DIY wellpoints

I my previous posts, I wrote about collecting rain water in a tank, and using that to flush the toilet in the house.  But what about when it when its not raining?  Would it be possible to extract water from the ground? I live in an area where the water table is quite shallow, so how hard could it be?

I started with 3m of 110mm pipe, and cut some small ‘teeth’ into the edge of one end.  I also drilled out lots of small holes over about half a meter of the same end.  Choosing a spot near the tank, I dug a shallow hole with a spade to get started, and jammed the 110mm pipe into the sand.

At first it was easy to twist and push deeper into the sand.  When it got stiffer, I lowered a hosepipe down the inside the pipe.  That loosened things up a bit, and soon filled up the pipe, pushing out muddy and sandy water.

It got stiffer and stiffer the deeper it went. It was easy to get it stuck, and I found out that hitting it down with rubber hammer was a sure way to jam it.  I drilled a hole in the top of the 110mm pipe, and put a section of 12mm round bar through it, padded with some irrigation pipe.  That made a handle that allowed the pipe to be twisted with a lot of force.
I found water at only 2m deep.  That doesn’t mean I could pump water up from there, because the water takes time to seep through the sand it is in, and pumping water out creates a ‘dimple’ in the water table, as shown here.

Once through the first layer of sand, I hit some darker soil, and then a layer of white clay.  When it wouldn’t go deeper, I disconnected the backwash pipe of the pool pump, and connected it to a 90 degree bend, and a long section of 40mm PVC pipe.  Turning on the pool pump briefly blasted the inside of the 110m pipe clear, and allowed it to be pushed deeper..

When most of the 2m pipe was in the ground I let the hole drain and settle for a day, and then carefully twisted and lifted the 110mm pipe.

When it became impossible to go deeper, I cut some 20mm re-bar to have a point at one end, and lower this into the pipe.  By lifting it and letting it drop, it was possible to smash through some hard layers.  The 50mm pipe with a hose pipe pushing water down it washed out the debris after doing that.

When the 3m pipe was level with the ground, I prepared a sieve, using some 50mm thick walled pipe, a plug, and a 16mm to 40mm adaptor.  The slits were cut with a hacksaw, and the holes drilled out to 3mm.

After flushing out a bit more soil from below the base of the 3m pipe, I poured in same small drainage stones, about 5mm size, lowered the sieve attached to a length of 15mm irrigation pipe until the tip was about 3.5m below ground, and poured in more stone.  I hoped the stone would surround the sieve, and form a permeable collection area. When the sieve was definitely covered by stone, I added some coarse sand, and when the hole was filled to about 2.5m, a layer of clay as an air barrier.  The rest was filled with a mixture of clay and sand.

I repeated the process, with some variation, to make two more wellpoint holes.  I used a 50mm PVC pipe to make the hole, which was much faster than using the 110mm pipe.  To flush it out, a 40mm PVC pipe fitted down the 50mm pipe, and was very effective in flushing out sand and soil.  It was also useful putting a 45 degree T-piece on the top of the 40mm pipe, with a short section to allow the sandy and muddy water to be directed away from the hole (the hose pipe would go into the top, as pictured). The 20mm re-bar came in handy again when I got to hard layers.
These two holes where shallower, and one of the the collection pipes ended up at about 2.5m, and the other at about 3.6m down.  I went right down to 5.4m, by first using a 3m length of 50mm pipe, and when it was almost fully underground, allowing it to drain and dry overnight, then carefully twisting and lifting it out.  I was surprised that the hole did not collapse when doing that.

From the experience of sinking the holes, I found that below a thin layer of top soil, there was about 2m of soft sand, followed by a thin later of hard clay, followed by about a meter of more soft sand.  At around 3.5m down I hit a very hard chalky layer, which continued to about 5m below ground level.  At 5m there seemed to a hard yellowish layer, and the water I flushed it with came out creamy yellowish, and slightly acidic, in that it stung a small cut I had on my hand.  At about 5.5m below ground, there was a totally solid layer that the 20mm rebar just bounced off without penetrating at all.  Perhaps a geologist reading this can try and guess what all those layers were?

The sieve arrangement used above did not fit inside the 50mm pipe, so instead I bought a small stainless steel sieve.  An adaptor screwed into that, and into a length of irrigation pipe.  For one hole I used 12mm pipe, and 15mm for the other.  It seemed that the 12mm pipe would hold a lower volume of water, and so be less weight for the pump to lift.  Also, at the low flow rates I expected, a thicker pipe would not have any advantage.  It would be interesting to test this somehow, but for now its just conjecture.

Next step was to somehow connect these three pipes from the wellpoints to the pump.  How hard could it be?