Water well drilling report in Surin near Rattanaburi

I married a Thai woman from Baan Khok Kong, Nong Bua Ban, Rattanaburi District, Surin in the summer of 2019 in the USA. We will be living 6 months a year in the USA, and perhaps 3-4 months a year in Thailand.

We have begun building a house on her land, and the first thing we did was have a well drilled in November 2019. I'm sharing our experience in case it helps others. I had difficulty finding good information about well drilling.

First, here is what I discovered about the hydrology of Surin. Surin is a big flat sedimentary plain well-suited to growing one crop of rice a year. As there is little irrigation water available, no commercial crops are grown in the hot dry season from December to June. The soil is red clay. Salinity buildup in the soil due to fertilizer is a problem, compounded by the presence of rock salt layers in the soil.

Underlying the clay  deep down are layer(s) of gravel, starting at 30-35 meters deep or so. Before the upper clay sediment was deposited, field termites removed the sand grains from the gravel while working, leaving a porous layer. This is where you will find water.

We hired a local well driller who says he is 'the best in Surin'. He quoted 22,000 THB to drill a well up to 50 meters deep, including the upper casing, but not the pump or pipes.

He promptly drove up in a mid-size pickup with rustic drilling rig mounted in back. A small pool was dug nearby, and filled with water from a neighbor. The drilling tower was tipped up, and a carbide-tipped drill of about 20cm diameter was mounted. Drilling commenced by hand-crank starting the small diesel engine. A powerful stream of water forced through the drilling pipe flushed out the drilled dirt into the pond, where it settled. The pond served as a recirculating water supply.

3 meter pipe sections were added periodically. After going down about 12 meters, a 20cm PVC pipe was forced down the hole as a sleeve. Then a 10mm bit was inserted into the casing, and drilling continued. The hole from here on down was not cased. I hope this is sufficient casing to keep out surface water!

Around 35m deep, lots of small gravel began appearing in the upwelling water. The drillers stopped for the evening. Drilling continued the next morning to 40-45 meters. The well driller recommended not going any further, as in his experience, there was danger of hitting very salty water. So we stopped drilling, and the following day purchased a submersible pump at an agricultural supply store in nearby Rattanaburi. An American-made pump (Schaefer Legend by Ferguson) was recommended as more durable than the less expensive Chinese versions. In our case, at 40 meters deep, we were told that a 1 HP model was appropriate. The pump, pipe and supplies cost 16,000 THB. It includes a control box up in the pump house, where the starter capacitor is housed, so you can replace it without pulling the pump.

The well driller installed the pump at no extra charge, and started it up. It appears so far that our well can yield 5-6 liters per minute if pumping steadily, at least in the dry season. It could be more, we're still testing. Pump faster, and you can draw it down below the pump. As our 1 HP pump will pump 100 liters per minute, it would seem that a smaller pump would have been quite adequate. Oh, well. A smaller pump would use less electricity, but it's too late now. We're not a farm, and will just have 3 bedrooms and a small garden. This pump draws about 7 amps.

We will pump water up into a 1,050 liter tank at ground level, and then using a small automatic constant pressure pump to supply the house from the tank. We are storing grey water separately for irrigation, so one or two tankfuls a day should be plenty. We'll build a small pump house around the tank and house pump.

As they used detergent to clean out the well post-drilling, I have not tasted the water, so I have no idea if it is brackish (salty) yet. I probably will have a sample tested. I doubt that we'll use it as drinking water.

All in all, I'm glad to have a reliable independent source of water in Surin, and found the well driller competent and cost-effective. Is it cost-effective overall vs. buying water from the village? I don't know yet. I'll be happy to answer inquiries.

Our well system entails a submersible pump that lifts water up to a 1,050 liter tank at ground level.

From there, a little 'constant pressure' pump will supply the house and grounds with water on demand from the tank. Unlike systems common in the USA, there is no pressurized water tank.

In order to make all this work automatically, two 'float' controllers are needed. One is to turn the submersible pump off when the tank becomes full, and back on when it is not.

A second is needed to turn the 'constant pressure' pump off if the water in the tank falls too low.

These are opposite functions. I had a hard time explaining this to our local small town farm store where we bought the submersible pump. All they had was a 'drain' type sensor, which turns a pump on when the water in a tank is too high, and off when it gets low again.

We had to go into a bigger town (Surin) to a HomePro store (one of our favorites, with a very big selection) in order to find a controller that can do either, depending on how you wire it. So two of these, at 760 THB each, will do the job.

I'll have to mull over how to keep the submersible pump from cycling too much. What I want is for it to turn off when the tank is full, but not turn on again until it is only ⅓ full or less. What you don't want is for it to turn on repeatedly  for a short time when the tank drops to ⅞ full.

Correction: the submersible pump is made by Franklin Electric. Don't try calling them for technical support. They don't give it to homeowners. I tried calling to ask whether it was bad for the pump to continue running after the water level drops below the intake (which happens whenever it pumps the well level down). That is a second control issue I have not yet resolved.

I have found a solution for the control of my submersible pump. In short, the problem is that the 1 hp pump draws the water level in the well down in about 4 minutes, after pumping about 400 liters up to our 1000 liter tank.

Though we have a float valve to shut the pump off when the tank is full, something is required to prevent the pump from continuing to run dry indefinitely if the tank is not full. The well seems to recover in about an hour.

I ordered a Hunter X-Core XC2 irrigation controller from Lazada. In about a week it arrived. I also ordered a 24 volt coil Omron relay, and a 220 volt coil power control Omron relay that can control 10 amps 220v.

The Hunter controller has a very useful feature that allows you to set multiple start times, and
'cycle' and 'soak' intervals. (Whole programming is easy but complex. Write me if you need it)

The controller now turns on station 1 for 4 minutes once an hour. This turns on the 24v relay, which turns on the 220v relay. Then, if the tank is not full, the pump runs either for a full 4 minutes, or until the float valve turns the pump off at tank full time.

Sounds kind of kludgy, but it works smoothly. The Hunter controller retains its program memory and clock time during power outages and resumes when the power comes back on.

This meets our needs, as we are residential, not a farm, and 400 liters per hour is more than adequate. By having our own well, we are assured of a steady water supply even in a drought or storm situation.

When I have time, I will calculate how much our water cost is compared with the village supply.

My next task is to find out how to get our well water tested. Any suggestions?

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