this space, if this option is elected. The well screen and inner casing
shall be firmly attached, and lowered into the hole by a method which will
allow for control of the rate of fall of the well screen and inner casing
at all times. Well screen and inner casing shall not be dropped or allowed
to fall uncontrolled into the hole. The inner casing shall extend up
through the outer casing to [_____] meters [_____] feet [above][below]the
ground surface. Approved centering devices shall be installed at a spacing
of 120 degrees, between the outer casing and inner casing prior to well
construction at [intervals not exceeding [8][_____]meters [25] [_____]feet
along the length] [the top of the inner casing and the bottom of the outer
casing]. If the screen length is greater than [8] [_____] meters [25]
[_____] feet, a [1] [_____] meter [3] [_____] foot length of blank casing
shall be placed in the middle of the screen interval for placement of
centering devices.
Centering devices shall not be placed on the screened
interval, or within the bentonite seal, if used.
3.3.4
Construction of Filter Pack
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NOTE: If the natural formation is developed as the
well filter, then this paragraph may be deleted. If
development of the well is done after the filter
pack is installed, but before the bentonite, or
annular seal is installed, additional filter pack
material may have to be added, if the level of the
top of the filter pack drops below the specified
elevation for the top of the filter pack. When
installing extraction, or injection wells at HTRW
sites, the top of the filter pack should be no more
than 1.5 m (5 feet) above the top of the screen.
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After the screen and inner casing have been concentrically set in the hole
below the outer casing, the approved filter pack shall be constructed
around the screen by filling the entire space between the screen and the
wall of the hole in the water bearing stratum with filter pack material. A
tremie pipe having an inside nominal diameter of not less than [40] [_____]
mm [1-1/2] [_____]inches shall be lowered to the bottom of the well between
the hole and screen. The tremie pipe shall be arranged and connected, at
the surface of the ground, to water pumping and graveling equipment so that
water and filter material, fed at uniform rates, are discharged as the
filter material fills the hole from the bottom up. The tremie pipe shall
be raised at a rate that will keep the bottom of the pipe no more than
[1][___] m [3][___] feet above the filter material level at all times. If
the Contractor desires to use methods of placing filter material other than
those specified, the details of the method and equipment proposed shall be
submitted to the Contracting Officer, before filter pack placement is
begun; however, dumping filter pack material from the surface of the ground
and agitating the well in an effort to settle the filter will not be
allowed. The filter pack shall be installed continuously and without
interruption until the filter pack has been placed to within [300 mm 1 foot
of the top of the inner casing] [1.5 m 5 feet of the ground surface] [
[10][_____] m [30] [_____] feet above the top of the screen]. The depth to
the top of the filter pack shall be directly measured, and recorded. Any
water added to the filter pack material shall be obtained in accordance
with paragraph Water Source. Filter pack material shall be protected from
contamination prior to placement by either storing it in plastic lined
bags, or in a location protected from the weather and contamination on
plastic sheeting. Filter pack material shall not be allowed to freeze
SECTION 02521
Page 25
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