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How to make wells clean following flooding

Brief project / assignment description: Small village with very poor road access (since bridge washed away). Main problem on rebuilding village is expected to be lack of clean water. All local wells contaminated by flood water. English church is sending approx £500 - £1000 to village where church member has family.

Full details of technical support request: How to make wells clean following flooding? What resources and skills are required? Should this be possible with locally available materials, or do we need to buy and send equipment from UK or buy in Accra?



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Suggest solutions need to be seen as

1) appropriate for dealing with immediate health risks 2) longer preventative solutions

Short term solutions probably consist of providing households with access to low tech/input solutions to disinfect potable water (10l/day/person) for immediate drinking, cooking and washing needs, such as domestic chlorination or UV sterilization using plastic bottles (not foolproof as this discussion illustrates ) together with promoting good hygiene practice. As well as giving households appropriate solutions, the wells/water sources will require disinfection using chlorine or similar chemical agents

Longer term solutions are the usual ones about protecting wells and bore holes from contamination from surface water, appropriate design and location of latrines and regular water testing


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EiE pages 252 and 253 are a good start. Reassuring users that water is safe again may also be an issue although almost certainly easier in case of flooding as here, rather than real or imaginary dead animal and human bodies as in say Kosovo. Reopening ceremony?


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Very basic process used in tsunami for saltwater pollution (recommended by the local Water Supply & Drainage board) and have seen similar in Cambodia for flooded wells

  1. clear the area around the well to remove debris, roots and
    even top fill that may contaminate ground water 2. put clean fill around top of well and compact in layers
  2. (a) pump out water to 50 or 60 percent of depth. (b) Bleach powder to clean well walls if lined (c) Take out loose mud and dirt from the well (d) allow well to recharge (e) Pump again to 50 or 60 % depth and allow to recharge 4. Repeat 3 if monitored quality not suitable 5. Before consumption use bleach powder to chlorinate - overnight (Please check but I think normal chlorine dose is about 0.1 to
    0.2 mg / litre)

Instead of a whole water testing set - cheaper and easier is I
think the spelling is "Haq's" kits - test for a single contaminant and is in an easy to use packet

Do not empty the well to its bottom Do not clean two or more wells close together at same time


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Excreta disposal in emergencies page 94 – 104 addresses these problems and is available on web at:


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Just a note of caution when pumping out dirty water from wells, assuming the strata are permeable (this will be the case if they are hand dug wells and may be the case if they are drilled). Make sure you discharge the water at some distance (several 10s of metres) from the well so as to avoid recirculation of contaminated water.


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Further to Tim Foster's message I would agree that Engineering in Emergencies (page 252 - 253) has some good information on this subject. It is also worth looking at Section 13.3.3 on disinfection. If Richard does not have this book with him in the field I could scan and send these pages but apparently I am not allowed to do this without the written permission of the publishers. Perhaps Toby could help with this if necessary.

Instead I attach a couple of pages from "Hand Dug Wells and their Construction" by S.B.Watt and W.E. Wood. This is also an IT Publications but in 1979 they did not put in the clause forbidding any reproduction.

While pumping out and disinfection will be needed after a flood. The effects of the disinfection will not last more than a few days. All open wells are prone to contamination and they should be protected with headworks that could include a cover slab or a raised wall to prevent water from running in. The surrounding area should be fenced and any potential contaminating activities such as clothes or personal washing or livestock watering should be removed from the immediate vicinity of the well.

One common source of contamination is people using their own buckets to draw water. These buckets are put down anywhere and pick up contamination. It is better to use a single bucket in the well which is tethered to stop it from being taken elsewhere. Better still is to use a hand pump, but only if the support facilities exist in the form of trained technicians and a supply chain for spare parts.

The costs of a simple disinfection would be low, chlorine should be available in some form in Accra and bleach would be available in most small towns/large villages in Ghana. If your project also wants to build headworks you will also need cement, reinforcing bars and aggregate, all of which should be available locally.

One important safety issue is that the exhaust fumes from any motorised dewatering pump must not be allowed to enter the well if people are working underground. There have been cases of people being asphyxiated and the same fate befalling people who try to rescue the first victims.


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This is not as bad as the tsunami affected wells as there is no question of the aquifer being contaminated with salt water. The wells should be cleaned out by physically removing any debris and sludge and then dewatering using a pump. Petrol driven pumps are most widely available but a submersible pump driven off a generator is even better. Dewatering by hand using buckets is a perfectly good option if the inflow is low enough and would certainly help to avoid potential problem #1 below. Two points to watch out for are: #1. there is a risk of destabilising the walls of the well if the dewatering draws the well down too far - a lot of wells in Sri Lanka were lost permanently for this reason #2. the contaminated water from within the well should be discharged far enough away from the well that it can not seep back in


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I attach two factsheets. The one on floods and water supplies may be of interest to Richard - although it does not say much about rehabilitation. He may be more interested in some of the papers presented at the WEDC conference in Sri Lanka that dealt with well rehabilitation after the tsunami (e.g. People can search the conferences by year (Sri Lanka was 2006) or by a keyword in the title at

If the quality of the well water can't be quickly rectified then the technical briefs on household-level treatment may also be of interest to Richard:,

The second file that I attach may be of interest to the earlier enquirer (whose name I have forgotten) who was interested in latrines in flooded areas.


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2014-01-20 10:43:00 -0500
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Jan 20 '14