TM 5-818-5/AFM 88-5, Chap 6/NAVFAC P-418
strata (with or without gravel and cobbles) may be en-
Well A
countered in drilling the holes for the specified wells.
137-ft
260-ft
Logs and wood debris have also been encountered in
Total
depth
Well C
depth Well B
making borings and drilling wells at some locations at
2
2
1
1
the site.
Calcium (ppm)
105
95
165
244
9
19
13
Iron (total) (ppm)
8
(b) Depth of wells. The wells shall be installed to
<0.1
<0.1
<0.1
<0.1
a depth so that the top of the specified length of screen
Total Alkalinity
(100 feet) is set approximately 5 feet below the top of
405
479
567
480
(CaCO 3) (ppm)
Carbon Dioxide
fine (or coarser) sand as determined at the time of
120
95
120
110
(CO2) (ppm)
drilling by the C.O.R. The elevation at which the top of
d. Deep-well dewatering system.
the screen shall be set is shown on certain logs of bor-
(1) Scope. The work provided for herein consists
ings along the line of the dewatering wells. The top of
of furnishing all labor, material, equipment, and tools
to construct, develop, test pump, and disinfect the fil-
to be set will probably vary from what is shown on the
ter sand, well, and pump for the dewatering wells to be
boring logs. The hole drilled for the wells will be
installed around the perimeter of the excavation at the
logged by the C.O.R. If buried logs or boulders are en-
locations shown on the drawings and as specified here-
countered which, in the opinion of the C.O.R., render
in. The work also includes installation of the pumps,
it impractical to advance the drill hole to the design
diesel engines, gear drives, couplings, discharge pipes,
depth, the C.O.R. may adjust the depth in order to uti-
valves, fittings, flow measurement devices, and dis-
lize the well in the system at the depth actually ob-
charge pipe.
tained, or he or she may request the Contractor to
(2) Design. The deep-well system specified has
abandon the well, plug the hole by backfilling, and
construct another well at an adjacent location.
deep sand stratum beneath the excavation to elevation
(c) Drilling. The dewatering wells shall be
- 26.0 feet beneath the dam, elevation - 29.0 feet be-
drilled by the reverse rotary method to a depth which
neath the lock chamber, and elevation - 35.0 feet be-
will permit setting the top of the screen in fine (or
neath the gate bays for a design Red River stage of ele-
coarser) sand as determined at the time of drilling by
vation of 60.0 feet (estimated maximum river stage for
the C.O.R. The water level in the sump pit and the well
a frequency of 1 in 20 years). The purpose of the deep-
shall be maintained a minimum of 8 feet above the
well system is to lower the hydrostatic head in this
sand stratum so as to prevent seepage into the bottom
riser pipe, filter, and backfill have been placed. Drill-
of the excavation and to prevent any heave of imper-
ing of the well shall be carried out so as to prevent any
vious soil strata that overlie the deep sand formation
appreciable displacement of materials adjacent to the
in certain areas of the excavation. It is imperative that
hole or cause any reduction in the yield of the well. (A
there be no heave of the bottom of the excavation dur-
temporary surface casing with a minimum length of
ing either Phase II or Phase III construction of the lock
20 feet shall be set prior to the start of drilling.) The
and dam. If evaluation of the pumping test made at
diameter of the hole drilled for the well shall be 28 to
the completion of unwatering the Phase I excavation
30 inches. The hole shall be advanced using a reverse-
indicates the need for additional dewatering wells,
rotary drill rig with a (minimum) 5-inch I.D. drill stem.
pumps, engines, discharge piping, and appurtenances,
While drilling and installing the well, the drill hole
the Government will design the supplemental system
shall be kept full of (natural) drilling fluid up to the
and furnish the design to the Contractor for installa-
ground surface with turbidity of about 3000 parts per
tion. The Contractor will be reimbursed for the cost of
million. No bentonite drilling mud shall be used while
installing any supplemental wells, pumps, engines,
drilling or installing the well. Silt may be added to the
discharge piping, and appurtenances, when completely
drilling water to attain the desired degree of muddi-
installed and ready for operation. The Contractor shall
ness (approximately 3000 parts per million) if nec-
be responsible for designing any features of the well
esary. If natural turbid water, or with silt added,
system not specifically covered by these specifications
proves insufficient to keep the hole stable, an ap-
or drawings.
proved organic drilling compound such as Johnson's
(3) Installation of wells.
Revert, or equivalent, may be added to the drilling
(a) Location of wells. The dewatering wells shall
fluid. The Contractor shall dig a sump pit large enough
be installed at the designated locations. Soil conditions
to allow the sand to settle out but small enough so that
in the areas where the wells are to be installed are de-
some silt is kept in suspension. The drilled hole shall
picted in a general way by the boring logs made around
be 3 feet deeper than the well screen and riser to be in-
the excavation. Subsurface conditions and stratifica-
stalled in the hole. All drilling fluid shall be removed
tion are erratic at this site, and clay, silt, and sand
G-12