Many types of trench exist, suited to different purposes and soil conditions.
Typical pipeline trench cross section details with dewatering system this drawing available in autocad format.


typical trench section in autocad fromat

Installation of Dewatering System -
Once the pipe is strung out, the loaders are in place, and the stone is stockpiled close
to the work zone, installation can begin.
The operator will start the engine on the trencher, and will begin turning the chain.
The chain on the trencher has cutters that will do the digging. As the chain begins
turning the operator will begin lowering his boom into the ground. Once he has
started to lower his boom, the pipe will begin pulling itself into the ground.
After the chain boom is a few feet in the ground, the operator will then stop to allow
the excavator to pour stone into the stone chute, and then in the hopper as well. This
will allow stone to be placed into the cut right away. Now that the stone has been
placed into the chute, the operator of the trencher can begin lowering his boom into
the ground the rest of the way, keying into the weathered shale layer. As the boom
reaches the desired depth, the operator will begin tracking the machine away from
where it originally set in the ground. This will allow the pipe to pull itself into the
ground. This will continue until the trencher reaches the end of the system.
Meanwhile, an excavator will fill the stone hopper with 3/8" Class A washed stone
from a rock box being pulled by the excavator and continually filled by the front end
loader. The excavator will continue to feed the trenching equipment until the
machine reaches the end of the system. As the chain is turning in the ground it will
bring up the soils out of the ground and place them back over the trench, backfilling
the trench as it goes. Afier trench is compacted and graded to match existing ground,
some additional excavated materials will be left on top of the ground upon
completion, the materials will be stockpiled in a location that has positive drainage
toward the retention pond.
Once the machine reaches the end of the system and the solid pipe has been laid in
the ground for a few feet, the operator can raise his boom out of the ground. This will
leave a solid pipe sticking out of the ground at each end. The purpose for the solid
pipe is so that the dewatering can take place from the drainage pipe at the bottom of the cut, and not allow the system to suck air where it begins and ends. This procedure
will be the same for each system installed.

Pumping of Dewatering Systems -

After the system(s) is installed, a 4" Wellpoint Pumnp will be placed at the desired end
of the system(s) as per figure 5 and 8 in RECON's Work Plan. A short solid pipe will
be coupled to the end of the system to allow it to reach the pump. After the temporary
holding tanks are constructed the pump(s) will then be started up with the vacuum
relief valve open (to allow slow build up of vacuum so the sock does not get plugged
up). The contractor will then let the system pump for as long as desired before
excavation. Water levels will be checked periodically through the existing
piezometers/wells to monitor ground water levels.
Breakdown and Loading of MTLLC Trencher -
At the end of the installation of the dewatering systems, the contractor will use the
excavator to remove the stone hopper and chute off of the trencher and load it
back on the trailer. After the trencher is decontaminated and has passed the
Unrestricted Release criteria as per the Radiation Health & Safety Plan (RHASP) the
trencher will be loaded back onto the lowboy and chained down for transporting back
to MTLLC's yard.
RECON will provide any necessary decontamination of the hopper, chute, service
truck(s), trailer and machine.
MTLLC has agreed to adopt the Environmental Health & Safety Plan (EHASP) and
RIHASP plans set forth by RECON. The equipment that MTLLC will bring will be
decontaminated prior to arrival on site.
When the dewatering trench can no longer be utilized RECON will cut off protruding
piping six feet (6') below grade at each sump and cap the ends. RECON then will
backfill, level and grade area.