Environmental Engineering Reference
In-Depth Information
the assumption for the following field activity describing the installation of a
shallow monitoring well. Items you will need include:
• Polyvinyl chloride (PVC) pipe (a wide range of diameters are available but 5.1-
cm diameter is very common)
• PVC well screen (see Fig.
3.42c
for examples of commercially made screens.
See the section on piezometer installation for making screens from regular pipe)
• Associated couplings and caps and PVC cement
• Bucket auger and associated hardware (8.9-cm (3.5-in.) diameter is common)
• Supply of medium sand (approximately 5-L but amount will vary depending on
the diameter of the augered hole relative to the diameter of the monitoring well)
• Shovel
• Tamping rod (handle of the shovel or unused sections of auger rod can suffice)
• Hand saw
• Sledge hammer
• Tape measure or folding rule
• Water-level measurement device (e.g., chalked-steel tape, electric tape)
• Notebook, hand lens, sediment-sample bags
First, select a location for installation of the water-table monitoring well. The
well should be located so that it is representative of conditions along a specific
reach or area of the wetland. Criteria that are commonly considered when locating a
water-table well include topographic gradient, vegetative cover, aspect, geology
and soil type. Once the location is selected, use a shovel to remove the vegetation
from an approximately 0.25-m
2
area surrounding the intended well site. Note the
vegetative cover and organic soil type and thickness.
Install an appropriate auger head on a section of rod (Fig.
3.42a
) (closed-head for
sand and loosely consolidated sediment, open-head for cohesive sediment) and
begin turning the auger in a clockwise direction until the auger bucket is full.
Remove the bucket from the hole and shake or push the sediment out of the auger
head (Fig.
3.42b
), allowing the sediment to fall onto a clean surface, such as a board
or tarp. Record the depth of the hole with a tape measure. Describe the sediment in
the field notebook. Place a sample from the auger in a sample bag for later lab
analysis of percent organic matter and grain-size distribution. Repeat this process
until you reach the water table or the intended depth. As you auger deeper, you may
need to add one or more rod extensions to the soil-auger assembly. You also may
encounter large rocks that inhibit continued augering. Persistence will sometimes
get you past a rock or rocky layer, but you also may have to abandon the hole and
try again a short distance away.
The water table may not necessarily be obvious if the permeability of the
sediment is small enough that water does not readily flow into the auger hole.
In some cases, squeezing the sediment with your hand can indicate whether the
sediment is saturated or not. If the sample was removed from below the water table,
water will be released from the sediment as you squeeze the sample. In settings
where the sediment is sandy and poorly cohesive, it is likely that saturated sediment
will slump back into the hole as sediment below the water table is removed. The
