How to Dig A Water Well for a Milkfish (Bangus) Pond

How to Dig a Water Well for a Milkfish (Bangus) Pond
 
In our farm, we have an old hand pump that draws fresh water from a relatively shallow well. We use it to water plants, wash colored clothes, clean pond implements (like drums, pails, basins, nets) and transport vehicles, clean fish for cooking, bathe pigs, pet dogs, etc.

For drinking water, the local water company supplies it.

Last week, we needed to dig another well. A deeper one.

This time, we dug a deeper well (more than 20 feet) and inserted a 4-inch diameter PVC pipe casing.

For what purpose? To draw not fresh water, but salty water for our bangus pond.

Without salinity, we know from experience that stocking bangus fry (especially the younger ones, about a week old) will not be possible. They’ll just simply die. So the pond must be slightly saline or brackish. Same with vannamei prawn post larvae.

Note: the local wild fry can survive in fresh water, but not the imported “Indonesian wild” fry (more easily available from direct importers).

It’s only January and our grow-out pond was drained and ready to be stocked.

But we still have no pond water of suitable salinity. During previous years, we just depended on the opening of the village canal during the dry season months of April/May which provides brackish water once a year to our close-system ponds.

What to do? We have four options: (a) apply rock salt to the pond, (b) let the pond go idle and wait for the opening of the brackish water canals - but this will happen only in April or May of each year, (c) buy the local wild milkfish ("bangus") fry which tolerate fresh water – downside is we can’t grow prawns in unsalted water, or (d) dig a water well to draw saline water from below the ground.

We chose option D for its long-term benefit. There’s initial cost for materials and labor (including cost of diesel-powered water pump if you don't have one yet), but after that we’ll have a ready source of saline water for the pond. With salty water, we’ll be assured of good survival rate for bangus fry as well as vannamei post larvae every year.

Following are the procedures on how we dug a water well as a source of salty water for the pond:

1. Buy the following materials for the water well:

a. 2 pcs. PVC pipe, 4 inch diameter and 10 feet per pipe (Note: total length of pipe would be 25 feet, but I have an extra 4 feet pipe on hand)

b. PVC elbow

c. PVC pipe cement

 

PVC pipes, elbow, pipe cement

d. Diesoline for the water pump

Note: Why go down 20 to 25 feet? I have no idea, except that my technician told me that based on their experience digging water wells, if they dig up to 20-25 feet in ponds in Binmaley, Pangasinan, northern Philippines (which is near the Lingayen Gulf) they are able to tap salty water. If they dig to a shallower well, they get fresh water.

Our regular fresh water well is only 10 feet deep and it’s able to draw fresh water.

Maybe, there’s a second aquifer (salty) below the first one (fresh). That’s only my layman's personal opinion.

Anyway, let’s carry on.

2. Make sure the following items are available in the farm:

a. Strips of rubber cut from old bicycle inner tubes

b . Water pump – preferably diesel (cheaper than gasoline), this will be used for drawing well water after the well is dug up

An old but still workable diesel-powered water pump

c. Water pump flexible hoses and clips

d. Metal drilling pipe, 12 feet, 1.5 inch diameter (provided by the 4-man crew, who are also my pond workers)

 

A 12-foot metal drilling pipe

e. Drilling water pump with matching narrower flexible hoses 15 feet long (provided by the drilling crew to be used when digging the well)

Note: Later, you need to buy the diesel-powered water pump and flexible hoses, if you don’t have one already, to pump out the water from the water well.

3. Get a foot-long piece of tree branch 4 inches in diameter; sharpen one end and insert the other end inside the 4 inch diameter PVC pipe. Fasten with nail at opposite sides to keep the sharpened wood stake in place.

 

See pointed wooden end attached to PVC pipe

4. Build a fire using firewood and tinder (small twigs and dry leaves). Put the boring metal (rod) in the middle of the fire to make it hot.

Boring metal rods made hot by fire from burning firewood and coals

5. Using the hot rod, bore a total of 75 holes (15 holes along the length of a 2 foot-line from the bottom of the pipe; repeat for a total of 5 parallel lines around the PVC pipe). See above photo in Step 3.

6. Cover the holes with a net, wrapping it around the bottom part of the PVC pipe. Secure with string. Also tie the net down to the pipe with rubber strips.

This will prevent entry of sand and earth materials into the pipe while letting in water during pumping operation.

Bottom part of PVC pipe with holes being covered by net

Securing the net by tying strings and reinforcing with rubber strips

7. Connect another 10 foot PVC pipe to the first one using PVC pipe cement (making the total length 20 feet). 

Note: in our case we connected an extra 4-foot long PVC pipe to extend total length to 24 feet.

8. Dig a foot deep hole in the exact spot in the pond where the well will be dug up.

Note: In our case, we already have an existing borehole which is 10 feet deep. (There's a 10-foot metal pipe casing inside the hole, so we lifted it up and transferred it to another location). Afterwards, we just had to deepen the borehole from 10 feet to 24 feet.

An existing inactive 10-foot borehole or well with an old metal pipe still inserted (top part is covered by plastic)

Lifting the existing metal pipe casing from our inactive 10-foot well, before digging deeper up to 24 feet.

But for those building a new well, don’t worry. The technique and procedure used in digging the well is the same whether one is starting from a foot-deep hole or from a 10-footer hole.

9. Set up the diesel water pump and attach the inlet pipe to a flexible hose. Tie down one end of the hose in the pond so it can draw pond water.

Setting up the water pump (this is shown in Step 2) and tying down the inlet hose to the bottom of the pond to draw water into the hole

Note: Later the digging crew discovered that they can't connect a narrow hose to the 4-inch outlet valve of the pump (which should connect to the 1.5 inch diameter metal digging pipe). So they had to use another water pump (see below).

A replacement water pump used for digging the well (it has a narrower flexible hose that can connect to the metal digging pipe)

10. Attach a 15-foot flexible hose to the outlet pipe of the water pump (see photo above). Wrap rubber strips around the joint to prevent air leaks.

11. Attach the 15-foot hose to the metal drilling pipe; wrap rubber strips around the joint (see photo above).

12. Start the water pump and prime the water pump with water.

13. Insert the 12-foot metal drilling pipe into the existing borehole.

Note: The water pump creates water pressure into the hole. This technique of digging is referred to as jetting. It’s the water pressure or jet that erodes the bottom materials of the borehole or loosens the sediments. Eroded sand and other particles at the bottom are forced out by water pressure to the side of the digging pipe and up into the surface. 

It only works for soft, sandy, fine-grained sediments as those found in fish ponds. Other materials like gravel are too heavy to be lifted by the return flow of pumped water under this technique.

Pumping water from the pond to the metal drilling pipe and flexible hose into the well; water jet creates pressure and erodes or loosens the material at the bottom of the well to gradually deepen it

14. Continue pumping in water into the borehole using an up and down motion. 

Water jetting process being continued by inserting the metal drilling pipe/hose through which water is being pumped into the well (up and down motion)

15. When borehole is deep enough, insert the PVC pipe to serve as well casing.

Trying out the PVC pipe if well or borehole is already deep enough (from the photo, well needs to be dug deeper)

16. If borehole depth is not yet sufficient and well needs additional depth, insert drilling pipe (with water jet) between borehole and pipe (that is, outside the pipe but inside the well).

Digging further to deepen the well; jet stream being pumped through the metal pipe goes into the well but outside the PVC pipe

This will loosen the sand and earth materials between the side of the borehole and the PVC pipe and allow pushing the pipe down some more.

17. Afterwards, insert the metal drilling pipe (with water jet) into the PVC pipe itself so that water jetting is done from inside the pipe down to the bottom.

Metal drilling pipe and flexible hose carrying the pumped water being inserted into the PVC pipe itself

18. Push down the PVC pipe until the required depth and clearance above ground is reached.

PVC pipe pushed down by the digging crew until the required clearance from ground level is reached

19. Attach an elbow to the 4–inch diameter PVC pipe.

A PVC elbow was attached to the upper end of PVC pipe; a 4-inch flexible hose going to the water pump is attached to the elbow

20. Attach a flexible hose to the elbow (see photo above). Wrap rubber strips around the joint.

21. Detach the drilling water pump used in drilling and install the water well pump to be used to draw out water.

Our old diesel-powered water pump now reinstalled in place; will be used to pump out salty water into the pond using 4-inch flexible hoses

Note: the drilling water pump is the equipment provided by the drilling crew, while the water well pump (diesel-operated) is ours.

The difference is that the drilling water pump has a smaller diameter hose that can be attached to the 1.5 inch diameter metal drilling pipe, while ours has only 4 inch diameter flexible hoses.

22. Inspect all joints to make sure that the water pump is sealed by rubber strips at the joints (no air leakage). Start the pump and prime with water.

23. Continue running the water pump until saline water starts to come out.

Our water pump now pumping out well water (of suitable salinity) from the newly dug 24-foot well into the pond

Note: Initially, fresh water is pumped out but after a while slightly salty water comes out. As the pumping continues, salinity reading improves. Our target is only 7 to 10 ppt (parts per thousand)(range we think is conducive to bangus fry growth; ours is the bigger fry – we avoided buying the young fry this year).

A FAO study shows that bangus larvae which are 7 days old are very sensitive to salinity, tolerating only 16 to 20 ppt. In contrast, 21 day old fry can tolerate much lower (near zero) or even very salty water (70 ppt). The typical fry used to stock a pond measure 10 mm to 17 mm and are around 2 to 3 weeks old (14 days to 21 days old).

Lesson for fry buyers – buy the bigger fry if they’re available to have a higher survival rate for the batch you’re stocking in your pond (more tolerant of stress and salinity changes).

Please see the related 2-part Youtube videos below. Thanks for watching guys!
 
 


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