The Video:

I thought this video was more interesting than some of the recent ones.  Hopefully you enjoy it also.

The Story:

I got there a bit early and got to sweeping off my newly poured concrete, but I was really doing some last minute thinking about where the well should go.  Factors to consider range from ease of hookup now, to constructing around it and eventually living with it.

The well drilling crew from Cribley Well Drilling arrived and we settled on a location they could access.  They actually wanted to put it about 10 or 15 feet out from the house, but it would have made it difficult later as I tried to get equipment and trucks around my house…  I had originally wanted it further around the side of the house (which is why the camera angle had been set up that way), but they didn’t think they could drive the truck over there because of the soft sand, and if they did, the well would have been too far from the building and in the way later.  Eventually, they agreed to get it as close as they could to the front of the house.  The main constraint was needing room for the large drill fluid recycling tank behind the well head.  The final location will end up behind a retaining wall, out of the way.

I dug to level the ground for this tank and they filled it with water from the second truck.

The drill bit was a 9 inch tricone bit.  As an engineer, I have worked on computer simulations for these for my companies “oil and gas” clients, so I know that these are designed for crushing rock and stone.  As the bit turns, the three roller “cones” rotate to break-up and scrape away rock.  Water is pumped in thru the shaft, both to cool the bit and to push the debris out the hole.  You can find an animation here…  It was definitely overkill for drilling in my soft sand, but it got the job done.

They started things off without water, just to locate the hole…  But then they pulled the bit up again and added a spout collar to direct the drill fluid (water with a bit of bentonite clay mixed in) into the recycle tank.  Sand and gravel settles out in the first section of the tank and the cleaner water/clay mixture flows over to the other end of the tank where a hose sucks it back into the truck and thru the drill shaft and down into the well again.  If they didn’t recycle the water, it would take a large swimming pool worth and would make a huge mess.  Every now and then they would need to dig (or dump) the sediment out of the tank.

After they drill the first piece (with the bit on the end) in to the ground, it is time to add an extension to the shaft.  The $600,000 Versa-Drill rig is designed and built for streamlining this task.

It comes equipped with two hydraulically activated wrenches.  First, the one at the bottom comes out of the back of the truck to hold the lower portion of the shaft still.  The operator runs the drill backwards for a moment to loosen the end piece and then pulls back the “wrench”.

Then they raise the drill up to the top of the mast.  The rig also has a carousel with 15 extensions (capable of drilling 300 ft with what they brought, but they can bring additional shafts if necessary). The carousel rotates the next 20ft shaft section into position and the rig screws its self in loosely.  The second hydraulically operated “wrench” moves into place to hold the new shaft section still while the drill tightens into it.  Then the new shaft is moved into place above the previous piece.

The lower end is threaded in with the shaft below it held in place by the lower hydraulic wrench… and the rig can drill the next 20 ft down.  This process was repeated 20ft at a time, over and over. See the video.

On my site, it was nothing but sand for the first 116 ft.   Then they hit gravel and it made a lot of noise…  Enough to bring me out of my mobile office to see what was going on.  That layer only lasted about 4 ft and they were back to sand.  My neighbor, who lives higher on the hill, came to check it out and told us that he hit water after only 117 ft.  Actually, the same guy who drilled my well had also done the neighbors, but with an older version of the drill rig.  He said that the water table is definitely not flat.

My well didn’t reach “water bearing fines” until about 185 ft…  At nearly 16$ per ft, just for drilling, that difference adds up. The guys from Cribley joked that they wanted to drill further to help pay off their new six hundred thousand dollar rig (yes, he mentioned that price several times and that Obama was letting him write it all off in one year)…  But they stopped at 186ft.

The Versa-Drill V-100NG drilling rig comes equipped with 500/200 air, 3×4 centrifugal mud pump, 15 rod carousel (3½” x 20″, 9GPM water injection, built in 2″ Bowie grouter, 12K winches with job booms, hose reel, and mounted on a 2014 Peterbilt 340 6×6.

 

With the water table reached, they began the process of pulling out the drill, piece by piece, back on to the carousel.  It was pretty much the inverse of the previous process, but went much more quickly.

The next step was inserting PVC casing into the well to keep it from collapsing.  The first piece, the well intake, was special with perforations to let the water in…  The rest were just 6” PVC tubes.  They glued one into the next and lowered it down, repeat.

Since the 6 inch tubes were dropped into a 9 inch hole, there was still some space around the outside.  Leaving this open would let sand fall down the gap and clog the well tip.  To prevent this, they inserted a flexible 1” white tube into that space.  Like before, they put down 20′ at a time and just pushed (without glue) one section into the next.  They pushed it down to just above the water bearing layer.  Actually, they did it so fast, the time-lapse camera didn’t really catch it.  Once it was ready to go, they started mixing bentonite clay into a slurry and pumping it down into the well (at 35$ per bag, you can count them in the video, I didn’t want to).  As they did so, they pulled up the white tube.  This effectively filled the gap around the pipe with clay that would hold the pipe in place without letting water flow around it or sand get down into the water bearing fines…

Done drilling, it was time to clean up the equipment and pack up…

Overall, they ended up digging nearly 40% deeper than the 135ft that I had estimated.  That increased my cost a couple thousand dollars over the initial estimate (but they have not set the bill yet and it has been over a month). On the plus side, they estimated my well was producing about 50 gallons per minute, which is quite a bit more than the 18 g/m pump that I planned to install.  That means I will have more water than I need, which is a good thing.  Pumping well water is also much cheaper than city water.  At current electric rates, I will pay about 25¢ per 1000 gallons.  My current rate for city water/sewer is about ~8$/thousand gallons.  If we used the 400 gallons per day that the standard American family uses, the well drilling should pay itself off in a little over 5 years.  That swells to 16 years if I include paying off the septic field (which also went about 30% over budget).

 

They will send a different crew to dig a trench and run water pipes to my mechanical room.  A third crew will eventually install the pump and pressure tank after my mechanical room floor is poured. That will need to wait for spring.

The Mistakes:

I don’t know if I made any here yet.  It probably helped that I had experts do the actual work.  But if I find out about any later, I will come back and add it here.  ;^)

The only think I can think of was that after the job was over, there was a lot of bentonite laying on the ground in the area…  It holds the water well and stayed annoyingly squishy for days after the rain passed.  I knew it would be a drainage barrier, so I didn’t want to bury it in place…  Instead I decided to spread it out (with the skid-steer), thinking that might even improve the properties of my surrounding sand…  However, a little of that stuff goes a long way and even spread out, it just made the sand squishy and more difficult to deal with.  I should have just scooped it all up and saved it for later.