Introduction Hi, I’m Jesse Dickinson, a hydrologist with
the US Geological Survey.
We’re here in the San Pedro Basin in Southeastern Arizona, and we’re going to demonstrate
how to measure hydraulic head in an artesian well.
Materials: The materials needed include:
A pipe wrench, A plug for the well, A clear plastic column that can be attached vertically
to the opening of the well , Plumbers tape to ensure a tight fit to the well and to minimize
leaking, A pencil or pen if using a water level field form, or a device for electronic
data entry, A ruler or tape for measuring the height of water in the plastic tube, A
level to ensure that the ruler or tape is perpendicular to the land surface
Instructions: Step 1) Determine you are at the correct well
from the well description and locate the documented measuring point(s) and land surface datum
from well photo or diagram.
Step 2) If necessary, use a pipe wrench or other tool to remove any plugs in order to
gain access to the well.
Step 3) Apply plumbers tape to ensure a tight fit between the well opening and the plastic
pipe to minimize leaking.
Step 4) Connect a length of transparent plastic pipe tightly to the well.
Step 5) Gradually close any other opening to the flowing well.
If pressure is applied suddenly, the well could be permanently damaged by the “water-hammer
effect” by caving of the aquifer material, breakage of the well casing, or damage to
the distribution lines or gauges.
Step 6) Ensure that all flow from the well stops so that a static water-level measurement
can be made.
Step 7) Rest the ruler or measuring tape on the measuring point (MP) and use the level
to check that the ruler or tape is perpendicular to the land surface.
Use the scale to read the height above the measuring point that the water has risen in
the plastic pipe.
Step 8) Record the date and time of the measurement on a Water Level Measurement Field Form or
a digital screen input form.
Because the water level is above the measuring point, this is a negative number.
Step 9) Record the measuring point (MP) correction length on the “MP correction” row of the
field form or select the MP used from the electronic data entry form.
Subtract the MP correction length from the true “water level below measuring point”
value to get the depth to water above the land surface datum as a negative number.
The MP correction is positive if the MP is above the land surface, or negative if it
is below the land surface.
On the field form, record the water level in the “WL below LSD” column.
Step 10) Make a check measurement by performing the previous steps.
Record the check measurement on the field form or electronic data entry form.
If the check measurement differs from the original measurement by greater than 0.1 or
0.2 foot, continue to measure the water height until the reason for a lack of agreement is
determined or the results are found to be reliable.
Complete the “final measurement for GWSI” portion of the paper or digital field form.
Step 11) Gradually remove any plugs to the flowing well.
If pressure is applied or released suddenly, the well could be damaged.
Step 12) Remove the clear plastic pipe from the opening of the well.
Step 13) Attach any other plugs to well openings.
Limitations: Keep in mind the following limitations of
this method.
Low-pressure head measurements are most feasible when the head is less than six feet above
the land surface.
Measurements are commonly accurate to 1/10th of a foot.
All flow from the well should be shut down so that a static water level measurement can
be made.
However, the time required to reach a static pressure after flow discontinues may range
from hours to days.
Since a true static measurement may be impractical, record the time after shutting off the flow
for each measurement.
Advantages: An advantage of a method for low pressure
measurement is that it is generally simpler, faster, safer, and more accurate than a method
for high pressure measurement.
Disadvantages: A disadvantage is that this method may be
impractical for wells with heads greater than 5 to 6ft above the land surface.