Measuring Groundwater with Electric Tape

Video Transcript
Download Video
Right-click and save to download

Detailed Description

This video demonstrates how to measure water levels in wells using an electric tape.

Details

Image Dimensions: 480 x 360

Date Taken:

Length: 00:04:36

Location Taken: Tucson, AZ, US

Transcript

Introduction:
Hi, this video demonstrates methods for measuring

water levels in wells using an electric tape.

The electric tape 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, Water
for testing the probe, The Electric Tape , A

PDA for electronically recording measurements,
A cloth, Soap & water for cleaning the probe,

A Water Level Measurement Field Form & writing
utensil

Instructions:
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) Ensure that the electric tape is working
properly by dipping the probe into tap water

and observing whether the indicator is functioning
properly to indicate a closed circuit.

Make sure that all readings are made by using
the same deflection point on the indicator

scale, light intensity, or sound so that measurements
are consistent.

Step 4) Lower the probe slowly into the well
until the indicator indicates that the circuit

is closed and that the water surface in the
well is contacted.

Place the nail of the index finger on the
insulated wire at the measuring point and

read the depth to water on the graduated tape.

Step 5) Record the date and time of the measurement
on a Water Level Measurement Field Form or

a digital screen input form.

This is automated with electronic data entry
software like “Monkeys.”

Record this value on the row “hold.”

If a correction is needed, record the correction
amount on the row “tape correction” and

subtract from the “hold” value.

Record this difference in the row “water
level below measuring point.”

Step 6) Record the measuring point correction
length on the “MP correction” row of the

field form.

The MP correction is positive if the MP is
above the land surface, or negative if it

is below the land surface.

Subtract the MP correction length from the
true “water level below measuring point”

value to get the depth to water below or above
the land surface datum.

Step 7) Pull the tape up and make a check
measurement by performing the previous steps.

Record the check measurement on the field
form.

If the check measurement differs from the
original measurement by greater than 0.02

foot, continue to measure the water depth
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 field form.

Step 8) Close the well with a pipe wrench,
making sure the lid is securely fastened.

Step 9) After completing the measurements,
disinfect and rise the part of the tape that

was submerged, as described in the National
Field Manual in order to reduce the possibility

of contamination of other wells by the tape.

Note *The electric tape should first be calibrated
against a reference steel tape.

The reference tape should be kept in the office
and used only for calibrating other tapes.

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, and when measuring

deep water levels because of tape expansion
and stretch.

Advantages
This approach has several advantages.

The electric tape is superior to a steel tape
when water is dripping into the well or condensing

on the side casing walls.

When a rapid series of measurements are needed,
such as during an aquifer test, because measurements

are obtained quickly and the tape does not
need to be lifted from the well for each reading.

It is also superior in wells that are being
pumped, where the splashing of the water surface

can have little impact on measurements, whereas
the splashing can produce additional wetted

marks on steel tapes that do not indicate
the depth to water.

Disadvantages
This method however, has several disadvantages.

The electric tape is more difficult to keep
calibrated than a steel tape.

The electric connections can fail and require
maintenance.

The electric tape requires battery power.

The cable jacked is subject to wear and tear,
which can sever the electric circuit.

The electric tape may not give accurate readings
if the water in the well has a very low specific

conductance.