What to do to rehabilitate or upgrade existing wells?
I’m working in an area with lots of existing wells, some of them being used and others not any more. I’m not sure of which elements on the well I should check to estimate the works to be done or to decide if it would cheaper to rehabilitate an existing well or to dig a new one.
William hit the nail directly on the head. One additional concept is that some improvement is better than none. We have different conditions in highland Guatemala. Drilled wells may be more sustainable and less costly than any hand dug well. Residents are not likely to abandon their hand dug wells which could contaminate drilled well. If you have a plentiful, shallow acquirer, electricity and a local NGO, most any drilled well will be an improvement over a hand dug well.
The best way for you to estimate the works to be done on the existing well is to identify the potential sources of pollution and to assess the soil conditions, knowing that the rehabilitated well should be safe from contamination and should provide the required quantity of water to the users.
Firstly, if you have access to a portable water quality tester, you could check some basic water quality parameters, to identify potential sources of pollution or even to check some toxic parameters. For example in Zimbabwe, we knew that many aquifers were contaminated with high level of fluoride and that there is not so much to do. We systematically checked this parameter and excluded some wells and boreholes with high fluoride levels from our campaign. Again, in Zimbabwe we were also checking E.Coli to evaluate the faecal contamination of ground water and nitrates/nitrites to make sure that the surrounding fields where farmers were using fertilizers were not affecting the water quality.
Then, check the possible routes of contamination and which technical solution you could think:
- Surface pollution > Improve the slab, wellhead, apron, sanitary seal and drainage channel
- Contamination by rope and bucket > Propose another water lifting device (idealistically available locally)
- Contamination by surroundings of the well > Erect a fence around the water point
- Infiltration of polluted surface or underground water > Improve the environment and prevent pollutions (location of the latrines, of the dumping areas, of the fields, etc.)
Discuss with the well’s users, the water committee (if there’s any) and people living near the well to know more about the behaviour of the well (i.e. fluctuations of water level) and to sensitise them on the risks of contamination.
Then, you may need to improve the lining of the well, rehabilitating/repairing the existing one or constructing a new one. You’ll need to evaluate it properly, because in some cases, for example if you need to destroy the existing lining, over-dig the well and erect a new line, it may worth constructing a new well.
For instance, in Zimbabwe, we did the rehabilitation of traditional wells, in a granitic area, so in a very stable ground (fracture zone). In this case, we had to use explosive to over-dig the existing wells and to increase the yield and we did a bottom-up lining, the concrete rings being casted directly inside the well.
In DRC, we had to rehabilitate lined and non-lined wells, in an area with unstable ground. In some cases, we were just abandoning the existing well and decided to dig a new one. We were looking at several parameters:
- The diameter of the existing well: if the well was smaller than our pre-casted concrete rings, we had to re-bore it before lining it as any other kind of well. If the diameter was bigger than our rings, good for us, we could directly lining it, bottom-up.
- State of the existing lining: if there was an existing lining, and if it was in a ...
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