Repairing, Cleaning and Disinfecting Hand Dug Wells | Bleach

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Hand dug wells may need repairing, cleaning and disinfecting after inundation by flood water, inundation of seawater as in the case of a tsunami, materials entering as the result of mudslides or as a result of hurricanes, or simply after long periods of limited maintenance or neglect. If work has been undertaken on the well to try to increase its yield through, widening or lining the well, then cleaning and / or disinfection will also be appropriate. This Technical Brief identifies the process for repairing, cleaning and disinfecting hand dug wells and also discusses the OXFAM kits which can be used for these processes.
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  Repairing, cleaning and disinfecting hand dug wells Hand dug wells may need repairing, cleaning and disinfecting after inundation by flood water, inundation of seawater as in the case of a tsunami, materials entering as the result of mudslides or as a result of hurricanes, or simply after long periods of limited maintenance or neglect. If work has been undertaken on the well to try to increase its yield through, widening or lining the well, then cleaning and / or disinfection will also be appropriate. This Technical Brief identifies the process for repairing, cleaning and disinfecting hand dug wells and also discusses the OXFAM kits which can be used for these processes. Hand dug wells Hand dug wells can come in many forms, from simple holes in the ground with limited protection, to covered wells with a handpump for extracting the water. It is important when rehabilitating wells or cleaning and disinfecting them that wherever possible, the source of contamination will be prevented from re-entering the well. If the cause of contamination was an unusual event such as a flood, the process of cleaning and disinfection may be enough. Care should also be taken to ensure that the headwalls, drainage curtain and any protective covers are in good condition to prevent the well becoming contaminated again from every day, non-disaster related routes. Repairing, cleaning and disinfecting wells Steps to repair, clean and disinfect hand dug wells 1.Determine the history of the well from the users –how deep it was srcinally, what was the previousyield of the well versus the current yield of the welletc.2.Determine the equipment need to empty, repair,clean, disinfect and dewater the well, including theitems required to ensure the safety of workers.3.Undertake any repairs to the headwalls, drainagecurtain, sanitary seal, cover and liftingmechanisms, which are possible before emptyingand / or disinfecting the well.4.Empty the contents of the well – water, sludge anddebris.5.Repair damage to the inside of the well - deepen,undertake localised repairs to the well lining, oradd a lining depending on the need.6.Clean the walls of the well using a 200 mg/l chlorinesolution and long handled broom.7.Disinfect the water in the well with a 50 – 100 mg/lchlorine dosage (depending on the level of contamination), and leave for a minimum of 30minutes.8.Dewater the well and allow it to fully recharge.9.After recharge check the chlorine residual in the water.10.Where necessary repeat the process of dewateringand recharging the well until, the chlorine level hasreduced to 0.5mg/l or below.11.Make any final repairs to the well cover and waterlifting mechanism. Safety Care must be taken when working around or inside of wells. Risks when repairing and maintaining wells a)Poisonous gases, particularly carbon monoxide, canenter the well from diesel or petrol engines poweringpumps.b)Inhaling chlorine gases when cleaning the walls of thewell. Wherever possible the walls of the well should becleaned from the surface using a long handled brush.c)Incoming water filling up the well and a person insidenot being able to exit the well quickly enough.d)Items falling into the well from the surface or collapseof the well walls if not lined or protected.e)People falling into the well from the surface if the welldoes not have a headwall or other protection.f)Faulty equipment such as ladders, ropes, tripods,hooks, buckets. OXFAM Technical Briefs – Repairing, cleaning and disinfecting hand dug wells 1  Health & safety good practice 1.Under no circumstances must a diesel or petrolpowered pump or its associated engine be loweredinto a well and their gases must be diverted awayfrom the well even when they at ground level. Thisis essential as carbon monoxide is heavier than airand can sink to the lowest level. This could causeasphyxiation and death to the workers inside thewell. Many people have died inside wells fromcarbon monoxide poisoning.2.People involved in well repair, cleaning anddisinfection should be fully trained on the risks andgood health and safety practice.3.Use a well tripod or other locally developedstructure to facilitate safe entry to and exit fromthe well for the people removing debris or repairinginside the well. This is particularly useful for deeperwells.4. 5. hould be kept clear of objects 6. The working area should be fenced, a kerb constructed (of there is no headwall), and at least 2m around the well swhich could fall in. Keep a reliable person on top of the well at all times when people are in the well to operate the ladders. 8. twigs/branches can help to clear then hygienic r and can also be used to desludge pit latrines. winch system. Secure any 7.Keep the well ventilated.No smoking, matches, or naked lights except foruse to test the air by lowering a lighted candle intothe well prior to entry. If the flame extinguishesthen do not enter the well. Lowering and raising alarge brush of air in a well. Repair / improve structures Consider potential contamination routes to the well and make any appropriate repairs to the headwalls, sanitary seal, drainage curtain, cover, lifting mechanism and fencing, to ensure that the well will remaiafter cleaning and disinfecting the well. Removing dirty water and sludge Hurricanes, floods and other natural disasters can leave wells filled with sludge and other debris. These wells will require specialised pumps to remove the sludge and debris as normal dewatering pumps will quickly become damaged. OXFAM has a portable desludging / dewatering pump kit (see box) which can dewater wells to a depth of about 15m. It can cope with solids up to 50mm in diameteWhen well depths aredeeper than 15m, two of these pumps can beattached in series to reacha maximum depth of about35m. Submersible dewatering / desludging pump with generator, Code WSDP/6 Submersible dewatering / desludging pump with generator – OXFAM Code WSDP/6 ã Lightweight electrical dewatering pump kit for handlingheavily contaminated water with solids up to 50 mm indiameter. ã The maximum head of the Heron pump is 20m. Thispackage is designed to dewater wells at around a depthof 15 m. If higher heads are required, then twoWSDP/6s can be coupled together to give a maximumhead of 40 m (7 m 3  /hr at 35 m head). ã This pump does not pump air, but it does not need tobe submersed to pump, as with the second pump whenpumping in series. But when switching on there shouldalways be water in the pump chamber or the seals willburn out after 1–2 minutes. ã The purpose of the base plate is to prevent the legs of the pump sinking into the mud causing the impeller totry and drill itself downwards, which results in the pumpbecoming clogged up. If the base plate is not presenteither suspend the pump just above the muddy bottom,turn it on its side or put it in a large perforated bucket. ã If the pump is near its maximum pumping depth thecanvas layflat may need to be attached to a stake at thetop of the well to prevent sliding back into the well. A hose connector can be attached to the end of the layflatto make it easier to tie to a stake. ã The Heron pump can be used for desludging latrine pits. Well tripod Kit, codeWT6/1 OXFAM Technical Briefs – Repairing, cleaning and disinfecting hand dug wells 2 People who enter inside the well should wear safety helmets and have rope securely fastened to them  Dewatering a well with a dewatering pump and compressor Dewatering when there is no sludge The traditional method of dewatering a well is to use large buckets to bale the water out manually. The buckets can be suspended and lowered into and raised from the well using the tripod and winch. A limitation of this method is where the yield of the well is too high to allow the water to be removed quickly enough manually and hence it will not be possible to reach the bottom of the well for cleaning, deepening or repair. Where the well was simply inundated with water or simply needs emptying for cleaning or deepening purposes, an engine with compressor and an electric submersible pump can be used. However, care must be taken not to damage the cables and hence risk electrocution if the cable touches water in the well. If there is no need to remove debris from the bottom of the well or to repair the well, then it is not necessary to dewater before disinfecting it. Removing solid materials / deepening hand dug wells / repair Once the well has been emptied, and water is being removed, debris can be manually excavated from the bottom of the well and then lifting it to the surface in buckets using a winch. Minor repairs can be made to the lining of the well or more major works can be undertaken to deepen the well, or to line a well which was previously unlined. If there is time and it is felt appropriate, then this could also be an opportune moment to upgrade an open well to improve its cover or lifting mechanism, but this is probably not appropriate in the early stages of a fast onset emergency. Whilst inside the well inspect the lining for any cracks, particularly in the first few meters from the ground surface, which should be sealed to prevent ingress of contaminated water from the surface. To repair cracks, chisel out the area around the crack and use a stiff mortar (mix 1:3 cement to sand) and keep wet for 24 hours before putting the well back into operation. Cleaning the walls of the well Using a long handled firm broom (with extensions made from thin GI pipe and sockets if necessary) clean the sides of the well with a chlorine solution of 200mg/l (refer to the section on the following page for details of how to make up this solution). Where the well is shallow enough undertake this process from outside of the well, but if there is a need to enter into the well then particular care must be taken as the strong chlorine solution will give off dangerous gases. The person undertaking the work must wear protective clothing, including gloves, overalls, goggles and a face mask with a filter. Wherever possible, also provide a strong air flow inside the well, such as through making locally designed bellows to blow fresh air into the well during the process. The strong chlorine solution should remain on the walls of the well for at least 30 minutes before allowing the well to refill. OXFAM Technical Briefs – Repairing, cleaning and disinfecting hand dug wells 3  Disinfecting the well When the well has recharged the water should be treated with a chlorine solution which will leave a free residual of 50mg/l in the well (or up to 100mg/l in particularly bad conditions). The chlorine should be allowed to stand in the water for at least 30 minutes, but preferably several hours, before it is pumped out from the well. To mix the chlorine solution in the well, use a clean rock on the end of a long rope and move the rock around in the water, lifting it up and down while moving it around the well. An alternative method to mix the solution is to use a bucket and keep on drawing water and then pouring it back into the well. For effective chlorination, ideally the water should have a turbidity of < 5TU and a pH of > 6.0 and <8.0. Use a pooltester with Phenol Red tablets and turbidity tube to test these parameters. If the water is found to have a pH of less than 6.0, hydrated lime can be added. But with such a high dosage of chlorine (50mg/l or above) and a long retention time (over 30 mins and preferably several hours), there should be no problem if the pH is >8.0, unless the pH is significantly higher. If the turbidity of the water in the well is >5TU, then the well can be dewatered and recharged before chlorination to ensure effective chlorination. However, with the high dosage, the chlorination should be effective against some turbidity. If unable to reduce the turbidity < 5TU and in doubt, increase the dosage from 50mg/l. Preparing the chlorine solutions Preparation of 1 litre of 1% chlorine solution (1% chlorine solution has 10g / litre, or 10,000 mg/l, or 10 mg/ ml), Ref: Davies & Lambert, 2002, 2 nd  Edition Chlorine source Available chlorine % Quantity required Approx measure High Test Hypochlorite (HTH) granules 70 14g 1 heaped teaspoon Bleaching powder 34 30g 2 heaped teaspoons Stabilized tropical bleach 25 40g 3 heaped teaspoons Liquid household disinfectant 10100ml7 tablespoonsLiquid laundry bleach 5 200ml 14 tablespoons  Antiseptic solution 1 1 litre No need to adjust as it is a 1% solution Important tips for using chlorine 1.The strength of chlorine reduces quite rapidly overtime and hence some allowances should be madefor the age of the chlorine.2.Do not mix chlorine in a metal container aschlorine reacts with metal.3.Chlorine is a hazardous chemical and should behandled with care. It can irritate skin and eyes andHTH powder or strong solutions produce gaseswhich are dangerous to breathing.4.Chlorine must be stored in a cool, dry, wellventilated and dark location and should not bestored in the same room which a night watchmanis using for sleeping in. Calculating how much chlorine is required  A 1% stock solution made up as in the table above, has approximately 10g/l = 10 mg/ml of active chlorine. To make a 200 mg/l solution for cleaning the well walls:  Add the following volume of 1% soln. to 1 litre of water 200 mg/l = 20 ml / each litre of water 10 mg/ml Calculate the volume of the water in the well using the following equation:  Vol of water in the well = 3.14 x Dia 2  x depth of water 4 Measure the depth of the well using a rock on the end of a piece of rope. Drop the rock slowly to the bottom of the well. When the rope is withdrawn from the water, the wet part of the rope can be measured to determine the depth. To obtain 50 mg/l of free chlorine in the well, then for each 1m 3  of water (1,000 litres): a)Using a 1% solution: Use 1,000 l x 50 mg/l = 5,000 ml = 5 litres of 1% soln 10 mg/ml b)Using 70% HTH (which has 70% active chlorine) andusing a heaped tablespoon to measure it (which equates approximately to 14g per spoon): Quantity of chlorine required = (dosage x volume of water) (chlorine % x 10) So, for 1,000 litres, the qty required is: Qty of HTH = 50 mg/l x 1,000 litres = 71.4 mg 70% x 10 1 heaped tablespoon = approx 14g Number of heaped tablespoons required = 71.4 / 14 = 5.1   OXFAM Technical Briefs – Repairing, cleaning and disinfecting hand dug wells 4
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