Environmental Engineering Reference
In-Depth Information
7.9.3.2 Excavation Method
The excavation method is most appropriate for sampling topsoil. Leaf litter is
removed from the soil surface. The top of the excavation hole is leveled by removing
soil with a trowel or knife and checking with a carpenter's level. Soil is removed with
a trowel. The hole is lined with a single piece of Saran wrap or similar waterproof
material. The hole is then filled with water from a graduated container. The
excavated volume is determined by subtracting the final water volume in the
container from the initial water volume. Another approach, which does not require
Saran wrap, is to fill the hole with dried sand of a known bulk density. Sand is poured
into the hole from a container with a known weight of sand. After filling the hole, the
container of sand is weighed again. The volume (cm
3
) of the soil cavity is calculated
as “difference in sand weight (g)/sand bulk density (g/cm
3
)”.
7.9.3.3 Can Core Method
With a core method, a cylindrical metal sampler with a known volume is used to
extract soil samples for bulk density determinations. Core samplers may be a hydrau-
lically driven probe mounted on a vehicle (e.g., Giddings Probe), a double-cylinder,
hammer-driven core sampler, or a simple metal can open at both ends. Use of the first
two types of samplers is discussed by Blake and Hartge (
1986
). In this section, we
discuss use of a small can. The can dimensions are not critical (except in calculations)
but the diameter of the can should exceed the height of the can. Horizons should be
sampled individually as they can vary significantly in bulk density. Tall cans make it
more difficult to sample individual soil horizons. A representative size is 6.5-cm
diameter and a 4.5-cm height. Three samples are collected from each horizon starting
with the surface horizon and working down. At the sampling point, leaf litter is
removed from the soil surface which is then smoothed to create a flat horizontal
surface. The can is placed end down onto the soil surface and pressed into the soil by
hand. This step can be facilitated by laying a board across the top of the can and
tapping it lightly with a rubber mallet or hammer. However, care should be taken to
avoid compacting the core. For horizons thinner than the height of the can, care must
be taken to preclude simultaneously sampling multiple horizons. Dig out the inserted
can plus a little of the surrounding soil and cut off the excess soil so the soil sample is
flush with the top of the can. Empty the contents of the can into a sample bag. In each
case, the thickness of the sampled horizon and the thickness of the core samplemust be
recorded. To sample subsurface horizons, dig down to the top of the target horizon and
repeat the steps presented above.
7.9.3.4 Clod Method
The clod method is the most appropriate method for soil samples deep in the profile
where it is difficult to determine volume
in situ
. In this method, clods are coated
