TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418
wellpoints with a 10-inch auger prior to driving and
minute at a total dynamic head (TDH) equal to 50 feet.
jetting the 12-inch sanding casing to grade. Any such
The Contractor shall be responsible for designing and
predrilling should be accomplished in a manner which
installing the electrical system for powering the sub-
will not cause any caving of the hole as it is drilled. In
mersible pumps in the relief wells. The electrical sys-
jetting the sanding casing for the wellpoints, provision
tem shall meet the local electrical code and be ap-
shall be made to prevent jet water from spraying over
proved by the Contracting Officer. Each pump shall be
sidewalks and streets being used for pedestrians
provided with a starter and fuse disconnect with a
and/or vehicular traffic, and from running over or into
clearly visible red light mounted on the control panel
streets being used by such. The Contractor will be re-
that shows red when the pump is running. A motor
sponsible for disposal of jet water in a manner satisfac-
generator with a capacity capable of starting all of the
tory to the City and the Construction Manager.
submersible pumps in the relief wells at one time shall
be provided and hooked into the electrical system at all
(e) Each jet-eductor wellpoint shall be provided
with a suitable strainer at the top of the pressure riser
times. This generator shall be operated to keep the
pumps in the relief wells running in event of power
pipe to prevent the entrance of any particles, which
failure. It shall be maintained in first class condition,
might clog the jet-eductor nozzle, and a stopcock or
valves, which will permit isolating the wellpoint to
protected from the weather, and started at least twice
permit pressure testing and pumping the wellpoint
a week to check its operating condition.
(c) The bottom of the screens for the relief wells
separately if desired.
shall be installed at or slightly below the bottom of the
(5) Pressure relief wells and pumps. The pressure
semipervious stratum as encountered during installa-
relief wells shall be installed at the locations specified.
tion. They shall be installed using the same procedure
These wells are to reduce the hydrostatic head in the
semipervious stratum below the excavation to eleva-
as specified for the wellpoints except that in all proba-
tion 250.0 feet or lower as measured by the B piezome-
bility it will be necessary to predrill the holes to grade
ters installed in this same stratum at the locations, as
with a lo-inch auger because of the difficulty in jetting
through some of the clay strata to be penetrated. After
subsequently specified.
the (12-inch) sanding casing has been driven and jetted
(a) The screens for the relief wells shall be 10
to grade, the well screen and riser pipe shall be cen-
feet long and shall be installed in the semipervious
tered accurately and lowered to within 1 foot of the
stratum at about elevation 235 1 foot. The screens
bottom of the casing. Filter Sand B poured into the
shall have a nominal diameter of 4 inches. They may
sanding casing around the well riser pipe in a heavy
be manufactured of slotted Schedule 40 PVC pipe,
steady stream until the filter sand is at least 5 feet
Johnson wire-wrapped screen, or other approved
screen. The screens shall be covered with 30-mesh
above the top of the screen; the remainder of the hole
brass or stainless steel gauze or slotted with #20 slots
may be filled with clean medium sand. The sanding
with a minimum open area of 5 percent. The riser pipe
casing shall then be immediately pulled. After the well
has been installed, it shall be promptly pumped with a
shall also have a 4-inch nominal diameter; it may be
centrifugal pump capable of producing a 25-foot va-
either PVC plastic pipe or steel. The screen portion of
cuum until the effluent is clear. The submersible pump
the wells and up for a distance of 5 feet above the top
of screen shall be surrounded with a clean, washed uni-
then shall be lowered and suspended in the well with
form filter sand (B) with the following gradation:
the intake of the pump at about the top of the well
screen. The pump or discharge pipe shall be provided
Filter Sand B
U.S. Standard
Percent Passing
with a check valve, and the connection between the
Sieve Size
10
95-100
discharge pipe from the pump to header pipe shall be
20
58-90
provided with a gate valve which will permit removal
30-73
30
of the pump if necessary. The top of the well shall be
40
5-50
sealed with a suitable well cap or plate provided with a
0-25
50
70
0-8
hole through which a sounding line may be lowered to
determine the water level in the well when testing and
Suppliers who can furnish Filter Sands A and B are as
monitoring the system. A full-scale pumping test shall
follows:
be run on the completed system to determine its ade-
Filter Sand
Filter Sand
Supplier
A
B
quacy and pumping rate. This test shall be run for a
-
-
minimum of 6 hours. The water level in the B piezome-
-
1.
-
-
-
2.
ters and in the wells and flow from the system shall be
-
-
-
3.
measured at the following intervals after the start of
pumping: 10 minutes, 30 minutes, 1 hour, 2 hours, 3
(b) Pumps for the relief wells shall be submersi-
hours, 4 hours, and 6 hours.
ble pumps suitable for installation in 4-inch nominal
(d) All of the submersible pumps shall be new,
diameter wells with a capacity of 3 to 10 gallons per
G-6
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