We dug a new bore well in our apartment complex. We encountered rock at 80 ft and a steel casing pipe of 6 inch dia was inserted upto 85 ft. Further drilling was done upto 410 ft. We touched the water source at 285 ft. The yield was estimated to be about 2.5 inch. The driller was paid after measurement.
After 3 weeks, for fixing pump, the depth was measured and unfortunately it was found to be stuck at 125 ft . Since no slush was found during drilling, the opinion is obstruction at 125 ft is not due to silting but may be due to a boulder or a splinter pushed by ground water pressure after drilling.
The driller says it is not his fault and offered to flush and put a screen pipe below casing pipe for full depth. The cost is almost the same as that of digging a borewell. We want a second opinion on this. Ours is a association and we are answerable for the extra cost.
We arranged a temporary pump and put it at 110 ft and pumped for 3 days to check the yield. We could pump for 10 hrs continuously and we measured discharge by filling a drum and got 2700 litres per hour, almost steady. At the end of 10 hrs the discharge dropped sharply. We presumed that the water level in the well must be reaching the pump level in 10 hrs of initial level (we have not measured level) probably 60 ft at the beginning of pumping. Even stopping the pumping for 2 hrs is recouping the discharge.
With this data we could infer the following:
1. The yield of the well is at least 2700 liters per hour and could be more if we lower the pump still further upto say 300 ft.
2. The obstruction at 125 ft is rock splinter because during 3 days of pumping we could not see any slush or muddy water.
3. Probability of any mud or stones falling in is not there since there is no annular gap between casing and ground bore and casing is MS hence could not have collapsed.
4. By flushing through air we can try to dislodge the splinter or we can ascertain that the silting from bottom has not taken place. But we have to spend money for this which can be avoided if we take the chance of going for rock flushing by drilling which will cost more money. We have to decide on alternatives.
5. By putting the pump at present tried 110 ft only which can still give the yield of 2700 liters per hour we can use for a couple of years.
I request your kind advice regarding the course of action that needs to be taken for optimum benefit. I would like to further add that this bore well was dug as back up for the existing one and we need not entirely depend on the yield of this alone. If it serves at least 50 percent of the requirement, it is enough.
Regards,