Establishing a Permanent Measuring Point and Reference Marks at a Well

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Detailed Description

This video demonstrates how to establish permanent reference points and markers at a well site.
 

Details

Date Taken:

Length: 00:07:58

Location Taken: Raleigh, NC, US

Video Credits

Post Production: Corey Shaw

Transcript

(guitar music)

- [Instructor] This video demonstrates

techniques to establish a
permanent land surface datum,

nearby reference marks,
and a measuring point

from which groundwater levels
at a well are measured.

The materials needed include keys,

wrenches, or other tools
to access the well,

an engineer's ruler or
measuring tape graduated

in feet, tenths, and hundredths of feet,

a field notebook and a writing implement,

a groundwater site inventory,

GWSI System Groundwater
Site Schedule form,

metal file and permanent marker,

spray paint, hammer and cold chisel,

survey monuments, such as
a nail, spike, or tablet,

camera, protractor,
calculator, or other tools

to calculate angles and lengths,

topographic map or rod,
leveling instrument,

leveling note sheets,
and differential GPS.

Step one, establish land surface datum.

The land surface datum at a
well is a fixed reference mark

located at or near the land surface

that can be used to measure the altitude

of the land surface datum,

as well as the distance
from the land surface datum

to the measuring point.

Locate a stable, permanent
location near the well

to establish the land surface datum.

The land surface datum
should be in a location

that can be clearly defined,

clearly marked, and easily located.

Additionally, the land surface datum

should be close enough to the well

to facilitate measuring from
it to the measuring point,

and it should be accessible to
a survey rod or GPS antenna.

Step two, mark the land surface datum

using a survey monument, brass marker,

or chiseled mark in the concrete pad

at the base of the surface casing.

Step three, take a photograph
of the land surface datum

and document the description
in the field notebook.

If the land owner does not
allow marking of the well,

then describe the land surface datum

as accurately as possible.

Step four.

The altitude of the land surface datum

must be determined for each site.

Locate the well, following
the instructions in GWPD 5.

At a minimum, the
altitude can be estimated

from a topographic map.

Depending upon the use of the
measurements from the well,

it may be preferable to
determine the altitude

of the land surface datum
using differential leveling

or differential GPS techniques.

Document the measurements in the

GWSI groundwater site schedule.

Step five, establish the measuring point.

The measuring point is
a permanent, stable,

clearly-defined and marked reference point

used to measure the water level in a well.

It is often located at
the top of the casing

in an observation well,

or at an access point
at a production well.

To establish a measuring point for a well,

choose a point on the casing

where a leveling rod could
be set directly on it,

and a measuring tape can
hang freely into the well

when it is in contact
with the measuring point.

If the casing does not
have a horizontal rim,

it is preferable to
establish the measuring point

on the high or low side of the rim.

Step six.

Using a file, lightly
mark the measuring point

on the well casing.
Optionally, mark the measuring point

by a permanent marker or spray paint.

Step seven.

Take a photograph of the measuring point

and document the description
in the field notebook.
If the measuring point cannot be marked

directly on the casing,

clearly define it in the field notes.

Step eight, measuring
point correction length.

Depending on the use and storage

of measurements from the well,

the altitude of the
measuring point of a well

with a vertical stick-up

may be surveyed from a geodetic benchmark

using differential leveling

or differential GPS techniques.

The measuring point correction length

is the distance the measuring tape travels

from the measuring point to the plane

of the land surface datum.

If the measuring point is
above the land surface datum,

the measuring point correction
is a positive number.

If the measuring point is
below the land surface datum,

the measuring point correction
is a negative number.

Simple vertical well.

Measure the measuring
point correction length

in feet above or below the
land surface datum directly

with a steel tape, or
by differential leveling

if the objectives of the measurement

require a precise altitude.

More complicated non-vertical well.

If the well stick-up does not allow

the water level tape to hang vertically

from the measuring point through the plane

of the land surface datum,

the measuring point correction
cannot be measured directly.

Instead, the length along
the measurement path

between the measuring point
and the land surface datum

must be computed using geometry.

The resulting measuring
point correction length

will be greater than the vertical distance

between the land surface
datum and the measuring point.

Step nine.

Document any calculations to determine

the measuring point correction
length in the field notebook.

Document the measurements

in the GWSI Groundwater Site Schedule.

Step ten, establish
additional reference marks.

A reference mark is a nearby datum

established by a permanent marker

that is used to periodically
check the measuring point

and/or land surface datum,

or to reestablish the measuring
point or land surface datum

should the original be
destroyed or changed.

Establish at least one
clearly-marked reference mark

near the well,

such as a benchmark, a lag
bolt set in a telephone pole,

a spike in a mature tree, a
mark on a permanent structure,

or a poured concrete post.

More than one reference
mark is preferable.

Locate a reference mark a
distance away from the well

to assure that circumstances
that damage the well

do not also damage the reference mark.

Take photographs,

and record a description
of the site reference mark

in the field notebook.

Step eleven, establish
the vertical relation

between the measuring
point and reference marks

by differential leveling.

Document the vertical relation between

the measuring point and reference marks.

At each subsequent site visit,

visually inspect the measuring
point, land surface datum,

and reference marks.

Document any damage,

and recheck the vertical
relation if damage is noted.
If no damage is apparent,

the vertical relation
between the measuring point

and reference mark should be confirmed

at three-to-five year intervals.

(guitar music)

Accuracy.

Keep in mind the following
accuracy limitations

of this method.

The accuracy of the measuring
point, reference mark,

and land surface datum altitude

depends upon the measurement ethic used.

The accuracy of the measurement
point correction length

depends upon the configuration
of the measuring point

with respect to the land surface datum,

angle of deviation from vertical,

the ability of the hydrographer
to determine the tape path,

and the measurement method used.

(guitar music)