1WHO/SEARO Technical Notes for Emergencies Technical Note No. 2

Cleaning and disinfectionof boreholes in emergencies

WHO Regional Office for South-East Asia

Steps of rehabilitationFigure1 outlines a 5 stage approach to cleaning anddisinfecting boreholes after natural disasters. It is anemergency approach designed to rehabilitateboreholes so they produce water of a similar qualityto that supplied before the disaster.

Step 1: Assessment of damageThe disaster may have damaged the above groundor below ground parts of the borehole. This mayhave lead to contamination of the borehole. The firststep must be to assess the extent of the damage tothe borehole and pump. The following actions shouldhelp you to make your assessment.

Meet with community leaders and ask them tobriefly outline which boreholes serve whichsections of the community.

Assess the type and extent of damage to the topof the well.

Remove the handpump or mechanised pumpfrom the borehole.

Estimate the amount of silt and debris in theborehole using a steel pipe the length of wholedepth of the well.

Check if borehole casing is damaged or out ofline. Do this by inserting the steel pipe. If it is outof line the pipe will catch against the side of theborehole. If this happens, select other sites.

Test the pump (and motor) to see if they are stillworking or what repairs are necessary

Estimate resources needed for repairs (person-nel, equipment, time and materials)

Select the boreholes that are used most and areeasiest to repair first.

Broken handpump

Figure 1. Steps for cleaning anddisinfecting a borehole

Step 1:Assessment of damage

Step 2:Rehabilitation of borehole

Step 3:Pump test borehole

QUESTIONDoes quantity equal demand?

Step 4:Disinfection of borehole

Step 5:Dewater borehole

Flush boreholeNo

Yes

2 WHO/SEARO Technical Notes for EmergenciesTechnical Note No. 2

150mm thick (cast in situ)

Borehole casing

Compacted clay

Hardcorefoundation

Concreteslab

2.5m - 3.5m diameter apron

5000 litre water tanker

Water hose

Water tableWater table

3m3m3mCasingCasing

Water pumpand compressor

Compressed air hose

Water overflowingto waste

High pressure water hose

ScreenScreen

Cleaning and disinfection of boreholes in emergencies

Step 2: Rehabilitation of wellsBefore the borehole can be cleaned, all silt anddebris should be removed. The following steps maybe followed:

1. If not already removed, take out the pump andmotor from the borehole and clean and repairthem.

2. Flush the sediment from borehole using com-pressed air or water. Place compressor hose inborehole andblow out sediment.

3. To remove the silt from the borehole filter insertthe end of the compressed air hose at the headof the filter. Open valve until water starts comingout of the top of the well. Close valve 1 and openvalve 2 until no more air is heard comming out.Repeat until water coming out of the borehole isclear.

Removal of pump

Flushing out a borehole Sanitary seal

Removing silt with a compressed air hose

Vent to atmosphere

Valve (2) closed

Compressed air supply

Valve (1) open

Compressed air lifts column ofwater - go to step 3 as soon aswater is seen to erupt at surface(or for a set time 1-3 seconds)

3WHO/SEARO Technical Notes for Emergencies Technical Note No. 2

Stand to support pipe

Borehole casing

Water tableWater table

Measuring tape with float onthe end to measure depth towater level

Oil drum to collectand measure waterflow

Submersible pump

4. Reseal the top of the borehole using a claysanitary seal built around top of borehole.

5. Construct or repair the drainage apron and headwall around the borehole to prevent surfacewater, insects and rodents entering the borehole.

6. Replace the pump in the hole and check that it isworking and the water it is producing is clear ofsilt. If the water is silty remove pump and flushborehole . If after two flushes the bore is produc-ing slity water, the underground filter is probablybroken and no further attempt at repair shouldbe made.

Step 3: Pump Test

Handpumps:Once the pump is replaced in the borehole, operateit in the normal way. If it is a handpump ask the localcommunity to assess whether the amount producedis similar to what was produced before the disasterand to compare how easy the pump is to use. Ifpumping is difficult and a small amount of water isproduced it could be a blockage or broken pump.Recheck the pump mechanism and reflush theborehole.

Motorised PumpMeasure how much water the pump produces usingthe procedure shown in Box 1 and the figure below.

Compare the flow rate with what was producedbefore the disaster. If it is significantly less check thepump and motor for damage and/or flush theborehole again. If this does not change the flow rateeither accept the lower flow or abandon the hole.

Step 4: Disinfection of boreholeFollowing the rehabilitation of the borehole, test thelevels of turbidity and pH to ensure that chlorinationwill be effective. This can be done using simple handheld equipment similar to that shown in Figure 6.Never chlorinate turbid water because the sus-pended particles can protect the microorganisms.Table 1 outlines why pH and turbidity are importantand what can be done to ensure guideline levels aremet.

If the turbidity of the well water is greater than 5NTUafter the cleaning and rehabilitation stage, pump outthe water, allow the well to refill and then retestturbidity levels.

Illustration of pump test

Cleaning and disinfection of boreholes in emergencies

Box 1.Estimate flow rate from a borehole

Put a bucket under the outlet frPut a bucket under the outlet frPut a bucket under the outlet frPut a bucket under the outlet frPut a bucket under the outlet from theom theom theom theom thepump and measurpump and measurpump and measurpump and measurpump and measure how long it takes toe how long it takes toe how long it takes toe how long it takes toe how long it takes tofill.fill.fill.fill.fill.

Amount of water pumped in 1 hour is:Amount of water pumped in 1 hour is:Amount of water pumped in 1 hour is:Amount of water pumped in 1 hour is:Amount of water pumped in 1 hour is:

BB

AxC −⎟⎠⎞

⎜⎝⎛

WherWherWherWherWhere:e:e:e:e:A =A =A =A =A = The volume of the bucket in litrThe volume of the bucket in litrThe volume of the bucket in litrThe volume of the bucket in litrThe volume of the bucket in litresesesesesB =B =B =B =B = Number of seconds taken to fill theNumber of seconds taken to fill theNumber of seconds taken to fill theNumber of seconds taken to fill theNumber of seconds taken to fill the

bucketbucketbucketbucketbucketC =C =C =C =C = 3600 seconds3600 seconds3600 seconds3600 seconds3600 secondsQ =Q =Q =Q =Q = flow (litrflow (litrflow (litrflow (litrflow (litres/hour)es/hour)es/hour)es/hour)es/hour)

Table 1. Physico-chemical parameters 1

Parameter

pH

Turbidity

WHO GDWQ

6 – 8

< 5NTU(20NTU emergencylimit)

Why?

pH of 6.8-7.2 is required to reducelevel of chlorine required.

High turbidity (>5NTU) requiresmore chlorine to oxidise organicmatter

Corrective Action

If pH is less than 6 add hydratedlime (calcium hydroxide)

Dewater well and rebleach welllining using chlorine solution

4 WHO/SEARO Technical Notes for EmergenciesTechnical Note No. 2

Cleaning and disinfection of boreholes in emergencies

The WHO endorses the disinfection of drinking waterin emergency situations. There are various ways ofdisinfecting wells but the most common is chlorina-tion as it leaves a residual disinfectant in the waterafter chlorination.

The chlorine compound most commonly used iscalcium hypochlorite as high test hypochlorite (HTH)in powder or granule form. Also used is sodiumhypochlorite in liquid bleach form. Each chlorinecompound has a different amount of usable chlorinedepending on the quantity of time the product hasbeen stored or exposed to the atmosphere. The besttype of chlorine in an emergency is HTH as thisnormally contains 50 to 70% chlorine. Box 2 outlinemethods for calculating appropriate chlorine dosesfor HTH granule chlorine.

NOTE: Bleach gives off chlorine gas which is verydangerous. Try to clean the well lining using abrush on the end of a series of connected 25mmdiameter metal pipes.

The amount of chlorine needed will depend on thevolume of water in the borehole. Add 1 litre of 0.2%chlorine solutions for every 100 litres of water in theborehole. Leave the water undisturbed for at least 30minutes.

NOTE: Do not allow anyone to use the boreholeduring the cleaning process. The water will have astrong concentration of chlorine that will give it abad taste and smell and could be dangerous.

Step 5: Dewater boreholeFollowing the contact period, dewater the boreholeonce again using compressed air. When the boreholehas refilled, wait a further 30 minutes and measurethe chlorine concentration using a comparator. If theresidual chlorine concentration is less than 0.5mg/lthe borehole is safe to use. If the concentration isgreater than 0.5mg/l, remove all the water from thewell again and repeat the process.

World Health OrganizationRegional Office for South-East AsiaMahatma Gandhi MargNew Delhi, 110002,India

This information has been prepared by WEDCAuthor: S.Godfrey Series Editor: R. A. Reed Design: G. McMahon Illustrations: R. J. Shaw Graphics: Ken ChattertonWater, Engineering and Development Centre, Loughborough University, Leicestershire, UK.Phone: +44 1509 222885 Fax: +44 1509 211079 E-mail: WEDC@lboro.ac.uk www.lboro.ac.uk/wedc

Phone: (+91-11) 2337-0804Fax: (+91-11) 2337-8438E-mail: wsh@whosea.org

http://www.whosea.org

Box 2.Disinfecting a borehole using Calcium Hypochlorie (HTH)

Equipment:Equipment:Equipment:Equipment:Equipment:20 litr20 litr20 litr20 litr20 litre buckete buckete buckete buckete bucketHTH Chlorine granuals or powderHTH Chlorine granuals or powderHTH Chlorine granuals or powderHTH Chlorine granuals or powderHTH Chlorine granuals or powder

MethodMethodMethodMethodMethodFill the bucket with clear water frFill the bucket with clear water frFill the bucket with clear water frFill the bucket with clear water frFill the bucket with clear water from theom theom theom theom theborborborborboreholeeholeeholeeholeehole

Add 50g of HTH powder and stir untilAdd 50g of HTH powder and stir untilAdd 50g of HTH powder and stir untilAdd 50g of HTH powder and stir untilAdd 50g of HTH powder and stir untildisolveddisolveddisolveddisolveddisolved

Calculate the volume of water in theCalculate the volume of water in theCalculate the volume of water in theCalculate the volume of water in theCalculate the volume of water in theborborborborborehole using the forehole using the forehole using the forehole using the forehole using the formula:mula:mula:mula:mula:

V = V = V = V = V = πππππDDDDD22222 x h x h x h x h x h44444

WherWherWherWherWhereeeee V =V =V =V =V =volume of water in thevolume of water in thevolume of water in thevolume of water in thevolume of water in theborborborborborehole (m3)ehole (m3)ehole (m3)ehole (m3)ehole (m3)

D =diameter of the borD =diameter of the borD =diameter of the borD =diameter of the borD =diameter of the borehold (m)ehold (m)ehold (m)ehold (m)ehold (m)h =h =h =h =h = depth of water in thedepth of water in thedepth of water in thedepth of water in thedepth of water in the

borborborborborehole (m)ehole (m)ehole (m)ehole (m)ehole (m)πππππ = 3.142 = 3.142 = 3.142 = 3.142 = 3.142

For everFor everFor everFor everFor every cubic meter of water in the welly cubic meter of water in the welly cubic meter of water in the welly cubic meter of water in the welly cubic meter of water in the welladd 10 litradd 10 litradd 10 litradd 10 litradd 10 litres of chlorine solution (half aes of chlorine solution (half aes of chlorine solution (half aes of chlorine solution (half aes of chlorine solution (half abucket)bucket)bucket)bucket)bucket)

ResourcesGodfrey, S., Ball, P., 2003, Making Boreholes Work –

Rehabilitation strategies from Angola, 29th WEDCconference, Abuja, Nigeria

Ball, P., 1999, Drilled Wells, SKAT publication,Geneva, Switzerland