2.2.1
Stainless Steel Screens
ASTM A 312/A 312M, Type 304, Schedule 40S, continuous slot construction,
wire wound, with flush threaded joint ends.
2.2.2
PVC Screens
ASTM D 1785, PVC 1120, NSF wc or NSF pw, Schedule [40] [80], screen,
Schedule 80, machine-slotted construction, flush threaded joint ends.
Slots shall be even in width, length, and separation.
2.3
PRIMARY FILTER PACK
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NOTE: The primary filter pack selected should have
a 30 percent finer (d-30) grain size that is 4 to 10
times greater than the d-30 grain size of the
aquifer. For extraction wells, select a primary
filter pack with a d-30 grain size 8 to 10 times
greater than the d-30 grain size of the aquifer.
The uniformity coefficient (60 percent passing,
d-60/10 percent passing, d-10) should be less than
2.5, and ideally in the 1.0 to 1.5 range. Primary
filter should extend 600 to 1500 mm 2 to 5 feet
above the top of the well screen. The secondary
filter should be a minimum of 300 mm one foot thick,
preferably 600 mm 2 feet thick.
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Provide clean, durable, well-rounded, and washed quartz or granite, with
less than 5 percent non-siliceous material. The filter pack shall not
contain organic matter or friable materials. The filter pack shall allow
free flow of water in the well, and shall prevent the infiltration of
aquifer materials. Filter pack shall have a 30 percent finer than (d-30)
grain size of [_____] mm inch, and a uniformity coefficient less than [2.5]
[_____], in accordance with ASTM C 117 and ASTM C 136.
2.4
SECONDARY FILTER PACK
Gradation in accordance with ASTM D 5092. Provide clean, durable,
well-rounded, and washed quartz or granite. Pack shall not contain organic
matter or friable materials.
2.5
ANNULAR SEALANTS
2.5.1
Bentonite Seal
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NOTE: Sodium bentonite is most widely used,
however, calcium bentonite may be more appropriate
for high calcium environments. Bentonite seal
should be placed above the secondary filter and
approximately 600 to 1500 mm 2 to 5 feet above the
highest well screen.
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Provide powdered, granular, pelletized, or chipped [sodium] [calcium]
montmorillonite in sealed containers from a commercial source, free of
impurities. Diameter of pellets shall be less than one fifth the diameter
SECTION 02525N
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