USDA Forest Service Res. Note RMRS-RN-9. 2001 1

Abstract—The fabrication and use of three tools to assist

in the manual installation of shallow ground water observation wells are described. These tools are easily fabricated at a local machine shop. A method for calibrating

pressure transducers is also described.

Keywords: instrumentation, pressure tranducers, observation wells, piezometers

Ground water elevations are typically determined

from observation wells or piezometric wells. In streamside areas, the subsurface free water elevation is often

monitored in studies of riparian plant communities,

nutrient transport, and seasonal waterflow direction.

While professional well drilling is limited by accessibility and cost, it is possible to manually install shallow

wells along riparian and floodplain corridors. In the

past, we have attempted to dig shallow wells with a soil

auger. However, soil augers are easily stopped by rocks

or gravel, and the walls of the hole tend to collapse before

the casing can be installed. Digging pits and backfilling

around the casing is another method, but it causes a large

amount of soil disturbance. The simple tools described

here dig holes up to 10 feet deep with minimal soil

disturbance, eliminate the problem of collapsing

walls, and can often break through or work around

cobbles and gravel. These tools are easily fabricated

at a local machine shop. In addition, a tool for calibrating

pressure transducers for shallow wells and piezometers is

described.

United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

Research Note

RMRS-RN-9

January 2001

Guide for Fabricating and

Installing Shallow Ground Water

Observation Wells

Carolyn C. Bohn

Carolyn C. Bohn is a Hydrologist on the Aquatics/Watershed

Research Work Unit, Rocky Mountain Research Station, Boise, ID.

She received a B.A. degree in zoology from the University of Washington, and an M.S. degree in rangeland watershed management

from Oregon State University. She joined the former Watershed

Research Work Unit of the Intermountain Research Station in 1988,

supporting studies of logging effects on sediment production, riverbed recovery from sedimentation, and riparian ground water.

Description of Tools _____________

Well-Drilling Tools

The tool used to initially make the hole in the

ground for the well casing has three components: an

outer sleeve, an inner core, and a pounder. The core is

a solid iron rod that fits inside the iron pipe called the

sleeve and is pointed on the bottom. When the core is

in place, the point extends beyond the end of the

sleeve. The lower end of the sleeve is beveled to match

the angle of the core’s pointed end so that the end of

the core-sleeve assembly forms one continuous point.

The opposite end of the core is equipped with a pounding cap that prevents the core from falling through the

sleeve. The cap provides a solid surface by which the

core and sleeve assembly may be simultaneously

driven into the ground. With the core inside the

sleeve, the pointed end of the assembly is positioned

at the site of the well. The core-sleeve assembly is

driven into the ground with a modified hand-held

fencepost pounder. Typically, commercial fencepost

pounders are not strong enough to withstand pounding the heavy core-sleeve assembly through gravel

and cobbles, so instructions for fabricating a heavily

reinforced pounder are provided. For maximum depth,

use the pounder until it touches the ground. Then

drive the assembly further with a sledge hammer or

turn the pounder upside down and pound with the

closed end of the pounder. Once the assembly has been

driven its full length (approximately 5 feet deep), the

core can be lifted out and replaced with PVC pipe for

well casing. After the casing is placed, the sleeve can

be removed by slipping a rebar handle through two

holes in the outer sleeve and pulling or jacking the

sleeve out of the ground. The casing remains in place

at the full depth of the hole. Ideally, the holes are

backfilled with sand around the casings, although

native material is also acceptable. The casing/groundsurface interface should be sealed with bentonite
2 USDA Forest Service Res. Note RMRS-RN-9. 2001

(available from well-drilling suppliers). It is easiest to

pound the assembly into wet soils, when the resistance is minimal. In saturated soils, installation time

may be as little as 15 minutes per well.

The length of the core-sleeve assembly limits the

depth of the hole to approximately 5 feet. Another tool

can be fabricated to drive down an additional 5 feet.

This tool consists of an 8 to 10 foot length of iron pipe

that has a machined metal point attached to one end,

along with holes and screen at the same end, which

allow the iron pipe to act as well casing. Unlike the

sleeve and core that are removed and reused, the black

pipe and steel point are driven into the ground and left

in place as well casing. To install this iron well casing,

the core-sleeve assembly that was first described is

driven into the ground to its full length. The core is then

removed and replaced with the iron pipe, metal point

first. The same pounder can be used to pound the iron

pipe the rest of its length. Then the pounder and sleeve

are removed, and the pipe is left in place as well casing.

Using the core-sleeve assembly to create the first 5 feet

of the hole allows use of a 10 foot pipe without pounding

from a ladder, and the sleeve reduces the frictional

drag on the pipe while it is being pounded down the last

5 feet. Any space around the pipe should be backfilled

with sand or native material, and the casing/ground

interface should be sealed with bentonite.

Some problems have been encountered with this tool.

Soil may plug the drilled holes in the pipe while it isdriven

into the ground, which can slow water transfer and,

therefore, the response of the water level inside the pipe.

Also, the iron pipe has rusted in some locations.

Pressure Transducer Calibration Device

Although most pressure transducers come with product information that can be used to convert the millivolt readings to depth of water, accurate conversions

require site-specific calibration through the full length

of wire, wire splices, and data logger that will handle

the signal. More importantly, transducers may drift

over time, particularly if vapor or moisture condenses

in the vent tubes. Therefore, it is good practice to

calibrate pressure transducers before installation, and

periodically during use if signs of drift are detected or

if changes in the hardware setup are made. This device

simply provides a tube to house a transducer temporarily above ground for calibration, and in which the

water level may be varied.

Fabrication of the

Well-Drilling Tools _______________

Materials for the sleeve, core, and pounder

5 feet of black iron pipe (2 inch od)

5 feet of black iron rod (1.5 inch diameter)

3 inch diameter disk (3⁄4 inch iron)

2 feet of 3⁄4 inch diameter rebar, or similar metal rod

7 feet 8 inches of black iron pipe (4 inch od, 1⁄8 inch

walls)

3-3⁄4 inch diameter disk (1 inch iron)

Two 2-foot iron rods (3⁄4 inch diameter)

The sleeve and core (fig. 1) will accommodate a 1 inch

PVC pipe (1-5⁄16 inch od) and a 1 inch diameter sensor.

Adjust the dimensions accordingly for larger sensors.

The prototype inner core was made by machining one

end of the 1.5 inch iron rod to a point using a 45 degree

angle. Although it was not tested, a 30 degree angle

could also be used, and might be easier to pound in. The

3 inch diameter disk was then securely welded the to

the other end for the pounding cap. This rod is the inner

core.

Bevel one end of the 2 inch black pipe to match the

slope of the point of the core. Beginning the bevel

about 0.5 inch above the pipe end easily approximates

the 45 degree slope. Drill a 1 inch hole straight through

both walls of the pipe about 2 inches from the unbeveled

end. Slide the rebar through these holes after installing the casing to use as a handle for pulling the pipe out

Figure 1—Sleeve and core.

3.0 in

64.0 in 66.25 in

1.5 in

core

1.5 in for

45 angle o

0.75 in

2.0 in

Hollow sleeve

od = 2.0 in

id = 1.562 in
USDA Forest Service Res. Note RMRS-RN-9. 2001 3

of the ground. The pipe can also be jacked out of the soil

by placing a handyman jack under this handle.

The 4 inch pipe will form the body of the pounder

(fig. 2). The 3⁄4 inch rods are bent into handles that are

welded to the body with 2 inch long welds, and the disk

of 1 inch iron is welded inside one end of the body.

Triangles of iron can be welded beneath the handles for

additional support. This design evolved from less heavily

reinforced prototypes that did not withstand the repeated pounding.

Materials for the PVC well casings

5 feet of 1 inch thin wall PVC pipe

plastic screening

#6 cork or rubber stopper

PVC primer and glue

The 5 foot holes made by the core-sleeve assembly are

cased with 1 inch thin wall PVC. Plug the bottom of the

PVC with a #6 rubber stopper or cork prior to installation to keep soil from pushing up into the well. The

lower 8 to 12 inches of the pipe are perforated for water

entry, and then screened against larger soil particles.

Perforate the pipe either with drilled holes (the size of

the holes is not critical; 1⁄4 inch holes work well) or with

slits cut with a hacksaw. The plastic window screening available at most hardware stores works well

because it can be glued tightly to the outside of the

perforated part of the pipe with PVC glue. Apply the

PVC primer and glue to the pipe where the top, bottom,

and seam of the screen will be, followed by tightly

wrapped screen. More glue can be applied to the seam of

the screen if necessary to prevent loose edges. The glue

dries quickly. An alternative to homemade perforations

and screening may be commercial threaded well screen

and threaded PVC (Miner and Simon 1997). The top

opening may be closed with a cork or a #6 rubber

stopper, or fit with a PVC threaded coupler and plug.

Slip-on caps are also available, but very difficult to

remove after they have been buried under snow. A

small vent hole should be drilled just below the bottom

of the cork or plug to prevent pressure buildup from

trapped air.

Materials for the 10 foot pipe and well point

10 feet of 1 inch black iron pipe

steel point, machined as in figure 3

tension pins

epoxy glue

plastic screening

4 in

1.7 ft

1.0 ft

Optional

reinforcement

Figure 2—Pounder.

Enlargement of point

~1.0 in

(to fit inside 1 inch pipe)

stem

1.0 in

1.38 in

approx. 2.0 in

10.0 ft

Figure 3—Point for 10 foot pipe (not drawn to scale).
4 USDA Forest Service Res. Note RMRS-RN-9. 2001

The point can be fabricated at a local machine shop;

the cost will probably depend on the quantity ordered.

The stem of the point fits inside the 1 inch pipe and can

be held in place with tension pins and/or quick setting

epoxy. Alternatively, the stem of the point and the

inside of the pipe can be threaded to fit each other.

Before the point is installed, perforate the lower end of

the pipe with drilled holes for water entry. (The length

of pipe that is perforated will depend on the study

objectives. Eight inches is a reasonable length for most

observation wells.) The drilling will leave burrs on the

inside of the pipe, which can be smoothed down with a

file. The screen for the metal casing must be rolled and

slipped inside the pipe before the point is installed.

Close the top of the casing with a #5.5 rubber stopper

after installation is complete. Drill a vent hole just

below the bottom of the stopper to prevent pressure

buildup from trapped air.

Sensors _______________________

Once a well casing is in place, the well can be

instrumented with a number of different types of sensors to detect the free water surface in the well. The

most common sensors are pressure transducers for automatic data logging, well level sensors for individual,

instantaneous measurements, and ground cork with a

Figure 4—Calibration tube for pressure transducers (not drawn to scale).

stick for the single highest stage. While pressure transducers are the most versatile, they are expensive and

require periodic calibration and other handling for

optimal results (Hvorslev 1951).

Materials for calibration tube

5 feet of 3 inch diameter plexiglass tube (or other

clear plastic tube)

4 inch square or circle of plexiglass

circle bubble level

6 feet of slotted angle iron, 14 gauge (or what is

available at local hardware store)

3⁄4 inch pipe hanger strap

3⁄4 inch plywood triangle, approximately 26 inches across x

15 inches high

six 1⁄4 x 3⁄4 inch bolts with 12 nuts

eight 5⁄16 x 3⁄4 inch lag screws

three 3⁄8 x 2-1⁄2 inch carriage bolts, with 6 washers, 3

nuts, and 3 wing bolts

Duco Cement

tape measure

small spring clamp

The dimensions of the parts used for the calibration

tube assembly are not critical, although it is best if the

height of the tube approximates the range of operation

for the pressure transducer. The prototype (fig. 4) used

a 3 inch diameter tube because that was the best price
USDA Forest Service Res. Note RMRS-RN-9. 2001 5

available locally in a 5 foot length. Seal the bottom of

the tube with the flat square or circle of plexiglass with

a generous application of the Duco Cement. Do not trim

the excess because it helps stabilize the tube. Cut the

slotted angle iron into two 6 inch and two 30 inch

pieces. The rough ends can be filed smooth or dipped in

liquid plastic tool handle dip, if desired. Center the

plexiglass tube on the base. Cut two 13 inch lengths of

pipe hanger. Place them on opposite sides of the tube

about 2-1⁄2 feet above the base and pinch them together

with 2 bolts and nuts where they extend past the tubes

so that they encircle the tube. Stand the longer lengths

of slotted angle iron on end on the base so that one side

of one piece lines up with one end of the pipe hanger,

and the other piece lines up with the other end. Adjust

the pipe hangers and attach the angle irons and pipe

hangers with nuts and bolts. Lay the two remaining

angle irons on the base, just outside of the vertical long

pieces with the upright sections toward the tube, and

perpendicular to the 26 inch side of the base. Line up

holes in the short angle irons with holes in the vertical, longer angle irons, and attach with bolts and nuts.

Mount the short angle irons to the base with lag

screws. Because it is important that the assembly be

level for proper calibration, the carriage bolts are used

as leveling feet at each corner of the triangular base.

Drill slightly oversized holes in the base for the bolts,

thread the wing nuts onto the bolts upside down, add

a washer to each bolt, and slide the bolts through the

holes from the underside of the base. Fit the remaining

washers and nuts onto the ends of the bolts, leaving

the nuts loose. Glue the circle bubble level onto the base

near the tube. Level the assembly by threading the

wing nuts up or down at each corner. The tape measure

and spring clamp will be used during calibration.

Calibrating Pressure Transducers

Suspend the pressure transducer inside the tube, at

the bottom, by clipping its cord to the top of the tube

with a small spring clamp (a battery clamp works well).

The transducer must hang straight for accurate measurement. This was accomplished by taping three short

pieces of 1⁄2 inch PVC pipe to the pressure transducers

with electrical tape, and worked well. Other, less clumsy

setups are certainly available to the imaginative. Once

the transducer is set in the tube, hook the end of the

tape measure to the top edge of the tube and measure

along the outside of the tube to the exact level of the

sensing point on the transducer. Then add small increments of water: fill to the sensing point on the transducer, and continue filling incrementally until the tube

is filled. Carefully measure the water level height of

each increment and record it along with the voltage

across the transducer at the data logger for each increment. The difference between the level of the transducer and each water level is the head of water. Regress

the voltages with the water heads to calculate the

relationship between the two. (You can also measure

from the bottom up to the transducer and water levels,

but it is more difficult to keep the tape straight.)

Other Sensor Problems

Regardless of the type of sensor you chose, you will

need to know the elevation of the top of the pipe to

calculate the elevation of the water surface from its

stage (Hvorslev 1951). You can then measure down to

the water surface with a well level sensor, or other

devices, to calculate the elevation of the water surface

and the sensor. Pressure transducers must be vented

to ambient air pressure through one or two small tubes

to function properly. These tubes are usually bundled

with the electrical wires, but must terminate in a dry

environment so vapor does not accumulate in the tube.

Desiccant holders, or “dry boxes” are available commercially, or it is also possible to fabricate a satisfactory dry box if you can change desiccant regularly. The

“dry box” container must be able to hold desiccant and

accept the end of the vent tube while limiting moisture

transfer and allowing the air pressure to equilibrate

with the ambient pressure. For example, fill a baby

bottle with desiccant and push the vent tube into the

desiccant through the nipple (clip the end of the nipple

if necessary). Indicator desiccant is highly recommended. Even though the electrical wires may reach

some distance, keep the vent tubes as short as is

practical because the moisture cannot diffuse out efficiently over several yards.

References _____________________

Hvorslev, M. Juul. 1951. Time lag and soil permeability in groundwater observations. Bull. 36. Vicksburg, MS: Waterways Experiment Station, Corps of Engineers. 50 p.

Miner, James J.; Simon, Scott D. 1997. A simplified soil-zone monitoring well. Restoration and Management Notes. 15(2): 156-160.
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ROCKY MOUNTAIN RESEARCH STATION

RMRS

The Rocky Mountain Research Station develops scientific information and technology to improve management, protection, and use of

the forests and rangelands. Research is designed to meet the needs

of National Forest managers, Federal and State agencies, public and

private organizations, academic institutions, industry, and individuals.

Studies accelerate solutions to problems involving ecosystems,

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and diseases. Studies are conducted cooperatively, and applications

may be found worldwide.

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