and analysis procedure must meet the project ob-
ers are used, subsamples can be removed through
jectives). All of the issues concerning how to
the open ends, or if constructed of a plastic mate-
handle and prepare samples must be resolved be-
rial, they can be cut at any point to allow access.
fore the sampling activity. The following sections
Subsurface materials taken for VOC characteriza-
discuss in greater detail the various steps and some
tion should be brought to the surface as quickly
of the criteria for selecting a method of subsample
as possible and remain undisturbed until they are
preparation and on-site analysis. Subsurface bulk
subsampled. This subsampling operation should
sample collection is discussed prior to discrete
be performed without delay (within several min-
sampling activities, since this is the logical se-
utes) to limit losses of VOCs through the open ends
quence of events when characterizing the vadose
of the coring tube. Temporarily capping the ends
zone. The procedures presented for the collection
of the core barrel liner is not recommended, since
of subsurface bulk samples and for obtaining and
sheets of Teflon or aluminum foil are not adequate
processing discrete samples are consistent with the
VOC vapor barriers (Hewitt and Lukash 1996).
latest revision of the ASTM D4547 (American So-
The number of bulk samples that can be brought
ciety for Testing and Materials 1998), and with the
to the surface in 8-hour period ranges anywhere
EPA SW846 Methods 5021 and 5035 (U.S. EPA
from 10 to 100, depending on the sampling depth,
1997a, 1997c).
sampling intervals, type of geological formation,
and the equipment used.
Subsurface bulk soil sample collection
A study comparing subsurface sampling equip-
There are at least two steps involved in perform-
ment, which meets the guidelines provided here
ing subsurface soil sampling: the retrieval of a bulk
for subsampling and rapid on-site analysis (within
sample from the depth of interest, and the subse-
48 hr), was recently completed by the U.S. EPA's
quent transfer of subsamples to volatile organic
Environmental Technology Verification Program
analysis (VOA) vials. To obtain subsurface bulk
(U.S. EPA 1998a, b, c, and d). The main purpose of
samples, usually a hollow tube designed to ob-
this effort was to compare different subsurface
tain an intact cylindrical core of material is used.
sampling technologies. The technologies com-
Coring tubes typically range in size from 1.5 to 4
pared were (1) a conventional hollow stem augur-
in. (3.8 to 10 cm) in diameter, and one to several
ing and split spoon sampler, (2) Large-Bore Soil
feet (meters) in length. Coring tubes are filled by
Sampler (Geoprobe Systems), (3) JMC Environ-
being hydraulically pushed (i.e., geoprobe and
mentalist's Subsurface Probe (Clements Associ-
penetrometer), hammered, or vibrated in a previ-
ates, Inc.), (4) Dual Tube Liner Sampler (Art's
ously undisturbed formation. For sampling activi-
Manufacturing & Supply, Inc.), and (5) the
ties within the first 6 m, manually operated cor-
Simulprobe sampler. The following criteria were
ing devices can often be used, while equipment
used to compare these bulk soil sampling systems:
mounted in a pickup truck (small vehicle) can of-
sample recovery (i.e., volume obtained), contami-
ten reach up to 15 m in many geological forma-
nant concentration, sample integrity (e.g., cross-
tions. When sampling at depths below 15 m, of-
contamination between sampling locations), reli-
ten it is necessary to use larger and less mobile
ability, rate of sample collection, and cost.
equipment, for instance, a drilling rig equipped
Two sites were selected for this study, one be-
for hollow stem augering or a 20-ton or larger cone
ing characterized as having clay soils and the other
penetrometer truck.
as a sandy soil. At both sites, cis-1,2-dichloro-
Two of the more commonly used coring devices
ethene, trichloroethene, and tetrachloroethene
for subsurface sample collection and retrieval are
were present, while 1,1,1-trichloroethane was
the split-spoon corer and core barrel liners. Once
present at only one of the sites. Samples were col-
filled and returned to the surface, the ends of the
lected from discrete locations in the subsurface
split-spoon corer and one side of the core barrel
between a depth of 1 to 12 m that had been previ-
are removed, so that one-half of the surface area
ously identified as having high or low levels of
of the bulk sample can be exposed for
contamination present (i.e., greater than or less
subsampling. The split-spoon corer and many
than 0.2 mg/kg). Samples were obtained at seven
randomly selected positions within a 3.2- 3.2-m
other types of hollow coring devices can also be
equipped with a core barrel liner. Core barrel lin-
specified grid, at several different locations on each
ers fit snugly within a corer and come in a variety
site, using each of five subsurface samplers listed
of lengths and materials (stainless steel, brass,
above and the subsampling procedures cited be-
Teflon, rigid plastics, etc.). When core barrel lin-
low. Table 1 shows the average sampling rate for
2
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