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Plastic casing pipe and couplings shall be schedule [80][___], threaded
flush joint (or other joint type as approved by the Contracting Officer)
and conform to ASTM F 480 and ASTM D 1785.
2.2
WELL SCREENS
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NOTE: Well screens will be specified when the
developed well requires assurance of relatively free
entry of water into the casing at low velocity, when
surrounding sand from the unconsolidated formation
must be prevented from entering the intake, or when
a structural retainer is required to support the
borehole in the unconsolidated material. Type of
screen and casing will be designer's option and
nonapplicable type of screen will be deleted. Metal
screens and casings will be specified when strength
of screen and casing must be greater than that
provided by plastic or when maximum open area for
the screen diameter is required. Plastic screens
and casing may be specified when water quality is
such that screen selection requires
corrosive-resistant materials, or when economy is of
prime importance. Blanks in the well screen may be
appropriate if more than one water bearing zone is
encountered in an aquifer, or when it is necessary
to place a centering device (centralizer) in the
screened area. However, screening more than one
aquifer in the same well should be avoided whenever
possible due to the possibility of
cross-contamination.
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Well Screens shall be a minimum of [100] [_____] mm [4] [_____] inches
nominal diameter, and shall be directly connected to the bottom of the
inner casing by an approved method. The length of the screen shall be
sufficient to provide an intake area capable of passing not less than the
minimum required yield of the well, at an entrance velocity not exceeding
30.5 mm/s 0.1 fps. The opening, or slot size of the screen, shall be
[[____] mm [____] inch][determined by the Contractor][designed based on
analysis of the distribution of the grain size of the [aquifer materials
encountered during drilling][artificial filter pack]], be compatible with
the material surrounding the screen, and shall be submitted for approval as
part of the well installation plan. The well screen shall be of sufficient
size and design to hold back and support the [gravel used in the filter
pack envelope] [and] [in-situ material surrounding the screen]. The
screen and all accessories required for satisfactory operation shall be
essentially standard products of manufacturers regularly engaged in the
production of such equipment. Field constructed screen is not acceptable.
"Blanks" in the well screen may be utilized in nonproductive zones, or
where centering devices are needed in the screened area, and shall be
considered "casing." The bottom section, below the screen, shall be sealed
watertight by means of a [flush threaded] [welded] end cap of the same
material as the well screen.
SECTION 02521
Page 17
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