Water Well

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Water Well
We have boreholes that is required to supply water to a community. There are two wells almost 150 m apart. One well is performing really well while the other well has performed really bad. For instance the drawdown test for one well stabilizes at 58 m while the water level at the start of pumping is 50 m and the discharge rate is 32 l/s average. Now, the second well drawdown test shows that the water doesn't stabilizes and goes down to almost 176 m from 57 m at the start while the discharge rate is only 11 l/s. Can anyone please tell me is the second well sustainable if yes what is the sustainable or safe yield from this well?

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8 Answers

  1. Surely the flow source is blocked by rocks.You can either drill further down or make a new well further away from problematic well.

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  3. Due to the (reduced) yield of the wells in a well field, several wells are needed. The distance between two consecutive wells should be , in theory, two times the influence radius. As the latter can be very high and location of wells would induce significant construction and operation complications, it is necessary in most of the cases, to select a < 2xR, where a is the distance between two consecutive wells and R is the influence radius, therefore the infiltration curves can overlap, and the yield of each well decreases. For this reason, the number of wells must be increased by 20%.

  4. Dear you have not mentioned what type rock type you had tapped? Its seems like fracture aquifer i have seen similar cases within fractured aquifer. Also may i know type of drilling fluid used during drilling? Any way during pumping of of the productive well start monitoring the second and see are you getting any DD there or not. If its a fracture aquifer then the nonproductive well might missed the productive fracture system in that case getting sustainable yield wont be a possibility, you can try another DD test with a lesser flow and see if you are getting any stability in the DD, and form there you can drive a safe yield with lesser flow. If its because of drilling fluid use of bentonite as media then you might clogged the productive zones, in that case there are some chemical treatment is available and those are little difficult option considering drinking water well and another option is effective well development. Good luck 

  5. You have already got many answers, but very important issue is the distance between two wells, usually well should be at least 500 meters away from another, else while pumping cone of depression goes down and poorly installed well affected with low yield and extra drawdown. 

    If same pump using for two wells, the second was defenitly installed wrongly, could be filters placement were not in right layers. You can stop the good one for few hours and run only the bad performing one and observe what is going on, if it gives almost the similar result no doubt of installation fualt. 

  6. It depend of :1°) it physical caracteristics (size, hydrogéology), and 2°) Pumping duration. Any way, this second well is certainly fed by a reservoir of trapped water and under a low load which does not ensure a consequent rate of renewal when pumping. It is therefore not advisable to subject it to long-term energetic pumping (avoid including it in a major project). On the other hand, it could be used for village hydraulic with needs limited to domestic consumption.

  7. It is not unusual to see two identical wells perform differently on the same site. It sounds to me as though groundwater is being accessed via fissures and fractures within the wells and it may simply be that the more productive well penetrated more fractured ground, gaining greater flows, whilst the second well did not intercept as many productive fractures.

    In answer to your question regarding sustainability, this is answered by slowing the pump speed / controlling flow until the pumping water level  stays above the pump unit by perhaps 5m. A drawdown from 57m to 176m demonstrates that the second well is simply a poor producer. If you want to try and improve things, you could try and develop it - possibly with acid if its drilled through limestone. This can help enormously...Good luck

  8. i suggest you use the water tower method and stop wasting time.water tower can work anywhere and can serve more people per time period.from the whitewall wastecare services in sierra leone,uniwoca@gmail.com