINED PLANE (DIP NOTED
IN DEGREES) NEEDED TO ARREST GRAVITY-
INDUCED DNAPL MOVEMENT
1.1
1.2 1.3 1.4 1.5
DNAPL Density (kg/cubic meter)
1.6
1.7
Figure 5-12. Neglecting the capillary pressure gradient, the upslope hydraulic gradient required to
arrest DNAPL movement downslope along an inclined capillary barrier is a function of
DNAPL density and capillary barrier dip.
-------
5-26
0.9-
0.8-
0.7-
0
-t-^
Q)
0.6-
THE STABLE POOL LENGTH IN A HYDROSTATIC
SYSTEM MEASURED PARALLEL TO AN INCLINED
CAPILLARY BARRIER WITH A DIP GIVEN IN
DEGREES FOR A HOST MEDIUM WITH A THRESHOLD
ENTRY PRESSURE OF 1000 PASCALS. To determine the
stable pool length given a different host medium threshold
entry pressure, multiply the length shown by the different
threshold entry pressure (in Pascals) and divide by 1000.
90 degrees
1.1
1.2 1.3 1.4 1.5
DNAPL Density (kg/cubic meter)
1.6
1.7
Figure 5-13. The stable DNAPL pool length above an inclined capillary barrier is a function of
DNAPL density and capillary barrier dip.
-------
5-27
contained within a particular volume of fractured media,
it is necessary to evaluate fracture porosity. Semi-regular
fracture patterns, such as those depicted in Figure 5-14,
are discernible in many fractured clay and rock units.
Using the fracture porosity equations provided in Figure
5-14, it is possible to calculate fracture porosities and
void volumes given estimates of fracture spacing and
aperture. For example, fracture porosity is shown as a
function of these parameters for the matches model
(Figure 5-14b) in Figure 5-15. Estimates of the volume
of DNAPL present in fractures can be obtained by
multiplying the void volume by a DNAPL saturation
estimate. Where present, the distribution of DNAPL in
fractures is typically very complex and not amenable to
accurate volume calculation. Volume calculation is
further complicated because some DNAPL typically will
migrate from the fractures into larger pore openings (i.e.,
root holes, dissolution cavities, sand laminations, etc.)
that intersect the fracture walls.
5.3.12 How do fluid viscosity and density affect the
velocity and distance of DNAPL migration?

The velocity and distance of DNAPL migration will be
controlled, in part, by DNAPL density and viscosity. The
rate of DNAPL sinking generally increases with
increasing DNAPL density (and gravity gradient) and
decreasing DNAPL viscosity. As a result, chlorinated
solvents sink much more rapidly through the subsurface
than coal tar/creosote (Figure 3-1).

The lateral migration of DNAPL is also affected by
DNAPL fluid density and viscosity. As noted in Chapter
4.10, hydraulic conductivity is directly related to fluid
density and inversely related to fluid viscosity. Given the
wide range of DNAPL viscosities (Figure 3-1), the rate
and distance of DNAPL movement due to gravity and/or
hydraulic gradients may be significantly greater for low
viscosity (thin) DNAPLs than high viscosity (thick)
DNAPLs. Where multiple DNAPLs are present at a
contamination site, consideration should be given to the
implications of variable DNAPL density and viscosity on
transport potential. Measurement on DNAPL samples
collected from the subsurface are recommended because
chemical aging and mixing (with other DNAPLs or water)
can modify DNAPL properties.
5.3.13 What hydraulic gradient will be required to
Initiate the lateral movement of a DNAPL pool or
globule?

The hydraulic gradient, ^ across a DNAPL pool or
globule required to initiate lateral DNAPL movement can
be estimated as
g
(5-30)
where Pd is the threshold entry pressure of the host
medium or fracture and L is the length of the DNAPL
pool or globule perpendicular to the hydraulic gradient
(WCGR, 1991). This scenario is illustrated and Equation
5-30 is solved for a range of Pd and L values in Figure 5-
16. As shown, the requisite hydraulic gradient increases
with (1) increasing Pd (i.e., increasing interfacial tension,
decreasing contact angle, and decreasing pore radius) and
(2) decreasing pool/globule length. The hydraulic
gradient required to sustain DNAPL movement typically
increases with time and distance of DNAPL movement.
This is because the length of the Pod/globule is
shortened as residual DNAPL is retained at its trailing
edge.

Residual DNAPL also can be mobilized by increasing
hydraulic gradients. The capillary number, N,., the ratio
of capillary to viscous forces, provides a measure of the
propensity for DNAPL trapping and mobilization. It is
defined as the product of intrinsic permeability, water
density, gravitational acceleration constant, and hydraulic
gradient divided by the interfacial tension. The critical
value, N*, of the capillary number is defined as the value
at which motion of some of the DNAPL blobs is
initiated. Based on experimental data, Wilson and
Conrad (1984) noted a strong correlation between
displacement of residual DNAPL and the capillary
number when the hydraulic gradient was greater than that
producing the critical value of the capillary number. The
hydraulic gradient necessary to initiate blob mobilization
for various permeabilities and interfacial tensions is
shown in Figure 5-17. As may be seen, in very permeable
media (e.g., gravel or coarse sand), it is theoretically
possible to obtain sufficient hydraulic gradients to remove
all DNAPL blobs. In soils of medium permeability (e.g.,
fine to medium sand), some of the residual can be
hydraulically removed. In less permeable media, removal
is not possible, unless surfactants are used to drastically
reduce interfacial tension.
-------
5-28
(a) Slides Mode
n = b
(b) Matches Mode!
n = 2b
f ~7T~
(c) Cubes Model
n = 3b
nf — fracture porosity
a = fracture spacing
b = fracture aperture
Figure 5-14. Fracture porosity equations for the slides, matches, and cubes fracture models where a is
the fracture spacing and b is the fracture aperture.
-------
5-29
1.0000:
0.1000:
CO
o

O
Q.

1
I
co
0.0100:
0.0010:
0.0001
0.01
0.10 1.00

Fracture Spacing (m)

X
x,^
^

X.
x^
x^

X.
"X^
x^

~*x
— ^

\
^

A
M
~

10 microns

^ —
s

/
^
^
"X,

X
^ —
"\.

f
~y^
>

100 microns
x,

X
/
/

*•

«s

~5
Jf
w
\
^
10 microns
V

300 microns

x^
X^
"X^
/

V
— *fe —
/—
X

"x.
"X^
X^

"\^
x^
X^

/
/
/

— ^,

"X,

Fracture poroi
fracture model
various frac
fracture aperture:
To determine I
slides" model, div
he fracture poros
mu

— •
^
m

I
I
1 millimeter

/\
S,

/
irties for the "matches* ;
see Figure 5-1 4b) given
rture spacings and
i (noted for plotted lines) .
racture porosity for the
ide by two. To determine
ity for the "cubes" model, :
tiply by 1.5. ;

x^
x^
X^

\^
^s^
X,.

3 millimeters

^
m
x^

"x^

—f —
/

x,.

10.00
Figure 5-15. Fracture porosity is a function of fracture spacing and aperture.
-------
5-30
Injection Well
Extraction Well
Aquifer
Hydraulic Gradient
^- \
\\\\\ . \ \ \ \
Fine —grained
capillary barrier
UJ
Q
<
CC
CD
O
1E+03
1E+02==
1E+01 = =
1E+00
1E-01 =
1E-02
CC
Q

I
UJ
b 1E-03
CO
O
UJ
DC
1E-04
1E-05:
1E-06
HYDRAUUC GRADIENT ACROSS A DNAPL
POOL OF LENGTH, L, WHICH MUST BE
IMPOSED TO EXCEED THE THRESHOLD
ENTRY PRESSURE OF THE HOST MEDIUM
AND INITIATE POOL MOVEMENT
I—I—I I I I III
I 1—I I I I III
100
100000
HOST MED. THRESHOLD ENTRY PRESSURE (Pa)
Figure 5-16. The hydraulic gradient required to initiate lateral movement of a DNAPL pool or globule
is directly proportional to the threshold entry pressure of the host medium and inversely
proportional to pool length.
-------
5-31
10
0.1
0.01
0.001
x10
-3
(dyne/cm)
10'8 10'7 10'6 10'5 10'4 10'3

I - GRAVEL - 1
10
'1
CLEAN SAND-
SILTY SAND 1
k(cm2)
Figure 5-17. Hydraulic gradient, J, necessary to imitate DNAPL blob mobilization (at N*) in soils of
various permeabilities, for DNAPLs of various interfacial tensions, a. The upper curve
represents the gradient necessary for complete removal of all hydrocarbons (N^), with o -
10 dynes/cm (from Mercer and Cohen, 1990; after Wilson and Conrad, 1984).
-------
5-32
5.3.14 How long does DNAPL in the saturated zone take
to dissolve completely

As discussed in Chapter 4.7, complete dissolution of
DNAPL in the saturated zone can take decades or
centuries due to limits on chemical solubility,
ground-water velocity, and vertical dispersion. DNAPL
pools will be particularly long-lasting, compared to
residual DNAPL ganglia and fingers, because of their low
water-DNAPL contact area.

Most simply, the time, t, needed to completely dissolve a
DNAPL source can be estimated as
t = m /
(5-31)
where m is the DNAPL mass, vi is the average interstitial
groundwater velocity, n is the effective porosity, and, A is
the cross-sectional area containing DNAPL through
which groundwater flow exits with a dissolved DNAPL
concentration, C,.

For example, consider aim3 volume of sandy soil with a
residual DNAPL content of 30 L/m3. If it is assumed that
the hydraulic conductivity is 10"3 cm/s, the hydraulic
gradient is 0.01 and the porosity is 0.30, then groundwater
flows through this hypothetical sandy soil at a rate of 0.03
m/d. Furthermore, assuming that DNAPLs dissolve into
groundwater to 10% of their solubility, then for PCE
(density of 1.63 g/cm3 and solubility of 200 mg/L),
approximately 744 years would be required to dissolve the
DNAPL PCE.

DNAPL dissolution from residual and pool sources was
recently examined by Anderson et al. (1992a) and
Johnson and Pankow (1992), respectively. For
rectangular DNAPL pools, Johnson and Pankow (1992)
defined a surface-area-averaged mass-transfer rate, M,
(M/L2/T), as
M, - [(4Dvvi)/(trLi()]w
(5-32)
where Dv is the coefficient of vertical dispersion (L2/T), ^
is the average interstitial groundwater velocity (L/T), Lp
is the length of a DNAPL pool in the direction of
groundwater flow (L), n is the effective porosity, and CSA:T
is the saturation concentration (M/L3). The coefficient of
vertical dispersion is calculated as
where D,, is the effective aqueous diffusion coefficient
(L2/T)i and a, is the vertical transverse dispersiviry (L).

Assuming that the areal dimensions of the pool do not
vary during dissolution, the time, td (T), required for
complete DNAPL pool dissolution can be estimated as
(Johnson and Pankow, 1992)
td = Ph L,, n pn sn / M.
(5-34)
where Ph is the pool height, pn is the DNAPL density
(M/L3), and sn is the DNAPL saturation. For example,
assuming for a particular TCE-sand system that C^T is
1100 g/m3, n is 0.35, sn is 1.0, De is 2.7 X 10"10 m%, a, is
0.00023 m, and Ph is 0.01 L,, Johnson and Pankow (1992)
calculated TCE pool dissolution times for four pool
lengths as shown in Figure 5-18.
5.3.15 Given a DNAPL source of dissolved groundwater
contamination how do you determine the
movement of a dissolved plume?

A dissolved plume generally moves with the flowing
groundwater. Thus, a site investigation needs to
determine groundwater flow directions in three
dimensions using water-level data from monitor wells.
Dissolved chemicals from DNAPLs also sorb to the soil
matrix to varying degrees. The rate of movement is
retarded due to this process, which may be characterized
by the retardation factor, Rf. The following example
shows how the retardation factor is used to determine the
relative movement of three different chemicals that may
form dissolved plumes from DNAPLs.

At a hypothetical site, 1,1,1-trichloroethane (TCA),
trichloroethene (TCE), and methylene chloride (MC)
have been released into the subsurface from a tank
storage area causing development of dissolved TCA, TCE,
and MC plumes. Which of these chemicals is expected to
move the fastest in the groundwater?

An indicator of a chemical's tendency to partition
between groundwater and soil is the organic carbon
partition coefficient, K^. Values of K,,,. for DNAPL
chemicals are given in Appendix A This coefficient is
related to the distribution coefficient, K,,, by the
following
Dv = Dt + (v,
(5-33)
(5-35)
-------
5-33
700
10m pool ~ 3500 L
4 m pool ~ 224 L
2 m pool ~ 24 L
VELOCITY (m/d)
Figure 5-18. Dissolution time versus average interstitial groundwater velocity for four different TCE pool
lengths (reprinted with permission from ACS, 1992).
-------
5-34
where 4e is the fraction of total organic carbon content in
terms of grams of organic carbon per gram of soil. In
natural soils, !„. values range from <0.001 to >0.05.
Assuming a f^ of 0.017, the distribution coefficients for
TCA, TCE, and MC are 2.58, 2.14, and 0.15 ml/g,
respectively, as shown in Table 5-2.

The distribution coefficient is related to the retardation
factor, Rfc by
R, - [1 + (Pb/n) KJ
(5-36)
where n is porosity and pb is the bulk density of the
porous media. Bulk mass density is related to particle
mass density, p,, by the following
Pb = P. (1-n)
(5-37)
where p, = 2.65 g/cm3 for most mineral soils. If porosity
is 0.3, then by Equation 5-37, Pb = 1.85 g/cm3, and by
Equation 5-36, the retardation factors for TCA, TCE, and
MC are 16.9, 14.2, and 1.93, respectively (Table 5-2).

Therefore, the relative order of transport velocity in
groundwater is MC, followed by TCE, and then TCA.
That is, if all three chemicals were released to
groundwater at the same time, MC should create the
largest dissolved plume and move the fastest whereas
dissolved TCA should move the slowest and have the
smallest plume.
5.3.16 Given a DNAPL source of vapor contamination in
the vadose zone how do you determine the
movement of the vapor plume?

There are models available for evaluating this question,
as exemplified by the analysis provided in Chapter 5.3.20.
To examine the relative movement of various chemicals
from a complex DNAPL source, consider the same
chemicals that were used in the dissolved plume example:
1,1,1-trichloroethane (TCA), trichloroethene (TCE), and
methylene chloride (MC). Which of these chemicals
would be expected to migrate farthest from the source
area in the vapor plume?

Although diffusion is the primary transport mechanism in
the vadose zone, the effects of sorption and dissolution
reactions can retard the vapor front. Potential localized
density effects are noted in Chapters 4.8 and 8.4. The
retardation factor for the vapor phase is defined as
(Mendoza and McAlary, 1990)
R. = 1 + n./(n,K'H) + Pb K,/(n.K'H) (5-38)

where n. is the water-filed porosity (dimensionless), n, is
the air-filled porosity, K*H is Henry's Law constant
(dimensionless, see Equation 5-44), Pb is the soil bulk
density (M/V), and, Kj is the solid-liquid distribution
coefficient (mg/g solid per mg/ml liquid).

This retardation factor is constant if the water content of
the soil does not change and is analogous to the
retardation factor, R, for the movement of chemicals in
the saturated zone. The second term in Equation 5-38
represents the partitioning of the chemicals from the gas
phase to the water phase. The third term represents the
partitioning from the gas phase, through the water phase,
to the solid phase. Henry's Law constant values are
provided in Appendix A.

As shown in Table 5-2, vapor phase retardation factors
and the relative order of movement for TCA, TCE, and
MC are calculated based on K'H values of 0.599, 0.379,
and 0.084, respectively, and by assuming that pb = 1.85
g/cm3, and n, = n, = 0.50. The relative order of
movement in soil gas is MC, followed by TCA, and then
TCE. This order differs from that in groundwater.
5.3.17 What will be the chemical composition of a
dissolved plume associated with a DNAPL source?

Several approaches are available to characterize the
composition and concentrations of chemicals dissolved
from a DNAPL source into groundwater. The most
direct and reliable approach is to have groundwater
sampled downgradient and close to the DNAPL source
submitted for comprehensive chemical analysis. A second
approach is to conduct an equilibrium dissolution study
by placing a sample of the DNAPL in a sample of the
local groundwater (or tapwater). A few options for
performing dissolution studies are provided in Chapter
12.

If samples cannot be obtained, or if it is desirable to
predict the dissolved chemical concentrations over time,
then theoretical calculations can be made based on
knowledge of DNAPL source chemistry. For DNAPLs
comprised of a mixture of chemicals, the effective
solubility of each component in groundwater can be
estimated using Worksheet 7-1 in Chapter 7. Based on
the effective solubility concept, Mackay et al. (1991)
present equations to estimate (1) the equilibrium
concentrations of dissolved chemicals in groundwater in
-------
5-35

Table 5-2. Parameters and values used to calculate the relative order of transport velocity for TCA, TCA, and
MC and Chapter 5.3.15 (reprinted from ACS, 1992).

Chemical

1,1,1-
Trichloroethane
(TCA)
Trichloroethene
(TCE)
Methylene Chloride
(MC)

K«
(m(/g)

152

126

8.8

K«
(ml/g)

2.58

2.14

0.15

16.9

14.2

1.93

IPH

0.599

0.379

0.084

55.8

73.3

34.9

Relative
Order of
Movement ia
Groundwater
3

Relative
Order of
Movement in
Vapor
2

-------
5-36
contact with a NAPL of defined composition; (2) changes
in aqueous and NAPL phase chemical concentrations
with time due to NAPL depletion by dissolution; and (3)
the water flow volume (or time) required for a defined
depletion of the component within the NAPL mass. For
example, the dissolution characteristic of a mix of
chlorobenzene, 1,2,4-trichlorobenzene, and 1,2,3,5-
tetrachlorobenzene as a function of water leaching with
time are shown in Figure 5-19.
5.3.18 What is the equivalent mass/volume of DNAPL
contained within a dissolved groundwater plume?

Mackay and Cherry (1989) show several examples of
organic plumes in sand-and-gravel aquifers that extend 0.5
to 1.0 km from the source area (Table 5-3). Using these
plumes, they compute an equivalent DNAPL volume in
terms of liters or drums of DNAPL As depicted in
Table 5-3, only a few liters of NAPL are required to
create large dissolved plumes. This is further illustrated
by the following example.

Groundwater at a hypothetical site has been
contaminated with trichloroethene (TCE) concentrations
which vary between 100 to 10,000 yg/L. The affected
water-table aquifer is a sand overlying a silty clay. The
aquifer has a saturated thickness of approximately 10 ft,
and the facility occupies an area of 680 ft by 130 ft
(approximately two football fields). If TCE mass in soil
above the water table and separate-phase TCE mass are
ignored, what is the dissolved and sorbed mass of TCE in
the aquifer underlying the facility? What is this equal to
in terms of DNAPL TCE volume?

The total mass (MT) is equal to the dissolved mass plus
the sorbed mass, or
MT = n C VT R
(5-41)
MT = (C n VT) + (S Pb VT)
(5-39)
where C is the dissolved concentration (ML"3), n is
porosity, VT is the total volume (L3), S is the mass of the
sorbed chemical per unit mass of solid, and pb is the bulk
mass density of the porous medium (ML"3).

For linear sorption, the sorbed mass, S, is related to the
dissolved mass through the distribution coefficient (K,,):
S =
(5-40)
where R is the retardation factor defined by

R = [1 + (Pb/h)KJ (5-42)

Thus, Equation 5-41 shows that the total mass is equal to
the dissolved mass times the retardation factor.

For the site involving TCE, VT = 680 ft X 130 ft X 10 ft
= 884,000 ft3. Further, it is estimated that the sand has
a porosity of 0.3; thus, there are 265,200 ft3 of water in
the saturated media. Using the definition of
concentration, the amount of mass required to cause a
concentration of 1 u.g/L in the water throughout the site
(265,200 ft3 = 7,509,668 L) is 7.51 grams of TCE. TCE
has a density of 1.46 g/cm3. Using the density, the volume
of separate-phase (DNAPL) TCE required to cause a
concentration of 1 jig/L throughout the site is only 5.14
cm3 (or 0.00514 L or 0.00136 gallons). This does not
include sorption.

The sorbed phase can be estimated using the organic
carbon partition coefficient (K^) for TCE, which is 126
ml/g. The fraction of organic carbon (f^) is assumed to
be approximately 0.001. The distribution coefficient is
calculated as
K, = fx K,, = 0.126
(5-43)
Substitution of (5-40) into (5-39) and rearranging terms
yields
which is used in Equation 5-42 to calculate a retardation
factor of 1.78.

Using this information, the volume required to produce
a range of TCE concentrations throughout the site is
presented in Table 5-4. The volume is expressed in
gallons of DNAPL TCE. As may be seen, only a small
amount of DNAPL TCE is required to cause a rather
large plume; less than two gallons, if not sorbed, will
contaminate the entire site to above 1,000 jig/L, where
the maximum contaminant level (MCL) for TCE is 5
lig/L. If the TCE is sorbed, the volume of DNAPL TCE
required to cause the same levels of concentration in the
dissolved phase is approximately doubled.

This example illustrates two important points. First
small amounts of DNAPL can potentially contaminant
large volumes of water above MCLs. Second, at many
sites, there is an attempt to estimate mass in place, and
use this to estimate clean-up times. This calculation,
while interesting, has a large uncertainty associated with
-------
5-37
en
E

c
o
c
0)
u
c
o
o
+ chlorobenzene

1,2.4-TCB

71.2,3.5-TeCB
10000 20000 30000

woter/CB mixture volume ratio, Q
40000
Figure 5-19. Measured and predicted dissolution characteristics for a mixture of chlorobenzenes: 37%

chlorobenzene, 49% 1,2,4-trichlorobenzene, 6.8% 1,2,3,5-tetrachlorobenzene, 3.4%

pentachlorobenzene, and 3.4% hexachlorobenzene (from Mackay et al, 1991). The water/CB

(chlorobenzene) volume ratio, Q, is the volume of water to which the chlorobenzene mixture

was exposed divided by the initial volume of chlorobenzene mixture.
-------
5-38
Table 5-3. Equivalent DNAPL mass associated with some relatively well-documented organic contaminant
plumes in sand-gravel aquifers (modified from Mackay and Cherry, 1989).
SITE LOCATION AND PLUME
MAP
Ocean City, NJ
Mountain View, California
Cape Cod, Ma.
Gloucester, Ont.
San Jose, Cat.
Denver, Colorado
PRESUMED
SOURCES
chemical plant
electronics plant
sewage
infiltration beds
special waste
landfill
electronics plant
trainyard, airport
PREDOMINANT
DNAPL
CONTAMINANTS
Trichloroethene
1,1,1-Trichloroethane
Tetrachloroethene
Trichloroethene
1,1 ,1 -Trichloroethane
Trichloroethene
Tetrachloroethene
1,4-Dioxane
Freon 113
1,1,1-Trichloroethane
Freon 113
1,1 -Dichloroethene
1,1,1-Trichloroethane
Trichloroethene
Dibromochloropropane
PLUME
VOLUME
(LITERS)
5,700,000,000
6,000,000,000
40,000,000,000
102,000,000
5,000,000,000
4,500,000,000
ESTIMATED CHEMICAL
MASS DISSOLVED IN
PLDME (AS EQUIVALENT
DNAPL VOLUME IN
LITERS OR SS-GAL
DRUMS)
15,000 (72 drums)
9800 (47 drums)
1500 (7 drums)
190 (0.9 drum)
130 (0.6 drum)
80 (0.4 drum)
0
I
5 km
J
Flow
-------
5-39
Table 5-4. Volumes of TCE required to produce a range of TCE concentrations in 884,000 ft 3of aquifer
assuming porosity = 0.3 and K^ = 0.126.
Dissolved
TCE(|ig/L)
100
1,000
10,000
DNAPL TCE (gal)
Dissolved Phase
0.1359
1.359
13.59
Dissolved and Sorted
0.2419
2.419
24.19
Note: a barrel usually contains 55 gallons.
-------
5-40
it. For this example, any mass or volume of DNAPL that
might be present at the site (e.g., as residual saturation)
could greatly exceed the estimated mass in place. This, in
turn, could have significant consequences on remediation
and extend clean-up times.
5.3.19 What is the relationship between concentrations in
soil gas and groundwater?

The interaction of soil gas and groundwater can be
complex If equilibrium conditions exist, then Henry's
Law can be used to describe this relationship and used to
address a number of issues. For example, assuming that
the aqueous and gaseous phases are in equilibrium, and
that a vapor plume of TCE has migrated away from a
residual DNAPL source in the vadose zone, what gas
concentrations are required to produce aqueous
concentrations of 5 |ig/L?

To answer this question, Henry's Law can be used, but in
a form slightly different from that provided in Equation
4-17. A second method of defining Henry's Law constant
is:
(5-44)
where C. is the molar concentration in air (mole/m3), C.,
is the molar concentration in water (mole/m3), and K'H is
the alternate form of Henry's Law constant
(dimensionless).

Equations 5-44 and 4-17 are related using the ideal gas
law as follows:

K'H = KH/(RgT) = 41.6 KH at 20°C (5-45)

where T is the temperature of water (°K), and Rf is the
ideal gas constant (8.20575 x Iff3 atm-m3/mol-K).

Using Appendix A, the Henry's Law constant for TCE is
9.10 x 10"3 atm-m3/mol. Using Equation 5-45, this
converts to a dimensionless Henry's Law constant of
0.379. Substituting this into Equation 5-44 indicates that
a gas concentration of only about 2 jig/L would be in
equilibrium with groundwater containing 5 jig/L TCE.
The water containing TCE might be a small layer on top
of the water table. Thus, monitor well results that sample
over a larger vertical distance would yield lower
concentrations.
5.3.20 Given a DNAPL source in the vadose zone, how
can you evaluate the movement of a vapor plume?
What are the conditions that favor vapor transport
away from a DNAPL source in the vadose zone
that would allow soil-gas monitoring?

These questions have been addressed by several modeling
studies (e.g., Silka, 1986; Mendoza and McAlary, 1990)
and are answered using an analytical solution below.

Assuming that DNAPL fully penetrates the vadose zone,
then vapors from this source are transported away by
diffusion in the radial direction. This transport is affected
by vapor-phase retardation. For this simplified situation,
the vapors are assumed not to interact with the water
table (lower boundary) or the land surface (upper
boundary). Furthermore, the vadose zone is assumed to
be infinite in extent.

The differential equation governing unsteady, diffusive,
radial flow is given by
[l/r(dCJdr)] =
(5-46)
where the air-filled porosity, n,, is assumed to be
constant, and where

D* = Dr. (5-47)

T. = n,"3Vt (Millington and Quirk, 1961) (5-48)

and, (Mendoza and McAlary, 1990)

R, = 1 + n, /(n.K'H) + pb K, /(n,K'H) (5-49)

Parameter definitions and values used in this assessment
are provided in Table 5-5.

To solve this equation, it is assumed that the vadose zone
initially contains no chemical vapors. Therefore, the
initial conditions are C, = 0 for all r at t = 0. The
boundary away from the DNAPL source is assumed to be
far enough away that it remains uncontaminated.
Therefore, C, = 0 at r = » for t 2: 0.

The boundary at the DNAPL is assumed to be
maintained at a constant concentration as the DNAPL
generates chemical vapors according to Raoult's Law
(Equation 4-18). That is, the volume concentration in
the gas phase is:
Cg = mol/vol = n/V
(5-50)
-------
5-41
Table 5-5. Parameter values for assessment of TCE diffusion and nomenclature used
in Chapter 5.3.20.
PARAMETER
total porosity, n,
bulk density, pb
bulk water content, nw
air-filled porosity, n,
tortuosity factor, T,
air diffusion coefficient, D
effective diffusion coefficient, D*
dimensionless Henry's Law constant, K'H
distribution coefficient, Kj
retardation factor, R,
source concentration, C,
source radius, r,
ideal-gas constant, R
vapor pressure of the pure solvent, P°A
temperature (°K), T
radial distance from source, r
time, t
mole fraction, X,
concentration in air, C,
VALUE
0.3
1.65 g/ml
0.06
0.24
0.40
8 x HT> m2/s
3.2 x 10^ mVs
0.39
0.01 ml/g
1.82
3.28 mol/m3
1m
8.2057 x 10-5 m3 atm/(mol °K)
0.079 atm
293.15
variable
variable
1
computed, variable
-------
5-42
From the ideal gas equation,

PV = i
or
n/V =
(5-51)
(5-52)
But P is total pressure or the sum of the partial pressures
of each component. Thus, from Raoult's Law,

C* - XAP\/RgT (5-53)

Thus, the initial and boundary conditions are as follows:
C, (r,0) = 0
(5-54)
C, (r., t) = C. (from Equation 5-53) (5-55)

C, (oo, t) = 0 (5-56)

The general solution for this governing equation subject
to the above initial conditions as solved using LaPlace
Transform techniques can be found in Carslaw and Jaeger
(1959). The solution, as presented in Carslaw and Jaeger
(1959), is given in integral form for the full time domain
and in asymptotic series form for the early time domain.
To generate answers covering the full time domain, the
integral form of the solution comprised of the zero-order
Bessel functions,
C, = C, + 2C, ITT f"exp (-D'uh/R.)*
Jo

J0 (ur) Y0 (ur.) - Y0 (ur) J0 (ur.)
(5-57)
needs to be numerically integrated.

To circumvent potential problems associated with trying
to numerically integrate a solution comprised of
oscillatory functions, the answers can also be generated by
numerical inversion of the solution in the LaPlace
domain. The governing equation in the LaPlace domain
(Carslaw and Jaeger, 1959) is as follows:
+ [l/r(dCjdr)] = pR/D*; C,=0, r>r, (5-58)
where
C. (r,, P) =

and its solution is of the form
where
C. = [C. K, (qr)] / [p K,, (qr.)]
q = (p R, /D*)»
(5-60)
(5-61)
(5-62)
C. (oo.p) = 0
(5-59)
Herein the solution is generated by taking the above
solution in the LaPlace domain and inverting it
numerically using the DeHoog et al. (1982) algorithm.

To perform some example calculations, TCE is considered
and data are used, in part, from Mendoza and McAlary
(1990). Data are presented in Table 5-5. The source
concentration in Table 5-5 is in mol/m3; this can be
converted to mg/L using the molecular weight of TCE
(131.5 g/mol) to give a source concentration 433 mg/L
gas. The source radius is assumed to be 1 m, that is, r, =
1. The problem defined by these data is referred to as
the base case.

The results of the base case are shown in Figure 5-20(b),
which contains plots of vapor concentration versus radial
distance for three times after emplacement of the
DNAPL source. As may be seen, immediately next to the
DNAPL source, the vapor concentrations approach the
source concentration. A few meters away from the
DNAPL source, the concentrations decrease rapidly. As
expected, the concentrations increase away from the
source with time.

These results are helpful in estimating how far vapors will
extend from a DNAPL source, and how fast they will
migrate. This analytical solution is based on a number of
assumptions: (1) diffusion only, as described by Pick's
second law, (2) partitioning coefficients are linear and the
system is at local equilibrium, (3) use of Millington-Quirk
tortuosity (Equation 5-48), (4) soil properties are
uniform, (5) soil system is isothermal and chemical
properties are constant, (6) the chemical is conservative,
and (7) there is no interaction with upper and lower
boundaries. In general, these assumptions allow the
vapors to migrate farther and faster than if recharge
events and condensation on the water table were
considered.

It is of interest to see how sensitive the solution is to
variations in parameters. For example, vapor diffusion
-------
5-43
70 80 90 100
Radius (meters)
(a)
Radius (meters)
Radius (meters)
(c)

Figure 5-20. Radial vapor diffusion after 1, 10, and 30 years from a 1.0 m radius DNAPL source for a
vapor retardation factor of 1.8 and diffusion coefficient of (a) 1.6 X lO^mVsec, (b) 3.2 X
10-" mVsec, and (c) 4.8 X lO* mVsec.
-------
5-44
coefficients are provided in Appendix A. As shown, for
most DNAPL chemicals, the diffusion coefficients are
similar. If the diffusion coefficient is increased and
decreased by 50%, the results in Figure 5-20(a) and (c)
are obtained, respectively. The concentrations are similar
to those in Figure 5-20(b), with the higher diffusion
yielding higher concentrations.

Another parameter that can vary is the source
concentration. For this problem, the solution is linear.
Therefore, as the source concentration changes, the
solution can be scaled either up or down depending on
whether the source concentration increases or decreases.

The final parameter that affects the solution is the vapor
retardation factor. As indicated in Equation 5-49,
retardation increases with increasing water content and
increasing distribution inefficient, and decreases with
increasing air-filled porosity and increasing Henry's Law
constant. Less mobile vapors have a high R, and more
mobile vapors have a low& The most mobile situation
occurs when K,, = n. = 0 and R, = 1. The effect of
varying the vapor retardation factor is demonstrated in
Figure 5-21 for R. = 1 (a), R. = 10 (b), and R. = 100
(c). The unretarded case is shown in Figure 5-21(a), in
which the vapor concentrations are transported the
farthest. As expected, with increasing R,, transport is
more limited.

Thus, for soil-gas monitoring, the optimal conditions are
those that promote vapor transport. These include (1)
high vapor pressure of the pure solvent to allow a high
source concentration, (2) low water content (dry
conditions), and (3) high Henry's Law constant.
5.4 NUMERICAL SIMULATION OF IMMISCIBLE
FLUID FLOW

Although petroleum reservoir simulators have been used
to model immiscible fluid flow for more than 20 years
(Peaceman, 1977; Crichlow, 1977), with few exceptions, it
is only within the past decade that multiphase flow codes
have been utilized to examine NAPL contamination
problems (e.g., Arthur D. Little, Inc., 1983; Abriola and
Finder, 1985a, b; Guswa, 1985; Faust, 1985b; Faust et al,
1989; Osborne and Sykes, 1986; Kuppusamy et al., 1987;
Parker and Lenhard, 1987a; Lenhard and Parker, 1987b;
and Kueper and Frind, 199la, b). Similarly, within the
past few years, a variety of simulators have been
developed to examine vapor transport from subsurface
NAPL sources (e.g., Baehr, 1987; Silka, 1986 Mendoza
and Frind, 1990a, b). Reviews of multiphase flow codes
are provided by Abriola (1988) and Camp Dresser and
McKee (1987). The following discussion is adapted from
Mercer and Cohen (1990) and Abriola (1988).

Early recognition of NAPL movement in groundwater as
a two-fluid flow phenomenon is attributed to van Dam
(1%7). Later, several models were developed to describe
mathematically the flow of NAPL in the subsurface (Mull,
1971, 1978; Dracos, 1978; Holzer, 1976; Hochmuth and
Sunada, 1985). Common to each of these is the
assumption of negligible capillarity (piston-like flow).

Brutsaert (1973) presents an early code used to examine
multifluid well flow that accounts for capillarity. The
model is radial and based on a finite-difference
approximation. Later, Guswa (1985) developed a one-
dimensional (vertical) finite-difference, two-fluid flow
simulator. Faust (1985b) extended this work to
accommodate two dimensions as well as a static air phase,
a necessary step to simulate NAPL flow in the vadose
zone. A model similar to Faust's model (1985), which did
not consider an air phase, was applied to the Hyde Park
Landfill, Niagara Falls, New York by Osborne and Sykes
(1986). Abriola and Pinder (1985a,b) developed a two-
dimensional model that also considers volatilization and
dissolution. A similar model is presented in Corapcioglu
and Baehr (1987) and Baehr and Corapcioglu (1987).
Subsequently, Parker and Lenhard (1987) and Lenhard
and Parker (1987a) incorporated hysteretic constitutive
relations. More recently, a three-dimensional model that
extends Faust's (1985b) model is described in Faust et al.
(1989); Kueper and Frind (199la) presented a two-
dimensional, vertical slice model formulated in terms of
wetting phase saturation and pressure, and Guarnaccia et
al. (1992) developed a two-dimensional, two-phase code
to simulate NAPL emplacement and subsequent removal
through dissolution in near-surface saturated
environments.

Because of previous reviews on immiscible flow models,
a detailed review is not provided herein. The basic
governing equations are presented for completeness,
along with constitutive relationships that concern many of
the properties discussed in the Chapter 4. This discussion
follows closely that presented by Abriola (1988).
-------
5-45
70 80 90 100
Radius (meters)
(a)
2030405060 70 SOW 100
Radial Vapor Diffusion
DNAPI source D=3.2E-06sq.meters/$ec;Ra=10.0
Radius-1.0 rr
(b)
Radial Vapor Diffusion
0-3.2E-06 3q.meters/sec;Ra=iOO.O
0 10 20
405060 70 8090 100
Radius (meters)
Figure 5-21. Radial vapor diffusion after 1, 10, and 30 years from a 1.0 m radios DNAPL source for a
diffusion coefficient of 3.2 X lO^mVsec and vapor retardation factors of (a) 1, (b) 10, and
(c) 100.
-------
5-46
5.4.1 Mass Balance Equations

The equation development begins with the mass balance
equation for species i in phase a, where a stands for soil,
air, water, and NAPL or a subset of these. A species is
defined as a specific chemical that is present in one or
more phases. The mass balance equation is written as
(Abriola, 1988):
- V • J,« = S«
where: v" is the mass average velocity of the a phase; w"
is the mass fraction of species i in the a phase; ea is the
fraction of volume occupied by the a phase; p" is the
intrinsic mass density of the a phase; J* is the non-
advective flux of a species i in the a phase; S* represents
the exchange of mass of species i due to interphase
diffusion and/or phase change; Rj" represents an external
supply of species i to the a phase; and V is the differential
operator.

The first and second terms in Equation 5-63 represent
mass accumulation of species i in phase a and mass
movement due to advection of the phase, respectively.
Mass transport due to non-advective effects (i.e.,
dispersion and diffusion) is incorporated by the third
term. The first term on the right side of Equation 5-63,
S", is a source/sink term to account for phase changes;
and the second term, Rj* accounts for the destruction or
creation of the species due to biological or chemical
transformations.
Equation 5-63 is constrained by
and
(5-64)
(5-65)
based on the definitions of mass and volume fraction.
Also, when mass is lost from one phase due to interphase
exchange, an equal amount of mass is gained by another
phase, or:
0
(5-66)
phase or alternatively summing over all phases based on
Equation 5-63.
5.4.2 Immiscible Flow Equations

Equation 5-63 can be simplified by assuming that there is
no mass exchange between phases and no chemical or
biological transformations and by summing over all
species to yield (Abriola, 1988):
at
(Pxv) = o
(5-67)
where use has been made of constraint Equation 5-64.
The non-advective flux terms, which deal with relative
motion of the species within a phase, also sum to zero.
Equation 5-67 has been used to model the flow of NAPLs
with chemical or physical properties that can be
considered spatially invariant.

In general, one equation is written for each of the four
phases: soil(s), air(a), water(w), and NAPL(N). If the
porous medium is incompressible (porosity is constant in
time), then the soil equation is not needed. Similarly,
assuming the gas phase remains at atmospheric pressure,
the gas equation also can be deleted to yield:

n J (sap°) + V • (pXnV) = 0 a = w,N (5-68)

where n is porosity and sa is the saturation of the a phase
(ea = ns0). Finally, if the fluids are treated as
incompressible, then:
n?-(sa) + V • (sanv") = 0 a = w,N (5-69)
al
5.4.3 Compositional Equations

For the interphase transfer of mass (i.e., the formation of
a dissolved plume or the transport of organic vapors),
balance equations for each species are written. The
species balance equations are obtained by summing
Equation 5-63 over all phases to yield (Abriola, 1988):
+ V-(p
-------
5-47
where a = a,s,w,N and constraint 5-66 has been
incorporated. The right side of Equation 5-70 is zero for
nonreactive species. The number of equations that are
required depend upon the number of species. If the soil
matrix is rigid, the soil species equation may be deleted.
Solving Equation 5-70 yields fluid distributions and
compositions in time and space.
5.4.4 Constitutive Relations

Assuming it is valid, Darcy's law may be substituted into
a system of mass balance equations (such as Equation 5-
68 or 5-70) to derive the equations governing multiphase
fluid flow in a porous medium. For example, consider
NAPL flow in a rigid matrix (Faust et al., 1989):
(5-71)
n.(s0p") - v • [P" " • (W- p°g)] = 0
al r*«
Equation 5-71 is formulated in the unknowns P°, which
are continuous in space. Porosity n and intrinsic
permeability k are assumed known properties of the
matrix. Generally, viscosity (|ia), a weak function of
pressure, is assumed constant. For the incompressible
fluid case, p* is a constant. In general, however, density
will depend on the fluid pressure, P°. Thus, fluid density
may be expanded in terms of fluid pressure by
incorporating /3°, the impressibility of the a phase. For
slightly compressible fluids, /3" is essentially constant.

Capillary pressure and relative permeability, which can
exhibit hysteretic behavior, are generally considered
functions of saturation as described in Chapter 4. For
example, based on the van Genuchten k,,, - sa - Pc model
described by Luckner et al. (1989) and Guarnaccia et al.
(1992):

s« = (s. . SJ / (1.0 - v), (0 < s^ < 1) (5-72)

s« = [(1 - *„) - s.)] / (1.0 - sj, (0 < ^ < 1) (5-73)

SM = 1 / [1 + (a hc)T (5-74)

(5-75)

(5-76)
where s,, is the effective wetting phase saturation, s,,, is
the effective nonwetting phase saturation, s^ is the
wetting phase residual saturation, SK is the nonwetting
phase residual saturation, h«. = Pl ~ IVj COj ^*>-//J

where Kj** is the partition coefficient of species i between
the a and ft phases. Partition coefficients are defined as
functions of phase compositions and pressures and may
be determined from solubility relations and Henry's Law
constants (Appendix A). See, for example, Corapcioglu
and Baehr (1987), Baehr and Corapcioglu (1987), and
Baehr (1987).
5.4.5 Model Utility

Although NAPL models can, in theory, simulate a variety
of problems, the data required for applications are
generally lacking. Examples of the application, and
limitations, of using an immiscible flow code to simulate
-------
5-48
DNAPL migration at two hazardous waste sites in
Niagara Falls, New York are given by Faust et al. (1989).
Heterogeneity influences NAPL flow and solute transport;
however, spatial variability of pore size (affecting
displacement pressures) and intrinsic permeability are
rarely sufficiently defined to permit accurate prediction.
Therefore, use of multiphase flow codes is limited by the
difficulties associated with measuring field-scale ?„($„) and
KT(SW) relations and characterizing media heterogeneity.
As noted in Chapter 4, the theoretical description of mass
transfer in porous media has not been adequately
developed, and also adds uncertainty to any modeling
approach. Currently, immiscible flow models are used
most frequently for hypothesis testing in a
conceptualization mode, particularly at NAPL
contamination sites where extensive research has already
been conducted.
-------
6 DNAPL SITE CHARACTERIZATION
OBJECTIVES/STRATEGIES

Site characterization, a process following the scientific
method, is performed in phases (see Figure 6-1). During
the initial phase, a hypothesis or conceptual model of
chemical presence, transport, and fate is formulated based
on available site information and an understanding of the
processes that control chemical distribution. The
potential presence of DNAPL at a site should be
considered as part of this early hypothesis. A variety of
DNAPL conceptual models are described in Chapter 5.

Based on the initial hypothesis, a data collection program
is designed in the second phase to test and improve the
site conceptual model and thereby facilitate risk and
remedy assessment. As such, site characterization efforts
should focus on obtaining data needed to implement
potentially feasible remedies. After analyzing the newly
squired data within the context of the initial conceptual
model, an iterative step of refining the hypothesis is
performed using the results of the analysis, and additional
data may be collected. As knowledge of the site increases
and becomes more complex the working hypothesis may
take the form of either a numerical or analytical model.
Data collection continues until the hypothesis is proven
sufficiently.

During implementation of a remedy, the subsurface
system often is stressd. This provides an opportunity to
monitor and not only learn about the effectiveness of the
remediation, but to learn more about the subsurface.
Therefore, remediation (especially pilot studies) should be
considered part of site characterization, yielding data that
may allow improvements to be made in the conduct of
the remediation effort. Specific objectives, strategies, and
concerns related to DNAPL site investigation are
discussed in this chapter.
6.1 DIFFICULTIES AND CONCERNS

The difficulty in evaluating chemical presence, transport,
risk and remediation at DNAPL sites is compounded by
the following factors (USEPA, 1992).

• j "The relative importance of the forces that control
the rate, flow direction, and ultimate fate of DNAPL
is different from the relative importance of those that
control the distribution of dissolved phase plumes.
DNAPL behavior is only loosely coupled to that of
groundwater. Movement of DNAPLs is remarkably
sensitive to the capillary properties of the subsurface,
and the distribution of those properties
controls the distribution of the DNAPL.
Thus, knowledge of geologic conditions is
relatively more important than knowledge of
hydrologic conditions for adequate
characterization of DNAPL sites."

• 2 "Obtaining a detailed delineation of subsurface
DNAPL distribution is difficult and may be
impractical using conventional site characterization
techniques. DNAPL migrates preferentially through
relatively permeable pathways (soil and rock
fractures, root holes, sand layers, etc.) and is
influenced by small-scale heterogeneities (such as
bedding dip and slight textural changes) due to
density, capillary forces, and viscous forces. As a
result, the movement and distribution of DNAPL is
difficult to determine even at sites with relatively
homogeneous soil and a known, uniform DNAPL
source. This difficulty is compounded by fractured
bedrock, heterogeneous strata, complex DNAPL
mixtures, etc. The relative importance of small-scale
heterogeneities may depend on the volume of the
release [i.e., diminish with increasing release
volume]."

•3 "DNAPL in fractured media poses exceptionally
difficult problems for site investigation and
remediation because fracture networks are complex,
DNAPL retention capacity (mass of DNAPL per
volume of rock) is generally small, and the depth to
which DNAPL may penetrate can be very large."

•4 "Failure to directly observe DNAPL at a site does not
mean it does not exist. Often, only very low aqueous
concentrations of DNAPL constituents are detected
in monitor wells at known DNAPL sites." These
concentrations, however, may greatly exceed drinking
water standards.

•5 "DNAPLs can be broadly classified on the basis of
physical properties such as density, viscosity, and
solubility. Of the various types of DNAPLs found in
the subsurface, chlorinated solvents and creosote/coal
tar are apparently the most common. These two
types of DNAPLs, however, present groundwater and
remediation problems of a very different nature due
to the differences in their physical properties. Some
of the conclusions applicable to one are not generally
applicable to the other. Physical characteristics can
guide the choice of characterization and remediation
options."
-------
NOTE:

Characterization should be conducted in a
phased, evolutionary manner s(arfinj with
review of available data. Early field work
should focus on areas beyond the DNAPL
zone and use noninvasive methods in the
DNAPL zone Each characterization
activity should be designed to test the
conceptual model in a manner that will
increase the capacity to perform risk
and remedy analysis.

To limit the potential for promoting
contaminant migration, avoid: (I) conducting
unecessary field work; (2) drilling through
capillary barriers beneath DNAPL; (3) pumping
from beneath DNAPL zones; and, (4) using
invasive characterization or remediation
methods without due consideration for the
potential consequences.
REVIEW EXISTING DATA
(CHAPTER 7)
tndustiy type ond processes used
Documented use or disposal of ONAPL
Available site, local, or regional
investigation reports
Corporate/client records
Government records
University, library, historical society records
Interviews with key personnel
Aerial photographs
UNDERSTANDING OF THE DNAPL PROBLEM,
DNAPL AND MEDIA PROPERTIES, AND
TRANSPORT PROCESSES
(CHAPTERS 3. 4, & 5)
DEVELOP INITIAL CONCEPTUAL MODEL
i
SITE CHARACTERIZATION ACTIVITIES
NON1NVASIVE METHODS
(CHAPTER 8)

Surface geophysics
Soil gas analysis
INVASIVE METHODS
(CHAPTER 9)

Test pits
Borings
Wells
Hydraulic tests
LABORATORY METHODS
(CHAPTER 10)
DELINEATE

DNAPL

SOURCE
AREAS

EXAMINE
SUSPECT AREAS

Floor drains and sumps
Catch basins
Pits, ponds, lagoons
Other disposal areas
Septic tanks
Leach fields
French drains
Sewers
Process tonks
Wastewater tanks
USTs
Aboveground tonks
Chemical storage areas
Chemical transfer areas
Pipelines
Waste storage areas
Loading dock areas
Wort areas
Discolored soils
Stressed vegetation
Disturbed earth
Disturbed low-lying areas
DETERMINE

DNAPL

ZONE

Delineate
mobile
DNAPL
Estimate
saturations
Delineate
residual
DNAPL
UORE DATA IS NEEDED
REFINE THE CONCEPTUAL MODEL
L
RISK ASSESSMENT
-j REMEDY
I

SITE REMEDIATION
fD LONG-TEF
MONITORING
1
DETERMINE THE

NATURE, EXTENT,
MIGRATION RATE,

AND FATE OF

CONTAMINANTS

NATURE AND EXTENT
DNAPL
Aqueous phase
groundwater contamination
Adsorbed soil ond
rock contamination
Soil gas
contamination
Surface water
and sediment
contamination

MIGRATION RATE
DNAPL
Aqueous phose chemicals
Flow directions
ond velocities

FATE
DNAPL dissolution
DNAPL volatilization
DNAPL immobilization
Adsorption ond
degradation of
aqueous and vapor
phase contaminants
ON
i
to
Figure 6-1. DNAPL site characterization flow chart.
-------
•6 "The risk of causing DNAPL remobilization must be
assessed during site investigation. Conventional
drilling technologies have a high potential for
promoting vertical DNAPL movement. The
appropriate investigation strategy is dependent on
site-specific conditions, including the geology and the
type of DNAPL."

•7 "Nonintrusive, low-risk investigation methods such as
surface geophysical techniques and reviews of site
history and existing data should first be used to
develop and improve the conceptual model of
DNAPL presence and lessen the risks associated with
subsequent drilling. Currently, surface geophysical
methods capable of delineating DNAPL and the
availability of geophysicists training in investigating
DNAPL problems are extremely limited. However,
even routine, noninvasive geophysical techniques can
be used to evaluate site geology, which has a great
influence on DNAPL migration."

•8 "Site characterization should be a continuous,
iterative process, whereby each phase of investigation
and remediation is used to refine the conceptual
model of the site. The time required to define site
characteristics cannot easily be reduced because of
the heterogeneous, site-specific nature of subsurface
environments and the evolutionary [investigatory]
process required. However, the information required
to implement early containment of dissolved-phase
contamination is less extensive that required to
design final remedial alternatives."

•9 "The complexity of the DNAPL problem dictates that
site investigators have a sophisticated knowledge of
DNAPL contaminant hydrology. Most decisions
regarding site investigations and cleanup depend on
site-specific conditions."

In essence, the impetus to characterize the complexities
associated with DNAPL presence at contamination sites
derives from three fundamental truths.

• The behavior of subsurface DNAPL cannot be
adequately defined by investigating miscible
contaminant transport due to differences in properties
(fluid and media) and principles that govern DNAPL
and solute transport (see Chapters 4 and 5).

• DNAPL can persist for decades or centuries as a
significant source of groundwater and soil vapor
contamination.
• Without adequate precautions or understanding of
DNAPL presence and behavior, site characterization
activities, such as drilling and aquifer testing, may
result in expansion of the DNAPL contamination zone
and increased remedial costs.

Thus, characterization of DNAPL presence, transport,
and fate is required to perform an adequate assessment of
site risks and remedies, and to minimize the potential for
inducing unwanted DNAPL migration during remedial
activities.
6.2 OBJECTIVES AND STRATEGIES

The ultimate objective of characterizing a contaminated
site is to be able to assess risk and select appropriate
remedial measures. Specific objectives of a DNAPL site
investigation are incorporated within the DNAPL site
characterization flow chart given in Figure 6-1. selected
aspects of site characterization objectives and strategies
are discussed below.
6.2.1 Regulatory Framework

Regulations drive cleanups, hence, site characterization,
at hazardous waste sites. Two laws that provide the
framework for site investigation and remediation at
hazardous waste sites are the Resource Conservation and
Recovery Act (RCRA) and the Comprehensive
Environmental Response, Compensation, and Liability
Act (CERCLA), or Superfund. RCRA deals with active
sites, whereas CERCLA addresses the cleanup of inactive
and abandoned hazardous waste sites.

Under RCRA site characterization occurs during the
RCRA Facility Investigation (RFI). The RFI is used to
evaluate the nature and extent of the release of hazardous
waste and hazardous constituents and to gather necessary
data to support a Corrective Measure Study (CMS). The
CMS is used to develop and evaluate corrective measures
and recommend the final corrective measure. Under
CERCLA the analogous process is known as a Remedial
Investigation/Feasibility Study (RI/FS). The purpose of
the RI/FS is to assess site conditions and evaluate
alternatives to the extent necessary to select a remedy.

Guidance for conducting site characterization studies
pursuant to CERCLA and RCRA regulations is provided
by USEPA (1988) and USEPA (1989a), respectively.
Emphasis is placed on rapid characterization of site risk
-------
6-4
and selection of a remedy or corrective measure that
meets certain criteria. For groundwater cleanups, the
criteria are risk based and include Maximum Contaminant
Levels (MCLs), Alternate Concentration Limits (ACLs),
detection limits, and natural (background) water quality.
These criteria are well below the aqueous solubility of
chemicals forming DNAPLs. Therefore, characterizing
DNAPL prior to site remedy selection is critical to setting
remedial objectives and ensuring that clean-up goals are
met.
6.2.2 Source Characterization

Objectives of source characterization include
determination of: mobile and residual DNAPL
distributions, DNAPL volumes, DNAPL imposition and
fluid properties, stratigraphic controls on DNAPL
movement, etc. (Figure 6-1). As indicated in Figure 6-1,
site conditions, especially stratigraphy, should be
examined initially away from suspected DNAPL source
areas. Stratigraphic exploration can be used to identify
capillary barriers that may effectively limit the downward
movement of DNAPL. If possible, suspected DNAPL
source areas should first be investigated using noninvasive
techniques (Chapter 8) such as soil gas analysis and
surface geophysical methods to reduce the risk of
mobilizing contaminants.

Depending on site conditions, soil gas analysis may be
used to reveal volatile DNAPL source areas. Surface
geophysical methods including ground penetrating radar,
complex resistivity, and electromagnetic induction
methods have successfully detected aqueous and
nonaqueous-phase organic contaminants at a very limited
number of sites. More routinely, surface geophysical
methods are employed to provide information on the
stratigraphic layering and boundaries, depths to
groundwater and bedrock, disturbed earth limits, and
buried waste presence. Such information can be used to
focus invasive characterization of source areas and to
reduce the risk of causing undesirable DNAPL
movement.

Invasive subsurface exploration methods, such as drilling
and test pit excavation, will continue to be relied upon
for characterizing DNAPL source areas. Subsurface
samples should be examined carefully, and analyzed
chemically as needed, as drilling progresses to identify the
presence of DNAPL pools and residual zones, and barrier
layers. As a general rule, borings should be discontinued
upon encountering a barrier layer beneath a DNAPL
zone (Chapter 9).
6.2.3 Mobile DNAPL Delineation

Above residual saturation, DNAPL will flow unless it is
immobilized in a stratigraphic trap or by hydrodynamic
forces. Mobile DNAPL is a moving contaminant source
from which chemicals dissolve into groundwater and
volatilize into soil gas. Dissolution may continue for
decades or centuries due to the undiluted nature of the
DNAPL and limits on solubility and groundwater flow
rates. DNAPL migration can greatly expand the vertical
and horizontal extent of subsurface contamination. This
is because gravity may force DNAPL to sink to depths
and in directions that are not downgradient hydraulically
from the DNAPL entry location (the initial source area).
Therefore, a primary focus of many DNAPL site
characterization studies will be to delineate the presence
of mobile DNAPL to facilitate assessment of containment
and recovery options.

Unfortunately, the subsurface DNAPL distribution may
defy definition, particularly at sites with heterogeneous
strata, fractured media, and multiple DNAPL release
locations. Experience at DNAPL sites indicates that the
distribution of highly mobile chlorinated solvents is
typically much more difficult to define than that of less
mobile creosote/coal tar. This appears related to:
(1) the larger volumes of creosote/coal tar typically
released at wood-treating and manufactured gas facilities
versus the smaller volume of chlorinated solvents released
at many industrial and waste disposal sites; (2) the
difficulty observing chlorinated solvents (which are often
colorless) versus the relative ease of observing brown or
black creosote/coal tar in the field; and/or, (3) the much
higher ratio of density to viscosity of many chlorinated
solvents compared to creosote/coal tar which promotes
more rapid and distant movement of the former from the
DNAPL entry locations. Conversely, creosote/coal tar are
more likely to remain near the release areas. Benefits
and risks of characterizing the subsurface distribution of
mobile DNAPL must be made on a site-specific basis.
6.2.4 Nature and Extent of Contamination

As indicated in USEPA (1988), the ultimate objective of
site characterization is to determine the nature and extent
of contamination so that informed decisions can be made
regarding remediation based on the determined level of
-------
6-5
risk. As a source of multimedia contamination, the
nature and extent of separate phase DNAPL and related
chemical contamination needs to be determined in the
affected media. DNAPL chemicals may contaminate soil,
bedrock, ground-water, surface water, surface water
sediments, and air.

Focusing on groundwater, this assessment includes
analysis of groundwater flow and chemical transport.
Emphasis is often placed on the latter component
through intensive groundwater quality monitoring. This
information is used to help: (1) identify contaminants,
(2) determine the distribution and concentration of
contaminants, (3) determine sources of contaminants, and
(4) determine the contaminant phase - dissolved, sorbed
or nonaqueous.

In determining the nature and extent of groundwater
contamination, it is important to estimate the
hydrogeologic characteristics that influence the
contaminant distribution. These characteristics include:
(1) stratigraphy, (2) hydraulic properties of aquifers and
confining beds, (3) hydraulic gradients, (4)
recharge/discharge rates, and (5) sorption potential. If
fractures are present, an evaluation should be made of
their orientation, spacing, and vertical and lateral extent.
The spatial distribution of hydraulic properties, gradients,
and contaminants can be very complex, requiring vertical
as well as horizontal assessment. Groundwater
contamination is often conceptualized as forming plumes.
At some sites, however, heterogeneities in hydraulic
properties (especially in fractured media) and a complex
distribution of contaminant sources may result in very
erratic contaminant distributions.
6.2.5 Risk Assessment

The Risk Assessment Guidance for Superfund (RAGS)
(USEPA, 1989b) presents the general approach to
conducting a risk assessment. Although this approach
can be applied to DNAPL sites, the document does not
discuss DNAPLs. The baseline risk assessment discussed
in RAGS consists of four main steps. Relevant
information identified through data collection and
evaluation (step 1) is used to develop exposure (step 2)
and toxicity (step 3) assessments. Risk characterization
(step 4) summarizes and integrates both toxicity and
exposure steps into quantitative and qualitative
expressions of risk.
The risk assessment determines if the site warrants
remedial action and if so, helps determine risk-based,
site-specific remediation goals. For groundwater,
preliminary remediation goals at CERCLA sites are often
established based on readily available chemical-specific
applicable or relevant and appropriate requirements
(ARARs) such as maximum contaminant levels (MCLs)
for drinking water. For chlorinated solvents that have
MCLs, their aqueous solubilities exceed their respective
MCLs (Table 3-4). Thus, at DNAPL sites, a risk
assessment will most likely require some form of
remediation.
6.2.6 Remedy Assessment

Site characterization data is ultimately used to evaluate
the design and operation of remedial measures at
DNAPL sites. Specific data requirements vary between
alternative remedial technologies. Therefore, acquisition
of site characterization data should be phased and
become more focused with respect to remedy selection as
the site conceptual model becomes more refined.

Groundwater restoration in the DNAPL zone is
impractical, in large part, because there are no proven
remedial technologies for completely removing subsurface
DNAPL in reasonable time frames (except for excavation
where feasible). Depending on site-specific conditions,
the objectives of DNAPL site remediation may include:

• removal of mobile DNAPQ;

• excavation of the DNAPL contamination zone;

• containment of the DNAPL contamination zone;

• containment of contaminated groundwater beyond the
DNAPL contamination zone; and,

• restoration of contaminated groundwater beyond the
DNAPL zone to permit beneficial uses.

USEPA (Clay, 1992) recently recommended that remedial
strategies at DNAPL sites include:

• expeditious containment of aqueous phase plumes and
extraction of mobile DNAPL where possible;

• phased implementation of carefully monitored and
documented remedial measures; and,
-------
6-6
• modification of remedial measures and goals as
warranted based on the monitoring data.

Various remedial technologies that are potentially
applicable at DNAPL contamination sites are discussed
in Table 6-1. Technologies for DNAPL recovery are
generally unproven under field-scale conditions; and there
are no methods available, or series of methods, which
have been demonstrated to completely remove DNAPL
from the subsurface.

DNAPL recovery operations are ongoing at relatively few
sites. Off-the-shelf remedial measures used at DNAPL
sites have typically been limited to excavation, cut-off
walls, and relatively simple pump-and-treat systems.
There are, however, many DNAPL recovery and
treatment technologies being developed which have
undergone limited laboratory and pilot-scale field testing
(Table 6-1). A major goal of ongoing research is to
develop DNAPL recovery and treatment systems that can
be used in series to optimize site cleanup. USEPA is
currently funding a long-term research effort by the
Robert S. Kerr Environmental Research Laboratory to
evaluate innovative remedial technologies and develop
guidance documents related to DNAPL site remediation
and performance assessment (Clay, 1992).

Removal of mobile DNAPL generally involves some form
of pumping, which requires knowledge of permeability
and DNAPL distribution and properties. Options for in-
situ treatment of groundwater and residual DNAPL
include biodegradation and enhanced oil recovery (EOR)
technologies (Table 6-1). For both of these options, the
spatial distribution of permeability must be estimated to
optimize delivery of nutrients, oxygen, or EOR fluids to
the matrix and to allow movement of microbes or
contaminants. The presence and characteristics (e.g.,
density, viscosity, and interfacial tension) of DNAPL need
to be determined to assess the feasibility of EOR. If
EOR is used to mobilize DNAPL at residual saturation,
DNAPL flow must be controlled carefully. Otherwise,
previously clean portions of the subsurface may become
contaminated during remediation.

To design an efficient hydraulic containment system, the
components of the groundwater flow system (i.e.,
permeability distribution, hydraulic gradients, boundary
conditions, etc.) must be defined. Aquifer sorption
properties, including the distribution of organic carbon
content, must be estimated to assess dissolved chemical
removal efficiency and clean-up times. For each chemical
or chemical class, data required for remediation decisions
include characteristics related to: (1) leaching potential
(e.g., water solubility, organic carbon partition
coefficient); (2) volatilization potential (e.g., vapor
pressure, Henry's Law constant); (3) degradation
potential (e.g., half life, degradation products); and (4)
chemical reactivity (e.g., hydrolysis half life, chemical
kinetics). Additionally, the potential for chemical
precipitation and plugging should be estimated using
major cation/anion chemistry of the groundwater when
considering the feasibility of injection well and/or surface
treatment options.

Characterization data and considerations relevant to the
assessment of remedial options that are potentially
applicable to DNAPL contamination sites are further
described in Table 6-1.
-------
Table 6-1. Remedial options potentially applicable to DNAPL Contamination sites (modified from USEPA, 1992).
METHOD
Hydraulic
Containment

Containment
using
Physical
Barriers

APPLICATION
Hydraulic
containment is
used to prevent
the undesired
migration of
chemicals
through the
saturated zone.

Capillary and
low permeability
barriers (fine-
grained walls)
can be
constructed to
limit NAPL
migration.

PROCESS
Hydraulic containment of DNAPL and dissolved
chemicals can be achieved by pumping groundwater
from wells and/or drains. Fluid flow control can be
augmented by injecting water through wells and/or
drains, and by the installation of physical barriers (cut-
off walls and landfill coven). Monitor wells are
utilized to determine whether or not the specified
hydraulic gradients have been obtained and chemical
migration has been arrested.

Low permeability, fine-grained barrier walls (i.e.,
slurry walls, concrete walls, sheet piling with grouted
joints, etc.) can be constructed to impede the lateral
migration of non-wetting DNAPL below the water
table. Where possible, barrier walls should be keyed
into a low permeability, capillary barrier layer beneath
the DNAPL contamination zone.

EFFECTIVENESS / ADVANTAGES / LIMITATIONS
Long-term hydraulic containment will be needed at many
DNAPL sites because residual and trapped pools of
DNAPL are long-term sources of groundwater
contamination. The effectiveness of a hydraulic
containment system depends largely on the adequacy of the
design and operation of the system. Containment is eased
where there is a continuous barrier layer that prevents
downward DNAPL migration. Downward migration can be
arrested at some sites by creating an upward hydraulic
gradient into the DNAPL zone that exceeds the density
difference between DNAPL and water. Vertical hydraulic
containment of DNAPL, however, has yet to be
demonstrated in the field. The main drawbacks to hydraulic
containment systems are cost and the need for long-term
operation.

Barrier walls can provide cost-effective control over NAPL
migration in favorable settings. Barrier walls have not been
tested, however, to determine their capacity for long-term
impedance of NAPL migration. Small fractures or openings
will facilitate DNAPL breakthrough. The long-term
integrity of engineered subsurface barriers is not well-known.
Consideration must be given to the compatibility of barrier
wall materials with subsurface chemicals, the potential for
inducing migration during wall construction, and changes to
the hydrogeologic system effected by wall emplacement.
EXPERIENCE
The components of a
hydraulic containment
system (wells, drains,
cut-off walls, and
covers) have been
widely used for
contamination site
remediation and other
applications. Although
hydraulic containment
is generally a proven
migration control
technology, its success
depends on adequate
design and
implementation.
Cutoff walls have been
installed as part of
containment systems at
many sites.

REFERENCES
Cherry et al. (1990),
Cohen et al. (1987),
Mackay and Cherry
(1989), Mercer et al.
(1990)

Cherry et al. (1990);
Sale et al. (1988)

-------
Table 6-1. Remedial options potentially applicable to DNAPL Contamination sites (modified from USEPA, 1992).
METHOD
APPLICATION
PROCESS
EFFECTIVENESS / ADVANTAGES/ LIMITATIONS
EXPERIENCE
REFERENCES
Product
Recovery by
Pumping
Mobile NAPL
can be pumped
from wells or
drains.
Mobile NAPL can be pumped from wells and drains
utilizing single pumps to extract total fluids or NAPL
only, or using individual pumps to withdraw water and
NAPL separately.
Wells should be placed in stratigraphic traps to optimize
recovery where NAPL pools are present. Long-term
recovery is increased by maintaining a maximum thickness
and saturation of NAPL adjacent to the well. This can be
achieved by pumping NAPL and water separately. Pumping
water above a DNAPL pool causes DNAPL upwelling which
works to increase the formation transmissivity to DNAPL
flow. A dual pumping system can be operated using wells or
drains. Overpumping the NAPL may result in truncation of
the NAPL layer at the well edge and significantly reduce the
formation transmissivity to NAPL flow. Pumping may cause
NAPL to enter previously uncontaminated sections, thereby
enlarging the contaminated zone. In shallow, unconfined
formations, it will generally not be possible to significantly
diminish the NAPL residual saturation by increasing
hydraulic gradients alone. Pumping can be used to remove
mobile NAPL and reduce the potential for continued NAPL
migration, however. Vacuum-enhanced pumping may be a
way to increase gradients for improved mobilization and
hydraulic control.
A great deal of
experience has been
acquired by the oil
industry pumping
LNAPL from crude oil
reservoirs and by the
environmental industry
pumping petroleum
products from
contaminated shallow
formations. Little
documentation is
available, however,
regarding DNAPL
product recovery at
contamination sites.
Blake et al. (1990),
Ferry et al. (1986),
McWhorter (1991),
Sale et al. (1988 and
1989), Sale and
Piomek (1988),
Schmidtke et al.
(1987), Villaume
(1991), Wisniewski et
al. (1985)
Soil Flushing
by Flooding
with Water,
Steam,
Surfactants,
Alkaline
Agents,
Polymers,
and
Cosorvents
[see specific
flood EOR
technologies
below]
In situ soil
flushing can be
used to enhance
recovery of
NAPLs,
adsorbed
chemicals, and
dissolved
chemicals from
the saturated or
unsaturated
zone.
Injection wells or drains, or surface application
delivery systems are used to flood the contaminated
zone with flushing solutions and sweep the
contaminants to recovery wells or drains (i.e.,
surfactants, cosolvents, alkaline agents, polymers,
steam, etc.). Drains are typically used to effect line-
drive sweeps; wells are typically used to effect line-
drive or five-spot sweeps. The flood enhances
recovery of NAPL by reducing interfacial tension,
reducing NAPL viscosity, lowering the mobility ratio,
increasing solubility, and/or increasing hydraulic
gradients (i.e. raising the capillary number). Recovery
of adsorbed and/or dissolved chemicals is also
enhanced by these processes. Displaced NAPL and
chemicals are recovered by pumping wells and/or
drains. At the conclusion of the flood, the flushing
solution can be displaced to the recovery system by
injecting water via the delivery system. Soil flushing
may be used as an intermediate process in a train of
remedial measures.
Soil flushing is most effective in permeable, uniform media.
It can be used to speed the permanent reduction or removal
of contaminants from the subsurface. Heterogeneous and
low permeability soils will generally result in reduced sweep
efficiency, longer project duration, and less successful
recovery. It will generally not be possible to remove all
NAPL from sites with substantial NAPL presence. Soil
flushing can, however, be used to reduce the NAPL residual
saturation to levels below the immobile saturation at
ambient site conditions. The movement of contaminants
mobilized by the flood must be carefully controlled to
prevent detrimental migration. Consideration must also be
given to: Ihe loricity, nature and fate of Ihe flushing
solution and potential adverse reactions (permeability
reduction, impairment of biodegradation rates, etc.) caused
by the solution. Site-specific bench and pilot-scale field tests
are generally recommended prior to implementation of a
field-scale remedial project. The site-specific application of
EOR methods may prove to be effective within a train of
treatment measures to remediate NAPL-contaminated sites.
Although the oil
industry has made
extensive use of
flooding technology to
enhance oil recovery,
few in-situ soil flushing
operations have been
conducted at
contamination sites. In
general, the application
of soil flushing
technologies to
remediate
contamination sites is at
the pilot-test stage and
the effectiveness of
these technologies in
environmental
applications is
unknown.
Sims (1990), USEPA
(1990a and 1990b)
[see specific flooding
technologies below]
-------
Table 6-1. Remedial options potentially applicable to DNAPL Contamination sites (modified from USEPA, 1992).
METHOD
EOR Using
Water
Flooding

EOR Using
Thermal
Methods
(Steam or
Hot Water
Flooding)

APPLICATION
Waterflooding
can be used to
increase the
recovery of
NAPL from the
saturated zone.

Thermal
methods (steam
or hot water
flooding) can be
used to increase
NAPL recovery.

PROCESS
Referred to as secondary recovery by the oil industry,
waterflooding involves the injection of water in wells
or drains to hydraulicalty sweep NAPL toward
production wells. Recovery can be enhanced because
injection/extraction systems (i.e., line-drive and five
spot systems) allow for the development and
sustenance of increased hydraulic gradients and flow
rates, elimination of dead zones, and overall improved
flow control management.
High-temperature steam is injected via wells into the
contamination zone. The steam yields heat to the
formation and condenses into a zone that acts as a hot
water flood. Coupled with the continuous injection of
steam behind it, this hot water drives NAPL to the
recovery wells. NAPL recovery is enhanced because:
(1) the NAPL becomes less viscous and more mobile
upon heating; (2) NAPL solubility may be increased
by the higher temperatures; (3) volatile NAPL
vaporizes, moves ahead of the hot water and then
condenses to form a NAPL bank; and, (4) the
increased NAPL saturation in the NAPL condensate
bank provides increased NAPL transmissivity and,
under favorable conditions, results in a snowball
effect.

EFFECTIVENESS / ADVANTAGES / LIMITATIONS
Refer to the soil flushing comments.

The application of thermal methods to enhance DNAPL
recovery at contamination sites may become more popular
based on the successful use of steam injection by the oil
industry, the encouraging results of limited lab and pilot-
scale testing of steam injection for DNAPL recovery, and
the fact that additional chemicals need not be injected to
recover the contaminants. Heating may convert DNAPL to
LNAPL, thereby promoting mobility due to buoyancy forces.
Costs may be high due to heat loss and the need to heat
large volumes of subsurface materials.
Refer to the soil flushing comments.

EXPERIENCE
Although routinely
utilized for secondary
recovery by the oil
industry, waterflooding
has been utilized to
recover NAPL at only a
few environmental
contamination sites.

There were
approximately 200
active thermal EOR
projects in the United
States in 1986. Steam
and hot water
displacement of NAPLs
at contamination sites
has been evaluated in a
few laboratory and pilot
Meld studies.

REFERENCES
Anderson (1987c),
Donaldson et al.
(1989), Rathmell et al.
(1973), Sale and
Piontek (1968), Sale et
al. (1989), Sale et al.
(1988)

Blevins et al. (1984),
Boberg (1988),
Donaldson et al.
(1989), Doschcr and
Ghassemi (1981),
Goyal and Kumar
(1989), Hunt et al.
(1988a and 1988b),
Leuschner and
Johnson (1990),
Mandl and Volek
(1969), Menegus and
Udell (1985), Miller
(197S), Offeringa et al.
(1981), Prats (1989),
USEPA (1990b),
Volek and Pryor
(1972), Willman et al.
(1961), Yortsos and
Gavalas (1981)
-------
Table 6-1. Remedial options potentially applicable to DNAPL Contamination sites (modified from USEPA, 1992).
METHOD;
EOR Using
Surfactant -
Water
Flooding

EOR Using
Alkaline
Water
Flooding

APPLICATION
Surfactant
flooding can be
used to increase
NAPL recovery
during a flood
operation.

Alkaline flooding
can be used to
increase NAPL
recovery during
a flood
operation.

PROCESS
Surfactant solution is injected as a slug in a flooding
sequence to decrease the interfacial tension between
NAPL and water by several orders of magnitude (i.e.,
from 20-50 dynes/cm to less than 0.01 dynes/cm). The
development of ultra-low interfacial tension effects a
commensurate 3-5 orders-of-magnitude increase in the
capillary number (N^) which is the ratio of viscous to
capillary forces, sometimes expressed as Na=fiv/0^
where ft and v are the viscosity and Darcy velocity of
the displacing fluid, a is the interfacial tension, and <£
is the pore volume. Ultra-low interfacial tension and
higher capillary numbers improve the NAPL
displacement efficiency of a flood, promote the
coalescence of NAPL ganglia and development of a
NAPL bank in front of the surfactant slug, and result
in increased NAPL recovery and reduced NAPL
residual saturation. Surfactant flooding can also
enhance NAPL recovery by causing increased NAPL
wetting, solubilization, and emulsification. Surfactants
used in EOR operations by the oil industry include
petroleum sulfonates, synthetic sulfonates, ethoxylated
sulfonates, and ethoxylated alcohols.
Alkaline waterflooding is an EOR process where
inexpensive caustics such as sodium carbonate, sodium
silicate, sodium hydroxide, and potassium hydroxide
are mixed with the injection water. The alkaline
agents raise the pH of the flood and react with
organic acids that are present in oil. This reaction
generates surfactants at the oil-water interface and
leads to improved oil recovery due to (1) greatly
reduced interfacial tension, (2) emulsification effects,
and (3) wettability reversals, which can mobilize
entrapped oil ganglia. Alkaline waterflooding may be
used in conjunction with other EOR methods; for
example, it is reported to be an effective preflush for
surfactant-polymer floods.

EFFECTIVENESS / ADVANTAGES / LIMITATIONS
The high cost of surfactant chemicals has limited the
commercial application of surfactant flooding by the oil
industry. Using surfactant solutions to enhance NAPL
recovery at contamination sites, however, may be more
attractive given the higher costs associated with waste site
remediation. At many sites, reducing interfacial tension will
be the only practical way to mobilize residual NAPL. Refer
to the soil flushing comments.

NAPLs must have acidic components to react with the alkali
agents to form surfactants. Alkaline flooding is relatively
cheap compared to some other EOR methods, but alkali
consumption due to reaction with porous media may be a
limiting factor. Refer to the soil flushing comments.

EXPERIENCE
There were
approximately 30 active
EOR field-scale
projects using
surfactant injection in
the U.S. in 1980.
Surfactant flooding by
the oil industry for
EOR is limited by its
high cost relative to
other EOR methods.
The use of surfactant
flooding to enhance
NAPL recovery at
contamination sites is in
its infancy. Surfactants
were used in a soil
flushing solution of
alkaline, polymer, and
surfactant agents to
boost DNAPL recovery
at the Laramie Tie site.
Numerous alkaline
waterflood EOR
projects have been
conducted by the oil
industry (approximately
40 were reported begun
in the U.S. between
1979 and 1981). Use of
alkaline flooding to
boost NAPL recovery
at contamination sites is
in its infancy. Alkaline
agents were used in a
soil flushing solution of
alkaline, polymer, and
surfactant agents (A-P-
S) to enhance DNAPL
recovery at the Laramie
Tie Plant.
REFERENCES
Akstinat (1981),
Beikirch (1991),
Donaldson et al.
(1989), Ellis et al.
(1985), Flumerfelt et
al. (1981),Fountain
(1991), Gogarty
(1983), Hesselink and
Faber (1981), Manji
and Stasiuk (1988),
Nash (1987), Nelson
et al. (1984),
Neustadter (1984),
Novosad (1981), Pitts
et al. (1989), Salagar
et al. (1979), Shah
(1981), Sharma and
Shah (1989) Tuck et
al. (1988)

Breit et al. (1981),
Campbell (1981),
Castor et al. (1981),
Donaldson et al.
(1989), Janssen-
VanRosmalen and
Hesselink (1981),
Kumar et al. (1989),
Mayer et al. (1983),
Nelson et al. (1984),
Pitts et al. (1989), Sale
et al. (1989), Surkalo
(1990)

-------
Table 6-1. Remedial options potentially applicable to DNAPL Contamination sites (modified from USEPA, 1992).
METHOD
EOR Using
Polymer
Water
Flooding

EOR Using
Chemically-
Enhanced
Dissolution

APPLICATION
Polymer flooding
can be used to
increase NAPL
recovery during
a flood
operation.

Cosolvents can
be used to
increase the
dissolution and
recovery of
NAPL and
adsorbed
chemicals from
the subsurface.

PROCESS
Polymers are large molecules (molecular weight
greater than 200 with at least 8 repeating units) that
can be dispersed in a waterflood to increase the
viscosity of the flood, thereby reducing the mobility
ratio and improving the volumetric sweep efficiency
(NAPL recovery). The mobility ratio is defined as the
mobility of the displacing fluid (relative
permeability/Viscosity for waterflood) divided by the
mobility of the displaced fluid (relative
permeability/viscosity for NAPL). Lower mobility
ratios favor NAPL displacement and recovery. An
effective polymer will impart a high viscosity at low
concentration. Only two types of polymers are
commonly used by the oil industry (polyacrylamides
and polysaccharides). In EOR operations, polymer
flooding is often used as part of a phased injection
sequence consisting of: (1) a preflush to adjust the
pH and salinity of the reservoir; (2) surfactants and/or
alkaline agents to reduce interfacial tension; (3)
polymer solution to increase viscosity and improve
displacement efficiency, and (4) waterflood to displace
the mobilized oil and EOR solutions.

Cosolvents injected into a contamination zone via
wells or drains increase the dissolution of NAPLs and
adsorbed chemicals. Continued flooding of the
contamination zone with Cosolvents or another flood
(water, polymers, etc.) drives the elutriate to
production wells or drains. The elutriate may be
treated and recycled through the system.

EFFECTIVENESS / ADVANTAGES / LIMITATIONS
The advantage of polymer flooding is that it improves the
volumetric sweep efficiency of a water flood process. By
itself, polymer flooding will not, however, mobilize trapped
residual NAPL. Potential limitations include: the risk of
reduced injectivity caused by wellbore plugging, increased
project durations and slowed recovery due to the lower
absolute flood mobility, polymer degradation, excessive cost.
Refer to the soil flushing comments.

Refer to the soil flushing comments.

EXPERIENCE
Polymer flooding had
been initiated at about
180 field-scale EOR
projects in the U.S. by
the mid 1980s. There is
debate in the oil
industry, however,
regarding whether or
not polymer flooding by
itself provides more
than a small
incremental recovery.
Use of polymers to
boost NAPL recovery
at contamination sites is
in the early
development stage.
Polymers were used in a
soil flushing solution of
alkaline, polymer, and
surfactant agents (A-P-
S) to enhance DNAPL
recovery at the Laramie
Tie Plant.
Miscible flooding with
carbon dioxide and/or
hydrocarbon solvents
has been tested at
numerous sites for
EOR by the oil
industry. Several
bench- and pilot-scale
studies have been
conducted on in-»itu
cosolvent flushing
technology at
contamination sites with
variable success.
REFERENCES
Caenn et al. (1989),
Chauveteau and
Zaitoun (1981),
Donaldson et al.
(1989), Hesselink and
Faber(1981), Labaste
and Vk> (1981), Lin et
al. (1987), Liftman
(1988), Pitts et al.
(1989), Sale et al.
(1989), Shah (1981),
Surkalo et al. (1986),
Yen et al. (1989)

Blackwcll (1981),
Fountain (1991),
Groves (1988),
Mehdizadeh et al.
(1989), Nash (1987),
Nash and Traver
(1986), Rao et al.
(1991), Sayegh and
McCaffery (1981),
Taber (1981), USEPA
(1990s and 1990b)

-------
Table 6-1. Remedial options potentially applicable to DNAPL Contamination sites (modified from USEPA, 1992).
METHOD
Pumping
Chemicals
Dissolved in
Groundwater
(Pump-and-
treat)

In -Situ
Aeration
in the
Saturated
Zone (Air
Sparging and
UVB Wells)

APPLICATION
Dissolved
chemicals can be
removed from
the saturated
zone by pumping
groundwater.

Air stripping can
be applied below
the water table
to remove
volatile
contaminants
from the
saturated zone.

PROCESS
Contaminated groundwater is pumped from wells or
drains using conventional technology. Recovery rates
can be optimized by fine-tuning pumping rates, well
locations, etc.

Volatile contaminants below the water table can be
stripped by injecting air through wells. Vaporized
volatile* move with the air to the unsaturated zone
and are recovered using a vacuum extraction system.
Another in-situ groundwater stripping process is
known as the Underpressure- Vaporizer- Well (UVB)
method in which contamianted groundwater is
stripped by air at negative pressures in a special
filtered well. The contaminated gas is collected and
treated at the well head.
EFFECTIVENESS / ADVANTAGES / LIMITATIONS
Pump-and-treat is typically utilized as part of a hydraulic
containment or aquifer restoration program. DNAPL,
where present, will be a long-term source of groundwater
contamination that will prevent restoration. Due to the
relatively low solubility of most DNAPLx, pumping is
generally not an effective method for removing DNAPL
from the subsurface.

In-situ air injection will be most effective removing low
molecular weight, volatile compounds. Little documentation
is available regarding the effectiveness, advantages or
limitations of air sparging and UVB wells.

EXPERIENCE
Recovery of dissolved
chemicals by pumping is
a widely-used, proven
technology, but not for
removal of NAPL.

The application of in-
situ air stripping of
groundwater is very
limited. The UVB Well
method is currently in
use at several sites in
Germany.

REFERENCES
Anderson et al. (1987,
1992a and 1992b),
Feenstra and Cherry
(1988), Hunt et al.
(1988a), Johnson
(1991), Johnson and
Pankow (1992), Keely
(1989), Mackay and
Cherry (1989), Mercer
etal. (1990), Mercer
and Cohen (1990),
SchwiUe (1988)
Blake et al. (1990),
Hen-ling et al. (1990),
Herrling and
Buermann (1990)

-------
Table 6-1. Remedial options potentially applicable to DNAPL Contamination sites (modified from USEPA, 1992).
METHOD
Vacuum
Extraction
(VE)

APPLICATION
VEcan be used
to remove
volatile
chemicals from
the unsaturated
zone and to
prevent
uncontrolled
migration of
volatile
chemicals in soil
gas. If the water
table is lowered,
VEcan be used
to remove
residual NAPL
from below the
original water
table elevation.

PROCESS
Using unsaturated zone wells equipped with blowers
or vacuum pumps, air is forced through soils
contaminated with volatile chemicals. The air flow
generates advective vapor fluxes that change the
vapor-liquid equilibrium, inducing volatilization of
contaminants. The resulting vapors are collected and
treated. Positive differential pressure systems induce
vapor flow away from the control points and negative
differential pressure systems induce vapor flow toward
control points. Experience had demonstrated that
generation of negative differential gas pressures
typically provides the most favorable field results.

EFFECTIVENESS / ADVANTAGES / LIMITATIONS
Vacuum extraction is most effective removing low molecular
weight, volatile chemicals (dimensionless Henry's Law
Constant > 0.01) from homogeneous, permeable media.
Intermittent vacuum extraction operation is generally more
efficient than constant operation. Vacuum extraction
systems can be installed using off-the-shelf components and
conventional drilling methods. Vacuum extraction is less
effective at removing volatile chemicals from heterogeneous
and low permeability soils and is ineffective removing
volatile chemicals from the saturated zone. Because it
induces water table upwelling, vacuum extraction can result
in groundwater contamination where chemicals are located
just above the water table. Groundwater recovery wells
located adjacent to vacuum extraction wells may be
necessary. Alternatively, lowering the water table to allow
volatile chemical recovery by vacuum extraction may
promote DNAPL remobilization and sinking.

EXPERIENCE
In-situ vacuum
extraction processes
have been employed at
more than 100
contamination sites in
the United States.

REFERENCES
Agretot et al. (1965),
Ardito and Billings
(1990), Baehr et al.
(1989), Blake et al.
(1990), Blake and
Gates (1986), Crow et
al. (1985 and 1987),
DiGiulio and Cho
(1990), Dunlap (1984),
Gierke et al. (1990),
Hutzler et al. (1989),
Johnson et al. (1988,
1990a and 1990b),
Jury et al. (1990),
Mackay et al. (1990),
Marley and Hoag
(1984), Massmann
(1989), McClellen and
Gillham (1990),
O'Connor et al.
(1984), Pedersen and
Curtis (1991),
Rathfelder (1989),
Rathfelder et al.
(1991), Regalbuto et
al. (1988), Sims
(1990), Stephanatos
(1988), Texas ResJnst.
(1984), Thornton and
Wootan (1982),
Wilson et al. (1987),
USEPA (1989e,
1990a)
-------
Table 6-1. Remedial options potentially applicable to DNAPL Contamination sites (modified from USEPA, 1992).
METHOD
Steam and
Hot Air
Injection to
Enhance
Vacuum
Extraction

Radio
Frequency
Heating
(RFH) to
Enhance
Vacuum
Extraction

APPLICATION
Vacuum
extraction in the
unsaturated zone
can be enhanced
by steam and
hot air injection.

Vacuum
extraction of
chemicals that
volatilize in the
temperature
range of 80° to
300° C can be
enhanced by
using radio
frequency
heating of
contaminated
soil.

PROCESS
Steam or hot air injected into or below the zone of
soil contamination can improve the effectiveness of
vacuum extraction systems. Heating and increased soil
gas movement caused by steam and hot air injection
raise the vaporization rate of volatile and some semi-
volatile compounds. Additionally, contaminated soil
water and low viscosity NAPLs can be physically
displaced by the condensate that forms in front of the
steam zone.

In situ radio frequency heating (RFH) involves
heating soil with electromagnetic energy in the radio
frequency band (typically 6.7 MHz to 2.5 GHz).
Using a modified radio transmitter as a power source,
energy is transmitted to the zone targeted for
decontamination via electrodes placed in an array of
boreholes. This energy heats the soil to temperatures
between ISO" and 300° C Volatilized chemicals are
recovered with soil gas for treatment by applying a
vacuum to selected hollow electrodes. A rubber sheet
barrier may be spread over the soil surface to provide
thermal insulation and prevent fugitive emissions.

EFFECTIVENESS / ADVANTAGES / LIMITATIONS
In general, steam or hot air injection will increase the
effectiveness of a vacuum extraction system.
Heating will reduce the viscosity and interfacial surface
tension of residual or trapped DNAPL in the unsaturated
zone, which may result in uncontrolled migration. Similarly,
accumulation of DNAPL at the steam condensate front may
result in uncontrolled downward or lateral migration of the
DNAPL.

In general, RFH will increase the effectiveness of a vacuum
extraction system. The technology is only applied to the
unsaturated zone and its use is precluded where buried
metal objects are present. As with vacuum extraction, this
method is best suited to sites where volatile chemicals are
present at shallow depth in homogeneous, coarse-grained
soils. The uniformity of heating provided by RFH (which
occurs due to dielectric heating mechanisms rather than the
thermal conductivity of the soil), however, may result in
more uniform decontamination than achieved using steam or
hot air injection methods and may make this method more
applicable to heterogeneous soils. Heating will reduce the
viscosity and possibly the interfacial surface tension of
residual or trapped DNAPL in the unsaturated zone, which
may result in uncontrolled migration.

EXPERIENCE
Successful laboratory
and pilot-scale field
studies have been
conducted using steam
and hot air stripping to
enhance vacuum
extraction recovery of
solvents and petroleum
contaminants from soil.
Two different systems
have been used: (1) a
mobile unit consisting
of a hollow stem auger
rig outfitted for
steam/air injection and
vacuum extraction of
vapors; and (2) a fixed
system of injection and
extraction wells.
Several bench- and
pilot-scale tests and
limited field-scale
testing have been
conducted using RFH
to remove 70% to 99%
of various solvents, jet
fuel, and PCBs from
shallow soils. Although
RFH continues to be in
the pilot- and field-scale
demonstration stage, at
least one company has
announced the
availability of RFH on
a commercial basis.
REFERENCES
Hunt et al. (1988b),
Houthoofd et al.
(1991), Johnson and
Guffey (1990), Lord et
al. (1987, 1988, 1989,
and 1991), Udell and
Stewart (1989 and
1990), USEPA (1990a
and 1990b)

Dev (1986), Dev et al.
(1988), Dev and
Downey (1989),
Houthoofd et al.
(1991), Sims (1990),
Sresty et al.(1986),
USEPA (1990a,b)

-------
Table 6-1. Remedial options potentially applicable to DNAPL Contamination sites (modified from USEPA, 1992).
METHOD
Bio-
remediation

Containment
by Solidifica-
tion,
Stabilization,
and/or
In-Situ
Vitrification

APPLICATION
Bioremediation
involves
enhancement of
natural processes
to degrade
hazardous
chemicals in the
subsurface.

Solidification,
stabilization, and
in-situ
vitrification are
used to
immobilize
subsurface
contaminants.

PROCESS
Naturally occurring microbes can be used to degrade
and/or detoxify hazardous chemicals in the subsurface.
Bioremediation approaches include: (1) stimulation of
biochemical mechanisms for degrading chemicals; (2)
enhancement by delivery of exogeneous acclimated or
specialized microorganisms; (3) delivery of cell-free
enzymes; and (4) vegetative uptake. Typically, oxygen
and nutrients are delivered to the contamination zone
via wells and/or drains to increase the rate of aerobic
biodegradation.

Waste solidification involves mixing cementing agents
with soil to mechanically bind subsurface contaminants
and thereby reduce their rate of release. Cementing
agents (such as pozzolan-portland cement, lime-flyash
pozzolan, and asphalt systems) can be combined with
contaminated soils by injection, in-situ mechanical
mixing, or above ground mechanical mixing. During
waste stabilization, reagents are used to convert
contaminants to their least toxic, soluble, or mobile
form.
In-situ vitrification utilizes an electrical network (125
or 138kV) to melt contaminated soils and sludges at
temperatures of 1600 to 2000° C. Electricity is
transmitted from a power source into contaminated
soil via large electrodes. Organic contaminants are
pyrolized and inorganic contaminants are incorporated
within the vitrified mass. Vapors can be captured at
the surface for treatment.
EFFECTIVENESS / ADVANTAGES / LIMITATIONS
Adequate characterization of the hydraulic conductivity
distribution is necessary to achieve efficient delivery of
oxygen, nutrients, and/or microbes within the contaminated
zone. Many NAPLs are toxic to microbes and/or resistant
to biodegradation. As a result, degradation may be limited
to the periphery of NAPL contamination zones.
Degradation may generate other undesirable chemicals.
Bench and pilot studies are recommended. Bioremediation
is typically used as a "polishing" step following the
application of other chemical recovery and treatment
processes.

Obtaining complete and uniform mixing of the solidifying
and/or stabilizing agents with the contaminated soil is a
critical factor determining the success of
solidification/stabilization systems.
Successful application of these methods becomes more
difficult with increasing depth. Costs are high, but may be
competitive with other remedies. Bench studies and pilot
field tests are generally necessary. Mixed, complex wastes
present special challenges. Volatilization, mobilization, and
migration of contaminants may be caused by these
processes. The long-term stability and leaching
characteristics of contaminated materials that have been
solidified, stabilized or vitrified is unknown.

EXPERIENCE
Efforts to stimulate
biodegradation have
been employed at full
field-scale at numerous
contamination sites with
varying degrees of
success and
documentation.

Several different
solidification-
stabilization processes
have undergone pilot
tests and full-scale field
demonstrations. Six
full-scale
demonstrations of in-
situ vitrification have
been conducted at the
DOE Hanford site, and
more than 90 in-situ
vitrification tests of
various scales have been
conducted on PCB
wastes, and other solid
combustibles and liquid
chemicals.
REFERENCES
Downey and Elliot
(1990), Hinchee
(1989), Hinchee et al.
(1990), Leuschner and
Johnson (1990),
Lokke (1984), Novak
et al. (1984), Jhaveri
and Mazzacca (1983),
Lee et al. (1988), Lee
and Ward (1984),
Kuhn et al. (1985),
Miller et al. (1990),
Piontek et al. (1989),
Raymond (1974), Sims
(1988), Sims (1990),
Suflita and Miller
(1985), USEPA
(1990a and 1990b),
Vogel et al. (1987),
Wilson et al. (1986),
Wilson and Rees
(1985), Yaniga and
Mulry (1984)
Cullinane et al. (1986),
Fitzpatrick et al.
(1986), Sims (1990),
USEPA (1990a and
1990b)

-------
Table 6-1. Remedial options potentially applicable to DNAPL Contamination sites (modified from USEPA, 1992).
METHOD
Excavation
APPLICATION
Excavation is
used to remove
contaminated
materials from
the subsurface.
PROCESS
Conventional excavating methods are used to remove
contaminated materials from the subsurface for
subsequent incineration, treatment and/or disposal.
EFFECTIVENESS / ADVANTAGES / LIMITATIONS
Excavation can be a very effective site remedy where
contaminant penetration is limited to shallow soils and
where shallow contamination hot spots are identified. The
cost and difficulty of excavation increases with the depth of
contaminant migration and generally becomes prohibitive in
bedrock. Additional concerns include potential fugitive dust,
liquid, and gas emissions caused by excavating contaminated
materials, and the possibility that DNAPL may have
migrated beneath the excavation limit, thereby reducing the
effectiveness of excavation as a remedy.
EXPERIENCE
Excavation of
contaminated materials
is a widely-used remedy
of proven value in
appropriate situations.
REFERENCES

ON
I

ON
-------
7 DNAPL SITE IDENTIFICATION AND
INVESTIGATION IMPLICATIONS

Determining DNAPL presence should be a high priority
at the onset of site investigation to guide the selection of
site characterization methods. Knowledge or suspicion of
DNAPL presence requires that special precautions be
taken during field work to minimize the potential for
inducing unwanted DNAPL migration. DNAPL presence
may be inferred from information on DNAPL usage,
release, or disposal at a site, and/or by examination and
analysis of subsurface samples. However, due to limited
and complex distributions of DNAPL at some sites, its
occurrence may be difficult to detect, leading to
inadequate site assessments and remedial designs.

Guides for evaluating the potential occurrence of DNAPL
at contamination sites have recently been prepared by
Newell and Ross (1992) and Cherry and Feenstra (1991).
This chapter is derived from these and several related
documents. A decision chart to evaluate the presence the
DNAPL at a site is provided as Figure 7-1.
7.1 HISTORICAL SITE USE

As discussed in Chapter 3, DNAPL contamination is
associated with industries and processes that utilize or
generate DNAPL chemicals (such as halogenated
solvents, creosote/real tar, and PCB mixtures) and with
waste disposal sites used by these businesses. Industries
and industrial processes with a high probability of
historical DNAPL release, and DNAPL chemicals which
may contribute to contamination problems, are listed in
Table 7-1.

Assessment of the potential for DNAPL contamination
based on historical site use information involves careful
examination of: landuse since site development; business
operations and processes; types and volumes of chemicals
used and generated; and the storage, handling, transport,
distribution, generation, dispersal, and disposal of these
chemicals and operation residues. Methods for
conducting research on historic developments at
suspected contamination sites are provided in
environmental audit guidance documents (i.e., BNA,
1992; Wilson, 1990; Marburg Associates and Parkin,
1991). Site use information is available from numerous
sources (Table 7-2). Suspect site areas often associated
with contamination are listed in Table 7-3.

The potential for DNAPL contamination at a site based
on historical information can be estimated using the
decision chart (Figure 7-1) in conjunction with Table 7-1.
Although this potential increases with the size and
operating period of a facility, industrial process, or waste
disposal practice (Newell and Ross, 1992), relatively small
and short-term releases from pipeline leaks, overfilled
tanks, or other sources can also create significant DNAPL
contamination problems.
7.2 SITE CHARACTERIZATION DATA

Preexisting site characterization data is available at many
sites being investigated. The potential for DNAPL
contamination should be evaluated at the start and during
the course of new field studies. As outlined in Figure 7-
1, DNAPL presence can be: (1) determined directly by
visual examination of subsurface samples; (2) inferred by
interpretation of chemical analyses of subsurface samples;
and/or (3) suspected based on interpretation of
anomalous chemical distribution and hydrogeologic data.
7.2.1 Visual Determination of DNAPL Presence

Ideally, DNAPL presence can be identified by visual
examination of soil, rock, and fluid samples. Direct visual
detection may be difficult, however, where the DNAPL is
colorless, present in low concentration, or distributed
heterogeneously. Methods to visually detect DNAPL in
subsurface samples are identified in Table 7-4 and
discussed in Chapter 9.10.
7.2.2 Inferring DNAPL Presence Based on Chemical
Analyses

Indirect methods for assessing the presence of DNAPL in
the subsurface rely on comparing measured chemical
concentrations to effective solubility limits for
groundwater and to calculated equilibrium partitioning
concentrations for soil and groundwater (Feenstra, 1990;
Feenstra et al., 1991; Sitar et al, 1990; Mackay et al,
1991). Chemical concentrations and distributions
indicative and/or suggestive of DNAPL presence are
described in Table 7-4.

Where present as a separate phase, DNAPL compounds
are generally detected at <10% of their aqueous
solubility limit in groundwater. This is due to the effects
of non-uniform groundwater flow, variable DNAPL
distribution, the mixing of groundwater in a well, and the
reduced effective solubility of individual compounds in a
multi-liquid NAPL mixture (see Chapter 4, Chapter
9.10.2, and Worksheet 7-1). Typically, dissolved
-------
7-2
Do Site Characterization
Data Indicate Presence
of DNAPL?
Does Historical Site Use
Information Indicate
Presence of DNAPL?
Has DNAPL
n detected visually in
monitor wells, groundwaler, soil
or rock samples
see Table 7-4
Does the
industry type suggest a
high probability of historical
DNAPL release?
Table 7-1
Does a
process or waste
practice employed at the site
suggest a high probability of
historical DNAPL release?
(see Table 7-1
Do chemical
analyses of groundwater
or soil indicate the presence
of DNAPL?
(see Table 7-4)
Were any
DNAPL chemicals use
in apreciable quantities (>10-
50 drums/yr) at the site'
see Table 7-1)
Do chemical
analyses of groundwater
or soil indicate the possible
presence of DNAPL?
see Table 7-4)
IS
DNAPL
PRESENT
NO
Are
the available
site characterization data
adequate to conclude that DNAPL
is not present at the site?
(see Table 7-5
I X II X II
II XII-
DNAPL SITE ASSESSMENT
IMPLICATIONS MATRIX
(see Table 7-6)
Figure 1- 1. DNAPL occurrence decision chart and DNAPL site assessment implications Matrix
(modified from Newell and Ross, 1992).
-------
7-3

Table 7-1. Industries and industrial processes using DNAPLs and some DNAPL chemicals (modified from
Newell and Ross, 1992).
INDUSTRIES/BUSINESSES USING DNAPLS
PROCESSES INVOLVING DNAPLS
DNAPL CHEMICALS
Chemical manufacturing
Solvent manufacturing, reprocessing, and/or
packaging
Commercial dry cleaning operations
Electronic equipment manufacturing
Computer component manufacturing
Metal parts/products manufacturing
Aircraft and automotive manufacturing,
maintenance, and repair operations
Machine shops and metal works
Tool-and-die plants
Musical instrument manufacturing
Photographic film manufacturing and processing
Plastics manufacturing
Pharmaceutical manufacturing
Illicit drug manufacturing
Flame retardant materials manufacturing
Refrigerants manufacturing
Military equipment manufacturing and
maintenance
Manufacturing/processing of septic
system/plumbing cleaners
Manufacturing of typewriters, printers, and
copiers
Printing presses and publishing operations
Textile processing, dying, and finishing
operations
Pesticide and herbicide manufacturing
Wood preservationAreating plants
Manufactured gas plants (prevalent between the
mid-1800s to mid-1900s)
Steel industry coking operations
Asphalt processing and distribution plants
Coal tar distillation plants
Transformer/capacitor oil production,
reprocessing, and disposal operations
Waste disposal sites
Metal cleaning/degreasuig
Storage of solvents (and other
DNAPLs) in drums in uncontained
areas
Tool-and-die operations
Paint removing/stripping
Metal machining
Loading and unloading of solvents (and
other DNAPLs)
Solvent storage in underground and
aboveground tanks
Textile cleaning operations
Dry plasma etching of semiconductor
chips
Aniline
Carbon tetrachloride
Chtordane
Chlorobenzene
Chloroform
2-Chlorophenol
Chlorotoluene
Dibutyl phthalate
1,2-Dichlorobenzene
13-Dichlorobcnzene
1,1 -Dichloroethane
1,2-Dichloroethane
1,1 -Dichloroethene
trans-l,2-Dichloroethene
cis-l,2-Dichloroethene
1,2-Dichloropropane
cis-l,3-Dichloropropene
trans-13-Dichloropropene
Diethyl phthalate
Dimethyl phthalate
Ethylene dibromide
Hexachlorobutadiene
Hexachlorocyclopentadiene
Malathion
Methylene Chloride
Nitrobenzene
Parathion
Polychlorinated Biphenyls
1,1,2,2-Tetrachloroethane
Tetrachloroethene
1,2,4-Trichlorobenzene
1,1,1-Trichloroet hane
Trichloroethene
1,1,2-Trichk>rofluoromet hane
1,1,2-Trichlorotrifluoroethane
Coal tar
Creosote
-------
7-4
Table 7-2. Sources and types of site history information.
Sources
Documents
Types of Available Information
Corporate
Owner/
Operator
Records
Account books (purchase journals, sales journals, cash
journals, ledgers); warehouse receipts; inventory records;
corporate archives; internal division annual reports; deeds;
chemical process documents; waste generation and
disposal documents; detailed site maps; chemical storage,
distribution, transport, and utilization, documents;
chemical spill and release incident reports; historic
photographs; and environmental consulting reports.
Details regarding the storage, transport, use, generation,
accidental release, and disposal of chemicals and wastes.
Municipal
and/or
County
Offices
Tax Assessor records
Fire Department records
Public Works Department records
Building Department records
Utility Department records
Sewer Department records
Sanitation Department records
Public Health Department records
Information on current and past owners; total area of
parcel; site history; current and historical use of adjacent
land; utilities, sewage and water supply maps and
systems; historical maps; underground storage tank and
waste discharge permits; chemical and hazardous waste
inventories; maps of drainage features; building records;
plot plans; waste disposal location maps; information on
use, manufacture, storage, and discharge of hazardous
materials and wastes; investigation and incident reports.
State
Government
Waste Management Board
Regional Water Quality Board
Health Department
Information on active and inactive hazardous materials
treatment, storage, and disposal sites; hazardous waste
permits and registrations; notices of violation; regulatory
and enforcement action documents; and reports on
leaking storage tanks and contamination incidents.
Federal
Government
USEPA records
Contamination site listings including the Comprehensive
Environmental Response Compensation and Liability
Information System (CERCLIS) list; the National
Priority List of Superfund sites; and the RCRA TSD list;
site investigation and incident reports; UST, CERCLA,
and RCRA records.
US Geological Survey records
Topographic and geologic maps; geologic/hydrogeologic
reports; environmental contamination reports; aerial
photographs.
US Department of Commerce
Manufacturers census data with information on products
shipped and materials consumed.
Universities,
libraries,
historical
societies
Theses, archives, historical information
Information on site development, ianduse, waste
disposal, manufacturing activities, geology, hydrogeotogy,
etc.
Key
Personnel
Interviews
Information regarding all aspects of site history.
Miscella-
neous
Aerial photographs: have been taken by private
companies and public agencies every few years to several
per year throughout much of the U.S. dating back to circa
1940. Listings of available public and private aerial
photographs for given locations and periods are available
from the National Cartographic Information Center in
Reston, Virginia.
Information regarding site development, Ianduse, waste
disposal practices, manufacturing activities, loading dock
locations, pipeline and tank locations, settling or
retention ponds, ponded fluid, stained soils, distressed
vegetation, disturbed soils, etc.
Maps: topographic, geologic, and hydrogeologic maps are
available from the U.S. Geological Survey, State
Geological Surveys, and University geology departments.
Fire insurance maps dating back to the 1800s which depict
manufacturing facilities and potential fire hazards such as
tank locations are available for all regions of the U.S.
from the Sanbom Map Company in Pelham, NY. Historic
maps are available from local universities, historical
societies, and libraries.
Information regarding site development, Ianduse, waste
disposal locations, manufacturing activities, storage tank
locations, etc.
-------
7-5

Table 7-3. Industrial site was frequently associated with contamination.
COMMON SUSPECT AREAS AT POSSIBLE
DNAPL SITES
Floor drains
Sumps
Catch basins
Pits, ponds, lagoons, and other disposal areas
Septic tanks
Leach fields
French drains
Sewer systems
Process tanks
Wastewater tanks
Underground tank areas
Aboveground tank areas
Chemical storage areas
Chemical transfer areas
Pipelines
Waste storage areas
Loading dock areas
Work areas
Discolored soils
Discolored water
Stressed vegetation
Disturbed earth
Low-lying disturbed areas
-------
7-6

Table 7-4. Determinant, inferential, and suggestive indications of DNAPL presence based on examination of
subsurface samples and data (based on Newell and Ross, 1992; Cherry and Feenstra, 1991; and
Cohen et al., 1992).
DETERMINING DNAPL PRESENCE
BY VISUAL EXAMINATION OF
SUBSURFACE SAMPLES
INFERRING DNAPL PRESENCE
KY INTERPRETING CHEMICAL
ANALYSES
SUSPECTING DNAPL PRESENCE
BASED ON ANOMALOUS FIELD
CONDITIONS
Methods to delect DNAPL in wells:

• NAPIVwater interface probe detection
of immiscible phase at base of fluid
column
• Pumping from bottom of fluid column
and inspecting retrieved sample
• Retrieving a transparent, bottom-
loading bailer from the bottom of a
well and inspecting the fluid sample
• Inspecting fluid retrieved from the
bottom of a well using a mechanical
discrete-depth sampler
• Inspecting fluid retained on a
weighted cotton string that was
lowered down a well
Methods to enhance inspection of fluid
samples for DNAPL presence:

• Centrifuge sample and look for phase
separation
• Add hydrophobic dye (such as Sudan
IV or Red Oil) to sample, shake, and
look for coloration of DNAPL
fraction
• Examine UV fluorescence of sample
(many DNAPLs will fluoresce)
• Assess density of NAPL relative to
water (sinkers or floaters) by shaking
solution or by using a syringe needle
to inject NAPL globules into the
water column

Methods to detect DNAPL hi soil and
rock samples

• Examine UV fluorescence of sample
(many DNAPLs will fluoresce)
• Add hydrophobic dye and water to
soil sample in potybag or jar, shake,
and examine for coloration of the
NAPL fraction
• Conduct a soil-water shake test
without hydrophobic dye (can be
effective for NAPLs that are neither
colorless nor the color of the soil)
• Centrifuge sample with water and
look for phase separation
• Perform a paint filter test, in which
soil is placed in a filter funnel, water
is added, and the filter is examined for
separate phases
Chemical analysis resolts from
which DNAPL presence can be
inferred (with more or less certainly
depending on the strength of the
overall data):

• Concentrations of DNAPL
chemicals in groundwater are
greater than 1% of the pure phase
solubility or effective solubility
(refer to Worksheet 7-1)

• Concentrations of DNAPL
chemicals on soils are greater than
10,000 mg/kg (equal to 1% soil
Concentrations of DNAPL
chemicals in groundwater
calculated from water/soil
partitioning relationships and soil
samples are greater than pure
phase solubility or effective
solubility (refer to Worksheet 7-2)

Organic vapor concentrations
detected in soil gas exceeds 100-
1000 ppm
Field conditions that suggest DNAPL
presence:

• Concentrations of DNAPL
chemicals increase with depth in a
pattern that cannot be explained
by advective transport

• Concentrations of DNAPL
chemicals increase up the hydraulic
gradient from the contaminant
release area (apparently due to
contaminated soil gas migration
and/or, DNAPL movement along
capillary and/or permeability
interfaces that slope counter to the
hydraulic gradient)

• Erratic patterns of dissolved
concentrations of DNAPL
chemicals in groundwater which
are typical of DNAPL sites due to
heterogeneity of (1) the DNAPL
distribution, (2) the porous media,
(3) well construction details, and
(4) sampling protocols

• Erratic, localized, very high
contaminant concentrations in soil
gas, particularly located just above
the water table (where dense gas
derived from DNAPL in the
vadose zone will tend to
accumulate)

• Dissolved DNAPL chemical
concentrations in recovered
groundwater that decrease with
time during a pump-and-treat
operation, but then increase
significantly after the pumps are
turned off (although complexities
of contaminant desorption,
formation heterogeneity, and
temporal and spatial variations of
the contaminant source strength
can produce similar results)

• The presence of dissolved DNAPL
chemicals in groundwater that is
older than potential contaminant
releases (using tritium analysis for
age dating) suggests DNAPL
migration (Uhlman, 1992)

• Deterioration of wells and pumps
(can be caused by DNAPL; i.e.,
chlorinated solvents degrade PVC)
-------
7-7
Worksheet 7-1: Calculation of Effective Solubility (from Newell and Ross, 1992; after Shiu et al.,
1988; and Feenstra et al., 1991)
For a single-component DNAPL, the pure-phase solubility of the organic constituent can be used to
estimate the theoretical upper-level concentration of organics in aquifers or for performing
dissolution calculations. For DNAPLs comprised of a mixture of chemicals, however, the effective
solubility concept should be employed:

S", = Xft

where

S"j = the effective solubility (the theoretical upper-level dissolved-phase concentration of a
constituent in groundwater in equilibrium with a mixed DNAPL; in mg/1)

X| = the mole fraction of component i in the DNAPL mixture (obtained from a lab analysis
of a DNAPL sample or estimated from waste characterization data)

S, = the pure-phase solubility of compound i in mg/1 (usually obtained from literature
sources)

For example, if a laboratory analysis indicates that the mole fraction of trichloroethylene (TCE) in
DNAPL is 0.10, then the effective solubility would be 110 mg/1. This is derived by multiplying the
pure phase solubility of TCE by the TCE mole fraction:

1100 mg/1 * 0.10 = 110 mg/1.

Effective solubilities can be calculated for all components in a DNAPL mixture. Nearly insoluble
organics in the mixture (such as long-chained alkanes) will reduce the mole fraction and effective
solubility of more soluble organics, but will contribute little dissolved-phase organics to
groundwater.

Please note that this relationship is approximate and does not account for non-ideal behavior of
mixtures, such as co-solvency, etc.
-------
contaminant concentrations >1% of the aqueous
solubility limit are highly suggestive of NAPL presence.
Concentrations <1%, however, do not preclude the
presence of NAPL.

In soil, contaminant concentrations in the percent range
are generally indicative of NAPL presence. However,
NAPL may also be present at much lower soil
concentrations. Feenstra et al. (1991) detail an
equilibrium partitioning method for assessing the
presence of NAPL in soil samples based on determining
total chemical concentrations, soil moisture content,
porosity, organic carbon content, approximate
composition of the possible NAPL, sorption parameters,
and solubilities. This method is outlined in Chapter
9.10.2 and Worksheet 7-2.
7.2.3 Suspecting DNAPL Presence Based on Anomalous
Conditions

Subsurface DNAPL can lead to anomalous chemical
distributions at contamination sites. For example,
dissolved chemical concentrations in horizontally-flowing
groundwater may increase with depth beneath a waste site
due to the density-driven downward movement of
DNAPL. Anomalous field conditions suggestive of
DNAPL presence are noted in Table 7-4, and
characteristics of extensive field programs that can help
indicate the absence of DNAPL are listed in Table 7-5.
7.3 IMPLICATIONS FOR SITE ASSESSMENT

If DNAPL presence is determined or suspected, special
consideration must be given to (1) devising an effective
site investigation strategy, and (2) preventing inducement
of unwanted chemical migration during field activities.
Implications of DNAPL presence on site assessment
activities are highlighted in Table 7-6.
-------
7-9

^Worksheet 7-2: Method for Assessing Residual NAPL Based on Organic Chemical Concentrations
iin Soil Samples (from Newell and Ross, 1992; after Feenstra et al., 1991)
To estimate if NAPLs are present, a partitioning calculation based on chemical and physical analyses
of soil samples from the saturated zone (from cores, excavation, etc.) can be applied. This method
tests the assumption that all the organics in the subsurface are either dissolved in groundwater or
adsorbed to soil (assuming dissolved-phase sorption, not the presence of NAPL). By using the
concentration of organics on the soil and the partitioning calculation, a theoretical pore-water
concentration of organics in groundwater is determined. If the theoretical pore-water concentration
is greater than the estimated solubility of the organic constituent of interest, then NAPL may be
present at the site. A worksheet for performing this calculation is presented below, see Feenstra et
al. (1991) for the complete methodology.
Step 1: Calculate Se{, the effective solubility of organic constituent of interest. See Worksheet
7-1.

Step 2: Determine K^ the organic carbon-water partition coefficient from one of the following:

• Appendix A and associated references or

• Empirical relationships based on K^, the octanol-water partition coefficient, which also is
found in Appendix A. For example, K^ can be estimated from K^, using the following
expression developed for polyaromatic hydrocarbons:

Log K^ = 1.0 * Log K^ - 0.21

Step 3: Determine f^, the fraction of organic carbon on the soil, from a laboratory analysis of
clean soils from the site. Values for f,,,. typically range from 0.03 to 0.00017 mg/mg.
Convert values reported in percent to mg/mg.

Step 4: Determine or estimate pb, the dry bulk density of the soil, from a soils analysis. Typical
values range from 1.8 to 2.1 g/ml(kg/l). Determine or estimate 9w, the water-filled
porosity.

Step 5: Determine Kd, the partition (or distribution) coefficient between the pore water (ground
water) and the soil solids:
Step 6: Using Ct, the measured concentration of the organic compound in saturated soil in
mg/kg, calculate the theoretical pore water concentration assuming no DNAPL (i.e., Cw
in mg/1):
Cw =
(Kd * pb + 6w)

Step 7: Compare Cw and S° (from Step 1):

Cw > S' suggests possible presence of DNAPL
Cw < 8° suggests possible absence of DNAPL
-------
7-10

Table 7-5. Characteristics of extensive field programs that can help indicate the absence of
DNAPL (modified from Newell and Ross, 1992).
• Absence of conditions listed in Table 7-4 that are indicative or suggestive of DNAPL
presence

• Numerous monitor wells, with screens in topographic lows on the surface of fine-
grained, relatively impermeable units

• Multi-level fluid sampling capability

• Numerous organic chemical analyses of soil samples at different depths using GC or
GC/MS methods

• Well-defined site stratigraphy, using numerous soil borings, a cone penetrometer survey,
test pits, and/or geophysics

• Numerous subsurface explorations (test pits and/or borings) in the areas of contaminant
release

• Data from pilot tests or "early action" projects that indicate the site responds as
predicted by conventional solute transport relationships, rather than by responding as if
additional sources of dissolved contaminants are present in the aquifer
-------
7-11

Table 7-6. Implications of DNAPL presence on site assessment activities (see Figure 7-1) (modified from
Newell and Ross, 1992).
CATEGORY
IMPLICATIONS FOR SITE ASSESSMENT
I
CONFIRMED
OR HIGH
POTENTIAL
FOR DNAPL
AT SITE
The risk of spreading contaminants increases with the proximity to a potential
DNAPL zone. Special precautions should be taken to ensure that drilling does not
create pathways for continued vertical migration of free-phase DNAPLs. In DNAPL
zones, drilling should be suspended when a low-permeability unit or DNAPL is first
encountered. Wells should be installed with short screens (< 10 feet). If required,
deeper drilling through known DNAPL zones should be conducted only by using
double or triple-cased wells to prevent downward migration of DNAPL. As some
DNAPLs can penetrate fractures as narrow as 10 microns, special care must be taken
during all grouting, cementing, and well sealing activities conducted in DNAPL
zones.

In some hydrogeologic settings, such as fractured crystalline rock, it is impossible to
drill through DNAPL with existing technology without causing vertical migration of
DNAPL down the borehole, even when double or triple casing is employed.

The subsurface DNAPL distribution is difficult to delineate accurately at some sites.
DNAPL migrates preferentially through selected pathways (fractures, sand layers,
etc.) and is affected by small-scale stratigraphic changes. Therefore, the ultimate
path taken by DNAPL can be very difficult to characterize and predict.

In most cases, fine-grained aquitards (such as clay or silt units) should be assumed to
permit downward migration of DNAPL through fractures unless proven otherwise in
the field. At some sites, it can be exceptionally difficult to prove otherwise even
with intensive site investigation.

Drilling in areas known to be DNAPL-free should be performed before drilling in
DNAPL zones in order to form a reliable conceptual model of site hydrogeology,
stratigraphy, and potential DNAPL pathways. In areas where it is difficult to form a
reliable conceptual model, an "outside-in" strategy may be appropriate drilling in
DNAPL zones is avoided or minimized in favor of delineating the outside dissolved-
phase plume. Many fractured rock settings may require this approach to avoid
opening further pathways for DNAPL migration during site assessment.
II
MODERATE
POTENTIAL
FOR DNAPL
AT SITE
Due to the potential risk for exacerbating groundwater contamination problems
during drilling through DNAPL zones, the precautions described for Categoty I
should be considered during site assessment. Further work should focus on
determining if the site is a DNAPL site.
Ill
LOW
POTENTIAL
FOR DNAPL
AT SITE
DNAPL is not likely to be a problem during site characterization, and special
DNAPL precautions are probably not needed. Floating, less-dense-than-water
nonaqueous phase liquids (LNAPLs), sorption, and other factors can complicate site
assessment and remediation activities, however.
-------
-------
8 NONINVASIVE CHARACTERIZATION
METHODS

Noninvasive methods can often be used during the early
phases of field work to optimize the cost-effectiveness of
a DNAPL site characterization program. Specifically,
surface geophysical surveys, soil gas analysis, and
photointerpretation can facilitate characterization of
contaminant source areas, geologic controls on
contaminant movement (i.e., stratigraphy and utilities),
and the extent of subsurface contamination. Conceptual
model refinements derived using these methods reduce
the risk of spreading contaminants during subsequent
invasive field work.

Measurements made at or just below ground surface using
geophysical and soil gas surveying cost much less than
invasive methods of subsurface data acquisition such as
drilling, monitor well installation, sampling, and chemical
analyses. Although less costly, subsurface data squired
indirectly using noninvasive methods are also less
definitive than data squired directly. As a result,
invasive techniques (i.e., borings and monitor wells) are
usually needed to confirm interpretations derived using
noninvasive methods.

The applicability of noninvasive methods must be
evaluated on a site-specific basis. Advantages and
limitations of surface geophysical methods, soil gas
analysis, and aerial photograph interpretation are
discussed in Chapters 8.1, 8.2, and 8.3, respectively.
8.1 SURFACE GEOPHYSICS

Several surface geophysical survey techniques have been
used with varied success to enhance contamination site
characterization since the late 1960s. Surface methods
utilized most commonly with proven effectiveness for
specific applications include ground-penetrating radar,
electromagnetic (EM) conductivity, electrical resistivity,
seismic, magnetic, and metal detection. At contamination
sites, geophysical surveys are usually conducted to: (1)
assess stratigraphic and hydrogeologic conditions; (2)
detect and map electrically conductive contaminants; (3)
locate and delineate buried wastes and utilities; (4)
optimize the location and spacings of teat pits, borings,
and wells; and (5) facilitate interpolation of subsurface
conditions among boring locations.
8.1.1 Surface Geophysical Methods and Costs

The application of surface geophysical methods to
groundwater and contamination site investigations is the
subject of several reviews (Zohdy et al., 1974; Benson et
al, 1982; Rehm et al., 1985; GRI, 1987; USEPA, 1987;
Benson, 1988, 1991) and many published case studies (see
references in Table 8-1). An expert system for selecting
geophysical methods based on site-specific conditions and
investigative objectives is provided by Olhoeft (1992).
Detailed procedures for instrument operation are
provided in product manuals. Capabilities, operating
principles, and limitations of the most common surface
geophysical survey methods are described in Table 8-1
and include the following.

• Ground-penetrating radar (GPR) is used to measure
changes in dielectric properties of subsurface materials
by transmitting high-frequency electromagnetic waves
into the subsurface and continuously monitoring their
reflection from interfaces between materials with
different dielectric properties. GPR is primarily used
to help delineate site stratigraphy, buried wastes, and
utilities.

• Electromagnetic conductivity methods measure the bulk
electrical conductance of the subsurface by recording
changes in the magnitude of electromagnetic currents
that are induced in the ground. The measured
currents are proportional to the bulk electrical
conductivity of the subsurface and can be interpreted
to infer lateral stratigraphic variations, and the
presence of conductive contaminants, buried wastes,
and utilities.

• Electrical resistivity methods measure the bulk electrical
resistance (the reciprocal of conductance) of the
subsurface directly by transmission of current between
electrodes implanted at ground surface. Electrical
resistivity can be used to aid determination of site
stratigraphy, water-table depth, conductive
contaminant plumes, and buried wastes.

• Seismic refraction and reflection methods use
geophones implanted in the ground surface and
seismographs to measure and record the subsurface
transmission of sound waves generated using a
hammer blow or explosive device at a point source.
Seismic waves are reflected and refracted as they pass
through media with different elastic properties
enabling interpretation of geologic layering and waste
zone geometry based on analysis of wave arrival times.
-------
Table 8-1. Summary of various surface geophysical survey methods (modified from Benson, 1991; Gretsky et al., 1990; O'Brien and Gere, 1988).
METHOD AND
TARGETS
OPERATING
PRINCIPLES/DESCRIPTION
OPERATING PARAMETERS, ADVANTAGES, DISADVANTAGES
REFERENCES
GROUND-
PENETRATING
RADAR

• stratigraphy (layering
and lateral
variations)
• water table in coarse
media
• metallic and
nonmetallic buried
drums, tanks, and
pipes
• bedrock surface
• fracture zones
• very limited capacity
to delineate NAPL
presence
High-frequency electromagnetic (<100 to
1000 MHz radio) waves transmitted from a
radar antenna at the ground surface are
reflected from interfaces between
subsurface materials with contrasting
dielectric properties back to a receiving
antenna. The reflections are amplified,
processed, and displayed in real-time on a
recorder and/or color video monitor. Such
contrasts are due to changing clay content,
fluid content, dielectric constants, porosity,
fracture density, bedding, cementation, the
presence of manmade objects, the bedrock
surface, etc. The depth of penetration
(and measurement of reflected waves) is
proportional to the receiving antenna
response time.
Provides a continuous visual profile of shallow subsurface objects, structure, and lithology in real
time.
The graphic output can often be interpreted in the field; thereby facilitating direction of the
survey.
Traverse rates range from 600 to 6000 ft/hr for detailed studies and up to 10 mph for low-
resolution reconnaissance work.
Depth of penetration is site-specific; typically between 6 and 30 ft. Radar penetration increases in
coarse, dry, sandy, or massive rock; and decreases with increasing clay content, fluid content, and
fluid conductivity.
Approximate and relative depths are calculated using simple interpretative methods and
assumptions. Depth calibrations, however, require careful onsite work and are often nonlinear.
Depending on the frequency used, GPR provides very high resolution from an inch to a few feet.
The survey can be optimized to local conditions by changing antennas (frequency). High
frequency provides the best resolution; lower frequency provides deeper penetration.
GPR can be used in fresh water and through ice to obtain profiles of sediment depth.
Access is limited due to bulkiness of GPR equipment.
Limited use during wet weather.
A variety of processing options can be used to enhance data interpretation and presentation.
Quantitative interpretation is difficult. The data can be affected by various sources of system
Benson (1991);
Benson and
Glaccum (1979);
Benson et al.
(1982); Benson
and Yuhr
(1987); Koerner
et al. (1981);
Olhoeft (1984;
1986); Redman
et al. (1991);
Wright et al.
(1984)
ELECTRO-
MAGNETIC
CONDUCTIVITY

• detection and
mapping of
conductive
contaminant plumes
• stratigraphy
(layering and lateral
variations)
• waste disposal areas
containing metallic
and nonmetallic
buried drums
• USTs and buried
pipes
• fracture zones
• very limited capacity
to delineate NAPL
presence
Electromagnetic methods measure changes
in the bulk subsurface electrical
conductivity (also referred to as terrain
conductivity). A transmitter induces
circular eddy current loops in the
subsurface. The magnitude of the induced
current is proportional to and altered by
the terrain conductivity in the vicinity of
the loop. Each current loop generates a
magnetic field which is proportional to the
current magnitude. A portion of the
generated magnetic field is measured by
the EM receiver and results in an output
voltage that is proportional to terrain
conductivity. Terrain conductivity
generally increases with increasing (1)
subsurface fluid conductivity, (2) clay
content, (3) fluid content, and, (4) porosity
(including fracture porosity).
Interpretation is typically qualitative based
on consideration of spatial variability,
anomalies, and the aforementionpd farfnrs
Profiling or vertical sounding data can be acquired from various depths between 2 and 200 ft by
combining measurements from various common EM systems and by varying the coil orientation
and/or spacing between the EM transmitter and receiver. Compared to the resistivity method,
however, EM has reduced vertical sounding resolution due to the limited number of transmitter-
receiver spacings available.
The influence of subsurface materials on the measured EM conductivity decreases with depth; a
confounding factor that must be considered when interpreting EM data.
Continuous EM profiling can be obtained from 2.5 to 50 ft providing increased survey speed,
density, and resolution. Data can be recorded on an analog strip chart or digital data logger.
Spatial variability and anomalies can be caused by several factors, thereby confounding unique
interpretation of conductivity measurements.
Various objects emit noise and interfere with EM surveys including natural atmospheric noise,
power lines, buried metal objects, radio transmitters, buried pipes and cables, fences, vehicles, and
buildings.
Limited use in wet weather.
Frequency-domain EM systems measure changes in continuously transmitted currents. Time-
domain EM systems measure changes in cyclically induced currents. Time-domain systems offer
enhanced vertical sounding capability to depths of 150 to >1000 ft.
Frequency-domain EM systems measure in-phase and out-of-phase components of EM
conductivity. The in-phase component responds to magnetic susceptibility and can be used to
detect metals. The out-of-phase component measures electrical conductivity.
Benson et al.
(1982); Davis
(1991); Grady
and Haeni
(1984);
Greenhouse and
Slaine (1983);
Greenhouse and
Monier-Williams
(1985); Griffith
and King (1969);
Ladwig (1983);
McNeill (1980);
Slaine and
Greenhouse
(1982);
Rumbaugh et al.
(1987); Stewart
(1982); Telford
et al. (1982);
Zohdy et al.
-------
Table 8-1. Summary of various surface geophysical survey methods (modified from Benson, 1991; Gretsky et ah, 1990; O'Brien and Gere, 1988).
METHOD AND
TARGETS
OPERATING
PRINCIPLES/DESCRIPTION
OPERATING PARAMETERS, ADVANTAGES, DISADVANTAGES
REFERENCES
ELECTRICAL
RESISTIVITY

• detection and
mapping of
conductive
contaminant plumes
• stratigraphy
(layering and lateral
variations)
• waste disposal areas
containing metallic
and nonmelallic
buried drums
• fracture zones
• very limited capacity
to delineate NAPL
presence
Electrical resistivity methods measure the
bulk electrical conductivity of the
subsurface in a manner different from the
EM Conductivity method. Electrical
current is transmitted into the ground from
a pair of surface electrodes and the voltage
drop due to bulk subsurface resistivity is
measured at the surface between a second
pair of electrodes. The depth of
measurement increases with, but is
generally less than, the electrode spacing.
Of the various electrode spacing
geometries used, the Wenner array, with
four electrodes equally spaced along a line
and the two transmitting electrodes at each
end, is the simplest. As the reciprocal of
conductivity, electrical resistivity generally
decreases with increasing (1) subsurface
fluid conductivity, (2) clay content, (3)
fluid content, and, (4) porosity (including
fracture porosity).
Survey speed is slower than with EM methods because of need with resistivity to drive electrodes
into the ground. Station measurements are made; continuous measurements are not possible.
Profiling or vertical sounding data can be acquired from various depths by using different
electrode spacings. Because the current electrodes can be spaced at any distance (assuming site
access), resistivity is capable of providing better vertical resolution of subsurface conductivity than
EM methods (which rely on fixed intercoil lengths).
The vertical sounding technique, however, requires that subsurface conditions be relatively
consistent laterally.
Results are amenable to qualitative interpretation based on observed spatial variability and
anomalies. However, quantitative interpretation of stratigraphic layering can be made based on
vertical soundings.
Spatial variability and anomalies can be caused by several factors, thereby confounding unique
interpretation of resistivity measurements.
The influence of subsurface materials on the measured resistivity decreases with depth; a
confounding factor that must be considered when interpreting EM data.
Resistivity is affected less than EM methods by noise associated with power lines, buried metal
objects such as pipes and cables, fences, vehicles, and buildings. Thus, resistivity can be used to
provide reliable measurements in some locations near metal objects where EM is of little use.
Limited use in wet weather.
Benson et al.
(1982);
Cartwright and
McComas
(1968); Griffith
and King (1969);
Mooney
(1975,1980);
Orellana and
Mooney (1966);
Rodgers and
Kean (1980);
Stollar and Roux
(1975); Sweeney
(1984); Telford
et al. (1982);
USEPA (1978);
Urish (1983);
Warner (1969);
Zohdy et al.
(1974)
SEISMIC
REFRACTION AND
REFLECTION

• bedrock surface
• depth to water table
• locate fractures,
faults, and buried
bedrock channels
• characterize rock
type and degree of
weathering
• stratigraphy
(layering and lateral
variations)
• depth of landfills,
trenches, and
disturbed zones
The subsurface transmission of seismic
waves emitted from a point source are
measured using geophones implanted in
the ground along a straight line and
recorded digitally by a seismograph. The
seismic source may be the impact of a
sledge or mechanical hammer on a steel
plate, or an explosive device.
Compressional, shear, and surface seismic
waves radiate from the energy source. The
compressional waves are refracted and
reflected as they pass through media with
different seismic velocities (densities).
Refracted and/or reflected compressional
wave travel times associated with different
source-to-geophone wave paths are
interpreted using analytical models to
determine the depth to a one or more
geologic units.
Seismic refraction is generally used for shallow investigations (<200 ft depth). A refraction survey
may require a maximum source-to-geophone distance of up to five times the depth of investigation.

Given sufficient velocity contrast between adjacent horizontal layers, as many as three or four
layers can be delineated using seismic refraction. A lower velocity layer under a higher velocity
layer and thin layers, however, cannot be resolved using the refraction method.
Geophone spacing can be varied from a few to hundreds of feet depending on the desired
measurement depth and resolution. For shallow investigations, 12 or 24 geophones may be
positioned at equal spacings as close as 5 to 10 ft and seismic waves may be initiated separately at
each end of the line.
Seismic reflection can be used for much deeper investigations (to >1000 ft). It is similar to GPR
in that the depth of measurement is as a function of wave reflection travel time.
Seismic data is collected as station measurements and surveying is slow compared to continuous
measurement methods.
Data interpretation is confounded by heterogeneous subsurface conditions.
Use may be limited during wet and very cold weather.
Seismic methods are subject to interference from vibration noise associated with various natural
and cultural sources (i.e., walking, machinery, and vehicles).
Benson et al.
(1982); Griffith
and King (1969);
Haeni (1986);
Hunter et al.
(1982);
Lankston and
Lankston
(1983); Mooney
(1980); Palmer
(1980); Redpath
(1973); Steeples
(1984); Sverdrup
(1986); Telford
et al. (1982);
Zohdy et al.
(1974)
-------
Table 8-1.
Summary of various surface geophysical survey methods (modified from Benson, 1991; Gretsky et al., 1990; O'Brien and Gere, 1988).
METHOD AND
TARGETS
OPERATING
PRINCIPLES/DESCRIPTION
OPERATING PARAMETERS, ADVANTAGES, DISADVANTAGES
REFERENCES
MAGNETICS

• buried ferrous metal
objects (drums,
pipelines, USTs,
etc.)
• waste zones
containing ferrous
metal
Magnetometers are used to measure the
strength of the earth's magnetic field and
respond to ferrous metals perturb the
earth's natural magnetic field. Two
common types of magnetometers are
available: the total field magnetometer and
the gradiometer. Typically, a hand-held
magnetometer is used to measure total
magnetic field intensity along a grid,
allowing detection of anomalies associated
with shallow buried ferrous metal objects.
A nearby base station can be used to
during the survey to record background
diumal variations in the earth's magnetic
field.
• Magnetometers respond only to ferrous metals (iron or steel).
• Magnetometers provide greater depth range than metal detectors: single drums and drum masses
can be detected at depths to 20 and 60 ft, respectively, using a total field magnetometer.
• The total field magnetometer response is proportional to the ferrous target mass and inversely
proportional to cube of the distance to the target. Gradient measurements using a gradiometer
are inversely proportional to the fourth power of the distance to the target and thus minimize
interferences but are less sensitive than total field measurements.
• Magnetometers can be used to provide continuous or station measurements, and can be mounted
on vehicles for coverage of large sites.
• Magnetometer response is subject to interference noise from many sources including steel fences,
buildings, vehicles, iron debris, utilities, ferrous soil minerals, vehicles, etc.
• Data interpretation may be confounded by heterogeneous subsurface conditions and/or the
presence of iron-rich geologic media (such as greensands and red hematitic soils).
• Magnetometry may also be used to study regional geologic conditions, and occasionally to map the
bedrock surface.
Breiner (1973);
Gilkeson et al.
(1986); Telford
et al. (1982);
Zohdy et al.
(1974)
METAL DETECTORS

• shallow buried metal
objects (drums,
pipelines, USTs,
etc.)
• shallow waste zones
containing metal
Metal detectors sense ferrous and
nonferrous metals. The area of detection
is typically 1 to 3 ft (equal to the detector
coil size or spacing). The depth of
detection is commonly limited to less than
10 ft because the response is proportional
to the target cross-section and inversely
proportional to the sixth power of the
distance to the target.
Metal detectors are routinely used to locate buried cables and pipes.
Quart-size metal objects and drum masses can be detected to depths of 3 and 10 - 25 ft,
respectively.
Buried and above-ground metal objects (cars, fences, buildings, etc.) can interfere with
measurements.
-------
8-5
• Magnetometer surveys are used at contamination sites
to measure the perturbation to the earth's magnetic
field caused by buried ferrous metal objects such as
steel drums, ferrous metal waste in landfills, and iron
pipes.

• Metal detectors are used to sense ferrous and
nonferrous metals at shallow depths, thereby allowing
detection of shallow metal pipelines, drums, and waste
zones containing metal.

The success of a noninvasive geophysical survey depends
on several factors. Reasonable survey objectives should
be developed based on consideration of the site
conceptual model, characterization requirements, and
available methods. Generally, discrete (station) or
continuous survey measurements are made along transect
or grid lines. Station and transect line spacings and
orientation should be commensurate with the expected
size and geometry of the subsurface targets (i.e., buried
channels, contamination plumes, drums, etc.). As shown
in Figure 8-1, the enhanced resolution provided by
continuous measurements compared to station
measurements may be critical to accurate data
interpretation. For methods lacking continuous
measurement capability, resolution generally increases
with decreased station spacing. Success requires that the
survey method be capable of measuring the subsurface
properties (and anomalies) of interest, and the existence
of sufficient contrast in the measured subsurface
properties. Finally, the survey should be conducted by an
experienced field crew using functional instrumentation
and interpreted by personnel knowledgeable about both
geophysical survey data analysis and site conditions.

Surface geophysical equipment is available for rent or
purchase from several distributors in North America that
advertise in technical journals such as Ground Water
Monitoring Review. It will generally be cost-effective,
however, to contract an experienced firm (or individual)
to design, conduct, and interpret surface geophysical
surveys at contamination sites. Estimated equipment
rental, equipment purchase, and survey contract prices in
1992 dollars based on quotes from distributors and
geophysical surveyors are given in Table 8-2. These
prices do not include mobilization or shipping fees.
8.1.2 Surface Geophysical Survey Applications

Geophysical surveys can provide relatively quick and
inexpensive information on subsurface conditions over a
wide area. Inferences derived therefrom during the early
phase of a DNAPL site investigation can be used to
optimize the mat-effectiveness of subsequent invasive
field work. Drilling locations can be selected to test the
refined site conceptual model and examine geophysical
anomalies. Geophysical data can facilitate interpolation
of limited well or boring data and reduce the number of
wells/borings needed to adequately characterize a site.
Similarly, sequential measurements can be made along
transects between wells to augment a detection
monitoring program. The utility of alternative methods
for various site characterization applications is rated in
Table 8-3 based upon experience at a large number of
contamination sites (Benson, 1988).
8.1.2.1 Assessing Geologic Conditions

A more detailed summary of the applicability of different
surface geophysical methods for assessing stratigraphic
and hydrogeologic renditions is given in Table 8-4. For
survey speed and resolution, ground-penetrating radar and
EM conductivity are probably the two best techniques for
mapping lateral variations in soil and rock (Benson,
1991). Radar performance, however, is highly site-specific
and typically limited to depths less than 30 ft. High-
resolution seismic methods can provide detailed bedrock
surface profiles and are sometimes used to provide
vertical information at depths below effective radar
penetration. Examples of stratigraphic interpretations
derived from surface geophysical data are given in Figure
8-2.
8.1.2.2 Detecting Buried Wastes and Utilities

The feasibility of using different surface geophysical
survey methods to locate buried wastes and utilities is
summarized in Table 8-5. Ground-penetrating radar and
EM-conductivity are recommended for detecting non-
metallic buried waste; and EM-conductivity,
magnetometers, and metal detectors are well-suited for
detecting metallic waste. Metal detector use is typically
limited to a depth of less than 10 ft, and magnetometers
respond only to ferrous metals. The in-phase component
of EM-conductivity responds to magnetic susceptibility
and should be used to detect ferrous metals. Seismic,
electrical resistivity, and magnetic methods can be used to
-------
8-6
DATA OBTAINED FROM
STATION
MEASUREMENTS
DATA OBTAINED FROM
CONTINUOUS
MEASUREMENTS
Figure 8-1. Comparison of station and continuous surface EM conductivity measurements made along
the same transect using an EM-34 with a 10 m coil spacing (from Benson, 1991). The
electrical conductivity peaks are due to fractures in gypsum bedrock.
-------
8-7
Table 8-2. Surface geophysics equipment rental, equipment purchase, and contract surveying estimated prices in
1992 dollars not including mobilization or shipping fees.
Method
Rental Price
&Ue Price
Contractor Price
Ground
Penetrating
Radar
GSSI SIR-3 with one antenna: SlOO/d,
$700Mk, $3000/mo
GSSI SIR-10 with one antenna: $195/d,
$1365Avk, $5850/mo
GSSI SIR-3 with one antenna:
$20,000-25,000
GSSI SIR-10 with one antenna:
$40,000-$47,000
Daily charge for equipment and
field crew is $200043500. This
price includes subsequent data
analysis and reporting. Typical
daily coverage is 5000 ft of
continuous measurement.
EM
Conductivity
Geonics EM31: $39-65/d, $273-450/wk,
$1170-$1360/mo
Geonks EM34-3: $55/d, $385-$740/wk,
$1650-$2240/mo
Geonics EM34-3XL: $66/d, $462-$825/wk,
$1980-$2480/mo

Digital dataloggers for Geonics meters:
$150-$260/wk

Geonics Protem EM47: $125/d, $875/wk,
$3750/mo
Frequency Domain EM Systems
Geonics EM31 (20 ft penetration):
$12,985
Geonics EM34-3 (variable depth to
200ft): $18,900
Geonks EM34-3XL (variable depth to
200ft): $21,285
Geonics EM38 (shallow penetration to
5ft): $6250
Datalogger $4000-54800

Time-Domain EM Systems
Protem 47/P (Profiling for depths to
330ft): $39,240
Protem 47/S (Soundings 15 to 500 ft):
$41300
Daily charge for equipment and
field crew using Geonics EM
Conductivity instruments is
S2000-S3000 for 8-hrs Geld work.
This price includes subsequent
data analysis and reporting.
Typical daily profiling survey
coverages are: 1000 station
measurements or several
thousand feet of continuous
measurements using the EM31;
and 100 to 250 station
measurements using the EM34.
Typical coverage for Time-
Domain soundings is 6 to 12
soundings per day.
Electrical
Resistivity
ABEM Terrameter SAS-300B/C $25-$45/d,
$175-$315/wk, $750-$1350/mo
ABEM SAS 2000 Booster $19-$25/d, $133-
$175/wk, $570-$700/mo
Soiltest Stratameter R-50 (200-500 ft
operating depth): $5000
Bison "BOSS" offset sounding system
Model 2365: $5995
Bison signal averaging earth resistivity
receiver/transmitter $9995
ABEM Terrameter SAS-300C with
cable and four electrodes: $12,790
ABEM SAS 2000 Booster $7295
Daily charge for equipment and
field crew is $2000-$3000 for 8-
hrs field work. This price
includes subsequent data analysis
and reporting. Typical daily
soundings survey coverage is 6 to
12 soundings per day with 10 to
15 electrode array spacings per
sounding.
Seismic
GeoMetrics ES1225F (12-channel with
filters) with phones: $53/d, $371/wk,
$1590/mo
GeoMetrics ES2401&8 Hz phones (24-
channel): $128/d, $896/wk, $3840/mo
Bison 9000 series DIFP Seismograph: 48-
channel, $200/d; 24-channel, $175/d; 12-
channel, $150/d
Bison 7000 series DIFP seismograph: 24-
channel, $129/d; 12-channel, $80/d
Bison 12-channel 5000 series DIFP
seismograph: $70/d
ABEM Miniloc 36 channels with geophones
and cable: $70/d, $490/wk, $2100/mo
ABEM Terraloc Mark 6 24-channel
seismograph: $125/d, $87S/wk, $3750/mo
Bison digital instantaneous floating
point (DIFP) signal slacking
seismograph with standard accessories
(various models)
12-channel: $12^00-42,500
24-channel: $25,200-$S5,600
48-channel: $58,700-$85,500
%-channel: $143300
120-channel: $173,200.
ABEM Miniloc refraction seismograph
with geophones and cable: $18,000
ABEM Terraloc Mark 6 seismograph
24 channels: $41,000
48 channels: $48,000
Daily charge for equipment and
field crew is $3200-$5000 for 8-
hrs field work. This price
includes subsequent data analysis
and reporting. Typical daily
seismic (refraction or reflection)
survey coverage includes 4 to 6
spreads per day using 12 or 24
geophones (or approximately
1500 ft of survey line).
Magnetom-
melers
GeoMetrics G816 portable magnetometer
$10/d, $70/wk, $300/mo
GeoMetrics G856AX extended memoray
magnetometer $14/d, $98/wk, $420/mo
GEM GSM-19G: $40-$50/d, $280-350Mc,
$1200-$1500/mo
GEM GSM-19 field unit/base station:
$10,000
GSM-19 gradiometen $5,000
GSM-19 VLF: $6,000
GSM-19 "Walking Mag" option: $3500
GEM GSM-8 Magnetometer $5000
Daily charge for equipment and
field crew is $2000-$3000 for 8-
hrs Geld work. This price
includes subsequent data analysis
and reporting, and (for at least
one contractor) includes the
simultaneous operation of two
magnetometers. Typical daily
survey coverage includes approx.
750-1000 station measurements
per instrument per day.
-------
Table 8-3. Applications of selected surface geophysical survey methods (modified from Benson, 1988).
APPLICATION
Evolution of natural geologic and hydrologic conditions
Depth and thickness of soil and rock layers and vertical
variations
Mapping lateral variations in soil and rock (fractures, karst
features, etc.)
Depth of water table
Evaluation of subsurface contamination and post-closure
monitoring
Inorganics (high TDS and electrically conductive)
Early warning contaminant detection
Detailed lateral mapping
Vertical extent
Changes of plume with time (flow direction and rate)
Post cleanup/closure monitoring
Organics (typically nonconductive)
Early warning contaminant detection
Detailed lateral mapping
Vertical extent
Changes of plume with time (flow direction and rate)
Post clean-up/closure monitoring
Location of buried wastes and trench boundaries
Bulk waste trenches without metal
Bulk waste trenches with metal
Depth of trenches and landfill
Detection of 55-gallon steel drums
Estimates of depth and quantity of 55-gallon steel drums
Location of utilities
Buried pipes and tanks
Potential pathways of contaminant migration via conduits and
permeable trench backfill
Abandoned wells with metal casing
GftL

la
la
3

3
3
3
3
3

3
2a
2a
3
3

1
1
2
2a
2a

1
1
3
KM
COND.

2
1
2

1
1
2
1
1

3
2
3
3
3

1
1
3
2
3

Ic
2
NA
ELEC
RE&

1
2
1

2
2
1
2
2

3
3
2
3
3

2
2
2
NA
3

NA
NA
NA
SEISMIC

1
2 (refr.)
1 (refl.)

NA
NA
NA
NA
NA

3
3
2
NA
NA

NA
NA
NA
METAL
VET.

NA
NA
NA

NA
NA
NA
NA
NA

NA
la
NA
la
2

Ic
2
2
MAG.
NETICS

NA
NA
NA

NA
NA
NA
NA
NA

NA
Ib
NA
1
1

Ib
2
Ib
Notes: 1 = Primary choice under most field conditions a = shallow
2 = Secondary choice under most field conditions b = Assumes ferrous metals to be present
3 = Limited field application under most field conditions c = Assumes metals to be present
NA = Not applicable
This table is intended as a general guide. The application ratings given are based upon actual experience at a large number of sites. The
rating system is based upon the ability of each method to produce results under general field conditions when compared to other methods
applied to the same task. One must consider site-specific conditions before recommending an optimum approach. Site-specific
conditions may dictate the choice of a method rated 2 or 3 in preference to a method rated 1.
-------
8-9
Table 8-4. Surface geophysical methods for evaluating natural hydrogeologic conditions (modified from
Benson, 1991).
Metbod
Ground-
penetrating
radar
EM
Conductivity
(Frequency
Domain)
EM
Conductivity
(Time Domain)
Electrical
Resistivity
Seismic
Refraction
Seismic
Reflection
Magnetics
General Application
Highest resolution of any
method for profiling and
mapping
Very rapid profiling and
mapping
Soundings
Soundings or profiling and
mapping
Profiling and mapping soil
and rock
Profiling and mapping soil
and rock
Profiling and mapping soil
and rock
Continuous
Measurements?
Yes
Yes (to 50 ft)
No
No
No
No
Yes
DepUi of Penetration
Typically less than 30 ft; to
100 ft under ideal conditions
To 200 ft
To >1000 ft
No limit, but commonly used
to a depth of a <300 ft
No limit, but commonly used
to < 300 ft
To >1000 ft
No limit, but commonly used
to <300 ft
Major Limitations
Penetration limited by
increasing clay content, fluid
content, and fluid conductivity
Affected by cultural features
including metal fences, pipes,
buildings, and vehicles
Cannot be used to provide
measurements shallower than
about 150 ft
Requires good ground contact
and long electrode arrays;
integrates a large volume of
subsurface; affected by cultural
features including metal fences,
pipes, buildings, and vehicles
Requires considerable energy
for deeper surveys; sensitive to
ground vibrations
Very slow surveying; requires
extensive data reduction;
sensitive to ground vibrations
Only applicable in certain rock
environments; limited by
cultural ferrous metal features
Note: Actual results depend on site-specific conditions. In some applications, an alternate method may provide better results.
-------
FINE
QUARTZ
SANO
CLAY
LOAM
APPROXIMATEtY 400 FEET •
40
_g 50
-------
Ml
Table 8-5. Surface geophysical methods for locating and mapping buried wastes and utilities (modified from
Benson, 1991).
Method
Ground-
penetrating radar
EM Conductivity
Electrical
Resistivity
Seismic
Refraction
Magnetometry
Metal Detection
Bulk Wastes Without Metals
Very effective in coarse, dry,
sandy soil or massive rock;
sometimes effective to obtain
shallow boundaries in soils
with poor GPR penetration
Excellent to depths less than
20 it
Good; soundings may provide
depth
Fair; may provide depth
Not applicable
Net applicable
Bulk Wastes With Metals
Very effective in media
with good GPR
penetration; sometimes
effective to obtain shallow
boundaries in soils with
poor GPR penetration
Excellent to depths less
than 20 ft
Good; soundings may
provide depth
Fair; may provide depth
Very good for ferrous
metal only; deeper
sensing than metal
detectors
Very good for shallow
ferrous and non-ferrous
metals
S&Gailon Drums
Good if soil conditions
permit sufficient GPR
penetration; may provide
drum depth
Very good; may identify
single drum to 6-8 ft
Not applicable
Not applicable
Very good for ferrous
metal only; deeper
sensing than metal
detectors
Very good for shallow
ferrous and non-ferrous
metals
Pipes and Tanks
Very good for metal
and non-metal tanks
and pipes if soil
conditions permit
sufficient GPR
penetration; may
provide object depth
Very good for metal
tanks
Not applicable
Not applicable
Very good for ferrous
metal only, deeper
sensing than metal
detectors
Very good for shallow
ferrous and non-ferrous
metals
Note: Actual results depend on site-specific conditions. In some applications, an alternate method may provide better results.
-------
8-12
estimate the depth to the base of a landfill. Examples of
geophysical survey measurements over buried wastes and
pipes are shown in Figure 8-3.
8.1.2.3 Detecting Conductive Contaminant Plumes

The application of surface geophysical survey methods to
map conductive contaminant plumes is summarized in
Table 8-6. A two-fold strategy is generally employed to
map conductive contaminant plumes: (1) potential
preferential pathways for contaminant transport such as
buried channels, fracture zones, or sand lenses, are
delineated using applicable methods (Table 8-4); and, (2)
conductive contaminants (i.e., dissolved ions in
groundwater) are mapping using electrical resistivity or
EM conductivity. The application of electrical methods
to map contaminated groundwater was initiated in the
late 1960s (e.g., Cartwright and McComas, 1968; Warner,
1969) and popularized during the 1980s (see references in
Table 8-1). Examples of contaminant plume detection
using electrical resistivity and EM conductivity are shown
in Figure 8-4.
8.1.2.4 Detecting DNAPL Contamination

Subsurface DNAPL is generally a poor target for
conventional geophysical methods. Although ground-
penetrating radar, EM conductivity, and complex
resistivity have been used to infer NAPL presence at a
very limited number of sites (e.g., Olhoeft, 1986; Davis,
1991), direct detection and mapping of non-conductive
subsurface DNAPL using surface geophysical techniques
is an unclear, and apparently limited, emerging
technology (WCGR, 1991; USEPA, 1992).

Ground-penetrating radar was used to monitor the
infiltration of tetrachloroethene following a controlled
spill under relatively ideal conditions at the Borden,
Ontario DNAPL research site (Annan et al., 1991;
Redman et al., 1991; WCGR, 1991). Subtle changes in
ground-penetrating radar reflectivity patterns at different
times before and after release of the tetrachloroethene
appear to document its downward migration and pooling
on a capillary barrier. At a coal tar spill site, Davis
(1991) inferred the presence of large volumes of
subsurface coal tar DNAPL based on low conductivity
anomalies detected using EM surveys. Others, however,
have concluded that surface geophysical methods have
very limited capacity to detect NAPL (Pitchford et al.,
1989) and that their use for this purpose should be
considered with caution (Benson, 1991).

The value of surface geophysics at most DNAPL sites will
be to aid characterization of waste disposal areas,
stratigraphic conditions, and potential routes of DNAPL
migration. Objectives and methods for using surface
geophysical surveys to evaluate DNAPL site
contamination are described in Table 8-7. The use of
geophysical surveying for direct detection of NAPL is
currently limited by a lack of: (1) demonstrable methods,
(2) documented successes, and (3) environmental
geophysicists trained in these techniques (USEPA, 1992).
8.2 SOIL GAS ANALYSIS

Soil gas analysis became a popular screening tool for
detecting volatile organic chemicals in the vadose zone at
contamination sites during the 1980s (Devitt et al., 1987;
Marrin and Thompson, 1987; Thompson and Marrin,
1987; Kerfoot, 1987, 1988; Marrin, 1988; Marrin and
Kerfoot, 1988; Tillman et al., 1989a, b). The American
Society for Testing and Materials (ASTM) is in the
process of developing a standard guide for soil gas
monitoring in the vadose zone. Soil gas surveys generate
extensive chemical distribution data quickly at a fraction
of the cost of conventional invasive methods and offer the
benefits of real-time field data. Consideration should be
given to its use during the early phases of site
investigation to assist delineation of DNAPL in the
vadose zone, contaminant source areas, contaminated
shallow groundwater, and contaminated soil gas; and,
thereby, guide subsequent invasive field work.
8.2.1 Soil Gas Transport and Detection Factors

Many DNAPLs, including most halogenated solvents,
have high vapor pressures and will volatilize in the vadose
zone to form a vapor plume around a DNAPL source as
described in Chapters 4.8 and 5. Volatile organic
compounds (VOCs) dissolved in groundwater can also
volatilize at the capillary fringe into soil gas. Although
this latter process is poorly understood (Barber et al.,
1990), it may be enhanced by water-table fluctuations
(Lappala and Thompson, 1983). Equilibrium vapor
concentrations are probably never attained in the field,
however, due to rapid vapor diffusion above the water
table (Marrin and Thompson, 1984).
-------
8-13
(a)
1-
Three Buried 55
!
' •* 1
Gallon Drums ' '
1" 1
1 I
' t 1 1
.1 _ ' tf
1
. 1
' ft
(c) (d)

Figure 8-3. Examples of geophysical survey measurements over buried wastes (from Benson et al,
1982; Technos, 1980): (a) a gradiometer magnetometer survey over metal drums buried in
a trench measuring approximately 20 ft by 100 ft by 6 ft deep; (b) a metal detector survey
of the same trencch; (c) a ground-penetrating radar image showing three buried drums; and
(d) shallow EM conductivity survey data at the Love Canal landfill showing the presence
of large concentrations of conductive materials and buried iron objects (i.e., drums)
associated with chemical waste disposal areas at each end of the landfill.
-------
8-14

Table 8-6. Surface geophysical methods for mapping conductive contaminant plumes (modified from Benson,
1991).
Mapping Permeable Pathways, Bedrock Channels, etc.

The fundamental approach to evaluating the direction of groundwater flow and the possible extent of a contaminant plume is by
determining the hydrogeologic characteristics of the site (refer to Table 8-4).
Mapping Conductive Inorgank or Mixed Inorganic-Organic Contaminants

Conductive contaminant* (inorganics or organic-inorganic mixtures) can be mapped using electrical methods (electrical resistivity and EM
conductivity) and sometimes using ground-penetrating radar when the ionic strength of the contaminated fluids sufficiently exceeds that of
background fluid. The higher specific conductance of the contaminated pore fluid acts as a tracer which can be mapped using electrical
surface geophysical methods.
Note: Actual results depend on site-specific conditions. In some applications, alternate methods may provide better results.
-------
SHALLOW MEASUREMENTS OF
POLLUTANT PLUME
(0-15 FEET DEEP)
(a)

s* — " "
N
1
~ 340'

-
240
240
DEEP MEASUREMENTS OF
POLLUTANT PLUME
(0-45 FEET DEEP)
Figure 8-4. Examples of conductive plume detection using: (a) shallow and (b) deep electrical
resistivity surveys at an approximately 1 square mile landfill with values given in ohm-feet;
and (c) a continuous EM conductivity survey showing a large inorganic plume (center
rear) (from Benson, 1991).
-------
Table 8-7. Surface geophysical methods for evaluating DNAPL site contaminations.
Objective
Delineate limits of waste disposal areas
Delineate buried utility corridors
Map stratigraphy, particularly permeable
pathways and the surfaces of fine-grained
capillary barrier layers and bedrock, to
determine potential routes of DNAPL
migration and stratigraphic traps
Delineate conductive inorganic contaminant
plumes that may be associated with DNAPL
contamination
Delineate geophysical anomalies that may
result from an accumulation of DNAPL
Methods
Following review of historical documentation, interviews, aerial photographs,
and available site data, consider use of GPR, EM conductivity, magnetometer,
and metal detection surveys (see Table 8-5).
Following review of historical documentation, utility records, interviews, aerial
photographs, and available site data, consider use of GPR, EM conductivity,
magnetometer, and metal detection surveys (see Table 8-5).
Following review of aerial photographs and available site, local, and regional
hydrogeologic data, consider use of GPR, EM conductivity, electrical resistivity,
and seismic surveys (see Table 8-4).
Following review of available data on waste disposal practices, chemical
migration, and hydrogeologic conditions, consider use of EM conductivity,
electrical resistivity surveys (see Table 8-6).
Consider using GPR to infer DNAPL accumulations at shallow depths in low
conductivity soils because DNAPL presence will probably alter the dielectric
properties of the subsurface (Olhoeft, 1986; WCGR, 1991). Abo consider
using electrical methods to infer DNAPL accumulation based on the presence
of low conductivity anomalies (Davis, 1991). Note that the use of surface
geophysical methods for direct detection of DNAPL presence is an emerging,
but limited technology, that may not be cost-effective. Very few geophysicists
are experienced in the application of surface survey methods for DNAPL
detection. These applications, therefore, should be treated with caution.
Note: Actual survey results depend on site-specific conditions. At some sites, an alternate method may provide better results.
-------
8-17
Experiments conducted at the Borden, Ontario DNAPL
research site suggest that soil gas contamination will
usually be dominated by volatilization and vapor phase
transport from contaminant sources in the vadose zone
rather than from groundwater, and that the upward
transport of VOCs to the vadose zone from groundwater
is probably limited to dissolved contaminants that are
very near to the water table (Hughes et al., 1990a; Rivett
and Cherry, 1991; Rivett et al., 1991; Chapter 8.2.4).
Rivett and Cherry (1991) attribute the limited upward
diffusion of groundwater contaminants to the low vertical
transverse dispersivities (mm range) which are observed
in tracer studies. Soil gas contamination, therefore, is not
a reliable indicator of the distribution of DNAPL or
groundwater contamination at depth below the water
table.

VOCs in soil gas diffuse due to the chemical
concentration gradient. Modeling analyses indicate that
contaminated vapors can diffuse tens of yards or more
from a DNAPL source in the vadose zone within weeks
to months (Mendoza and McAlary, 1990; Mendoza and
Frind, 1990a,b) and that transport velocities can be
reduced significantly by vapor-phase retardation (Chapter
5.3.20). Field experiments involving trichloroethene
(TCE) vapor transport in a sand formation confirm the
modeling study findings (Hughes et al., 1990a). These
experiments demonstrate the formation of significant
groundwater plumes from a solvent vapor source in a thin
(< 12 ft thick) vadose zone over a period of weeks.

Volatilization of contaminants with high molecular
weights and saturated vapor concentrations (Table 4-6)
can engender density-driven gas migration in media with
high gas phase permeability (i.e., kg > 1 X 10~n m2 in
uniform media) (Falta et al., 1989; Sleep and Sykes, 1989;
Mendoza and Frind, 1990b; Mendoza and McAlary, 1990).
Density-driven gas flow causes VOCs to sink and move
outward above (and dissolve in) the saturated zone. This
relative density effect should decrease with decreasing
VOC concentrations and increasing distance from a
contaminant source.

Although advective processes due to density effects or
high vapor pressure gradients may influence VOC
migration, gaseous diffusion is considered the
predominant vapor transport mechanism at most sites
(Marrin and Kerfoot, 1988). At steady-state, solute flux
is proportional to the air-filled porosity, the VOC
diffusion coefficient, and the gas-phase concentration
gradient.
Vapor transport can cause shallow groundwater
contamination in directions opposite to groundwater
and/or DNAPL flow. The resulting groundwater
contamination plumes can have high dissolved chemical
concentrations, but tend to be very thin in vertical extent,
and occur close to the water table.

Subsurface geologic heterogeneities, soil porosity,
moisture conditions, VOC source concentrations, and
sorption equilibria can significantly affect VOC gradients
in soil gas (Marrin and Thompson, 1987). For example,
false negative interpretations may result from the
presence of vapor barriers (perched groundwater, clay
lenses, or irrigated soils) below the gas probe intake.
Thus, sample locations and depths influence the measured
vapor concentrations. Profiles of soil gas concentrations
under a variety of field conditions are illustrated in Figure
8-5.

Several chemical characteristics indicate whether a
measurable vapor concentration can be detected (Devitt
et al., 1987; and Marrin, 1988). Ideally, compounds such
as VOCs monitored using soil gas analysis will: (1) be
subject to little retardation in groundwater; (2) partition
significantly from water to soil gas (Henry's Law constant
>0.0005 atm-mVmole); (3) have sufficient vapor pressure
to diffuse significantly upward in the vadose zone
(>0.0013 atm @ 20° C); (4) be persistent; and (5) be
susceptible to detection and quantitation by affordable
analytical techniques. Vapor pressures, solubilities, and
Henry's Law constants for DNAPL chemicals are plotted
in Figure 8-6 and given in Appendix A.

A generalized flowchart for conducting a soil-gas survey
is provided in Figure 8-7. Under typical conditions, 20 to
40 soil gas grab samples can be squired per day for
analysis. The cost to obtain and analyze soil gas samples
using lab-grade gas chromatography with appropriate
detectors typically ranges between $115 and $195 per
sample in 1992 dollars. This cost includes report
preparation, but not mobilization fees. Methods of soil
gas sampling and analysis are discussed below.
8.2.2 Soil Gas Sampling Methods

Soil gas sampling methods have been reviewed by Devitt
et al. (1987), Marrin and Kerfoot (1988), GRI (1987), and
Tillman et al. (1989b). Essentially, there are two basic
types of sample acquisition: (1) grab sampling and (2)
passive sampling.
-------
8-18
(A)
Depth
voc
concentration
(B)
Depth
VOC
concentration
(C)
Depth
voc
concentration
(D)
.- » •-•„**
"
Depth
VOC
concentration

Depth
VOC
concentration
(A) Homogeneous porous material with sufficient air-filled porosity
(B) Impermeable subsurface layer (e.g., clay or perched water)
(C) Impermeable surface layer (e.g., pavement)
(D) Zone of high microbiological activity (circles and wavy
lines indicate different compounds)
(E) VOC source in the vadose zone
Figure 8-5. Soil gas concentration profiles under various field conditions (reprinted with permission ACS,
1988).
-------
1 Aniline
2 Benzyl chloride
3 Bis(2-chloroethyl)ether
4 Bis(2-chloroisopropyl)ether
S Bromobenzene
6 Bromochloromethane
7 Bromoethane
8 Bromoform
9 Butyl benzyl phthailate
10 Carbon disulfide
11 Carbon telrachloride
12 Chlorobenzene
13 2-Chloroethyl vinyl ether
14 Chloroform
IS 1-Chloro-l-nitropropane
16 2-Chlorophenol
17 4-Chlorophenyl phenyl ether
18 Chloropicrin
19 m-Chlorotoluene
20 o-Chlorotoluene
21 Dibromochloromethane
22 Dibutyl phthalate
23 1,2-Dichlorobenzcrne
24 1,3-Dichlorobenzene
25 1,1 Dichloroethane
26 1,2-Dichloroethane
27 1,1-Dichloroethenie
28 trans-l,2-Dichlorc>elhene
29 1,2-Dichloropropane
30 Dichlorvos
31 Dielhyl phthalate
32 Dimethyl phthalate
33 Ethylenedibromicle
34 Hexachlorobutadiene
35 Hexachlorocyclopcntadiene
36 1-lodopropane
37 Malathion
38 Methylene chloride
39 Nitrobenzene
40 Nilroethane
41 1-Nitropropane
42 2-Nltrololuene
43 Parathion
44 PCB-1016
45 PCB-1221
46 PCB-1232
47 PCB-1242
48 PCB-1248
49 PCB-1254
50 Pentachloroelhanc
51 1,1,2,2-Tetrabromoethane
52 1,1,2,2-Tetrachloroethane
53 Tetrachloroethene
54 Thiophcne
55 1,2,4-Trichlorobenizene
56 1,1,1-Trichloroethane
57 1,1,2-Trichloroethane
58 Trichloroethene
59 1,1,2-Trichloronuoromethane
60 1,1,2-Trichlorotrifluoroethane
0.1
0)

W
OT
0)
O
D.
OJ
0.0001 =
1E-09
0.0001
0.001
100
1000
Solubility (mol/cubic meter)
Figure 8-6. Solubility, vapor pressure, and Henry's Law Constants for selected DNAPLs (refer to Appendix A).
-------
8-20
Develop site conceptual model of
contaminant sources and distributions
Select tracer gases
Select sampler type and sampling methods
Select analytical method(s)
Prepare QA sampling plan
Conduct pilot test of sampling and analysis procedures in an
area of known contamination. Sample at several depths to
determine the vertical profile of soil gas concentrations
and select a sampling target depth
Evaluate pilot test results and modify
sampling and analysis methods as necessary
Consider sampling gas from existing subsurface structures
(such as wells, basement sumps and drains, and sewers)
Design a sampling grid based on the site
conceptual model and investigation objectives
Conduct soil gas survey
Modify/augment sampling grid based on real-time
data acquisition (if possible)
Plot and contour data and make interpretations
Consider value of additional soil gas surveying
Figure 8-7. Flowchart for conducting a soil-gas survey.
-------
8-21
Grab sampling typically involves driving a small-volume
hollow probe with a conical tip to a depth of 3 to 10 ft,
pumping soil gas from the probe, and collecting a sample
from the moving soil gas. Samples are usually taken from
a depth of at least 3 ft to diminish the effects of surface
contamination, changes in barometric pressure and
temperature, rainfall, and air pollution (Tillman et al.,
1989b). The transient effects related to weather can be
minimized by conducting the soil gas survey in the
shortest time possible. Probes can be inserted to greater
depths from the bottom of a hollow-stem auger hole.
Vertical profiles of soil gas concentrations can be
developed by taking samples from different depths at the
same location.

Although there are many different probe designs (Dewitt
et al., 1987), small-diameter hollow steel probes with
conical tips and openings just above the tip to allow soil
gas entry (Figure 8-8) are used most frequently to
minimize soil disturbance and the mixing of air with soil
gas. Before insertion, the probes are cleaned and purged
using an inert gas or filtered air. The hollow probes can
be pushed into the ground hydraulically or pneumatically,
hammered in using a variety of manual or mechanical
hammers, or inserted into holes created by a hand-held
rotary percussion drill or a drive rod.

A small volume of soil gas (e.g., 3 to 10 liters) is
withdrawn using a pump to purge the sampling system,
and the sample is taken for immediate onsite analysis, or
encapsulated (preferably in glass or stainless steel
containers) for subsequent laboratory analysis. Samples
taken for VOC determination should be analyzed within
two days of collection. Continuous or excessive pumping
should be avoided; it may dilute soil gas with surface air
or distort the actual soil gas concentration patterns.
After sampling has been completed, the probes can be
removed hydraulically or by use of a jacking device.

Grab sampling of hydrophobic compounds can also be
accomplished by pumping soil gas through an adsorbent
collection medium such as charcoal or a carbonized
molecular sieve adsorbent (USEPA-ERT, 1988a,b).
Instructions regarding pumping rates and durations are
provided along with commercially available sorbent traps.
Generally, trapped soil gas contaminants are desorbed
thermally or using a solvent prior to chemical analysis.

Primary advantages of dynamic grab sampling include: its
low cost relative to drilling the quick acquisition and
analysis of samples (e.g., 40 to 70 samples per day
reported by Tillman et al., 1989b); its noninvasive nature;
and its documented utility. Onsite analysis of grab
samples also allows efficient field direction of the soil gas
survey. Problems may include: the potential collection
of unrepresentative samples due to excessive pumping,
disturbance to the vadose zone, and air leakage into the
sampling apparatus; plugging of sampling syringes by
pieces of the rubber septum and of the probe screens with
wet cohesive soils; and misinterpretation of results due to
complex chemical or hydrogeologic conditions (Hughes et
al., 1990b; Devitt et al., 1987).

Passive sampling provides an integrated measure of VOC
concentrations over the duration of sample collection
and thereby may overcome short-term perturbations due
to variable weather conditions or other factors. Typically,
a sorbent material such as activated carbon is placed
below ground within a hollow probe, sampling chamber,
or can for an extended period to trap VOCs that diffuse
through soil gas (Figure 8-9). The sampling duration can
be varied to promote accumulation of a detectable
quantity of trapped contaminant. The sorbent is then
retrieved and submitted for analysis. Passive soil gas
sampling is used infrequently at contamination sites.
Among other reasons, this is because: (1) the long
sampling times involved are inconvenient (2) the volume
of soil gas sampled is not measured making determination
of soil gas concentrations impossible; and, (3) chemical
degradation may affect sampling results due to the length
of the sampling period.

To further delineate the nature and extent of subsurface
contamination, gas sample-s derived from the headspace of
capped wells and jars containing drill cuttings, basement
sumps and drains, sewer lines, etc. can also be analyzed
using the following methods. It should be noted that
basements and utility corridors can act as vapor sinks,
inducing the transport of contaminated soil gas from
source areas.
8.2. Soil Gas Analytical Methods

Selection of an analytical method for soil gas depends on
the sensitivity, selectively, and immediacy of analytical
results required for a particular survey. Devitt et al.
(1987) provide a detailed comparative review of
alternative methods of soil gas analysis, including
portable VOC analyzers (i.e., Flame lonization Detectors,
FIDs, Photoionization Detectors, PIDs, and IR analyzers);
portable gas chromotographs (GCs) with various
detectors; and laboratory grade GCs with various
detectors which can be installed in a mobile laboratory.
-------
B
-10 CC GLASS SYRINGE
SYRINGE
NEEDLE
k ADAPTER FOR SAMPLING SOIL-GAS PROBE
HOSE
CLAMP,
•SILICONE RUBBER
TUBE
IN. TUBING
^•SILICONE RUBBER TUBE CONNECTION
TO VACUUM PUMP
CLEAR TUBING SLEEVE CONNECTOR
(DISPOSABLE)
SOIL-GAS FLOW DURING SAMPLING
3/4 IN. GALVANIZED PIPE
5-7 FT.
1 V
U.NJ
•DETACHABLE DRIVE POINT
Figure 8-8. Soil gas probe sampling apparatus: (a) close-up view of syringe sampling through
evacuation tube; and (b) hollow soil gas probe with sampling adapter (from Thompson
and Marrin, 1987).
-------
3-23
Ground Surface
Ferromagnetic
Wire
Figure 8-9. Passive soil gas sampling apparatus (from Kerfoot and Barrows, 1987).
-------
8-24
Following chromatographic separation, soil gas samples
can be analyzed using a (Devitt et al., 1987):

• Flame ionization detector (FID) for analysis of nearly
all organic compounds;

• Photoionization detector (PID) for measuring
aromatic hydrocarbons concentrations;

• Electron capture detector (BCD) for selective
measurement of halogenated organic compound
concentrations;

• Hall electrolytic conductivity detector (HECD) for
specific determination of halogenated compounds,
nitrogen species, and sulfur species; and,

• flame photometric detector (FPD) for determination
of sulfur and phosphorous compounds.

Typical analytes and products detectable by soil gas
surveys are listed in Table 8-8. The advantages and
limitations of specific analytical methods are described in
Table 8-9.
8.2.4 Use of Soil Gas Analysis at DNAPL Sites

Several published case studies are available that describe
the application of soil gas survey techniques to delineate
DNAPL chemical contamination (Glaccum et al., 1983;
Voorhees et al., 1984; Spittler et al., 1985; Wittmann et
al., 1985; Devitt et al., 1987; Marrin and Thompson, 1987;
Thompson and Marrin, 1987; Kerfoot, 1987; Newman et
al., 1988; Shangraw et al., 1988; Marrin and Kerfoot,
1988; Bishop et al., 1990; Hughes et al., 1990a; Rivett and
Cherry, 1991). Studies during the 1980s generally
indicated the utility of soil gas surveying for delineating
VOC source areas and VOC-contaminated groundwater
(e.g., Marrin and Thompson, 1987; Thompson and
Marrin, 1987). Examples of the correlation between
halogenated solvent concentrations in soil gas and
dissolved in groundwater at three different sites is shown
in Figure 8-10.

More recently, controlled and highly-documented field
experiments were conducted at the Borden, Ontario
DNAPL research site to investigate the behavior and
distributions of TCE in soil gas caused by (1) vapor
transport from a DNAPL source in the vadose zone and
(2) dissolved transport with groundwater from a DNAPL
source below the water table (Hughes et al., 1990a; Rivett
and Cherry, 1991). As shown in Figures 8-11 and 8-12,
the extent and magnitude of soil gas contamination
derived from the vadose zone soure was much greater
than that derived from the groundwater source.

TCE concentrations in soil gas associated with the plume
of contaminated groundwater having TCE concentrations
greater than 1000 ug/L leas than 5 ft below the water
table were generally <1 ug/L in a limited zone around the
source (Figures 8-lla and 8-12a). Rivett and Cherry
(1991) believe that the soil gas contamination at the
groundwater source site actually derived from accidental
TCE spillage above the water table during the source
emplacement, rather than from upward diffusion of TCE
from contaminated groundwater. The vadose zone source
produced TCE concentrations in soil gas and groundwater
over a much wider area than the groundwater source site.
The TCE in groundwater derived from the vadose zone
source, however, was less concentrated than at the
groundwater source site and was restricted to the upper
5 ft of the saturated zone.

Rivett and Cherry (1991) provide the following
interpretation of the observed TCE distributions.

"High vapor concentrations are transported
laterally by diffusion in the vadose zone from the
residual. Groundwater underlying the vapor
plume is contaminated by partitioning from the
vapor. In addition, during recharge events
infiltration is contaminated after passage through
the vadose zone residual or vapor and transported
to groundwater. Any rise in the water table would
be into a zone containing contaminated soil gas
and thus groundwater contamination would
follow. The wide shallow groundwater plume
observed at Site B is a result of the above
processes and is entirely derived from source
materials in the vadose zone. . . . Due to lateral
transport of vapors in the vadose zone, the
groundwater plume produced will be much wider
than the source of residual NAPL. Thus,
although similar source widths were used at Sites
A and B, the groundwater plume derived from
vapor contact at site B will be much wider than
the plume at Site A that is only subject to
transverse dispersion in the groundwater zone,
which is a weak process (Sudicky, 1986; Sudicky
and Huyakorn, 1991) . . . The process of upward
transport of VOCs [from groundwater to soil gas]
is probably only really important for the
partitioning of very shallow water table
-------
8-25
Table 8-8. Typical analytes and products detectable by soil gas surveys (modified from Tillman et al.,
1990a).
Acetone
Benzene
1-Butane
n-Butane
Carbon Tetrachloride
Chloroform
1,1-Dichloroethane (1,1-DCA)
1,1-Dichloroethene (1,1-DCE)
trans- 1,2-Dichloroethene (1,2-DCE)
Ethane
Ethylbenzene
Isopropyl Ether (DIPE)
Methane
Methylene Chloride (Dichloromethane)
Methyl Ethyl Ketone (MEK)
Methyl-Isobutyl Ketone (MIBK)
Methyl-Tert Butyl Ether (MTBE)
Propane
Tetrachloroethene (PCE)
Toluene
1,1,1-Trichloroethane (1,1,1-TCA)
1,1,2-Trichloroethane (1,1,2-TCA)
Trichloroethene (TCE)
1,1,2-Trichlorotrifluoroethane (Freon-113)
Xylenes
Cleaning Fluids
Coal Tar
Creosote
Degreasers
Diesel Fuel
Gasoline
Heating Oil
Jet Fuel
Solvents
Turpentine
-------
8-26

Table 8-9. Advantages and limitations of several soil gas analytical methods (modified from Devitt et
al., 1987).
METHOD
ADVANTAGES
LIMITATIONS
Portable VOC
Detectors
Portable FID
Analyzer (e.g.,
Century OVA)
Portable PID
Analyzer (e.g.,
HNU,
Photovac TIP)
Portable Hot-
Wire Detector
(Bacharach
TLV Sniffer)
Easy to transport to the field
Minimum operator training required
Elimination of sample collection steps minimizes
uncertainties and expense of sample collection,
storage and transport
Immediate analysis provides guidance for
additional sampling
Flame ionization detectors use a hydrogen-fed
flame to ionize organic gases and generate a
current that is proportional to concentration
Capable of detecting all organic compounds
Sensitivity is to <1 ppmv (methane) without the
GC option
Less variability in instrument response to
different organic compounds than with FIDs
Less susceptible to than PIDs to interference by
high humidity
FIDs can be operated in a survey mode or, with
appropriate attachments, in a GC mode
The GC option can be used with proper
standards to separate, identify, and quantitate
individual organic compounds in soil gas to the
ppt or low ppb level
An ultraviolet light is used to ionize gas or vapor
molecules which are then collected and produce
a current which is proportional to concentration
Capable of monitoring many organic and some
inorganic gases and vapors
Sensitivity to 0.1 ppmv (benzene); detection
range is approximately 0.1 to 2000 ppmv
No fuel or flame required
With the 10.2 eV lamp, alcohols, halogenated
alkanes, and most inorganic gases have no
response; alkanes have little or no response; and
alkenes, aromatics, organosulfur compounds, and
carbonyl compounds have high response
With the 11.7eV lamp, all organic compounds
except methane produce instrument response
Vapors are catah/ticalty combusted using a hot-
wire
Similar advantages to FIDs
Sensitive to approximately 2 ppm; detection
range is approximately 2 to 10,000 ppmv
Limited sensitivity due to lack of an anatyte
concentration step; typical detection limit is 1
ppmv
Limited selectivity and interference problems
because of the lack of a separation step; variable
response to different compounds
Limited accuracy because of the inability to
calibrate adequately for chemical mixtures
Relatively large sample volumes required

High humidity will reduce the relative response
Successful use of the GC mode requires
significant operator training and experience, and
equipment maintenance

Approximate cost of Century System OVA-128 is
$6,800.
The energy generated by the lamp must exceed
the ionization potential of the target chemical to
permit detection
The instrument's response to different chemicals
varies
UV lamp intensity declines slowly with age, but
can be compensated for during instrument
calibration
Airborne dust can interfere with UV light
transmission and reduce readings
High humidity can condense on the UV lamp and
reduce the light transmission, and also can
decrease the ionization of chemicals, thereby
reducing readings
PIDs cannot detect light hydrocarbons, such as
methane

Approximate cost of a HNU meter is $4300 in
1992 dollars.
• Similar disadvantages as FIDs

• Approximate cost of a Bacharach TLV Sniffer is
$2000 in 1992 dollars.
-------
Table 8-9. Advantages and limitations of several soil gas analytical methods (modified from Devitt et
al., 1987).
METHOD
ADVANTAGES
LIMITATIONS
Portable and
Field GC Units
with various
detectors
• GC units can be used to separate a mixture of
gaseous compounds prior to detection;
• Several portable VOC analyzers have GC
options, including the Photovac PID and the
Century OVA FID, allowing individual
compounds to be monitored and quantitated to
the ppb range
• These instruments are easy to transport
• Portable GCs are most effective on samples with
large concentrations of easy-to-separate VOCs
• Field GC units contain temperature controlled
ovens and a variety of injectors and detectors
facilitating better precision and accuracy
• No temperature control for the portable GC
column hinders high resolution compound
separation
• Reproducible retention times are difficult to
replicate in the field using portable GCs due to
temperature variation

• Estimated cost in 1992 dollars for GC units
without a detector is from $2500 to >$30,000.
Lab-grade GC
Units with
various
detectors or
MS
• rasl analytical response with better-controlled
analytical conditions; can typically process 50-70
samples per day
- Produces highest quality data
• Provides significantly lower detection limits for a
wider range of compounds than possible using a
portable GC
• Detection limits can be in the ppt range
• Can be mounted in a mobile van
• Requires significant operator training
• Lab-grade GC units are expensive
-------
3-28
627 62S
WELL NUMBER
(a)
IOf)00-\
I IO IOO

WATER fyg/L)
IflOO 10,000
(b)

Figure 8-10. Correlations between halogenated solvent concentrations in shallow soil gas sampled between 3
and 8 ft below ground and underlying groundwater: (a) chloroform along a transect perpendicular
to the direction of groundwater flow at an industrial site in Nevada (reprinted with permission from
ACS, 1987); and, (b) 1,1,2-trichlorotrifluoroethane (Freon 113) at an industrial site in California
(from Thompson and Marrin, 1987).
-------
3-29
SITE A
SITE B
GROUNDWATER ZONE SOURCE
VADOSE ZONE SOURCE
0.01
0.001
20
1000 !
40
i
SOURCE
60 m
I
PILOT VAPOUR
EXTRACTION SITE
N
0.001
SOURCE
SOIL GAS

GROUNDWATER
Figure 8-11. Aerial extent of soil gas and groundwater contamination derived from TCE emplaced
below the water table (Site A) and in the vadose zone (Site B) (from Rivett and Cherry,
1991). All values in ug/L. Refer to Rivett and Cherry (1991) for details.
-------
8-30
100-
tt-
n-
O
i
GROUND SURFACE
001

0074

0»

0.344

0.15}
0134
0

0017

OCX

0019
0

0.001

0.003

O.OM
0.001
WATER TABLE
:=i:?:-
IX
SOURCE
FLOW
ij 5 5 5£ *
DISTANCE FROM SOURCE (m)
(a)
102-
101-
100-
97-
86-
CROUHD SU tr*C t

ORIGINAL!
SOURCE I
ass
am 3
0.17
aas7
&4 01
4.6
21 .•
37
WATER TABLE
4 If
29 \876

M100
xee
FLOW
13
•••.... 1710
*"*"«.......
96
B 23 202
143 33J.,,
764 2
650 ..-.-•"' 0
'"26'
304
E £ £ £ 5 S S S nET o
DISTANCE FROM SOURCE (m)
Figure 8-12. Longitudinal profiles showing the extent of soil gas and groundwater contamination
parallel to the direction of flow and through the source areas derived from TCE
emplaced (a) below the water table (Site A) and (b) in the vadose zone (Site B) (from
Rivett and Cherry, 1991). All values in ug/L. Refer to Rivett and Cherry (1991) for
details.
-------
8-31
contamination to the soil gas. These experiments
and real site soil gas surveys confirm transfer is
occurring, however it may be expected that in
non-arid climatic regions, after sufficient time and
travel distance, continued recharge onto the
shallow plume may prevent partitioning to the soil
Rivett and Cherry describe several conceptual models of
soil gas contamination that may arise from different
DNAPL release scenarios. These models are provided in
Table 8-10 and illustrate that soil gas surveying can be
generally useful to delineate VOC contamination in the
vadose zone and in shallow groundwater, but may fail to
discern areas of deeper groundwater contamination that
are not coincident with shallow soil gas contamination
due to vapor transport.

Finally, although soil gas surveying has been used
successfully to assist delineation of vadose zone and
shallow groundwater contamination at many sites, it can
provide misleading results if subsurface conditions are not
understood adequately. Thus, interpretations of regarding
the subsurface VOC distribution derived from a soil gas
survey must be confirmed by analysis of soil and fluid
samples taken at depth.
8.3 AERIAL PHOTOGRAPH INTERPRETATION

Aerial photographs should be squired during the initial
phases of a site characterization study to facilitate analysis
of waste disposal practices and locations, drainage
patterns, geologic conditions, signs of vegetative stress,
and other factors relevant to contamination site
assessment. Additionally, aerial photograph fracture trace
analysis should be considered at sites where bedrock
contamination is a concern.
8.3.1 Photointerprelation of Site Conditions

Government agencies have made extensive use of aerial
photographs since the 1930s for the study of natural
resources (Stoner and Baumgardner, 1979). For example,
the U.S. Soil Conservation Service uses aerial
photographs for soil mapping the U.S. Department of
Agriculture analyzes photos to check farmer compliance
with government programs; and the U.S. Geological
Survey uses photos to map and interpret geologic
conditions. During contamination site investigations, the
U.S. Environmental Protection Agency and others analyze
historic aerial photographs to document waste disposal
practices and locations, geologic conditions, drainage
patterns, pooled fluids, site development including
excavations for pipelines and underground storage tanks,
signs of vegetative stress, soil staining, and other factors
relevant to assessing subsurface chemical migration
(Phillipson and Sangrey, 1977).

Most photointerpretation involves qualitative stereoscopic
analysis of a series of historic aerial photographs available
for a particular site. For example, selected waste disposal
features at a manufacturing site that were noted on aerial
photographs taken during 1965 and 1966 are shown in
Figure 8-13. Historical topographic maps and/or
topographic profiles can also be derived from aerial
photographs by use of analytical stereoplotting
instrumentation. Such quantitative analysis facilitates
examination of drainage patterns, land recontouring
associated with waste disposal, waste volumes, etc.

Conventional aerial photography has been produced on
behalf of government agencies for the entire United
States. Much of the photography is vertical black and
white coverage of moderate scale, typically about 1:20,000.
Aerial photographs and remote sensing images are
available through several agencies (Table 8-11). In
particular, the National Cartographic Information Center
(NCIC) in Reston, Virginia catalogs and disseminates
information about aerial photographs and satellite images
available from public and private sources. NCIC will
provide a listing of available aerial photographs for any
location in the United State-s and order forms for their
purchase. Historic aerial photographs taken every few
years dating back to the 1940s are available for many
parts of the United States.
8.3.2 Fracture Trace Analysis

Fracture trace analysis involves stereoscopic study of
aerial photographs to identify surface expressions of
vertical or nearly-vertical subsurface zones of fracture
concentrations (Figure 8-14). In fractured rock terrain,
particularly in karst areas, groundwater flow and chemical
transport are usually concentrated in fractures.

Lattman (1958) defined a photogeologic fracture trace as
"a natural linear feature consisting of topographic
(including straight stream segments), vegetation, or soil
tonal alignments, visible primarily on aerial photographs,
and expressed continuously for less than one mile . . .
[that are not] related to outcrop pattern of tilted beds,
-------
Table 8-10. Conceptual models (longitudinal sections) of soil gas and groundwater contamination resulting from
NAPL releases (modified from Rivett and Cherry, 1991).
QROUND SURFACE
SHALLOW GROUNDWATER PLUME
AQUIFER BASE
(a) A VOC vapor plume develops around NAPL in the vadose zone and contaminates shallow groundwater in an area larger than the NAPL
source area. The shallow groundwater VOC plume moves downgradient hydraulically and repartitions to the soil gas; thus forming a zone of
shallow groundwater and soil gas contamination wider than the NAPL source zone. Soil gas monitoring near the NAPL source detects direct
VOC vapor transport from the NAPL source. At some distance downgradient hydraulically, soil gas monitoring delects VOCs thai have
diffused from the shallow groundwater VOC plume.
SOURCE
(b) If NAPL does not substantially penetrate the water table, soil gas and groundwater concentration patterns will be similar to case (a).
SOURCE
(c) For the unusual case where NAPL has been injected or emplaced below the water table without being present in the vadose zone, or where
VOC transport in groundwater at depth has advanced far beyond the vapor plume that has migrated from the NAPL source, upward diffusion
of VOCs from groundwater to soil gas may be negligent, particularly where recharge causes a downward component of groundwater flow.
SOURCE
(d) Where DNAPL has sunk below the water table, a vapor plume will develop around the residual DNAPL in the vadose zone and a dissolved
plume will emanate from the DNAPL in the saturated zone. Vapor transport will contaminate shallow groundwaler over an area wider than the
DNAPL source. The deeper dissolved chemical plumes will generally be narrower and more concentrated than the shallow groundwater plume
that results from vapor transport. If the hydrogeoiogic conditions are complex, several distinct dissolved plumes may migrate at different rates
and in different directions. Thus, soil gas monitoring will provide information on the extent of shallow groundwater contamination, but may not
be a reliable indicator of deeper groundwater contamination.
ZONE OF
DEPLETED
DNAPL RESIDUAL
FIGURE 8.e
DNAPL POOL
DNAPL RESIDUAL
D
SOIL GAS PLUME
GROUNDWATER PLUME
(e) DNAPL trapped in pools below the water table may continue to dissolve in groundwater after the residual DNAPL in the vadose zone has
been completely depleted. For this case, soil gas contamination may be limited to the area above where the shallow groundwater plume has
migrated to, or where the deeper groundwater plume reaches the water table. Note, however, that several processes will work to prolong soil
gas contamination in the zone of depleted DNAPL, including adsorption/desorption, and the slow movement of water and dissolved chemicals in
relatively low permeability portions of the vadose and saturated zones.
-------
NOfE:
All buildings, homes, paved
and dirt roods, fence lines.
th« baseball field, and
Eastern, Middle, and West-
ern Creek are displayed
according to their current
configuration for reference.
965-1966
GRAPHIC SCALE
200 0 100 200
i Disturbed
v surface
\ materials

Landfill
•\

Drainage
channel
from
lagoon \ \
The 5/19/66 photos
show an open—bed
truck with about
10 drums backed
up to the trench
on the west side
of the dirt road.
Trench
discharge
Trenches
(oil pits)
with ponded
fluid
Several drums are
visible above the
ponded fluid in
this trench and
fluids are draining
from the trench
to the north.
Extent of
lagoon fluids
Disturbed
earth
alignment
Figure 8-13. Selected waste disposal features identified at a manufacturing site using aerial
photographs taken between 1965 and 1966.
-------
8-34

Table 8-11. Sources of aerial photographs and related information.
National Cartographic Information Center
U.S. Geological Survey National Center
Reston, Virginia 22092

U.S. Department of the Interior
Geological Survey
EROS Data Center
Sioux Falls, South Dakota 57198

Western Aerial Photograph Laboratory
Administrative Services Division
ASCS-USDA
2505 Parley's Way
Salt Lake City, Utah 84109

The National Climatic Center
National Oceanic and Atmospheric Administration
Federal Building
Asheville, North Carolina 28801
-------
8-35
700
Figure 8-14. Relationship between fracture traces and zones of subsurface fracture concentration
(from Lattman and Parizek, 1964).
-------
8-36
lineation and foliation, and stratigraphic contacts." A
lineament is a similar feature that is expressed for more
than one mile in length. Numerous papers document the
application of fracture trace analysis to hydrogeologic
investigations (e.g., Lattman and Parizek, 1964; Siddiqui
and Parizek, 1971; Parizek, 1976; Parizek, 1987). A
manual on the principles and techniques of fracture trace
analysis was prepared by Meiser and Earl (1982).

Fracture trace analysis is widely used to site productive
wells and guide the placement of bedrock monitor wells
at contamination sites. The significance of preferential
groundwater flow along fracture zones for monitoring
contaminant migration is illustrated in Figure 8-15.
Extensive contaminant migration occur undetected if
monitor wells are located in low permeability rock
between zones of fracture concentration. A case study
involving fracture trace analysis to define and remediate
TCE contamination in fractured bedrock was described by
Schuller et al. (1982).
-------
8-37
LEGEND!
FLOW DIRECTION OF LEACH ATE
ENRICHED GROUND WATER
LEACHATE ENRICHED
GROUND WATER
Figure 8-15. Preferential migration of contaminants in fracture zones can bypass a detection
monitoring system (from USEPA, 1980).
-------
9 INVASIVE METHODS
9.2 RISKS AND RISK-MITIGATION STRATEGIES
Following development of the site conceptual model
(Chapter 5) based on available information (Chapter 7)
and noninvasive field methods (Chapter 8), invasive
techniques will generally be required to advance site
characterization and enable the conduct of risk and
remedy assessments. Various means of subsurface
exploration are utilized to directly observe and measure
subsurface materials and conditions. Generally, these
invasive activities include: (a) drilling and test pit
excavation to characterize subsurface solids and liquids;
and (b) monitor well installation to sample fluids, and to
conduct fluid level surveys, hydraulic tests, and borehole
geophysical surveys. Invasive site characterization
methods are described in numerous texts (Table 2-1; e.g.,
USEPA, 1991a). Their application to DNAPL site
investigation is discussed in this Chapter.
9.1 UTILITY OF INVASIVE TECHNIQUES

Invasive field methods should be used in a phased manner
to test and advance the site conceptual model based on
careful consideration of site-specific conditions and
DNAPL transport processes. Although the methods
selected for invasive study are site-specific, their
application will generally be made to (Chapter 6; Figure
6-1):

• delineate DNAPL source (entry) areas (Figure 9-1);

• define the stratigraphic, lithologic, structural, and/or
hydraulic controls on the movement and distribution of
DNAPL, contaminated groundwater, and contaminated
soil gas,

• characterize the fluid and fluid-media properties that
affect DNAPL migration and the feasibility of
alternative remedies;

• estimate or determine the nature and extent of
contamination, and the rates and directions of
contaminant transport;

• evaluate exposure pathways; and

• design monitoring and remedial systems.
The risk of enlarging the zone of chemical contamination
by use of invasive methods is an important consideration
that must be evaluated during a DNAPL site
investigation. DNAPL transport caused by site
characterization activities may: (1) heighten the risk to
receptors, (2) increase the difficulty and cost of site
remediation, and/or (3) generate misleading data, leading
to development of a flawed conceptual model, and flawed
assessments of risk and remedy (USEPA, 1992).

Drilling, well installation, and pumping activities typically
present the greatest risk of promoting DNAPL migration
during site 'investigation. Drilling and well installations
may create vertical pathways for DNAPL movement. In
the absence of adequate sampling and monitoring as
drilling progresses, it is possible to drill through a
DNAPL zone without detecting the presence of DNAPL
(USEPA, 1992). Increased hydraulic gradients caused by
pumping may mobilize stagnant DNAPL. Precautions
should be taken to minimize these risks. If the risks
cannot be adequately minimized, alternate methods
should be used, if possible, to achieve the characterization
objective; or the objective should be waived. It is
important to consider the question, "Is this data really
necessary?"

Conventional drilling methods have a high potential for
promoting downward DNAPL migration (USEPA, 1992).
Special care should be exercised, in particular, to avoid
causing the downward movement of mobile, perched
DNAPL or DNAPL-contaminated soil that may result
from drilling through a barrier layer. Similarly, DNAPL
may sink preferentially along the inside or outside of a
well. Specific conditions which may result in downward
DNAPL migration include:

• an open borehole during drilling and prior to well
installation;

• an unsealed or inadequately sealed borehole;

• a well screen that spans a barrier layer and connects an
overlying zone with perched DNAPL to a lower
transmissive zone;

• an inadequately sealed well annulus that allows
DNAPL to migrate through: (a) the well-grout
interface, (b) the grout, (c) the grout-formation
interface, or (d) vertically-connected fractures in the
disturbed zone adjacent to the well; and,
-------
9-2
DNAPLZONE
(contains free-phase
and/or residual DNAPL)
DISSOLVED
CONTAMINATION ZONE
DNAPL ENTRY LOCATION
(such as a former waste pond)
Groundwater Flow Direction
Figure 9-1. Defined areas at a DNAPL site (from USEPA 1992).
-------
• structural degradation of bentonite or grout sealant, or
well casing, due to chemical effects of DNAPL or the
groundwater environment.

To minimize the risk of inducing DNAPL migration as a
result of drilling, site investigators should:

• avoid unnecessary drilling within the DNAPL zone,

• minimize the time during which a boring is open;

• minimize the length of hole which is open at any time;

• use telescoped casing drilling techniques to isolate
shallow contaminated zones from deeper zones;

• utilize the site conceptual model (knowledge of site
stratigraphy and DNAPL distribution), and carefully
examine subsurface materials brought to the surface as
drilling progresses, to avoid drilling through a barrier
layer beneath DNAPL (i.e., stop drilling above or at
the top of the barrier layer);

• consider using a dense drilling mud (i.e., with barium
sulfate additives, also known as barite) to prevent
DNAPL from sinking down the borehole during
drilling;

• select optimum well materials and grouting methods
based on consideration of site-specific chemical
compatibility and,

• if the long-term integrity of a particular grout sealant
is questionable, consider placing alternating layers of
different grout types and sealing the entire distance
between the well screen and surface to minimize the
potential for vertical migration of DNAPL.

Pumping from beneath or adjacent to the DNAPL zone
can induce downward or lateral movement of DNAPL,
particularly in fractured media due to the development of
relatively high fluid velocities. In general, groundwater
should not be pumped from an uncontaminated aquifer
directly beneath a capillary barrier and overlying DNAPL
zone. The risk of mobilizing stagnant DNAPL by
pumping groundwater can be assesed using equations
provided in Chapter 5.3.

The risk of causing DNAPL migration generally increases
where there is fractured media, heterogeneous strata,
multiple release locations, large DNAPL release volumes,
and barrier layers that are subtle (e.g., a thin silt layer
beneath sand) rather than obvious (e.g., a thick soft clay
layer beneath sand). At many sites, the DNAPL zone can
be adequately characterized by limiting drilling to shallow
depths. Characterization of deeper units can be
accomplished by deeper borings and wells beyond the
edge of the DNAPL zone.

Two basic strategies for invasive site characterization
referred to as the outside-in and inside-out approaches
are described as follows by USEPA (1992).

"The outside-in strategy of conducting initial invasive
characterization outside suspected DNAPL areas
and working toward the source has the advantage of
allowing acquisition of significant geologic and
hydrogeologic data at relatively low risk. These data
can be used to refine the conceptual model and
guide additional investigations. However, it should
be noted that uncertainty exists in determining the
extent of the suspected DNAPL area at any site.
One disadvantage to the outside-in approach is that
much additional time and expense may be incurred
during the study if characterization is started too far
from the suspected DNAPL zone. At some sites, it
may be appropriate to avoid drilling directly within
areas of known or suspected DNAPL contamination
and focus on characterizing dissolved contaminant
plumes migrating from source areas. However,
drilling in suspected DNAPL areas may be required
to provide the necessary information for site
characterization and remedial design (e.g., assessing
the presence and locations of DNAPLs and for
application of in situ restoration technologies).

The inside-out approach of initially drilling within
areas suspected to be the most contaminated and
subsequently drilling in more remote areas to define
the extent of contamination has been the traditional
approach for many site investigations. One
potential advantage of this method is that fewer
boreholes may be required to determine the extent
of contamination when investigation is started within
an area of known contamination and progresses
outward. The obvious disadvantage to this strategy
is the increased potential for providing pathways for
rapid downward migration of DNAPLs. The
increased risks of remobilizing certain high mobility
DNAPLs (e.g., chlorinated solvents) may render the
inside-out approach the least desirable strategy at
certain sites. This strategy appears to be most
applicable at DNAPL sites where the immiscible
fluids are relatively immobile (e.g., many creosote
-------
9-4
and coal tar sites). The relative time and cost
advantages of the inside-out approach may be offset
by additional investigation and remediation costs
incurred if DNAPLs are mobilized to greater depths.

The choice of characterization strategy depends on
the conceptual model of the site and the physical
properties of the contaminants. Immiscible liquids
with relatively high densities and low viscosities (e.g.,
chlorinated solvents) will be relatively more mobile
than less dense, more viscous liquids (e.g., creosote
or coal tar). More mobile liquids represent greater
risk for spreading contamination to deeper zones
during site characterization. In addition, these
contaminants may have migrated considerably
farther from the DNAPL entry location than less
dense, more viscous liquids. The use of site history
and noninvasive techniques may provide useful
information for guiding invasive study. However, it
will generally not be possible to determine the
extent of immiscible liquids prior to invasive study.
Locations for invasive study must be chosen using
the best available site specific information and
knowledge of DNAPL contaminant transport
principles. Regardless of whether the outside-in or
inside-out approach is chosen, characterization
should proceed from shallow depths to greater
depths. In this manner, more information is
acquired concerning shallow geologic features and
contamination and the risk of mobilizing DNAPLs
to greater depths during drilling is reduced."
9.3 SAMPLING UNCONSOLIDATED MEDIA

Subsurface explorations (i.e., test pits and borings) permit
direct measurement of stratigraphic, hydrogeologic, and
contaminant conditions. Soil and waste zone sampling is
conducted to pursue the site characterization goals
outlined in Figure 6-1. Overburden sampling locations
are selected to test and verify the site conceptual model.
The numbers and locations of borings and samples
required during a site characterization study depend on
site-specific conditions and objectives. Estimated costs of
drilling and test pit excavation in 1987 dollars are
provided in Table 9-1.

The value of subsurface exploration relies, in large part,
on the types and quality of measurements made and
recorded during the investigation. Information which
should be considered for logging is listed in Table 9-2. In
addition to describing soil characteristics such as texture,
consistent, and moisture state, it is important to
document visual and olfactory (if consistent with site
safety plans) observations, and vapor monitoring
detections, of contaminantt presence. Inner sections of
retrieved samples should be inspected to avoid
misinterpreting core surfaces that may be contaminated
during sampling. Particular care should be taken to
examine soil fractures, ped faces, and macropores for
NAPL presence. Methods for visual detection of NAPL
presence are described in Chapter 9.10.
9.3.1 Excavations (Test Pits and Trenches)

Excavating test pits and/or trenches can be a very rapid
and cost effective means to:

• characterize the nature and continuity of shallow
overburden stratigraphy, including the macropore
distribution;

• identify, delineate, and characterize waste disposal and
grossly contaminated areas;

• help determine the horizontal and vertical extent of
shallow contamination;

• locate and examine buried structures, tanks, pipelines,
etc. and their bedding/backfill that may act as
contaminant reservoirs or preferential pathways; and,

• acquire samples for chemical and physical analyses.

Guidelines for test pit and trench excavation, sampling,
and backfilling are provided by USEPA (1987) and USDI
(1974).

The main advantage of excavation for site characterization
is that it provides an opportunity to examine a large,
continuous subsurface section. As a result, excavations
can reveal conditions such as subtle or complex
stratigraphic relations, soil fracture patterns,
heterogeneous NAPL distributions, and irregular disposal
areas, that can be difficult to characterize by examining
drill cuttings or samples. The potential risk of causing
DNAPL migration is limited by the relatively shallow
depth of excavation.

Limitations and/or disadvantages of excavation as a site
characterization tool include: the limited depth of
exploration using a backhoe; the diminished view of
excavation sidewalls with depth due to shadows, viewing
-------
9-5
Table 9-1. Drilling and excavation costs in April, 1987 dollars (from GRI, 1987).
ITEM
Drilling
Soil Boring* (3%")
Rock Coring
Stainless Steel Screen (2",
installed)
Stainless Steel Riser Pipe (2",
installed)
PVC Screen (2", installed)
PVC Riser Pipe (2", installed)
Protective Casing
Shelby Tube Samples (3")
Water Truck Rental
Steam Cleaner Rental
Steam Cleaning Time
Stand By Time
Drilling in Level C Protection
(Add)
Mobilization and
Demobilization (200 miles)
Test Pit Excavation
Small Rubber Tired Backhoe
and Operator
Large, Track-Mounted
Backhoe (2 yd3 shovel) and
Operator
Mobilization and
Demobilization
HIGH COST
$39/rt
$5om
$375/5 ft
$37/ft
$50/5 ft
$8/5ft
$150/each
$125/each

$125/day
$140/hr
$140/hr
$125/hr
$1250

IXWCOST
$i8/R
$40/ft
$175/5 ft
$nm
$35/5 ft
$5/5 ft
$90/each
$40/each

$60/day
SllZtur
$112/hr
$35/hr
$900

MEAN COST
$28/ft
$44/ft
$252/5 ft
$21/ft
$43/5 ft
$6/5ft
$113/each
$85/each
$400/day
$85/day
$125/hr
$125/hr
$87/hr
$1075
$70 - $110/hr
$100 - $170/hr
$50 - $100/hr
-------
9-6
Table 9-2. Information to be considered for inclusion in a drill or test pit log (modified from
USEPA 1987; Aller et al., 1989).
General:
• Project name/number
• Hole name/number
• Date started and finished
• Hole location; map and elevation
Weather conditions
Rig type, bit size/auger size
Classification system used
(e.g., Unified Soil Classification)
Geologist's name
Driller's name
Sheet number
Information Columns:
• Depth
• Sample location/number
• Low counts and advance rate
• Percent sample recovery
• Narrative description
• Depth to saturation
Well construction details
Other remarks
Narrative Geologic Description:
• Soil/rocktype
• Soil/rock texture and structure
• Color (Munsell) and stain
• Petrology and mineralogy
• Friability
• Moisture content (dry, moist, wet)
• Degree of weathering
• Presence of carbonate
• Fractures, joints (orientation, size,
and spacing)
• Bedding nature and spacing
• Soil gradation or plasticity
• Discontinuities descriptions
• Water-bearing zones
• Formation strike and dip
• Fossils
• Depositional structures
• Organic content
• Solution cavities
• Rock core total breakage and breaks/ft
Particle roundness or angularity
Estimate of density of granular soil
or consistency of cohesive soil (usually
based on standard penetration test)
Slickensides
Roots, rootholes
Residual or relict structure
Buried horizons
Disturbed earth, waste materials
Rock Quality Designation (RQD)
Sampling Information:
• Types of samplers) used
• Diameter and length of samplers)
• Number of each sample
• Start and finish depth of each sample
• Percent sample recovery
Split-spoon sampling •
+ size and weight of drive hammer
+ number of blows required to
penetrate each 6-inch interval
+ free fall distance used to drive sampler
Thin-walled sampling
+ ease or difficulty pushing sampler
+ psi required to push sampler
Rock coring
+ core barrel drill bit design
+ penetration rate
+ fluid gain or loss
Drilling Observations:
• Loss of circulation
• Advance rates
• Rig chatter
• Water-levels
• Changes in drilling method/equipment
• Drilling difficulties
* Amount of water yield/loss during
drilling at different depths
Caving/hole stability
Amount of air used; air pressure
Running sands
Amounts and types of drilling fluids
used
Well Construction Details:
• Well Design:
4- casing length, schedule, and diameter
+ joint type
+ screen length, schedule, and diameter
-I- screen slot size
+ percent open area in screen
-I- filter pack depth interval •
+ elevations of top of casing, bottom
and top of protective casing, ground
surface, bottom of borehole, bottom
and top of well screen, annular seal
and grout intervals, etc.
+ well location coordinates and map
+ other backfill materials and intervals
Materials: <
+ casing and screen
+ filter pack (i.e., grain size analysis)
+ sea] and physical form
+ slurry or grout mix

Installation:
+ drilling method
+ drilling fluids
+ source of water
•f timing
+ method of sealant/grout emplacement
+ volumes of all materials used
Development:
+ time and date
+ water level elevation before
after development
+ development method
+ time spent developing well
4- volume of fluid removed
+ volume of fluid added
+ clarity of water and sediment before
and after development
+ amount of sediment at well bottom
+ pH, specific conductance, and
temperature readings
Other Remarks:
• Chemical odors
• Sample fluorescence
• NAPL sheens or presence
• HNU or OVA readings
Sample shipping reference
Equipment failures
Deviations from drilling protocols
Photograph cross-reference
Air-monitoring data
Hydrophobic dye test results
Equipment decontamination
procedures
-------
9-7
angle, and distance (binoculars can enhance sidewall
viewing); potential sidewall stability problems, of
particular concern near structures, utilities, and roads;
potential airborne release of contaminated vapors and
dust; potential creation of a preferential pathway for
contaminant transport along a trench; potential increased
waste handling requirement and potential subsidence
problems after the excavation has been backfilled
9.3.2 Drilling Methods

Borings and monitor wells are installed to evaluate
subsurface stratigraphic, hydrogeologic, and contaminant
conditions. Selection of drilling locations, depths, and
methods is based on available information regarding site
conditions. The potential for causing DNAPL migration
by drilling through a barrier layer should be considered
before and during drilling and hence minimized (Chapter
9.2).

Drilling methods applicable to contamination site
investigations are documented by Aller et al. (1989),
Driscoll (1986), Davis et al. (1991), GeoTrans (1989),
Hackett (1987, 1988), Clark (1988a), GRI (1987), USEPA
(1987), Rehm et al. (1985), Barcelona et al. (1985),
Cambell and Lehr (1984), Acker (1974), USDI (1974),
Morgan (1992), and ASTM (1990a). Additionally, the
adaptation and use of cone penetrometers for delineating
contaminated groundwater and soil during the past
several years has been described by Robertson and
Campanella (1986), Lurk et al. (1990), Smolley and
Kappmeyer (1991), Christy and Spradlin (1992), and
Chiang et al. (1992). These methods are described
briefly, and their applications and limitations are noted,
in Table 9-3. Diagrams depicting several drilling methods
are shown in Figure 9-2.

Selecting a drilling method generally involves a trade-off
between the advantages and limitations of the different
techniques. Due to the risks associated with drilling at
DNAPL sites, special consideration should be given to
drilling methods which allow for: (1) continuous, high-
quality sampling to facilitate identification of DNAPL
presence and potential capillary barriers, and (2) highly-
controlled well construction and hole abandonment.

Drilling in unconsolidated media at DNAPL sites is most
commonly done using hollow-stem augers with split-
spoon sampling. Riggs and Hatheway (1988) estimate
that greater than 90 percent of all monitor wells in
unconsolidated media in North America are installed
using hollow-stem auger rigs. A detailed summary of
drilling, sampling, and well construction methods using
hollow-stem auger drill rigs is provided by Hackett (1987,
1988). Despite the advantage of drilling with hollow-
stem augers, DNAPL can flow down through the
disturbed zone along the outside of the augers and/or
possibly enter the hollow stem auger through joints and
then sink to the bottom of the boring (WCGR, 1991).

Some potential for causing vertical DNAPL migration is
associated with all drilling methods. When drilling at
DNAPL sites, this potential can be minimized by careful
consideration of drilling strategies (Chapter 9.2).

Boreholes which are abandoned (not used for well
construction) should be properly sealed to prevent
vertical fluid movement in the borehole. Typically, this
involves pumping a grout mixture through a tremie pipe
and filling the hole from the bottom up to prevent
segregation, dilution, and bridging of the sealant (Aller et
al., 1989). Compositions and characteristics of various
grouts are summarized in Table 9-4. Several investigators
have reported that organic immiscible fluids cause
permeability enhancement in bentonite clay which is
frequently used as a sealant or grout additive for well
construction and borehole abandonment (Anderson et al.,
1981; Palombo and Jacobs, 1982; Brown et al., 1984;
Evans et al., 1985; Abdul et al., 1990). Hydrophobic
organic liquids tend to shrink the bentonite swelling clay
structure and thereby produce fractures. Where DNAPLs
are present, the use of bentonite, may be inappropriate
(except perhaps as a minor-component grout additive).
One strategy to limit vertical migration is to emplace
layers of different sealants to fill the borehole (or well
annulus). Thus, degradation of one sealant type will have
a limited deleterious effect.
9.3.3 Sampling and Examination Methods

Soil or waste samples brought to the surface are typically
examined to log some of the characteristics listed in Table
9-2. Drill cuttings or core material can be screened for
volatile organic contaminant presence using portable
instruments such as an organic vapor analyzer (OVA) and
a HNU meter. Methods for visual detection of NAPL
presence in soils are described in Chapter 9.10. Samples
are also taken for detailed chemical analyses and to
characterize media properties (i.e., wettability, capillary
pressure and relative permeability curves, porosity, etc.;
Chapter 10).
-------
9-8
Table 9-3. Drilling methods, applications, and limitations (modified from Aller et al., 1989; GRI,
1987; Rehm et al., 1985; USEPA, 1987).
METHOD
APPLICATIONS/ADVANTAGES
LIMITATIONS
HAND AUGERS - A band auger
is advanced by turning it into the
soil until the bucket or screw is
filled. The auger is then removed
from the hole. The sample is
dislodged from the auger, and
drilling continues. Motorized units
are also available.
• Shallow soil investigations (0 to IS ft)
• Soil samples collected from the auger
cutting edge
• Water-bearing zone identification
• Contamination presence examination;
sample analysis
• Shallow, small diameter well installation
• Experienced user can identify stratigraphic
interfaces by penetration resistance
differences as well as sample inspection
• Highly mobile, and can be used in confined
spaces
• Various types (i.e., bucket, screw, etc.) and
sizes (typically 1 to 9 inches in diameter)
• Inexpensive to purchase
• Limited to very shallow depths
(typically < IS ft)
• Unable to penetrate extremely dense
or rocky or gravelly soil
• Borehole stability may be difficult to
maintain, particularly beneath the
water table
• Potential for vertical cross-
contamination
• Labor intensive
SOLID-FLIGHT AUGERS -- A
cutter head (2 2-inch diameter) is
attached to multiple auger flights.
As the augers are rotated by a
rotary drive head and forced down
by either a hydraulic pulldown or a
feed device, cuttings are rotated up
to ground surface by moving along
the continuous flighting.
• Shallow soils investigations (< 100 ft)
• Soil samples are collected from the auger
flights or using split-spoon or thin-walled
samplers if the hole will not cave upon
retrieval of the augers
• Vadose zone monitoring wells
• Monitor wells in saturated, stable soils
• Identification of depth to bedrock
• Fast and mobile; can be used with small
rigs
• Holes up to 3-ft diameter
• No fluids required
• Simple to decontaminate
• Low-quality soil samples unless split-
spoon or thin-wall samples are taken
• Soil sample data limited to areas and
depths where stable soils are
predominant
• Unable to install monitor wells in
most unconsolidated aquifers
because of borehole caving upon
auger removal
• Difficult penetration in loose
boulders, cobbles, and other material
that might lock up auger
• Monitor well diameter limited by
auger diameter
• Cannot penetrate consolidated
materials
• Potential for vertical cross-
contamination
HOLLOW-STEM AUGERS -
Hollow-stem augering is done in a
similar manner to solid-flight
augering. Small-diameter drill rods
and samplers can be lowered
through the hollow augers for
sampling. If necessary, sediment
within the hollow stem can be
cleaned out prior to inserting a
sampler. Wells can be completed
below the water table using the
augers as temporary casing.
• All types of soil investigations to < 100 ft
below ground
• Permits high-quality soil sampling with
split-spoon or thin-wall samplers
• Water-quality sampling
• Monitor well installation in all
unconsolidated formation
• Can serve as a temporary casing for coring
rock
• Can be used in stable formations to set
surface casing
• Can be used with small rigs in confined
spaces
• Does not require drilling fluids
• Difficulty in preserving sample
integrity in heaving (running sand)
forsaations
• If water or drilling mud is used to
control heaving will invade the
formation
• Potential for cross-contamination of
aquifers where annular space not
positively controlled by water or
drilling mud or surface casing
• Limited auger diameter limits casing
size (typical augers are: 6Vt-\n OD
with 3V4-in ID, and 12-in OD with 6-
in ID)
• Smearing of clays may seal off
interval to be monitored
-------
9-9
Table 9-3. Drilling methods, application, and limitations (modified from Aller et al., 1989; GRI,
1987; Rehm et al.; 1985; USEPA, 1987).
METHOD
APPLICATION&>ADVANTAGES
LIMITATIONS
DIRECT MUD ROTARY -
Drilling fluid is pumped down the
drill rods and through a bit
attached to the bottom of the rods.
The fluid circulates up the annular
space bringing cuttings to the
surface. At the surface, drilling
fluid and cuttings are discharged
into a baffled sedimentation tank,
pond, or pit. The tank effluent
overflows into a suction pit where
drilling fluid is recirculated back
through the drill rods. The drill
stem is rotated at the surface by
top head or rotary table drives and
down pressure is provided by pull-
down devices or drill collars.
Rapid drilling of clay, silt, and reasonably
compacted sand and gravel to great depth
(>700 ft)
Allows split-spoon and thin-wall sampling
in unconsolidated materials
Allows drilling and core-sampling in
consolidated rock
Abundant and flexible range of tool sizes
and depth capabilities
Sophisticated drilling and mud programs
available
Geophysical borehole logs
• Difficult to remove drilling mud and
wall cake from outer perimeter of
filter pack during development
• Bentonite or other drilling fluid
additives may influence quality of
ground-water samples
• Potential for vertical cross-
contamination
• Circulated cutting samples are of
poor quality; difficult to determine
sample depth
• Split-spoon and thin-wall samplers
are expensive and of questionable
cost effectiveness at depths > ISO ft
• Wireline coring techniques for
sampling both unconsolidated and
consolidated formations often not
available locally
• Drilling fluid invasion of permeable
zones may compromise integrity of
subsequent monitor well samples
• Difficult to decontaminate pumps
AIR ROTARY - Air rotary drilling
is similar to mud rotary drilling
except that air is the circulation
medium. Compressed air injected
through the drill rods circulates
cuttings and groundwater up the
annulus to the surface. Typically,
rotary drill bits are used in
sedimentary rocks and down-hole
hammer bits are used in harder
igneous and metamorphic rocks.
Monitor wells can be completed as
open hole intervals beneath
telescoped casings.
Rapid drilling of semi-consolidated and
consolidated rock to great depth (>700 ft)
Good quality/reliable formation samples
(particularly if small quantities of drilling
fluid are used) because casing prevents
mixture of cuttings from bottom of hole
with collapsed material from above
Allows for core-sampling of rock
Equipment generally available
Allows easy and quick identification of
lithologic changes
Allows identification of most water-bearing
zones
Allows estimation of yields in strong water-
producing zones with short "down time"
• Surface casing frequently required to
protect top of hole from caving
• Drilling restricted to semi-
consolidated and consolidated
formations
• Samples reliable, but occur as small
chips that may be difficult to
interpret
• Drying effect of air may mask lower
yield water producing zones
• Air stream requires contaminant
filtration
• Air may modify chemical or
biological conditions; recovery time
is uncertain
• Potential for vertical cross-
contamination
• Potential exists for hydrocarbon
contamination from air compressor
or down-hole hammer bit oils
AIR ROTARY WITH CASING
DRIVER - This method uses a
casing driver to allow air rotary
drilling through unstable
unconsolidated materials.
Typically, the drill bit is extended 6
to 12 inches ahead of the casing,
the casing is driven down, and then
the drill bit is used to clean
material from within the casing.
• Rapid drilling of unconsolidated sands,
silts, and clays
• Drilling in alluvial material (including
boulder formations)
• Casing supports borehole, thereby
maintaining borehole integrity and reducing
potential for vertical cross-contamination
• Eliminates circulation problems common
with direct mud rotary method
• Good formation samples because casing
(outer wall) prevents mixture of caving
materials with cuttings from bottom of hole
• Minimal formation damage as casing pulled
back (smearing of silts and clays can be
anticipated)
• Thin, low pressure water-bearing
zones easily overlooked if drilling not
stopped at appropriate places to
observe whether or not water levels
are recovering
• Samples pulverized as in all rotary
drilling
• Air may modify chemical or
biological conditions; recovery time
is uncertain
-------
9-10
Table 9-3. Drilling methods, applications, and limitations (modified from Aller et al., 1989; GRI,
1987; Rehm et al., 1985; USEPA, 1987).
METHOD
AmJCATlONS/ADVANTACES
LIMITATIONS
DUAL-WALL REVERSE
ROTARY - Circulating Quid (air
or water) is injected through the
annulus between the outer casing
and drill pipe, flows into the drill
pipe through the bit, and carries
cuttings to the surface through the
drill pipe. Similar to rotary drilling
with the casing driver, the outer
pipe stabilizes the borehole and
reduces cross-contamination of
fluids and cuttings. Various bits
can be used with this method.
• Very rapid drilling through both
unconsoiidated and consolidated formations
• Allows continuous sampling in all types of
formations
• Very good representative samples can be
obtained with reduced risk of
contamination of sample and/or water-
bearing zone
• Allows for rock coring
• In stable formations, wells with diameters
as large as 6 inches can be installed in open
hole completions
• 1 imitrd borehole size that limits
Avanetrr of monitor Wells
« In unstable formations, well
diameters are limited to
approximately 4 inches
• Equipment available more common
in the southwest U.S. than elsewhere
• Air may modify chemical or
biological conditions; recovery time
is uncertain
• Unable to install filter pack unless
completed open hole
CABLE TOOL DRILLING - A
drill bit is attached to the bottom
of a weighted drill stem that is
attached to a cable. The cable and
drill stem are suspended from the
drill rig mast. The bit is
alternatively raised and lowered
into the formation. Cuttings are
periodically removed using a
bailer. Casing must be added as
drilling proceeds through unstable
formations.
• Drilling in all types of geologic formations
• Almost any depth and diameter range
• Ease of monitor well installation
• Ease and practicality of well development
• Excellent samples of coarse-grained media
can be obtained
• Potential for vertical cross-contamination is
reduced because casing is advanced with
boring
• Simple equipment and operation
• Drilling is slow, and frequently not
cost-effective as a result
• Heaving of unconsoiidated materials
must be controlled
• Equipment availability more common
in central, north central, and
northeast sections of the U.S.
ROCK CORING -- A carbide or
diamond-tipped bit is attached to
the bottom of a hollow core barrel.
As the bit cuts deeper, the rock
sample moves up into the core
tube. With a double-wall core
barrel, drilling fluid circulates
between the two walls and does
not contact the core, allowing
better recovery, dean water is
usually the drilling fluid. Standard
core tubes are attached to the
bottom of a drill rod and the
entire string of rods must be
removed after each core run.
With wireline coring, an inner core
barrel is withdrawn through the
drill string using an overshot
device that is lowered on a wireline
into the drill string.
Provides high-quality, undisturbed core
samples of stiff to hard clays and rock
Holes can be drilled at any angle
Can detect location and nature of rock
fractures
Can use core boles to run a complete suite
of geophysical logs
Variety of core sizes available
Core holes can be utilized for hydraulic
tests and monitor well completion
Can be adapted to a variety of drill rig
types and operations
• Relatively expensive and slow rate of
penetration
• Can lose a large quantity of drilling
water into permeable formations
• Potential for vertical cross-
contamination
-------
9-11
Table 9-3. Drilling methods, applications, and limitations (modified from Aller et al., 1989; GRI,
1987; Rehm et al., 1985; USEPA, 1987).
METHOD
APPLICATIONS/ADVANTAGES
LIMITATIONS
CONE PENETROMETER -
Hydraulic rams are used to push a
narrow rod (04., 1-5-inch
diameter) with a conical point into
the ground at a steady rate.
Electronic sensors attached to the
test probe measure tip penetration
resistance, probe side resistance,
inclination and pore pressure.
Sensors have also been developed
to measure subsurface electrical
conductivity, radioactivity, and
optical properties (fluorescence
and reflectance). Cone
penetrometer tests (CPT) are
generally performed using a special
rig and a computerized data
collection, analysis, and display
system. To facilitate interpretation
of CPT data bom numerous tests,
CPT data from at least one test
per site should be compared to a
log of continuously sampled soil at
an adjacent location.

References: Robertson and
Campanella (1966), Lurk et al.
(1990), Smolley and Kappmeyer
(1991), Christy and Spradlin
(1992), Edge and Cordry (1989),
and, Chiang et al. (1992).
Efficient tool for ttratigrapnic logging of
soft soils
Measurement of some soil/Quid properties
(e.g., tip penetration resistance, probe side
fraction, pore pressure, electrical
conductivity, radioactivity, fluorescence),
with proper instrumentation, can be
obtained continuously rather than at
intervals; thus improving the detectability
of thin layers (i.e., subtle DNAPL capillary
barriers) and contaminants
There are virtually no cuttings brought to
the ground surface, thus eliminating the
need to handle cuttings
Process presents a reduced potential for
vertical cross-contamination if the openings
are sealed with grout from the bottom up
upon rod removal
Porous probe samplers can be used to
collect groundwater samples with minimal
loss of volatile compounds
Soil gas sampling can be conducted
Fluid sampling from discrete intervals can
be conducted using special tools (e.g., the
Hydropunch1" manufactured by Q.E.D.
Environmental Systems of Ann Arbor,
Michigan)
Unable to penetrate dense geologic
conditions (i.e., hard clays, boulders,
etc.)
Limited depth capability (depends on
• Soil samples cannot be collected
for examination or chemical
analyses, unless special equipment
is utilized
Only very limited quantities of
groundwater can be sampled
Limited well construction capability
Limited availability
-------
9-12
Auger
connection
Flighting^
Cutter head
Screw Auger Bucket Auger

(a)
Rod to cap
adapter
Auger
connector
(b)
Auger
connector
Auger
head
Replaceable
carbide insert
auger tooth
Cone
penetrometer -
rod
Side friction-
sensor
CP test probe
(1)
Tip penetration
resistance sensor
Pump
Borehole-\
wall
|/-Casing
pit
Cuttings circulated
- to surface through
casing

-Tricone
bit
Air supply

Top-head
drive

Mast
Casing
driver
Discharge
for cuttings
Casing
Drill pipe
r Drive
shoe
-Drill
^ bit
(0
Figure 9-2. Schematic diagrams of several boring methods: (a) screw and bucket augers, (b) solid stem auger,
(c) hollow-stem auger, (d) cone penetrometer test probe, (e) mud rotary, and (f) air rotary with a
casing driver (reprinted with permission, EPRI, 1985).
-------
9-13

Table 9-4. Borehole and well annulus grout types and considerations (modified from Aller et al, 1989; Edil et al,
1992).
BENTONTTE AND BENTONTTE-CEMENT GROUTS: Bentonite is a hydrous aluminum silicate comprised primarily of montmorilkmite
clay. The volume of bydrated bentonite in water is typically 10 to IS times greater than that of dry bentonite because water is incorporated
within the expanding clay lattice. The low permeability and expansion of bentonite in water are desirable properties for sealing abandoned
boreholes and well annular spaces. Bentonite grouts are best prepared using mechanical mixers and should be pumped under pressure in
place from the base of the interval to be grouted through a Iremie pipe. Bentonite grouts should be mixed in batches so that they can be
pumped before becoming too viscous. Bentonite grout should not be placed in the vadose zone because it will dry, shrink, and fracture.
Bentonite grout may also shrink and fracture in the presence of hydropbobic NAPLs. Several available bentonite grout types are described
below.

Bentonite Slurry Grant is commonly prepared by mixing dry bentonite powder in fresh water at a ratio of 15 Ibs of bentonite to 7 gallons of
water to make 1 ft3 of slurry. Thick slurries may gel prematurely and be impossible to emplace. Due to their low solids content, bentonite
slurries tend to settle as liquid bleeds off, requiring the emplacement of more slurry.

Quick-Gel® BcntonUe Drilling Mod Grout is slurry of sodium bentonite and water that is marketed primarily as a drilling mud. Grouts of
varying viscosity and strength can be obtained by mixing different proportions of Quick Gel*, water, and sand. Slurries containing sand
appear more stable than pure Quick Gel*. Edil et al. (1992) found that Quick Gel* slurries of different sand content and viscosity form
poorer annulus seals than neat cement, cement-bentonite, and Benseal* -bentonite slurry grouts.

Volclay® Bentonite Powder Grout is a commercial bentonite-based clay grout that is formulated for sealing boreholes and well annular
spaces. Edil et al. (1992) mixed 2.1 Ibs of Volclay* per gallon of water and added 2 Ibs of magnesium oxide powder as a setting inhibitor to
each 50 Ibs of Volclay* slurry. They determined that Volclay* grout has a stiff gel structure which adheres to PVC but not steel well
casing; and that it is not as effective a well sealant as neat cement, cement-bentonite, and Benseal9 -bentonite slurry grouts.

Benseal® - Benlonlte Slurry Grout is a mixture of Benseal9, a granular nondrilling mud grade bentonite developed for use in sealing and
grouting well casings, and bentonite powder with water. Edil et al. (1992) mixed 30 Ibs of Natural Gel* (a natural, unaltered bentonite
powder) with 100 gallons of water, and then used a venturi pump to mix in 125 Ibs of Benseal* to the slurry. They found that this grout
adheres to steel and PVC casing, has low permeability, good swelling characteristics, and flexibility, and is an excellent sealant.

Bentonite-Cement Grout is a slurry incorporating 5 to 6 gallons of water and 2 to 6 Ibs of bentonite powder for each 94 Ibs (1 ft3) of
Portland cement. Bentonite improves the workability of the cement slurry, reduces slurry density, and reduces grout shrinkage during setting.
Edil et al. (1992) found the addition of 5 Ibs of bentonile per 94 Ibs of cement forms a rigid well annulus seal with low permeability and high
durability; and that the grout adheres to steel casing, but appeared to allow some infiltration along the grout-PVC casing interface.

Benlonlte Pellets can be used to seal borehole or well annulus intervals. Wet pellets, however, tend to stick to well casing and borehole walls,
and bridge high above their intended placement depth. A tamper can be used to break up bridges, but this technique becomes ineffective at
depths greater than approximately 20 ft. Pellets can be frozen using refrigeration or liquid nitrogen to increase their fall distance.
PORTLAND CEMENT: Neat cement is a mixture of Portland cement (ASTM C-150) and water in the proportion of 5 to 6 gallons of clean
water per bag (94 Ibs or 1 ft3) of cement. Five types of Portland cement are produced: Type I for general use; Type II for moderate sulfate
resistance of moderate heat of hydration; Type III for high early strength; Type IV for low heat of hydration; and Type V for high sulfate
resistance. Type I is most widely-used in well construction or hole abandonment. A typical 14 Ib/gallon neat cement slurry with a mixed
volume of IVi ft3 will have a set volume of 1.2 ft3, reflecting a 17% shrinkage. The setting time ranges from 48 to 72 hrs depending primarily
on water content.

Common additives include: (1) 2 to 6% bentonite to reduce shrinkage, improve workability, reduce density, and produce a lower cost per
volume of grout; (2) 1 to 3% calcium chloride to accelerate the setting time and thereby create higher early strength, of particular value in
cold climates; (3) 3 to 6% gypsum to produce a quick-setting very hard cement that expands upon setting; (4) <1% aluminum powder to
produce a quick-setting strong cement that expands upon setting; (5) 10 to 20% ftyash to increase sulfate resistance and provide early
compressive strength; (6) hydroxylated carboxytic acid to retard setting time and improve workability without compromising set strength; and
(7) diatomaceous earth to reduce slurry density, increase water demand and thickening time, and reduce set strength.

Edil et al. (1992) found neat cement grout forms a rigid seal with low permeability and high durability that adheres fairly well to steel and
PVC casing. Kurt and Johnson (1982), however, report that neat cement annular seals are subject to channeling between the casing and
grout due to temperature changes during curing, swelling and shrinkage during curing, and poor bonding between the ground and casing.
Cement shrinkage can produce fractures, thereby degrading the integrity of the grout seal. Cement slurries can infiltrate the well sandpack,
particularly if well development occurs prior to when the cement has completely set. Thus, a minimum of 1 to 2 ft of filter pack is usually
extended in the annulus above the top of the well screen. The high heat of cement hydration can compromise the integrity of thermoplastic
casing. Cement is a highly alkaline substance with a pH that ranges from 10 to 12. This can alter groundwater pH.
-------
9-14
Unconsolidated media sampling methods are described by
Davis et al. (1991), Aller et al. (1989), Clark (1988a),
GRI (1987), USEPA (1987), Driscoll (1986), Rehm et al.
(1985), Acker (1974), USDI (1974), ASTM (1990a),
Zapico et al. (1987), Clark (1988b), Ostendorf et al.
(1991), McElwee et al. (1991), Starr and Ingleton (1992),
and Christy and Spradlin (1992). High-quality soil
sampler method descriptions, advantages, and limitations
are provided in Table 9-5. Diagrams depicting several
samplers are shown in Figure 9-3.

Soil samples submitted for chemical analysis are
frequently collected using split-spoon samplers. Typically,
soil from the inner portion of the core is removed from
the spoon and placed in a sample jar containing air. This
procedure may result insignificant loss of volatile organic
compounds (VOCs) from the soil sample during storage
and handling (WCGR, 1991). For example, an analytical
laboratory log of a soil sample taken this way at the Love
Canal DNAPL site in Niagara Falls, New York (New
York State Department of Health, 1980) notes "oily film
found in desiccation crack although it evaporated
quickly."

The loss of VOCs can be reduced by storing samples in
VOA vials, and minimized by placing samples in jars
containing methanol followed by analysis of the solvent
(WCGR, 1991). Care must be taken to avoid exposure of
the methanol to contaminated materials (other than the
soil sample) or air. Trichloroethene concentrations
detected in soils that were stored in wide-mouth jars with
air and in jars with methanol are compared in Table 9-6
(WCGR, 1991). The data show that storing soil in ajar
with air may result in a significant underestimation of
VOC concentrations. Volatile loss can also be minimized
by sealing the ends of core barrel samplers and submitting
sealed samples directly to the laboratory (Cherry and
Feenstra, 1991). Finally, samples should be kept
refrigerated, analyzed quickly, and not agitated to limit
volatile loss.
9.4 ROCK SAMPLING

Bedrock drilling and sampling are conducted to
characterize the extent of contamination in the
subsurface. Drilling in rock is primarily accomplished
using rotary and coring methods (Table 9-3; Figure 9-2).
Drilling method references are given in Chapter 9.3.
Bedrock characteristics which should be considered for
logging are listed in Table 9-2.
Drilling in rock typically poses a significantly greater risk
of promoting vertical DNAPL movement than drilling in
unconsolidated media. This is due to the brittle and
heterogeneous, fractured nature of rocks. Fracture
networks in rock are usually ill-defined. Similarly, the
distribution of DNAPL in rock fractures is typically
difficult to predictor characterize (Figure 5-8a). Factors
to consider when evaluating the distribution of DNAPL
in rock fractures include: (1) fracture orientations,
spacings, and apertures, (2) DNAPL density, viscosity, and
interfacial tension, (3) DNAPL release volume, (4) the
DNAPL pool height driving density flow, and (5)
hydraulic gradients. When drilling in rock, DNAPL can
enter and exit the borehole unpredictably via fractures
and drilling may create or widen fractures in the near-well
environment. Where possible, drilling through bedrock
contaminated with DNAPL should be avoided. Where
drilling is necessary, the risk minimization strategies listed
in Chapter 9.2 should be implemented as practicable.

An example protocol for characterizing fractured bedrock
at DNAPL sites is that utilized at the S-Area Landfill
CERCLA site in Niagara Falls, New York (Conestoga-
Rovers and Associates, 1986). The drilling sequence for
coring, hydraulic testing, and grouting the LockPort
Dolomite is illustrated in Figure 9-4 and adapted with
slight modification from Conestoga-Rovers and Associates
(1986) below.

(1) At each bedrock survey well location, the overburden
will be penetrated using a hollow-stem auger drill rig
as follows:

(a) Drilling at each location will advance to the
bedrock/overburden interface taking continuous
split-spoon samples of the overburden materials.
The augers will penetrate to refusal on
competent bedrock. Eight-inch ID augers will be
required for this operation. Once the augers are
seated on top of the rock,the auger plug will be
advanced an additional 6 inches into the rock to
create a pilot hole for the 6-inch diameter
permanent steel casing.

(b) A clean six-inch diameter permanent steel casing
(1A to Vi inch wall thickness) will be inserted
through the augers (or through a temporary
casing) and will be seated and properly scaled
into the top of the bedrock so as to ensure that
no overburden groundwater has access to the
borehole. Seating and sealing of permanent
casing into the top of the bedrock will be
-------
9-15
Table 9-5. Soil sampler descriptions, advantages, and limitations (modified from Acker, 1974; Rehm et al.,
1985 Aller et al., 1989).
METHOD DESCRIPTION
ADVANTAGES
UMTTATIONS
SPLIT-SPOON (SPLIT-BARREL) SAMPLERS
The Standard Penetration Test procedure for
driving a split-spoon sampler to obtain a
representative soil sample and a measure of soil
penetration resistance is described by ASTM Test
Method D1586-S4. The split-spoon sampler is 18
to 30 inches long with a lV4-inch ID and made of
steel. It is attached to the end of drill rods,
lowered (typically through a hollow-stem auger) to
the bottom of the borehole which must be dean,
and then hammered into the undisturbed soil by
dropping a 140-lb weight a distance of 30 inches
onto an anvil that transmits the impact to the drill
rods. The number of blows required to drive the
sampler each 6-inch interval is counted to
determine penetration resistance. Continuous or
noncontinuous samples can be taken, and various
other split-barrel diameter sizes are available.
These samplers can also be pushed into the ground
rather than hammered.
High quality samples can be
evaluated for mineralogical,
stratigraphic, physical, and
chemical properties
Steel, brass or plastic liners
can be used with split-spoon
samplers so that samples can
be jested to minimi?^ changes
in sample chemical and
physical conditions prior to
delivery to a laboratory
Relatively inexpensive
Widely available
Hammering creates a stress that can
consolidate and alter the sample
Sample transfer from the split spoon
can result in disaggregation of
cohesionless soil
Sample handling exposes soil to
atmosphere and may result in loss of
volatile chemicals
Cannot penetrate rock, cobbles, and
some gravels
Poor recovery of some loose or
flowing cohesionless samples
(although sample retainers can be
used to minimize this problem)
THIN-WALL (SHELBY) OPEN-TUBE SAMPLERS
Open-tube thin-wall samplers consist of a connector
bead and a 30 or 36 inch long thin-wall steel,
aluminum, brass, or stainless steel tube which is
sharpened at the cutting edge. The wall thickness
should be less than 2Yi% of the tube outer
diameter, which is commonly 2 or 3 inches. The
sampler is attached via its connector bead to the
end of drill rods, lowered (typically through a
hollow-stem auger) to the bottom of the borehole
which must be clean, and then pushed down into
the undisturbed soil using the hydraulic or
mechanical pulldown of the drill rig. This
procedure is described by ASTM Method D1S87-
83. The Central Mining Company (CME) recently
developed a S-ft long continuous thin-wall sampling
system. The tube is kept in place by a latching
mechanism that allows the sample to be retracted
by wireline when full and replaced with an empty
tube.
• Provides undisturbed samples
in stiff, cohesive soils and
representative samples in soft
to medium cohesive soils
• High quality samples can be
evaluated for mineralogical,
stratigraphic, physical, and
chemical properties
• Sample can be preserved and
stored within the sample tube
by sealing its ends, thereby
minimizing sample
disturbance prior to lab
analysis
• Widely available
• Relatively inexpensive
The sampler should be at least six
times the diameter of the longest
particle size to minimize disturbance
of the sample
Large gravel or cobbles can disturb
the finer grained soil within which
they are embedded and/or can
damage the sampler walls
Due to thin wall and limited
structural strength, the sampler
cannot be easily pushed into dense or
consolidated materials
Generally not effective for
cohesionless soils
THIN-WALL PISTON CORE SAMPLERS
These samplers consist of a thin-wall tube, with an
internal piston, and mechanisms to control
movement between the piston and tube. Thin-wall
piston samplers are typically set up and pushed into
the ground in the same manner as thin-wall open-
tube samplers. The internal pistons generate a
vacuum on the sample as the sampler is withdrawn
from the hole. Starr and Ingleton (1992) recently
developed a drive point piston sampler to collect
high quality core samples of sands, silts, and clays
without drilling fluids or a drilling rig to a depth of
approximately 30 ft.
• Provides undisturbed samples
in cohesive soils, silts, and
sands above or below the
water table
• Vacuum enables recovery of
cohesionless soils
• High quality samples can be
evaluated for mineralogical,
stratigraphic, physical, and
chemical properties
• Sample can be preserved and
stored within the sample tube
by sealing its ends, thereby
minimising sample
disturbance prior to lab
analysis
As with open-tube sampler, large
particles may disturb sample or
damage sampler walls and the
sampler cannot be easily pushed into
dense or consolidated materials
If used with a clam shell fitted auger
head, only 1 sample can be obtained
per borehole because the dam shell
will not dose after being opened;
continuous sampling not possible
Some piston samplers require use of
drilling fluid for hydrostatic control
Not as widely available as split-spoon
or open-tube samplers
Relatively expensive
CORE BARREL SAMPLERS (see ROCK
CORING description in Table 9-3)
See ROCK CORING advantages
in Table 9-3
See ROCK CORING limitations in
Table 9-3
-------
Head assembly -
Split barrel .
Spacer,
Shoe
" Liner
- Head assembly
• Cap screw
• Tube
Upper drive
head with left
threaded pin
Piston cable
Hardened drive
shoe
Schematic
Inner core barrel
"(dedicated)
. Outer core barrel
Pision with ruooer
washers & brass
''spacers
bearings
Inrwr H""9e'
JV lube ^""^
„<..„ assembly
" Reaming
Os
(a)
(b)
(c)
Figure 9-3. Schematic diagrams of a (a) split-spoon sampler, (b) thin-wall open-tube sampler, and (c) thin-wall piston sampler used to obtain
undisturbed soil samples; and of a (d) double-tube core barrel used to obtain rock core (modified from Aller et al., 1989).
-------
9-17
Table 9-6. Comparison of trichloromethene (TCE) concentrations determined after storing soil samples
in jars containing air versus methanol; showing apparent volatilization loss of TCE from
soil placed in jars containing air (from WCGR, 1991).
SPUT-SPOON SAMPLE PLACED JK WIDE-MOUTH JAR
CONTAINING AIR AND 'THEN SUB-SAMPLED,
EXTRACTED, AND ANALYZED
Sumpfe Depth (ft BCS)
5.0 - 7.0
20.0-20.5
30.0-30.5
TCE Ooceolration (me/Kg)
2.2
9.2
<0.022
BPUT«SPOON SAMPLE PLACED IN WIDE-MOUTH JAR
CONTAINING METHANOL TO PRESERVE VOLATILES
AND SUBSEQUENT ANALYSIS OF THE SOLVENT
Sunpk Depth (II BGS)
7.0
20.0
30.0
TCE Concentration (»*/K«)
3,100
420
210
-------
OVERBURDEN
6"t STEEL
CASINO
IS* INTERVALS
CEMENT/BENT ONITE
OROUT SUPPLY
PIPE
INFLATABLE
PACKER
BEDROCK
NX CORE BARREL
NX CORE LOCKPORT IN 15'
INTERVALS. ONCE INTERVAL
IS COMPLETED, PUMP 1.5
TIMES THE VOLUME OF
WATER INJECTED £»
CONDUCT I HOUR
PUMP/PACKER TEST
INSERT PACKER £. PRESSURE
GROUT PREVIOUSLY TESTED
INTERVAL ALLOWING GROUT
TO SET OVERNIGHT.
r
OVERBURDEN
—OROUT
— 40 STEEL CASING
- CEMENT/BENTONITE
OROUT SUPPLY PIPE
BEDROCK

• INFLATABLE PACKER
GASPORT

MEMBER
OVERBURDEN
• 4" t STEEL CASINO
VO
i
^^
oo
IS* INTERVALS
ONCE SET, ENLARGE
GROUTED INTERVAL TO
6'0. ONCE ENLARGED,
PRESSURE TEST
INTERVAL. IF FAILURE
OCCURS RE-GROUT
INTERVAL. CONTINUE
CORING, PUMP TESTING,
GROUTING (A REAM
SEQUENCE UNTIL TOP
OF GASPORT MEMBER
IS CONTACTED.
ONCE GASPORT MEMBER
IS MET INSTALL 4"0
STEEL CASING USING
INFLATABLE PACKER TO
PRESSURE GROUT CASING
IN PLACE.
AFTER GROUT SET,
CONTINUE CORING £.
PUMP TESTING TO TOP
OF ROCHESTER SHALE.
Figure 9-4. The drilling sequence for coring, hydraulic testing, and grouting through the Lockport Dolomite utilized at the Occidental
Chemical Corporation S-Area DNAPL site in Niagara Falls, New York (from Conestoga-Rovers and Associates, 1986).
-------
9-19
completed as shown in Figure 9-5 and described
below

(i) Seat the casing into the top of rock taking
care to center the casing,

(ii) Insert an inflatable packer through the 6-
inch diameter casing to within 12 inches of
the bottom of the hole and pump grout
under pressure through the packer via the
drill rod and into the annular space
between the casing and the auger/temporary
casing inside wall. Continue pumping
grout until it is observed at ground surface.
As grouting progresses, remove the augers
(or temporary casing) from the permanent
casing, and add grout as required. All
grout will be placed using positive
placement procedures. Upon completion
of grouting, the casing will be tapped firmly
into the pilot hole using the 140 Ib
hammer.

(iii) The materials required to grout wells shall
consist of Portland cement and clean water.
Hydrated lime may be ridded to facilitate
placing of the grout mixture. Bentonite
will be necessary to reduce shrinkage. All
additives will be added in accordance with
ASTM standards. Cement grout placed to
seal the annular space between permanent
well casing and an oversized hole shall be
mixed in the proportion of not less than
five or more than six gallons of water to
one 94-lb bag of cement. Hydrated lime
(ten percent by volume) may be needed to
facilitate pumping and bentonite (3% by
volume) will be needed to prevent
shrinking.

(iv) The packer will be released and the grout
will be allowed to set for 48 hours before
drilling continues.

(v) The grout seal will be tested by conducting
a hydraulic test modified from USDI (1974,
p.575). After drilling through the grout
until rock is encountered, the casing is
filled with water. The water-level decline,
AH, from the top of the casing is measured
over a five minute period. The seal shall
be regrouted if the water level declines by
more than that calculated by
AH = (5.5 K H t) / (IT r)
(9-1)
where H is the head of water applied (top
of casing minus initial water-level), r is the
casing radius, t is the teat duration, and K
is the allowable grout hydraulic conductivity
(IX 10-5 cm/sec). Any consistent units
may be used.

(c) All drilling rods used in the overburden materials
will be cleaned prior to the bedrock coring
operation to prevent cross-contamination from
the overburden into bedrock.

(2) Drilling of the Lockport Dolomite will be carried out
in 15-ft increments to facilitate testing of the bedrock
formation. The drilling sequence will be completed
as shown in Figure 9-4 and described below.

(a) Collect continuous NX rock core (3-inch OD
hole, 2.2-inch OD core) of the top 15-ft bedrock
internal. The drill water will be spiked with an
approved tracer (see 2c).

(b) Insert a high volume pump (10 gpm minimum) to
remove 1 to 1 Vi. times the volume of water
introduced to the formation during the coring
operation.

(c) Insert a packer/pump assembly as shown in
Figure 9-6. Inflate the packer and pump test the
15-ft bedrock interval for one hour. Collect a
groundwater sample for chemical analysis if
interval yields £ 0.3 gpm during the last 15
minutes of the test. The sample will also be
analyzed for the drill water tracer to account for
dilution effects in the analytical results.

(d) Remove the packer/pump assembly and insert a
packer system 2 ft above the top of the tested
bedrock interval and pressure grout the interval.
Grouting pressure will not be allowed to exceed
0.7 psi per foot of overlying earth. The cement
will be quick set cement (type 3 with accelerator)
and allowed to set overnight. In cases where an
interval yielded < 0.3 gpm during the last 15
minutes of the 1 hour pump test, grouting will be
optional. Control samples of the grout will be
observed to document the quality of the set.
-------
OVERBURDEN
SPLIT SPOON SAMPLER
112"0.0. AUGERS
•4IZ"0 BOREHOLE
6 0STEEL CASINO
OVERBURDEN
CEMENT/BENTONITE
GROUT SUPPLY PIPE
—± I2"O.D. AUGER REMOVAL
BOREHOLE
6"0 PERMANENT
STEEL CASINO
INFLATABLE PACKER

"> GROUT
BEDROCK
6 PILOT BORING BEDROCK
Auger and continuous
split spoon to top of
competent bedrock.
Once to top of competent
bedrock, install 6"-diameter
steel casing inside augers
to top of bedrock.
Install inflatable packer inside 6"-diameter steel casing
(within 12" of bottom of hole), inflate, and commence
pumping grout through the packer, forcing grout to ground
surface. Remove augers adding grout as required to
maintain continous grout envelope. Once all augers have
been removed, seat 6"-diameter casing into rock by
driving with 140 Ib. hammer until refusal.
Figure 9-5. Overburden casing installation procedure utilized prior to drilling into the Lockport Dolomite at the Occidental Chemical
Corporation S-Area DNAPL site in Niagara Falls, New York (from Conestoga-Rovers and Associates, 1986).
-------
9-21
'

r
OJ
"tJ
s
ro
-------
9-22
After the set time, the grout will be drilled out
using 6-inch diameter enlarging tools and flushed
for one minute or until clear water return is
observed. The 15-ft interval will be pressure
tested. The test will consist of installing and
inflating a packer at the top of the previously
tested interval and applying a constant head of
water on the sealed interval. The water loss must
be less than that calculated by (USDI, 1974,
p.576)
Q = (2 IT K L H) / ln(L/r)
(9-2)
where Q is the constant rate of flow into the
hole, K is the maximum allowable hydraulic
conductivity (IX10"5 cm/see), L is the length of
the test interval, H is the differential head of
water, and r is the radius of the tested interval.
If the interval fails this teat, it will be regrouted
and retested.

(e) Remove the pressure testing assembly and core
an additional 15 ft of bedrock.

(!) Packer/pump test this 15-ft bedrock interval.
Continue coring, pump testing, groundwater
sampling, grouting, and pressure testing in 15-ft
intervals through the upper more permeable
portion of the Lockport Dolomite down to the
top of the Gasport Member of the formation.

(g) Once the top of the Gasport Member has been
contacted, a 4-inch diameter black steel casing
will be inserted into the borehole and grouted
into place using the procedure outlined for
overburden casing installation.

(h) Once the grout has set, the coring and testing
will continue in 15-ft increments to the top of the
Rochester Shale Formation. When available, all
hydraulic test and chemical analysis data will be
evaluated to select the appropriate interval in the
lower Lockport Dolomite for completing a
permanent monitor well.

(i) If NAPL is encountered in the borehole, a
decision will be made to:

(i) continue to test and grout in accordance
with the plan;
(ii) grout the borehole and attempt to
complete the testing in a nearby boring, or,

(iii) grout the borehole and assume that NAPL
extends to the top of the Rochester Shale
Formation.

Results of the bedrock drilling program at the S-Area site
(Conestoga Rovers and Associates, 1988) were presented,
in part, on geologic cross sections as exemplified in
Figure 9-7. Although the drilling and testing protocols
developed for S-Area and other chemical waste sites in
Niagara Falls were designed to minimize the potential for
cross-contamination, the extent to which DNAPL
migration might have been facilitated by drilling is
unknown.

If DNAPL is observed in fractures of cores obtained
during drilling, samples can be placed in jars and
submitted to a laboratory for extraction and analysis. For
determination of non-volatile DNAPL components,
WCGR (1991) suggests using a solvent-soaked gauze pad
to wipe the NAPL-contaminated fracture surface and then
submitting the gauze pad to a laboratory for extraction
and analysis.
9.5 WELL CONSTRUCTION

Monitor wells are installed to characterize immiscible
fluid distributions, flow directions and rates, groundwater
quality, and media hydraulic properties. Pertinent data
are acquired by conducting fluid thickness and elevation
surveys, fluid sampling surveys, hydraulic tests, and
borehole geophysical surveys. The locations and design
of monitor wells are selected based on consideration of
the site conceptual model and specific data collection
objectives.

Well construction methods and concerns are discussed in
numerous references, including Nielsen and Schalla
(1991), Aller et al. (1989), Barcelona et al. (1983, 1985),
USEPA (1986, 1987, 199la), ASTM (1990b), Driscoll
(1986), GeoTrans (1989), Cambell and Lehr (1984), and
NWWA (1981). These documents provide detailed
information on: drilling techniques, well design, well
materials (casing, screen, sandpack, sealant, and grout),
well construction/ installation methods, and well
development. Details of multiple-level monitoring
systems that can be installed in a single drill hole are
discussed by Ridgeway and Larssen (1990), Cherry and
-------
C

WEST

9901
WATERBEARING ZONE
SITE SPECIFIC PARAMETERS EXCEEDED
WATERBEARING ZONE
GENERAL PARAMETERS EXCEEDED
WATERBEARING ZONE
NO PARAMETERS EXCEEDED
NON-WATERBEARING ZONE
NAPL NOT DETECTED
WATERBEARING ZONE
NON-S-AREA NAPL DETECTED
C'

EAST

590
LOCKPOHT
GROUP
CLINTON
GROUP
GEOLOGIC CROSS-SECTION C-C1
S-AREA REMEDIAL INVESTIGATION
Occidental Chemical Corporation
Figure 9-7. Results of the Lockport Dolomite characterization program at the S-Area DNAPL site reflect heterogeneous subsurface
conditions (from Conestoga Rovers and Associates, 1988). The non-S-Area DNAPL detected at depth in Well OW207-87 has
different chemical and physical properties than S-Area DNAPL, and is believed to derive from another portion of the Occidental
Chemical Corporation plant site (Conestoga-Rovers and Associates, 1988).
-------
9-24
Johnson (1982), Black et al. (1986), Korte and Kearl
(1991), and Welch and Lee (1987).

The design and construction of wells at DNAPL sites
require special consideration of (1) the effect of well
design and location on immiscible fluid movement and
distribution in the well and near-well environment (2)
the compatibility of well materials with NAPLs and
dissolved chemicals; and (3) well development options.

Inadequate well design can increase the potential for
causing vertical DNAPL migration and misinterpretation
of fluid elevation and thickness measurements. Although
much theoretical and experimental research has been
conducted to examine the relationship between LNAPL
presence in wells and formations (Mercer and Cohen,
1990; van Dam, 1967; Zilliox and Muntzer, 1975; Schiegg,
1985; Abdul et al., 1989; Fiedler, 1989; Farr et al., 1990;
Kemblowski and Chiang, 1990; Lenhard and Parker, 1990;
Hampton, 1988; Hampton and Miller, 1988; de Pastrovich
et al., 1979), relatively little work has focused on
interpreting measurements of DNAPL thickness and
elevation in wells. Adams and Hampton (1990)
conducted physical model experiments to evaluate the
effects of capillarity on DNAPL thickness in wells and
adjacent sands. Based on their experiments, field
experience, and the principles of DNAPL movement, it is
apparent that several factors may cause the elevation and
thickness of DNAPL in a well to differ from that in
formation and/or lead to vertical DNAPL migration.
These factors include the following.

• If the well screen or casing extends below the top of a
DNAPL barrier layer, the measured DNAPL thickness
may exceed that in the formation by the length of the
well below the barrier layer surface (Mercer and
Cohen, 1990) as shown in Figure 9-8.

• If the well bottom is set above the top of a DNAPL
barrier layer, the DNAPL thickness in the well may be
leas than the formation thickness as shown in Figure 9-
9.

• If the well connects a DNAPL pool above a barrier
layer to a deeper permeable formation, the DNAPL
elevation and thickness in the well are likely to be
erroneous and the well will cause DNAPL to short-
circuit the barrier layer and contaminate the lower
permeable formation as shown in Figure 9-10. The
height of the DNAPL column at the well bottom will
tend to equal or be less than the critical DNAPL
height, ZB, required to overcome the capillary resistance
offered by the sandpack and/or formation (Adams and
Hampton 1990; Chapter 5.1).

• NAPL which enters a coarse sandpack may sink to
the bottom of the sandpack rather than flow through
the well screen (Figure 9-1 1). Small quantities of
DNAPL may elude detection by sinking down the
sandpack and accumulating below the base of the well
screen.

• Similarly, if the bottom of the well screen is set above
the bottom of the sand pack and there is no casing
beneath the screen, small quantities of DNAPL may
elude detection by sinking out the base of the screen
and into the underlying sandpack as shown in Figure 9-
12.

• Sand packs generally should be coarser than the
surrounding media, however, to ensure that mobile
DNAPL can enter the well. Screen or sandpack
openings that are too small may act as a capillary
barrier to DNAPL flow (Figure 9-13).

• If the well screen is located entirely within a DNAPL
pool and water is pumped from the well, DNAPL will
upcone in the well to maintain hydrostatic equilibrium
causing the DNAPL thickness in the well to exceed
that in the formation as shown in Figure 9-14 (Huling
and Weaver, 1991; Villaume, 1985).

• The elevation of DNAPL in a well may exceed that in
the adjacent formation by a length equivalent to the
DNAPL-water capillary fringe height where the top of
the pool is under drainage conditions (WCGR, 1991;
Adams and Hampton, 1990) as shown in Figure 9-15.

• DNAPL will not flow into a well where it is present at
or below residual saturation or at negative pressure.

As demonstrated above, the relationship of the well
screen to mobile DNAPL and capillary barriers can
govern the thickness of DNAPL in a well and the
potential for vertical DNAPL migration in the well
environment. A well that is completed to the top of a
capillary barrier and screened from the capillary barrier
surface to above the DNAPL-water interface is most
likely to provide DNAPL thickness and elevation data
that are representative of formation conditions.
Consideration must be given to the risks and the risk-
minimization strategies listed in Chapter 9.2 during well
design and construction activities.
-------
9-25
MEASURED DNAPL THICKNESS > POOL THICKNESS
Figure 9-8. The measured thickness of DNAPL in a well may exceed the DNAPL pool thickness by the length of
the well below the barrier layer surface (after Ruling and Weaver, 1991).
MEASURED DNAPL THICKNESS < POOL THICKNESS
Figure 9-9. The measured DNAPL thickness in a well may be less than the DNAPL pool thickness by the distance
separating the well bottom from the capillary barrier layer upon which DNAPL pools.
-------
9-26
WELL CROSS-CONTAMINATION: DNAPL THICKNESS
AND ELEVATION MEASUREMENTS POTENTIALLY MISLEADING
DNAPL
New DNAPL pool
Figure 9-10. DNAPL elevation and thickness measurements in a well are likely to be misleading where the well is
screened across a capillary barrier with perched DNAPL.
DNAPL SINKS TO BASE OF COARSE SANDPACK
Figure 9-11. DNAPL that enters a coarse sandpack may sink to the bottom of the sandpack rather than flow through
the well screen and thereby, possibly escape detection.
-------
9-27
DNAPL SINKS THROUGH WELL AND SANDPACK
Thin
DNAPL-I
Figure 9-12. DNAPL that enters a well from above may flow out of the base of the well screen and into the
underlying sandpack (or formation).
FINE-GRAINED SANDPACK RESISTS DNAPL ENTRY
4 4
.Thin DNAPL pool *
Figure 9-13. Sandpacks should be coarser than the surrounding media to ensure that the sandpack is not a capillary
barrier to DNAPL movement.
-------
9-28
DNAPL UPCONING DUE TO GROUNDWATER PURGING
Figure 9-14. Purging groundwater from a well that is screened in a DNAPL pool will result in DNAPL upconing in
the well (after Huling and Weaver, 1991).
DNAPL RISE IN WELL DUE TO CAPILLARY PRESSURE
Waste Pit
Residual!
Top of DNAPL pool is
undergoing drainage
DNAPL
pool
Figure 9-15. The elevation of DNAPL in a well may exceed that in the adjacent formation by a length equivalent to
the DNAPL-water capillary fringe height where the top of the DNAPL pool is undergoing drainage
(invasion by DNAPL) (after WCGR, 1991).
-------
9-29
The compatibility of well materials with NAPLs and
highly contaminated groundwater should also be
evaluated during well design (Nielsen and Schalla, 1991;
Aller et al, 1989; Driscoll, 1986; Barcelona et al., 1983,
1985). Advantages and disadvantages of different casing
and screen materials are summarized in Table 9-7. Steel
casing is generally recommended where DNAPLs,
particularly halogenated solvents, may be present because
of its strength and chemical resistance to solvents. Steel,
however, is susceptible to corrosion caused by long-term
exposure to groundwater with low pH, hydrogen sulfide
present, or high concentrations of dissolved oxygen (>2
mg/L), carbon dioxide ( >50 mg/L), or chloride ( >500
mg/L) (Aller et al., 1989). Stainless steel generally
provides better resistance to corrosion than carbon steels.
Another potential drawback of steel casing is that
hydrophobic organic liquids may preferentially wet steel
(Arthur D. Little, Inc., 1981) and result in vertical
DNAPL migration along the outside of well casings that
are not adequately sealed with grout. Fluoropolymeric
(Teflon) and fiberglass materials are also resistant to
organic solvents, but lack the strength of steel. The high
cost of fluoropolymers also limits their widespread use.
Halogenated solvents can degrade PVC and ABS
thermoplastics. These materials should not be used for
well construction where they will come into contact with
halogenated solvents.

Well annular seals are composed of several different
stable and low hydraulic conductivity materials. The
composition and characteristics of various sealant grouts
are given in Table 9-4 and discussed by Edil et al. (1992),
Aller et al. (1989), Nielson and Schalla (1991), Driscoll
(1986), and Barcelona et al. (1983, 1985). As described
in Chapter 9.3.2, hydrophobic organic liquids may cause
bentonite to shrink and fracture, and its use, therefore,
may be inappropriate at DNAPL sites (except perhaps as
a minor component grout additive).

Monitor wells are typically developed after construction
to remove fine grained particles and drilling fluid residues
from the borehole and near-well environment. Various
well development methods, including overpumping,
backwashing, mechanical surging, and high velocity
jetting, are discussed by Aller et al. (1989), GeoTrans
(1989), Kraemer et al. (1991), and Driscoll (1986). Well
development should be limited in wells containing
DNAPL to gentle pumping and removal of fine particles
to minimize DNAPL redistribution. Measurements
should be made of immiscible fluid stratification in the
well prior to and after development.
9.6 WELL MEASUREMENT OF FLUID THICKNESS
AND ELEVATION

Fluid elevation and thickness measurements are made in
wells to assist determination of fluid potentials, flow
directions, and immiscible fluid distributions. With
knowledge of DNAPL entry areas, the surface slope of
capillary barriers, hydraulic data, and other observations
of DNAPL presence, well data can be evaluated to infer
the directions of DNAPL migration. Interpretation of
fluid data from wells containting NAPL may be
complicated by several factors related to the measurement
method, fluid properties, well design, or well location
(Chapter 9.5). DNAPL in wells, therefore, should be
evaluated in conjunction with evidence of geologic
conditions and DNAPL presence obtained during drilling.

Methods for acquiring groundwater level data are
reviewed by Dalton et al. (1991), EPRI (1989), USEPA
(1986), and Ritchey (1986). Techniques for measuring
immiscible fluid elevations and thicknesses in wells
(Mercer and Cohen,1990; Ruling and Weaver, 1991; API,
1989; GRI, 1987; Sanders, 1984) are summarized below.

While conducting immiscible fluid level and thickness
measurements, care should be taken to slowly lower and
raise the measuring device within the well to avoid
disturbing the immiscible fluid equilibrium and creating
emulsions. Similarly, measurements should be made prior
to purging activities. The cost of purchase and
decontamination of the measuring device should be
considered when selecting a measurement method,
particularly given uncertainties involved in interpreting
NAPL thickness and elevation data.
9.6.1 Interface Probes

Most interface probes employ an optical device to
distinguish the air-fluid interface and a conductivity
sensor to distinguish NAPL-water interfaces (Sanders,
1984). These probes are typically 1 to 1% inches in
diameter, 9 inches long, and attached to a tape guide that
is sequentially marked in 0.01 or 0.05 ft increments.
Interface probes should be slowly lowered to the well
bottom and then raised to survey the distribution of
immiscible fluids within a well. Different audible signals
are emitted upon contact with NAPL (e.g., a continuous
tone) and water (e.g., an intermittent tone).

Under ideal conditions, interface probes can be used to
detect NAPL layers that are as thin as 0.01 ft, and
-------
9-30

Table 9-7. Advantages and disadvantages of some common well casing materials (modified from
Driscoll, 1986; GeoTrans, 1989; and Nielsen and Schalla, 1991).
TYPE
ADVANTAGES
DISADVANTAGES
FLUOROPOLYMERS
tucfa as porytetrafluoro-
ethyene (PTFE), tetra-
fluoroethyiene (TFE), and
fluorinated ethylene
propylcne (FEP)
Excellent cfaemical resistance to organic
chemicals and corrosive environments;
practically insoluble in all organic liquids
except a few fluorinated solvents
Lightweight
High impact strength
Lower tensile strength and wear resistance
compared to other plastics, iron, or steel
Expensive relative to steel and other plastics
THERMOPLASTICS:
POLYVINYLCHLORIDE
(PVC) AND
ACRYLONITRILE
BUTADIENE STYRENE
(ABS)
Lightweight
Easy workability (with threaded couplings)
Inexpensive compared to Quoroporymen and
steel
Resistant to alcohols, aliphatic hydrocarbons,
weak and strong alkalies, oils, strong mineral
acids, and oxidizing acids
Completely resistant to galvanic and
electrochemical corrosion
High strength-to-weight ratios, and resistant
to abrasion
More reactive than PTFE
Poor chemical resistance to aromatic
hydrocarbons, esters, ketones, and organic
solvents
Much lower tensile, comprcssive, and
collapse strength than steel or iron
May adsorb or elute trace organic*
PVC glues, if used, may contribute organic
chemicals to well water
STAINLESS STEEL
such as Type 304 and
Type 316
Stronger, more rigid, and less iemperature-
sensitive than plastic materials
Good chemical resistance to organic
chemicals
Resistant to corrosion and oxidation
Readily available
Expensive
May catalyze some organic chemical
reactions
May corrode if exposed to long-term
corrosive conditions and leach chromium
Heavy
CARBON STEEL
Stronger, more rigid, and less temperature-
sensitive than plastic materials
Less expensive than stainless steel or teflon
Expensive
Rusts easily, providing high sorptive and
reactive capacity for many metals and
organic chemicals
Subject to corrosion (under conditions of
low pH, high dissolved oxygen, H^S
presence, > 1000 mg/L total dissolved
solids, > 50 mg/L CO^ or > 500 mg/L CT
Heavy
GALVANIZED STEEL
Stronger, more rigid, and less temperature-
sensitive than plastic materials
Expensive
Will rust if galvanized coating is scratched
Resistance to corrosion provided by zinc
coating may be short-lived
May be source of zinc
Heavy
-------
9-31
measure NAPL layer thickness to within 0.01 to 0.10 ft.
A comparison of LNAPL thickness measurements made
using an interface probe, hydrocarbon gauging paste, and
a bailer in Table 9-8 evidences the utility of an interface
probe. Interface probes, however, may produce spurious
results in the presence of conductive NAPLs, emulsified
NAPL, or viscous NAPL that coats the sensors. To
minimize the latter problem, the air-fluid interface is best
measured by lowering the probe from air into fluid to
avoid the effects of dripping fluid when raising the probe
through the air-fluid interface. Similarly the NAPL-water
interface is best measured by lowering or raising the
probe from water into NAPL to minimize the problem of
NAPL coating the conductivity sensor which would
increase the measured NAPL thickness (Sanders, 1984).
Standard electric line water-level probes can detect
interfaces between non-conductive NAPL and water, but
may fail to identify interfaces between LNAPL and air.

Interface probes are expensive (typically $900 to $2000)
and widely available (e.g., see the Ground Water
Monitoring Review Annual Buyers Guide Summer issue).
9.6.2 Hydrocarbon-Detection Paste

Hydrocarbon-detection paste changes color within
seconds upon contact with liquid hydrocarbons. For
DNAPL measurement, a thin film of hydrocarbon-
detection paste can be applied to the bottom of a
measuring tape, gauge line, or rod that is lowered to the
well bottom. Upon retrieval, the DNAPL column depth
and thickness will be revealed by the zone of paste color
change. If there is LNAPL floating on the water column,
all of the paste that is lowered into the fluid column will
change color, thereby preventing measurement of DNAPL
at the well bottom.

Water-detection paste that changes color upon contact
with water can be used to measure the thickness of NAPL
floating on the water column in a well. A thin film of the
water-detection paste is applied to the bottom of a tape,
gauge line, or rod that is lowered to below the expected
base of the floating product layer, retrieved, and then
inspected to determine the depth to and thickness of the
floating NAPL.

Detection paste methods may provide NAPL thickness
measurements that are accurate to within 0.01 ft under
favorable conditions (API, 1989; Testa and Paczkowski,
1989). Tests conducted by Sanders (1984) suggest that
this method tends to overestimate NAPL thickness (Table
9-8). Measurements made using these pastes are slow
relative to use of an interface probe. If the paste is
applied to a disposable weighted string or wire, however,
the time and cost associated with equipment
decontamination may be eliminated.

Hydrocarbon- and water-detection pastes cost
approximately $1 to $2 per ounce. Numerous
measurements can be made per ounce. According to a
detection paste manufacturing representative (Kolor Kut
Products Company, Houston, Texas), detection paste
compositions are propriety and include no hazardous
ingredients.
9.6.3 Transparent Bailers

Transparent bottom-loading bailers can be used to
measure NAPL thickness in a well. For DNAPL
thickness measurement, the bailer is gently lowered to the
well bottom and then raised back to the surface. The
thickness of DNAPL in the well can be estimated by
measuring the DNAPL column height in the bailer. If
the thickness exceeds the bailer length, then additional
samples must be taken using a bailer or other method to
determine the top of the DNAPL column. The additional
sampling, however, should not be made until the DNAPL
returns to equilibrium in the well. NAPL rise due to
displacement by the bailer may result in slight
overestimation of its thickness in a well. Alternatively,
leakage from the bottom of the bailer while it is being
raised may result in an underestimation of DNAPL
thickness. For floating NAPL, the bailer should be long
enough so that its top is in air when its check valve is in
water. Care should be taken to ensure that an
equilibrium height of LNAPL has entered the bailer
before lowering it into the water layer.

Transparent bottom-loading PVC bailers (1.66 inch
diameter) cost approximately $40, $50, and $70 apiece for
2,3, and 5-ft lengths, respectively. Disposable bailers can
be obtained for less.
9.6.4 Other Methods

Various other methods are available to estimate DNAPL
thickness and elevations in wells. For example,
measurements can be made by taking small fluid samples
from specific depths using either an inertial lift pump
(e.g., Waterra Pumps Ltd, Toronto, Ontario), a peristaltic
-------
9-32
Table 9-8. Comparison of measured LNAPL thicknesses using water-detection passte, a clear bottom-
loading bailer, and an interface probe (from Sanders, 1984).
Measurement Method
Water Detection paste on a
stick*
Clear bottom-loading
baiter"
Interface probe***
3 Incite* Gasoline
Aw.
{tad»*>
3.60
Z58
3.18
Standard
Deviation
0.21
0.16
0.11
1 Inch Gasoline
Ave.
(iaeheft)
138
0.82
1.14
Standard
Deviation
0.13
0.13
0.11
3 Inches Kerosene
Ave.
(tocbtt)
336
Z46
3.12
Standard
Deviation
027
0.18
0.08
t Inch Kerosene
Ave.
(Indies)
1.12
0.80
1.10
Slandaid
Deviation
0.75
0.12
0.12
Notes: Ave. means average. Five tests were conducted with each method and Quid thickness.
'Gauging stick - 8-ft Bagby Stick Co.; McCabe, Inc. water-detection paste.
"Surface sampler - 1%-inch OD, 12-inches long, bottom-loading bailer.
"*ORS interface probe (manufacture date circa 1984).
-------
9-33
pump, or a discrete-depth mechanical (Kemmerer type)
sampler; or by measuring the length of DNAPL (if it
contrasts visually with water) that coats a weighted string
that has been retrieved from the bottom of a well.
9.7 WELL FLUID SAMPLING

Fluid sampling surveys should be conducted at potential
DNAPL sites to examine wells for the presence of
LNAPLs and DNAPLs. NAPL samples can be tested for
physical properties and chemical composition (Chapter
10). Well sampling methods are described in numerous
references (i.e., Herzog et al., 1991; Barcelona et al, 1985,
1987; USEPA, 1986, 1987, 1991a; GRI, 1987; Rehm et al.,
1985).

Prior to sampling, immiscible fluid stratification should be
measured in wells as described in Chapter 9.6. Various
sampling devices can be employed to acquire fluid
samples from the top and bottom of the well fluid
column. Villaume (1985) recommends use of a bottom-
loading bailer or mechanical discrete-depth sampler for
collecting DNAPL samples. Huling and Weaver (1991)
suggest that the best DNAPL sampler is a double check
valve bailer which should be slowly lowered to the well
bottom and then slowly raised to provide the most
reliable results. DNAPL can be sampled from wells with
a shallow water table (<25 ft deep) with a peristaltic
pump and from depths to approximately 300 ft using a
simple inertial pump (e.g., Waterra Pumps Ltd, Toronto,
Ontario; Rannie andNadon, 1988). An advantage of the
peristaltic and inertial pumps is that fluid contact is
confined to inexpensive tubing (and a foot-valve with the
inertial pump). The cost to decontaminate or replace
DNAPL-contaminated equipment is usually a major
factor in selecting a sampling method (Mercer and
Cohen, 1990).
9.8 ASSESSING DNAPL MOBILITY

Goals of DNAPL site characterization include
determining the extent of mobile DNAPL and the
feasibility of DNAPL containment and recovery options.
Monitoring DNAPL levels in wells over time may provide
evidence of DNAPL mobility (Hiding and Weaver, 1991).
DNAPL mobility can also be assessd based on: (1)
observations and measurements of DNAPL saturation in
subsurface media samples and (2) DNAPL pumping
experiments. DNAPL containment and recovery pumping
methods and considerations are described in Table 6-1.
At many sites, DNAPL migration from a release location
may cease at residual saturation or be immobilized in a
stratigraphic trap within days to weeks. Factors which
may cause DNAPL to flow slowly and therefore remain
mobile for longer periods include relatively low DNAPL
viscosity and media permeability. Long-term mobility is
also promoted where large quantities of DNAPL have
been released to the subsurface and where there is an
ongoing or episodic release (e.g., a leaking tank or drums
that rupture periodically in a landfill). Finally, increased
hydraulic gradients, a fluctuating water table, and
increased DNAPL wetting of the porous medium with
time possibly due to mineral surface chemistry
modifications, may cause remobilization of stagnant
DNAPL. As such, slow long-term migration of DNAPL
is possible at some sites.
9.9 BOREHOLE GEOPHYSICAL METHODS

The application of borehole geophysical methods to
groundwater investigations is described by Keys and
MacCary (1976), Keys (1988), Benson (1991), Driscoll
(1986), GRI (1987), Guyod (1972), Rehm et al. (1985),
Cambell and Lehr (1984), Michalski (1989), and USEPA
(1987). Borehole geophysical surveys involves lowering a
logging tool, also known as a sonde, down a well or
boring to make physical measurements as a function of
depth (Figure 9-16). A sensing element within the sonde
measures the property of interest and converts it into
electrical signals. These signals are transmitted to the
surface through a cable and recorded digitally or by using
an analog strip chart. Several types of geophysical log
may be made, sometimes simultaneously, in the same
borehole.

Borehole geophysical surveys are conducted to
characterize lithologies, correlate stratigraphy between
borings, identify fracture zones, estimate formation
properties (e.g., porosity and density), identify intervals
containing conductive dissolved contaminants, etc. The
utility and limitations of various techniques are
summarized in Table 9-9 and example logs are shown in
Figure 9-17. These methods provide continuous high-
resolution measurements of subsurface conditions. As
such, they can be used to distinguish thin layers and
subtle stratigraphic features which may influence
contaminant movement.

The use of geophysical surveys at DNAPL contamination
sites is discussd by WCGR (1991) and Annan et al.
(1991). Sequential borehole surveys were made before,
-------
9-34
RECORDER DRIVE
CABLE-MEASURING SHEAVE
A.C.
POWER
SOURCE
REGULATED
RECORDER
DEPTH
INDICATOR
SIGNAL CONDITIONING
ZERO POSITIONING
SENSITIVITY
TIME CONSTANT
ETC.
DOWNHOLG
POWER
(NOT UNIVERSAL)
LOGGING
SPEED AND
DIRECTION
LOGGING CONTROLS
Figure 9-16. Schematic diagram of borehole geophysical well logging equipment (from Keys and
MacCary, 1976)
-------
Table 9-9. Utility and limitations of borehole geophysical methods for site characterization (modified from Benson, 1991; Rehm et al., 1985;
Keys and MacCary, 1971).
METHOD
Electrical
Resistivity
Spontaneous
Potential (SP)
Natural
Gammma
Gamma
Gamma
(Density)
Neutron-
Neutron
(Porosity)
EM Induction
UTILITY
Electrical resistivity logs record apparent electrical resistivity as a function
of depth within the saturated zone. The voltage drop due to the electrical
resistance of the formation fluids and media is measured using two current
and two potential electrodes. Several tools with different electrode spacing*
are commonly utilized to evaluate stratigraphy (i.e., clay content and
fracture density) and fluid conductivity (i.e., high ionic strength
contaminated groundwater). Resistivity logs are used by the petroleum
industry to evaluate water and oil saturations. High resistivity in porous
sands may reflect NAPL presence.
Spontaneous potential logs measure natural potential differences between
the borehole fluid and adjacent media. SP logs are used to help
characterize and correlate stratigraphy (layer type, thickness, etc.).
Natural gamma logs measure the amount of natural gamma radiation
emitted along the length of the borehole. The natural gamma-emitting
radioisotopes (K-40 and daughter products of thorium and uranium decay)
are preferentially adsorbed in clay and shale layers. The natural gamma
log, therefore, is primarily used to reveal the presence of clay and shale
layers (i.e., DNAPL capillary barriers).
Gamma gamma logs measure the response of media adjacent to the boring
to gamma radiation that is emitted from a radiation source in the logging
tool. The amount of radiation detected is inversely related to formation
density. Formation porosity can be calculated using the gamma gamma log
if the formation bulk density is known.
The neutron logging tool contains a radiation source and detector. The
detector output is proportional to the water content (hydrogen content) of
the borehole environment. Neutron logs can provide estimates of moisture
content in the vadose zone, total porosity in the saturated zone, the water
table elevation, and the rate of fluid infiltration.
EM induction logs record the bulk electrical conductivity of the near
borehole environment are used, in conjunction with other data, to identify
lithology, correlate stratigraphy, and infer fluid conductance. Highly
conductive (high ionic strength) zones of contaminated groundwater can be
identified using this method. Additionally, thick intervals with high organic
NAPL saturation may be revealed as low conductivity anomalies.
Can method be used hi foUowing
conditions?
Caning
Dncased/FVC/Steel
Yes/No/No
Yes/No/No
Yes/Yes/Yes
Yes/Yes/Yes
Yes/Yes/Yes
Yes/Yes/No
Saturated
Unsatarated
Yes/No
Yes/No
Yes/Yes
Yes/Yes
Yes/Yes
Yes/Yes
Radius of
Measurement
12-60"
Near
borehole
surface
6-12"
6"
6-12"
30"
ABectefHele
Diameter and Mad
Significant to
minimal depending
on probe used
Significant and
highly variable
Moderate
Significant
Moderate
Negligible
-------
Table 9-9. Utility and limitations of borehole geophysical methods for site characterization (modified from Benson, 1991; Rehm et al., 1985;
Keys and MacCary, 1971).
METHOD
Temperature
Fluid
Conductivity
Flow
Caliper
Video
tmtiw
Temperature logs provide a continuous record of fluid temperature with
depth. Preferential inflow zones may be indicated by an increase or
decrease in groundwater temperature.
A specific conductance probe is used to record fluid conductivity with
depth. This data may be used to assess groundwater conductivity, inflow
zones, contamination zones, etc.
Fluid movement logging utilizes impeller flowmeters, thermal flowmeters,
and various tracer detection systems to measure the groundwater inflow
rate as a function of boring depth. Variation in the groundwater inflow
rate may derive from well construction details, hydraulic head differences,
and/or variable hydraulic conductivity. Most frequently, an impeller-type
flowmeter is used to identify zones of preferential inflow.
Spring-loaded feelers extend from the calipcr logging tool, follow the
borehole wall, and continuously measure the hole diameter. Caliper logs
record the outer diameter of a well or open boring and can be used to
locate fractures and cavities in an open borehole. Caliper logs are also
used to establish correction factors for other measurements influenced by
hole size.
Small-diameter video cameras can be lowered down a borehole to inspect
for casing corrosion, well condition, leaks, fractures zones, etc.
Cut method be wed in foflowtng
conditions?
Casing
Unowed/PVC/Sletl
Yes/No/No
Yes/No/No
Yes/No/No
Yes/Yes/Yes
Yes/Yes/Yes
Srtarated
tlDMterated
Yes/No
Yes/No
Yes/No
Yes/Yes
Yes/Yes
RadtaHoT
MeMBKmeni
Within
borehole
Within
borehole
Within
borehole
To limit of
sensor,
typically 2-3'
Within
borehole
Affect of Hole
Dimeter md Mad
NA
NA
NA
NA
NA
-------
Sponianeoui RivsLvly Resisliv.ty Hydrojeolog* inlerpretilMXt G»mm» Neution log Cahpef
potential mecroiog ud.at.of> rjdul.on d'*me!«t
c
U

30
50
-.60
C
C INTERPRETJTIOH DRILLtR^ LOC
SOIL ANO RIVED
ALLUVIUM
S P
RESISTIVITY
SAND
AND
GRAVEL
TILL
SAND
AND
GRAVEL
TILL OR
CLAY
GRAVELY
CLAY
TILL OR
CLAY
GRAVEL
WITH
SILT OR
CLAY
TILL
OR
CLAY
GRAVEL
WITH
SILT ORCLA
TOP SOIL
STONY
CLEAN,
WATER-
BEARING
GRAVEL
CLAY AND
HARDFKN
GRAVEL,
WATER
BEARING
CLAY AND
HARDPAN
DIRTY
GRAVEL
FRESH
WATER
SANO
FRESH
WATER
SANO
BRACK.
WATER
SANO
SALT
WATER
SANO
THIN CLAY LATER

THIN CLAY LAYE3
VO
(a)
(b)
(c)
Figure 9-17. Examples of borehole geophysical logs: (a) six idealized logs (from Cambell and Lehr, 1984); (b) a gamma log of unconsolidated
sediments near Dayton, Ohio (from Morris, 1972); and (c) an idealized electrical log (from Guyod, 1972).
-------
9-38
during, and after a controlled release of tetrachloroethene
(PCE) at the Borden DNAPL research site (WCGR,
1991). The infiltration of poorly-conductive PCE into the
Borden sand was tracked with some success by EM
induction, resistivity, and neutron logging. Generally,
however, pre-contamination baseline surveys will be
unavailable and subsurface conditions will be more
complex than at the Borden site. High resistivity or low
EM induction values in coarse soil may reflect NAPL
presence. Overall, the potential value of using borehole
geophysical surveys to delineate NAPL presence and
saturation is poorly defined.
9.10 IDENTIFICATION OF DNAPL IN SOIL AND
WATER SAMPLES

Significant cost savings can be realized during a site
investigation if DNAPL presence can be determined
directly by visual examination of soil and groundwater
samples rather than indirectly by more costly chemical
analyses (Chapter 10). Direct and indirect methods for
detecting and/or suspecting the presence of DNAPL in
the subsurface are described briefly in Chapter 7.2 and
Table 7-4, and in more detail below.
9.10.1 Visual Detection of NAPL in Soil and Water

Under ideal conditions, NAPL presence can be identified
by visual examination of soil or groundwater samples.
Direct visual detection may be difficult, however, where
the NAPL is clear and colorless, present at low
saturation, or distributed heterogeneously. There is little
documentation of practical methods to directly identify
NAPL in soil or water (Huling and Weaver, 1991).

Although not well-documented, ultraviolet (UV)
fluorescence analysis and phase separation techniques
such as centrifugation and soil-water shake tests have
been used with varied success to identify NAPL presence
at some contamination sites. Recently, Gary et al. (1991)
demonstrated a method to extract NAPL from soil by
shaking a soil-water suspension with a strip of
hydrophobic porous polyethylene in a glass jar for 3 to 4
hours. Estimates of NAPL content were derived by
gravimetric analysis of the strips before and after the
extinction process. This method is described in Chapter
10.2 and its use at a crude-oil spill site is documented by
Hess et al. (1992).
A series of experiments was conducted by Cohen et al.
(1992) to test the hypothesis that simple and inexpensive
methods can be used to visually identify clear, colorless
NAPL in soil and water samples. The procedures and
findings reported by Cohen et al. (1992) are condensed
below.

Seventy-eight samples were prepared in a random
sequence by adding varying amounts of clear, colorless
NAPL (kerosene, chlorobenzene, or tetrachloroethene)
and water to soil in scalable polyethylene bags. Three
soils were utilized in the experiments: a pale-yellowish
orange (10YR 8/6, Munsell color notation of hue,
value/chroma), well-sorted, subrounded to subangular,
medium quartz sand; a moderate brown (5Y 4/4),
saprolitic silt loam; and, a black (Nl), organic-rich, silt
loam top soil. The quantities of soil and fluid used to
prepare samples were calculated to provide a range of
NAPL saturations from 0.01 to 0.23. Blank samples were
prepared by adding water without NAPL to the soil
sample. For dissolved contaminant samples, water
containing an equilibrium concentration of dissolved
NAPL (derived from water in contact with NAPL) was
introduced to the soil sample. Of the 78 samples: 56
contained NAPL, 11 contained dissolved contaminant
levels, and 11 were blanks.

The soil samples were then examined for NAPL presence
by two investigators who were unaware of the sample
contents using the following procedures (Figure 9-18):

(1) Three minutes after each sample was prepared, the
accumulated organic vapor concentration was
measured using a Flame lonization Detector
(Foxboro Century OVA Model 128 calibrated with
methane) by inserting the FID probe into an opened
comer of the sample bag.

(2) An unaided visual examination was then made
through the sample bags to inspect for NAPL
presence. Examination results were categorized as:
"A" if NAPL was identified as present based on visual
evidence, "B" if NAPL presence was suspected based
on visual evidence; or "C" if there was no visual
evidence of NAPL presence.

(3) An examination was then made of the UV
fluorescence of the samples using an inexpensive,
portable, battery-powered UV light (Raytech
Industries' Versalume™ model; cost » $50). The 4-
watt broad spectrum lamp emits both shortwave UV
(2536 A) and longwave UV (3000 to 4000 A)
-------
9-39
Prepare Sample
OVA Analysis
Unaided Visual Inspection
UV Fluorescence Examination
Soil-Water Shake Test
Centrifugation of Soil-Water Shake Test Suspension
Hydrophobia Dye Soil-Water Shake Test
Centrifugation of Hydrophobic Dye Soil-Water Shake Test Suspension
Figure 9-18. Sequence of NAPL detection procedures utilized by Cohen et al. (1992).
-------
9-40
simultaneously. The examination was made in a dark
room by scanning the sample bag with the UV light.
The bags were manipulated during the examination to
squeeze fluid against the bag beneath the lamp, and
the samples were categorized using the A, B, or C
classification. Examination of samples without NAPL
provided a check on the presence of mineral or shell
fluorescence in the samples.

(4) Following the fluorescence examination,
approximately 20 cm3 of sample was transferred using
a spoon into a 50-mL, polypropylene centrifuge tube.
Twenty mL of water was added to the subsample and
the tube was shaken by hand for approximately 10
seconds to create a soil-water suspension. An
unaided visual inspection was then made for NAPL
presence (A, B, or C rating) by peering through the
tube walls and at the fluid surface.

(5) The subsample was then centrifuged at approximately
1250 rpm for one minute. The subsamples were
inspected as described above and rated for NAPL
presence.

(6) After the centrifuge test, approximately 2 mg (an
amount that would rest on the edge of a toothpick)
of Sudan IV, a nonvolatile hydrophobic dye, was
placed in the centrifuge tube. Sudan IV is a
relatively inexpensive (100 g cost $19 from Aldrich
Chemical Co.), reddish-brown powder that dyes
organic fluids red upon contact, but is practically
insoluble in water at ambient temperatures. Like
many other solvent dyes, Sudan IV is an irritant and
possible mutagen with which skin or eye contact
should be avoided. Although widely used to colorize
NAPL flow experiments (Schwille, 1988, for
example), minimal use has been made of solvent dyes
such as Sudan IV and Oil Red O to detect NAPL in
soil and water at contamination sites. The contents
of the tube were then mixed by shaking manually for
approximately 10 to 30 seconds and examined for
NAPL presence. NAPL presence was rated A, B, or
C, and, a notation of the relative NAPL density and
quantity was made when apparent.

(7) The final step in the soil examination procedure was
to centrifuge the dyed subsample at approximately
1250 rpm for one minute, and then peer through the
tube walls and at the fluid surface to assess NAPL
presence and relative density and quantity.
Examination results are summarized in Table 9-10 and
Figure 9-19 and conclusions regarding the utility of each
examination method are highlighted below.

• OVA Measurement — Analysis of organic vapors in soil
sample headspace is an effective screening procedure
which may be used, in some cases, to infer NAPL
presence. As shown in Figure 9-20, OVA
concentrations for samples containing NAPL ranged
from 60 to >1000 ppm compared to maximum
concentrations of 30 ppm and <20 ppm in dissolved
contamination and blank samples, respectively. The
poor correlation between NAPL saturation and OVA
concentration indicates that OVA measurements
cannot interpreted to estimate NAPL saturation.
Measured organic vapor concentrations are sensitive to
the effective contaminant volatility, sample
temperature, and sample handling.

• Unaided Visual Examination - Identification of clear,
colorless NAPL in soil by unaided visual examination
is very difficult. Using this method, the sample
examiners were unable to determine NAPL presence in
any of the 56 NAPL-contaminated soil samples.

• UV Fluorescence Analysis - Fluorescence refers to the
spontaneous emission of visible light resulting from a
concomitant movement of electrons to higher and
lower energy states when excited by UV radiation.
Many DNAPLs fluoresce (Konstantinova-Schlezinger,
1961) including (1) nearly all aromatic or
polyaromatic hydrocarbons (having one or more
benzene ring) such as coal tar, creosote, and PCBs; (2)
nearly all DNAPL mixtures that contain petroleum
products; (3) many unsaturated aliphatic hydrocarbons
(such as trichloroethene and tetrachloroethene); and,
(4) all unsaturated hydrocarbons with conjugated
double bonds. Note that: unsaturated refers to
hydrocarbons having carbon atoms that are bonded
together by one or more double or triple bonds;
aliphatic hydrocarbons contain carbon chains and no
carbon rings; and conjugated double bonds refer to at
least two double bonds that are separated by only one
single bond. Saturated aliphatic hydrocarbons, such as
carbon tetrachloride and dichloromethane, generally do
not fluoresce unless mixed with fluorescent impurities.
This can result from industrial processes and waste
disposal practices. UV fluorescence has been utilized
for decades by the oil industry to identify petroleum
presence in drill mud, cuttings, and cores. Several
standard examination methods using extractants to
-------
9-41
Table 9-10. Summary of Test Results (Note: A = NAPL presence apparent based on visual examination; B = NAPL
presence suspected based on visual examination; and C = no visual evidence of NAPL presence).
Method
OVA
Headspace
Analysis
using an FID
Unaided
Visual Exam
UV
Fluorescence
Exam
Soil-Water
Shake Test
Exam
Centrifu-
gation Exam
Hydrophobic
Dye Shake
Test Exam
Centrifu-
gation of
Hydrophobic
Dye Shake
Test Sample
Sample categories are based upon estimated NAPL saturations as a
percent. The volume of NAPL mixed with 172 g of soil and sufficient mL
of water to constitute a total fluid content of 35 mL is also given.
Blank
Samples
(No
NAPL)
1.4 - 4.8
ppm(see
Dotes)
0 A
OB
11 C
1 A
IB
9C
OA
1 B
IOC
OA
IB
IOC
OA
OB
11 C
OA
1 B
IOC
Dissolved
Samples
(No
NAPL)
1.4-30 ppm
OA
OB
11C
OA
2B
9C
OA
2B
9C
OA
1 B
IOC
OA
OB
11 C
OA
OB
11 C
1%
(035
mL)
120-
>1000
ppm
OA
OB
11 C
4A
1 B
6C
OA
4B
7C
OA
4B
7C
4 A
2B
5C
5A
1 B
5C
2#>%
(ImL)
50-
>1000
ppm
OA
IB
11 C
9A
1 B
2C
2A
6B
4C
2A
5B
5C
8A
1 B
3C
9A
2B
1 C
5.71%
(2mL)
60-
>1000
ppm
OA
3B
8C
9A
1 B
1 C
OA
9B
2C
4A
3B
4C
10 A
OB
1 C
11 A
OB
OC
11.43%
(4mL)
100-
>1000
ppm
OA
6B
5C
11 A
OB
OC
2A
SB
1 C
6A
1 B
4C
11 A
OB
OC
11 A
OB
OC
22£6%
(8mL)
65-
>1000
ppm
OA
7B
4C
11 A
OB
OC
3A
7B
1 C
3A
4B
4C
11 A
OB
OC
11 A
OB
OC
Notes and Conclusions
1. An effective screening method which may be used, in
some cases, to infer NAPL presence.
2. Organic vapor concentration depends on contaminant
volatility: measured concentrations were much higher in
chterobenzeae and PCE samples than kerosene samples.
3. Two Wank samples had OVA concentrations of <10
and <20 ppm due to residual vapors from prior
samples.
1. Unable to identify presence of colorless NAPL.
2. NAPL presence was suspected in some samples with
higher NAPL saturation based on fluid sudsiness.
1. Very effective simple test for fluorescent NAPLs.
2. One false positive in 22 blank or dissolved samples.
3. Only 3 false negatives in 45 samples with estimated
NAPL saturations between 1% and 23%.
4. Sensitivity depends on fluorescent intensity of NAPL:
at low NAPL saturations, kerosene and chlorobenzene
were easier to detect than tetrachloroethene.
5. Greater visual contrast evident between milky while
fluorescence and darker soils.
6. Adding more water to the contaminated soil sample
improved the detectability of NAPL in some cases by
bringing more fluorescent fluid to the polybag wall.
1. Difficult to positively identify clear, colorless NAPL.
2. At relatively high saturations (between 1% and 23%),
NAPL presence was usually suspected based on fluid
characteristics at the fluid-air interface.
3. As a result, colorless LNAPL (kerosene) was easier to
detect than colorless DNAPL (chlorobenzene and
tetrachloroethene) using the shake test.
1. Fairly effective for identification of LNAPL (kerosene),
but not DNAPLs, based on fluid characteristics at the
fluid-air interface.
2. Seventeen false negatives in 45 samples with estimated
NAPL saturations between 1% and 23%; only 15
positive NAPL identifications in these 45 samples.
1. Very effective simple test.
2. No false positives in 22 blank or dissolved samples.
3. Identified NAPL presence in 40 of 45 samples with
estimated NAPL saturations >1%. False negatives
recorded in only 4 of these 45 samples.
4. Dye coloration obvious even in black topsoil samples.
5. NAPL density relative to water was correctly
determined in 21 samples and misjudged in 1 sample.
6. Can be used to estimate quantity of NAPL in sample.
1. Slight enhancement of hydrophobic dye shake test.
2. No false positives in 22 blank or dissolved samples.
3. Identified NAPL presence in 42 of 45 samples with
estimated NAPL saturations >1%. False negative
recorded in only 1 of these 45 samples.
4. NAPL density relative to water was correctly
determined in 43 samples and misjudged in 3 samples.
5. Can be used to estimate quantity of NAPL in sample.
-------
a
CTQ
I
O
—b
2
C-
fD
O
=
=
s
O
C-
n
O
sr
a
n
JD
Q.

<0
CO
0)
.0
Unaided
Visual
UV
Fluorescence
Soil-Water
Shake
Test
Centrifu-
gation
Hydrophobic
Dye Shake
Test
Centrifugation
of the Dye
Shake Test
LEGEND:
Correct determination
of NAPL presence
or absence
NAPL suspected
present when
it was present
NAPL suspected
present when
it was absent
-------
9-43
-0 A - -e
• Chlorobenzene
O Kerosene

A Tetrachloroethene
0 Blank
5 10 15 20

% NAPL Saturation
Figure 9-20. OVA concentrations plotted as a function of NAPL type and saturation (from Cohen et
al, 1992). OVA measurements shown as 1000 ppm are actually > 1000 ppm. Dissolved
contaminant samples are treated as 0% NAPL saturation samples.
-------
9-44
leach cuttings within a UV lamp metal viewing box (a
fluoroscope) are described by Swanson (1981) and
Halliburton Co. (1981).

UV fluorescence examination proved to be a simple
and very effective method for identifying the presence
of fluorescent NAPLs in dark soils. The fluorescence
of each NAPL type was milky white. Due to the
greater visual contrast of milky fluorescence against
darker soils, this method was much more effective with
the moderate brown silt loam and black silt loam
samples than with the pale-yellowish orange medium
sand samples. Overall, UV fluorescence was somewhat
less effective than the hydrophobic dye methods
(Figure 9-19 and Table 9-10). The addition of water to
some soil samples enhanced the ability to detect NAPL
fluorescence.

1 Soil-Water Shake Test — Shaking soil with water in ajar
can be used to detect NAPL where sufficient visual
contrast exists between the NAPL soil, and water (as
was demonstrated by the hydrophobic dye shake test).
However, the examiners were only able to positively
identify NAPL in 7 of the 56 soil samples
contaminated with clear, colorless NAPLs. In 34 of the
56 NAPL-contaminated samples, NAPL presence was
suspected at the fluid-air interface based on distinctive
fluid characteristics of floating LNAPL (kerosene) or
DNAPL held by surface tension. This was most
apparent in samples containing relatively large LNAPL
(kerosene) saturations.

1 Centrifugation -- Centrifugation of soil samples mixed
with water was an effective method for identifying
clear, colorless LNAPL (kerosene) based on fluid
characteristics at the fluid-air interface, but was
ineffective for identifying DNAPL (chlorobenzene and
tetrachloroethene). Its utility probably could have
been enhanced by using a syringe needle to extract
fluid from the top and bottom of the fluid column in
the centrifuge tube for further inspection.

Hydrophobic Dye Soil-Water Shake Test -- Mixing a tiny
amount of hydrophobic dye (Sudan IV) with NAPL-
contaminated soil and water proved to be a simple and
effective means for identify ing the presence of NAPLs
in soil, particularly in the medium sand samples. This
method allowed for determination of NAPL density
relative to water and estimation of NAPL volume in
many samples. Comparison of visual estimates of
NAPL volume (or saturation) with actual
measurements (such as described by Gary et al., 1991)
may provide a basis for "calibrating" visual estimates

• Centrifugation of Hydrophobic Dye Shake Test
Suspension — Centrifugation of the hydrophobic dye
shake teat samples provided some enhancement of
NAPL detectability (Figure 9-19), and, like the
hydrophobic dye shake teat, was particularly effective
with the medium sand samples. Overall, this combined
procedure provided the most accurate results of the
visual methods tested to determine NAPL presence in
soil.

The ease of determining NAPL presence in soil is directly
related to the magnitude of visual contrast between
NAPL, water, and soil. Cohen et al. (1992) recommend
that dye shake tests be conducted in plastic containers
(e.g., polypropylene tubes) because hydrophobic NAPLs
generally wet plastic better than glass, thereby enhancing
NAPL detection on the container wall. The visual
contrast afforded by using hydrophobic dye to tint NAPL
red is generally greater than that provided by UV
fluorescence and much greater than that associated with
the interfacial characteristics of colorless immiscible
fluids. Of the methods tested, therefore, the hydrophobic
dye techniques, followed by UV fluorescence, most
facilitated the determination of NAPL presence in the
soil samples.

After completing the soil testing program, 0.05 mL of
kerosene, chlorobenzene, and tetrachloroethene were
added individually to 40 mL of water in three 50 mL
centrifuge tubes. A blank sample was prepared using 40
mL of water and no NAPL The samples were visually
examined after: (a) the initial mixing, (b) Centrifugation
at 1250 rpm for one minute; (c) adding approximately 2
mg of Sudan IV dye; and, (d) Centrifugation of the dye-
fluid mix at 1250 rpm for one minute.

During the unaided visual examination of the water
samples, the presence of NAPL was suspected in each of
the three samples with NAPL but not in the blank, due
to the contrast of fluid characteristics at the fluid-air
interface. Phase separation caused by Centrifugation
eliminated this contrast and the visual evidence of NAPL
presence. Mixing hydrophobic dye with the samples
instantaneously revealed the presence and density relative
to water of the 0.05 mL of kerosene, chlorobenzene, and
tetrachloroethene present in the three contaminated 40
mL samples (volumetric NAPL content = O. 125%).
Subsequent Centrifugation separated the dyed NAPL from
-------
9-45
the clear water, thereby facilitating determination of the
volumetric NAPL to water ratio in a graduated centrifuge
tube.

Of the methods tested, the hydrophobic dye methods,
followed by UV fluorescence (for fluorescent NAPLs),
offer the most simple, practical, and effective means for
direct visual identification of clear, colorless NAPL in
contaminated soil samples. These methods can be
utilized in the field or in a lab with minimal time and
material expense. Known background and NAPL-
contaminated samples should be examined in addition to
unknown samples, where possible, to check for
interferences and site-specific NAPL responses. For
volatile NAPLs, analysis of organic vapors in soil sample
headspace can be used to screen samples for further
examination and, possibly, to infer NAPL presence. The
NAPL in water experiments demonstrate that the
presence of very small quantities of clear, colorless NAPL
in water can be quickly identified by mixing in a tiny
amount of hydrophobic dye. At some sites, however,
careful unaided visual examination of soil and water
samples, or use of an undyed shake test, may be sufficient
to detect NAPL presence.
9.10.2 Indirect Detection of NAPL Presence

As noted in Table 7-4, NAPL presence may be inferred
where:

(1) groundwater concentrations exceed 1% of the pure
phase or effective aqueous solubility of a NAPL
chemical;

(2) NAPL chemical concentrations in soil exceed 10,000
mg/kg (> 1% of soil mass);

(3) NAPL chemical concentrations in groundwater
calculated from soil-water partitioning relationships
and soil sample analyses exceed their effective
solubility;

(4) organic vapor concentrations detected in soil gas (or
sample head space) exceed 100 to 1000 ppm; or,

(5) observed chemical distribution patterns suggest NAPL
presence (see Table 7.4).

Examples are provided below to further explain the
concept of effective solubility and how soil-water
partitioning relationships can be used in conjunction with
soil analyses to assess DNAPL presence.
9.10.21 Effective solubility

Effective solubility based on Raoult's Law is discussed in
Chapter 4.7, Chapter 5.3.17, and Worksheet 7-1, and by
Feenstra et al. (1991), Feenstra (1990), Mackay et al.
(1991), Sitar et al. (1990), Banerjee (1984), Leinonen and
Mackay (1973) and Shiu et al. (1988). For mixtures of
liquid chemicals, the dissolved-phase concentrations in
equilibrium with the NAPL mixture can be estimated by
(9-3)
where S* is the effective aqueous solubility of liquid
constituent i (mg/L), Xj is the mole fraction of liquid
constituent i in the NAPL mixture, and, S, is the pure-
phase solubility of liquid constituent i (mg/L). Aqueous
solubility data for numerous DNAPL chemicals are
provided in Appendix A. Example calculations of
effective solubilities for multi-liquid DNAPLs are given in
Table 9-11.

Laboratory analyses suggest that Equation 9-3 is a
reasonable approximation for mixtures of sparingly
soluble hydrophobic organic liquids that are structurally
similar (Banerjee, 1984) and that effective solubilities
calculated for complex mixtures (e.g., petroleum products)
are unlikely to be in error by more than a factor of two
(Leinonen and Mackay, 1973). Greater errors are
expected where high concentrations of cosolvents, such as
alcohols, may significantly increase the solubility of
DNAPL components (Rao et al., 1991).

Many DNAPL mixtures are comprised of liquid and solid
chemicals (e.g., coal tar and creosote). For organic
chemicals that are solids at the temperature of interest
but in liquid solution within a NAPL, the correct value of
Sj for calculating S" is that of the subcooled liquid
chemical (Mackay et al., 1991). Solubilities reported in
chemical data handbooks (including Appendix A) are
usually for the pure solid compound in contact with water
(Feenstra et al., 1991). The Sj of a subcooled liquid
chemical exceeds the solid solubility at temperatures
below the compound's melting point. It can be estimated
by
(9-4)
-------
9-46
where S^,,^ is the solid solubility at temperatures below
melting point, TB is the compound melting point (°K),
and T is the system temperature (°K) (Mackay et al,
1991). For example, naphthalene with a solid solubility
of 33 mg/L and a melting point of 80.2 "C (353.35 "K) has
a subcooled liquid solubility at 25 °C (298.15 °K) of 118
mg/L (33 mg/L divided by 0.28). Values of subcooled
liquid solubility are also provided by Miller et al. (1985)
and Eastcott et rd. (1988). Example calculations of
effective solubilities for DNAPL components which
include organic compounds that are solids at the
temperature of interest are given in Table 9-11.

At sites with complex and varied DNAPL mixtures, or
where DNAPL samples cannot be obtained for analysis,
reliable estimation of the effective solubilities of DNAPL
components will be confounded by deficient knowledge of
DNAPL composition (constituent mole fractions). The
significance of this uncertainty regarding DNAPL
composition can be assessed by sensitivity analysis (i.e.,
making bounding assumptions regarding imposition to
determine the range of possible effective solubilities).
Given site-specific samples of DNAPL and groundwater,
effective solubilities can also be determined by conducting
equilibrium dissolution experiments (Chapter 10.11).
9.10.2.2 Assessing NAPL Presence in Soil Based on
Partitioning Theory

Chemical analyses of soil typically indicate the total
quantity of each analyte determined as a chemical mass
per unit dry weight of soil sample. The analytical
determination includes, and does not distinguish between,
mass sorbed to soil solids, dissolved in soil water,
volatilized in soil gas, and, contained in NAPL, if present.
Feenstra et al. (1991) describe a method for evaluating
the possible presence of NAPL in soil samples based on
equilibrium partitioning theory which is summarized in
Worksheet 7-2 and below. NAPL presence can be
inferred where chemical concentrations determined in a
soil sample exceed the theoretical maximum chemical
mass that can be adsorbed to soil solids, dissolved in soil
water, and volatilized in soil gas.

The method requires measurements or estimates of: total
chemical concentrations in the soil sample, soil moisture
content (n,, volume fraction), soil dry bulk density (pb,
g/cmj), soil porosity (n, volume fraction), soil organic
carbon content (f^, mass fraction), and, the organic
carbon to water partition coefficient (K^ cm3/g),
dimensionless Henry's Constant (K^.) partitioning
coefficient, and effective solubilities for the compounds of
interest. Using these data, the apparent soil water
concentration, C.,,, of a particular compound can be
calculated from the total soil concentration by assuming
equilibrium partitioning (Feenstra et al., 1991):

C_ = (Q pb) / (K, Pb + n. + K«. n.) (9-5)

where Q is the total soil concentration of a particular
analyte, Kj (cmVg) is the soil-water partition coefficient
(Kj = KO,. X fo,.), ancj n, (volume fraction) is the air-filled
porosity (n, = n - n,). For saturated soil samples
(Feenstra etal., 1991),
w = (C, Pb) / (K, Pb + n.)
(9-4)
NAPL presence can be inferred if the calculated apparent
soil water concentration, C.,,, exceeds the effective
solubility, S', of compound of interest. The reliability of
conclusions regarding NAPL presence depends on the
validity of partitioning coefficients, effective solubilities,
chemical analyses, and other data utilized in this method.
Example applications of this method are illustrated in
Figure 9-21. As shown, log-log graphs of Ct versus Cm
for different values of {„. (or Kj) can be used to facilitate
rapid evaluation of soil analyses and sensitivity analysis.
9.11 INTEGRATED DATA ANALYSIS

There is no practical cookbook approach to site
investigation or data analysis. In addition to the
noninvasive, invasive, and laboratory procedures described
in Chapters 8, 9, and 10, respectively, many additional
methods can be used to enhance contamination site
evaluation. In particular, consideration should be given
to the use of tracers (Davis et al., 1985; Hendry, 1988;
Uhlmann, 1992), interpreting chemical distributions and
ratios (e.g., Hinchee and Reisinger, 1987), and conducting
hydraulic tests.

Each site presents variations of contaminant transport
conditions and issues. Site characterization, data analysis,
and conceptual model refinement are iterative activities
which should satisfy the characterization objectives
outlined in Figure 6-1 as needed to converge to a final
remedy.

During the process, acquired data should be utilized to
guide ongoing investigations. For example, careful
examination of soil, rock, and fluid samples obtained as
-------
9-47
Table 9-11. Example effective solubility calculations (using Equations 9-3 and 9-4) for a mixture of
liquids with an unidentified fraction (DNAPL A) and a mixture of liquid and solid
chemicals (DNAPL B).
Compound
DNAPL A
Trichloroethene
Tetrachloroethene
Unidentified Compounds
(assume different
molecular weights)

DNAPL B
Chlorobenzene
1,2,4-Trichlorobenzene
1,2,3,5-Tetrachlorobenzene
Pentachlorobenzene
Hexachlorobenzene
Molecular
Weight fc)

13139
165.83
1001
2002
3003

11Z56
181.45
215.89
250.34
284.78
Melting
Poin»
«c

-73
-19

-46
17
54.5
86
230
*
Matt

0.23
0.46
0.31

0.43
0.15
0.21
0.05
0.16
Mate
per Kg
of
DNAPL

1.751
2.774
3.1001
1.5502
1.0333

3.820
0.827
0.973
0.200
0.562
Mole
Fraction

0.22961
0.28822
031503
036381
0.45672
0.49913
0.40661
0.25522
0.18593

0.599
0.130
0.152
0.031
0.088
Solubility
<«*/L»

1100
150

500
19
2.89
0.83
0.005
Subcooled
Liquid
Solubility
{mg/L)

NA
NA

NA
NA
5.66
3.33
0.534
Effective
Solubility
<««8/L}

252.61
317.02
346.S3
54.61
68.52
74^

299.
2.46
0.863
0.104
0.047
Notes: NA = not applicable; for DNAPL A, superscripts ', 2, and 3 correspond to assumptions that the molecular mass of the
unidentified DNAPL fraction is 100, 200, and 300 g., respectively.
-------
9-48
10,000
1,000
MEASURED SOIL
CONCENTRATION
(mg/kg)
100
10

J
r

V
X

(*
f
'

C\."
&
t
'

1 ^
a\o J
i >•
/ .
»'
f
•

X
yf

•
f

£
r

/
^

«*

(
^
,0

^
, r J
• s
, o\o ,
X

*
•

J
/

/
^

^
/
3°

-i '
?
^
^
J'
^''

10 100 1,000 10,000

CALCULATED PORE-WATER CONCENTRATION (mg/L)
Figure 9-21. Relationship between meaasured concentration of TCE in soil (Ct) and the calculated
apparent equilibrium concentration of TCE in pore water (C^) based based on: K^. = 126,
bulk density (pb) = 1.86 g/cm3; water-filled porosity (nj = 0.30; air-filled porosity (na)
= 0; and three different values of organic carbon content (f^) (from (from Feenstra et al.,
1991). NAPL presence can be inferred if C^ exceeds the TCE effective solubility.
-------
9-49
drilling progresses should be made to identify DNAPL
presence and potential barrier layers and thereby guide
decisions regarding continued drilling, well construction,
and/or borehole abandonment. Geologic fluid elevation,
and chemical distribution data should be organized
(preferably using database, CAD, and/or GIS programs)
and displayed on maps that are updated periodically to
help determine the worth of additional data collection
activities. With continued refinement of the site
conceptual model, the benefit cost, and risk of additional
work can and should be evaluated with improved
accuracy. This is the advantage of a flexible, phased
approach to site characterization.
-------
-------
10 LABORATORY MEASUREMENTS:
METHODS AND COSTS

Chemical and physical properties of contaminants and
media are measured to evaluate chemical migration and
clean-up alternatives at DNAPL-contaminated sites.
These chemical and physical properties are defined and
their significance with regard to DNAPL contamination
is discussed in Chapters 4 and 5. Methods used to
determine DNAPL composition and DNAPL-media
properties are described briefly in this chapter. Estimated
costs in 1992 dollars are provided for some of the test
apparatus and method determinations based on
quotations from equipment catalogs and laboratories
specializing in analytical chemistry or petroleum reservoir
analysis. Actual costs will vary and may be increased due
to special hazardous material handling requirements.
Additional information regarding the advantages,
limitations, and costs of using different analytical methods
can be obtained from analytical laboratories and
instrument vendors. Physical properties of pure DNAPLs
are given in Appendix A.
10.1 DNAPL COMPOSITION

DNAPL chemicals may be non-hazardous and require no
special treatment, or, they may be found on USEPA's
Priority Pollutant List (PPL) or the Target Compound
List (TCL). The chemical makeup of the DNAPL sample
will affect the Health and Safety Plan, the Risk Analysis,
the Remedial Action Plan (RAP), and the Feasibility
Study (FS).

The organic content of soils or groundwater at
contamination sites is often a complex mixture of
chemicals. Immiscible fluid samples can be fractionated,
or split into several portions, using a separator funnel
(Figure 10-1) or a centrifuge. A methodological flow
chart for analysis of complex hydrocarbon mixtures is
given in Figure 10-2. This flow chart was developed for
a manufacturted gas site with low and high molecular
weight organic compounds and can be adapted to site-
specific conditions. All analytical results are considered
to evaluate the total fluid chemistry of complex mixtures
(labeled the "Puzzle Fitting and Structural Parameter
Correlation" in Figure 10-2).

For NAPL organic samples, the customary methods of
analysis are infrared (IR) spectrometry, high resolution
nuclear magnetic resonance (NMR) spectrometry, gas
chromatography (GC), high performance liquid
chromatography (HPLC), and mass spectrometry (MS).
These analyses require expensive, high sensitivity
instrumentation maintained in controlled environments
and are beat performed by trained technicians in fixed
laboratories. Laboratories may request several liters of a
sample but can analyze much smaller specimens if large
volume samples cannot be obtained. Inorganic
contaminants, not considered in this discussion, can be
determined by atomic absorption (AA), differential
thermal analysis (DTA), ion chromatography (1C), and X-
ray diffraction (XRD).

Composition analyses may be either qualitative or
quantitative, or both. A qualitative analysis will only
identify a compound's presence and will not determine
the purity or percentage composition of a mixture.
Preliminary site investigations may focus on a qualitative
analysis to indicate the constituents of concern.
Quantitative analyses identify a compound's presence and
determine the purity or the percentage composition of
each component of a mixture. Quantitative analyses are
usually required to provide data for site characterization,
feasibility, risk assessment, and treatability studies. A
brief description of a qualitative method, infrared (IR)
spectrometry, and two quantitative methods, gas
chromatography (GC) and high performance liquid
chromatography (HPLC) coupled with mass spectrometry
(MS), are presented below. The applicability and cost of
various analytical methods for characterizing different
types of DNAPLs are summarized in Table 10-1.
10.1.1 Infrared (IR) Spectrometry

Infrared spectrometry is primarily used as a non-
destructive method to determine the structure and
identity of compounds; it may also be used to determine
compound concentrations. The total infrared spectrum
extends from 0.75 to 400 micrometers (fim) but the area
of most usefulness lies between 2.5 to 16 jim. Infrared
means "inferior to red" because the radiation is adjacent
to but slightly lower in energy than red light in the visible
spectrum. Identification and quantitation of compounds
results from comparing spectral data of sample unknowns
with known compounds. Most molecules are in modes of
rotation, stretching, and bending at frequencies found in
the infrared spectral region and each molecule has its
own distinctive infrared spectrum or "fingerprint".
Infrared spectrophotometers emit an infrared beam that
is split, half passing through the sample and half by-
passing the sample. The difference in energy of the two
halves is compared and reduced to a plot of percent
absorbance versus wavenumber or wavelength. Two types
of IR spectrophotometers are used: dispersive and
-------
10-2
Water
DNAPL
Figure 10-1. Use of a separatory funnel to separate immiscible liquids (redrawn from Shugar, G. J., and J.T.
Ballinger, 1990. Chemical Technician's Ready Reference Handbook. Reprinted with permission
from McGraw-Hill Book Co.).
-------
10-3
CONTAMINATED SITES
LOCATION AND
BACKGROUND
1\N\\N
SAMPLE
COLLECTION
Cation
Exchange
I Capacity
SAMPLE HISTORY,
GEOLOGICAL AND
TOPOLOGICAL DATA
Preliminary Examination
and Tests
Transmission
Electron
Microscopy
Thermal
Gravimetric
Analysis
Thermal
Chroma tographyN
\
SSS;
Bulk
Density
Soil
Texture
Energy
Dispersive
Spectrometry
Organic
Matter
Content
Degassing and
Gas Chromatography
GC-Thermal
Conductivity
Detector
GC-Flame
lonizotion
Dectector
GC-Nitrogen
Phosphorous
Detector
GC-Electron
Capture
Detector
GC-Hall
Electrolytic
Conductivity
Detector

GC-Mass
Spectrometry
GC-ln(rarec
Soectroscosy
Extraction with Solvent
Intermediate Molecular Weight
Low Molecular Weigh'.
High Performance
Liquid
Chromatography
HPLC-Moss
Spectrometry
High Resolution
Mass
Spectrometry
GC-lnfrared
Spectroscopy
GC-Mass
Spectrometry
GC-Electron
Capture
Detector
GC-Fiame
Photometry
Detector
Demineralization
Metals
Atomic
Absorption
^U^UI^JLItJM *_
-------
10-4
Table 10-1. Analytical methods and estimated costs (in 1992 dollars) to determine chemical composition.
Analysis
Add Extractables
Appendix DC Volatile*
Organic Compounds (VOCs)
Appendix DC Semivolatiles
(SVOCs)
Appendix DC Organochlorine
Pesticides
Appendix DC Herbicides
Appendix DC Organo-
phosphate Pesticides
Appendix DC Metals
Appendix DC Cyanide
Appendix DC Sulfide
Biochemical Oxygen Demand
BTEX (Benzene, Toluene,
Ethylbenezene, Xylenes)
BTEX and Naphthalene
BTEX and MTBE
Carbamate Pesticides
Carbon (Total Organic)
Chemical Oxygen Demand
Chlorinated Pesticides/PCBs
plus Organophosphates
Matrix
wA»w
w/ww
sw
wAvw
sw
w/ww
sw
w/ww
sw
w/ww
sw
w/ww
sw
wAvw
sw
w/ww
sw
w/ww
sw
w/ww
wAvw
sw
wMw
sw
wAvw
sw
w/ww
sw
w/ww
sw
w/ww
sw
w/ww
sw
Method
EPA 625
SW-846 8270
SW-846 8270
SW-8468240
SW-846 8240
SW-846 8270
SW-846 8270
SW-846 8080
SW-846 8080
SW-S46 8150
SW-846 8150
SW-846 8140
SW-846 8140
SW-846
SW-846
SW-846 9012
SW-S46 9012
EPA 376.1
SW-846 9030
EPA 405.1
EPA 602 or SW-846
8020
SW-846 5030/8020m
EPA 602 or SW-846
8020
SW-846 5030/8020m
EPA 602 or SW-846
5030/8020
SW-846 5030/8020m
EPA 531.1
California SOP 734
EPA 415.1
EPA 415.1m
EPA 410.4
EPA 410.1
SW-846 8080m, 8140
SW-846 8080m, 8140
Sample Size and
Container
3 X 1000 mL, G(am)
3 X 1000 mL, G(am)
100 g, G
2X40 mL,G
100 g,G
3 X 1000 mL, G(am)
100 g, G
3 X 1000 mL, G(am)
100 g,G
3 X 1000 mL, G(am)
100 g, G
3 X 1000 mL, G(am)
100 g, G
1000 mL,P
100 g,G
500mL,P
100 g, G
500mL,G
100 g,G
100 mL, P/G
2 X 40 mL, G
100 g,G
2 X 40 mL, G
100 g, G
2X40 mL,G
100 g, G
2 X 250 mL, G(am)
100 g, G
125mL,G
20 g, G
100 mL, P/G
100 g, G
2 X 1000 mL, G(am)
100 g, G
Preservation
Cool, 40Q Na^Oj
Cool, 40C; Na^Oj
Cool, 40C
Cool, 40C, HC1 to pH<2;
(No Headspace)
Cool, 40C
Cool, 40Q Na^Oj
Cool, 40C
Cool, 40Q NajSjOj
Cool, 40C
Cool, 40C; Na^Oj
Cool, 40C
Cool, 40C; Na^Oj
Cool, 40C
Cool, 40Q HN03 to pH<2
Cool, 40C
Cool, 40C; NaOH to pH>12
Cool, 40C
Cool, 40C; NaOH, ZnAc
Cool, 40C
Cool, 40C
Cool, 40C; HC1 to pH<2 (No
Headspace)
Cool, 40C
Cool, 40C; HC1 to pH,2
(No Headspace)
Cool, 40C
Cool, 40C; HC1 to pH<2 (No
Headspace)
Cool, 40C
MCA to pH of 3
Cool, 40C
Cool, 40C; H^OA to pH<2
Cool, 40C
Cool, 40C; HjSO4 to pH<2
Cool, 40C
Cool, 40C; Na2S2O3
Cool, 40C
Holding:
Tune
7/40 d
7/40 d
14/40 d
14 d
14 d
7/40 d
14/40 d
7/40 d
14/40 d
7/40 d
14/40 d
7/40 d
14/40 d
6 mo.
6 mo.
14 d
14 d
7d
7d
2d
14 d
14 d
14 d
14 d
14 d
14 d
28 d
7/40 d
28 d
28 d
28 d
28 d
7/40 d
14/40 d
E»t.
Cost
$350
$400
$470
$415
$450
$690
$760
$270
$315
$225
$270
$200
$245
$294
$374
$55
$75
$16
$60
$33
$84
$115
$100
$135
$90
$125
$200
$245
$25
$95
$29
$29
$225
$275
-------
10-5
Table 10-1. Analytical methods and estimated costs (in 1992 dollars) to determine chemical composition.
Analysis
Cyanide (Total)
Dicodn (Screen)
Flashpoint
GC Fingerprint (Qualitative)
GC Fingerprint
(Quantitative)
GC VOCs Purgeable
Aromatics-Halocarbons
GC VOCs Purgeable
Aromatics
GC VOCs Purgeable
Halocarbons
GC VOCs Library Search
HPLC (High Performance
Liquid Chromatography)
Potynuclear Aromatic
Hydrocarbons (PAHs)
Metals by ICP (Inductively
Coupled Plasma)
Naphthalene by GC
Naphthalene by GC/MS
Oil & Grease (Gravimetric)
Oil & Grease/Total
Petroleum Hydrocarbons
PCBs
Petroleum Materials
Contamination - GC
Fingerprint (Qualitative)
Maids
w/ww
sw
w/ww
sw
w/ww
oil
w/ww
sw
oil
w/ww
w/ww
sw
w/ww
sw
VI/VfW/B
w
w/ww
sw
w/ww
sw
w/ww
sw
w/ww
sw
w/ww
sw
w/ww
w/ww
sw
oil
oil
Method
SW-846 9012
SW-346 9012
EPA 625
EPA 625 m
ASTMD-93
SW-846 8015m
SW-846 8015m
SW-846 8015m
SW-846 8015m
SW-846 5030/8010/8020
SW-846 5030/8020
SW-846 5030/8020m
SW-846 5030/8010
SW-846 5030/8010m
NA
SW-846 8310
SW-846 8310
SW-846 6010
SW-846 6010
SW-846 8020
SW-846 5030/8020m
SW-846 8270
SW-846 8270
EPA 413.1
SW-846 9071
EPA 413.2
EPA 418.1
SW-846 8080
SW-846 8080
EPA 600/4-81-045
SW-846 8015m
Sample Size and
Container
500mL,P
100 g,G
2 X 1000 mL, G
100 g,G
200mL,G
20mL,G
2 X 1000 mL, G
200 g,G
20mL,G
2X40 mL,G
2 X 40 mL, G
100 g, G
2X40 mL,G
100 g, G
NA
2 X 1000 mL, G(am)
100 g,G
500 ml, P/G
100 g, G
2X40 mL,G
100 g, G
3 X 1000 mL, G
100 g, G
2 X 1000 mL, G
50g,G
2 X 1000 mL, G
2 X 1000 mL, G(am)
100 g, G
20mL,G
20mL,G
Presetvatiott
Cool, 40Q NaOH to pH>12
Cool, 40C
Cool, 40Q Na^Oj
Cool,40C
NA
NA
Cool, 40C (No Headspace)
Cool, 40C
NA
Cool, 40C; HC1 to pH<2 (No
Headspace)
Cool, 40Q HC1 to pH<2 (No
Headspace)
Cool, 40C
Cool, 40Q HC1 to pH<2 (No
Headspace)
Cool, 40C
NA
Cool, 40C
Cool, 40C
Cool, 40Q HNO3 to pH<2
Cool, 40C
Cool, 40C; HC1 to pH<2 (No
Headspace)
Cool, 40C
Cool, 40C; Na^Oj
Cool, 40C
Cool, 40C
Cool,40C
Cool, 40C
Cool, 40C; Na^Oj
Cool, 40C
NA
NA
Holding
Tune
14 d
14 d
7/40 d
14/40 d
30 d
NA
14 d
14 d
NA
14 d
14 d
14 d
14 d
14 d
NA
28 d
7/40 d
6 mo
6 mo
14 d
14 d
7/40 d
14/40 d
28 d
28 d
28 d
7/40 d
14/40 d
NA
NA
Bit.
COM
$55
$75
$350
$420
$38
$70
$120
$140
$120
$125
$90
$110
$110
$145
$55
$200
$245
$325
$345
$100
$135
$400
$470
$55
$85
$100
$115
$145
$80
$70
-------
10-6
Table 10-1. Analytical methods and estimated costs (in 1992 dollars) to determine chemical composition.
Analysis
Petroleum Materials
Contamination - GC
Fingerprint (Quantitative)
Total Petroleum
Hydrocarbons (TPH)
Phenolks
Priority Pollutants - VOCs
byGC/MS
Priority Pollutants -
Acid/Base Neutral
Extractables by GC/MS
Priority Pollutants - Metals
Target Anafyte List (TAL)
Metals
Target Compound List
(TCL) - VOCs
Target Compound List
(TCL) - SVOCs
Target Compound List
(TCL) - Pesticides/PCBs
Total Organic Halogen
(TOX)
Total Tcoricity Characteristic
Leaching Procedure (TCLP)
Analysis
Matrix
w/ww
sw
oil
w/ww
sw
w/ww
sw
w/ww
sw
wAww
sw
w/ww
sw
w/ww
sw
wAvw
sw
w/ww
sw
wAww
sw
w/ww
sw
oil,
solvent
w/ww
sw
Method
SW-S46 8015m
SW-846 8015m
SW-846 8015m
EPA 418.1
EPA 418.1m
SW-846 9066
SW-846 9066
SW-846 8240
SW-846 8240
SW-846 8270
SW-846 8270
SW-846
SW-846
EPA CLP
EPA CLP
EPA CLP 3/90 SOW
EPA CLP 3/90 SOW
EPA CLP 3/90 SOW
EPA CLP 3/90 SOW
EPA CLP 3/90 SOW
EPA CLP 3/90 SOW
SW-846 9020
SW-846 9020m
SW-846 9020m
SW-846
8080/8150/8240/8270
Federal Register 6/29/90
Sample Size and
Container
2 X 1000 ml, G
200 g,G
20ml, G
2 X 1000 mL, G
100 g, G
500mL,G
100 g, G
2X40 mL,G
100 g, G
3 X 1000 mL, G(am)
100 g, G
1000 mL,P
100 g, G
1000 mL,P
100 g, G
2 X 40 mL, G
100 g, G
3 X 1000 mL, G (am)
100 g, G
2 X 1000 mL, G(am)
100 g,G
4X250mL,G
50g,G
20 g, G
3 liters
2 liters
Preservation
Cool, 40C (No Headspace)
Cool, 40C
NA
Cool, 40C
Cool, 40C
Cool, 40Q HjSO., to pH<2
Cool, 40C
Cool, 40Q HC1 to pH<2 (No
Headspace)
Cool, 40C
Cool, 40C; Na^Oj
Cool, 40C
Cool, 40C; HNO3 to pH<2
Cool, 40C
Cool, 40Q HN03 to pH<2
Cool, 40C
Cool, 40C; Hd to pH<2 (No
Headspace)
Cool, 40C
Cool, 40Q Na^Oj
Cool, 40C
Cool, 40C; Na2S203
Cool, 40C
Cool, 40Q H2SO4 to pH<2
(No Headspace)
Cool, 40C
Cool, 40C

Holding
Tune
14 d
14 d
NA
28 d
28 d
28 d
28 d
14 d
14 d
7/40 d
14/40 d
6 mo
6 mo
6 mo
6 mo
10 d
10 d
ex.5d
ex.lOd
ex.5d
ex. 10 d
28 d
NA
NA

Est.
Cost
$120
$140
$100
$70
$105
$55
$75
$270
$305
$540
$610
$210
$270
$376
$456
$270
$305
$540
$610
$290
$330
$70
$130
$70
$1800
$2000
NOTES: w/ww indicates water or wastewater; sw indicates soil or solid waste; G indicates glass; P indicates plastic; (am) indicates amber; NA
indicates not applicable; the cost to analyze a NAPL sample will generally approximate that shown for sw media.
-------
10-7
fourier transform. Results are available on-line when
using a dedicated microprocessor.

Sample volumes of 500 to 1000 mL are recommended for
laboratory analytical work. Simple FT/IR analyses are
priced from $50 to $75 each unless the unknowns are not
available in the laboratory's library. FT/IR offers a rapid
preliminary screening of organic compounds. FT/IR
equipment can be used onsite by a trained technician or
scientist in a climate-controlled trailer.
10.1.2 Chromatography

"Chromatography" was derived from the words
"chromatus" and "graphien" meaning "color" and "to write"
in Tswett's technique for separating plant pigments.
Tswett's experiment discovered the varying color affinities
for a column packing when the color mixture was washed
through the column. All chromatographic processes have
a fixed (stationary) phase and a mobile (fluid) phase.
Several analytical methods and separation processes have
been developed from this phenomenon.

USEPA methods are primarily based on gas or liquid
Chromatography (GC or HPLC), with enhancements such
as mass spectrometry to determine organic chemicals.
Peaks observed by these GC and HPLC instruments are
not readily identifiable in most cases unless another
instrument is coupled to the Chromatography. Of several
possible couplings, mass spectrometry (MS) is the most
generally useful. With MS, these analytical methods are
referred to as GC/MS and HPLC/MS. GC is typically
used for compounds that readily vaporize (either fully or
partially), are not thermally labile, and may be carried
through the instrument in the gas phase. HPLC is used
for compounds that are nonvolatile, thermally labile, and
solubilized so that a solution of the sample and a solvent
carry the unknown through the instrument.
10.1.2.1 Gas Chromatography/Mass Spectrometry (GC-
MS)

One of the most rapid and useful separation techniques
is GC. Samples are injected into a heated block,
vaporized, and transported to a separation column by a
carrier gas (usually helium if mass spectrometry is to
follow), 'he sample is fractionated in the separation
column. Column effluent proceeds through a detection
device and exits the Chromatography (Figure 10-3).
Two types of GC units are used: gas-liquid and gas-solid
Chromatography. The most frequently employed method,
gas-liquid Chromatography, uses a liquid deposited on a
solid support and is also called partition Chromatography.
The various components of the sample are separated by
the liquid as they pass through the column. In gas-solid
(also known as absorption) Chromatography, the various
sample components are absorbed on the surface of the
solid as they pass through the column.

In both types of GC, various compounds are selectively
absorbed by the stationary phase and desorbed by fresh
carrier gas as the sample passes through the column.
This process occurs repeatedly as the compounds move
through the column. Compounds having a greater affinity
for the stationary phase reside longer in the column than
those that have lesser affinity for the stationary phase. As
the individual compounds exit the column, they pass
through a detector that emits a signal to a recording
device.

Thermal conductivity and flame ionization detection
devices are most commonly utilized with GC units.
Thermal conductivity is used to quantify major
components and flame ionization provides high sensitivity
to trace amounts of compounds. Other detection devices
are available that are sensitive to sulfur, nitrogen,
phosphorous, and chlorine.

When GC/MS is used, the sample that exits the GC is
forwarded to the mass spectrometer. The MS produces
gas phase ions, separates the ions according to their mass-
to-charge ratio, and emits a flux detected as an ion
current. A mass spectrum is generated by measuring ion
currents relating to the values of the mass-to-charge ratio
over a particular mass range. Fast repetitive scanning and
computerized data acquisition allow up to 1600 MS scans
in an half-hour GC run.

Generally, compounds may be classified as inorganic or
organic. Organic compounds are generally subclassified
as volatiles, semi-volatiles, and pesticides in the regulatory
field for contaminated sites. DNAPLs are organic and
may be found in all three subclassifications.

Most laboratories use USEPA's Statement of Work 846
(SW-846) as the source of their standard analytical
routines. A typical analytical methodology for liquid or
solid waste samples includes determination of volatiles,
semi-volatiles, and pesticides that are found on the Target
Compound List (TCL) or Priority Pollutant List (PPL).
Sample sizes range from 100 g of soil or solid materials
-------
10-8
Sample
injection
point
Column oven
Detector

1
(2)
1
1
Column
i
i
I
(5)
(1)
Carrier gas
Recorder/integrator
Figure 10-3. Schematic of a gas chromatography (redrawn from Shugar, G.J., and J.T. Ballinger, 1990. Chemical
Technician's Ready Reference Handbook. Reprinted with permission from McGraw-Hill Book
Co.).
-------
10-9
to between 3 and 5 L for liquid samples. The laboratory
cost for determination of aqueous TCL compounds
(including volatiles, semi-volatiles, pesticides/PCBs, and
inorganic) typically ranges from $1500 to $2000.
Ml/solid samples cost between $1700 and $2200 for
similar analysis of volatiles, semi-volatiles,
pesticides/PCBs, and inorganics. Of these rests, between
$500 and $600 is for inorganic (metals) analyses. Analysis
of volatile organic compounds using Method 8240 costs
between $150 and $300 per sample, depending the
requested number of analytes. Similarly, the cost for
analysis of semi-volatile organic compounds using Method
8260 ranges between $350 and $600. If the site has been
targeted by USEPA and requires a contract lab program
(CLP), the estimated cost to analyze 20 samples for TCL
parameters, with site-specific quality control and
additional required QC samples, is $40,000 to $45,000.
10.1.2.2 High Performance Liquid Chromatography with
Mass Spectrometry (HPLC/MS)

Liquid chromatography (LC) is used to analyze
compounds within a sample that are not volatile or
thermally labile, but are soluble in a solvent suitable for
the chromatography. Whereas GC can be used to analyze
only about 20% of all organic compounds, 80% of all
organic compounds can be determined using LC. High
Performance (also known as High Pressure) Liquid
Chromatography (HPLC) is used to determine
formaldehyde and polynuclear aromatic hydrocarbons
following USEPA methods 8315 and 8310, respectively.
The HPLC column is packed with small beads, either
coated or a homogeneous resin, that require high
pressure to force the liquid to flow through the column.
Most analyses are run at pressures in the range of 4,000
psi using pumps that produce an almost pulse-free flow
rate of several mL per minute. Ultraviolet (UV)
spectrophotometer or differential refractometer detectors
provide signals to a computerized recording and analyzing
system. When coupled with a mass spectrometer, the
column effluent passes through a thermospray device to
vaporize the sample and then the vaporized sample enters
the mass spectrometer for continued analysis.

Laboratories typically request 100 g of solid or 2 L of
liquid for analysis. Analytical costs range from $150 to
determine the concentration of a single compound to
$700 to determine the concentrations of a mixture of
compounds such as polynuclear aromatic hydrocarbons
(PAHs).
10.2 SATURATION

Several methods have been described in literature for
determining DNAPL saturation in porous media (Amxy
et al., I960). The most common method is to extract the
organic DNAPLs from the soil with a suitable organic
solvent (i.e., ethanol) and make a gravimetric or HPLC
determination of the DNAPL in the solvent. Analytical
laboratories charge between $300 to $800 and require a
minimum of 1 kg of solid sample for this analysis.
Solvent extraction of DNAPL and standard gravimetric
analysis to provide saturation estimates may be made in
an onsite trailer if personnel have a balance (accurate to
0.0001 g), constant weight crucibles, separatory funnels,
and ovens or evaporation chambers.

A standard laboratory method for determining immiscible
fluid saturation that has been utilized by the petroleum
industry employs a modified ASTM method (Dean-Stark)
as shown in Figure 10-4. The test employed is essentially
a distillation where an LNAPL solvent (toluene, naphtha,
or gasoline) in a heated reservoir is vaporized and then
passes through a core (or plug) of porous media. As the
solvent vapor passes through the core, water and NAPL
are evaporated from the core and carried off by the
solvent vapor. The solvent vapor and any vaporized
NAPL and water are condensed and drains into a
graduated receiving tube where the water settles to the
bottom of the tube and the solvent is refluxed back into
the reservoir over the core sample. The core can be
completely cleaned in this apparatus (removing all water
and NAPL to produce a clean, dry sample for porosity
and other tests).

The water saturation can be determined directly by
measuring the volume of condensed water and dividing by
sample porosity. NAPL saturation, sn, is determined
indirectly by weighing the core sample (1) prior to
extraction and (2) after extraction, cleaning, and drying of
the core sample, by
sn = (mT - md -
(vn pn)
(10-1)
where mT is the wet sample mass, md is the dry sample
mass, DV, is the extracted water mass, vn is the sample
pore volume, and pn is the NAPL density.

If this analysis is completed by chemical analysis rather
than gravimetrically, then it will cost approximately $25
per sample by spectrophotometric determination.
However, if chlorinated hydrocarbons are present, the
-------
10-10
Condenser

Graduated tube
JJThimble a
nd core
Solvent

Electric heater
I/
Figure 10-4. Modified Dean-Stark Apparatus for extracting NAPL from soil or rock sample (redrawn from
Amyx, J.W., D.M. Bass, Jr., and R.L. Whiting, 1960. Petroleum Reservoir Engineering,
Reprinted with permission from McGraw-Hill Book Co.).
-------
10-11
analysis is completed with GG/MS at a cost of $500 per
sample.

Saturation can also be determined using a centrifuge and
solvent to extract and trap water and NAPL from a core
sample. The fluid volumes are measured, and used in
conjunction with mass and porosity measurements to
determine NAPL and water saturation.

Several experimental methods to determine NAPL
saturation are presented in the literature. Two such
methods described below are not common analytical
laboratory determinations and may be costly to replicate.

Gary et al. (1991) developed a method to determine
NAPL saturation that relies on water to displace organic
compounds from hydrophilic soils and porous
polyethylene to absorb the displaced organic liquid. The
method is reported to be adaptable to field conditions
and should be applicable to volatile, semivolatile, and
non-volatile organic compounds. The method procedure
involves the following steps.

(1) Cut several strips of porous polyethylene from a 3.2
mm thick sheet having a pore size range between 10
(im and 20 |im. Efficient extraction is reported by
using at least 1 g of dry porous polyethylene for each
0.5 mL or NAPL in the sample. Porous polyethylene
sheets are available from Porex Technologies
(Fairburn, Georgia) and other vendors, and cost
approximately $120 for a 44" X 44" X 3.2 mm thick
sheet.

(2) Oven dry the strips, record their weights, and pretreat
the strips by wrapping in oil-wet (such as Soltrol 220)
tissue paper. Allow the strips to equilibrate
overnight and then reweigh them. The oil treatment
is done to ensure maximum hydrophobicity.

(3) Weigh, to the nearest 0.001 g, 20 g of the soil sample
and place it and a polyethylene strip in a 50 mL glass
vial fitted with a Teflon cap.

(4) Add 20 mL of water to the vial and stopper the vial.
Place the vial on a mechanical shaker and gently rock
it for 3-4 hours.

(5) Remove the porous polyethylene strip from the vial,
wash any soil particles from the strip using a stream
of water from a wash bottle, and then brush off any
water droplets with a tissue paper. Weigh the strip
and determine the mass that has been adsorbed.
(6) Oven dry the soil at 105°C for a minimum of 12
hours to determine the initial water content of the
sample.

(7) Determine the percent saturation of water and
DNAPL by using correction factors to account for
errors induced by the presence of hydrophobic soil
sectors (see Gary et al., 1991).

A second experimental method is adapted from a
procedure described by Gary et al. (1989b) that is
applicable to DNAPLs with low (semivolatile) to
negligible (non-volatile) vapor pressures. A simple
description of the method is as follows.

(1) Weigh 100 g sample of soil to the nearest 0.001 g and
record the weight.

(2) Place the sample in petri dish and the petri dish in a
silica gel desiccator under vacuum. Allow the sample
to remain in the desiccator for five days during which
time the water will vaporized from the soil and be
deposited on the silica gel.

(3) After five days, reweigh the soil sample to determine
the water content of the soil.

(4) Place the soil sample in a centrifuge tube, add a
solvent such as ethanol, and agitate the sample for
several minutes. Centrifuge the tube and then decant
the ethanol. Place the solvent in a weighed petri
dish, allow the ethanol to evaporate at room
temperature, and then reweigh the petri dish to
determine the amount of organic material extracted.

(5) The extraction technique should be repeated from
four to seven times until there is no evidence of
further DNAPL extraction.
10.3 DENSITY (SPECIFIC GRAVITY)

Several methods for determining the density (and/or
specific gravity) of liquids and solids are described below.
10.3.1 Displacement Method for Solids

In the displacement method, a solid sample is weighed to
determine its mass and then immersed in a graduated
cylinder containing a known volume of water. Density is
calculated by dividing the mass of the object by the
-------
10-12
change in volume in the graduated cylinder. A balance
suitable for density analysis costs between $150 and $200
and a graduated cylinder costs between $10 and $20.
10.3.2 Density of Liquids by Westphal Balance Method

The density of a liquid can be determined by employing
Archimedes' principle that the mass of a floating object
is equal to the mass of the liquid it displaces. Based on
this principle, Weatphal and chain balances are used to
determine the volume displacement of liquids by an
object of known, constant mass. If one of the liquids is
water, the density and/or specific gravity may be
determined. A Westphal balance is illustrated in Figure
10-5.

This type of balance should be calibrated with water prior
to each determination and the index end of the balance
should be positioned for equilibrium. Once the index is
set, the container of water (SG= 1.000) is removed, the
plummet dried, and the plummet is immersed in the
liquid sample. The moveable weight on the beam is then
adjusted until the balance is once again in equilibrium
and the specific gravity is read directly from the beam
scale. A chain balance uses a moveable chain to establish
balance equilibrium.

Westphal balances cost approximately $250 complete with
carrying case. Chain balances cost approximately $800
without a carrying case.
interface, and the temperature is recorded. Wide and
narrow range hydrometers are available. Individual
hydrometers cost approximately $20 and a set of eight
hydrometers (covering the specific gravity range from
0.695 to 2000) with a thermometer included costs
approximately $160.
10.3.5 Density of Liquids by Mass Determination

The density of a liquid at a measured temperature can be
determined by weighing the mass of a known volume of
liquid in a container of known mass. The mass of the
empty container is subtracted from the mass of the full
container and the resultant liquid mass is divided by its
volume. The cost of a balance suitable for density
analysis can be obtained for less than $200.
10.3.6 Certified Laboratory Determinations

If certifiable and high precision measurements are
required, 100 g of solid samples or 1 L of liquid samples
are typically required by laboratories. Certified results
using American Society of Testing Materials (ASTM)
methods usually cost between $10 and $24 per sample.
10.4 VISCOSITY

Methods of viscosity measurement include the following.
10.3.3 Density of Liquids by Densitometers

Hand-held portable densitometers are available that give
direct LCD readouts of specific gravity and the
temperature. The liquid is aspirated into the
measurement tube and the determination is performed
automatically. The units cost approximately $2000.
10.3.4 Specific Gravity Using a Hydrometer

Perhaps the simplest and least expensive for field use, this
method involves use of a hydrometer (calibrated,
weighted, glass float), thermometer, and cylinder. After
the cylinder is filled with sufficient NAPL to allow the
hydrometer to float, it is placed in the NAPL and allowed
to come to rest without touching the walls of the cylinder
(Figure 10-6). The liquid specific gravity is read from the
graduated scale on the hydrometer stem at the liquid-air
10.4.1 Falling Ball Method

A ball falling through a viscous liquid will accelerate until
it attains a constant velocity that is inversely proportional
to fluid viscosity. The amount of time required to fall a
known distance can be measured using a stopwatch. A
falling ball viscometer is shown in Figure 10-7. After
inverting the tube to capture the ball in the cap, it is
returned to the upright position and filled with the liquid
sample. The top cap is then twisted to release the ball
and the time required to fall between the two sets of
parallel lines is recorded. A set of three tubes can be
obtained having viscosity ranges of 0.2 to 2.0 cp, 2.0 to 20
cp, and 20 to 1000 cp, at a cost of approximately $120
each. These tubes are easy to use and convenient for
field measurements.
-------
10-13
Balance weight
Figure 10-5. Schematic of a Westphal balance (redrawn from Shugar, G.J., and J.T. Ballinger, 1990. Chemical
Technician's Ready Reference Handbook. Reprinted with permission from McGraw-Hill Book
Co.).
-------
10-14
DNAPL
Figure 10-6. Use of a glass hydrometer for specific gravity determination (of a DNAPL with a
specific gravity of approximately 1.13 at the sample temperature).
-------
10-15
\J
Figure 10-7. Schematic of a falling ball viscometer. Viscosity is measured by determining how
long it takes a glass or stainless steel ball to descend between the reference lines
through a liquid sample.
-------
10-16
10.4.2 Falling Needle Method

An adaptation of the falling ball method uses glass
needles of varying density measuring 4 inches long and
0.065 inches in diameter. This method was designed to
reduce wall interferences and eddy currents possible in
falling ball units. The falling needle units cost
approximately $3800 if the time is measured manually
with a stopwatch, or $7900 with automatic timing and
viscosity readout. The units can measure viscosities
ranging from 10 to 2,400,000 cp.
10.4.5 Certifed Laboratory Analyses for Viscosity

Independent testing laboratories use various methods,
typically require a 500 mL sample, and will charge
approximately $30 to $40 per viscosity determination.
10.5 INTERFACIAL TENSION

Methods to determine surface tension and interfacial
liquid tension are described below.
10.4.3 Rotating Disc Viscometer

Viscosities from 10 to 8,000,000 cp can be measured with
a rotating disc viscometer. A spindle is selected and
mounted on the unit, a rotating speed is selected, and
then the spindle is immersed in the liquid. The amount
of time required for the spindle to return to constant
speed is measured and converted to a direct digital
readout in centipoises. Units cost approximately $1750.
10.4.4 Viscosity Cups

Kinematic viscosities from 15 to 1627 cSt (centistokes)
can be measured using viscosity cups (Figure 10-8).
Direction for using 44 mL capacity Zahn (or equivalent)
viscosity cups are as follows.

(1) The viscosity cup is completely immersed vertically in
the test liquid.

(2) The cup is then quickly raised above the liquid
surface and a timer is started simultaneously.

(3) The time for the liquid to drain through a hole at the
cup bottom is measured until observation of the first
distinct break in the efflux stream.

(4) The drainage duration is then used to calculate the
kinematic viscosity using either a table or equation.

Five Zahn cups are available for approximately $80 each
to measure various liquid viscosity ranges: 15 to 78 cSt
(cup #1); 40 to 380 cSt (cup #2); 90 to 604 cSt (Cup
#3); 136 to 899 cSt (Cup #4); and 251 to 1627 cSt (Cup
#5).
10.5.1 Surface Tension Determination by Capillary Rise

The wetting force of a liquid is equal to the gravitational
force on a liquid that has risen in a capillary tube. After
measuring the capillary rise of a fluid sample in a tube,
surface tension can be calculated by
a = (r h p g) / (2 cos
(10-2)
where a is the surface tension in dynes/cm, p is the
density of the liquid in g/mL, h is the height of the
capillary rise in cm, r is the internal radius of the tube in
cm, is the contact angle, and, g is the acceleration due
to gravity (980 cm/s2). The apparatus for determining
surface tension by capillary rise is shown in Figure 10-9.

To measure capillary rise, gentle suction is applied to
raise the fluid sample to the top of the capillary tube, and
then released to allow the fluid to decline to an
equilibrium position. This measurement should be
repeated several times to provide reliable data. The
surface tension of the liquid is then calculated using
Equation 10-2. The presence of air bubbles within the
liquid column will result in inaccurate data. Between
samples, the capillary tube should be cleaned and dried,
and accuracy checks should be made periodically using a
liquid of known surface tension (such as water). The
temperature of samples should be maintained and
documented because surface tension decreases with rising
temperature. Capillary rise measurement apparatus are
available from laboratory supply vendors for about $65.
10.5.2 du Nouy Ring Tensiometer Method

Surface or liquid interfacial tension can be determined
directly using a tensiometer employing the du Nouy ring
method in accordance with ASTM D971 and D1331. The
force necessary to separate a platinum-iridium ring from
-------
10-17
Figure 10-8. Use of a viscosity cup to determine kinematic viscosity. Liquid viscosity is
determined by measuring how long it takes for liquid to drain from a small hole at
the bottom of a viscosity cup.
-------
10-18
a -
hr
2 cose
Liquid
where h « height of liquid column

r = internal radius of tubing

F = gravitalional force = force upward

6 - angle of contact

o - surface tension
Figure 10-9. Determination of surface tension by measuring capillary rise and contact angle (redrawn from
Shugar, G.J., and J.T. Ballinger, 1990. Chemical Technician's Ready Reference Handbook.
Reprinted with permission from McGraw-Hill Book Co.).
-------
10-19
the liquid's surface (either at a liquid-air or liquid-liquid
interface) is measured to the nearest +/- 0.25 dynes/cm.
Manual and semi-automatic units are available and range
in price from $2200 to $2800. Interfacial tension
determinations made by a testing laboratory cost
approximately $40 per sample.

10.6 WETTABILITY

Numerous quantitative and qualitative methods have been
proposed for measuring wettability (Anderson, 1986b;
Adamson, 1982). Five quantitative methods that are
generally used are described below.
10.6.1 Contact Angle Method

Using the sessile drop contact angle method, a drop of
DNAPL is formed at the end of a fine capillary tube and
brought in contact with the smooth surface of a porous
medium under water within a contact angle cell (Figure
10-10). The drop of DNAPL is allowed to age on the
medium surface and the contact angle can be measured
and documented by taking photographs, preferably with
enlargement using special photomacrographic apparatus.

Generally, a single, flat, polished mineral crystal and oil
brine water is used in petroleum engineering studies; but
for applications to DNAPL-groundwater-media systems,
the smooth surface may be a rock thin section, clay
smeared on a glass slide, the top of a cohesive soil sample
that has been sliced with a knife, or a relatively flat
surface of silt or sand. The water should be actual or
simulated groundwater. Water advancing and water
receding contact angles typically vary due to hysteresis
and can be measured by using the capillary tube to
expand and contract the volume of the DNAPL drop.
Alternatively, a modified sessile drop method can be
utilized whereby the drop of DNAPL is positioned
between two flat, substrates that are mounted parallel to
each other on adjustable posts in the contact angle cell.

As noted in Chapter 4.3, NAPL wetting has been shown
to increase with aging (contact time) during contact angle
studies. Thus, an assessment of the significance of aging
should be considered, and the contact duration associated
with each measurement should be noted.

The representativeness of contact angle measurements is
uncertain. Although Melrose and Brandner (1974)
contend that contact angles provide the only
unambiguous measure of wettability, Anderson ( 1986b)
notes that contact angle measurements cannot take into
account the effects of media heterogeneity, roughness,
and complex pore geometry.

Contact angle measurements range in price from $1200 to
$1500 when accomplished by petroleum laboratories
10.6.2 Amott Method

The Amott method measures the wettability of a soil or
rock core based on the immiscible fluid displacement
properties of the NAPL-water-media system (Amott,
1959; Anderson, 1986b). Four fluid displacements are
performed combining imbibition and forced drainage to
measure the average wettability of the sample. The
method relies on the spontaneous imbibition of the
wetting fluid into the sample and, for consolidated media,
involves the following steps (Anderson, 1986b).

(1) The core sample is prepared by centrifugation under
water until residual NAPL saturation, sm is attained.

(2) The core sample is then immersed in NAPL and the
volume of water that is spontaneously displaced by
the NAPL is measured after 20 hours.

(3) The core sample is then centrifuged under NAPL
until the irreducible water saturation, s^ is reached,
at which time, the total volume of water displaced is
measured, including that spontaneously displaced by
immersion in the NAPL.

(4) The core sample is then immersed in water and the
volume of NAPL spontaneously displaced by the
water is measured after 20 hours.

(5) Finally, the core sample is centrifuged under water
until sm is reached and the total volume of NAPL
displaced is measured.

For unconsolidated sediments which cannot be
centrifuged, the displacements are achieved by forced flow
through the sample core.

Although Amott (1959) selected an arbitrary time period
of 20 hours for the spontaneous NAPL and water
imbibition steps, Anderson (1986b) recommends that the
core samples be allowed to imbibe to completion (which
may take from several hours to several months) or for a
period of 1 to 2 weeks.
-------
10-20
Figure 10-10. Use of a contact angle cell and photographic equipment for determination of
wettability. A small DNAPL drop is aged on a flat porous medium surface under
water.
-------
10-21
Results of these displacements are expressed by the
"displacement by NAPL" ratio (SJ and the "displacement
by water" ratio (6W). The displacement by NAPL ratio is
the water volume displaced by spontaneous imbibition
alone (V,^,) to the total volume displaced by imbibition
and forced displacement (V,,):
V / V
vwip ' »wt
(10-3)
The displacement by water ratio (5.) is the ratio of the
NAPL volume displaced by spontaneous imbibition alone
(V^) to the total NAPL volume displaced by imbibition
and forced displacement (Sot)
,/VB
(10-4)
For water wet media, 5W is positive and approaches unity
with increasing water wetness, and 5n is zero. Similarly,
for NAPL wet media, 5n is positive and approaches unity
with increasing NAPL wetness, and 8W is zero. The main
limitation of the Amort wettability test is its insensitivity
for near neutral wettability (i.e., contact angles between
60° and 120°). The approximate relationship between
wettability, contact angle, and the Amott and USBM
wettability indexes is shown in Table 10-2.

Petroleum laboratories charge approximately $1500 for
wettability determinations by the Amott Method.
10.6.3 Amott-Harvey Relative Displacement Index

A relative wettability index known as the Amott-Harvey
modification can be calculated by first driving the cores to
sre prior to initiating the test. A relative wettability index
is then calculated where
= 6W -
(10-5)
A system is defined as water wet when 0.3
-------
10-22
Table 10-2. Approximate relationship between wettability, contact angle, and the USBM and
Amott wettability indexes (from Anderson 1986b).
Method
Contact Angle:
Minimum
Maximum
USBN wettability index
Amott wettability index
Displacement-by-water ratio
Displacement by NAPL ratio
Amott-Harvey wettability index
Water-Wet
0°
60 to 75°
Wnear 1
Positive
Zero
0.3 < I < 1.0
Neutrally Wet
60 to 75°
105 to 120°
WnearO
Zero
Zero
-0.3 < I < 0.3
NAPL-W«t
105 to 120°
180°
W near -1
Zero
Postive
-1.0 < I < -0.3
-------
10-23
WATER WET LOG A|/A2 = 0.79
0 100
AVERAGE WATER SATURATION, PERCENT
OIL WET LOG At /Ay = -0.51
-10
0 V 100
AVERAGE WATER SATURATION , \PERCENT
10
NEUTRAL LOG A,/A2=- O.OO
-10
0 \ 100
AVERAGE WATER SATURATION,! PERCENT
Figure 10-11. USBM wettability measurement showing (a) water-wet, (b) NAPL-wet, and (c) neutral conditions
(reprinted with permission from Society of Petroleum Engineers, 1969).
-------
10-24
displacement methods based on the establishing
successive states of hydraulic equilibrium, and (2) dynamic
methods based on establishing successive states of steady
flow of wetting and nonwetting fluids. Displacement
methods are utilized more commonly than dynamic
methods.

Several methods to determine P^s,) relations are
described briefly below. Some of these methods can
utilize the actual immiscible fluids of interest (i.e., the
cylinder and diaphragm methods) to determine P^s,)
curves; others utilize alternative nonwetting fluids
(mercury) or air to displace water from an initially water-
saturated sample. As discussed in Chapter 4.4, the
capillary pressure measured for a particular nonwetting
fluid saturation can be scaled using interfacial tension
measurements to estimate the capillary pressure for a
different NAPL for the same saturation and soil. Amxy
et al. (1960) provide a comparison of Pc(sw) curves
determined for the same media using several different
methods.
10.7.1 Cylinder Methods for Unconsolidated Media

Methods to determine drainage and imbibition P
curves for DNAPL-water-unconsolidated media samples
were recently described by Kueper and Frind (1991),
Wilson et al. (1990), and Guarnaccia et al. (1992). The
procedure utilized by Kueper and Frind (1991) is
described below.

A schematic of a Pc(s») test cell is provided in Figure 10-
12. As shown, the porous media sample is placed in the
stainless steel cylinder and the water burette and NAPL
reservoir are connected to the cell. The porous ceramic
disk has a DNAPL breakthrough pressure exceeding the
range of test pressures thereby preventing DNAPL
passage.

After the sample is completely saturated with water, the
initial water and DNAPL pressures are recorded. The
water pressure is equal to the water level in the outflow
burette. The DNAPL pressure can be calculated based
on the DNAPL density and the levels of the DNAPL-
water interface and the overlying water surface. The
value of Pc is then calculated as the DNAPL pressure
minus the water pressure.

The Pc is then increased incrementally by raising the
height of the DNAPL reservoir and the system is allowed
to come to equilibrium. As the DNAPL reservoir is
rasied, the threshold entry pressure, Pd, is eventually
exceeded and the DNAPL begins to displace water from
the porous media sample. The volume of water displaced
as a result of each incremental increase in Pc is measured
to determine the relationship between Pc and saturation.
Saturation can also be determined by gravimetric analysis
of the core (Wilson et al., 1990) or by gamma radiation
techniques (Guarnaccia et al., 1992). Eventually, upon
reaching the irreducible water saturation (&„), no
additional water is displaced by further raising the
DNAPL pressure.

To determine the imbibition curve, the DNAPL/water
reservoir is then lowered in increments until the residual
DNAPL saturation (sro) is reached and lowering of the
DNAPL/water reservoir does not allow further imbibition
of water into the sample. The raw data are plotted as
shown in Figure 4-9 producing the main drainage and
imbibition P^s,) curves from which the values of s,,, sra,
Pd, can be determined.
10.7.2 Porous Diaphragm Method (Welge Restored State
Method)

Very similar to the cylinder method described above, the
Welge static method is also based upon the drainage of a
sample initially saturated with water (Welge and Bruce,
1947; Welge, 1949). A schematic diagram of the test
apparatus is given in Figure 10-13. The methodology
involves the same general procedure as the cylinder
method.
This procedure may take 10 to 40 days to yield a
drainage curve due to the slow equilibration process that
follows incremental pressure adjustment (which takes
longer and longer as &„ is approached). Suitable
modifications to the test apparatus and procedure can be
made to derive imbibition curves.

Determination of Pc(sw) drainage curves by the Welge
method costs approximately $350 for a 6-point air-water
or air-NAPL curve, $770 for a 6-point water-NAPL curve,
and $1525 for drainage and imbibition water-NAPL
curves.
10.7.3 Mercury Injection Method

Another displacement method, the mercury injection
method (Purcell, 1949), can be used to reduce the time
needed to determine a P^s,) curve. Mercury is a very
-------
10-25
XT—K-t-Parafilm
,Water
^ Glass
Reservoir

DNAPL
•4.3 cm diameter
r
^--^.jcmaiameter
j stainless steel cylinder
:':::::; :*:;:•:•::•: •:•:•: •:•:•:•:!::: •:•:•'::: '••'• •:•:•:• fy
Teflon Plug
^ Parafilm
•s

Water
Burette
-Fritted
Glass Disk
Figure 10-12. Schematic of a P,^) test cell (modified from Kueper et al., 1989).
-------
10-26
Nitrogen pressure
Saran tube

oil
Nickel plated
spring
Tissue paper to
improve contact
Ultra fine
fritted glass disc
Neoprene
stopper
Core
Graduated
/
tube
.Seal of
oil
Wetting
fluid
_ _ |
Figure 10-13. Schematic of the Welge porous diaphragm
Welge and Bruce, 1947).
device (modified from Bear, 1972; and,
-------
10-27
dense, nonwetting fluid even in mercury-air-media
systems. The test procedure is as follows.

(1) The core or porous medium sample is placed in a
sample chamber and the chamber is evacuated to a
very low pressure using a vacuum pump.

(2) Mercury is then forced into the sample under
incremental pressure steps and the nonwetting fluid
saturation is determined by measuring the volume of
mercury injected during each step.

(3) Mercury injection is continued in small incremental
pressure steps until the sample is saturated with
mercury or a predetermined maximum pressure is
attained.

Using this method, equilibrium is attained during each
pressure step in a matter of minutes rather than hours or
days and much higher capillary pressures can be tested
than when using the porous diaphragm.

Capillary pressure curve determinations by mercury
injection cost approximately $375 for a drainage curve
and $800 for both drainage and imbibition curves.
10.7.4 Centrifuge Method

The centrifuge method is another static test used to
reduce the equilibration time associated with determining
the P^s,,) curve (Amyx et al., 1960; Slobod and Chambers,
1951). Using this method, a complete P^s.) can be
derived within a few hours. The procedure is outlined
below.

(1) A sample is saturated with water (to determine the
drainage curve) and placed in a centrifuge tube with
a small, graduated burette on the end as shown in
Figure 10-14.

(2) The centrifuge is started and maintained at a
predetermined rotation velocity. Fluid displaced by
the increased gravitational force collects in the
burette. When no more fluid drains from the
sample, the drained wetting fluid volume is
measured to determine its saturation at the
corresponding rotation velocity. The centrifugal
force is increased incrementally by raising the
rotation velocity until there is no additional fluid
displacement.
Centrifuge rotation velocity is related to Pc by (Bear,
1972):
where <•> is the angular velocity of the centrifuge and rl
and r2 are the radii of rotation to the inner and outer
faces of the sample.

Laboratory determination by the centrifuge method costs
approximately $500 for determination of air-water, air-
NAPL, or water-NAPL curves, and $1000 for water-
NAPL drainage and imbibition curves.
10.7.5 Dynamic Method Using Hassler's Principle

Brown (1951) reported a dynamic method based on
Hassler's principle that is used for both capillary pressure
and relative permeability determinations. This method
controls the capillary pressure at both ends of a test
sample. A schematic of Hassler's apparatus is presented
in Figure 10-15. The test procedure is as follows (Bear,
1972; Osoba et al., 1951).

(1) A sample is placed between two porous membranes
or plates permeable only to the wetting fluid (Figure
10-15). These membranes allow the wetting phase
(water), but not the nonwetting phase (gas) to pass,
and facilitate uniform saturation throughout the
sample even at low test flow rates.

(2) The sample is first saturated by the wetting fluid
prior to placement in the test apparatus. Each
membrane is divided into an inner disc (B) and an
outer ring (A).

(3) To initiate the test, the wetting fluid and nonwetting
fluid are introduced through ring A and via the
radial grooves on the inner face of this ring,
respectively. Wetting phase pressure is measured
through disc B and the capillary pressure equals to
difference in pressure between the wetting and
nonwetting phases at the inflow face.

(4) When equilibrium of wetting and nonwetting phase
flow rates is attained, the sample is removed and
saturation is determined gravimetrically.
-------
10-28
0-Rlng
Support disk
Tube body
Seal cap
Core holder body
Window
Figure 10-14. Schematic of a centrifuge tube with graduated burette for determining Pr(sJ
relations (redrawn from Amyx, J.W., D.M. Bass, Jr., and R.L. Whiting, 1960. Petroleum Reservoir
Engineering. Reprinted with permission from McGraw-Hill Book Co.).
-------
10-29
Gas outlet
Gas inlet
Mil Porous liji
i Sample UH
Liquid
burette
Semipervious
disc
Isolated
semipervious
discB
Metal sleeve
Liquid inlet
Grooves on
inner face
of disc A
Porcelain (semipervious) disc
Figure 10-15. A schematic of Hassler's apparatus used for P^s*) and relative permeability
measurements (modified from Bear, 1972; and Osoba et al., 1951).
-------
10-30
10.8 RELATIVE PERMEABILITY VERSUS
SATURATION

There are four primary means to acquire relative
permeability data (Amyx et al, 1960; Honapour et al,
1986): (1) laboratory measurements using steady-state
fluid flow, (2) laboratory measurements using transient
fluid flow, (3) calculations based on Pc(sw) data, and (4)
calculations from field data. The utilization of Pc(s,,) data
to estimate relative permeability relationships is discussed
in Chapter 4.6. The calculation of relative permeability
based on field data is described by Honarpour et al.
(1986). Most commonly, relative permeability is
measured using laboratory methods, particularly steady-
state tests, which are described below. For a detailed
discussion of many methods to determine two- and three-
phase relatively permeability and related factors, refer to
Honarpour et al. (1986).
10.8.1 Steady State Relative Permeability Methods

The many steady state relative permeability methods
utilize the same general procedure (Bear, 1972). A soil
or rock sample is mounted in a test cell as shown in
Figure 10-15. Two fluids (NAPL and water) are injected
into and through the sample at a steady rate via different
piping systems. After 2 to 40 hours depending on the
media permeability, steady flow rates are obtained such
that the ratio of NAPL:water is the same in the inflow
and outflow. At this equilibrium, the flow rates are
measured and saturations are determined by fluid balance
calculations, gravimetrically, or other methods. The
injection ratio is then modified incrementally to remove
more of the wetting fluid. Flow, pressure, and saturation
measurements are made for each fluid upon equilibration
following each injection rate change. Desaturation tests
involve draining water from an initially water-saturatd
sample. Resaturation refers to tests that begin with an
initially NAPL-saturated sample.

Permeability values associated with each saturation are
calculated by
= qn
and
kw(sw) =
(10-7)
(10-8)
where: kn(sw) and kw(sw) are the permeabilities of NAPL
and water at the given water saturation (sj, respectively
q,, and qw are the measured NAPL and water flow rates,
respectively; |in and (i, are the absolute viscosities of the
NAPL and water, respectively; and ^ and i,, are the
pressure gradients imposed on the NAPL and water,
respectively. Relative permeabilities of NAPL, k,,,, and
water, k,., are equal to these permeability values divided
by the respective intrinsic fluid permeabilities at complete
saturation. Two-phase relative permeability curves, like
that shown in Figure 4-1 la, are derived by measuring
relative permeability at many s, values.

Steady-state relative permeability tests costs
approximately $3000 each for the desaturation and
resaturation curves.
10.8.2 Unsteady Relative Permeability Methods

Unsteady flow relative permeability methods are reviewed
by Honarpour et al. (1986). More recently, Wilson et al.
(1990) provide a detailed description of apparatus and a
procedure developed to perform unsteady relative
permeability measurements in soil-water-NAPL systems.

The cost to determine NAPL-water relative permeability
curves using unsteady flow methods is approximately
$2000 each for desaturation and resaturation curves.
10.9 THRESHOLD ENTRY PRESSURE

The threshold entry capillary pressure, Pd, that must be
exceeded to drive nonwetting DNAPL into a water-
saturated medium is determined during the Pc(sw) tests
described in Chapter 10.7. If only the value of Pd is of
interest, the test can be concluded after the DNAPL
pressure has been raised incrementally to a sufficient level
to initiate DNAPL movement into the core sample. The
initial fluid movement can be determined by (1)
observing the first drainage of water from the core
sample; and/or, (2) the initial movement of an air bubble
placed using a syringe needle within a capillary tube
upstream from the core sample plug.
10.10 RESIDUAL SATURATION

Residual saturation is normally determined in conjunction
with relative permeability or P^s,) testing at no
additional cost. If the entire relative permeability or
P^s,,) curves are not required, residual NAPL saturation
can be obtained by (1) raising the NAPL pressure and
-------
10-31

allowing water drainage to proceed until the maximum
NAPL saturation and irreducible water content are
obtained, and then, (2) waterflooding the sample at
hydraulic gradients representative of field conditions until
no additional DNAPL flows from the core sample. The
core sample can then be analyzed for DNAPL saturation
by one of the methods described in Chapter 10.2
10.11 DNAPL DISSOLUTION

DNAPLs are soluble to a variable degree in water and
will be leached by infiltration and groundwater as
discussed in Chapter 4.7. The dissolved chemistry derived
from water contact with DNAPL can be assessed directly
by analysis of DNAPL-contaminated groundwater
samples, and indirectly by equilibrium calculation
methods or laboratory dissolution studies. A few
dissolution study options are described briefly below.
The equilibrium aqueous concentrations of DNAPL
components in groundwater can be assessed by placing
DNAPL and (real or simulated) groundwater in a closed
jar at the prevailing groundwater temperature. After four
hours of contact, samples of water, excluding DNAPL,
can be taken for chemical analysis to determine the
dissolved phase composition.

Simple leaching experiments can also be conducted in
which water is passed through a sample of DNAPL-
contaminated porous media to simulate vadose zone or
saturated conditions. The experiments can be designed to
represent various field conditions (e.g., DNAPL pools or
ganglia, variable flow rates, and variable background
groundwater chemistry). Details of laboratory studies on
NAPL dissolution are described by van der Waarden et
al. (1971), Fried et al. (1979), Pfannkuch (1984), Hunt et
al. (1988a,b), Schwille (1988), Anderson (1988), Miller et
al. (1990), Zalidis et al. (1991), and Mackay et al. (1991).

Leachability is also a regulatory basis for classifying
contaminated soil as a hazardous waste. The USEPA
Toxic Characteristic Leach Procedure (TCLP) involves
leaching a solid sample with an acidic leaching solution to
simulate climatic conditions expected to occur at landfills.
Remediation of contaminated soils must meet the TCLP
regulatory levels for the metals and organic compounds
listed in Table 10-3. TCLP analyses are performed by
independent laboratories and require elaborate sample
extraction, quality control, and chain-of-custody records.
-------
10-32

Table 10-3. TCLP regulatory levels for metals and organic compounds (Federal Register
March 29, 1990).
Constituent
Arsenic
Barium
Cadmium
Chromium
Lead
Mercury
Selenium
Silver
Benzene
Carbon tetrachloride
Chlordane
Chlorobenzene
Chloroform
o-Cresol
m-Cresol
p-Cresol
2,4-D
1,4-Dichlorobenzene
1,2-Dichloroethane
1 , 1 ,-Dichloroethene
mg/L
5
100
1
5
5
0.2
1
5
0.5
0.5
0.03
100.
6.
200.
200.
200.
10.
7.5
0.5
0.7
Constituent
2,4-Dinitrotoluene
Endrin
Heptachlor (and its eporide)
Hexachlorobenzene
Hexachlorobutadiene
Hexachloroethane
Lindane
Methoxychlor
Methyl ethyl ketone
Nitrobenzene
Pentachlorophenol
Pyridine
Tetrachloroethene
Toxaphene
2,4,5-TP (Silvex)
Trichloroethene
2,4,5-Trichlorophenol
2,4,6-Trichlorophenol
Vinyl Chloride

mg/L
0.13
0.02
0.008
0.13
0.5
3.
0.4
10.
200.
2.
100.
5.
0.7
0.5
1.
0.5
400.
2.
0.2

-------
11 CASE STUDIES

Case histories can illustrate special problems associated
with DNAPL sites. Lindorff and Cartwright (1977)
discuss 116 case histories of groundwater contamination
and remediation. USEPA (1984a and b) presents 23 case
histories of groundwater contamination and remediation.
Groundwater extraction was evaluated at 19 sites by
USEPA (1989c). These 19 sites were rexamined and
expanded to 24 sites in Phase II of the USEPA study
(Sutter et al, 1991). At 20 of the 24 sites, chemical data
collected during remedial operations exhibit trends
consistent with the presence of DNAPL (USEPA 1991b).
However, except at the sites contaminated with creosote,
DNAPL was generally not discovered directly during site
sampling activities. Chemical waste disposal sites where
DNAPL was observed are discussed by Cohen et al.
(1987). In the discussion that follows, several sites
described in these references are used to illustrate
characterization aspects of DNAPL sites.
11.1 IBM DAYTON SITE, SOUTH BRUNSWICK, NJ.

The IBM Dayton site was featured in an article in the
Wall Street Journal (Stipp, 1991) describing the limitations
of aquifer restoration caused by the presence of DNAPL.
This case history was selected to illustrate how undetected
and unsuspected DNAPL can influence remediation and
monitoring.
11.1.1 Brief History

The site is located in the Township of South Brunswick,
New Jersey (see Figure 11-1). In December 1977, organic
contaminants, primarily 1,1,1-trichloroethane (TCA) and
tetrachloroethene (PCE), were discovered in public
supply well SB 11. Subsequent to this discovery, several
investigations were conducted to locate source(s) of
contamination and remediate groundwater contamination.
These investigations identified three industries that were
contamination sources. Figure 11-2 shows these facilities
and their associated TCA plumes. Plumes of other
chemicals showed similar distribution; TCA is used
because it was the most widely distributed and almost
always occurred with the highest concentration (Roux and
Althoff, 1980). Note that Plant A in this figure is the
IBM facility that was determined to be the major
contributor to the contamination at SB 11.

In January 1978, SB11 was shut down and IBM began a
site assessment (USEPA, 1989c). During 1978, more
than 60 monitor wells and 10 onsite recovery wells were
installed; the first groundwater extraction began in March
1978. To limit the spread of contamination, pumping
resumed from SB11 in June 1978 with discharge going to
the sanitary sewer system. In addition, buried chemical
storage tanks that were the suspected source of IBM's
groundwater contamination were removed during the
summer of 1978 (USEPA, 1989c).

An additional four onsite extraction wells and ten
monitor wells were installed in 1979. Seven more
extraction wells were installed offsite in 1981 to intercept
the plume movement toward SB 11. At this time, nine
injection wells also were installed along the northeast
boundary of the IBM property (USEPA, 1989c). The
pump-and-treat system continued until September 9,
1984, at which time all parties agreed that further
reductions in contaminant concentrations could not be
achieved by continued operation of the six onsite
extraction wells and the seven offsite injection wells. The
parties also agreed to reactivate the extraction system if
offsite TCA concentration increased to above 100 jig/1.
Production well SB 11 continued to produce, but with a
well-head treatment system installed and an increased
pumping rate. Figure 11-3 shows the TCA plume as of
January 1985. In this figure, north has been rotated and
the buried chemical storage tanks that were removed were
located near wells GW32 and GW04.

Groundwater monitoring continual after the pump-and-
treat system was terminated. Results showed a gradual
increase in concentrations and a reemergence of the
contaminant plume, presumably due to the presence of
DNAPL in the aquifer. Figure 11-4 shows the TCA
plume as of June 1989. As a result, a new pump-and-
treat system began operation in the Fall of 1990
(Robertson, 1992). The new system is designed to
remediate the aquifer and contain the source (DNAPL).
As the aquifer is cleaned up, this portion of the
remediation system will be terminated; low-yield, source-
control pumping near GW32 and GW04 is expected to
continue indefinitely.
11.1.2 Site Characterization

According to Roux and Althoff (1980), the investigations
were designed to (1) define the subsurface lithology, (2)
determine directions and rates of groundwater movement,
and (3) define the extent of contaminant plumes.
General hydrogeology of the area was known based on
data from existing wells. The site is underlain by a water-
table aquifer known as the Old Bridge aquifer; this is
underlain by a confining bed known as the Woodbridge
-------
11-2
site location
Scale: l" = 2000'
Site Location Map
Portions of the U.S.G.S. 7 1/2
Minute Monmouth Junction, New Brunswick.
Jamesburg, and Hightstown Quadrangles
Figure 11-1. Dayton facility location map showing public water supply well SB11 (from Robertson,
1992).
-------
11-3
500 0 500 1000 FEET
EXPLANATION
500 MAXIMUM REPORTED CONCENTRATION
OF 1,1,1 TRICHLOROETHANE IN ppb
• WELL CONTAMINATED WITH
1,1,1 TRICHLOROETHANE

o WELL WITH NO DETECTABLE
1,1,1 TRICHLOROETHANE
APPROXIMATE EXTENT OF
1,1,1 TRICHLOROETHANE IN ORDERS
OF MAGNITUDE (DASHED WHERE
INFERRED)
Figure 11-2. TCA distribution in the Old Bridge aquifer in January 1978-March 1979 associated
with three facilities near SB11 (from Roux and Althoff, 1980).
-------
CWI8
- SHALLOW RECOVERY WELL
GW12
• CW46 - SHALLOW MONITORING WELL
CLUSTER

GW34Q - SHALLOW RECOVERY WEU
(HISTORICAL. CURRENTLY INACTIVE)

AGW09 _ SHALLOW MONITORING WELL
_ SHALLOW GEOMON
- SHALLOW INJECTION WELL
- CONCENTRATION CONTOUR
GW29
TCA - JANUARY 1985
.SCALE
icxr sir
-------
MOtJMOUrH JUNCTION ROAD
GWI8
- SHALLOW RECOVERY WELL
• GW46 - SHALLOW MONfTORING WELL
CLUSTER
CW34,
GW12
- SHALLOW RECOVERY WELL
(HISTORICAL, CURRENTLY INACTIVE)

- SHALLOW MONITORING WELL

- SHALLOW GEOMON

- SHALLOW INJECTION WELL

- CONCENTRATION CONTOUR
WATER
TREATMENT
FACILITY
GW29
SCALE
TCA - JUNE 1989
100" 30*
Chemical Concentration Contour Map
1,1.1 -Trlchloroethane
Shallow Aquifer - June 1989
""•" •* US/UU I "^ 3/19/92 I
* irrmm m-. BAH/CCR \ 8701 8-033-A
GROUNDWATER SCIENCES CORPORATION
-------
11-6
clay; and this is underlain by a confined aquifer known as
the Farrington aquifer. Highly productive, the Farrington
aquifer is tapped by many large-capacity wells, such as
SB11.

Eventually, 104 monitor wells were installed in the Old
Bridge aquifer, 44 monitor wells were installed in the
Farrington aquifer, and more than 25,000 groundwater
samples were analyzed (Robertson, 1992). using
lithologic logs, it was found that the Woodbridge clay was
discontinuous and was absent in the area of SB 11. This
early finding helped explain why SB 11 was contaminated
and is demonstrated in Figure 11-5. This absence of clay
provides direct access for large volumes of recharge from
the Old Bridge aquifer to the lower Farrington aquifer.
Thus, contaminants in the shallow aquifer can migrate
directly into the deeper aquifer.

As indicated, considerable water quality data were
collected, some of which is presented in the figures for
this case history. Although DNAPL was never directly
observed, TCA concentrations in the Old Bridge aquifer
were as high as 12,000 jig/1 (Roux and Althoff, 1980) and
PCE concentrations were as high as 8,050 jig/1
(Robertson, 1992). These concentrations are 0.8% and
5.37% of the aqueous solubilities for TCA and PCE,
respectively. Contamination in the Farrington aquifer
generally involves lower concentrations of these same
contaminants.

The suspected source of the contamination, buried
chemical storage tanks near monitor well GW32, was
removed in 1978, but no records have been obtained
indicating that soil samples were collected at that time
(USEPA, 1989c). In 1985 and 1986, soil samples taken
from boreholes contained a maximum soil concentration
of 13,255 ng/kg of total VOCs at a depth of 22.5 ft
(USEPA, 1989c). More details on soil sampling were not
available.
11.1.3 Effects of DNAPL Presence

Figures 11-6 through 11-8 show time versus six-month
average TCA and PCE concentrations for wells GW32,
GW16B, and GW25. The locations of these wells are
given in Figure 11-3. As shown, GW32 is an extraction
well near the suspected source area, where the highest
contaminant concentrations were detected. Well GW16B
is an onsite extraction well located downgradient of the
source. Monitor well GW25 is located further
downgradient near the property boundary.
Figure 11 -6 shows a fairly steady decline in concentrations
from 1978 to 1984. After the pump-and-treat system was
terminated in 1984, concentrations generally increased
with time. The PCE concentrations in 1988 are higher
than those determined before the onset of remediation.
The concentrations of TCA, however, have risen only
slightly and are well below those determined before
remedial activity. Site investigators speculate that this
indicates TCA depletion in the source area. TCA would
be expected to leach out more rapidly than PCE because
it is more soluble in water and leas strongly sorbed to soil
than PCE.

The trends in Figure 11-7 (well GW16B) are similar to
the trends observed in GW32, except for the decline in
concentration at the end of 1988. The concentrations in
Figure 11-8 are lower than those for wells closer to the
suspected source. The increases in concentrations after
1984 are more pronounced in GW25 than in GW16B and
GW32. In this case, concentrations after cessation of
extraction are higher than they were at the initiation of
remediation for both TCA and PCE. This might be due
to changes in flow conditions due to the increased
pumping at SB11, which is indicated on the figure.

The reappearance of elevated contaminant concentrations
after the onsite groundwater extraction system was shut
off led site investigators to suspect the presence of
DNAPL In retrospect, and given present-day knowledge
of DNAPLs, the types of chemicals (TCA and PCE), the
operational history (underground storage tanks), and the
relatively high concentrations (for PCE, 5.37% of its
aqueous solubility) should have indicated the potential for
DNAPL in the subsurface. This, in turn, should have
triggered more thorough source investigation and
remediation than what apparently was performed. From
a remediation viewpoint, this case history demonstrates
the need for source control. Ironically, this case history
also demonstrates that pump-and-treat technology did
work for cleaning up dissolved contamination.
11.2 UP&L SITE, IDAHO FALLS, IDAHO

This site was included in the 19-site study by USEPA
(1989c). It illustrates some of the problems associated
with creosote (dissolved and DNAPL) in a fractured
media. The material presented follows the discussion in
USEPA (1989c).
-------
WDC 81821 AO.02
NOTE: All Structure Contour
Line* art Approximate
MONITOniNC WELL

TOWNSHIP WELL SBIt
STRUCTURE CONTOUR ON
TOP OF CONFINING CLAY
ABSENCE OF CONFINING
CLAY
Source: REWAI. 1987.
SCALE IN FEET

Figure 3
STRUCTURE AND EXTENT MAP OF THE
WOODBRIDGE CLAY
IBM-DAYTON SITE
Figure 11-5. Structure and extent map of Woodbridge clay (from U.S. EPA, 1989).
-------
I—I—I—I—I—I—I—I—I—I—I—I
13,558
JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD
7878 79 79 80 8081 81 82 82 83 8384 84 85 85 86 8687 87 88 88
Compiled (rom various sources.
Figure 11-6. History of TCA ad PCE variations in extraction well GW32, six-month average concentrations in ppb (from U.S. EPA, 1989).
-------
6000
-•-TCA
I
-o-PCE
I
CD
(/)
rt
Q)
o

D)
C

E
3
Q.

0)
-^
"w
C
O
6^=0=^0^6—0—0—o—o-l-o—o
JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD

78 78 79 79 80 80 81 81 82 82 83 83 84 84 85 85 86 86 87 87
JJ JD

88 88
Compiled from various sources.
Figure 11-7. History of TCA and PCE variations in extraction well GW168B, six-month average concentrations in ppb (from U.S. EPA,

19891.
-------
JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD JJ JD
78 78 79 79 80 80 81 81 82 82 83 83 84 84 85 85 86 86 87 87 88 88
Compiled from various sources.
Figure 11-8. History of TCA and PCE variations in extraction well GW25, six-month average concentrations in ppb (from U.S. EPA, 1989).
-------
11-11
11.2.1 Brief History

As shown in Figure 11-9, the Utah Power & Light
Company (UP&L) pole treatment yard is located in the
southern part of Idaho Falls, Idaho, near the east bank of
the Snake River. The site was used for treating electrical
power poles by soaking them in a vat of heated creosote
and then allowing the excess creosote to drip off into a
receiving tank, before stockpiling the poles onsite. In
July 1983, creosote was found to be leaking from
underground piping connecting the treatment vat to a
storage tank Prior to this date, the facility had been
operating for approximately 60 years. In response to the
discovery of the leak, corrective action was initiated that
involved removal of the pole treatment equipment,
excavation of contaminated soil, and installation of a
bedrock (fractured basalt) pump-and-treat system.
11.2.2 Site Characterization

Subsequent to discovering the leak, a major effort was
initiated to remove creosote-contaminated soil and rock
Approximately 37,000 tons of soil were excavated between
July and September 1983 seating a pit 25 ft deep. Soil
samples were taken from 15 locations in the bottom and
walls of the pit to monitor the adequacy of the
contaminated soil removal, In addition, 15 borings were
drilled into the soil surrounding the pit and the bedrock
beneath it. A total of 21 soil and rock samples were
taken and analyzed for creosote compounds. Borings into
bedrock beneath the pit, but above the water table,
revealed the presence of creosote odors and DNAPL
creosote coating the drill rods. Further excavation into
the bedrock was thought to be impractical and the
bottom of the pit was lined with a 12-foot layer of
compacted clay in February 1984. The pit was
subsequently backfilled with clean gravel and capped in
1985.

In May 1984, eight additional bedrock borings were
drilled in the bottom of the excavation. These borings
ranged from 55 to 140 ft deep. Only the deepest boring
reached the water table at a depth of 122 ft. Evidence of
creosote was found in all eight borings based on odor and
creosote coating the drill rods. In addition, creosote
accumulations were found in the bottom of one boring,
which was sampled and analyzed. As shown in Table 11-
1, the highest organic concentrations are poly cyclic
aromatic hydrocarbons (PAHs). Properties of creosote
are discussed in Chapter 3.3.
Fifteen monitor wells were installed and one aquifer test
was conducted on the UP&L property. Four sets of
groundwater samples were collected in 1984 from the
onsite wells. In addition, 21 offsite wells were sampled.
Stratigraphic data from these wells and background
information on regional and site hydrogeology were used
to construct the east-west cross section given in Figure
11-10.

The interlayered basalts form the Snake River Plain
Aquifer, a regional source of water supply. The interflow
zones between the basalt flows are generally permeable
and allow horizontal movement of groundwater.
Fractures within the basalt flows tend to be concentrated
along the upper and lower surfaces of the flow. Vertical
movement of water between the interflow zones is via
fractures in the basalt. Excavation of the creosote-
contaminated gravel at the site in 1983 exposed the top
of a basalt flow, where vertical fractures spaced two to
four ft apart were observed. These fractures were filled
with sand and silt.

The basalt layers beneath the site were classified into
groups, labeled Basalt A through Basalt E, in Figure 11-
10. Each group may include several individual basalt
flows. The fracture zones and interflow zones in the
lower part of Basalt B, below the water table, were
designated as Aquifer #1. This zone is heterogeneous,
but relatively permeable, and generally occurs between
the water table and a depth of about 160 ft. Aquifer #1
is separated from the next lower aquifer by a very dense
basalt flow, which generally extends from shut 160 to
240 ft below ground surface. Below this is Aquifer #2,
corresponding to the interflow zone and weathered basalt
between the bottom of Basalt B and the top of Basalt C.

The water table is more than 100 ft below ground surface
and fluctuates seasonally with an amplitude of about 25
ft. There is a downward vertical hydraulic gradient.
Horizontally, flow is generally toward the southwest, but
the magnitude of the gradient is variable, reflecting the
heterogeneity of the basalt.
11.2.3 Effects of DNAPL presence

Recognizing that DNAPL creosote was present above the
water table, it was suspected that lateral migration of the
creosote might be controlled by the northwest dip of the
interflow zones between the basalt flows. However,
outside the immediate leak area, creosote was only found
above the water table in borings located to the south and
-------
11-12
UP&L POLE YARD
•
r
Figure 11-9. Location of the Utah Power and Light Pole Yard site in Idaho Falls, Idaho (from

USEPA, 1989).
-------
11-13
Table 11-1. Chemical analysis of a creosote sample taken from a borehole drilled into bedrock at
the UP&L Site (from USEPA, 1989). All values in mg/L unless otherwise noted.
INORGANICS
Calcium
Magnesium
Sodium
Potassium
Chloride
Fluoride
Sulfate (SO4)
Nitrate (N)
Total Dissolved Solids
Alkalinity (CaCOj)
Arsenic
Barium
Cadmium
Total Chromium
Iron
Lead
Manganese
Mercury
Selenium
Silver
54.
22.
85.
78.
46.
37.
27.
1.7
1800.
53000.
1.200
3.200
< 0.001
Z100
4900.00
3.000
110.00
0.0050
0.007
0.012
PESTICIDES
Endrin
Lindane
Methoxychlor
Toxaphene
2,4-D
2,4,5-TP
<0.001
<0.001
<0.01
<0.10
<1.0
<0.10
RADIOLOGICAL
Gross Alpha
Gross Beta
Radium-226
Radium-228
-------
11-14
Figure 11-10. East-west geologic cross section across a portion of the Utah Power and Light Pole
Yard site (modified from USEPA, 1989).
-------
11-15
southwest. It was concluded that the basalt is so densely
fractured and has enough vertical permeability that
creosote would sink to the water table, rather than
migrate laterally (Dames & Moore, 1985). This
conclusion has not been verified, however, because no
wells have been drilled into the bedrock to the northwest
in the direction of the dip of the interflow zones.

Pump-and-treat remediation was selected for this site.
Between October 1985 and April 1986, a six-month pilot
study of groundwater extraction and treatment was
conducted. The pilot study showed that more DNAPL
creosote was produced from the wells than had been
expected. The production of DNAPL creosote slugs
caused various operational problems. Creosote was found
to be incompatible with PVC, causing the piping to
time brittle and crack. DNAPL creosote in the waste
stream also caused some of the treatment processes to
clog, requiring more frequent maintenance than expected
In response to these problems, numerous changes to the
treatment plant were made during the period between the
end of the first pilot phase on April 29, 1986, and the
start of the second pilot phase in February 1987.
Additional wells were drilled and data collected prior to
the second pilot phase.

By the time of the second pilot phase, the treatment plant
had been expanded and the treatment processes modified
in response to experience gained from the first pilot
study. Most of the groundwater in the second phase was
produced from wells designed for extraction rather than
from monitor wells, as had been the case in the first pilot
phase. The plan for this phase was to expand the number
of recovery wells incrementally as experience was gained
concerning the behavior of the bedrock aquifers and the
treatment system. The groundwater extraction and
treatment system has continued operating since the
beginning of the second pilot study in February 1987. It
appears that the recovery system will continue operation
into the foreseeable future.

In addition to illustrating certain problems associated
with creosote, this example also illustrates how stressing
the groundwater system during remediation can produce
data that greatly aids understanding the groundwater
system. For complex sites, this type of phased approach
that combines aspects of site characterization with
remediation is recommended.
11.3 HOOKER CHEMICAL SITES, NIAGARA FALLS,
NEW YORK

Hooker Chemical and Plastics Corporation (now known
as Occidental Chemical Corporation or OCC) buried
large quantities of organic chemical manufacturing wastes
at the Love Canal, Hyde Park, S-Area and 102nd Street
landfill Superfund sites in Niagara Falls between 1942 and
1975 (Figure 11-11). Based on fragmentary chemical
production and process residue data, OCC estimated the
types and quantities of wastes buried at each site (Table
11-2). These wastes contain thousands of tons of
DNAPLs, including chlorinated benzenes, chlorotoluenes,
and chlorinated solvents such as carbon tetrachloride,
tetrachloroethene, and trichloroethene. DNAPLs
encountered in the subsurface at the Hooker sites are
typically brown-black mixtures containing numerous
compounds. Representative chemical analyses of DNAPL
samples from each site are given in Table 11-3.

Extensive remedial investigations have been conducted at
each site, in part, to characterize the nature and extent of
subsurface DNAPL contamination. The results of these
studies and hydraulic containment remedies developed
therefrom are described by USEPA (1982), Faust (1984;
1985a), Faust et al. (1990), Cohen et al. (1987), Finder et
al. (1990), OCC/Olin (1990), Conestoga-Rovers and
Associates (1988a,b), and others. Selected findings
regarding the presence and distribution of DNAPL at the
Hooker sites are described below.
11.3.1 Love Canal Landfill

The stratigraphy of the Love Canal area is illustrated in
Figure 11-12. The youngest sediments consist of
approximately 5 ft of silt loam and sandy loam. These
loams are underlain by older, varved glaciolacustrine silty
clay sediments. The upper 6 ft of silty clay (between
about 563 and 569 ft above MSL) are stiff and contain
interconnected prismatic fractures (i.e., major fracture
spacings on the order of 1 to 3 ft) and thin silt
laminations. Transitionally below the stiff silty clay are 6
to 14 ft of soft silty clay above 2 to 20 ft of glacial till.
The till is underlain by the Lockport Dolomite, a
fractured aquifer of regional extent.

Excavation of the Love Canal to enable generation of
hydroelectric power was abandoned after having barely
begun in the 1890s. Its dimensions prior to waste
disposal were approximately 3000 ft long, 40 to 100 ft
-------
11-16
Figure 11-11. Locations of waste disposal sites in Niagara Falls, including the Love Canal,
102nd Street, Hyde Park, and S-Area landfills (from Cohen et al, 1987).
-------
11-17
Table 11-2. Estimated quantities and types of buried wastes at the Love Canal, Hyde Park, S-
Area, and 102nd Street Landfills (Interagency Task Force, 1979).
Type of Waste
Chlorobenzenes
Benzylchlorides
Benzoylchlorides
Thionyl chloride
Trichlorophenol
Liquid disulfldes, monochlorotoluene,
and chlorotoluenes
Miscellaneous chlorinations
Metal chlorides
Miscellaneous acid chlorides
BHC cake including Lindane
Dodecyl mercaptans, chlorides, and
miscellaneous organo-sulfur
compounds
Sulfides and sulfhydrates
C-56 (hexachlorocyclopentadiene) and
derivatives
Thiodan (Endosulfan)
HEX acid
Na hypophosphite mud
BTFs and derivatives
Dechlorane (Mirex)
Calcium fluoride
Mercury brine sludge
Inorganic phosphorus
Organic phosphorus
Phenol tars
Brine sludge and gypsum
Tetrachlorobenzene
BHC, trichlorophenol,
trichlorbobenzene, and benzene
Na chlorite black cake
Graphite
Lime sludge
Brine sludge
Miscellaneous
ESTIMATED TOTAL
Love Canal
2,000
2,400
800
500
200
700
1,000
400
400
6,900
2,400
2,000
-
-
-
-
-
-
-
--
--
--
-
--
-
-
--
--
-
-
2,000
22,000
Hyde Park
16,500
3,400
6,200
-
3,300
2,600
1,600
100
1,200
2,000
4,500
6,600
5,600
1,000
2,100
1,000
8,500
200
400
100
100
4,400
-
-
--
-
-
--
-
--
7300
80,000
S-Area
19,900
1,600
3,300
4,100
200
2,200
400
900
400
--
600
4,200
17,400
700
500
-
--
-
--
--
--
200
800
-
-
--
--
--
--
-
5,700
63,000
102nd Street
-
-
--
--
--
--
-
-
-
300
—
-
--

--
20,000
-- •
--
-
-
1,300
<100
-
53,200
2,327
2,000
18,673
742
22,978
67,186
2,200
200,000
-------
11-18
Table 11-3. Chemical analyses of DNAPL sampled from the 102nd Street, S-Area, Love
Canal, and Hyde Park Landfills in Niagra Falls, New York (from OCC/Olin,
1990; Conestoga-Rovers and Associates, 1988a; Herman, 1989; and Shifrin,
1986).
COMPOUND
Benzene
Chlorobenzene
Dichlorobenzene
Trichlorobenzene
Tetrachlorobenzene
Pentachlorobenzene
Hexachlorobenzene
Toluene
Chlorotoluene
Dichlorotoluene
Total BHCs
Chloroform
Carbon Tetrachloride
Trichloroethene
Tetrachloroethene
Hexachloroethane
Hexachlorobutadiene
Hexachlorocyclopentadiene
Octachlorocyclopentadiene
Hexadecane
Cyclohexadecane
Trimethylpentene
Chloromelhylbenzene
Trichloro(melhyl, ethyl)benzene
Tetrachlorothiophene
Trichlorobiphenyl
Tetrachlorobiphenyl
Pentachlorocyclohexane
Endosulfan II
Mirex
Trichlorophenols
Phenol
Dichlorobenzotrifluorides
Chlorobenzotrifluorides
Methylbenzoate
Butylbenzoate
Trichlorotoluene
SUBTOTAL
102ND STREET
OW-38
0.07
0.64
1.9
7
33.3
11
0.52
0.037

0.057

0.27
0.46
0.053
0.046
0.056
0.21
0.24
0.07
0.54

56.5
S-AREA
OW-213F

0.8
0.6
11.5
32
6.4
1.6
0.1
0.9
0.9
0.4

1.0
0.4
13
1.1
4.2
12
14

0.3
0.1

101.3
LOVE CANAL
CW-90
0.25
1.1
0.91
20.5
71.6
18
0.59
0.%
1.17

2.8

1.7

119.6
HYDE PARK
0.09
0.36
0.19
1.50
2.31
0.43
0.32
1.29
3.00
4.90
0.08
0.09
0.06
0.16
2.10
0.12
0.62

1.20
1.20
1.70
1.20
130
1.09
1.60
26.91
-------
11-19
580-1
570-
97th St.
a;
>
HI
560-
c
pa

o 550-
-O
o
OJ
540-
530-
Fill, Silty Sand,

Sandy Silt
100
Fractured,

Hard Silty Clay
Soft Silty Clay
Glacial Till
Lockport Dolomite

200 Feet
99th St.
-r
Figure 11-12. A schematic geologic cross-section through the Love Canal landfill (from Cohen

et al., 1987).
-------
11-20
wide, and 7 to 16 ft deep. Drummed solid and liquid
chemical wastes were rolled from trucks into the
abandoned canal excavation and into pits dug adjacent to
the canal between 1942 and 1954. Some uncontained
solids and liquids were also disposed of in the landfill.

The waste disposal practice created an irregular landfill
surface that was elevated a few feet above adjacent
residential properties along portions of the site.
Chemical wastes, including DNAPL in drums, were buried
as high as the original ground surface at some locations.
The disposal of liquid chemicals in drums resulted in
drum failure due to corrosion and consolidation. This, in
turn, caused subsidence of cover soil, creation of
'potholes' and caved areas, exposure of displaced
chemicals including NAPL at the surface, emission of
chemical vapors, and increased recharge to the landfill.
Combined with the shallow water table, humid climate,
and limited permeability of the native soils, heavy
recharge promoted the development of a water table
mound at the site and periodic leachate seeps at the
landfill perimeter. Early water-level monitoring at the
site in the Spring of 1978 indicated that "the groundwater
table [was] located immediately below or at the land
surface" of the southern section of the landfill causing
overland flow and the development of leachate ponds in
low areas along the landfill perimeter (Conestoga-Rovers
and Associates, 1978). Basement drains and sewers
surrounding the landfill acted both as hydraulic sinks and
large monitor wells. DNAPL and chemical odors were
observed in various basement sumps and sewer locations.

During the first major offsite drilling program in which
soil borings were augered every 10 ft along a proposed
barrier drain line in backyards adjacent to the southern
sector of the landfill in late 1978, Earth Dimensions
(1979) discovered that an oily film appeared to displace
water in the fractures in the stiff silty clay layer at most
of the augered sites. Pungent odors were reported at
nearly all of the drill sites. These early observations of
DNAPL presence in the fractured silty clay layer resulted
in a decision to lower the leachate collection system drain
to the top of the soft silty clay layer. The perimeter drain
system was installed between 1978 and 1979 to provide
hydraulic containment.

A detailed study of chemical conditions in Love Canal
soils was undertaken jointly by Earth Dimensions (1980)
and the New York State Department of Health (1980).
Continuous split-spoon samples were taken at 64
locations in the immediate vicinity of the landfill.
Detailed logs were prepared to document the vertical
distribution of soil types, chemical odors, and NAPL; and
samples were analyzed for Love Canal chemicals (Figure
11-13). This and other studies documented that:

(1) DNAPL migration is highly correlated with portions
of the site where Hooker disposed of chemical wastes;

(2) DNAPL was commonly found in fractures and in thin
silty laminations (varves) in the stiff silty
glaciolacustrine clay;

(3) DNAPL was rarely found in deep root charnels in the
upper portion of the soft silty clay;

(4) DNAPL generally did not penetrate the soft silty clay
or underlying glacial till layers; and,

(5) The upper surface of DNAPL beneath residential
properties adjacent to the landfill (typically 565 to
567.5 ft) was at a lower elevation than the upper
surface of DNAPL observed during subsequent
drilling in the landfill (typically 568 to 571.5 ft).

The presence of DNAPL in hairline fractures and thin
laminations required careful dissection and inspection to
ensure its detection in the stiff silty clay soil samples.
Relatively low chemical concentrations (low ppm range)
were determined in some fractured silty clay samples with
DNAPL present. Factors contributing to the low
concentration of Love Canal chemicals detected in these
samples apparently include: dilution of NAPL
concentration during sample homogenization, loss of
volatiles during sample handling, and the failure to
conduct analyses for all NAPL components.

In 1986, 21 borings were made with continuous split-
spoon sampling and 15 monitor wells were completed
directly into waste (Figure 11-14) to examine fluid
elevations in the landfill, waste materials, and soils
beneath the landfill (E.G. Jordan G., 1987). To avoid
creating vertical pathways for chemical migration, each
boring was terminated upon retrieval of the first split-
spoon sample of undisturbed soil beneath the waste.
Elevations of immiscible fluid surfaces, the landfill
bottom, and DNAPL encountered in split-spoon samples
at each drilling location are given in Table 11-4. DNAPL
was observed in the chemical waste disposal areas from
the canal bottom to elevations ranging between 567 and
574 ft. Many of the split spoons and spoon samples were
coated with dripping DNAPL. DNAPL surface elevations
measured in the landfill wells ranged from approximately
566 to 574 ft.
-------
11-21
BOREHOLE NUMBER ' Survey DRILLING DATE.

STREET ADDRESS '"''67 97ttl st- BOREHOLE TYPE '
SURVEY LOCATION 60' from 97th Street curb along property
line 763-767 97tB Strett
WEATHER CONDITIONS_clU£_jujulS-

KEY:

«0«iccaHon crack •Oily liquid
• Ctwntfcal odor
97tti STREET — O-*-N

(
rfeT
8
JT)
rwF
5
4 .3 0-
r?7r
>i
• 12

PLAN VIEW
(not to teal*)
Soil Description
Comments
GROUND.
LEVEL u

N 6

i
JT
UJ
0 10

1 A

HnTGBI
sic
O - O /-\ O*
jO -O O>
&Y.O.7.O-
111
A^,Y-,^T^-

Sic :
PsssJijlJ!!

""•^
-------
11-22
: ijOLVIN
BtVD
200 FEET
Figure 11-14. Locations of well completed directly into the Love Canal landfill. The original canal
excavation is shaded, and is enclosed by an outer line designating the approximate landfill
limits.
-------
Table 11-4. DNAPL distribution and properties in wells completed directly into the Love Canal landfill (modified from Finder et al., 1990).
WELL
CW10
CW20
BRM10
CW30
CW40
CW50
CW60
CW70
CW80
CW90
CW105
CW108
FLUID
SURFACE IN
WELL
571.3
572.5
570.5
567.3
-
568.7
567.6
569.1
570.0
570.2
574.1
571.2
DNAPL
SURFACE IN
WELL
571.3
572.5
570.5
None
-
None
566.6
566.5
567.3-569.6
569.4
573.1

CANAL
BOTTOM
563.5
560.9
562.9
563.9
560.5
558.5
557.9
558.8
560.4
560.4
566.7
565.2
INTERVAL
WITH NAPL IN
SPLIT-SPOON
SAMPLES
562.9-568.3
562.2-567.0
563.6-571.4
None
561.9-562.7
None
556.9-571.4
558.8-571.3
558.5-572.5
560.1-569.1
562.7-574.2
562.7-563.2
MAIN
WASTE
TYPE
Chemical
Chemical
Chemical
Municipal
Municipal
Soil nil
Chemical
Chemical
Chemical
Chemical
Chemical
Soil fill
DNAPL
DENSITY
1.15-1.18
1.12
1.09-1.12

1.21-1.25
>1.50

1.18-1.20
1.09-1.22
1.08
DNAPL
VISCOSITY
(q>)
75-81
<17
44-50

21-36
<23

<18
37-270
<16
DNAPL SAMPLE
TEMPERATURE
(°FO
60-62
60
60-64

61-62
53-54

61-62
59-62
71
FLUID PUMPED
FROM WELL
4-5 gallons pumped: all
DNAPL
4-5 gallons pumped: all
DNAPL
3-4 gallons pumped: all
DNAPL

6 gallons pumped: all
DNAPL
Approx. 3 gallons
pumped: more water
than DNAPL

1.5 gallons pumped:
DNAPL and water
Approx. 3 gallons
pumped: mainly
DNAPL
4 gallons pumped:
approx. 30% DNAPL
and 70% water
to
OJ
-------
11-24
Pumping experiments were conducted in the Love Canal
wells during 1988 and 1990 to examine DNAPL fluids
(GeoTrans, 1988; J.R. Kolmer and Associates, 1990).
Typically, 3 to 5 gallons of fluid (equivalent to about 10
to 20 well volumes) were extracted from many of the 2-
inch diameter wells. DNAPL densities ranged from 1.09
to >1.50, and viscosities ranged from very thick (270 cp)
to watery (Table 11-4). At several wells, 3 to 6 gallons of
DNAPL were extracted without any water.

The disposal of large quantities of DNAPL created a
substantial DNAPL pool within Love Canal. Although
wastes were buried between 1942 and 1954, ongoing drum
corrosion provides a long-term mechanism for the release
of mobile DNAPL. Density-driven DNAPL migration
occurs primarily through the fractured silty clay layer at
the base of the DNAPL pool. Fractures, and probably
the silt laminations to a lesser extent, conducted DNAPL
toward basement and sewer drains. The soft silty clay
layer is an effective capillary barrier to DNAPL
penetration: it forms the bottom of the DNAPL site.
DNAPL that migrated to offsite properties (Figure 11-15)
was a moving contaminant source from which chemicals
dissolved into groundwater and volatilized into soil gas
and basement air.

Since the installation of the tile-drain system during the
late 1970s, approximately 30,000 gallons of DNAPL have
been collected and stored in holding tanks at the onsite
leachate treatment plant. The perimeter drain system
appears to be an effective hydraulic barrier based on fluid
elevation and chemical monitoring. The pumping
experiments conducted in landfill wells demonstrate that
large quantities of DNAPL can probably be recovered
directly from wells in the landfill if incineration or some
other treatment technology can be shown to be cost-
effective at a site where long-term hydraulic containment
will be needed in any event.
11.3.2 102nd Street Landfill

The 102nd Street landfill is adjacent to the upper Niagara
River and a short distance south of Love Canal (Figure
11-11). Hooker disposed of approximately 77,00 tons of
predominantly inorganic wastes on the western 15.6 acres
of the 22-acre site between 1943 and 1971. During a
similar time period, Olin Chemical Corporation dumped
an estimated 66,000 tons of wastes on the eastern portion.
Approximately 10 to 15 ft of wastes were deposited above
alluvium at the river edge, raising a swampy area to the
grade of Buffalo Avenue to the north. The landfill was
closed in 1971 after the U.S. Army Corps of Engineers
ordered the companies to construct a bulkhead to prevent
erosion of wastes into the river.

The stratigraphy of the 102nd Street landfill site differs
from that at Love Carol due to erosion and sedimenta-
tion by the Niagara River. As shown in Figure 11-16, the
Lockport Dolomite is overlain by glacial till, soft silty
clay, river alluvium, and fill materials. The river eroded
the soft silty clay in the southern portion of the site and
replaced it with silt, sand, and gravel alluvium that
coarsens with depth and proximity to the river. The
alluvium pinches out near the northern site boundary. In
some areas along the southern site boundary, the silty
clay was completed eroded and the alluvium is underlain
directly by glacial till.

OCC/Olin (1990) undertook a comprehensive remedial
investigation at the site between 1985 and 1988 to
augment prior studies and facilitate evaluation of
remedial alternatives. Based on a review of historic
company documents, interviews with former personnel,
and interpretation of historic aerial photographs, the
companies identified suspected NAPL disposal areas at
the site as shown in Figure 11-17. All samples collected
during the remedial investigation, regardless of matrix
(i.e., soil, rock groundwater, river sediment, waste, etc.)
were examined visually for the presence of NAPL Static
groundwater was extracted from the top and bottom of
the water column in numerous overburden wells to
examine for NAPL presence. Where adequate volumes
could be obtained, DNAPL samples were taken for
laboratory examination of chemical and physical
properties.

DNAPL samples were analyzed for the USEPA Contract
Laboratory Protocol Target Compound List parameters
and an effort was made to identify the remaining
chromatogram peaks. Water content and major element
composition were also determined for some samples.
Resulting analytical mass balances ranged from 58 to 137
percent. OCC/Olin (1990) concluded that aliphatic
compounds, and high-molecular weight polymeric
compounds to a lesser extent, probably constitute the
majority of compounds not quantified by GC/MS analysis.
Water contents of the DNAPL samples ranged from 0.1
to 64%. Overall, DNAPL at the 102nd Street site was
determined to be composed primarily of chlorinated
benzenes. DNAPL densities and absolute viscosities
generally ranged between 1.3 to 1.6 g/cm3, and between 2
and 8 cp (at 25 to 40° C), respectively.
-------
11-25
CHEMICAL ODOR
X OR VAPOR IN
SOIL OR BASEMENT
CHEMICAL WASTE
DISPOSAL AREA
• NAPL NOTED
GROUNDWATER
CONCENTRATION
>10% OF THE
SOLUBILITY LIMIT
CHEMICAL ODOR
NOTED AT EACH
SITE AND NAPL
NOTED AT MOST
SITES

LEACH ATE OR
LIQUID WASTE
NOTED
CHEMICALS DETECTED
IN PONDED WATER.
GROUNDWATER, OR
SOIL
CHEMICALS NOT
pi DETECTED ABOVE
L-J 10 PPB IN
GROUNDWATER
PRIMARILY
MUNICIPAL
REFUSE
Figure 11-15. Areal distribution of DNAPL and chemical observations at Love Canal (north half
to the left; south half to the right).
-------
LASALLE EXPRESSWAY
ON

O
8?
OQ
s
oo o
• o

o
£
t-1
p
C/)

O
I
Uj 530
bOO -I
(Ml)
"I"
100
I
300
|-~
500
' T
700
1 ~-
BOO
I""
900
f
1200
~" I "
1300
1
1400
LEGEND

(Ml) T MQItlTORINO IN TD(VA1
HORIZONTAL DISTANCE (FEET)
WAFtH SURFACE
-------
BUFFAI0 AVENUE (RIVER ROAD)
OCCIDENTAL CHEMICAL CORPORATION
to
•^
NIAGARA tt/\£ft
LEGEND:

| ^ J SUSPECTED NAPL DISPOSAL AREA
SUSPECTED NAPL DISPOSAL AREAS
REMEDIAL INVESTIGATION
102nd Street Landfill Site
Figure 11-17. Suspected NAPL disposal areas at the 102nd Street Landfill (from OCC/Olin. 19901.
-------
11-28
Five separate areas of DNAPL presence were interpreted
at the site (Figure 11-18) based on differences in DNAPL
chemistry, knowledge of waste disposal history, and the
many data points (OCC/Olin, 1990). Within each area,
the DNAPL distribution is expected to be highly complex
Simplified conceptual cross sections were developed as
illustrated in Figure 11-19. As shown, DNAPL has
migrated downward by gravity and appears to have spread
along the stratigraphic interfaces at the top and bottom
of the alluvium. In the largest and most complex
DNAPL area (Area 5 on Figure 11-18), DNAPL appears
to be accumulating in a stratigraphic trap formed by the
surface of the clay-till capillary barrier (Figures 11-19 and
11-20). DNAPL was not observed within the silty clay,
glacial till, or bedrock at the site.

Based on borings in the Niagara River, and the apparent
stratigraphic trap present beneath the southern edge of
the site, it appears that the potential for offsite DNAPL
migration to beneath the Niagara River is very limited.
This potential will be further examined when additional
borings are installed offshore adjacent to the site to
facilitate detailed design of the site containment system
(OCC/Olin, 1990).
11.3.3 Hyde Park Landfill

The Hyde Park landfill is 2000 ft east of the deep gorge
formed by the Niagara River downstream from the Falls
(Figure 11-11). Between 1953 and about 1975, Hooker
disposed of an estimated 80,000 tons of liquid and solid
chemical wastes in trenches and pits at the this 15-acre
site (Table 11-2).

Approximately 15 to 30 ft of chemical waste at the site
are underlain by O to 10 ft of silty clay sediments which
overlie the Lockport Dolomite. The Lockport Dolomite
ranges from 60 to 140 ft thick in the vicinity of the
landfill. Groundwater flow in the bedrock can be
idealized as a sequence of flat-lying, water-bearing zones
(with significant bedding plane fractures) that are
sandwiched between water-saturated layers of reduced
permeability (Faust et al, 1990). Vertical fractures
provide an avenue for fluid transmission through the less
permeable layers.

Unlike the Love Canal and 102nd Street landfills where
fine-grained capillary barrier layers limit downward
DNAPL migration, there is no bottom to the DNAPL
site in the overburden at Hyde Park. The Hyde Park
landfill was excavated to bedrock in some areas, providing
a direct route for density-driven DNAPL migration into
the fractured Lockport Dolomite aquifer. As a result,
extensive and extremely complex distributions of DNAPL
and dissolved chemicals derived from the landfill are
present in the dolomite in the vicinity of the site.

The extent and degree of chemical contamination
emanating from the Hyde Park site was evaluated during
studies conducted by OCC in 1982 and 1983. A major
component of these studies involved drilling to determine
the extent of chemical contamination in the overburden
and bedrock. Borings were cored and tested in 15-ft
sections to the top of the Rochester Shale (bottom of the
Lockport Dolomite) in a manner similar to that described
in Chapter 9.4 along ten vectors radiating out from the
landfill perimeter (using the "inside-out" approach
discussed in Chapter 9.2). As noted in Chapter 9.4, the
degree of DNAPL migration induced by the drilling
program is unknown. Brown-black DNAPL was obvious
on many of the contaminated core sections. Along each
vector, survey wells were installed at 800 ft intervals until
a well showed no chemical parameters above the survey
levels. To better delimit the dissolved plume, a well was
then installed midway between the outer two wells.
Nearly 300 intervals in the Lockport Dolomite were
sampled by this procedure. The wells were grouted after
Wing.

This program revealed extensive subsurface migration of
DNAPL chemicals from the landfill. Hyde Park
chemicals were detected in seeps emanating from the
dolomite along the Niagara Gorge in 1984. Dissolved
chemical and DNAPL plumes determined from these
studies are delineated in Figure 11-21.

Immiscible flow modeling was conducted to conceptually
examine planned hydraulic containment and DNAPL
recovery options (Faust et al., 1989). The modeling
analyses demonstrate that:

(1) Viscosity should be measured to provide better
predictions of potential DNAPL recovery;

(2) Wells should be operated at pumping rates that do
not significantly dewater the aquifer adjacent to the
wells;

(3) Wells should be open primarily to the permeable
zones containing the highest saturations of DNAPL;
and,
-------
E (RIVER ROAD)
OCCIDENTAL \ CHEMICAL CORPORATION
PROPERTY LINE
SEWER BEDDING WEU
WASTE MONITORING WELL
ALLUVIUM MONITORING WEU
BEDROCK/OVERBURDEN INTERFACE I 1 HNAPL PRESENCE
MONITORING WEIL
BEDROCK MONITORING WEI I
USEPA LOVE CANAL WELL NESTS
BOREHOLES
IDENTIFIED BULKHEAD SEEP
MOST LIKELY LIMIT Of
HNAPL PRESENCE
APPROXIMATE MM! I Of
NIAGARA KIVEK
PSJ POSSIBtE SEEP BASED ON INSPECTION
MAY 5. 19B7
1O2nd Street Landfill Site
to
Figure 11-18. Approximate horizontal extent of DNAPL in fill and alluvium at the 102nd Street Landfill (from OCC/Olin, 1990).
-------
CROSS - SECTION A-A
CONCEPTUAL NAPL DISTRIBUTION
REMEDIAL INVESTIGATION
102nd Street Landfill Site
Figure 11-19. Typical conceptual DNAPL distribution along a cross-section at the 102nd Street Landfill (from OCC/Olin, 1990).
-------
11-31
T6f> OF GLACIOLACUST1NE CLAr
REMEDIAL INVESTIGATE
102nd Street Landfill Site
/ / TOP OF GLACIAL TILL
REMEDIAL INVESTIGATION
1O2nd Street Landfill Sit
Figure 11-20. The surface of the silty clay and glacial till capillary barrier layers appear to form a
stratigraphic trap beneath the south-central portion of the site (from OCC/Olin,
1990).
-------
11-32
I Bedrock APL Plume |

"
Bedrock MAPI Plume
u?.....-'/i -Z^-''-
X. .-z\
Overburden
NAPL Plume
A o n Overburden Wells

• • Bedrock Wells
Figure 11-21. Boundaries of dissolved chemical and DNAPL plumes emanating from the Hyde
Park Landfill (from Cohen et al., 1987).
-------
11-33
(4) DNAPL recovery rates should be monitored frequent-
ly on a well-by-well basis to aid prediction of DNAPL
recovery rates and to decide when to delete and/or
add new extraction wells.
11.3.4 S-Area Landfill

The S-Area is located within the OCC manufacturing
plant in Niagara Falls (Figure 11-11). The S-Area
property was partially reclaimed from the Niagara River
by dumping fill materials between 1938 and 1947.
Hooker buried an estimated 63,000 torts of liquid and
solid chemical residues at the site between the late 1940s
and 1961. Wastes were disposed of in 15 to 18 ft deep
parallel trenches, and some wastes were buried in tank
cars.

The discovery of contaminated sludge in water supply
tunnels cut into the Lockport Dolomite that convey river
water to the City of Niagara Falls water treatment plant
adjacent to the S-Area site (Figure 11-22) aroused
concern regarding chemical migration from the landfill in
1978. Subsequent investigations revealed that the clay-till
aquitard that is present at the 102nd Street landfill is
absent beneath a portion of the site. Whereas the clay-
till surface appears to form a stratigraphic trap for
DNAPL accumulation at the 102nd Street landfill,
discontinuity in the clay-till surface beneath the S-Area
site provides a conduit for DNAPL migration to the
Lockport Dolomite.

DNAPL and dissolved chemicals have migrated significant
distances from the S-Area landfill in overburden and
bedrock. Extensive drilling and testing surveys conducted
by OCC between 1986 and 1988 generally delineated the
extent of contamination at the site (Conestoga-Rovers
and Associates, 1988a,b). Protocols for drilling in
bedrock at S-Area are described in Chapter 9.4, and
observations of DNAPL in bedrock wells is shown in
Figure 9-7. Conestoga-Rovers and Associates (1988)
noted an increase in DNAPL density and decrease in
DNAPL viscosity with depth in the Lockport Dolomite
beneath S-Area.
and remediation activities. Knowledge or suspicion of
DNAPL presence requires that special precautions be
taken during field work to minimize the potential for
inducing unwanted DNAPL migration by drilling or
pumping. Delineation of subsurface geologic conditions
is crucial to site evaluation because DNAPL movement
can be largely controlled by the capillary properties of
subsurface media. It is particularly important to
determine, if practicable, the spatial distribution of fine-
grained capillary barriers and preferential DNAPL
pathways (e.g., fractures and coarse-grained strata).
Finally, the case studies evidence that it will usually be
necessary to control (i.e., contain or remove) DNAPL
zone contamination in order to attempt restoration of the
aquifer downgradient from the DNAPL source. Failure
to adequately consider DNAPL presence can lead to a
flawed assessment of remedial alternatives.
11.4 SUMMARY

The case studies illustrate several critical aspects of
DNAPL site evaluation. Assessing DNAPL presence
based on historic information, field observations, and
monitoring data is needed to guide site characterization
-------
11-34
• City Water
Treatment Plant
. Lagoons .* . v
Niagara River
• Overburden
o Bedrock
\ \
Figure 11-22. Proximity of the City of Niagara Falls Water Treatment Plant water-supply intake
tunnels to the S-Area Landfill (from Cohen et al., 1987).
-------
12 RESEARCH NEEDS

As awareness of DNAPL contamination increased in the
1990s, research was conducted to better understand the
behavior of DNAPL in the subsurface. Much of this
research was an expansion of the investigations performed
by Schwille (1988). DNAPL research is currently
focusing on remediation (National Center for
Groundwater Research, 1992). Through this progression
of DNAPL research, relatively little effort has been
expended on developing new site characterization tools or
methods for DNAPL sites.

What has generally occurred at DNAPL sites is that tools
and techniques utilized at contamination sites in general
have been applied with varying degrees of success.
Additionally, some new tools and methods have been
developed and others have been adapted to better satisfy
the requirements of a DNAPL site investigation. Site
characterization strategies have also evolved to more
closely match the special concerns and risks posed by
DNAPL presence.

Despite substantial progress, additional research on
DNAPL site characterization tools and methods is
warranted utilizing a variety of venues: laboratories,
controlled field sites with emplaced DNAPL, and
uncontrolled contamination sites. Additional research
and technology transfer efforts should focus on:

(1) Well drilling techniques to demonstrate the isolation
of DNAPL zones through the use of double-cased
wells or other techniques;

(2) Well and boring abandonment techniques to
demonstrate the efficacy of different grouting
mixtures and methods to prevent preferential vertical
fluid migration;

(3) The utility of surface and borehole geophysical
methods to better characterize DNAPL presence and
distribution, and stratigraphic controls on DNAPL
movement;

(4) The utility of soil gas surveying to better characterize
NAPL presence and related chemical migration;

(5) Methods to determine in-situ NAPL saturation (e.g.,
borehole geophysics, simple quantitative sample
analysis);
(6) Techniques to determine field-scale constitutive
relationships between saturation, capillary pressure,
and relative permeability;

(7) Practical field or laboratory techniques to delineate
mobile DNAPL from DNAPL in stratigraphic traps
from DNAPL at residual saturation;

(8) Additional cost-effective methods to determine
NAPL presence, composition, and properties;

(9) Techniques to better define site stratigraphy,
heterogeneity, and fracture distributions;

(10) The long-term capacity of capillary barriers (e.g.,
clayey soil layers) to prevent DNAPL movement,
including methods for determining barrier continuity
and time-dependent aspects of DNAPL-mineral
structure and wettability interactions;

(11) Identifying the limited characterization efforts
required to determine and implement appropriate
remedial measures at DNAPL contamination sites;

(12) Further optimization of characterization strategies
given different source, hydrogeologic, risk and
remedy considerations; and,

(13) Refinement of pilot test designs, protocols, and
monitoring requirements to determine the feasibility
and/or technical impracticality of alternative
remedial measures.
-------
-------
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APPENDIX A: DNAPL CHEMICAL DATA
A.1 DATA TABLE ENTRIES

Selected DNAPL chemical data are provided in Table A-
1. Types of data listed are described below.

The CAS# is a unique identifier given by the American
Chemical Society to chemicals included in the Chemical
Abstracts Service Registry System. It is utilized to access
several chemical databases and facilitates identification of
compounds with multiple and ambiguous names.

Empirical formula identifies the carbon, hydrogen, and
other elements within a particular compound.

Formula weight is the weight of one mole of a compound
which contains Avogadro's number of molecules
(6.022045 x 1023). It is calculated by summing the atomic
weights given by the compound empirical formula.

Specific density is the density of a compound at a
reference temperature, usually 20°C., divided by the
density of water, usually at 4° C. All values are given
using this convention, except where a different
temperature associated with the density of the compound
is given in the reference column.

Absolute viscosity, also known as dynamic viscosity, refers
to the internal friction derived from molecular cohesion
within a fluid that causes it to resist flow. It can be
defined as (Lucius et al., 1990): "the ratio between the
applied shear stress and the rate of shear" or the "force
per unit area necessary to maintain a unit velocity
gradient at right angles to the direction of flow between
two parallel plates a unit distance apart." Kinematic
viscosity equals the absolute viscosity divided by the liquid
density. Absolute viscosity values are given in centipoise
(cp) at 20° C. unless a different temperature is noted in
parentheses in the references column.

Boiling point is the temperature at which the vapor
pressure of a liquid equals or slightly exceeds atmospheric
pressure. Values are given in degrees C.

Melting point is the temperature, usually measured in
degrees C. at 1 atmosphere, at which the liquid and
crystalline phases of a substance are in equilibrium.

Aqueous solubility is the saturated concentration of a
compound in water at a given temperature and pressure
(20°C. and 1 atmosphere unless otherwise noted in the
references column). Representative values are listed for
compounds having multiple values reported in the
literature.

Vapor pressure is the partial pressure exerted by the vapor
of the liquid (or solid) under equilibrium conditions at a
given temperature, which is 20° C. unless otherwise noted
in the references column. A relative measure of chemical
volatility, vapor pressure is used to calculate air-water
partition coefficients (i.e., Henry's Law Constants) and
volatilization rate constants. Values are given in mm Hg
(or Torr).

Henry's Law Constants are air-water partition coefficients
that compare the concentration of a compound in the gas
phase to its concentration in the water phase at
equilibrium. Values are calculated by multiplying vapor
pressure (atm) by formula weight (g/mole) and then
dividing by aqueous solubility (g/m3) and listed in atm-
mVmole at 25° C.

KQC, a soil/sediment organic carbon to water partition
coefficient, is defined as:

v — <"* / f iA ^\
*Sx ~ ^"oc ' ^w \^-~ 1)

where C^. is the equilibrium concentration of a chemical
adsorbed to organic carbon in soil (mg chemical/kg
organic carbon), and C,, is the equilibrium concentration
of the same chemical dissolved in groundwater (mg
chemical/L of solution). Log K^ values are given in
units of mL/g. Representative values are listed for
compounds having multiple values reported in the
literature.
the n-octanol-water partition coefficient, defines the
ratio of solute concentration in the water-saturated n-
octanol phase to the solute concentration in the n-octanol
saturated water phase (Montgomery, 1991). It reflects the
relative affinity of a chemical for polar (water) or non-
polar (hydrophobic organic) media. Values are unitless.
Representative values are listed for compounds having
multiple values reported in the literature.

Vapor density is the mass of chemical vapor per unit
volume. It can be calculated as
VD = (P (FW)) / R K
(A-2)
where VD is vapor density (g/L), P is pressure (atm), FW
is formula weight (g/mol), R is the ideal gas constant
(0.0820575 atm-L/mol-K), and K is the temperature
(degrees Kelvin). Calculated values in g/L are provided
-------
A-2
Table A-l. Selected data on DNAPL chemicals (refer to explanation in Appendix A.)
DNAPL
Aniline
o-Anisidine
Benzyl alcohol
Benzyl chloride
Bis(2-chloroelhyl)ether
Bis(2-chloroisopropyl)ether
Bromobenzene
Bromochloromelhane
Bromodichloromelhane
Bromoethane
Bromoform
Butyl benzyl phthalate
Carbon disulfide
Carbon tetrachloride
Chlorobenzene
2-Chloroclhyl vinyl ether
Chloroform
1-Chloro-l-nitropropane
2-Chlorophenol
4-ChIorophenyl phenyi ether
Chloropicrin
m-Chlorololuene
o-Chlorotoluene
p-Chlorotoluene
Dibromochloromelhane
l,2-Dibromo-3-chloropropane
Dibromodifluoromethane
Oibulyl phthalate
1 ,2-Dichloro benzene
13-Dichlorobenzene
1,1-Dichloroeihane
1,2-Dichloroethane
1,1-Dichloroethene
trans-l,2-Dichloroethene
1 ,2-Dichloropropane
cis-l,3-Dich!oropropene
trans- 1 ,3-Oichloropropene
Dichlorvos
Diethyl phthalate
Dimethyl phthalate
Synonym
Benzenamine
2-Methoxybenzenamine
Benzenemethanol
Chloromethylbenzene
Bis( -chloroethyl)ether
Bis( -chloroisopropyl)ether
Phenyi bromide
ChlorobrDmomethane
Dichlorobromomethanc
Ethyl bromide
Tribromomethane
Benzyl butyl phthalate
Carbon bisulfide
Tetrachloromethane
Benzene chloride
(2-ChloroethoxyXthene
Trichloromethane
Chloronitropropane
o-Chlorophenoi
p-Chlorodiphenyl ether
Trichloronitromethane

2-Chloro-l-melhyIbenzene

Chlorodibromomelhane
DPCP
Freon 12-B2
Dibutyl-n-phthalate; DBP
o-Dichlorobenzene
m-Dichlorobenzene
1,1-DCA
Ethylenedichloride; 1,2-DCA
Vinylidcne chloride; 1,1 -DCE
trans-l,2-DCE
Propylene dichloride
cis-l,3-Dichloropropylene
trans-1 3-Dichloropropylene
No-Pest Strip
DEP
DMP
CAS#
62-53-3
90-04-0
100-51-6
100-44-7
111-44-4
108-60-1
108-86-1
74-97-5
75-27-4
74-96-4
75-25-2
85-68-7
75-15-0
56-23-5
108-90-7
110-75-8
67-66-3
600-25-9
95-57-8
7005-72-3
76-06-2
108-41-8
95-45-8
106-4M
124^8-1
96-12-5
75-61-6
84-74-2
95-50-1
541-73-1
75-34-3
107-06-2
75-35-4
156-60-5
78-87-5
10061-01-5
10061-02-6
62-73-7
84-66-2
131-11-3
Empirical
Formula
C6H7N
C7H9NO
C7H80
C7H7Q
C4H8C12O
C6H12C12O
C6H5BR
CH2BK3
CHBrC12
C2H5Br
CHBr3
C19H2004
CS2
CQ4
C6H5C1
C4H7C10
CHC13
C3H6CINO2
C6H5CIO
C12H9C10
CC13N02
C6H4CH3C1
C6H4CH3CI
C6H4CH3CI
CHBr2Cl
C3H5Br2CI
CBr2F2
C16H22O4
C6H4CI2
C6H4CI2
C2H4CI2
C2H4C12
C2H2C12
C2H2C12
C3H6C12
C3H4C12
C3H4C12
C4H7CI214P
C12H14O4
C10H10O4
Formula
Weight
(g)
93.13
123.15
108.14
126.59
143.01
171.07
157.01
129 39
163.83
108.97
25173
31231
76.13
153.82
112^6
106.55
11938
123.54
128J6
204.66
164.38
126.59
126.58
126.59
208.28
236.36
209.82
278.35
147.00
147.00
98.96
98.%
96.94
96.94
112.99
110.97
110.97
220.98
222.24
194.19
Ref.
b
b
a
a
b
a
b
b
a
b
a
a
a
a
a
a
a
b
a
a
b
f
f
f
a
b
b
a
a
a
a
a
a
a
a
a
a
b
a
a
Specific
Density
(g/«)
1.022
1.092
1.045
1.100
1.220
1.103
1.495
1.934
1.980
1.460
2.890
1.120
1.263
1.594
1.106
1.048
1.483
1.209
1.263
1.203
1.656
1.072
1.082
1.066
2.451
2.050
2.297
1.046
1.305
1.288
1.176
1.235
1.218
1.257
1.560
1.224
1.182
1.415
1.118
1.191
Ref.
b
b
a
a
b
a
b
b
a
b
a
a
a
a
a
a
a
b
a
a
b
f
f
f(25)
a
b
b
a
a
a
a
a
a
a
a
a
a
b(25)
a
a
Absolute
Viscosity
(cp)
4.40

7.76

2.14

0.99
0.57
1.71
0.418
2.02

0.37
0.97
0.80

0.58

2.25

0.75
0.75

20.30
1.32
1.04
0.44
0.80
0.36
0.40
0.86

35.00
17.20
Ref.
c

d(15)

c(25)

e(30)
h
e
d(15)
c

c
c
c

e(45)

h(38)
h(38)

c
c(25)
c(25)
c
c
c
c
c

c
c(25)
-------
A-3

Table A-l. Selected data on DNAPL chemicals (refer to explanation in Appendix A).
DNAPL
Ethylcne dibromide
Hexachlorobutadiene
Hexachlorocyclopentadiene
lodomethane
1-Iodopropane
Malathion
Methylene chloride
Nitrobenzene
Nitroethane
1-Nitropropane
2-Nilrotoluene
3-Nitrotoluene
Parathion
PCB-1016
PCB-1221
PCB-1232
PCB-1242
PCB-1248
PCB-1254
Penlachlorocthane
l,lA2-Tetrabromoethane
1,1^2-Tetrachloroethane
Tetrachloroethene
Thiophene
1,2,4-Trichlorobenzcne
1.1,1 -Trichloroelhane
1,1,2-Trichloroethane
Trichloroelhene
1,1,2-Trichlorofluoromethane
1 ,23-Trichloropropane
1,1,2-Trichlorotrifluoroelhane
Tri-o-cresyl phosphate

Water
Synonym
1,2-Dibromoethane; EDB
HCBD
HCCPD
Methyl iodide
Propyl iodide

Dichloromethane
Nitrobenzol
UN 2842
UN 2608
1 -Methyl-2-nitrobenzene
1 -Methyl-3-nitrobenzene

Aroclor 1016
Aroclor 1221
Aroclor 1232
Aroclor 1242
Aroclor 1248
Aroclor 1254
Ethane pentachloride
Acetylene tetrabromide
Acetylene tetrachloride
Perchloroethylene: PCE
Thiacylopentadiene
1,2,4-TCB
Methyl chloroform; 1,1,1-TCA
1,1,2-TCA
TCE
Freonll
Ally! trichloride
Freon 113
o-Cresyl phosphate

Ice
CAS#
106-93-4
87-68-3
77-47-4
74-88-4
107-08-4
121-75-5
75-09-2
98-95-3
79-24-3
108-03-2
88-72-2
99-08-1
56-38-2
12674-11-2
11104-28-2
11141-16-5
53469-21-9
12672-29-6
11097-69-1
76-01-7
79-27-6
79-34-5
127-18-4
110-02-1
120-82-1
71-55-6
79-00-5
79-01-6
75-69-4
96-18-4
76-13-1
78-30-8

7732-18-5
Empirical
Formula
C2H4Br2
C4CI6
C5CI6
CH3I
C3H7I
C10H19O6PS2
CH2O2
C6H5N02
C2H5N02
C3H7NO2
C7H7NO2
C7H7NO2
C10H14NO5PS
varies
varies
varies
varies
varies
varies
C2HO5
C2H2Br4
C2H2Q4
C2CI4
C4H4S
C6H3C13
C2H3C13
C2H3C13
C2HC13
CO3F
C3H5C13
C2O3F3
C21H21O4P

H2O
Formula
Weight
(g)
187.86
260.76
272.77
141.94
169.99
330.36
84.93
123.11
75.07
89.09
137.14
137.14
291.27
257.90
192.00
221.00
261.00
288.00
327.00
20128
345.65
167.85
165.83
84.14
181.45
133.40
133.40
13139
137.37
147.43
187.38
368.37

18.02
Rcf.
b
a
a
b
b
b
a
a
b
b
b
b
b
a
a
a
a
a
a
b
b
a
a
b
a
a
a
a
a
b
b
b

Specific
Density
(g/cc)
2.179
1.554
1.702
2.279
1.749
1.230
1.327
1.204
1.045
1.008
1.163
1.157
1.260
1.330
1.180
1.240
1392
1.410
1.505
1.680
2.875
1.595
1.623
1.065
1.454
1.339
1.440
1.464
1.487
1.3889
1.564
1.955

1.000
Ref.
b
a
a
b
b
X25)
a
a
K25)
K24)
b
b
b
a(25)
a(25)
a(25)
a(15)
a(25)
a(15)
b
b
a
a
b
a
a
a
a
a
b
b
b

Absolute
Viscosity
(cp)
1.72
Z45

0.52
0.84

0.43
2.01
0.66
0.80
2.37

193
4.8
8.2
24
65
700
2.75
9.79
1.75
0.89
0.65
1.42
1.20
0.12
OJ57
0.42

80.00

1.00
Ref.
c
c(38)

d(15)
d(15)

c
c
d(25)
d(25)
d

g(38)
g(38)
g(38)
g(38)
g(38)
g(38)
d(15)
d
c
c
d
c
c
c
c
c<25)

-------
Table A-l. (continued)
A-4
DNAPL
Aniline
o-Aniaidine
Benzyl alcohol
Benzyl chloride
Bis(2-chloroethyl)cther
Bis(2-chloroisopropyl)ether
Bromobenzene
Bromochloromethane
BromodichloFomethane
Bromoelhane
Bromoform
Butyl benzyl phthalate
Carbon dUulfide
Carbon tetrachloride
Chlorobenzene
2-Chloroelhyl vinyl ether
Chloroform
1-Chloro-l-nitFopropane
2-Chlorophenol
4-ChloFOphenyl phenyl ether
Chloropicrin
m-Chlorotoiuene
o-Chlorololucne
p-Chlorotoluene
Dibromochloromethane
1 ,2-Dibromo-3-chloropropane
Dibromodifluoromethane
Dibutyl phthalale
1,2-Dichlorobenzene
1,3-Dichlorobenzene
1,1-Dichloroethane
1,2-Dichloroethane
1.1-Dichloroelhene
lrans-1 ,2-Dichloroethene
1,2-Dichloropropane
cij-13-Dichloropropene
trans-l,3-Dichloropropene
Dichlorvos
Diethyl phthalate
Dimethyl phthalale
Boiling
Point
(deg.Q
184
224
205
179
179
187
156
68
90
38
149
370
46
77
132
108
62
142
175
284
112
160
159
162
117
1%
23
335
180
173
56
83
37
47
%
104
112

298
283
Ref.
b
b
a
a
b
a
b
b
a
b
a
a
a
a
a
a
a
b
a
a
b
f
f
f
a
b
b
a
a
a
a
a
a
a
a
a
a

a
a
Melting
Point
(deg.Q
-6
6
-15
-39
•47
-20
-31
•S7
-57
-119
8
-35
-112
-23
•46
-70
-63
<25
9
-8
-64
-48
-34
7
-22
6
-141
-35
-17
-25
-97
-35
-122
-50
-100
-84
-84

-40
0
Ref.
b
b
a
a
b
sax
b
b
a
b
a
a
a
a
a
a
a
b
a
a
b
f
f
f
a
b
b
a
a
a
a
a
a
a
a
a
a

a
a
Aqueous
Solubility
(mg/L)
3-50E-KM
1JOE+04
3.50E+04
4.93E+02
1.02E+04
1.70E+03
5.00E+02
1.67E+04
4.50E+03
9.14E+03
3.01E+03
Z82E+00
2.10E+03
8.00E+02
5.00E+02
l.SOE+04
8.00E+03
6.00E+00
2.85E+04
3 JOE +00
2.00E+03
4.80E+01
7.20E+01
4.40E+01
4.00E+03
l.OOE+03

1.01E+01
l.OOE+02
1.11E+02
5.50E+03
8.69E+03
4.00E+02
6.00E+02
2.70E+03
2.70E+03
2.80E+03
l.OOE+04
9.28E-I-02
4.29E+03
Ref.
b
b
a
a
b
a
b
b(25)
a(0)
b
a
a
a
a
a
a
a
b
a
a(25)
b
e
e
e
a
b

a
a
a
a
a
a
a
a
a
a
b
a
a
Vapor
Pressure
(mmHg)
3.00E-01
<0.1
<1
9.00E-01
7.10E-01
8^0E-01
3.30E-I-00
1.41E+00
5.00E+01
3.75E+02
4.00E+00
8.60E-06
198E+02
9.00E+01
9.00E+00
Z68E+01
1.60E-f02
5.80E+00
1.42E-KK)
2.70E-03
ZOOE+01
4.60E+00
2.70E-KH)
4.50E+00
7.60E+01
8.00E-01
6.88E+02
1.40E-05
l.OOE+00
2.30E+00
1.82E+02
6.40E+01
4.95E+02
2.65E+02
4.20E+01
2JOE+01
2.50E+01
1.20E-02
1.65E-03
1.65E-03
Ref.
b
b
a
a
b
a
b
b(25)
a
b
a
a
a
a
a
a
a
b(25)
a(25)
a(25)
b
e
f
e
a
b
b
a(25)
a
a(25)
a
a
a
a
a
a
a
b
a(25)
a(25)
Henry*! Law
Constant
(alm-m3/mo))
1J6E-01
1.25E-06

3.04E-04
1JOE-05
1.10E-04
2.40E-03
1.44E-03
2.12E-04
7.56E-03
5.32E-04
1JOE-06
1.33E-02
3.02E-02
4.45E-03
2JOE-04
3.20E-03
1.57E-01
8.28E-06
120E-04
8.40E-02
1.60E-02
6.25E-03
1.70E-02
9.90E-04
2.49E-04

6.30E-05
1.90E-03
3.60E-03
4.30E-03
9.10E-04
2.10E-02
3.84E-01
2.30E-03
1.30E-03
1.30E-03
5.00E-03
8.46E-07
4.20E-07
Ref.
b
b
a
a
b
a
b
b
a
b
a
a
a
a
a
a
a
b
a
a
b
e
e
e
a
b

a
a
a
a
a
a
a
a
a
a
b
a
a
-------
Table A-l. (continued)
A-5
DNAPL
Ethylene dibromide
Hexachlorobutadiene
Hexachlorocyclopentadiene
lodomethane
1-Iodopropane
Malathion
Methylene chloride
Nitrobenzene
Nitroethane
1-Nitropropane
2-Nitrotoluene
3-Nitrotoluene
Parathion
PCB-1016
PCB-1221
PCB-1232
PCB-1242
PCB-1248
PCB-1254
Pentachloroethane
1,1,2,2-Tetrabromoethane
1,1,2,2-Tetrachlorocthane
Tetrachloroethene
Thiophene
1,2,4-Trichlorobenzene
1,1,1-Trichloroelhane
1,1,2-Trichloroethane
Trichloroethene
1 ,1 ,2-Trichlorofluoromethane
1,23-Trichloropropane
1,1,2-Trichlorotrifluoroethane
Tri-o-cresyl phosphate

Water
Boiling
Point
(deg.Q
131
215
237
4Z4
102

40
211
115
130
222
233
375
325
275
290
325
340
365
159
239
146
121
84
210
74
114
87
24
142
48
410

100
Ref.
b
a
a
b
b

a
a
b
b
b
b
b
a
a
a
a
a
a
b
b
a
a
b
a
a
a
a
a
b
b
b

Melting
Point
(deg.Q
10
-21
-9
-66
-101
19
-95
6
-50
-108
-3
16
6

1
-35
-19
-7
10
-22
0
-36
-19
-30
17
-30
-37
-73
-111
-15
-35
-25

0
Ref.
b
a
a
b
b
b
a
a
b
b
b
b
b

a
a
a
a
a
b
b
a
a
b
a
a
a
a
a
b
b
b

Aqueous
Solubility
(mg/L)
4J2E+03
Z55E+00
1.10E+00
1.40E+04
1.06E+03
1.45E+02
2.00E+04
1.90E+03
4.50E+04
1.40E+04
6.00E+02
5.00E+02
1.20E+01
2.30E-01
5.90E-01
1.45E+00
100E-01
5.00E-02
5.00E-02
5.00E+02
7.00E+02
2.90E+03
1.50E+02
3.60E+03
1.90E+01
1.36E+03
4.50E+03
1.10E+03
1.10E+03

2.00E+02
3.00E-01

Ref.
b
a
a(22)
b
b(23)
b
a
a
b
b
b
b
b
a
a(24)
a(25)
a
a
a
b
b
a
a
b(18)
a(22)
a
a
a
a

b
b

Vapor
Pressure
(mmHg)
1.10E+01
1.50E-01
8.10E-02
3.75E+02
4.00E+01
1.25E-06
3.49E+02
1.50E-01
1.56E+01
7.50E+00
1.50E-01
1.50E-01
4.00E-04
4.00E-04
6.70E-03
4.60E-03
l.OOE-03
4.94E-04
6.00E-05
3.40E+00
l.OOE-01
5.00E+00
1.40E-1-01
6.00E+01
4.00E-01
l.OOE+02
1.90E+01
5.78E+01
6.87E+02
ZOOE+00
2.84E+02

1.75E-I-01
Ref.
b
a
a(25)
b
b(24)
b
a
a
b
b
b
b
b
a(25)
a(25)
a(25)
a
a(25)
a
b
b
a
a
b
a(25)
a
a
a
a
b
b

Henry's Law
Constant
(atm-m3/mol)
7.06E-04
2.60E-02
1.60E-02
5.48E-03
9.09E-03
4.89E-09
2.00E-03
2.45E-05
4.66E-05
8.68E-05
4.51 E-05
5.41E-05
8.56E-08

3.24E-04
4.64E-(-00
5.60E-04
3JOE-03
2.70E-03
2.45E-03
6.40E-05
3.80E-04
1.53E-02
2.93E-03
2.32E-03
1.80E-02
7.40E-04
9.10E-03
1.10E-01
3.18E-04
3.33E-01

Ref.
b
a
a
b
b
b
a
a
b
b
b
b
b

a
a
a
a
a
b
b
a
a
b
a
a
a
a
a
b
b

-------
A-6
Table A-l. (continued)
DNAPL
Aniline
o*Anuidine
Benzyl alcohol
Benzyl chloride
Bis(2-chloroethyl)ether
Bis(2-chlon>isopropyl)ether
Bromobenzene
Bromochloromethane
Bromodichloromethane
Bromoethane
Bromoform
Butyl benzyl phthalatc
Carbon disulfide
Carbon letrachloride
Chlorobenzene
2-Chloroethyl vinyl ether
Chloroform
1-Chloro-l-nitropropane
2-Chlorophenol
4-Chlorophenyl phenyl ether
Chloropicrin
m-Chlorotoluene
o-Chlorotoluene
p-Chlorotoluene
Dibromochloromethane
1 ,2-Dibromo-3-chloropropane
Dibromodifluoromethane
Dibutyl phthalate
1 ,2-Dichlorobenzene
1 3-Dichlorobenzene
1,1-Dichloroelhane
1,2-Dichloroethane
1,1-Dichloroelhene
lrans-l,2-Dichloroelhene
1,2-Dichloropropane
cis-13-Dichloropropene
trans-13-Dichloropropene
Dichlorvos
Diethyl phthalate
Dimethyl phthalate
LogKoc
(mUg)
1.41

1.98
128
1.15
1.79
233
1.43
1.79
2.67
2.45
232
2.47
2.64
1.68
0.82
1.64
334
2.56
3.60
0.82
3.08
3.20
3.08
1.92
2.11

3.14
2.27
2.23
1.48
1.15
1.81
1.77
1.71
1.68
1.68
9.57
1.84
1.63
Ref.
b

a
a
b
a
b
b
a
b
a
a
a
a
a
a
a
b
a
a
b
e
e
e
a
b

a
a
a
a
a
a
a
a
a
a
b
a
a
LogKow
0.90
0.95
1.10
230
1.58
2J8
3.01
1.41
1.88
1.57
2.30
4.78
1.84
2.83
2.84
1.28
1.95
4.25
2.16
4.08
1.03
3.28
3.42
3.3
2.08
2.63

4.57
3.40
3.38
1.78
1.48
2.13
2.09
2.28
1.41
1.41
1.40
2.35
1.61
Ref.
b
b
a
a
b
a
b
b
a
b
a
a
a
a
a
a
a
b
a
a
b
e
f
e
a
b

a
a
a
a
a
a
a
a
a
a
b
a
a
Vapor
Density
(g/L)
3.81
5.03
4.42
5.17
5.84
6.99
6.42
5.29
6.70
4.05
1033
12.76
3.11
6.29
4.60
436
4.88
5.05
5.25
836
6.72

8.51
9.66
8.58
11.38
6.01
6.01
4.04
4.04
3.%
3.%
4.62
4.54
4.54
9.03
9.08
7.94
Ref.
b
b
a
a
b
a
b
b
a
b
a
a
a
a
a
a
a
b
a
a
b

a
b
b
a
a
a
a
a
a
a
a
a
a
b
a
a
Relative
Vapor
Density
1.001

1.004
1.004
1.006
1.019
1.006
1309
2377
1.041
1.000
1.646
1.515
1.035
1.095
1.664
1.025
1.006
1.000
1.124
1.021
1.012
1.020
1.624
1.008
6.701
1.000
1.005
1.012
1.585
1.206
2.545
1.827
1.162
1.094
1.094
1.000
1.000
1.000
Interfacial
Liquid Tension
(dyn/cm)
5.8

39.8

48.4
45.0
37.4

32.8

40.0

30.0
37.0
30.0

23.8

Ref.

j
j
j

e(30)
<*23)
e

e(27)

Surface
Tension
(dyn/cm)
42.9

37.9

35.8
333

24.5
45.5

323
27.0
33.2

27.2

403

32.8
32.9
34.6

33.4
37.0
33.2
24.8
32.2
24.0
25.0
28.7
31.2

37.5

Ref.
c

e
h

h
c

c
c
c

e
h(25)
h(25)

c
c
c
c
c
c(15)
c
c
e

-------
Table A-l. (continued)
A-7
DNAPL
Ethyicne dibromide
Hexachlorobutadiene
Hexachlorocydopentadiene
lodomethane
1-Iodopropanc
Malathion
Methylene chloride
Nitrobenzene
Nitroethane
1-Nitropropane
2-Nitrololuene
3-Nitrotoluene
Parathion
PCB-1016
PCB-1221
PCB-1232
PCB-1242
PCB-1248
PCB-1254
Pentachloroelhane
l,lA2-Telrabromoethane
1 , 1 ^2-Telrachloroethane
Tetrachloroethene
Thiophene
1,2,4-Trichlorobenzene
1,1,1-Trichloroethane
1 ,1 ,2-Trichloroethane
Trichloroelhene
1,1,2-Trichlorofluoromelhane
1 ,23-Trichloropropane
1,1,2-Trichlorotrifluoroethane
Tri-o-cresyl phosphate
LogKoc
(mL/g)
1.64
3.67
3.63
136
2.16
2.46
0.94
2.01

3.07
4.70
2.44
2.83
3.71
5.64
5.61
3.28
2.45
107
2.42
1.73
3.98
2.18
1.75
2.10
2.20

2.59
3.37
Ref.
b
a
a
b
b
b
a
a

b
a
a
a
a
a
a
b
b
a
a
b
a
a
a
a
a

b
b
LogKow
1.76
4.78
5.04
1.69
149
2.89
1.30
1.95
0.18
0.87
2.30
2.42
3.81
5.88
2.80
3.20
4.11
6.11
6.47
2.89
2.91
2.56
2.60
1.81
4.02
2.47
2.18
2.53
2.53

2.57
5.11
Ref.
b
a
a
b
b
b
a
a
b
b
b
b
b
a
a
a
a
a
a
b
b
a
a
b
a
a
a
a
a

b
b
Vapor
Density
(g/L)
7.68
10.66
11.15
5.80
6.95
13.50
3.47
5.03
3.07
3.64
5.61
5.61
11.91

9.03
10.67

13.36
8.27
14.13
6.86
6.78
3.44
7.42
5.45
5.45
5.37
5.85

7.66
15.06
Ref.
b
a
a
b
b
b
a
a
b
b
b
b
b

a
a

a
b
b
a
a
b
a
a
a
a
a

b
b
Relative
Vapor
Density
1.080
1.002
1.001
2.943
1.259
1.000
1.897
1.001
1.033
1.021
1.001
1.001
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.027
1.001
1.032
1.088
1.152
1.003
1.479
1.091
1.272
4.415
1.011
3.062

Interfacial
Liquid Tension
(dyn/cm)
36.5

28.3
25.7

44.4

45.0

34.5

Ref.
e

j
j

e(25)

e(24)

Surface
Tension
(dyn/cm)
38.7

37.5
31.0

27.9
43.0

34.7

36.0
31.3

39.1
25.4
34.0
293
19.0

Ref.
c

e
e

c
c

c
c
c
c
c

-------
A-8
Table A-l. (continued)
DNAPL
Ethylene dibromide
Hexachlorobutadiene
Hexachlorocyclopenladiene
lodomethane
1-Iodopropane
Malalhion
Methylene chloride
Nitrobenzene
Nitroethane
1-Nitropropane
2-Nitrotoluene
3-Nitrotoluene
Parathion
PCB-1016
PCB-1221
PCB-1232
PCB-1242
PCB-1248
PCB-1254
Penlachloroethane
1,1-W-Tetrabromoelhane
l,lA2-Tetrachloroethane
Tetrachloroethenc
Thiophene
1 ,2,4-Trichlorobenzene
1,1,1 -Trichloroelhane
1,1,2-Trichloroethane
Trichloroethene
1,1,2-Trichlorofluoromelhane
1 ^3-Trichloropropane
1 ,1 ,2-Trichlorotrifluoroelhane
Tri-o-cresyl phosphate
Air
Diffusion
Coefficient
(sq.cmVscc)

1.02E-01
7.20E-02

7.40E-02

7.96E-02
7.90E-02
8.11E-02

Ref.

i
h

i
h
i

Water
Diffusion
Coefficient
(sq.cm/sec)

1.1E-06
7.6E-06

7.5E-06

8E-06
8E-06
8.3E-06

Ref.

c
c

h
h
c

Estimated
Half -life
in Soil
(days)
28-180
28-180
7-28
7-28

3-7
7-28
12-197

28-180

0.45-45
180-360

28-180
140-273
136-360
180-360
180-360
180-360
180-360

Estimated
Half-life in
Ground water
(days)
20-120
56-360
7-56
14-56

8-103
14-56
2-394

56-360

0.45-45
360-720

56-360
140-546
136-720
321-1653
360-720
360-720
360-720

RCRAorNJ
Action Level
Water
(mg/L)
4E-07
4E-03
2E-01

2E-01NJ
5E-03
2E-02

2E-01
5E-06*
5E-06*
5E-06*
5E-06*
5E-06*
5E-06*

2E-03
7E-04

7E-01
3E+00
6E-03
5E-03
IE +01
2E-01

RCRAorNJ
Action Level
Soil
(mg/kg)
8E-03
9E+01
6E+02

9E+01
4E+01

5E+02
9E-02*
9E-02*
9E-02*
9E-02*
9E-02*
9E-02*

4E+01
IE +01

2E+03
7E+03
1E+02
6E+01
2E+04
5E+02

-------
A-9
Table A-l. (continued)
DNAPL
Aniline
o-Anisidine
Benzyl alcohol
Benzyl chloride
Bis(2-chloroethyl)ether
Bis(2-chloroi30propyl)ether
Bromobenzene
Bromochloromethane
Bromodichloromethane
Bromoethane
Bromoform
Butyl benzyl phlhalale
Carbon disulfide
Carbon tetrachioride
Chlorobenzene
2-Ch'iorocthy! vinyi ether
Chloroform
1 -Chloro-1 -nilropropanc
2-Chlorophenol
4-Chlorophenyl phenyl ether
Chloropicrin
m-Chlorotoluene
o-Chlorotoluene
p-Chlorotoluene
Dibromochloromethane
l,2-Dibromo-3-chloropropane
Dibromodifluoromethane
Dibutyl phthalate
1,2-Dichlorobenzene
1 3-Dichlorobenzene
1,1-Dichloroelhane
1,2-Dichloroethane
1,1-Dichloroelhene
trans-l,2-DichIoroethene
1,2-Dichloropropane
cis-U-Dichloropropene
trans- 1 ,3-Dichloropropenc
Dichlorvos
Diethyl phthalate
Dimethyl phthalate
Air
Diffusion
Coefficient
(sq.cm./sec)
7.50E-42

8.92E-02
7.97E-02
7.50E-02

9.90E-02

4.20E-02

8.90E-02
8.90E-02
9.11E-02
9.11E-02

Ref.
c(30)

h
i
c(30)

c(23)

i
i
i
i

Water
Diffusion
Coefficient
(sq.cm/sec)

1.1E-05

7.9E-06

9.1E-06

4.1E-05

9.5E-06
9.5E-06

Ref.

h
c

Estimated
Half-life
in Soil
(days)

28-180

0.62-12
28-180
18-180

28-180
1-7

180-360
68-150

28-180

28-180
28-180

2-23
28-180
28-180
32-154
100-180
28-180

167-1289
5-11
5-11

3-56
1-7
Estimated
Half-life in
Ground water
(day.)

56-360

0.62-12
56-360
36-360

56-360
2-180

7-360
136-300

56-1800

14-180
56-360

2-23
56-360
56-360
64-154
100-360
56-132

334-2592
5-11
5-11

6-112
2-14
RCRAorNJ
Action Level
Water
(mg/L)
6E-03

2E+OONJ

3E-03
3E-01 NJ

3E-05

7E-01
7E+00
4E+00
3E-04
7E-01

6E-03

2E-01

1E-02 NJ
2E-06NJ

4E+00
6E-01 NJ
6E-01 NJ
7E-02 NJ
5E-03
7E-03
1E-01 NJ
5E-04NJ
1E-02
1E-02

3E+01
7E+OONJ
RCRAorNJ
Action Level
Soil
(mg/kg)
1E+02

5E+01

5E-01

2E+03
2E+04
8E+03
SE-fOO
2E+03

1E+02

4E402

8E+03

8E-1-00
1E-I-01

2E+01
2E+01

6E+04

-------
A-10
Table A-1. (continued)
DNAPL
Aniline
o-Anisidinc
Benzyl alcohol
Benzyl chloride
Bi5(2-chloroethyl)ether
Bis(2-chloroisopropyl)ether
Bromobenzene
Bromochloromethane
Bromodichloromethane
Bromoethane
Bromofonn
Butyl benzyl phthalate
Carbon disulfide
Carbon Ictrachloride
Chlorobenzene
2-Chloroelhyl vinyl ether
Chloroform
1-Chloro-l-nitropropane
2-Chlorophenol
4-Chlorophenyl phenyl ether
Chloropicrin
m-Chlorotoluene
o-Chlorotoluene
p-Chlorotoluene
Dibromochloromethane
l,2-Dibromo-3-chloropropane
Dibromodifluoromethane
Dibutyl phthalate
1,2-Dichlorobenzene
1,3-Dichlorobenzene
1,1-Dichloroelhane
1,2-Dichloroelhane
1 ,1-Dichloroethene
trans-l,2-Dichloroethene
1 ,2-Dichloropropane
cis-1 ,3-Dichloropropene
trans-lJ-Dichloropropene
Dichlorvos
Diethyl phthalate
Dimethyl phlhalate
Flash
Point
(deg.C)
70
30
93
60
55
85
51
NC

<-20
NC
110
-30
NC
28
16
NC
62
64

detonates

NC
77
NC
157
66
63
-6
13
-15
2
15.6
35
5.3
NC
140
146
Ref.
b
b(oc)
a
b
a
a
b
b

b
a
a
a
a
a
a
a
b
a

a
b(oc)
b
a
a
a
a
a
a
a
a
a
a
b
a
a
LEL
(%)
U

1.1

6.7

1.3

0.5
2.2
2
5.6
6.2
6.5
9.7
3.4
53
5.3

0.7
1.2
Ref.
b

a
a
a
a
a
a
a
a
a
a

a
a
UEL
(%)
11

113

7.1

15
9.2
9.2
16
16
15.5
12.8
14.5
14.5
14.5

Ref.
b

a
a
a
a
a
a
a
a
a
a

ACOIH
TWA
(ppm)
Ca2(7.6)
Ca 0.1 (0.50)

Ca 1 (5.2)

200(1060)

200(891)
0.5(5.2)

10(31)
Ca5(31)
75(345)

Ca 10 (49)
2(10)

0.1 (0.67)

(5)
50 (301) C

200(810)
Ca 10 (4)
Ca5(20)
200(793)
Ca 75 (347)
Ca 1 (4.5)
Ca 1 (4.5)
0.1 (0.90)
(5)
(5)
ACGIH
STEL
(ppm)

250 (1110)

250(1010)

Ca20(79)

Ca 110 (508)

NIOSH
IDLH
(ppm)
CalOO
Ca9.8

5000

3500

500
Ca300
2400

CalOOO
2000

803
1000

4000
CalOOO

4000
2000 ca

1152
Odor
Low
Threshold
(ppm)
5.25E-05

4.34E-02

3.17E+02

2.00E+02
5.13E+02

7.80E-03
9.54E+00
2.13E-01

5.12E+01

3J9E-03

8.12E-01

9.98E-03

ZOOE+00

1.10E+02
5.93E+00
5.04E-f02
8.47E-02
2J2E-01

Odor
High
Threshold
(ppm)
92

317

200
513

7
238
61

205

200
109
1009
498
131

-------
A-ll
Table A-l. (continued)
DNAPL
Ethylene dibromide
Hexachlorobutadiene
Hexachlorocydopentadiene
lodomethane
1-Iodopropane
Malathion
Methylene chloride
Nitrobenzene
Nitroethane
1-Nitropropane
2-Nitrotolucne
3-Nitrotoluene
Parathion
PCB-1016
PCB-1221
PCB-1232
PCB-1242
PCB-1248
PCB-1254
Pentachloroethane
1,1,12-Telrabromoethane
1,1.2,2-TetrachIoroethane
Tetrachloroethene
Thiophene
1,2,4-Trichlorobenzene
1,1,1-Trichloroethanc
l.U-Trichloroelhane
Trichloroethene
1,1,2-Trichlorofluoromethane
1 ^3-Trichloropropane
1,1,2-Trichlorotrifluoroethane
Tri-o-cresyl phosphate
Flash
Point
(deg.C)
NC
NC
NC
NC

NC
NC
88
28
34
106
101
NC
NC
141
152
176
193
222

NC
NC
NC
-1.1
105
NC
NC
312
NC
73.3
NC
225
Ref.
b
a
a
b

b
c
a
b
b
b
b
b
a
a
a
a
a
a

a
a
a
a
a
c
c
a
a
b
b
b
LEL
(%)

1.8
3.4
2.2
2.2
1.6

2.5

3.2

Ref.

a
b
b
b
b

UEL
(%)

6.6

10.5

12.6

Ref.

ACGIH
TWA
(ppm)
Ca
Ca 0.02 (0.21)
0.01 (0.11)
Ca2(12)

(10)
Ca 50 (174)
1(5)
100(307)
25(91)

(0.1)

1(14)
Ca 1 (6.9)
Ca 50 (339)

5(37)C
350 (1910)
Ca 10 (65)
Ca 50 (269)
1000 (5620) C
10(60)
1000 (7670)
(0.1)
ACGIH
STEL
(ppm)

Ca 200 (1357)

450 (2460)

Ca 200 (1070)

1250 (9590)

NIOSH
IDLH
(ppm)
400 ca

800 ca

364
5000 ca
200
1000
2300
200
200
1.6

CaO.9

CaO.3

CaSOO

1000
CaSOO

10000
CalOOO
4500
2.6
Odor
Low
Threshold
(ppm)
l.OOE+01
1.13E+00
134E-01

9.99E-01
1.55E+02
4.67E-03
2.02E+02
2.96E+02

4.00E-02

3.06E+00
4.65E+00

3.23E+00
9.95E+01

2.10E-01
4.98E+00

4.46E+01

Odor
High
Threshold
(ppm)
10
1
0

1
622
2
202
296

5
69

3
696

402
208

134

-------
A-12
for a reference temperature of 25° C. The vapor density
of dry air at 25° C and 1 atmosphere is 1.204 g/L.

Relative vapor density is calculated as the weighted mean
formula weight of compound-saturated air relative to the
mean formula weight of moist air (2.8.75 g/mol),

RVD = ((PIFW/760)+(29.0(760-vp)/760))/28.75 (A-3)

where RVD is the relative vapor density (unitless), P, is
the vapor pressure in mm Hg, and FW is the compound
formula weight (Schwille, 1988). Contaminated soil gas
with a high RVD will tend to sink in the subsurface.

Interfacial liquid tension between DNAPL and water
develops due to the difference between the greater mutual
attraction of like molecules within each fluid and the
lesser attraction of dissimilar molecules across the
immiscible fluid interface (Chapter 4.2). Values are given
in dynes per cm at 20" C. unless noted otherwise in the
references column.

Surface tension refers to the interfacial tension between a
liquid and its own vapor. Values are given in dynes per
cm at 20°C. unless noted otherwise in the references
column.

Air diffusion coefficients indicate the diffusivity of a
chemical vapor in air. Values are given in cmVs at 20° C.
unless noted otherwise in the references column

Water diffusion coefficients indicate the diffusivity of dilute
solutes in water at 20° C. unless noted otherwise in the
references column.

Low to high ranges of estimated chemical half-lives in soil
are given in days. These ranges were developed by
Howard et al. (1991) based on consideration of various
degradation processes and limited available data.

Low to high ranges of estimated chemical half-live in water
are given in days. These ranges were developed by
Howard et al. (1991) based on consideration of various
degradation processes and limited available data.

RCRA or NJ Action Levels for soil and water are proposed
chemical concentrations in shallow soil and groundwater
which would trigger conduct of a Corrective Measures
Study under the Resource Conservation and Recovery
Act (RCRA) (Federal Register, 7/2790; NJDEP,
10/14/91). Values are given in ppm. A "*" by each PCB
Aroclor series indicates that the proposed action level is
for total PCBs.

Flash point is the minimum temperature in degrees C. at
which a liquid or solid emits ignitable flammable vapors
given the presence of an ignition source such as a spark
or flame. Given flash point temperatures are determined
using the Tag closed cup (ASTM method D56) except
where (oc) in the references column is used to denote
open cup measurement (ASTM method D93). NC
indicates that the DNAPL is non-combustible.

LEL, the lower explosive limit, refers to the minimum
volumetric percent of a flammable gas or vapor in air at
which ignition or explosion can occur in the presence of
a spark or flame.

UEL, the upper explosive limit, refers to the maximum
volumetric percent of a flammable gas or vapor in air at
which ignition or explosion can occur in the presence of
a spark or flame.

ACGIH TWA values represent the time-weighted average
chemical concentration in breathing air, prescribed by the
American Conference of Governmental Industrial
Hygienists (ACGIH, 1990) to which nearly all workers
can be exposed without adverse effect during a normal 8-
hour work day and 40-hour work week. Values are given
in ppm, and in mg/m3 (in parentheses). Suspected or
confirmed carcinogens are denoted by Ca.

AGCIH STEL values represent the 15-minute time-
weighted average chemical concentration in breathing air,
prescribed by the American Conference of Governmental
Industrial Hygienists (ACGIH, 1990), to which nearly all
workers can be exposed without adverse effect. These
values should not be exceded during any 15-minute
period even if the TWA value is not exceeded. Values
are given in ppm, and in mg/m3 (in parentheses).
Suspected or confirmed carcinogens are denoted by Ca.

NIOSHIDLH values represent chemical concentrations
in breathing air specified by the National Institute of
Occupational Safety and Health (NIOSH, 1990) to be
Immediately Dangerous to Life and Health (IDLH).
They are maximum concentrations to which one could be
exposed for 30 minutes without suffering escape-impairing
or irreversible health effects. Concentrations are given in
ppm and in mg/m3 (in parentheses).
-------
A-13
Low and high odor threshold values represent a reported
range of minimum chemical vapor concentrations
detectable by the sense of smell as a noticeable change in
the odor of the system (Ruth, 1986).

Coded references that appear in the reference columns
include: a=Montgomery and Welkom (1990);
b=Montgomery (1991); c=Lucius et al. (1990); d=Mercer
et al. (1990); e=Mercer and Cohen (1990);
f=Verschueren (1983); g=Monsanto (1988); h=Tetra
Tech (1988); i=Mendoza and Frind (1990b); and, j=Dean
(1973). Most of these references provide compilations of
data reported by others and must be examined, therefore,
to determine the original data source.
-------
-------
APPENDIX B: PARAMETERS AND
CONVERSION FACTORS

Symbols and dimensions of selected parameters utilized
in this document are listed in Table B-l. Conversion
factors for length, area, volume, mass, time, density,
velocity, force, and pressure are given in Tables B-2 to B-
10, respectively.
Table B-l. Listing of selected parameters, symbols, and dimensions.
Parameter
Angle of dip
Concentration of chemical in soil gas
Concentration of chemical at source
Concentration of chemical in water
Contact angle
Contact area
Critical NAPL thickness or height
Density
Density, bulk
Density, NAPL
Density, water
Diffusion coefficient, air
Diffusion coefficient, effective
Displacement by NAPL ratio
Displacement by water ratio
Fraction organic carbon content
Gradient, hydraulic
Gradient, capillary pressure
Gradient, pressure due to gravity
Gravity, acceleration
Head, capillary (capillary rise of water)
Symbol
B
c,
C»
c.
c.
+
L2
*n
P
Pb
Pa
Pw
D
D*
«n
«w
'«
i
Jcp
ig
g
hc
Dimensions
degrees
moles/volume
mass/volume
mass/mass
moles/volume
mass/volume
mass/mass
moles/volume
mass/volume
mass/mass
degrees
length2
length
mass/volume
mass/Volume
mass/volume
mass/volume
length2Aime
length2Aime
dimension less
dimensionless
volume/volume
dimensionless
length/length
dimensionless
massAime
density/density
dimensionless
length/time2
length
-------
B-2
Table B-l. Listing of selected parameters, symbols, and dimensions.
Parameter
Head, pressure head due to NAPL gravity
Head, hydraulic
Hydraulic Conductivity
Ideal Gas Constant
Interfatial tension
(liquid and surface)
Mass, dry sample
Mass exchange coefficient
Mass exchange rate
Mass, wet sample
Mean soil particle diameter
Molecular weight
Mole fraction of compound A
Mole fraction of compound i
Partition coefficient, Henry's Law Constant
Partition coefficient, Henry's Law Constant, dimensionless
Partition coefficient, octanolAvater
Partition coefficient, organic carbon
Partition coefficient, sorption
Permeability, intrinsic
Permeability, relative
Permeability, relative (air)
Permeability, relative (NAPL)
Permeability, relative (water)
Pore size distribution index
Porosity
Porosity, air-filled
Porosity, effective
Porosity, total
Symbol
".
h
K
R
<7
"»d
nVL2A
nyt
«.
d
M
XA
*
KH
KH-
«„,
koc
ka
k
kr
k™
kn,
k»
A
n
n.
"e
it
Dimensions
length
length
lengthAime
R - 8.2057X10'5 m3atm/(mol °K)
force/length
mass
mass/lengthzAime
massAime
mass
length
mass/moles
dimensionless
dimensionless
(mass * length2) / (time2 * moles)
dimensionless
dimensionless
volume/mass
volume/mass
length2
dimensionless
dimensionless
dimensionless
dimensionless
dimensionless
volume/volume
dimensionless
volume/volume
dimensionless
volume/volume
dimensionless
volume/volume
dimensionless
-------
B-3
Table B-l. Listing of selected parameters, symbols, and dimensions.
Parameter
Porosity, bulk water content
Pressure
Pressure, capillary
Pressure due to gravity
Pressure, NAPL
Pressure, partial of chemical in gas phase
Pressure, threshold entry (displacement)
Pressure, vapor of pure solvent A
Pressure, vapor of the solution containing solvent A
Pressure, water
Radial distance
Radius, pore
Radius, pore body
Radius, pore throat
Radius, source
Retardation factor, dissolved phase
Retardation factor, vapor phase
Saturation
Saturation, effective nonwetting phase
Saturation, effective wetting phase
Saturation, NAPL
Saturation, residual
Saturation, residual nonwetting phase
Saturation, residual wetting phase
Saturation, water
Solubility, aqueous of compound i
Symbol
"w
p
PC
p,
PN
P
Pa
PA°
PA
PW
r
r
rP
rt
r,
Rf
R.
s
'«
S*
SD
*r
*nr
*wr
&w
Si
Dimensions
volume/volume
dimensionless
mass/(length*time2)
mass/(length*time2)
mass/(length*time2)
mass/(length*time2)
mass/(length*time2)
mass/(length*time2)
mass/(length*time2)
mass/(length*time2)
mass/(length*time2)
length
length
length
length
length
dimensionless
dimensionless
volume/Volume
dimensionless
volume/volume
dimensionless
volume/volume
dimensionless
volume/volume
dimensionless
volume/volume
dimensionless
volume/volume
dimensionless
volume/volume
dimensionless
volume/volume
dimensionless
mass/volume
mass/mass
-------
B-4
Table B-l. Listing of selected parameters, symbols, and dimensions.
Parameter
Solubility, effective aqueous of compound i
Tune
Tortuosity factor
Velocity, interstitial
Viscosity, absolute (also known as dynamic)
Viscosity, kinematic
Volume, NAPL displaced by spontaneous imbibition
Volume, NAPL displaced by spontaneous imbibition and forced
displacement
Volume, sample pore volume
Volume, water displaced by spontaneous imbibition
Volume, water displaced by spontaneous imbibition and forced
displacement
Volumetric retention capacity
Symbol
S*i
t
T.
V|
M
V
^
vnt
vo
v«p
v.,
R
Dimensions
mass/volume
mass/mass
time
dimensionless
lengthAime
mass/length/time
length2Aime
volume
volume
volume
volume
volume
volume/volume
dimensionless
-------
B-5
Table B-2. Length Conversion Factors (multiply by factor to convert row unit to column unit).

mm
cm
m
km
in
ft
yd
mi
mm
l.OOOOE+00
l.OOOOE-fOl
l.OOOOE+03
l.OOOOE+06
2J400E+01
3.0480E+02
9.1440E+02
1.6093E+06
cm
l.OOOOE-01
l.OOOOE+00
l.OOOOE+02
l.OOOOE+05
Z5400E+00
3.0480E+01
9.1440E+01
1.6093E+05
m
l.OOOOE-03
l.OOOOE-02
l.OOOOE+00
l.OOOOE+03
Z5400E-02
3.0480E-01
9.1440E-01
1.6093E+03
km
l.OOOOE-06
l.OOOOE-05
l.OOOOE-03
l.OOOOE+00
Z5400E-05
3.0480E-04
9.1440E-04
1.6093E+00
in
3.9370E-02
3.9370E-01
3.9370E+01
3.9370E+04
l.OOOOE+00
1.2000E+01
3.6000E+01
6.3360E+04
ft
3.2808E-03
3.2808E-02
3.2808E+00
3.2808E+03
8.3333E-02
l.OOOOE+00
3.0000E+00
5.2800E+03
yd
1.0936E-03
1.0936E-02
1.0936E+00
1.0936E+03
2.7778E-02
33333E-01
l.OOOOE+00
1.7600E+03
mi
6.2137E-07
6.2137E-06
6.2137E-04
6.2137E-01
1.5783E-05
1.8939E-04
5.6818E-04
l.OOOOE+00
Notes: mm = millimeters, cm=centimelers, m= meters, km = kilometers, in=inches, ft = feel, yd=yards, mi=miles; 1 micron (JUB) = 0.001 mm.
Table B-3. Area Conversion Factors (multiply by factor to convert row unit to column unit).

mm2
cm2
m2
km2
in2
ft2
yd2
mi2
mm
l.OOOOE+00
l.OOOOE+02
l.OOOOE+06
l.OOOOE+12
6.4516E+02
9.2903E+04
8.3613E+05
2.5900E+12
cm2
l.OOOOE-02
l.OOOOE+00
l.OOOOE+04
l.OOOOE+10
6.4516E+00
9.2903E+02
8.3613E+03
2.5900E+10
m2
l.OOOOE-06
l.OOOOE-04
l.OOOOE+00
l.OOOOE+06
6.4516E-O4
9.2903E-02
83613E-01
2.5900E+06
km2
l.OOOOE-12
l.OOOOE-10
l.OOOOE-06
l.OOOOE+00
6.4516E-10
9.2903E-08
8.3613E-07
ZS900E+00
in2
1.5500E-03
1.5500E-01
1.5500E+03
1.5500E+09
l.OOOOE+00
1.4400E+02
1.2960E+03
4.0145E+09
ft2
1.0764E-05
1.0764E-03
1.0764E+01
1.0764E+07
6.9444E-03
l.OOOOE+00
9.0000E+00
2.7878E+07
yd2
1.1960E-06
1.1960E-04
1.1960E+00
1.1960E+06
7.7160E-04
1.1111E-01
l.OOOOE+00
3.0976E+06
mi2
3.8610E-13
3.8610E-11
3.8610E-07
3.8610E-01
2.4910E-10
3.5870E-08
3.2283E-07
l.OOOOE+00
Notes: mm=millimeters. cm = centimeters, m=melers, km = kilometers, in = inches, ft=feet, yd=yards, mi = miles.
Table B-4. Volume Conversion Factors (multiply by factor to convert row unit to column unit).

mm
cm3
L
m3
km3
in'
ft3
yd3
mm3
l.OOOOE+00
l.OOOOE+03
l.OOOOE+06
l.OOOOE+09
l.OOOOE+18
1.6387E+04
2.8317E+07
7.6455E+08
cm3
l.OOOOE-03
l.OOOOE+00
l.OOOOE+03
l.OOOOE+06
l.OOOOE+15
1.6387E+01
2.8317E+04
7.6455E+05
L
l.OOOOE-06
l.OOOOE-03
l.OOOOE+00
l.OOOOE+03
l.OOOOE+12
1.6387E-02
2&317E+01
7.6455E+02
m3
l.OOOOE-09
l.OOOOE-06
l.OOOOE-03
l.OOOOE+00
l.OOOOE+09
1.6387E-05
2.8317E-02
7.6455E-01
km3
l.OOOOE-18
l.OOOOE-15
l.OOOOE-12
l.OOOOE-09
l.OOOOE+00
1.6387E-14
2.8317E-11
7.6455E-10
in3
6.1024E-05
6.1024E-02
6.1024E+01
6.1024E+04
6.1024E+13
l.OOOOE+00
1.7280E+03
4.6656E+04
ft3
3.S315E-08
3.5315E-05
3.5315E-02
3.5315E+01
3.5315E+10
5.7870E-04
l.OOOOE+00
2.7000E+01
yd3
1.3080E-09
1.3080E-06
1.3080E-03
1.3080E+00
1.3080E+09
2.1433E-05
3.7037E-02
l.OOOOE+00
Notes: mm = millimeters, cm = centimeters, L=liters, m=meters, km = kilometers, in=inches, ft=feet, yd=yards.
-------
B-6
Table B-5. Mass Conversion Factors (multiply by factor to convert row unit to column
unit).

mg
g
kg
oz (avoir.)
Ib (avoir.)
ton (net)
mg
l.OOOOE+00
l.OOOOE+03
l.OOOOE+06
2.8350E+04
4.5359E+05
9.0718E+08
g
l.OOOOE-03
l.OOOOE+00
l.OOOOE+03
Z8350E+01
4.5359E+02
9.0718E+05
kg
l.OOOOE-06
l.OOOOE-03
l.OOOOE+00
2.8350E-02
4.5359E-01
9.0718E+02
oz (avoir.)
3.5274E-05
3.5274E-02
3.S274E+01
l.OOOOE+00
1.6000E+01
3.2000E+04
Ib (avoir.)
2.2046E-06
2.2046E-03
2.2046E+00
6.2SOOE-02
l.OOOOE+00
ZOOOOE+03
ton (net)
1.1023E-09
1.1023E-06
1.1023E-03
3.1250E-05
5.0000E-04
l.OOOOE+00
Notes: mg=milligrams, g=grams, kg = kilograms, oz=ounces, lb=pounds.
Table B-6. Time Conversion Factors (multiply by factor to convert row
unit to column unit
time
s
min
hr
d
y
s
l.OOOOE+00
6.0000E+01
3.6000E+03
8.6400E+04
3.1536E+07
min
1.6667E-02
l.OOOOE+00
6.0000E+01
1.4400E+03
5.2560E+05
hr
2.7778E-04
1.6667E-02
l.OOOOE+00
2.4000E+01
8.7600E+03
d
1.1574E-05
6.9444E-04
4.1667E-02
l.OOOOE+00
3.6500E+02
y
3.1710E-08
1.9026E-06
1.1416E-04
Z7397E-03
l.OOOOE+00
Notes: s=seconds, min = minutes, hr= hours, d=days, yr=years.
Table B-7. Density Conversion Factors (multiply by factor to convert row
unit to column unit).

g/cm3
kg/m3
g^
lbs/in3
lbs/ft3
g/cm3
l.OOOOE+00
l.OOOOE-03
l.OOOOE-03
2.7680E+01
1.6018E-02
kg/m3
l.OOOOE+03
l.OOOOE+00
l.OOOOE+00
2.7680E+04
1.6018E+01
g^
l.OOOOE+03
l.OOOOE+00
l.OOOOE+00
2.7680E+04
1.6018E+01
lbs/in3
3.6127E-02
3.6127E-05
3.6127E-05
l.OOOOE+00
5.7871E-04
lbs/ft3
6.2428E+01
6.2428E-02
6.2428E-02
1.7280E+03
l.OOOOE+00
Notes: g/cm3=grams per cubic centimeter, kg/m3 = kilograms per meter, g/L=grams per
liter, Ibs/in3-pounds per cubic inch, Ib/ft3=pounds per cubic foot.
-------
B-7
Table B-8; Velocity Conversion Factors (multiply by factor to convert row unit to column unit).

cm/s
cm/a
m/»
mJd
m/yr
ft*
ft/a
ft/yr
cm/s
l.OOOOE+00
1.1574E-05
l.OOOOE+02
1.1574E-03
3.1710E-06
3.0480E+01
3.5278E-04
9.6651E-07
cm/d
8.6400E+04
l.OOOOE+00
8.6400E+06
l.OOOOE+02
Z7397E-01
Z6335E+06
3.0480E+01
83507E-02
nVs
l.OOOOE-02
1.1574E-07
l.OOOOE+00
1.1574E-05
3.1710E-08
3.0480E-01
3.5278E-06
9.6651E-09
m/d
8.6400E+02
l.OOOOE-02
8.6400E+04
l.OOOOE+00
Z7397E-03
Z6335E+04
3.0480E-01
83507E-04
m#r
3.1536E+05
3.6500E+00
3.1536E+07
3.6500E+02
l.OOOOE+00
9.6122E+06
1.1125E+02
3.0480E-01
ftA
3.2808E-02
3.7973E-07
3.2808E+00
3.7973E^)5
1.0403E-07
l.OOOOE+00
1.1574E-O5
3.1710E-08
ft/d
Z8346E+03
3.2808E-02
2^346E+05
3.2808E+00
8.9886E-03
8.6400E+04
l.OOOOE+00
Z7397E-03
ttfyr
1.0346E+06
1.1975E+01
1.0346E+08
1.1975E+03
3.2808E+00
3.1536E+07
3.6500E+02
l.OOOOE+00
Notes: cm/s =cen timers per second, cm/d = centimeters per day, m/s=meters per second, m/d= meters per day, m/yr= meters per year, ft/s=feet
per second, ft/d = feet per day, ft^T=feet per year.
Table B-9. Force Conversion Factors (multiply by factor to convert row
unit to column unit).

dyne
kgF
N
Ib
pdl
dyne
l.OOOOE+00
9.8070E+05
l.OOOOE+05
4.4480E+05
13830E+04
kgF
1.0200E-06
l.OOOOE+00
1.0200E-01
4J360E-01
1.4100E-02
N
l.OOOOE-05
9.8070E+00
l.OOOOE+00
4.4480E+00
13830E-01
Ib
2.2480E-06
Z2050E+00
2^480E-01
l.OOOOE+00
3.1080E-02
pdl
7.2330E-05
7.0930E+01
7.2330E+00
3.2174E+01
l.OOOOE+00
Notes: kgF=kilogram force, N= Newt on, lb=pound, pdl-poundal, 1 N = 1 kg'mA2.
Table B-10. Pressure Conversion Factors (multiply by factor to convert row unit to column unit).

aim
bar
cm (water)
in (water)
mm Hg
inHg
Pa
psi
atm
l.OOOOE+00
9^692E-01
9.6780E-04
Z4582E-03
13158E-03
33421E-02
9.8692E-06
6.8050E-02
bar
1.0133E+00
l.OOOOE+00
9.8062E-04
2.4907E-03
13332E-03
33864E-02
l.OOOOE-05
6.8952E-02
cm (water)
1.0333E+03
1.0198E+03
l.OOOOE+00
Z5399E+00
1.3596E+00
3.4533E+01
1.0198E-02
7.0314E+01
in (water)
4.0681E+02
4.0149E+02
3.9371E-01
l.OOOOE+00
S3527E-01
1J35%E+01
4.0149E-03
2.7683E+01
mm (Hg)
7.6000E+02
7J006E+02
73553E-01
1.8682E+00
l.OOOOE+00
Z5400E+01
7.5006E-03
5.1718E+01
in(Hg)
Z9921E+01
Z9530E+01
Z8958E-02
73551E-02
3.9370E-02
l.OOOOE+00
2.9530E-04
Z0361E+00
Pa
1.0133E+05
l.OOOOE+05
9.8062E+01
Z4907E+02
1.3332E+02
3.3864E+03
l.OOOOE+00
6.8952E+03
Ibs/in2
1.4700E+01
1.4508E+01
1.4227E-02
3.6135E-02
1.9342E-02
4.9129E-01
1.4508E-04
l.OOOOE+00
Notes: atm= atmospheres, bar=bars, cm = centimeters, in = inches, mm = millimeters, Pa=Pascals, lbs= pounds; 1 Pa = 1 N/m2, m=meters.
-------
-------
APPENDIX C: GLOSSARY
Adsorption refers to the adherence of ions or molecules in
solution to the surface of solids.

Air sparging refers to the injection of air below the water
table to strip volatile contaminants from the saturated
zone.

Advection is the process whereby solutes are transported
by the bulk mass of flowing fluid.
iation, a subset of biotransformation, is the
biologically mediated conversion of a compound to more
simple products.

Biotransformation refers to chemical alteration of organic
compounds brought about by microorganisms.

Bond number represents the ratio of gravitational forces
to viscous forces that affect fluid trapping and
mobilization. It can be given as a dimensionless number,
such that NB = Ap g r2 / a where Ap is the fluid-fluid
density difference, g is gravitational acceleration, r is a
representative grain radius, and a is the fluid-fluid
interfacial tension. For soils with a wide grain size
distribution, r can be replaced by intrinsic permeability.

BTEX is an acronym for Benzene, Toluene, Ethylbenzene,
and Xylenes, which are volatile, monocyclic aromatic
compounds present in coal tar, petroleum products, and
various organic chemical product formulations.

Bulk density is the oven-dried mass of a sample divided by
its field volume.

Capillary forces are interfacial forces between immiscible
fluid phases, resulting in pressure differences between the
two phases.

Capillary fringe refers to the saturated zone overlying the
water table where fluid is under tension.

Capillary hysteresis refers to variations in the capillary
pressure versus saturation relationship that depend on
whether the medium is undergoing imbibition or
drainage. Capillary hysteresis results from nonwetting
fluid entrapment and differences in contact angles during
imbibition and drainage that cause different wetting and
drying curves to be followed depending on the prior
imbibition-drainage history.
Capillary number represents the ratio of viscous forces to
capillary forces that affect fluid trapping and mobilization.
It can be given as Nc = k L, / a where k is the intrinsic
permeability, iw is the water phase pressure gradient, and
a is the fluid-fluid interfacial tension.

Capillary pressure causes porous media to draw in the
wetting fluid and repel the nonwetting fluid due to the
dominant adhesive force between the wetting fluid and
the media solid surfaces. For a water-NAPL system with
water being the wetting phase, capillary pressure equals
the NAPL pressure minus the water pressure.

CERCLA is an acronym for the Comprehensive
Environmental Response Compensation and Liability Act
of 1980 which established a national program in the U.S.
to respond to past releases of hazardous substances into
the environment. CERCLA created the Superfund for
financing remedial work not undertaken by responsible
parties. Approximately 1200 sites are scheduled for
cleanup under the CERCLA program.

CMS is an acronym for RCRA Corrective Measures
Study.

Conservative solutes are chemicals that do not reset with
the soil and/or native groundwater or undergo biological,
chemical, or radioactive decay.

Contact angle refers to the angle at a fluid-solid interface
which provides a simple measure of wettability. An
acute solid-water contact angle measured into the water
in a DNAPL-water system indicates that water, rather
than DNAPL, preferentially wets the medium (and vice
versa).

Critical DNAPL height typically refers to the height of a
DNAPL column required to exceed the threshold entry
pressure of a medium.

Density is the mass per unit volume of a substance.

Desorption is the reverse of sorption.

Diffusion refers to mass transfer as a result of random
motion of molecules; it is described by Pick's first law.

Dispersion is the spreading and mixing of chemical
constituents in groundwater caused by diffusion and
mixing due to microscopic variations in velocities within
and between pores.
-------
C-2
Dissolution is the process by which soluble organic
components from DNAPL dissolve in groundwater or
dissolve in infiltration water and form a groundwater
contaminant plume. The duration of remediation
measures (either clean-up or long-term containment) is
determined by: (1) the rate of dissolution that can be
achieved in the field, and (2) the mass of soluble
components in the residual DNAPL trapped in the
aquifer.

Distribution coefficient refers to the quantity of the solute
sorbed by the solid per unit weight of solid divided by the
quantity dissolved in the water per unit volume of water.

DNAPL is an acronym for denser-than-water nonaqueous
ghase liquid. It is synonymous with denser-than-water
immiscible-phase liquid.

DNAPL body refers to a contiguous mass of DNAPL in
the subsurface.

DNAPL entry location refers to the area where DNAPL
has entered the subsurface, such as a spill location or
waste pond.

DNAPL site is a site where DNAPL has been released
and is now present in the subsurface as an immiscible
phase.

Drainage refers to a process during which the saturation
of the wetting fluid is decreasing and the saturation of the
nonwetting fluid is increasing in a porous medium.

Effective porosity is the ratio, usually expressed as a
percentage, of the total volume of voids available for fluid
transmission to the total volume of the porous medium.

Effective solubility is the theoretical aqueous solubility of
an organic constituent in groundwater that is in chemical
equilibrium with a mixed DNAPL (a DNAPL containing
several organic chemicals). The effective solubility of a
particular organic chemical can be estimated by
multiplying its mole fraction in the DNAPL mixture by its
pure phase solubility.

Emulsion refers to a dispersion of very small drops of one
liquid in an immiscible liquid, such as DNAPL in water.

EOR is an acronym for enhanced oil recovery; EOR
refers to processes (such as cosolvent or steam flooding)
for recovering additional oil (or NAPL) from the
subsurface.

Fingering refers to the formation of finger-shaped
irregularities at the leading edge of a displacing fluid in
a porous medium which move out ahead of the main
body of fluid.

Free-phase NAPL refers to immiscible liquid existing in
the subsurface with a positive pressure such that it can
flow into a well. If not trapped in a pool, free-phase
DNAPL will flow vertically through an aquifer or laterally
down sloping fine-grained stratigraphic units. Also called
mobile DNAPL or continuous-phase DNAPL

Gravity drainage refers to the movement of DNAPL in an
aquifer that results from the force of gravity.

Halogenated solvents are organic chemicals in which one
or more hydrogen atoms in a hydrocarbon precursor such
as methane, ethane, ethene, propane, or benzene, has
been replaced by a halogen atom, such as chlorine,
bromine, or fluorine. Chlorinated solvents (e.g., 1,1,1 -
trichloroethane, trichloroethene, and tetrachloroethene)
have been widely utilized cleaning and degreasing
operations. Halogenated solvents are DNAPLs.

Henry's Law Constant is the equilibrium ratio of the
partial pressure of a compound in air to the
concentration of the compound in water at a reference
temperature. It is sometimes referred to as the air-water
partition coefficient.

Heterogeneity refers to a lack of uniformity in porous
media properties and conditions.

Hydraulic conductivity is a measure of the volume of water
at the existing kinematic viscosity that will move in a unit
time under a unit hydraulic gradient through a unit area
of medium measured at right angles to the direction of
flow.

Hydraulic containment refers to modification of hydraulic
gradients, usually by pumping groundwater, injecting
fluids, and/or using cut-off walls, to control (contain) the
movement of contaminants in the saturated zone.

Hydraulic gradient is the change in head per unit distance
in a given direction, typically in the principal flow
direction.
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C-3
Imbibition is a process during which the saturation of the
wetting fluid is increasing and the saturation of the
nonwetting fluid is decreasing in a porous medium.

Immiscible fluids do not have complete mutual solubility
and co-exist as separate phases.

Immobile NAPL is at residual saturation, or contained by
a stratigraphic (capillary) trap or hydraulic forces, and
therefore, cannot migrate as a separate phase.

Interface refers to the thin surface area separating two
immiscible fluids that are in contact with each other.

Interfacial tension is the strength of the film separating
two immiscible fluids (e.g., oil and water) measured in
dynes (force) per centimeter or millidynes per centimeter.

Interphase mass transfer is the net transfer of chemical
compounds between two or more phases.

Interstitial velocity is the rate of discharge of groundwater
per unit area of the geologic medium per percentage
volume of the medium occupied by voids measured at
right angles to the direction of flow.

Intrinsic permeability is a measure of the relative ease
with which a porous medium can transmit a liquid under
a potential gradient. Intrinsic permeability is a property
of the medium alone that is dependent on the shape and
size of the openings through which the liquid moves.

LNAPL is an acronym for less-dense-than-water
nonaqueous j>hase liquid. It is synonymous with less-
dense-than-water immiscible-phase liquid.

Linear soil partition coefficient refers to the ratio of the
mass concentration of a solute phase to its mass
concentration in the aqueous phase.

Macropores are relatively large pore spaces (e.g., fractures
and worm tubes) that characteristically allow the
enhanced movement of liquid and gas in the subsurface.

Mass exchange rate refers to the product of the mass
exchange coefficient (dissolution rate) and some measure
of NAPL-water contact area. It defines the strength of
the dissolved contaminant source.

Miscible means able to be mixed.
Mobile NAPL refers to contiguous NAPL in the
subsurface that is above residual saturation, not contained
by a stratigraphic (capillary) trap or hydraulic forces, and
therefore able to migrate as a separate phase is said to be
mobile.

Mobility is a measure of the ease with which a fluid moves
through reservoir rock; the ratio of rock permeability to
apparent fluid viscosity.

NAPL wet refers to media which are preferentially wet by
a particular NAPL rather than water.

PAH is an acronym for golycyclic aromatic hydrocarbons,
a group of compounds composed of two or more fused
aromatic rings (i.e., naphthalene, anthracene, chrysene,
etc.). PAHs are introduced into the environment by
natural and anthropogenic combustion processes (i.e.,
forest fires, volcanic eruptions, automobile exhaust,
coking plants, and fossil fuel power plants). Creosote and
coal tar are DNAPLs that contain a high PAH fraction.

Partitioning refers to a chemical equilibrium condition
where a chemical's concentration is apportioned between
two different phases according to the partition inefficient,
which is the ratio of a chemical's concentration in one
phase to its concentration in the other phase.

PCB is an acronym for Polychlorinated Biphenyl
compounds. PCBs are extremely stable, nonflammable,
dense, and viscous liquids that are formed by substituting
chlorine atoms for hydrogen atoms on a biphenyl (double
benzene ring) molecule. PCBs were manufactured
primarily by Monsanto Chemical Company for use as
dielectric fluids in electrical transformers and capacitors.

Phase refers to a separate fluid that co-exists with other
fluids.

Plume refers to a zone of dissolved contaminants. A
plume usually will originate from the DNAPL zone and
extend downgradient for some distance depending on site
hydrogeologic and chemical conditions. To avoid
confusion, the term "DNAPL" plume should not be used
to describe a DNAPL pool; "plume" should be used only
to refer to dissolved-phase organics.

Pool refers to a zone of free-phase DNAPL at the bottom
of an aquifer. A lens is a pool that rests on a fine-grained
stratigraphic unit of limited areal extent. DNAPL can be
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C-4
recovered from a pool or lens if a well is placed in the
right location.

Porosity is a measure of interstitial space contained in a
rock (or soil) expressed as the percentage ratio of void
space to the total (gross) volume of the rock.

Raoult 's Law relates the ideal vapor pressure and relative
concentration of a chemical in solution to its vapor
pressure over the solution: PA = XAPA° where PA is the
vapor pressure of the solution, XA is the mole fraction of
the solvent, and PA° is the vapor pressure of the pure
solvent. It can similarly be used to estimate the effective
solubility of individual DNAPL components in a DNAPL
mixture based on their mole fractions.

RCRA is an acronym for the Resources Conservation and
Recovery Act which regulates monitoring, investigation,
and corrective action activities at all hazardous treatment,
storage, and disposal facilities. RCRA will provide the
framework for environmental investigations and cleanup
at an estimated 5000 operating and closed facilities.

Relative permeability is the permeability of the rock to gas,
NAPL, or water, when any two or more are present,
expressed as a fraction of the single phase permeability of
the rock.

Residual saturation is the saturation below which fluid
drainage will not occur.

Retardation is the movement of a solute through a
geologic medium at a velocity less than that of the
flowing groundwater due to sorption or other removal of
the solute.

Retardation factors can be multiplied by the average linear
velocity of groundwater to determine the rate of
movement of dissolved chemicals. The retardation factor
equals [1 + (pb/nJKJ where pb is the bulk density of the
media, n is porosity, and Kj is the distribution coefficient
between media and water.

RFI is an acronym for RCRA Facility Investigation.

Risk assessment involves evaluation of the potential for
exposure to contaminants and the associated hazard.

Saturation is the ratio of the volume of a single fluid in
the pores to pore volume expressed as a percent and
applied to water, DNAPL, or gas separately. The sum of
the saturations of each fluid in a pore volume is 100
percent.

Soil flushing refers to the forced circulation (e.g., by use
of injection and extraction wells) of water, steam,
cosolvents, surfactants, or other fluids to enhance the
recovery of contaminants (i.e., immiscible, dissolved, or
adsorbed) from soil.

5*0/7 gas refers to vapors (gas) in soil above the saturated
zone.

5*0/7 gas surveys are used to collect and analyze samples of
soil gas to investigate the distribution of volatile organic
compounds in groundwater or soil.

Solidification/stabilization refers to several processes which
utilize cementing agents to mechanically bind subsurface
contaminants and thereby reduce their rate of release.

Solubility refers to the dissolution of a chemical in a fluid,
usually water. Aqueous solubility refers to the maximum
concentrations of a chemical that will dissolve in pure
water at a reference temperature.

Sorption refers to processes that remove solutes from the
fluid phase and concentrate them on the solid phase of a
medium.

Source characterization involves investigating conditions in
the areas of NAPL entry or release.

Specific gravity is the ratio of a substance's density to the
density of some standard substance, usually water.

Surface tension refers to the interfacial tension between a
liquid and its own vapor typically measured in dynes per
centimeter.

Threshold entry pressure is the capillary pressure that must
be overcome for a nonwetting NAPL to enter a water-
saturated medium. It is also known as the displacement
entry pressure.

Vacuum extraction refers to the forced extraction of gas
(with volatile contaminants) from the vadose zone,
typically to prevent uncontrolled migration of
contaminated soil gas and augment a site cleanup.
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C-5
Vadose zone is the subsurface zone that extends between
ground surface and the water table and includes the
capillary fringe overlying the water table.

Vapor plume refers to a zone of vapor in the vadose zone.

Vapor pressure is the partial pressure exerted by the vapor
(gas) of a liquid or solid substance under equilibrium
conditions. A relative measure of chemical volatility,
vapor pressure is used to calculate air-water partition
coefficients (i.e., Henry's Law constants) and volatilization
rate constants.

Viscosity is the internal friction derived from internal
cohesion within a fluid that causes it to resist flow.
Absolute viscosity is typically given in centipoise.
Kinematic viscosity is the absolute viscosity divided by the
fluid density.

Volatilization refers to the transfer of a chemical from
liquid to the gas phase.

Volumetric retention capacity is the capacity of the vadose
zone to trap NAPL which is typically reported in liters of
residual NAPL per cubic meter of media.

Water wet refers to media that are preferentially wetted by
water relative to another immiscible fluid.

Weathering is a process whereby preferential and selective
dissolution of relatively soluble and volatile NAPL
components leaves behind a less soluble residue.
Weathering causes the ratios of chemicals in the NAPL
and dissolved plume to change with time and space.

Wettability refers to the relative degree to which a fluid
will spread on (or coat) a solid surface in the presence of
other immiscible fluids.

Wetting fluid refers to the immiscible fluid which spreads
on (or coats) the solid surfaces of a porous medium
preferentially relative to another immiscible fluid. In
DNAPL-water systems, water is usually the wetting fluid.
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