Conducting Subsurface Environmental Investigations in Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 140

Handle

Stem

Bucket

Auger

FIGURE 4.9
Hand auger. (Photo by Daniel T. Rogers.)

method may be smeared from the sample collection method and (2) the sample probe must
be reinserted into the borehole after each sample is collected, and this action may lead to
cross-contamination or result in a gap in the depositional history of the area. Additional
care and scrutiny must be undertaken when characterizing subsurface geologic features
from samples collected using these methods.
Using a Geoprobe for soil sampling is the preferred technology in urbanized areas.
A Geoprobe is typically faster than other methods, can penetrate hard surfaces such as
pavement and concrete, and can be used inside buildings and other locations with lim-
ited access and space. Some Geoprobe drill rigs are capable of directional drilling, pro-
viding advantages in some unique situations. Soil samples collected using a Geoprobe
are typically 5 cm (2 in.) in diameter and either 2 or 4 ft long. The sample is collected
inside a plastic sleeve inserted into the bottom of a metal rod hydraulically pushed and
vibrated into the ground. There are drawbacks to the use of Geoprobe devices however.
First, great care must be taken not to “push” contaminated soil downward to lower lev-
els resulting in misidentification of the vertical extent of contamination. For this reason,
Geoprobe devices are not allowed in California when conducting remedial investiga-
tions. Second, the usefulness of a Geoprobe is limited to the vertical extent of its capabil-
ity, generally to within 6-9 m (20-30 ft). However, under favorable conditions, or using
a specially outfitted Geoprobe, depths of greater than 23 m (75 ft) have been achieved.
Finally, if a soil boring is to be converted to a semi-permanent monitoring well, a hol-
low stem, truck-mounted drill rig would need to be brought onto the site, resulting in
additional costs.
Soil samples collected from a hollow-stem auger drilling rig are typically 5 cm (2 in.)
in diameter and are 61 cm (2 ft) long. The sample is collected inside a plastic sleeve
inserted into a tool called a split-spoon. A split-spoon is a geotechnical soil sampling