shall be prevented from entering the well during construction. If there is
an interruption in work, such as overnight shutdown or inclement weather,
the well opening shall be closed with a watertight uncontaminated cover.
The cover shall be secured in place or weighted down so that it cannot be
removed except with the aid of the drilling equipment or through the use of
drill tools.
3.3.1
Setting Outer Casing
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NOTE: There is a provision for temporary casing, as
extraction and/or injection wells may not require a
permanent outer casing.
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The outer casing shall not be less than [200] [_____] mm [8] [_____] inches
in diameter. The hole shall be of sufficient size to leave a concentric
annular space of not less than [65] [_____] mm [2-1/2] [_____]inches and
not more than [150] [_____] mm [6] [_____]inches between the outside of the
outer casing and the walls of the hole. The annular space between the
outer casing and the walls of the holes shall be filled with cement grout.
Acceptable methods of grouting are detailed in AWWA A100; the approved
method shall specify the forcing of grout from the bottom of the space to
be grouted towards the surface. A suitable grout retainer, packer, or plug
shall be provided at the bottom of the inner casing so that grout will not
leak into the bottom of the well. Grouting shall be done continuously to
ensure that the entire annular space is filled in one operation. After
grouting is completed, drilling operations shall not be resumed for at
least [72] [_____]hours to allow proper setting of the grout.
3.3.2
[Temporary Casing
Temporary well casing of either iron or steel of sufficient length to case
to the bottom of all borings shall be available at the construction site.
The Contracting Officer will direct the use of a temporary casing to the
bottom of the boring during drilling and placement of screen, riser, and
filter pack when he believes it is necessary to provide adequate support to
the sides of the hole. When the walls of the boring will require support
only during development operations a temporary casing will be required to
extend only to a depth 1 m 3 feet below the top of the filter pack. The
temporary casing, shall have an inside diameter of not less than [_____] mm
inches, shall have sufficient thickness to retain its shape and maintain a
true section throughout its depth, and may be in sections of any convenient
length. The temporary casing shall be such as to permit its removal
without disturbing the filter pack, riser, or well screen. The setting of
temporary casing shall be such that no cavity will be created outside of it
at any point along its length. In the event the temporary casing should
become unduly distorted or bent it should be discarded and a new casing
should be used during installation of any additional well.]
3.3.3
Construction of Inner Casing and Screen
After the grout has set, the hole below the outer casing shall be reamed at
the required diameter, to the required depth, by an approved method which
will prevent caving of the hole before or during installation of the filter
pack, well screen and inner casing. In lieu of reaming, the entire well
may be drilled to the diameter of the filter pack with an annular space
between the inner casing and outer casing equal to the thickness of the
filter pack. The outer casing shall be increased in size to provide for
SECTION 02521
Page 24
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