Meera M Hira Smith, Ph.D.
In 1995,an International Conference in Calcutta, West Bengal, India that was organized by the School of Environmental Studies of Jadavpur University to portray the severity of the effects of arsenic in drinking water. The overwhelming picture was of a vast number of people being exposed to high levels of arsenic in drinking water obtained from shallow tubewells. In 1996, the number of victims who were suffering from diseases caused by arsenic in drinking water was estimated to be 220,000[i]. In the same year it was estimated that more than one million people in eight districts out of the sixteen districts of West Bengal, including 560 villages had arsenic-contaminated water[ii]. Since then numerous studies have been done on the source of arsenic, examination of hydro-geological and chemical hypotheses concerning the entry of arsenic into aqueous solution, and assessment of health effects.
International research studies have established that long term exposure to arsenic causes the following diseases[iii]:
Skin Lesions and Skin Cancer;
Internal Cancers – Bladder, Lung, Kidney;
Hypertension and Cardiovascular Diseases;
Peripheral Vascular Disease;
Numerous hypotheses have been formulated concerning the origin of arsenic in the shallow tubewells that were installed to stop morbidity and mortality caused by gastroenteritis that resulted from drinking surface water. One such theory is that there is fluctuation in the levels of underground water tables due to variations in rainfall and the extent of water mining in different parts of the state of West Bengal for use in agriculture. As a result there could be constant leaching of arsenic into different layers at different depths throughout the arsenic prone region.
To provide arsenic free water, different methods need to be considered depending on local conditions. Various mitigation plans and methods of providing arsenic-free water to the people have been proposed but with little consensus on strategies or plans of action, nor on decision criteria to be applied in specific local circumstances. When trying to decide how to proceed with plans for providing arsenic-free water, no comparative information could be found which would assist in making local decisions. The purpose of this paper is to present the results of investigations conducted in the hope that the information may be of value to other groups and communities making decisions in their particular circumstances about the best method for obtaining arsenic-free water.
To assess some of the methods to provide arsenic free drinking water and their advantages and limitations for particular villages of North 24 Parganas.
A comparative study of different methods of providing arsenic free water was undertaken. To do so various observations were made by visiting selected villages of North 24 Parganas where there are cases of arsenic caused diseases among the villagers. The different methods to provide arsenic free water are discussed below along with their advantages and limitations, and a comparative study of the costs of each method.
1. Deep Tube Wells
The investigation was started with deep tube wells because it has long been known that the lower aquifers, below 500 feet in many places of the alluvial Indo-Gangetic Plain, have low concentrations of arsenic. However contaminated deep tubewells that are more than 500 feet deep have been reported including those in the village called Ambikanagar of North 24 Parganas. These findings suggest caution in proceeding with deep tubewell plans.
The contamination is probably caused by cross contamination between aquifers that may result from improper installation of the tube wells. Geologist Dr. Asit Kumar Roy has reported a mechanism for the flow of underground water within the Gangetic alluvium[iv]. Concerning deep tubewells, he notes that when a deep tubewell is being installed, it should penetrate the non-contaminated impervious aquifer “fully” and the mouth of the pipe should touch the non contaminated aquifer fully. He also stated that if any sort of partial penetration were done, there would be transmission of contaminated water both horizontally and vertically between the aquifers. In addition, as noted by Dr. Timir Hore[v] of New Jersey, USA, deep tube wells should be sunk by the ‘Proper Method’, with casing and sealing.
The main reasons for disqualifying deep tube well for installation in the selected villages for this study in West Bengal were:
1. Non-availability of detailed local geological maps to identify the arsenic contaminated aquifer.
2. Lack of experience in the 'casing and sealing' method and difficulty of supervision of the proper installation of deep tube wells.
In order to make drinking water readily accessible, numerous deep wells would be required. Probably one for every ten households, which would be very expensive.
2. Low Cost River Water Treatment Plant at Gaighata
In Gaighata, another village of North 24 Parganas, a proposal to construct a Low-Cost-River-Water-Treatment Plant on the river Yamuna/Ichamati was considered. Apart from the large installation cost, the most important reasons for disqualifying the plan are:
1. The river Yamuna/Ichamati is highly polluted.
2. A separate chemical treatment plant would be required to remove the pollutants. This would increase the cost of installation and maintenance.
3. The volume of water in the summer season is not sufficient.
4. The cost of maintenance would be high.
3. Tanks filled from Natural Ponds
One of the ideal sources of arsenic free water is harvesting of rainwater. Rainwater can be harvested in many different methods one of which is Natural Ponds or “pukur”. The water of natural ponds does not contain any arsenic due to their shallow depth.
Pond water is contaminated by pathogens. To remove these pathogenic bacteria the water (a) needs to be treated either by storing the water in a tank or reservoir for chemical treatment or by using roughing filter also known as pond sand filter. The method of building tanks from natural pond is expensive and to maintain it people would have to contribute Rs. 25/- per month (see Table 1). The roughing filter system is more economic. Treating the natural pond water by the roughing filter would yield 1000 liters of potable water for Rs. 1.25.
(b) The other alternative is boiling water but this is expensive and inconvenient, and not likely to be fully complied with.
Disadvantages of the Natural Pond Method
The natural pond method has some serious disadvantages. Villages like Simuliapara, Chikonpara and Amkhola of Gaighata Block and Kamdebkathi of Deganga Block of North 24 Parganas were visited to get the opinion of the people about the natural pond.
1. The main reason for disqualifying the natural pond method is that in spite of being offered a rental contract, no pond owner was willing to have his pond used for this purpose because fish is a vital source of income as well as it is consumed.
2. Another equally important problem that was realized during investigative field trips was that the larger the number of beneficiary members the harder it would become to maintain the pond and water purification system. From one natural pond 400 hundred families would benefit. To collect money for maintenance could become difficult which might lead to closure of the system and a total failure. In West Bengal many community-based ponds, operating for other joint ventures such as fishing, have failed. Community organization in rural village settings works better when sustainability depends on smaller groups.
4. Community Filter
On another field trip, the use of two arsenic removal filters was assessed. In Amkhola, the filtering device was attached on top of the existing contaminated shallow tubewell. After being chemically treated the residue or the sludge was getting discharged and collected in an open concrete tank of about three-sq. ft. Ultimately the sludge that was to be discarded would contaminate the surface soil and water bodies unless it is properly removed from the collecting pit. Another filter at Mullickpur that was filtering the arsenic containing water had the sludge collected in a closed concrete tank of about four sq. ft.
Disadvantages of the Community filter
1. Proper disposal of sludge is a big problem for community filter systems. Some reports state that the spent medium can be disposed of easily as a non-hazardous material for land fill, road construction and asphalt industry. The problem is the maintenance of the filters, collection of the arsenic-rich sludge from the respective villages without causing any human, water or agricultural exposure. Proper systematic methods of collecting the sludge from individual villages should be designed and implemented with caution to avoid any sort of pollution in the future.
2. In contrast to the indigenous methods like ponds or dug wells, the use of some community filters require bringing outside technology into the community that creates problems of sustainability.
Table 1: COMPARISON OF VARIOUS METHODS OF PROVIDING
(Source of information: Local NGOs of North 24 Parganas, West Bengal)
From the above table it is clear that the capital cost per family (Rs. 1625) is highest in case of the natural pond and reservoir or tank system. Also the maintenance cost is high at Rs. 25 per month per family. The capital cost per family for the community filter system assessed is Rs. 650. The maintenance cost is low, but the problem in the long run would be in the safe disposal of the arsenic-rich sludge. The capital cost per family for the river water treatment plant would be higher than Rs.304 when unknown cost of the chemical plant would be added in. The maintenance cost is considerable. The domestic filters used to remove arsenic from the tube well water would be risky in the long run for they would add to polluting the environment in different ways.
Thus from this assessment of the different methods, it has been concluded that concrete dug wells, locally known as 'Indara', would be the cheapest form of providing arsenic free water to the community of North 24 Parganas. The capital cost per family is Rs. 266 and the maintenance cost estimate is Rs.10 per family per month. However this method requires care to make sure the wells do not develop bacteriological contamination.
6. Dug Wells or “Indara”(concrete) or “Kua” (earthen)
The specifications for concrete dug wells for North 24 Parganas, West Bengal, are:
The depth of each dugwell should not exceed 18 meters. In fact in North 24 Parganas the depth of a dugwell can be around 10 meters because the water table is high and at places it can be reached at 4 meters. The diameter of the well should be a minimum one meter and the height above the ground should also be minimum one meter to avoid any kind of drainage of water or dirt into the well especially during the monsoon season. A concrete boundary wall around the well should be built to stop people from tampering with it. A hand pump that will be located outside this boundary can be connected to the dugwell to draw out the water, rather than inserting buckets which are touched by human hands. In this manner, regular human contact with the well water can be totally avoided thereby reducing the risk of contamination.
Specifications for selecting the site:
To avoid any fecal contamination it is very important to make sure that there are no latrines within 100 feet of the well.
The coliform counts of almost similar dug wells used during pilot project in Bangladesh are shown on the table 2 and table 3.
The coliform test (refer to table 2) shows that four out of eleven water samples with coliform levels higher than 100. In fact two samples show very high levels of coliform. (Table 2: source - Dhaka Community Hospital, recent report of Bera Option Water)
Another study in a different area of Bangladesh showed (refer to table 3) one out of fourteen samples with total coliform count per 100 ml as high as 2200. The other 13 (93 %) of the total samples were zero. (Table 3: source - Dhaka Community Hospital, report dated 5.7.2000).
(a) To take care of the quality of water and its proper distribution, the consumers of water from each dugwell will form a beneficiary committee comprised of a president, a treasurer and a secretary. The beneficiary committee will be responsible for the welfare of the dugwell.
(b) To maintain potable quality of the water, it will be tested periodically by a reliable laboratory in the nearby city.
(c) The bacteriological tests are expensive, and to cover the expense Rs. 10.00 per month from each beneficiary family will need to be collected, including well cleaning and water disinfection.
(d) The report of the water analysis will be posted on a board together with a pie-graph denoting the quality of the water. The pie-graph will have the following information: Green - Safe to drink; Orange – Caution; Red – Unsafe and White – Dry.
(e) An arrow will be fixed on the circle that will be rotated according to the quality of water. The position of the arrow on green will denote that the water is safe to drink and when it is on orange it would signify caution.
That means the water after collection should be either boiled or treated with some chemical at individual's home or filtered to remove bacteria. The red color denotes the water is unsafe for drinking and the well should be cleaned and disinfected. White means the well is dry. At these times, expected to be between 0 and 2 months per year, people should go to the nearest non-contaminated source of water.
(f) The above diagram will be posted at every dugwell site. It will be drawn on a metallic sheet and nailed to the wall of the dugwell. To avoid any tampering the diagram will be protected by a net and kept locked all the time. Only the president and the secretary of the beneficiary committee will have access to it.
Some of the advantages and specifications for the use of dug wells which are being installed are: -
1. Availability of local skilled labor - The design and skill for digging such ‘dug wells’ is easily available locally. No scientific technology is required, and there is no toxic waste to dispose of. The advantage of concrete dug wells over earthen ones is that chances of pathogenic infections are lower, but local material, skills and labor are available to make concrete dug wells.
2. Primitive Method that is easily adaptable - Dug well, 'Indara' or ‘Kua’ is a traditional method that existed thirty years ago. This conventional method should not be hard to be adopted by the villagers.
3. Type and method – The dug wells should be made out of concrete rings. A roof made of fiberglass rectangular sheets that would permit solar radiation and prevent external contamination such as bird’s droppings and dirt particles can cover them. A nylon net of about one and half foot height should be placed on the mouth of the well to allow aeration. It is important not to cover the well totally with concrete or any opaque body.
4. Hand Pump - To draw out the water a hand pump needs to be connected to the dug well. This method of withdrawal of water will prevent contamination caused by the bucket or/and the rope. Hand pump technology is available since they were the method used for shallow tube wells that the dug wells will replace.
5. Beneficiary Committee - One dug well can be shared by as many as 35-40 families of four members each (140-160 persons). The water will be strictly used for drinking and cooking purpose. Supervision will be done by respective beneficiary committees.
6. Individual Preventive Water Treatments - Cleaning and disinfecting the dug wells will be done annually or bi-annually by trained laborers to remove pathogenic bacteria. The collected water should be treated at individual’s home when the arrow is in orange position, by any of the three following methods:
a) Boiling for more than ten minutes,
b) Adding zeoline tablets or a pinch of alum (‘phitkiri’ or ‘koppur’)
c) Using domestic filter that removes harmful bacteria.
While local circumstances may lead to different conclusions in different areas, it was concluded that the best solution for the particular villages in this investigation was to insert concrete dug wells, locally known as “Indara”.
It would be helpful if a detailed report of the entire arsenic prone region made available by the State Arsenic Board. The reports of all the work that have been done by governmental and non-governmental organizations so far in all the districts including the water test results, the methods provided in particular villages to supply arsenic free water, need to be combined. This would save a lot of time wasted during the process of gathering information from different departments. The State Arsenic Board should keep track of the extent of the arsenic work going on throughout the State. It should be made compulsory to send a report to the State Arsenic Board on the work or projects that each organization, governmental or non-governmental, have done, are doing or are planning to do. With the help of such reports, perhaps made available on the Internet, it would be easier for future planners to select the next village to adopt in a drinking water program. It is a waste of time to find later that the village in the plan has already been approached by other concerned organizations.
 Ph.D., Geography, Calcutta University. At present researcher in School of Public Health, University of California, Berkeley, California, USA.
[i] British Medical Journal, 1996, Vol: 313; 7048
[ii] Current Science, 1996;vol:70;976-986
[iii] Smith H Allan, Lingus O Elena, Rahman Mahfuzar, “Contamination of Drinking Water by Arsenic in Bangladesh: A Public Health Emergency”, Bulletin of World Health Organization, 2000, 78(9), pp. 1093-1103.
[iv] Roy Asit K. The past and the future of the effects of arsenic poisoning”. The article was published in Bengali in the science section of the journal “Desh” on 26 July 1997, pp. 113-119.
Timir Hore, newspaper article in Bengali newspaper, ‘Bartaman’,
published on 11th June 1999.