Measuring Groundwater with Steel Tape

Video Transcript
Download Video
Right-click and save to download

Detailed Description

This video demonstrates how to measure water levels in wells using a graduated steel tape.

Details

Image Dimensions: 480 x 360

Date Taken:

Length: 00:04:46

Location Taken: Tucson, AZ, US

Transcript

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.