Measuring Total Well Depth Using a Steel Tape - YouTube

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Detailed Description

This video demonstrates how to measure total well depth below land surface using a weighted, graduated steel tape.

Details

Date Taken:

Length: 00:06:13

Location Taken: Raleigh, NC, US

Video Credits

Additional Post Production by Corey Shaw, USGS

Transcript

(soft guitar music)

- This video demonstrates
techniques to measure the total

depth of a well below land
surface using a weighted

graduated steel tape.

A graduated steel tape
is commonly accurate

to 1/100th of a foot, but the
accuracy of the well depth

measurement decreases
with increasing depth.

Materials needed.

The materials needed
include keys, wrenches,

or other tools to access
the well, a steel tape

with brass, stainless steel or iron weight

that is heavy enough to
amplify the weight transfer

sensation when the bottom
of the well is struck.

The weight should be attached to a ring

on the end of the tape
with wire strong enough

to hold the weight but
not as strong as the tape

so that if the weight
becomes lodged in the well,

the tape can be pulled free.

Engineer's ruler, clean towels
or cloths, soap and water

for cleaning the steel tape
and weight, a field notebook,

Groundwater Site Inventory
System Groundwater Site Schedule

form, and a writing implement.

Step one: Determine you
are at the correct well

from the well description.

Step two: Open the well
and locate the documented

measuring point from the
well, photo or diagram.

Step three: Measure from
the zero point on the tape

to the bottom of the weight.

Record this number in the
field notebook as the length

of the weight interval.

Locate the measuring point
correction from a document

such as the well station
description, and record this number

in the field notebook as MP correction.

The MP correction is negative if the MP

is above land surface,
and positive if the MP

is below land surface.

Also record the serial
number of the steel tape

you will be using to make
the depth measurement.

Step four: Lower the weight
and tape slowly into the well,

until the weight reaches
the bottom of the well

and the tape slackens.

Step five: Partially withdraw
the tape from the well

until the weight stands
in a vertical position

but still touches the bottom of the well.

Pinch your thumb and index finger together

on the steel tape at the measuring point.

Note the depth below measuring
point on the steel tape.

Repeat the process of lowering
and withdrawing the tape

several times until a consistent
measurement is obtained.

Step six: Record the measurement
in the field notebook

as the tape reading held at the MP.

Step seven: Withdraw the
steel tape from the well

one to two feet, so that
the weight hangs freely

above the bottom of the well.

Repeat steps four, five, and six until two

consistent depth
measurements are obtained.

Step eight: Calculate the
total well depth below land

surface datum by adding the
value of the tape reading

held at the MP and the
length of the weight interval

to get the total well depth below MP.

The total well depth
below land surface datum

is calculated by subtracting
the MP correction

from the total well depth below the MP

if the MP is above ground, or
by adding the MP correction

to the total well depth below MP

if the MP is below ground.

Transfer the calculated
total well depth below land

surface datum to the
groundwater general site data

section of the GWSI
Groundwater Site Schedule

in field C28.

The recommended precision
of the measurement

is depth-dependent.

Step nine: Withdraw the tape.

Close and re-secure the well.

Step ten: After completing
the measurements,

disinfect and rinse the
part of the steel tape

that was submerged below water surface,

as described in the National Field Manual,

in order to reduce the
possibility of contaminating

other wells with the steel tape.

Keep in mind the following
limitations of this method.

Corrections to the
measurements are necessary

if the well casing is angled,
and when measuring the well

in deep wells because of
tape expansion and stretch.

This approach has several advantages.

The weighted graduated
steel tape is considered

to be the most accurate method
of measuring well depth.

It is also easy to use.

This method is not recommended
for measuring the depth

of wells that are being pumped.