Visit MS-Denmark

There have been many investigations and recommendations by international scientists that the drinking water derived from the groundwater - the aquifers - in Nepal, shows similar characteristics to those of the Bengal Basin, the Gangetic floods plains and the areas adjoining West Bengal. The Terai belt of Nepal (Cf. Figure 2, below) lies close to these areas and recently the same problem has been discovered in the groundwater of Nepal.

Department for Water, Sanitation and Sewage (DWSS) initiated the Arsenic investigations in Nepal in year 2000, by measuring 268 drinking water samples in Terai, (Cf. Figure 2: Map of Nepal showing the 17 Terai districts, where the Arsenic Contamination is highest. Page 23.) This investigation was done in Eastern Terai in the districts Jhapa, Morang & Sunsari. [Nirmal Tandukar: Arsenic Contamination in Groundwater in Rautahat District of Nepal - An Assessment and Treatment, M.Sc. Thesis, Institute of Engineering, Lalitpur, Nepal. 2000]. The data revealed that some ground water samples from the areas was contaminated with arsenic. The report showed that about 9 % of the total analyzed samples exceeded the WHO guideline value of 10 μg/l and the maximum concentration of arsenic was found to be 75 μg/l.

Nepal Red Cross Society (NRCS) supported by the Japanese Red Cross (JRCS) soon followed up in May 2000 and have so far been the leading stakeholder in Nepal in the measuring of the Arsenic crisis, having measured more than 12,000 (??Confirm) samples using an Atomic Absorption Spectrophotometer (AAS). This expensive but accurate measuring method can only be done in well equipped laboratories, which at present only are available in Kathmandu. This method raises the question of conserving the samples days or weeks. Cf. Chapter 10.7: Conservation of samples from the field. Page 42.

Today where an adequate and systematic monitoring programme for arsenic in groundwater in Nepal is the process of being carried out, and as around 17.000 wells have been measured, it is a well known fact that different Arsenic poisonous compounds are released into the groundwater, which is consumed by the largely unaware Nepali population.

The gravity flow schemes in the hills and the water supply in cities, which uses open water sources from open streams and rivers, piped to the users and tapped through a stopcock, are not affected to the same extent as the tube wells of the Terai belt of Nepal. However this needs to be investigated further and NEWAH have therefore started a research program to measure in the hills and in the cities to ensure the safety of these supplies.

Thus, as the problem of arsenic contamination is believed to be more severe in the installed tube wells of the Terai area, and the present national efforts are concentrated in this area. Cf. Figure 2, below. To date it is uncertain whether the arsenic problem in Nepal is only related to tube wells, as seems to be the case in Bangladesh. Geological speculations based on data from Bangladesh suggest that the arsenic problem in the Terai and south of Nepal may originate in the Himalayan mountain range. Cf. Chapter 3.1: The Chemical Explanation Page 19 and 0, page 67. The testing of certain surface sources, developed by NEWAH, at the foothills of the Himalayas, will reveal, whether this is a significant source of arsenic contamination. Especially the many thermal springs in Nepal should attract attention, if not for the hazardous effects, then for the research possibility to clarify if the Arsenic compounds in Terai and in the southern countries have connection to the Himalayan areas. One thermal source in the Jomosom area (?? What district) have a discharge of 30 litre/sec. This spring may cause health problems to the villagers below, if the water is not diluted sufficiently by arsenic free rivers before the water is used for human consumption, and the spring contains hazardous levels of Arsenic concentrations. Cf. Chapter 5: NEWAH’s initiative of testing Thermal Springs, page 27.

Investigations in Nepal have so far shown that the numerous wells in the southern lowlands - the Terai belt of Nepal are most seriously affected. The actual number of tube wells in these areas is unknown, since the major part is unregistered private wells, often of a poor construction. From an extrapolation of the Nawalparasi district, where the population is app. 600,000 and the number of wells have been counted to 34,000, [Kalawati Pokharel: RWSSSP paper, Internal communication, 2002] it can be estimated that 12 million people in the rural areas of the Terai presumably owns more than 650.000 hand pumped tube wells, equivalent to on average of 18-20 persons per well. Other estimates notes 300.000 wells (40 persons per well). The agency installed tube wells of a higher quality often calculates with the latter figure per well. Direct observation shows that today most households owe their own well, giving reason to believe that the former number is more correct.

As there until further are not developed any method to predict the concentrations in a well (See chapter 4.4, page 23 and Chapter 10.1: Correlation with other Substances, page 37) a strategic aim must therefore be to measure all or most of the wells both in Bangladesh, West Bengal and in Nepal for arsenic. In Bangladesh there are approximately 4.5 million public (installed by Government departments) and a total 9 million tubewells. An estimated 97% of the Bangladesh population of 120 million drink well water. Piped water supplies are available only to a small portion of the total population in Bangladesh.

Unfortunately all wells in Terai needs to be systematically tested, since investigations so far have revealed that it is impossible to predict the individual contamination, even if the adjacent wells 5 meters away have been tested. The concentration variations of adjacent wells have been shown by NEWAH to range from 10 to 600 µg/l. In Chapter 10.1: Correlation with other Substances, page 37 a discussion is done on the possibility to measure Iron in order to acquire an indication of the concentration of Arsenic.

On the basis of approximately 17,000 data sets collected and measured in Nepal by concerned stakeholders. Cf. Table 3, page 31, and partly processed by NEWAH, it can be estimated that a minimum of 30 % of all installed tube wells have arsenic levels above 10 µg/l. A minimum of 5 % have serious long-term health damaging concentrations of over 50 µg/l. The health implications of this can be seen in Chapter 2: The Adverse Health Effects, page 17, and from [Kim R. Adamsen: Medical Effects of Arsenic Ingestion, Internal note, 2002.]

The latest two years (2000-2002) intensified measuring gives rise to severe concern for another reason. Having participated actively and followed the debates and papers released from the Nepali stakeholders for the last two years, it seems that the percentage of the infected wells have increased over time. In year 2000 the percentages of tube wells above 10 and 50 µg/l was 17 and 2 % respectively. At that time approximately 1500 wells had been measured. It seems that the more the different stakeholders co-operate to measure, the higher these percentages becomes. This fact is indicated on Figure 3, below, as NEWAH have collected all papers and circulars the last two years. Naturally this might also be an effect of an increased knowledge among the stakeholders, where the Arsenic problems are most severe, and that we in a co-operation naturally try to measure the highest risk areas first.

Hence the precise percentages in Nepal should today be regarded as relatively unknown, but as can be seen from the figure a guess on 5 % above 50 µg/l, and that 30 % of all tube wells in Nepal are above 10 µg/l seems reasonably. Only when all wells, private, public and others have been measured these figures will be known more precisely. Never exactly, since the concentration in each well varies with season, pumped water prior to sampling, measuring method, conservation method etc.

If we in Nepal want to know these percentages without measuring all wells, a mathematical random selection spread equally over the country and a subsequent measuring of only these wells should be done. The Department of Water, Sanitation and Sewage (DWSS) are in the process of doing this, as a decision by The National Arsenic Steering Committee (NASC) of measuring two wells - randomly distributed - per km^{2 was taken late in 2001.}

The preliminary investigations in Nepal have shown that some samples collected in the villages situated close to the Indian border in the southern part of Nepal have even higher levels of Arsenic contamination that have been seen in the presumed worldwide worst affected areas: Bangladesh and West Bengal. The highest concentration in Bangladesh in groundwater is 1600 µg/l. The highest concentration in Nepal so far has been measured in Rupandehi district to 2600 µg/l.

The picture of the contaminated wells should also take the seasonal variation into consideration. NEWAH have shown that the individual Arsenic concentration in one well varies over time. The full picture of this investigation is yet to be finished, however DWSS [Nirmal Tandukar: Scenario of Arsenic Contamination in Groundwater of Nepal, M.Sc.(Environmental Engineering) Institute of Engineering, Nepal, 2000.] have shown that the number of affected wells above 10 µg/l is lower after the monsoon in November, possibly due to a dilution effect by the rainwater, which seeps fast down to the aquifer along the tube well pipe. This indication is, however based on data from only 121 wells and needs to be investigated further.

Furthermore a variation with the amount of water pumped prior to sampling is also to be expected, since this is an indication of the Arsenic concentration variation with depth of pumped up groundwater. The exact relationship between pump strokes prior to sampling and precise ground water depth will be difficult to determine, as different pumps are not constructed the same way. In Nawalparasi district NEWAH measured one well, which was said to pump water from 25 feet below to 10-50 µg/l total Arsenic. The neighbouring well 5 meters apart drew water from 65 feet down and showed a concentration of app. 300 µg/l. The depth of the two wells was not verified.

The Arsenic variation with depth can be seen on Figure 4 below. This figure shows that

[Nirmal Tandukar: Scenario of Arsenic Contamination in Groundwater of Nepal, M.Sc.(Environmental Engineering) Institute of Engineering, Nepal, 2000.] have - on the basis of app. 50 dataset - shown that depths between 20 and 150 feet (6 to 45 m) are to be considered as the highest risk area.

Taken from the report "The Arsenic Contamination of the Drinking Water in Nepal" by Anil Pokhrel, head of technical section of NEWAH & Kim Rud Adamsen, hydrology adviser of NEWAH

Download the whole report in MSWord format.