United States
Environmental Protection
Agency
Office of
Research and
Development
Office of Solid
Waste
and Emergency
Response
EPA/540/4-91/001
February 1991
ve/EPA Ground-Water Issue
SOIL SAMPLING AND ANALYSIS FOR
VOLATILE ORGANIC COMPOUNDS
T. E. Lewis, A. B. Crockett, R. L. Siegrist, and K. Zarrabi
The Regional Superfund Ground Water Fo-
rum is a group of ground-water scientists that
represents EPA's Regional Superfund Of-
fices. The forum was organized to exchange
up-to-date information related to ground-
water remediation at Superfund sites. Sam-
pling of soils for volatile organic compounds
(VOCs) is an issue identified by the Ground
Water Forum as a concern of Superfund de-
cision makers.
A group of scientists actively engaged in
method development research on soil sam-
pling and analysis for VOCs gathered at the
Environmental Monitoring Systems Labora-
tory in Las Vegas to examine this issue.
Members of the committee were
R. E. Cameron (LESC), A. B. Crockett
(EG&G), C. L Gerlach (LESC), T. E. Lewis
(LESC), M. P. Maskarinec (ORNL),
B. J. Mason (ERC), C. L. Mayer (LESC),
C. Ramsey (NEIC), S. R. Schroedl (LESC),
R. L Siegrist (ORNL), C. G. Urchin (Rutgers
University), L. G. Wilson (University of
Arizona), and K, Zarrabi (ERC). This paper
was prepared by The Committee for EMSL-
LV's Monitoring and Site Characterization
Technical Support Center, under the direction
of T. E. Lewis, with the support of the
Superfund Technical Support Project. For
further information contact Ken Brown, Center
Director at EMSL-LV, FTS 545-2270, or T. E.
Lewis at (702) 734-3400.
PURPOSE AND SCOPE
Concerns over data quality have raised many
questions related to sampling soils for VOCs.
This paper was prepared in response to some
of these questions and concerns expressed
by Remedial Project Managers (RPMs) and
On-Scene Coordinators (OSCs). The follow-
ing questions are frequently asked:
1. Is there a specific device suggested for
sampling soils for VOCs?
2. Are there significant losses of VOCs when
transferring a soil sample from a sampling
device (e.g., split spoon) into the sample
container?
3. What is the best method for getting the
sample from the split spoon (or other
device) into the sample container?
4. Are there smaller devices such as
subcore samplers available for collecting
aliquots from the larger core and effi-
ciently transferring the sample into the
sample container?
5. Are certain containers better than others
for shipping and storing soil samples for
VOC analysis?
6. Are there any reliable preservation proce-
dures for reducing VOC losses from soil
samples and for extending holding times?
This paper is intended to familiarize RPMs,
OSCs, and field personnel with the current
state of the science and the current thinking
concerning sampling soils for VOC analysis.
Guidance is provided for selecting the most
effective sampling device for collecting
Superfund Technology Support Center
for Monitoring and Site Characterization
Environmental Monitoring Systems
Laboratory Las Vegas, NV
Technology Innovation Office
Office of Solid Waste and Emergency Response,
U.5. EPA, Washington, D.C.
Water W. Kovafidc, Jr, Ph.O., Director
-------
samples from soil matrices. The techniques for sample collec-
tion, sample handling, containerizing, shipment, and storage
described in this paper reduce VOC losses and generally
provide more representative samples for volatile organic analy-
ses (VOA) than techniques in current use. For a discussion on
the proper use of sampling equipment the reader should refer
to other sources (Acker, 1974; U.S. EPA, 1983; U.S. EPA,
1986a).
Soil, as referred to in this report, encompasses the mass
(surface and subsurface) of unconsolidated mantle of weath-
ered rock and loose material lying above solid rock. Further, a
distinction must be made as to what fraction of the unconsoli-
dated material is soil and what fraction is not. The soil compo-
nent here is defined as all mineral and naturally occurring
organic material that is 2 mm or less in size. This is the size
normally used to differentiate between soils (consisting of
sands, silts, and clays) and gravels.
Although numerous sampling situations may be encountered,
this paper focuses on three broad categories of sites that might
be sampled for VOCs:
1. Open test pit or trench
2. Surface soils (< 5 ft in depth)
3. Subsurface soils (> 5 ft in depth)
INTRODUCTION
VOCs are the class of compounds most commonly encoun-
tered at Superfund and other hazardous waste sites (McCoy,
1985; Plumb and Ptehford, 1985; Plumb, 1987; Ameth et a!.,
1988). Table 1 ranks the compounds most commonly encoun-
tered at Superfund sites. Many VOCs are considered hazard-
ous because they are mutagenic, carcinogenic, or teratogenic,
and they are commonly the controlling contaminants in site
restoration projects. Decisions regarding the extent of contami-
nation and the degree of cleanup have far-reaching effects;
therefore, it is essential that they be based on accurate mea-
surements of the VOC concentrations present. VOCs, how-
ever, present sampling, sample handling, and analytical diffi-
culties, especially when encountered in soils and other solid
matrices.
Methods used for sampling soils for volatile organic analysis
(VOA) vary widely within and between EPA Regions, and the
recovery of VOCs from soils has been highly variable. The
source of variation in analyte recovery may be associated with
any single step in the process or all steps, including sample
collection, transfer from the sampling device to the sample
container, sample shipment, sample preparation for analysis,
and sample analysis. The strength of the sampling chain is only
as strong as its weakest link; soil sampling and transfer to the
container are often the weakest links.
Sample collection and handling activities have large sources of
random and systematic errors compared to the analysis itself
(Barcelona, 1989). Negative bias (i.e., measured value less
than true value) is perhaps the most significant and most
difficult to delineate and control. This error is caused primarily
by loss through volatilization during soil sample collection,
storage, and handling.
TABLE 1. RANKING OF GROUND WATER CONTAMINANTS BASED
ON FREQUENCY OF DETECTION AT 358 HAZARDOUS WASTE
DISPOSAL SITES
Contaminant
Detection Frequency
Trichtoroethene (V)
Tetrachtoroethene(V)
1,2-trans Dichbroethene (V)
Chloroform (V)
1,1-Dichloroethene(V)
Methyiene chloride (V)
1,1,1-Trichloroethane(V)
1,1-Dichloroethane(V)
1£-Dichloroethane(V)
Phenol (A)
Acetone (V)
Toluene (V)
bis-(2-Ethy)hexyl) phthalate (B)
Benzene (V)
Vinyl chloride
51.3
36.0
29.1
28.4
252
19.2
18.9
17.9
14.2
13.6
12.4
11.6
11.5
11.2
8.7
V » votatto, A « acid extncHble, B . base/neutral
Source: Plumb and PttcMord (1985).
There are currently no standard procedures for sampling soils
for VOC analyses. Several types of samplers are available for
collecting intact (undisturbed) samples and bulk (disturbed)
samples. The selection of a particular device is site-specific.
Samples are usually removed from the sampler and are placed
in glass jars or vials that are then sealed with Teflon-lined caps.
Practical experience and recent field and laboratory research,
however, suggest that procedures such as these may lead to
significant VOC tosses (losses that would affect the utility of the
data). Hanisch and McDevitt (1984) reported that any
headspace present in the sample container will lead to desorp-
tion of VOCs from the soft particles into the headspace and will
cause loss of VOCs upon opening of the container. Siegrist and
Jennsen (1990) found that 81% of the VOCs were lost from
samples containerized in glass jars sealed with Teflon-lined
caps compared to samples immersed in methanol in jars.
FACTORS AFFECTING VOC RETENTION AND
CONCENTRATION IN SOIL SYSTEMS
Volatile organic compounds in soil may coexist in three phases:
gaseous, liquid (dissolved), and solid (sorbed). [Note: "Sorbed"
is used throughout this paper to encompass physical and
chemical adsorption and phase partitioning.] The sampling,
identification, and quantitation of VOCs in soil matrices are
complicated because VOC molecules can coexist in these
-------
three phases. The interactions between these phases are
illustrated in Figure 1. The phase distribution is controlled by
VOC physicochemical properties (e.g., solubility, Henry's
constant), soil properties, and environmental variables (e.g.,
soil temperature, water content, organic carbon content).
O
I
8
O
I
0
e
a
GASEOUS
PHASE
) Timperaium.
I wrnd. fiumriity.
pressure,
mttasx features
VOLATILIZATION
+ (Henrys Law)
LIQUID
PHASE
EXTERNAL
FACTORS
(Linear Isotherm)
Tempamsuw,
Figure 1. Equilibrium relationships for phase partitioning of
VOCs in soil systems. See Table 2 for definitions
of abbreviations.
The factors that affect the concentration and retention of VOCs
in soils can be divided into five categories: VOC chemical
properties, soil chemical properties, soil physical properties,
environmental factors, and biological factors. A brief summary
of VOC, soil, and environmental factors is presented in Table 2,
which provides an overview of the factors that interact to control
VOCs in the soil environment at the time a sample is collected.
The cited references provide a more detailed discussion. The
chemical and physical properties of selected VOCs are further
described in Table 3. Note that many of these properties have
been determined in the laboratory under conditions (e.g.,
temperature, pressure) that may differ from those encountered
in the field. Devitt et al. (1987) offers a more exhaustive list.
Many VOCs exhibit extreme mobilities, particularly in the vapor
phase, where their gas diffusion coefficients can be four times
greater than their liquid diffusion coefficients. The vapor phase
migration is influenced by the moisture content of the soil which
alters the air-filled to water-filled pore volume ratio. The reten-
tion of VOCs by soil is largely controlled by reactions with the
solid phase. This retention is especially true for the finer
particles of silts and clays. The fine-grained particles (<2 mm)
have a large surface-to-volume ratio, a large number of reactive
sites, and high sorption capacities (Richardson and Epstein,
1971; Boucher and Lee, 1972; Lotse et al., 1968). Some
investigators attribute the greater sorption of VOCs onto fine-
grained particles to the greater organic carbon content of
smaller particles (Karickhoff et al., 1979).
Soil-moisture content affects the relative contributions of min-
eral and organic soil fractions to the retention of VOCs (Smith
et al., 1990). Mineral clay surfaces largely control sorption when
soil moisture is extremely low (<1%), and organic carbon
(Continued on page 7)
TABLE 2, FACTORS AFFECTING VOC CONCENTRATIONS IN SOILS
Factor
Common
Abbr. Units
Effects on VOC Concentrations in Soil
References
VOC Chemical Properties
Solubility
Henry's Constant
Vapor pressure
Organic carbon part, coeff.
Octanol/water part, coeff.
Boiling point
Soil/water distribution
coefficient
C. mg/L
«„ (atm-m3)/mole
v.p. mm Hg
«„. mg VOC/g C
K_
b.p.
mg VOC/
mg octanol
°C
[1 ]
Affects fate and transport in water, effects
water/air partit., influences organic carbon partit.
Constant of proportionality between the water and gas
phase concentrations; temperature and pressure dependent.
Affects rate of loss from soil.
Adsorption coefficient normalized for soil organic content.
Equilibrium constant for distribution of VOC between water
and an organic (octanol) phase. Gives estimate of VOC
partitioning into organic fraction of soil.
Affects co-evaporation of VOC and water from soil surface.
Equilibrium constant for distribution of contaminant between
solid and liquid phases.
Roy and Griffin (1985)
Shen and Sewell (1982)
Spencer etal. (1988)
Shen and Sewell (1982)
Farmer etal. (1980)
Voice and Weber (1983)
Voice and Weber (1983)
Voice and Weber (1983)
(Continued)
-------
TABLE 2. (CONTINUED)
Factor
Common
Abbr. Units
Effects on VOC Concentrations in Soil
References
Soil Chemical Properties
Cation exchange capacity CEC meo/100 g
Ion concentration
(activity)
pH
Total organic carbon content TOC mgC/gsoil
Soil Physical Properties
Particle size or texture
Specific surface area
Bulk density
Porosity
Percent moisture
Water potential
Hydraulic conductivity
s.a.
P.
e
%sand,
silt, day
mVg
g/cms
% (w/w)
m
m/d
Estimates the number of negatively charged sites on soil
particles where charged VOC may sorb; pH dependent.
Influences a number of soil processes that involve
non-neutral organic partitioning; affects CEC and
solubility of some VXs.
An important partitioning medium for non-polar, hydropnootc
(high K J VOCs; sorption of VOCs in this medium may be
highly irreversible.
Affects infiltration, penetration, retention, sorption, and
mobility of VOCs. Influences hydraulics as well as surface-
area-to-volume ratio (s.a.«Kd).
Affects adsorption of VOCs from vapor phase; affects soil
porosity and other textural properties.
Used in estimating mobility and retention of VOCs in soils;
will influence soil sampling device selection.
Void volume to total volume ratio. Affects volume,
concentration, retention, and migration of VOCs in soil voids.
Affects hydraulic conductivity of soil and sorption of VOCs.
Determines the dissolution and mobility of VOCs in soil.
Relates to the rate, mobility, and concentration of VOCs
in water or liquid chemicals.
Affects viscous flow of VOCs in soil water depending on
degree of saturation, gradients, and other physical factors.
Chbuetal.(1968)
Farmer etal. (1980)
Richardson and
Epstein (1971)
Karickhoff etal. (1979)
Spencer etal. (1988)
Farmer etal. (1980)
Shen and Sewell (1982)
Farmer etal. (1980)
Chiou and Shoup (1985)
Environmental Factors
Relative humidity
Temperature
Barometric pressure
R.H.
T
°C
mm H$
Could affect the movement, diffusion, and concentration of
VOCs; interrelated factors; could be site specific and dependent
upon soil surface - air interface differentials.
Chiou and Shoup (1985)
Wind speed
Ground cover
knots Relevant to speed, movement and concentration of
VOCs exposed, removed, or diffusing from soil surface.
% Intensity, nature, and kind, and distribution of cover
could affect movement, diffusion rates, and
concentration of VOCs.
-------
TABLE 3. CHEMICAL PROPERTIES OF SELECTED VOLATILE ORGANIC COMPOUNDS
Compound
Acetone
Benzene
Bromodichloromethane
Bromoform
Bromomethane
2-Butanone
Carbon bisulfide
Carbon tetrachloride
Chlorobenzene
Chloroethane
2-Chloroethylvinyl ether
Chloroform
Chlorornethane
Dibromochloromethane
1,2-Dichlorobenzene
1,3-Dichlorobenzene
1 ,4-Dichlorobenzene
1,1-Dichloroethane
1,2-Dichloroethane
1,1-Oichloroethene
trans-1 ,2-Oichloroethene
1 ,2-Dichloropropane
cis-1 ,3-Dichloropropene
trans-1 ,3,-Dichloropropene
Ethylbenzene
2-Hexanone
Methylene chloride
Methyiisobutylketone
Perchloroethylene
Styrene
1 ,1 ,22-Tetrachloroethane
Tetrachloroethene
Toluene
1,1,1-Trichloroethane
1,1,2-Trichloroethane
Trichloroethylene
Trichlorofluoromethane
Vinyl acetate
Vinyl chloride
Total xylenes
m.w.
(g/mote)
58
78
164
253
95
72
76
154
113
65
107
120
51
208
147
147
147
99
99
97
97
113
110
111
106
100
85
100
166
104
168
166
92
133
133
132
137
86
63
106
Solubilities
(mg/L @ 20°C)
Misrible
1780
7500
31 90 (@ 30°)
900
270000
2300
800
500
5740
8000
8348
3300
100
123 (@ 25°)
49 (@ 22°)
5500
8690
400
600
2700
2700
2800
152
3500
20000
17000
150
300
2900
150
515
4400
4500
700
1100(@25°)
25000
1100(@25°)
198
logK.,'
1.91
2.18
1.34
1.56
1.80
2.04
2.18
1.40
1.46
0.78
2.45
2.62
1.66
1.34
1.56
2.60
1.40
1.34
2.60
2.6 ?
2.07
2.78
2.18
2.19
2.14
2.09
2.68
1.59
2.60
2.46
logKJ
-022
2.11
2.10
1.19
026
2.64
2.84
1.54
1.97
0.91
224
3.38
3.38
3.39
1.79
1.48
2.06
1.99
3.15
1.38
1.25
1.46
2.60
2.95
2.60
3.40
2.69
2.50
2.07
2.29
0.73
1.38
K c
*H
-024
022
1.50
0.94
0.16
0.61
0.12
1.62
0.18
0.04
0.002
0.85
0.27
1.46
0.37
97.0
9400.0
Vapor Pressure
(mm@20°C)
270 (@30°)
76
50
6 (@ 25°)
1250
76
260
90
9
1000
160
3800
15 (@10.5°)
1
1
180
61
500
200 (@ 14")
42
34 (@ 25°)
43 (@ 25°)
7
2
349
6
14
5
5
18 (@25°)
22
100
19
60
687
115 (@25D)
2660 (@25°)
Organic carton partitioning coefficient.
Octanol/water partitioning coefficient.
Henry's Gas Law constant (dimension^) @ 20°C.
-------
TABLE 4. MICROBIOLOGICAL FACTORS AFFECTING VOCs IN SOIL SYSTEMS
Organism(s)
Compounds)
Conditions R»maric8/metabolitt<»)
Various soil microbes Pentachlorophenol
Aerobic tetra-, tri-, di-, and m-Chlorophenol (Kobayashi and Rrttman, 1982)
1,2,3- and 1,2,4-Trichlorobenzene Aerobic 2,6-; 2,3-Dichlorobenzene; 2,4- and 2,5-dichlorobenzene; CO,
(Kobayashi and Rrttman, 1982)
Various soil bacteria
Trichloroethane, trichloromethane, Anaerobic
methylchloride, chloroethane,
dichloroethane, vinylidiene chloride,
trichioroethene, tetrachloroethene,
methylene chloride,
dibromochloromethane,
bromochtoromethane
Reductive dehalogenation under anoxic conditions, (i.e., < 0.35 V)
(Kobayashi and Rittman, 1982)
Various soil microbes Tetrachloroethene
Anaerobic Reductive dehalogenation to trichloroethene.dichloroethene, and
vinyl chloride, and finally C02 (Vogel and McCarty, 1985)
Various soil microbes '3C-labeled trichioroethene
Anaerobic Dehalogenation to 1,2-dichloroethene and not 1,1 -dichloroethene
(Kleopferetal.,1985)
Various soil bacteria Trichioroethene
Aerobic Mineralized to C02 in the presence of a mixture of natural gas
and air (Wilson and Wilson, 1985)
Actinomycetes
chlorinated and non-chlorinated
aromatics
aerobic Various particle breakdown products mineralized by other
microorganisms (Lechevalier and Lechevalier, 1976)
Fungi
DDT
Aerobic Complete mineralization in 10-14 days (Johnsen, 1976)
Pseudomonassp.
Acinetobactersp-
Mc/OCOCCUSSp.
Aromatics
Aerobic Organisms were capable of sustaining growth in these compounds
with 100% biodegradation (Jamison et al., 1975)
Acetate-grown biofilm Chlorinated aliphatics
Chlorinated and nonchlorinated
aromatics
Aerobic No biodegration observed (Bouwer, 1984)
Methanogenic Nearly 100% biodegradation observed (Bouwer, 1984)
Aerobic Nearly 100% biodegradation (Bouwer, 1984)
Methanogenic No biodegration observed (Bouwer, 1984)
Blue-green algae Oil wastes
(cyanobactBria)
Aerobic Biodegradation of automobile oil wastes, crankcase oil, etc.
(Cameron, 1963)
-------
partitioning is favored when moisture content is higher (Chiou
andShoup, 1985).
Biological factors affecting VOC retention in soil systems can be
divided into microbiological and macrobiological factors. On the
microbiological level, the indigenous microbial populations
present in soil systems can alter VOC concentrations. Although
plants and animals metabolize a diversity of chemicals, the
activities of the higher organisms are often minor compared to
the transformations affected by heterotrophic bacteria and fungi
residing in the same habitat. The interactions between environ-
mental factors, such as dissolved oxygen, oxidation-reduction
potential (Eh), temperature, pH, availability of other compounds,
salinity, paniculate matter, and competing organisms, often
control biodegradation. The physical and chemical characteris-
tics of the VOC, such as solubility, volatility, hydrophobicity, and
Kaw, also influence the ability of the compound to biodegrade.
Table 4 illustrates some examples of the microbiological alter-
ations of some commonly encountered soil VOCs. In general,
the halogenated alkanes and alkenes are metabolized by soil
microbes under anaerobic conditions (Kobayashi and Rittman,
1982; Bouwer, 1984), whereas the halogenated aromatics are
metabolized under aerobic conditions. To avoid biodegradation
and oxidation of VOCs in soils, scientists at the U.S. EPA Robert
S. Kerr Environmental Research Laboratory in Ada, OK, extrude
the sample in a glove box.
On a macro scale, biological factors can influence the migration
of VOCs in the saturated, vadose, and surface zones (Table 5).
Biofilms may accumulate in the saturated zone and may biode-
grade and bioaccumulate VOCs from the ground water. The
biofilm, depending on its thickness, may impede ground-water
flow. Plant roots have a complex microflora associated with
TABLE 5. MACROBIOLOGICAL FACTORS AFFECTING VOCs
IN SOIL SYSTEMS
Factor
Zone
Effects
Biofilms
Plant roots
Animal burrows
holes
Saturated Biodegradation, bioaccumulation,
formation of metabolites that are
more or less toxic than parent
compound, thick biofilm may
retard saturated flow
Capillary fringe Mycorrihizal fungi may biodegrade
to vadose or bioaccumulate VOC, root
channels may serve as conduits
for VOC migration
Vadose
Vegetative cover Soil surface
May act as entry point for and
downward migration of surface
spills and serve as conduit for
upward VOC migration
Serve as barrier to volatilization
from soil surface and retard
infiltration of surface spills
them known as mycorrhizae. The mycorrhizae may enhance
VOC retention in the soil by biodegradation or bioaccumulation.
The root channels may act as conduits for increasing the
migration of VOCs through the soil. Similarly, animal burrows
and holes may serve as paths of least resistance for the
movement of VOCs through soil. These holes may range from
capillary-size openings, created by worms and nematodes, to
large-diameter tunnels excavated by burrowing animals. These
openings may increase the depth to which surface spills pen-
etrate the soil. A surface covering consisting of assorted vegeta-
tion is a significant barrier to volatilization of VOCs into the
atmosphere. Some ground-water and vadose-zone models
(e.g., RUSTIC) include subroutines to account for a vegetative
cover (Dean et al., 1989).
SOIL SAMPLING AND ANALYSIS DESIGN
Prior to any sampling effort, the RPM or OSC must establish the
intended purpose of the remedial investigation/feasibility study
(RI/FS). The goals of collecting samples for VOA may include
source identification, spill delineation, fate and transport, risk
assessment, enforcement, remediation, or post-remediation
confirmation. The intended purpose of the sampling effort drives
the selection of the appropriate sampling approach and the
devices to be used in the investigation.
The phase partitioning of the VOC can also influence which
sampling device should be employed. Computer models gener-
ally are used only at the final stages of a RI/FS. However,
modeling techniques can be used throughout the RI/FS process
to assist in sampling device selection by estimating the phase
partitioning of VOCs. The RPM is the primary data user for a Rl/
FS led by a federal agency. As such, the RPM must select the
sampling methodology to be employed at the site. Rgure 2
illustrates the sequence of events used to plan a VOC sampling
and analysis activity.
The domains of interest also must be determined. The target
domains may include surface (two dimensions) or subsurface
(three dimensions) environments, hot spots, a concentration
greater or less than an action limit, or the area above a leaking
underground storage tank. Statistics that may be generated
from the target domain data must be considered before a
sample and analysis design is developed. Possible statistics of
interest may include average analyte concentration and the
variance about the mean (statistics that compare whether the
observed level is significantly above or below an action level) as
well as temporal and spatial trends. Data must be of sufficiently
high quality to meet the goals of the sampling activity. The level
of data quality is defined by the data quality objectives (DQOs).
In RI/FS activities, sites are so different and information on
overall measurement error (sampling plus analytical error) is so
limited that it is not practical to set universal or generic precision,
accuracy, representativeness, completeness, and comparabil-
ity (PARCC) goals. The reader is referred to a user's guide on
quality assurance in soil sampling (Barth et al., 1989) and a
guidance document for the development of data quality objec-
tives for remedial response activities (U.S. EPA, 1987).
DQOs are qualitative and quantitative statements of the level of
uncertainty a decision maker is willing to accept in making
decisions on the basis of environmental data. It is important to
realize that if the error associated with the sample collection or
-------
DEFINE
GOAL
Soil population
• Location
Statistics
» Trend
» x, Std. dev,
• Comparison
Purpose
* Enforcement
• Remediation
• Source ID
CHARACTERIZE
SITE I
History
Process
Soil properties
Soil conditions
Existing data
Environmental
factors
3toF INTEREST.
Confidence
level
Bias
Precision
Action level
Analyte level
I
.SELECT
DESIGN
1
Split spoon
Piston samplers
Zero contain.
sampler
Shelby tube
Veihmeyer tube
Shovels
GC/MS
GC
Field GC
Methanol
extraction
•MINIMIZE RESOURCES
NO
FEASIBLE
YES
Refine draft S&A Plan
to meet goals
Field analysis
Visual
observations
Odors
Population
accesibiiity
qaMAXIMIZE INFORMATION • *H*MAX1MIZE QUAUTY
_,,,. DRAFT .
"•S&APLAN
Toots
Analytical methods
Holding times
No. of samples
Sample mass
Decontamination
QA/QC
Reid analysis
Handling
Random/
systematic design
Personnel
Budget
Time
Politics
«*FIELD -^-.
IMPLEMENTATION
.4DATA EVALUATION
^OBJECTIVE
NO
Figure 2. Flowcfjan for planning and Implementation of a soil sampling and analysis activity.
-------
preparation step is large, then the best laboratory quality
assurance program will be inadequate (van Ee et al., 1990).
The greatest emphasis should be placed on the phase that
contributes the largest component of error. For the analysis of
soils for VOCs, the greatest sources of error are the sample
collection and handling phases.
The minimum confidence level (CL) required to make a
decision from the data is defined by the DQOs. The minimum
CL depends on the precision and accuracy in sampling and
analysis and on the relative analyte concentration. Relative
error may be reduced by increasing either the number or the
mass of the samples to be analyzed. For instance, although
5-g aliquots collected in the field might exhibit unacceptable
errors, 100-g samples will yield smaller errors and might
therefore meet study or project requirements. Compositing soil
samples in methane) in the fieid also can reduce variance by
attenuating short-range spatial variability.
Field sampling personnel should coordinate with laboratory
analysts to ensure that samples of a size appropriate to the
analytical method are collected. For example, if the laboratory
procedure for preparing aliquots calls for removing a 5-g
aliquot from a 125-mL wide-mouth jar, as per SW-846, Method
8240 (U.S. EPA 1986b), then collecting a larger sample in the
field will not reduce total measurement error, because addi-
tional errors will be contributed from opening the container in
the laboratory and from subsequent homogenization.
Aliquoting of a 5-g sample in the field into a40-mL VOA vial that
can be directly attached to the laboratory purge-and-trap unit
significantly reduces loss of VOCs from the sample (U.S. EPA,
1991 a). Significant losses of VOCs were observed when
samples were homogenized as per Method 8240 specifica-
tions. Smaller losses were observed for smaller aliquots (1 to
5 g) placed in 40-mL VOA vials that had modified caps that
allowed direct attachment to the purge-and-trap device. The
procedure of collecting an aliquot in the field eliminates the
need for sample preparation and eliminates subsequent VOC
loss in the laboratory.
Field-screening procedures are gaining recognition as an
effective means of locating sampling locations and obtaining
real-time data. The benefits of soil field-screening procedures
are: (1) near real-time data to guide sampling activities, (2)
concentration of Contract Laboratory Program (CLP) sample
collection in critical areas, (3) reduced need for a second visit
to the site, and (4) reduced analytical load on the laboratory.
Limitations of field-screening procedures are: (1) a priori
knowledge of VOCs present at the site is needed to accurately
identify the compounds, (2) methodologies and instruments
are in their infancy and procedures for their use are not well
documented and. (3) a more stringent level of quality assur-
ance and quality control (QA/QC) must be employed to ensure
accurate and precise measurements. The potential benefits
and limitations associated with soil-screening procedures
must be carefully weighed and compared to the DQOs.
Certain sampling and analytical methods have inherent (imita-
tions on the type of QA/QC that is applicable. For example,
splitting soil samples in the field would not be appropriate for
VOA due to excessive analyte loss. The higher the minimum
CL needed to make a decision, the more rigorous the QA/QC
protocols must be. As VOC concentrations in the soil sample
approach the action or detection limit, the quantity and fre-
quency of QA/QC samples must be increased, or the number of
samples must be increased, to ensure that the data quality
obtained is appropriate to satisfy project objectives.
One critical element in VOC analysis is the appropriate use of trip
blanks. If a sample consists of a silty clay loam, a trip blank of
washed sand may not be realistic, for such a blank would not
retain VOC cross contaminants in the same way as the sample.
The trip blank soil matrix should have a sorptive capacity
similar to the actual sample. In addition, high-
concentration and low-concentration samples should be shipped
in separate coolers.
DEVICE SELECTION CRITERIA
The selection of a sampling device and sampling procedures
requires the consideration of many factors including the number
of samples to be collected, available funds, soil characteristics,
site limitations, ability to sample the target domain, whether or not
screening procedures are to be used, the size of sample needed,
and the required precision and accuracy as given in the DQOs.
The number of samples to be collected can greatly affect sam-
pling costs and the time required to complete a site characteriza-
tion. If many subsurface samples are needed, it may be possible
to use soil-gas sampling coupled with on-site analysis as an
integrated screening technique to reduce the area of interest and
thus the number of samples needed. Such a sampling approach
may be applicable for cases of near-surface contamination.
Ultimately, the sampling, sample handling, containerizing, and
transport of the soil sample should minimize losses of volatiles
and should avoid contamination of the sample. Soil sampling
equipment should be readily decontaminated in the field if it is to
be reused on the job site. Decontamination of sampling equip-
ment may require the use of decontamination pads that have
impervious liners, wash and rinse troughs, and careful handling
of large equipment. Whenever possible, a liner should be used
inside the sampling device to reduce potential cross contamina-
tion and carryover. Decontamination procedures take time,
require extra equipment, and ultimately increase site character-
ization costs. Ease and cost of decontamination are thus impor-
tant factors to be considered in device selection.
Several soil-screening procedures are in use that include
headspace analysis of soils using organic vapor analyzers: water
(or NaGI-saturated water) extraction of soil, followed by static
headspace analysis using an organic vapor analyzer (OVA) or
gas chromatograph (GC); colorimetric test kits; methanol extrac-
tion followed by headspace analysis or direct injection into a GC;
and soil-gas sampling. Reid measurements may not provide
absolute values but often may be a superior means of obtaining
relative values. These procedures are gaining acceptance.
Site Characteristics
The remoteness of a site and the physical setting may restrict
access aid, therefore, affect equipment selection. Such factors
as vegetation, steep slopes, rugged or rocky terrain, overhead
power lines or other overhead restrictions, and lack of roads can
contribute to access problems.
The presence of underground utilities, pipes, electrical lines,
tanks and leach fields can also affect selection of sampling
equipment. If the location or absence of these hazards cannot be
-------
established, it is desirable to conduct a nonintrusive survey of
the area and select a sampling approach that minimizes haz-
ards. For example, hand tools and a backhoe are more practical
under such circumstances than a large, hollow-stem auger. The
selection of a sampling device may be influenced by other
contaminants of interest such as pesticides, metals,
semivolatile organic compounds, radionudides, and explo-
sives. Where the site history indicates that the matrix is other
than soil, special consideration should be given to device
selection. Concrete, reinforcement bars, scrap metal, and lum-
ber will affect sampling device selection. Under some circum-
stances, it may not be practical to collect deep soil samples. The
presence of ordnance, drums, concrete, voids, pyrophoric ma-
terials, and high-hazard radioactive materials may preclude
some sampling and may require development of alternate
sampling designs, or even reconsideration of project objectives.
Soil Characteristics
The characteristics of the soil material being sampled have a
marked effect upon the selection of a sampling device. An
investigator must evaluate soil characteristics, the type of VOC,
and the depth at which a sample is to be collected before
selection of a proper sampling device. Specific characteristics
that must be considered are:
1. Is the soil compacted, rocky, or rubble filled? If the answer
is yes, then either hollow stem augers or pit sampling must
be used.
2. Is the soft fine grained? If yes, use split spoons, Shelby
tubes, liners, or hollow stem augers.
3. Are there flowing sands or water saturated soils? If yes, use
samplers such as piston samplers that can retain these
materials.
SOIL-GAS MEASUREMENTS
Soil-gas measurements can serve a variety of screening pur-
poses in soil sampling and analysis programs, from initial site
reconnaissance to remedial monitoring efforts. Soil-gas mea-
surements should be used for screening purposes only, and not
for definitive determination of soil-bound VOCs. Field analysis
is usually by hand-held detectors, portable GC or GC/MS,
infrared detectors, ion mobility spectrometers (IMS), industrial
hygiene detector tubes, and, recently, fiber optic sensors.
At some sites, soil-gas sampling may be the only means of
acquiring data on the presence or absence of VOCs in the soil.
For example, when the size and density of rocks and cobbles
at a site prevent insertion and withdrawal of the coring device
and prevent sampling with shovels and trowels, unacceptable
losses of VOCs would occur. Soil-gas measurements, which
can be made on site or with collected soil samples, can be used
to identify volatile contaminants and to determine relative
magnitudes of concentration. Smith et al. (1990) have shown
a disparity in soil-gas VOC concentrations and the concentra-
tion of VOCs found on the solid phase.
Soil-gas measurements have several applications. These in-
clude in situ soil-gas surveying, measurement of headspace
concentrations above containerized soil samples, and scan-
ning of soil contained in cores collected from different depths.
These applications are summarized in Table 6. Currently, no
TABLE 6. APPLICATIONS OF SOIL-GAS MEASUREMENT TECHNIQUES IN SOIL SAMPLING FOR VOCs
Application
Method*
Benefits/limitation*
Soil vapor Identify sources and extent
surveying of contamination. Distinguish
between soil and ground water
contamination. Detect VOCs
under asphalt concrete, etc.
Active sampling from soil probes
Mo 'Canisters, glass bulbs, gas
sampling bags. Passive sampling
onto buried adsorptive substrates.
Followed by GC or other analysis.
BENEFITS: Rapid, inexpensive screening of
large areas, avoid sampling yncontaminaieti areas.
LIMITATIONS: False positives and re§a*ss, miss
detecting bca&sd surface spis, disequilibrium
between adsorbed and vapor phase VOC
concentrations.
Soil headspace
measurements
Screen large numbers of soil
samples.
Measure headspace above
containerized soil sample.
Containers range troc
sandwich bags to VOA vials.
Use GC, vapor detectors, IMS, etc.
BENEFITS: More representative of adsorbed solid
phase concentration.
LIMITATIONS: Losses of vapor phase component
during sampling and sample transfer.
Screening Soil cores scanned to locate
soil cores depth where highsst VOC
levels are located.
Collect core sample (e.g., unlined
split spam) and scan for vapors near
core surface using portable vapor
monitor.
BENEFITS: Locate and collect soil from hot spot
in core for worst ease.
LIMITATIONS: Fstas negatives and positives,
environmental conditions can influence readings
(e.g., wind speed and direction, temperature, humidity).
10
-------
standard protocols exist for soil-gas analysis; many investiga-
tors have devised their own techniques, which have varying
degrees of efficacy. Independently, the American Society for
Testing and Materials (ASTM) and EPA EMSL-LV are preparing
guidance documents for soil-gas measurement. These docu-
ments should be available late in 1991.
The required precision and accuracy of site characterization, as
defined in the OQOs, affect the selection of a sampling device.
Where maximum precision and accuracy are required, sampling
devices that collect an intact core should be used, particularly for
more volatile VOCs in nonretenttve matrices. Augers and other
devices that collect highly disturbed samples and expose the
samples to the atmosphere can be used if lower precision and
accuracy can be tolerated. Collection of a larger number of
samples to characterize a given area, however, can compen-
sate for a less precise sampling approach. The closer the
expected contaminant level is to the action or detection limit, the
more efficient the sampling device should be for obtaining an
accurate measurement.
SOIL SAMPLING DEVICES
Table 7 lists selection criteria for different types of commercially
available soil sampling devices based on soil type, moisture
status, and power requirements. The sampling device needed
to achieve a certain sampling and analysis goal can be located
in Table 7 and the supplier of such a device can be identified in
Table 8. Table 8 is a partial list of commercially available soil
sampling devices that are currently in use for sampling soils for
VOC analysis. The list is by no means exhaustive and inclusion
(Continued on page 14)
TABLE 7. CRITERIA FOR SELECTING SOIL SAMPLING EQUIPMENT!
Obtains Most Operation Suitable Soil Relative Labor Manual
Core Suitable in Stony Moisture Sample Requirements or Power
Type of Sampler Samples Soil types Soils Conditions Size (# of Persons) Operation
A. Mechanical Sample Recovery
1. Hand-held Power augers
2. Solid stem flight augers
3. Hollow-stem augers
4. Bucket augers
5. Backhoes
No
No
Yes
No
No
Coh/coh'less
Coh/coh'less
Coh/coh'less
Coh/coh'less
Coh/coh'less
Unfavorable
Favorable
Fav/unfav
Favorable
Favorable
Intermediate
Wet to dry
Wet to dry
Wet to dry
Wet to dry
Large
Large
Large
Large
Large
2+
2+
2+
2+
2+
Power
Power
Power
Power
Power
B. Samplers
1. Screw-type augers
2. Barrel augers
a. Post-hole augers
b. Dutch augers
c. Regular barrel augers
d. Sand augers
e. Mud augers
3. Tube-type samplers
a. Soil samplers
b. Veihmeyer tubes
c. Shelby tubes
d. Ring-lined samplers
e. Continuous samplers
f. Piston samplers
g. Zero-contamination samplers
h. Split spoon samplers
4. Bulk samplers
.
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Con
Con
Con
Con
Gch'less
Con
Con
Con
Con
Coh'less
Con
Con
Con
Con
Con
Unfavorable
Unfavorable
Unfavorable
Unfavorable
Unfavorable
Unfavorable
Unfavorable
Unfavorable
Unfavorable
Favorable
Unfavorable
Unfavorable
Unfavorable
Unfavorable
Favorable
Intermediate
Wet
Wet
Intermediate
Intermediate
Wet
Wet to dry
Intermediate
Intermediate
Wet to intermediate
Wet to dry
Wet
Wet to intermediate
Intermediate
Wet to dry
Small
Large
Large
Large
Large
Large
Small
Large
Large
Large
Large
Large
Small
Large
Large
Single
Single
Single
Single
Single
Single
Single
Single
2+*
2+*
2+
2+*
2+*
2+*
Single
Manual
Manual
Manual
Manual
Manual
Manual
Manual
Manual
Both
Both
Power
Both •
Both
Both
Manual
t Adapted from U.S. EPA, 19B6a.
" AH hand-spiral Bd versions of samptefi, exetp lor continuous ssmplw, tan b» worte! by one person,
Ceh = cohesive.
11
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TABLE 8. EXAMPLES OF COMMERCIALLY AVAILABLE SOIL SAMPLING DEVICES
Manufacturers
Sampling Device
Specifications
Length (inches)
1,0, (inches)
Sampler Material Liners
Features
Associated Design &
Manufacturing Co.
814 North Henry Street
Alexandria, VA 22314
703-549-5999
Acker Drill Co.
P.O. Box 830
Scranton, PA
717-586-2061
AMS
Harrison at Oregon Trail
American Falls, ID 83211
Concord, Inc.
2800 7th Ave.N.
Fargo. ND 58102
Purge and Trap
Soil Sampler
Heavy Duty "Lynac"
Split Tube Sampler
Dennison Core Barrel
Core Soil Sampler
Dual Purpose Soil
Recovery Probe
Soil Recovery Auger
Speedy Soil Sampler
3
0.5
Stainless steel
18&24
1-1/2 to 4-1/2
Steel
24&60
1-7/8 to 6-5/16
2 to 12
1-1/2 to 3
Alloy, stainless
12, 18&24
3/4 and 1
4130 Alloy,
stainless
8 to 12
2&3
Stainless
48472
3/16 to 3-1/2
Stainless
Brass,
stainless
Brass
Stainless, plastic
aluminum, bronze
teflon
Butyrate, Teflon
stainless
Plastic, stainless
Teflon, aluminum
Acetate
Will rapidly sample soils
for screening by "Low Level"
Purge and Trap methods.
Split tube allows for easy
sample removal.
Will remove undisturbed
sample from cohesive soils.
Good in all types of soils.
Adapts to AMS "up & down"
hammer attachment. Use
with or without liners.
Adaptable to AMS extension
and cross-handles.
Automated system allows
retrieval of 24 in soil
sample in 12 sea
701-280-1260
Zero Contamination Unit
Hand-Held Sampler
CME
Central Mine Equip. Co.
6200 North Broadway
St Louis, MO 63147
800-325-8827
Continuous Sampler
60
2-1/2(05-3/8
Steel, stainless
Bearing Head Continuous 60
Sample Tube System 2-1/2
Steel, stainless
Butyrate
Butyrate
May not be suitable in
stony soils. Adapts to CMS
auger.
Versatile system. Adapts
to all brands of augers.
Diedrich Drilling Equip.
P.O. Box 1670
Laporte, IN 46350
800-348-8809
Heavy Duty Split
Tube Sampler
Continuous Sampler
18&24
2,2-1/2,3
Steel
60
3,3-1/2
Brass, plastic
stainless, Teflon
Brass, plastic
stainless, Teflon
Full line of accessories
are available.
Switch-out device easily
done.
(Continued)
12
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TABLE 8. (CONTINUED)
Manufactures
Sampling Device
•Specifications-
Length (inches)
I.D. (Inches)
Sampler Material
Liners
Features
Geoprobe Systems
607 Barney St.
Salina, KS
913-825-1842
Probe Drive
Soil Sampler
11-1/4
0.96
Alloy steel
Remains completely sealed
while pushed to depth in
soil.
Giddings Machine Co.
P.O. Drawer 2024
Fort Collins, CO 80522
303-485-5586
Coring Tubes
48&60
7/8 to 2-3/8
4130Molychrome
Butyrate
A series of optional 5/8 in
slots permit observation of
the sample.
JMC
Clements and Associates
R.R. 1 Box 186
Newton, IA 50208
800-247-6630
Environmentalist's
Sub-soil Probe
Zero Contamination
Tubes
36&48
0.9
Nickel plated
12,18 & 24
0.9
Nickel plated
PETG plastic,
stainless
PETG plastic,
stainless
Adapts to drop-hammer to
penetrate the hardest of soils.
Adapts to power probe.
Mobile Drilling Co.
3807 Madison Ave.
Indianapolis, IN 46227
800-428-4475
"Lynac" Split
Barrel Sampler
1B&24
1-1/2
plastic
Adapts to Mobile wireline
sampling system.
Softest, Inc.
66 Albrecht Drive
Lake Bluff, IL
800-323-1242
Zero Contamination
Sampler
Thin Wall Tube
Sampler (Shelby)
Split Tube Sampler
Veihmeyer Soil
Sampling Tube
12,18 & 24
0.9
Chrome plated
30
2-1/2, 3, 3-1/2
Steel
24
1-1/2 to 3
Steel
48472
3/4
Steel
Stainless,
acetate
Brass
Hand sampler good for
chemical residue studies.
Will take undisturbed samples
in cohesive soils and days.
Forced into soil by jacking,
hydraulic pressure or driving.
Very popular type of sampler.
Adapts to drop hammer for
sampling in all sorts of soils.
Sprague & Kenwood, Inc.
Scranton, PA 18501
800-344-8506
S & H Spirt Barrel
Sampler
18&24
2 to 3-1/2
Brass,
plastic
A general all-purpose
sampling device designed
for driving into material to
be sampled.
Note: This fat is not exhaustive. Inclusion in this 1st should not be construed as endorsement for use.
13
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in the list should not be construed as an endorsement for their
use.
Commonly, soil samples are obtained from the near surface
using shovels, scoops, trowels, and spatulas. These devices
can be used to extract soil samples from trenches and pits
excavated by back noes. A predeaned shovel or scoop can be
used to expose fresh soil from the face of the test pit A thin-
walled tube or small-diameter, hand-held corer can be used to
collect soil from the exposed face. Bulk samplers such as
shovels and trowels cause considerable disturbance of the soil
and expose the sample to the atmosphere, enhancing loss of
VOCs. Siegrist and Jenssen (1990) have shown that sampling
procedures that cause the least amount of disturbance provide
the greatest VOC recoveries. Therefore, sampling devices that
obtain undisturbed soil samples using either hand-held or me-
chanical devices are recommended. Sampling devices that
collect undisturbed samples include split-spoon samplers, ring
samplers, continuous samplers, zero-contamination samplers,
and Shelby tubes. These sampling devices can be used to
collect surface soil samples or they can be used in conjunction
with hollow-stem augers to collect subsurface samples. The soil
sampling devices discussed above are summarized in Table 9.
Devices where the soil samples can be easily and quickly
removed and containerized with the least amount of disturbance
and exposure to the atmosphere are highly recommended. U.S.
EP A (1986a) gives a more detailed discussion on the proper use
of drill rigs and sampling devices.
Liners are available for many of the devices listed in Table 9.
Liners make soil removal from the coring device much easier
and quicker. Liners reduce cross contamination between
samples and the need for decontamination of the sampling
device. The liner can run the entire length of the core or can be
precut into sections of desired length.
When sampling for VOCs, it .3 critical to avoid interactions
between the sample and the liner and between the sample and
the sampler. Such interactions may include either adsorption of
VOCs from the sample or release of VOCs to the sample.
Gillman and Q'Hannesin (1S90) studied the sorption of six
monoaromatic hydrocarbons in ground water samples by seven
materials. The hydrocarbons included benzene, toluene,
ethyibenzene, and a-, m-, and p-xylene. The materials exam-
ined were stainless steel, rigid PVC, flexible PVC, PTFE Teflon,
polyvinylidene fluoride, fiberglass, and polyethylene. Stainless
TABLE 9. SOIL SAMPLERS FOR VOC ANALYSIS
Recommended
Not Recommended
Split spoon w/liners
Shelby tube (thin wall tubes)
Hollow-stem augers
Veihmeyer or King tubes
w/liners
Piston samplers*
Zero contamination samplers*
Probe-drive samplers
Solid flight liners
Drilling mud auger
Air drilling auger
Cable tool
Hand augers
Barrel augers
Scoop samplers
Excavating tools, e.g., shovels, backhoes
' May sustain VOC losses if not used with care
steel showed no significant sorption during an 8-week period. All
polymer materials sorbed all compounds to some extent. The
order of sorption was as follows: rigid PVC < fiberglass <
polyvinylidene fluoride < PTFE < polyethylene < flexible PVC.
Stainless steel or brass liners should be used since they exhibit
the least adsorption of VOCs. Other materials such as PVC or
acetate may be used, provided that contact time between the
soil and the liner material is kept to a minimum. Stainless steel
and brass liners have been sealed with plastic caps or paraffin
before shipment to the laboratory for sectioning and analysis.
VOC loss can result from permeation through the plastic or
paraffin and volatilization through leaks in the seal. Acetate
liners are available, but samples should not be held in these
liners for any extended period, due to adsorption onto and
permeation through the material. Alternatively, the soil can be
extruded from the liner, and a portion can be placed into a wide-
mouth glass jar. Smaller aliquots can be taken from the center
of the precut liner using subcoring devices and the soil plug
extruded into VOA vials.
TRANSFER OF SOIL SAMPLES FROM DEVICE TO
CONTAINER
The sample transfer step is perhaps the most critical and least
understood step in the sampling and analysis procedure. The
key point in sample transfer, whether in the field or in the
laboratory, is to minimize disturbance and the amount of time the
sample is exposed to the atmosphere. It is more important to
transfer the sample rapidly to the container than to accurately
weigh the aliquot which is transferred, or to spend considerable
time reducing headspace. Therefore, a combination of a device
for obtaining the appropriate mass of sample and placement of
the aliquot into a container that can be directly connected to the
analytical device in the laboratory is recommended. Several
designs are available for obtaining a 5-g aliquot (or other size).
Most subcoring devices consist of a plunger/barrel design with
an open end. The device shown in Figure 3 was constructed by
Associated Design & Manufacturing Company (Alexandria,
VA). Other designs include syringes with the tips removed, and
cork borers (Table 8). The device is inserted into the sample and
an aliquot is withdrawn, Ths aliquot, which is of a known volume
and approximate weight, can then be extruded into a tared 40-
mL VOA vial. Routinely, the viaJ is then sealed with a Teflon-lined
septum cap. Teflon, however, may be permeable to VOCs.
Aluminum-lined caps are available to reduce losses due to
permeation. At the laboratory, the vial must be opened and the
contents of the vial must be transferred to a sparger tube. The
transfer procedure will result in significant losses of VOCs from
the headspace in the vial. The modified purge-and-trap cap
shown in Rgure 4 eliminates the loss of VOCs due to container
opening and sample transfer. The soil is extruded from the
subcorer into a tared 40-mL VOA vial and the modified cap is
attached in the field. In the laboratory, the vial is attached directly
to a purge-and-trap device without ever being opened to the
ambient air.
Use of subcoring devices should produce analytical results of
increased accuracy. In order to test this hypothesis, an experi-
ment was conducted in which a bulk soil sample was spiked with
800 ug/kg of different VOCs {Maskarinec, 1990), Three aliquots
were withdrawn by scooping, and three aliquots were withdrawn
by using the sub-corer approach. The results are presented in
Table 10. Although neither method produced quantitative recov-
ery, the subcorer approach produced results that were generally
14
-------
Figure 3. Small-diameter hand-held subcoring device made
by Associated Design & Manufacturing Company
(Alexandria, VA).
TABLE 10. LABORATORY COMPARISON OF STANDARD METHOD
AND SUBCORER METHOD
Standard
Method Subcorer
%of %of
Standard Subcorer Recovery Recovery
Compound Method* Method" of Spike of Spike
Chloromethane
Bromomethane
Chloroethane
1,1-Dichloroethene
1 ,1 -Dichloroelhane
Chloroform
Carbon tetrachloride
1 ,2-Dichloropropane
Trichloroethene
Benzene
1 ,1 ,2-Trichloroethane
Bromoform
1,1,2,2-Trichloroethane
Toluene
Chlorobenzene
Ethylbenzene
Styrene
50
31
78
82
171
158
125
147
120
170
78
30
46
129
57
68
30
1225
536
946
655
735
534
658
766
512
636
477
170
271
656
298
332
191
6
4
10
10
21
20
16
18
15
21
10
4
6
16
7
8
4
153
67
118
82
92
67
82
96
64
80
60
21
34
82
37
42
24
H9/kg(rt»3)
P9*9 (n-3)
Note: Standard method of sample transfer consists of scooping and subcorer
mtttod uses device shown in Figure 3. Soil samples were spiked wtri fiOO
W/kgofeachVOC.
five times higher than the standard approach, whereby the
contents of a 125-mL wide-mouth jar are poured into an alumi-
num tray and homogenized with a stainless steel spatula. A 5-
g sample is then placed In the sparger tube (SW-846, Method
8240). Several compounds presented problems with both
approaches: styrene polymerizes, bromoform purges poorly,
and 1,1,2,2-tetrachloroethane degrades quickly.
1/2" Stainless
Steel Body
O-Ring
1/16"
Teflon Ball
Receiving union from
Purge-and-Trap Device
1/2" Stainless
Steel Body
O-Ring
Hole Cap
40 ml_ Vial
Purge Needle
Figure 4. Modified purge-and-trap 40-mL VOA vial cap for
containerizing samples in the field. Vial is
attached directly to a purge-and-trap system
without exposure of sample to the atmosphere.
15
-------
In another study (U.S. EPA, 1991 a), a large quantity of well
characterized soil was spiked with 33 VOCs and was homog-
enized. From the homogenized material, a 5-g aliquot of soil was
placed in a 40-mL VOA vial and sealed with a modified purge-
and-trap cap (Figure 4). The remaining soil was placed in 125-
mL wide-mouth jars, the samples were shipped via air carrier
and were analyzed by GC/MS with heated purge and trap. The
40-mL VOA vials were connected directly to a Tekmar purge-
and-trap unit without exposure to the atmosphere. The wide-
mouth jars were processed as per SW-846 Method 8240 speci-
fications (U.S. EPA, 1986b). Table 11 compares the results of
the GC/MS analyses using the two pretreatment techniques.
The modified method (40-mL VOA vial with a modified cap)
yielded consistently higher VOC concentrations than the tradi-
tional Method 8240 procedure (U.S. EPA, 1986b).
The standard methods for VOC analysis, SW-846, Method 8240
and Test Method 624 (U.S. EPA, 1986b; U.S. EPA, 1982), call
for the containerizing of soil samples in 40-mL VOA vials or 125-
mL wide-mouth jars with minimal headspace. As previously
described, wide-mouth jars may not be the most appropriate
containers due to sample aliquoting requirements. Although
wide-mouth jars may be equally as effective as 40-mL VOA vials
in maintaining the VOC content of soil samples, the sample
preparation procedure that is required with jar-held samples
causes significant (>80%) loss of highly volatile VOCs (Siegrist
and Jennsen, 1990). However, if samples are collected in such
containers, it is important to ensure sample integrity, preferably
by using amber glass jars (lor photosensitive compounds) with
solid phenolic resin caps and foam-backed Teflon liners. Alumi-
num-lined caps are not available for the wide-mouth jars. Soil
should be wiped from the threads of the jar to ensure a tight seal.
The methanol-immersion procedure calls for the transfer of the
sample into a glass jar containing a known volume of chromato-
graphic-grade methanol (usually 100 mL) or in a 1:1 weight-to-
volume ratio of soil to methanol. This has the effect of preserving
the volatile components of the sample at the time the sample is
placed in the container. Furthermore, surrogate compounds can
be added at this time in order to identify possible changes in the
sample during transport and storage. The addition of methanol
So the sample raises the detection limits from 5 to 10 ng/kg to 100
to 500 u.g/kg, because of the attendant dilution. However, the
resulting data have been shown to be more representative of the
original VOC content of the soil (Siegrist and Jennsen, 1990;
Siegrist, 1990). In a comparison of transfer techniques, Siegrist
and Jennsen (1990) demonstrated that mJnimym losses were
obtained by using an undisturbed sample followed by immediate
TABLE 11. COMPARISON OF VOC CONCENTRATIONS IN SPIKED SOIL ANALYZED BY METHOD 8240 AND MODIFIED METHOD 8240
Concentration (ug/kg)
VOC
Bromomethane
Vinyl chloride
Chloroethane
Methylene chloride
Carbon disulfide
1,1-Dichloroethene
1,1-Dichloroethane
1 ,2-Dichloroetnene
Chloroform
1,1,1-Trichtoroethane
Cartoon tetrachloride
Vinyl acetate
1 ,2-Dichloroethane
cis-1 ,3-Dichloropropene
Trichloroethene
Benzene
Bromodichlorornetnane
Method
8240t
9
3
6
69
32
12
34
36
56
26
18
18
101
136
48
56
111
Method
8240ft
44
32
36
100
82
35
83
66
96
80
61
26
159
189
87
114
166
Difference
35"
29"
30"
31"
50"
23"
49"
30"
40"
54"
43"
8
58"
. 53*
39"
58*
55*
VOC
Dibromochloromethane
1,1,2-Trichloroethane
trans- 1 ,3-Dichloropropene
Bromoform
Tetrachloroethene
1 ,1 ,2,2-Tetrachloroethane
Toluene
Chlorobenzene
Ethylbenzene
Styrene
Total xylenes
KETONES
Acetone
2-Butanone
2-Hexanone
4-Methly-2-pentanone
Concentration iiiglkg) — •.
Modified
Method
8240f
121
142
154
116
62
13?
85
91
85
86
57
336
290
200
264
Method
8240tt
159
193
203
140
124
162
161
132
135
114
85
497
365
215
288
Difference
38
51
49
24
62"
25
76*
41"
50"
28*
28"
161*
75
. 15
24
t Method 8240 using 125-mL wide-mouth jar mixing subnmping in laboratory purge/trap analysis.
n Method 8240 using 40HHL vial. 5-g sampled in ttwteld. shipped to laboratory purge/trip analysis.
* ntffnmnn* •ifinifutanllu
unrarance s^nnicaiiiiy
fM^^inr Mtan A ua
grMtar tnan o, wi
ithP.imki« W^/H
lUI r •VtWJO Cw.Wlt
Mi P-value between 0.01
• Difference significantly greater than 0, with P-value between 0.01
and 0.05.
and 0.05, however data set contains zeros and make results suspect
Note: Values are means of dupficate analysis. Spike concentration was 300 ug/kg.
16
-------
immersion into methanoi. The results for six VOCs are shown in however, headspace did not seem to be a major contributor to
Figure 5. At high VOC spike levels (mg/kg) the investigators VOC losses (Maskarinec, 1990). In another study (U.S. EPA,
found that headspace within the bottle caused a decrease in the 1991 a), it was found that a 5-g sample collected from a soil core
concentration of VOCs in the sample. At lower spike levels, and placed in a 40-mL VOA vial provided consistently higher
concentration, ppm
TREATMENT A
UNDISTURBED SOIL
PLASTIC BAG
LOW HEADSPACE
TREATMENTB
UNDISTURBED SOIL
GLASS JAR
HIGH HEADSPACE
TREATMENTC
DISTURBED SOIL
GLASS JAR
LOW HEADSPACE
TREATMENTD
UNDISTURBED SOIL
GLASS JAR
LOW HEADSPACE
TREATMENTE
UNDISTURBED SOIL
GLASS JAR
METHANOL
TREATMENT A TREATMENTB TREATMENTC TREATMENT 0 TREATMENTE
METHYLENE CHLORIDE
1,2-DICHLOROETHANE
concentration, ppm
o i—
TREATMENT A TREATMENT B TREATMENTC TREATMENT D TREATMENT E
£3 1,1,1,-TRICHLOROETHANE
TOLUENE
TRICHLOROETHENE
CHLOROBENZENE
Figure 5. VOC recovery as a function of sample treatment
17
-------
VOC levels than a sample taken from the same core, placed in
a 125-mL wide-mouth jar, and later poured out, homogenized,
and a 5-g aliquot taken from the bulk material as per Method
8240 specifications.
SOIL SAMPLING SCENARIOS
The following recommendations for soil sampling and sample
handling are presented for the three general sampling sce-
narios described earlier.
1. Open Test Pit or Trench
Samples are often collected from exposed test pits or trenches
where remediation efforts are in progress. Sites may also be
encountered where large-diameter coring devices cannot be
employed. In such instances, crude sampling devices, such as
trowels, spoons, shovels, spades, scoops, hand augers, or
bucket augers must be used to excavate the soil.
The exposed face of an excavated test pit is scraped to uncover
fresh material. Samples are collected from the scraped face by
using a small-diameter, hand-held corer (Figure 3). If the
nominal 5-g sample is to be collected, the appropriate volume
(3 to 4 mL) is extruded into a tared 40-mL VOA vial and sealed
with a modified purge-and-trap cap (Figure 4). The vial is chilled
to 0° to 4°C and sent to the laboratory where the entire contents
of the vial are purged without opening the vial (U.S. EPA
1991b). Though this method minimizes losses of VOCs, the
small sample size may exhibit greater short-range spatial
variability than larger samples.
Alternatively, a small-diameter, hand-held soil corer (Figure 3)
can be used to collect a larger volume of soil. The soil is
extruded to fill a 40-mL VOA vial with a Teflon-lined septum cap
(minimal headspace), chilled, and sent to the laboratory. The
major weakness with this method is that VOCs are lost in the
laboratory during sample homogenization, preparation of
aliquots from a subsample, and the transfer to the extraction or
sparging device.
If large coarse fragments or highly compacted soils are encoun-
tered, the use of a hand-held corer may not be possible. In this
case crude sampling devices are used to rapidly collect and fill
(minimal headspace) a 125- or 250-mL wide-mouth glass jar.
The threads are wiped clean and the jar is sealed with a foam-
backed Teflon-lined cap. The jar is chilled immediately to 0° to
4°C for shipment to the laboratory. Losses of VOCs are consid-
erably greater with this method due to disruption of the matrix
and losses in the laboratory during sample preparation. Metha-
nol immersion may be more suitable for these matrices.
2. Surface Soils (< 5 ft deep)
The preferred soil sampling procedures reduce VOC losses by
minimizing sample disturbance during collection and transferto
a container. The collection of soil cores with direct extrusion into
a container accomplishes this goal. A larger-diameter coring
device (e.g., split-spoon sampler, Shelby tube, zero-contami-
nation sampler) is used to collect an intact sample from the
surface soil or from an augered hole. Many of these samplers
can be used with liners, an insert that greatly reduces the time
required to remove the soil and obtain a subsample. For
subsamples collected from split spoons or extruded large-
diameter cores, the section to be subsampled is scraped and
laterally subcored, onhe extruded soil is cut or broken to expose
fresh material at the depth or zone of interest, then longitudinally
subcored. For large-diameter cores that are collected in precut
liners, the liner sections are separated with a stainless steel
spatula, and a small-diameter hand-held corer is used to collect
a subsample from the center of the liner section. The uppermost
portion of the core should not be sampled, because it is more
likely to be cross contaminated. The small diameter corer
(Figure 3) is pushed into the soil, the outside of the corer is wiped
clean, and the required core volume (typically about 3 to 4 mL
or 5 g) is extruded directly into a tared 40-mL glass VOA vial and
sealed with a modified purge-and-trap cap (Figure 4). The vial
threads and lip must be free of soil to ensure an airtight seal.
3. Subsurface soils (> 5 ft deep)
The same sampling principles apply for the collection of deeper
soil samples. Collection of soil cores with direct extrusion into a
container greatly reduces the loss of VOCs. Tube-type samplers
such as split-spoon, Shelby tubes, and zero-contamination
samplers are used inside a hollow-stem auger to obtain an intact
sample from greater depths. The coring device is retrieved and
a subsample is obtained in a similar manner as that described
for surface soils.
METHANOL IMMERSION PROCEDURE
Soil collected by protocols outlined above can be placed in a
tared wide-mouth glass jar containing pesticide-grade methanol
(1:1 weight-to-volume ratio of soil to methanol). The immersion
of relatively large soil samples into methanol has the advantage
of extracting a much larger sample that is probably less prone to
short-range spatial variability. This is of particular advantage
with coarse-grained soils, materials from which it is hard to
obtain a 1-g to 5-g subsample for analysis.
Multiple small-diameter corers can be immersed in a single
methanol-filled jar to produce a composite sample.
Compositing becomes practical because VOCs are soluble in
methanol, thus reducing losses. Appropriately collected com-
posite samples can produce more representative data than a
comparable number of individual samples. Short-range spatial
variability is greatly reduced. Another advantage is the ability to
reanalyze samples. The main disadvantages of using methanol
include the requirements for handling and shipping the metha-
nol and the detection limit that is raised by a factor of about 10
to 20. For the methanol-immersion procedure, jars filled with
methanol and shipped to the laboratory are classified as a
hazardous material, flammable liquid and must be labelled as
per Department of Transportation specifications (49 CFR,
1982). If these disadvantages are unacceptable, then the
modified purge-and-trap procedure may be applicable.
FIELD STORAGE
Material containing VOCs should be kept away from the sample
and the sample container. Hand lotion, labeling tape, adhesives,
and ink from waterproof pens contain VOCs that are often
analytes of interest in the sample. Samples and storage contain-
ers should be kept away from vehicle and generator exhaust and
other sources of VOCs. Any source of VOCs may cause
contamination that may compromise the resulting data.
18
-------
Once samples are removed from the sampling device and
placed in the appropriate storage container, the containers
should be placed in the dark at reduced temperatures (0° to
4°C). Excessively cold temperatures (<-10°C) should be
avoided; studies have shown greater losses of analytes due to
reduced pressures in the container, sublimation of water, and
concomitant release of water-soluble VOCs into the headspace.
Upon opening the container, the vacuum is quickly replaced with
ambient air, thus purging out VOGs from the headspace
(Maskarineceta!., 1988V Extremely cold temperatures can also
loosen the seal on the container cap. Caps should be
retightened after 15 minutes at reduced temperatures. Samples
should be kept in ice chests while in route to the shipment facility
or laboratory. At temperatures above freezing, bacterial action
can have a significant impact on the observed soil VOC con-
centration. Numerous preservation techniques are being
evaluated at the University of Nevada Environmental Research
Center in Las Vegas and at Oak Ridge National Laboratory.
SHIPPING
Given the short holding times required for VOC analysis under
Method 8240 (10 days from sample collection to analysis),
samples are usually shipped via air carrier to the analytical
laboratory. Samples should be well packed and padded to
prevent breakage. Temperatures in cargo holds can increase to
more than 50°C during transit, therefore, the need for adequate
cold storage is critical. Styrofoam coolers are commercially
available to accommodate 40-mL and 125-mL glass containers.
Sufficient quantities of Blue Ice™ or Freeze-Gel™ packs should
be placed in the container to ensure that samples are cooled for
the duration of the shipment. A maximum-minimum thermom-
eter (non-mercury) should be shipped with the samples. If
sample containers are not adequately sealed, VOC losses can
occur. These losses may be exacerbated by the reduced
atmospheric pressures encountered in the cargo holds of air
carriers. Figure 6 illustrates the changes in temperature and
pressure in the cargo hold of various air carrier's aircraft. Three
major air carriers have been monitored and have shown similar
fluctuations in temperature and pressure (Lewis and Parolini,
1991). Lewis et al. (1990) noted decreases in VOC concentra-
tions in soil samples that were shipped compared to samples
that were analyzed in the field. If the container is of questionable
or unknown integrity, it should either be evaluated prior to use or
a previously characterized container should be used.
As discussed previously, samples that are immersed in metha-
noi have special shipping requirements. These samples must
be shipped as "Flammable Liquids" under Department of Trans-
portation (DOT) requirements. A secondary container is re-
quired for shipment of any item classified as a flammable liquid.
PRESERVATION
Improvements in operational factors such as sampling device
efficiency, sample transfer, containerizing, shipping, storage,
laboratory sample preparation, and analysis will reduce VOC
losses from soils. Two principal matrix-specific factors that can
contribute to the loss of VOC in soils are biodegradation and
volatilization. An effective preservation technique should act on
these matrix-specific factors to reduce losses of VOCs.
The required preservation technique for soil samples is storage
at 0° to 4°C in the dark. This technique retards biodegradation
15
14-
13
12
11
10
AIRBORNE
TEUPBUTURE
100
0 5 1015202530354045
O
o
£
¥
£
Q.
15
14
131
FEDERAL EXPRESS
10
\
lM
so
0)
2
« *
20 .0)
•5 0 51015202530354045
15
14-
a-
12
11
UPS
10
100
80
SO
40
20
•5 0 5 10 15 20 25 30 35 40 45
Elapsed Time (hr)
Figure 6. Temperature and pressure fluctuations recorded in
the cargo hold of various air carriers. Recording
device was shipped from Las Vegas, NV, to Pearl
River, NY, and returned.
19
-------
processes mediated by soil microorganisms. Some microorgan-
isms, however, such as fungi, are biologically active even at
4°C. Wolf et ai. (1989) investigated several methods (i.e.,
chemical and irradiation) for sterilizing soil and concluded that
mercuric chloride is one of the most effective preservatives that
causes minimal changes to the chemical and physical proper-
ties of the soil. Stuart et al.(1990) utilized mercuric chloride as an
antimicrobial preservative to stabilize ground-water samples
contaminated with gasoline. Other researchers (U.S. EPA
1991 a) have used mercuric chloride to retard biodegradation of
VOCs in soil samples. The soils were spiked with 150 ng/kg of
Target Compound List (TCL) VOCs and were preserved with 2.5
mg of mercuric chloride per 5 g of soil. The results indicated that
the amount of mercuric chloride needed to reduce biodegrada-
tion was directly related to the soil's organic carbon content. In
addition, the levels of mercuric chloride added to samples did
not interfere with sample handling or analysis. Currently, re-
search is underway to quantitate the required mercuric chloride
concentration as a function of soil organic content.
The loss of VOCs through volatilization is reduced by optimizing
sample handling procedures. When samples require laboratory
pretreatment, severe losses of VOCs (up to 100%) have been
observed. In order to minimize volatilization losses, several
preservatives have been examined (U.S. EPA 1991 a), including
solid adsorbents, anhydrous salts, and water/methanol extrac-
tion mixtures. The most efficient preservatives for reducing
volatilization of VOCs from soils have been two solid
adsorbents, Molecular Sieve - 5A™ (aluminum silicate desic-
cant) and Florasil™ (magnesium silicate desiccant). The addi-
tion of 0.2 mg per 5 g of soil greatly increased the recovery of
VOCs from spiked samples. The mechanism is believed to
involve the displacement of water from adsorption sites on the
soil particle and binding of VOCs to these freed sites. Currently,
research is in progress with soils obtained from actual contami-
nated sites.
LABORATORY PROCEDURES
Sample Storage
Most regulatory procedures specify storage of samples for VOA
at 4°C in the dark. Sample coolers should be opened under
chain-of-custody conditions, and the temperature inside the
cooler should be verified and noted. Samples should be trans-
ferred to controlled-temperature (4°C) refrigerators until analy-
sis. In many cases, insufficient cooling is provided during
transport. In these cases, data quality may be compromised.
Sample Preparation
The two most commonly used methods that satisfy regulatory
requirements for the analysis of soil samples for VOCs are direct
purge and trap and methanol extraction. Each procedure has
benefits and limitations with respect to sample preparation prior
to VOC analysis of soils.
The modified purge-and-trap procedure has the following char-
acteristics:
• Homogenization of contents of wide-mouth jar will cause
significant VOC losses. The collection of a 5-g aliquot in the
field and placement into a tared vial sealed with a modified
purge-and-trap cap is recommended.
• Surrogate addition should be made to the soil in the field, if
possible.
• May be more susceptible to short-range spatial variability.
• Samples should be brought to ambient temperature before
purging.
• May be more suitable for low-level samples.
The methanol-immersion procedure has the following charac-
teristics:
• The key is to minimize the time samples are exposed to the
atmosphere prior to immersion into methanol.
• Minimum detection limits can be raised by a factor of 10 to 20.
• The best option for sample archival because VOCs are highly
soluble in methanol.
• Large-mass samples can be extracted in the field in a 1:1 ratio
and the methanol extract shipped to the laboratory for
analysis.
• Can collect composite samples.
The analytical methods that can be used for the analysis of soils
for VOCs are summarized in Table 12. An analytical method
should be selected that is compatible with the recommended
sample collection and containerizing procedure discussed ear-
lier.
CONCLUSIONS AND RECOMMENDATIONS
Current research on sampling soils for VOC analyses answers
many of the questions asked by RPMs and OSCs who conduct
' site characterization and restoration.
1. There is no specific method or process that can be recom-
mended for sampling soils for VOA. A wide variety of
sampling devices are currently used for collecting soil
samples for VOA. Sampling device selection is site-specific,
and no single device can be recommended for use at all
sites. Several different samplers, which cover a broad
range of sampling conditions and circumstances, are rec-
ommended for obtaining representative samples for VOC
analysis (Table 7). Procedures may vary for different VOCs.
Experiments have shown that a procedure that collects an
undisturbed, intact sample with a device that allows direct
transfer to a sample container (e.g., split-spoon, Shelby
tube, or zero-contamination sampler) is superior to a more
disruptive procedure that uses a crude bulk sampler (e.g.,
shovel, trowel, scoop, or spade) for maintaining the integrity
of VOCs in a soil sample. Large-diameter tube-type sam-
pling devices are recommended for collection of near-
surface samples. The same types of devices can be used
in conjunction with hollow-stem augers for collecting sub-
surface samples.
2. Transfer of the sample from the sampling device to the
container is a critical step in the process. Losses of as much
as 80% have been observed during this step. The faster the
soil can be removed from the sampling device and
20
-------
Sample
Method Size
Extraction/analysis (g)
5030/8240 5
/8010
/8015
/8020
78030
/8260
5380/8240 5-100
/8010
/8015
/8020
/8030
/8260
5031 / 8240 5
/8010
/8015
/8020
/8030
/8260
3810/8240 10
/8010
/8015
/8020
/8030
/8260
3820 10
624 5
* U.S. EPA l?9§b
6 U.S. EPA, 19B2
TABLE
Sample
Preparation
Procedure
Purge and trap
Methanol extraction
- • i
Field purge
Heatto90°C
in water bath
and analyze
headspace
Hexadecane
extraction
followed by
GC/FID
Purge and trap
12. METHODS FOR VOC ANALYSIS OF SOIL
Data
Sensitivity Quality
(jog/kg) Objective Program
5-10 Litigation RCRA'
500-1000 Litigation RCRA
5-10 Semi- RCRA
quantitative
1000 Screening RCRA
for purgeable
organics
500-1000 Screening RCRA
prior to GC
orGC/MS
analysis
5-10 Litigation CLP"
Comments
Sample transfer to
purge and trap is
critical.
Sensitivity loss but
sample transfer
facilitated.
Sample can only be
analyzed once,
transfer and shipping
facilitated.
Can be performed
in the field.
FID responses vary
with type of VOC.
Similar to method
5030/8240 in
RCRASW-846.
21
-------
transferred into an airtight sample container, the smaller
the VOC loss. Liners make the removal and subsampling
of soil from the collection device more efficient
3. The best method for transferring a sample from a large-
diameter coring device (or exposed test pit) into a sample
container is by collecting the appropriate size aliquot (for
laboratory analysis) with a small-diameter, hand-held corer
and extruding the subsample into a 40-mL VOA vial, then
sealing the vial with a modified purge-and-trap cap. Alter-
natively, contents of the large-diameter coring device can
be sectioned and immersed in methanol.
4. Small-diameter, hand-held corers can be used for col-
lecting samples from a freshly exposed face of a trench or
test pit, or for obtaining a subsample from a large-diameter
coring device. The use of a small-diameter, hand-held
corer is recommended for obtaining subsamples from
liner-held soil. Collection of a sample of the appropriate
size for a particular analytical procedure is optimal. The
required size of aliquot can be extruded into a 40-mL VOA
vial and sealed with a modified purge-and-trap cap. The
possibility, exists of compositing several small-diameter
core samples by immersing them in a single jar containing
methanol.
5. Sample containers vary in terms of air-tightness. Data are
available to indicate that there is a decrease in pressure
and an increase in temperature in the cargo holds of certain
air carriers. This is the worst possible set of conditions for
maintaining VOCs in containerized soil samples. Intact
seals on storage containers and adequate cooling is thus
critical for maintaining VOCs in soil samples. Shipping and
holding-time studies have shown that vials and jars may be
equally suited for containing VOCs in soil samples, the
laboratory pretreatment step needed to obtain an aliquot
from a jar-held sample causes significant losses of VOCs.
Commercially available shipping packages with built-in
cooling materials (e.g., Freeze Gel Packs® or Blue Ice®)
are available. Whenever possible, an integrated sampling
approach should be employed to obtain the most represen-
tative samples possible. Soil-gas surveying coupled with
on-site soil sampling and analyses followed by the Re-
source Conservation and Recovery Act (RCRA) or CLP
laboratory analyses may provide valuable information on
the partitioning of VOCs at a site.
6. The current preservation technique for soil samples is
storage at 4°C in the dark. Biological activity may continue
at this temperature. The addition of mercuric chloride to the
soil may reduce biodegradation of VOCs. The amount of
mercuric chloride to be added, however, is a function of the
organic carbon content in the soil. The most promising
preservatives for reducing losses of VOCs through volatil-
ization are solid adsorbents such as Molecular Sieve - 5A™
and Florasil™.
22
-------
REFERENCES CITED
49 CFR, 1982! Code of Federal Regulations, 49, Parts 100 to
177, October 1, 1982, pp. 231.
Acker, W. L1974. Basic Procedures for Soil Sampling and Core
Drilling. Acker Drill Co., Inc., Scranton, PA, 246 pp.
Ameth, J.-D., G. Milde, H. Kemdorff, and R. Schleyer. 1988.
Waste deposit influences on groundwater quality as a tool for
waste type and site selection for final storage quality. In:
P. Baccini (Ed.) The Landfill: Reactor and Rnal Storage, Swiss
Workshop on Land Disposal of Solid Wastes, Gerzensee,
March, 14-17, pp. 399-415.
Barcelona, M. J. 1989. Overview of the Sampling Process. In:
Keith, L. H. (Ed.), Principles of Environmental Sampling, Ameri-
can Chemical Society, Washington, D.C., pp. 3-23.
Barth, D. S., B. J. Mason, T. H. Starks, and K. W. Brown. 1989.
Soil Sampling Quality Assurance User's Guide (2nd edition),
EPA 600/8-89/046, U.S. EPA, EMSL-LV, Las Vegas, NV,
March, 225 pp.
Boucher, F. R. and G. F. Lee. 1972. Adsorption of Lindane and
Dieldrin pesticides on unconsolidated aquifer sands. Env. Sci.
Tech. 6:538-543.
Bouwer, E. J. 1984. Biotransformatioh of organic
micropollutants in the subsurface. In: Petroleum Hydrocarbons
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