Introduction: Hi, this video demonstrates methods for measuring
water levels in wells using a graduated steel tape.
This method is commonly accurate to one one-hundredth of a foot.
It is most accurate when the depth to water is less than 200 feet below the land surface.
Materials: The materials needed include:
Keys to access the well, A Pipe Wrench, Steel Tape, Blue carpenter’s chalk, A PDA for
electronically recording measurements, A cloth, Soap and water for cleaning the tape, A Water
Level Measurement Field Form and writing utensil Demonstration:
Step 1) Determine you are at the correct well from the well description and locate the documented
measuring points and land surface datum from the well, photo or diagram.
If using electronic field data, pull up the file for the well, and also enter the serial
number of the tape used for measurement.
Step 2) Open the well with a pipe wrench.
Step 3) Estimate the depth to water in the well from previous measurements or from nearby
wells.
This is used to estimate the hold point on the tape.
Step 4) Apply chalk on the lower few feet of the tape by pulling the tape across a piece
of blue carpenter’s chalk.
This helps to identify the part of the tape that will be submerged.
Step 5) Lower the weight and tape into the well until the lower end of the tape with
chalk is submerged.
Lower the weight and tape slowly to prevent splashing.
Lower enough of the tape so that the hold point is at the top of the well.
Record the graduation value in the hold column of the water-level measurement field form.
Step 6) Quickly bring the tape to the surface before a wetted mark on the chalk can dry
or become difficult to read.
Record the length of the wetted chalk, which is called the “cut”, in the Cut row of
the water-level measurement field form.
Step 7) To get the depth below the measuring point, subtract the cut value from the hold
value.
Record this value in the water-level measurement field form.
Step 8) To get the water level below the land surface datum, first record the measuring
point correction length on the MP correction row of the field form.
The MP correction is positive if the measuring point is above the land surface, and negative
if it is below the land surface.
Subtract the MP correction from the water level below measuring point value to get the
depth to water below the land surface datum.
Step 9) Repeat the measurement, but use a different hold value.
If the repeated measurement is different by up to 0.02 foot, continue to make measurements
until the reason for a lack of agreement is determined or the results are considered to
be reliable.
Step 10) Complete the “final measurement for GWSI” portion of the field form.
Step 11) Disinfect and rinse the part of the tape that was submerged in order to reduce
the possibility of contamination of other wells by the tape.
Step 12) Close the well with a pipe wrench, making sure the lid is securely fastened.
Note * The steel tape should first be calibrated against another reference tape.
The reference tape should be kept in the office and used only for calibrating other tapes.
Be sure to maintain the tape in good working condition by periodically checking the tape
for rust, breaks, kinks, and possible stretching due to the suspended weight of the tape and
the weight at the end of the tape.
Limitations: Keep in mind the following limitations of
this method.
Oil, ice, or other debris may interfere with a water-level measurement.
Corrections to the measurements are necessary if the well casing is angled.
When measuring water levels that are greater than 500 feet, the tape may expand and stretch,
which may require some correction, or adjustment, to the measurement.
Advantages This approach has several advantages.
The steel tape is often considered to be the most accurate method for measuring water levels
in non-flowing wells, the method is fairly simple.
Wells with small entry ports may be accessed by the small tape diameter.
The tape may also have little interference with pump wiring.
Disadvantages However, this technique has several disadvantages.
The results may be unreliable if water is dripping into the well or condensing on the
well casing.
It is not recommended for wells that are currently being pumped.
The measurements may be time consuming and difficult if the water level is not initially
known.
The wetted chalk mark may dry before the tape is retrieved from the well under hot, dry
conditions, especially in deep wells.