The next technique for drilling in sand
involves using bentonite to hold the hole open. As we have already
seen, sand will quickly collapse on your drillpipe when drilling in
sand. When the drilling fluid contains dissolved bentonite it
creates a coating on the inside of the hole that keeps the sand from
collapsing, thereby holding the hole open.
It is absolutely critical that the
bentonite be thoroughly mixed with water before using. If you
haven't already done it, please review the page "Drilling Deeper with
BENTONITE" before going further
You can either use the modified drill
head shown below for adding bentonite or use the mud pump system.
Drillhead with valve on top for
Keep in mind that while bentonite helps
while you are drilling, it hurts when you start to pump the well.
The bentonite cake or coating keeps water away from the inside of the
hole and the well screen. It works against you when you start to
pump the well because it keeps water out of the hole. So, the
trick is to use enough to hold the hole open but not so much that you
seal the hole completely so no water from the surrounding sand can get
As information - later when you start
pumping the well, it is common for well production to start slowly and
improve as the flow of fresh water into the hole weakens the bentonite
My suggestion for the drillers using two
hoses as drilling fluid is to use plenty of bentonite as you are
drilling and then quit just before you get to depth.
For example, say you have a 10 foot
standing water level and your plan is to dig a 30 foot hole and put a
four foot well screen at the bottom. Use a two inch drillpipe.
Use plenty of bentonite for the first 25 feet. Then for the last
five feet don't use any bentonite. Just drill with pure water.
Even with the sand collapsing you will be able to drill a five foot hole
with no bentonite.
Then, while the water is still running
make up your well screen piece. Attach your four foot long 1.25
inch diameter well screen to about 27 feet of 1.25 inch PVC. This
will give you a 31 foot long well screen piece. Perfect for your
30 foot hole.
Make sure you have some help for this
Next, turn off the water supply from the
two hoses. Then, quickly:
1. Remove the drill head from the
two inch drill pipe.
2. Put the 1.25 inch well screen
pipe down through the two inch drillpipe.
3. Once the well screen pipe is in
place, pull the two inch drillpipe up and out of the ground. Be
sure and pull it straight up for the first ten feet so the well screen
pipe will not be pulled up with it. After that, the sand should
collapse on the bottom of the well screen pipe and hold it in place
while you remove the two inch pipe.
Pull the two inch pipe completely out of
the ground. You can re-use it on the next well you drill.
The remaining 1.25 inch PVC well screen piece is your well.
Hopefully about a foot of it will be sticking out of the ground.
Attach a pump and start pumping the well.
If you can arrange it, it is best to
attach a trash pump or a temporary pump when you first pump the well.
New wells typically produce sandy water and the sand will eat up the
plastic impeller in a pump. If you can pump out the sandy water
with a sacrificial pump or a mud pump, then your permanent pump will
both last longer and work better.
IF THE PIPE STICKS...
OK, so you were happily drilling away
and you were almost there and maybe you took a break, or the phone rang,
or whatever and the pipe stuck. You've got a nice deep hole with a
stuck pipe. You know you are in water because several days later
water is still standing in that two inch pipe.
Wait! Stop! Don't jump!
Crawl back in off the ledge of the basement window. You can still
use that hole.
If you want to get the pipe out of the
hole, please check out the page, "When the pipe sticks..."
If you want to use the pipe as it is, There are two techniques:
1st stuck pipe technique:
Attach your water supply to a 1.25 inch pipe. You can usually
adapt your two inch drillhead to the smaller pipe. Use the 1.25
inch drillpipe inside the stuck two inch drillpipe to drill the hole way
past the bottom of the stuck pipe. Use a little bentonite.
While you are doing this, it is usually a good idea to attach a two inch
Tee to the top of your stuck two inch pipe so the cuttings will be
directed to the side.
Once you get to the depth you want to
set your well screen, keep the water water running while you make up
your wellscreen pipe. I know this is wasteful of 1.25 inch PVC but
there is no way around it. Make up a 1.25 inch well screen pipe
with a three or four foot long piece of 1.25 inch diameter well screen
at the bottom and 1.25 inch diameter PVC above that.
Then similar to the protocol described
Turn off the water supply from the two
hoses. Then, really quickly:
1. Remove the drill head from the
1.25 inch drill pipe.
2. Pull the 1.25 inch drill pipe
out of the stuck two inch drillpipe ground and put the the 1.25 inch
well screen pipe back down down through the two inch drillpipe.
The idea is to take the drill pipe out
of the hole and then put the well screen pipe back down before the sand
collapses. It is likely you won't get quite as much back down as
you took out.
Sealing the well - After you finish and
have your well producing like you want it, you'll need to fill that two
inch pipe with bentonite or cement to keep groundwater out of your well.
2nd stuck pipe technique:
Simply use your stuck two inch pipe as a head start for a drive