It is well known that trace elements are essential and beneficial to human health in minute concentrations, as they play an important role in many metabolic processes and act as cofactors. However, exceeding their permissible intake is known to be toxic and has adverse effects on general body metabolism. One such trace element, which is ubiquitously distributed in soil, earth and water is fluoride. It is a fact that low amount of fluoride (0.3-1.0 mg/l) in drinking water is helpful in the prevention of dental caries and in treatment of osteoporosis. However, high intake of fluoride (>1.5 mg/l) in drinking water for a prolonged period is known to cause damage to the teeth enamel and eventually leads to skeletal complications that result in fluorosis.
Mehsana district in north Gujarat is located within the latitudes 230 03N to 240 09N and longitudes 710 23E to 720 52E. The region is rich in agricultural production but is largely dependent on groundwater, both for irrigation and drinking water requirements. During the last decade, large scale exploitation of groundwater for irrigation has led to fall in groundwater table at a rate of approximately 3m/yr, though groundwater mining condition have now been there for the last two decades. As a result, residents of the region face the following problems:
- Fluorides and other dissolved salts in drinking water have shown progressively increasing trend and have exceeded the safe limit in past two decades
- Chemical quantity of groundwater is also showing adverse impact on soil fertility and crop growth.
- With progressive decline of groundwater table, more electric power is required to lift the same quantity of water.
- The process of deterioration of groundwater quality continues unabated and progressively increasing proportion of the population is seen to the affected by fluorosis.
In the present area, with groundwater as the primary source for drinking and irrigation, it is necessary that all aspects related to the problem be fully investigated and a quantitative appraisal made to help long term planning. To make a comprehensive review of this multifaceted problem, Water Resources Research Foundation (WRRF), approached the Habitat and Environment Committee (HEC) of the Habitat International Coalition (HIC) with the present project proposal. Following is a report of the investigations, largely based on study of published and unpublished reports with various departments of the Govt. of Gujarat and in the research journals.
Geologically the area comprises un-consolidated alluvial sediments derived by fluvial transport from north-eastern catchment of Aravalli hills and are partly mixed with blown sands from southwest. The deposition took place during last 200 kyr (Late Quaternary). The site of deposition was the Cambay basin which was formed during Tertiary due to block faulting and has been a tectonically active region ever since. The earlier stages of deposition experienced sea level fluctuations, while the later stages witnessed a rather arid environment with large scale contribution of aeolian sands. Neo-tectonic movements also accompanied the sedimentation process (Patel, 1986). Thus the deeper layers have fluvio-marine origin, while the upper layers have fluvio-aeolian characters. The thickness of sediments is more than 1,000m and comprises alternate layers of clay, silt, sand and gravel that show pinching and swelling structure of layers. Recent work (Prasad et al, 1997) has shown that the mainland of Gujarat was separated from the Saurashtra by a narrow, shallow sea-link joining the Gulf of Kachchh with the Gulf of Khambhat until about 65-70 kyr ago. The sea then receded during the period of last major glaciation and the sedimentation front advanced westwards filling the former sea corridor.
Due to their high permeability, the coarser layers comprising of sandy and gravelly horizons formed the aquifers which are separated by semi-permeable silty and clayey horizons. Brackish to saline conditions are observed in deeper aquifers which are generally found below 250m depth but occasionally even at much shallower depths. The continuity of aquifers occasionally gets disrupted due to pinching of layers or fault displacement. According to Patel (1986), the lower aquifers are hydro-statistically under artesian conditions. The general gradient of aquifers is towards west and these merge in eastern direction, where along the foot hill zone of Palanpur-Kheralu, these are exposed and receive natural recharge. Towards their western extension, the deeper aquifers abut against a thrust plane near Radhanpur-Viramgam belt. Along this belt, tubewells tapping the deeper artesian aquifers show free flow at ground, have high temperature and saline water. Recently, excess dissolved helium has also been recorded from groundwater of those wells.
The upper aquifers are under semi-confined condition. They receive recharge (i) directly by seepage from the shallow unconfined aquifer, (ii) by lateral flow from the recharge zone of Palanpur-Kheralu foothill region in the east. The shallow unconfined aquifer receives direct recharge from (a) rainfall infiltration, (b) nearby stream flow and, (c) by return flow from the irrigation. As one moves westwards the groundwater progressively becomes saline.
Radiocarbon dating of groundwater from deeper aquifers showed that the groundwaters were 15-20 kyr old (Bhandari et al, 1986). This means that the water being pumped was recharged by rain 15-20 kyr ago and has been in contact with sediment grains for such a long period. It is hypothesised (Patel, 1986) that high fluoride levels in groundwater are a result of leaching of this element (along with others) from the sediments which have their provenance (source area) in the metamorphic rocks of Aravalli hills. In a groundwater mining situation, as it prevails in the Mehsana and neighbouring districts of Banaskantha, Gandhinagar and Ahmedabad, pumped water with a larger residence time in the aquifer is, therefore, likely to have higher salinity including higher fluoride. The high total dissolved solids (TDS) and fluoride contours appear to run NE-SW and there is general decrease towards the NE (Figure 6).
At places, the shallow groundwater also shows poor quality on local scale. This is attributed either to local stagnation or high concentration of toxic elements in the host sediments and, in some cases, due to industrial pollution.
The areas on the banks of the rivers draining the region, namely Saraswati, Rupen, Banas and other smaller streams get recharged during the rainy season (June to September). At such locations, groundwater levels are relatively higher and shallow aquifers supply good quality water.
The groundwater development in the region can be sub-divided in three phases
- Pre-1935 phase: Groundwater at shallow depth (5-10m) and obtained from dug wells by bullock and manual lifting of water.
- 1935-1955 Phase: Groundwater levels declined to 10-30m and dug-cum-bore wells become prevalent and diesel pump sets were used for lifting the water.
- Post 1955 Phase: Groundwater levels began to decline rapidly and from sixties the decline has been between 1-3m every year. Deep tubewells fitted with electric motors have been used to lift groundwater from 100-250m depth.
The deterioration in groundwater quality almost parallels the post 1955 phase, when with the advent of tubewells and electric motors the groundwater extraction went up many folds. Gradually, the soil fertility was being affected by irrigation with high TDS groundwater and several native crops disappeared. Presently, cash crops of bajari, cotton and jowar are grown in the region.
The Geological Survey of India carried out groundwater investigations in the Mehsana area as early as 1953-54. At the time of this investigation tubewell development in Mehsana district was in its initial phase. In 1969, the need for artificial groundwater recharge through wells by rainwater or water from other suitable sources to augment the natural infiltration and to improve the quality of groundwater was already being discussed.
A survey was conducted in eighteen fluoride endemic villages in Mehsana district of north Gujarat. The individuals affected with fluorosis were examined for apparent mottled teeth and skeletal complications. Samples of urine and blood of these individuals along with drinking water were collected and compared with samples obtained from Ahmedabad city. The analysis of water, urine and blood also showed significantly high fluoride levels in individuals affected with fluorosis. Several other parameters indicative of metabolic functions were analysed which clearly indicated adverse effect of high fluoride ingestion.
Government of Gujarat has identified a few schemes for solving the water supply problems of this regions. Some of the schemes are:
1. Dharoi Reservoir Dependent Scheme:
371 villages belonging to Kheralu, Sidhpur, Visnagar and Patan taluka, will be provided with the 68.86 MLD of water under group water supply scheme, at an estimated cost of Rs. 140 Crore (Rs. 1.4 billion).
2. Sabarmati River Dependent Scheme:
109 villages from Vijapur taluka will be provided with water drawn from Sabarmati river at an estimated cost of Rs. 36 Crore (Rs. 0.36 billion).
2. Narmada Canal Dependent Scheme:
111 villages belonging to Chanasma taluka, 118 villages belonging to Kadi taluka and a large number of villages belonging to Sami and Harij taluka will be provided with the water from Narmada main canal by constructing necessary off take points, storage tanks and filtration plants.
These schemes can provide water for drinking, but people require water for a variety of uses including agriculture and industry. Long term solutions must come from either inter-basin import of water on a large scale or local storage of annually renewable rain water in surface and underground reservoirs. Nature has endowed the Mehsana area with excellent groundwater basin capable of storing enormous quantity of water in reserve. Over the years this reserve has been drained and needs to be refilled through a programme of fresh groundwater recharge. Unfortunately the natural conditions of this area do not provide for large surface storage reservoirs by dam construction. The present sources of natural and artificial recharge contribute negligibly compared to the exploitation. Therefore, there is a need to provide drinking water from whichever surface reservoir that can be utilised for this purpose but, provision for agricultural domestic and industrial requirements must come from innovative groundwater recharge schemes and increasing the efficiency of application.
The top alluvial cover being highly porous and permeable, storage tanks can improve the recharge on a local scale. The tank supported recharge wells can enhance groundwater recharge significantly, provided such measures are taken in large numbers. Practically all villages in the area have at least more than one sufficiently large size pond for constructing such wells. The recharge capacity can be further increased when additional supply, other than rainwater, is arranged through feeder canal network. The foothills zone along Palanpur-Kheralu-Modasa is the identified natural recharge area for the deeper confined / semi-confined aquifers of Mehsana area. Specific measures must be undertaken to recharge shallow aquifers in this zone.
A pilot project for tackling the fluoride problem based on artificial recharge of groundwater using storm water runoff has been proposed for the village of Balisana in Mehsana district of Gujarat. The estimated cost of the project envisaging fluoride free potable quality water at the rate of 50 litre per person per day for human population of 12,000 plus a cattle population of 3,000 is Rs. 48.00 lakh only (=US$ 120,000.-), which is less than the estimated cost of a pipeline based group water supply scheme dependent on import of surface water.
In conclusion, it may be worth mentioning that a satisfactory resolution of the excess fluoride problem in drinking water, using storm water runoff for groundwater recharge of shallow aquifers as advocated in this chapter would additionally lead to (1) small saving in groundwater presently used in irrigation and, (2) over a period of few years, some induced recharge to deeper aquifers through leakage via intervening aquiclude layers. We also visualise a study improvement in groundwater recharge technology so that it will be possible to recharge larger amounts of storm runoff even for non-potable applications. Ultimately, the long term solution to the water problem of the region lies in conservation of rain water, both in surface and subsurface reservoirs and, renovation and reuse of waste water.
Table of Contents
Executive Summary i
Table of Contents Viii
List of Figures xi
List of Tables xiii
Chapter: 1 Introduction
History of groundwater development
Chapter: 2 Geological Background
Areas with fresh groundwater at all levels
Areas with fresh groundwater overlain by saline groundwater
Areas with saline groundwater at all levels
Chapter: 3 Fluorine in Environment
Sources of fluorine ingestion
Chapter: 4 Fluoride and Biological Tissues
Effect of fluoride on bones, skeletal system and skeletal fluorosis
Characteristic structural changes in fluorosed bones
Parts of a tooth
Structural parts of teeth
Effects of fluoride/ fluorosis on soft tissues/ organs/ systems
Fluoride toxicity, fluorosis and its effects on Red blood cells
Effects of fluoride poisoning on the gastro-intestinal mucosa
Urinary tract manifestations
Ligaments and blood vessels calcification
Chapter: 5 Fluoride Toxicity Studies in Mehsana District, North Gujarat
Fluoride toxicity on body fluids and metabolic indicators
Genotoxic effects of fluoride in Mehsana
Chapter: 6 Remedial Measures
Schemes based on defluoridation of drinking water
Defluoridation of water using Nalgonda technique
Mechanism of defluoridation by Nalgonda technique.
Salient features of Nalgonda technique.
When to adopt Nalgonda technique.
Fill-and-Draw defluoridation plant for small community.
Fill-and-Draw defluoridation plant for rural water supply.
Status of Defluoridation plants in Mehsana district.
Schemes based on import of surface water
Dharoi Reservoir Dependent Scheme
Sabarmati River Dependent Scheme
Narmada Canal Dependent Scheme
Chapter: 7 Innovative Methods
Tackling fluoride problem through groundwater recharge
A pilot project proposal for tackling fluoride problem in Mehsana district based on groundwater recharge.
Percolation well design
Appendix 1 Village-Wise Distribution of Fluoride in Drinking Water in Mehsana District, Gujarat, India.