KEEP IT SHAL­LOW

Tra­di­tional shal­low wells can sup­ply ar­senic-free wa­ter. All one needs to do is in­stall it with cau­tion

Down to Earth - - CONTENTS - SAYAN­TAN BERA |

Tra­di­tional dug wells can sup­ply ar­senic-free wa­ter

DE­SPITE FA­TAL CON­SE­QUENCES, about six mil­lion peo­ple in nine dis­tricts of West Ben­gal de­pend on ar­senic-con­tam­i­nated wa­ter.This colour­less and odour­less chem­i­cal is known to cause can­cer, res­pi­ra­tory dis­eases and even heart at­tack. Mil­lions of ru­pees have been spent to sup­ply ar­senic-free drink­ing wa­ter to the af­fected re­gions.The most common method is to set up treat­ment plants by us­ing tech­nolo­gies like fil­ter-based ad­sorp­tion, ion ex­change and co­ag­u­la­tion. But th­ese are ex­pen­sive and main­te­nance re­quires ex­per­tise,of­ten a chal­lenge for af­fected com­mu­ni­ties.

To pro­vide a cheap and has­sle-free tech­nol­ogy,USbased non-profit Project Well has in­tro­duced a mod­i­fied ver­sion of tra­di­tional dug wells in two af­fected dis­tricts, North 24 Par­ganas and Na­dia. Dug well, or kua as it is called lo­cally, was once ubiq­ui­tous across the coastal state.Over the past five decades,they have been re­placed by deep tube wells over con­cerns that wa­ter from shal­low aquifers eas­ily get con­tam­i­nated with sur­face runoff and co­l­iform that causes di­ar­rhoea. Over-ex­ploita­tion of ground­wa­ter in­stead com­pounded the prob­lem of ar­senic con­tam­i­na­tion.“The un­con­fined top aquifer is free of ar­senic con­tam­i­na­tion and gets recharged by sur­face and rain­wa­ter,” says Meera Smith, founder of Project Well. The non-profit uses its mod­ifed dug well tech­nol­ogy to tap wa­ter from this aquifer, but with cau­tion. It sinks the well through bor­ing.Skilled well dig­gers then cut the in­serted pvc pipe and stack con­crete rings around it un­til the height of the cylin­der reaches 5 m.If the site is in flood-prone area,the height of the cylin­der is kept 60-90 cm above the ground to pre­vent con­tam­i­na­tion from sur­face runoff.Lo­cal ma­sons then con­struct a plat­form next to the well and cover its mouth with a roof and a ny­lon net to pro­tect the wa­ter from get­ting dirty. A hand pump at­tached to the dug well ex­tracts the well wa­ter. The well wa­ter is then treated with the­o­line, a chlo­rine-based dis­in­fec­tant, for a month. It is de­clared fit for con­sump­tion only after lab­o­ra­tory tests show that the wa­ter is free from both ar­senic and co­l­iform.

So far, Project Well has in­stalled over 200 dug wells in West Ben­gal through its part­ner Aqua Wel­fare So­ci­ety.In Keota vil­lage of North 24 Par­ganas, over 80 fam­i­lies draw wa­ter from the well. “We need another well as peo­ple from neigh­bour­ing vil­lages also de­pend on it,” says Swarup Sarkar, whose house is next to the well. “No one wants to drink wa­ter from deep tube wells as most of th­ese are con­tam­i­nated with ar­senic,”he adds.Biswa­jit Kar­makar of Aqua Wel­fare So­ci­ety says vil­lage plumbers eas­ily in­stall the mod­i­fied de­sign,which costs 36,000.Main­tain­ing the well costs barely 50 a month.

The tech­nol­ogy,how­ever,has its own set of chal­lenges.Dug wells dry up dur­ing sum­mer months as they tap wa­ter from the top aquifer.About 10 per cent of the wells in­stalled by Project Well faces this prob­lem. “Bac­te­rial and pes­ti­cide con­tam­i­na­tion can­not be ruled out in dug wells,”says Anir­ban Gupta,fac­ulty at Ben­gal En­gi­neer­ing and Sci­ence Univer­sity. Gupta is part of a team that de­vel­oped a fil­ter­based tech­nol­ogy to check ar­senic con­tam­i­na­tion.The fil­ter uses gran­u­lar alu­mina to re­move ar­senic and is at­tached to hand pumps.It costs 75,000 and re­quires reg­u­lar main­te­nance.

Smith says none of the wells in­stalled by the non-profit has re­ported bac­te­rial con­tam­i­na­tion yet.“We have not tested for other con­tam­i­nants due to lack of funds,”she adds.

“A prob­a­ble so­lu­tion is to use a mix of both dug well and fil­ter­based tech­nolo­gies,”says Pradip Sen Gupta,for­merly a ge­ol­o­gist with the State Wa­ter In­ves­ti­ga­tion Direc­torate.

Project Well's dug well draws wa­ter from ar­senic-free top aquifer

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