Soon I will start the 4th time to drill a water well here in the Philippines and this time I want to make sure that it is done as correctly as possible.
The last one has been flooded by a typhoon on Dec 25th just one day before putting the casing and the first 2 trials have been technical disasters - the very first was too shallow and the second had a casing diameter of 1.5 Inch. The yield is horrible not only because of that the diameter also because of how the Filipino drillers prepare the pipes.

The bottom is open and for about half of the depth of the well they drill a couple of holes into the PVC casing. I gave them a picture and instructions to prepare a well screen at the bottom (using a hacksaw) but they did not follow this guidance. Thus I stopped them and that's why they could not finish on Dec 24th and so the flood could destroy the well on Dec 25th.
I asked them why they drilled the holes everywhere into the casing and the response was, that they don't really know where the water is and thus they drill holes everywhere such that there is water for sure. Well ....

Here the pre-conditions:

1. I have a Goulds GS2515 submersible pump with a Franklin Motor.
2. I have chosen a 6 Inch PVC casing for the well.
3. I have ordered a sanitary well seal and a Rubber Torque Arrestor on Amazon / Ebay.
4. I will be using a cycle stop valve and a small pressure tank for the provisioning of the water.
5. There will be a set of filters in the flow after the pressure pump with automatic backwashing.
6. Backfilling with gravel / sanitary seal will most likely not be possible given the technique used for drilling . I will talk with the drillers about this.
7. The water table is at about 15 feet.
8. The objective is to dig 70 feet deep - there are many successful installations nearby at about 70 - 80 feet. But this needs to be taken with caution given the "holes everywhere" technique here. The yields seem to be very good. The driller can't do more.
9. My objective would be to get at least 10 GPM yield from the well. My estimate is that I need about 1000 Gallons per day (we are constructing a restaurant / bar).
10. I need clean and partially potable water (espresso machine, ice maker, etc.).
11. The very first well was only 40 feet deep and the water contained E.Coli - that's why I wanted to get to the second aquifer. And I am sure now that there were holes almost up to the water table in the casing of that well.

And here my questions:

1. Well Screen: My plan is to cut slots into the PVC casing at the bottom for about 8 feet. 3 slots of 8 cm horizontally and this every 1 cm vertically. This will provide a well screen with about 750 slots. We will use a hacksaw for cutting the slots. Does this sound reasonable?
2. Well bottom: Should this be open or closed with a cap? If open then should I "throw" some gravel into the open casing? How can I prepare the bottom?
3. Contamination: Well number 3 has been flooded and has collapsed and so the water is presumably contaminated up to 70 feet. What would be the recommendation in respect to the preparation and positioning of well number 4? Shock Chlorination? Recommended distance from the well number 3? There is a river nearby and so should the new well be further away from the river?
4. Is there a technique to figure out where the 2nd aquifer starts and whether I am indeed in this second aquifer at 70 feet? I will instruct them to test the soil each meter such that we understand the layers of sand / clay, etc.

Great thanks for any help I can get!