TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418
plemental dewatering measures installed for control-
bridging of the sand in the "sanding" casing. As the fil-
ling the groundwater within the excavation.
ter material is placed in the well screen, 70 percent
(3) Installation of jet-eductor wells.
granular calcium hypochlorite shall be added to evenly
(a) Location and depth of wells. The jet-eductor
distribute a minimum of 2 pounds per ton of filter. The
wells shall be installed at the designated locations. Soil
method of placement shall be approved by the C.O.R.
conditions where the jet-eductor wells are to be in-
(d) Development of jet-eductor wells. Within 12
stalled are depicted in a general way by the logs of bor-
hours after installation of each well, it shall be devel-
ings made around the excavation. The wells should
oped by means of air-lifting. A 2-inch inner diameter
extend about 2 feet below the bottom of the pervious
air line shall be lowered in the well to within 1 foot of
strata being drained. The required depth of the wells
the bottom of the well and sufficient air be pumped
may vary considerably from those indicated on the
through the air line to cause the well to flow. For low-
drawings.
yielding wells, it may be necessary to add clear water
to help develop the well and remove any sand that may
shall be installed in the following manner:
have entered the screen. Air-lifting shall continue un-
Step 1. Predrill a 10- or 11-inch hole 2 feet
til all sand or filter material is removed from inside
below the silt or silty sand stratum to be drained. Hy-
the screen and water from the well flows clear. Each
draulic rotary, or auger, methods of drilling may be
well shall be developed for a minimum of 20 minutes.
used. No drilling muds or additives, other than clear
(e) Chlorination of well. Upon completion of in-
water, shall be used in drilling the hole for the well.
stallation of the well and prior to installing a cap on
The hole shall be kept full of water during the predrill-
the top of the riser, a minimum of 3 pounds of 70 per-
ing, and withdrawal of the auger, so as to minimize
cent granular calcium hypochlorite shall be dropped
caving.
into the well.
Step 2. After predrilling the hole to grade, it
(f) Well top. The 4-inch riser shall extend 6
shall be washed out by driving and jetting (with clear
inches above the ground surface and shall be sealed
water) a 12-inch "sanding casing" with a hole puncher
around the riser pipe for the jet-eductor pump. The
to the bottom of the predrilled hole.
well number shall be painted on the top of the riser
Step 3. After the "sanding casing" is driven and
pipe.
jetted to the required depth, it shall be washed clean
(g) Riser pipe. The 4-inch riser pipe for the wells
by jetting with clear water. The jet pump, pipe, and
shall be 15 feet in length. The filter sand shall extend
hose shall be of sufficient capacity to produce an up-
to within 8 to 10 feet of the berm surface; the space
ward velocity inside the casing to efficiently remove
around the riser pipe from the filter to the berm sur-
all material in the casing, so that the well screen and
face shall be grouted with an approved bentonite-ce-
riser can be set to grade. The "sanding casing" shall be
ment grout.
kept filled with water until the well screen and filter
(h) Well records. A report showing depth, eleva-
sand have been placed so as to prevent any "blow in" of
tions, date of installation, approximate rate of flow
the bottom of the hole.
during development, and any other data concerning in-
(c) Installation of well screen and filter sand.
stallation of each well will be completed by the C.O.R.
After the sanding casing has been cleaned by jetting
The water level in the well shall be recorded at the
and the clear depth in the casing checked by sounding
time of installation. The Contractor shall assist in ob-
with an approved device, the well screen shall be low-
taining the installation data. If the jet-eductors or
ered to the bottom of the casing. Particular care shall
pumps appear to be losing their efficiency with the
be exercised in handling and placing the screen so as
passage of time, the Contractor may be required to re-
not to damage it. Complete assembly of the screen and
develop and/or chemically treat the wells as directed
riser pipe on the ground surface will not be permitted.
by the Contracting Officer, the cost of which will be
Two or three connections shall be made to the assem-
paid for under paragraph 3 (Changes) of the General
bly as it is placed in the casing. Approved centralizers
Provisions of the Contract.
shall be furnished and attached to the screen at inter-
(4) Materials .
vals not greater than 20 feet. The design and attach-
(a) Riser pipe. The riser pipe and the 2-foot
ment of the centralizers to the well screen shall be sub-
blank pipe on the bottom of the screen shall be 4-inch
mitted to the C.O.R. for approval. The top of the riser
diameter, flush-joint Schedule 80, type 2110 PVC
pipe shall be securely covered or capped to prevent the
pipe.
filter sand from falling into the well. The method of
(b) Screen. The screen shall be 4-inch, Schedule
placement shall assure a fairly rapid, continuous, uni-
80, type 2110 PVC screen. The screen shall be slotted
form rate of placement of filter sand, which will
with .025-inch slots in sufficient numbers to give a
evenly distribute the filter sand around the screen.
minimum area of opening of 5 percent. The screen sec-
The rate of placing the filter sand shall not cause
tion of the well shall extend from the top of any semi-
G-18
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