This article throws light upon the five major pollutants of groundwater. The pollutants are: 1. Metals 2. Nitrate 3. Arsenic 4. Fluoride 5. Iron.
Ground Water: Pollutant # 1.
In general, ground water is mostly chemically and microbiologically non-polluted and thus safe for drinking and cooking in addition to agricultural or industrial uses. But in recent decades there were enormous amount of reports of ground water contamination of arsenic, fluoride or nitrate. This contamination causes serious health hazards in the long run.
It is well-known that ground water contamination with toxic metals principally takes place due to leaching from toxic waste dumps or from crustal layer of earth through biotransformation. Agricultural chemicals also leached into upper aquifers and thus contaminate the ground water.
Ground Water: Pollutant # 2.
Nitrate in ground water is primarily derived from mineralization of soil organic matter or from use of excessive nitrogen fertilizers. The nitrate content in supply water ranges from less than 1 mg NO3– per lit to around 50 mg NO3 per lit. The limit of 50 mg NO3 per lit was originally set to protect babies against methanoglobinaemia.
This is a condition where more than about 10% of the haemoglobin in the blood is converted into the methanoglobin form. It is a reversible condition, but death can occur only if more than 40% of the haemoglobin in the blood is converted because of reduced oxygen carrying capability. The condition methaenoglobinaemia occurs in young infants with high nitrate level in well water used for making milk formulae.
It has also been suggested that a high nitrate can reduce the body assimilation’ of iodine, thus causing goiter. It has also been suggested that an increased nitrate intake through drinking water carries an increased risk for bearing a malformed child in pregnant women.
Ground Water: Pollutant # 3.
Ground water arsenic contamination is known over the years in various parts of the world. However, the major incidence noted in Indian subcontinent is in West Bengal and Bangladesh region, where a vast tract is under the arsenic calamity. Several thousands of people are suffering from chronic arsenicosis through drinking of contaminated ground water.
The problem relating to arsenic contamination in ground water of West Bengal was first noticed in 1978 through a short study made by School of Tropical Medicine, Kolkata. Then, with the initiative of Public Health Engineering Dept., Govt. of West Bengal, an elaborate study was made during 1988-91 for making detailed report on the status of arsenic contamination of ground water.
All Indian Institute of Health & Hygiene, Central Ground Water Board, Centre for Man and Environment, State Water Investigation Directorate, and School of Environmental Sciences (Jadavpur University) participated in the detailed investigation on the said aspect.
The report indicates the fact that along a linear NNW-SSE tract extending from Kaliachak in Malda through Raninagar in Murshidabad, parts of Nadia and North 24 Parganas up to Baruipur in South 24 Parganas, the ground water between 10-80 m below ground level has been found to contain arsenic, at places above permissible Level of 0.05 mg/liter.
The area forms a part of the Ganga- Brahmaputra delta having a near surface succession of quaternary sediments of varying thickness. The arseniferrous belt lies entirely within the upper delta plain (UDP) characterised by a series of meander belts formed by rivers.
Arsenic content of ground water tapped at some depth within the same zone varies between wide limits. However, the maximum arsenic content occurs in ground water in the 20-60 m range, ranging from < 0.01 mg/lit up to a maximum of 2.0 mg/lit. There was no water samples (collected from ponds or dug- wells) containing arsenic above 0.01 mg/lit.
It has been established beyond doubt that water of the intermediate aquifer is polluted with arsenic. Neither the shallow first for the deep (third) aquifer contain arsenic above the permissible limit. The ground water in arseniferous areas is characterised by high iron, arsenic, Ca, Mg and bicarbonate with low chloride, sulphate and fluoride. The pH is about 7 to 8, which is very ideal for leaching of arsenic.
Further, it is speculated from the lithological and minerological analysis that the sources of the arsenic in the groundwater is primarily in the clayey sediments immediately above and intercalated within the intermediate aquifer.
These sediments were perhaps transported from the Chhotanagpur-Rajmahal highlands and deposited in sluggish meandering streams under educing conditions. Under such conditions arsenic got deposited partly as arsenious minerals, partly absorbed on surfaces of minerals or clay particles and the rest as organic complexes.
Arsenic content in ground water as measured in some areas of West Bengal is given in Table 11.8:
In many areas of West Bengal, the ground water-of shallow depth in particular—is contaminated with higher quantity of arsenic. It is now felt urgent to identify those sources and prevent the inhabitants not to consume such water.
In contrary, deeper tube well or dug well does not contain appreciable amount of arsenic. So it is wise to provide them either some deeper tube well or dug well or alternative source of treated surface water for drinking.
As the dissolved inorganic arsenical substance can make complex with various alum, it can easily be precipitated and then filtered for removal of contaminated arsenic. Many trials has already reached a great deal of success.
Yet much is needed to develop for promotion of efficacy at grass-root level. Chemical investigation with respect to routine urine and blood test for arsenic determination or its deposition in hairs or nails among the affected population is still quite inadequate.
Some arsenic removal technology currently adopted in arsenic affected area:
Further, the status of arsenic in crops and vegetable grown under shallow irrigation was not at all assessed in depth. There were enormous scopes for studying of arsenic in the ecosystem as a whole in near future.
Ground Water: Pollutant # 4.
Like arsenic, fluoride contamination was also reported since mid 1970s, in some districts of West Bengal and Assam. Earlier there were reports of surface water (dug well) contamination of fluoride in Andhra Pradesh. Due to such contamination, exposed community suffers very much in both short-term and long term basis.
There were reports of bony deformity and associated problems of locomotory organs .The children are more susceptible than the adults. There is a great need for identification of contaminated areas and also need for supply of clean non-contaminated water for cooking and drinking.
Government efforts to deal with the problem of fluoride contamination have focused primarily on providing safe drinking water through various schemes and the distribution of de-fluoridation plants at household and community levels. However, the main constraint to the success of these schemes has been lack of maintenance of these plants.
The Rajib Gandhi National Drinking Water Mission set up 427 de-fluoridation plants across the country, many of which are not in operation today. DANIDA initiated a rural water supply and sanitation project scheme in Karnataka’s four districts that include de-fluoridation. Central Government also proposes to provide 50,000 household water filters to families and groups of people at sub-sidised rates of Rs. 1,500-2,500 each.
An interesting scheme is being implemented in Punjab, where Uruguay gifted a modular water-treatment plant, the first of its kind in India, to the village of Talwandi Sabo. It was successfully implemented and now the Punjab Government has signed a MoU with the Uruguay Government for installing 20 such plants at a cost of Rs. 20 lakh each.
The compact plant requires little space, and purifies water with a mix of coagulation, sedimentation and filtration. According to the Ministry of Rural Development, fluoride mitigation centres are to be set up across the country. Currently in the first phase, centres are being proposed in three states of Andhra Pradesh, Rajasthan and Gujarat to increase the availability of potable water in villages.
Some technology intervention for removal of fluoride is given:
Ground Water: Pollutant # 5.
In most places in India, iron is also a major contaminant of ground water, so also drinking water too. There is also need for iron removal.
Control measures include providing alternate sources of water free from iron or treating iron contaminated water to within permissible limit of 1 mg/l with the help of iron removal plants. For treating iron contaminated water, the Rajib Gandhi Drinking Water Mission has approved the installation of 16,415 plants, out of which 9,355 plants have already been commissioned.
Iron removal from water supply can involve complex choices. The selection of an appropriate iron removal equipment would depend on the type and quantity of iron in the water, the characteristics of the water supply, other water treatment equipment in use, and the user’s requirements for cost, convenience of usage, and maintenance.