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The study area of Degana block lies in the Nagaur district of Rajasthan, about 85 km southeast of district headquarter Nagaur city. Geologically, Degana block has wide spectrum of rock formations ranging from Archaean Basement to Recent Alluvium. Older Alluvium, Tertiary Sandstone, Phyllites, Granites/Gneiss are hydrogeological formations demarcated in Degana block. Occurrence of high fluoride and T.D.S. in groundwater is a serious health hazard for drinking water. Concentration of high fluoride in some part of the study area (part of Banka Patti belt) causes Dental and Skeletal Fluorosis and other diseases. Exploitation of groundwater resources in the block has resulted in water level depletion and therefore the area is recommended for adoption of adequate measures for conservation of available groundwater resources.

The main objectives of the present study are to establish the Geology and hydrogeology of Degana Block of Nagaur district of Rajasthan. On the basis of detailed Hydrogeological investigations based on the chemical quality and availability of groundwater different potential zones identified in different formations and study severity of the fluoride problem in the study area. Appropriate measures suggested for minimizing the fluoride problem and to increase of groundwater recharge in the study area.

The relative accounts of the Geology, hydrogeology of Rajasthan and fluoride problem were provided by Underwood, 1977; Singh and Seimbi, 1988; Paliwal et al., 1997; Gouran and Vyas, 1998; Susheela, 1999; Soni et al, 1999; Vyas, 1999 and later on several attempts were made by different workers Vyas and Paliwal, 2001; Maanju et.al. 2003; Ozha, et al., 2003, Hussain et al., 2007; Vyas, 2010; Vyas, 2015 and Chauhan and Vyas, 2021 to study the subject.

Geology and Hydrogeology

Geologically, Nagaur district is occupied by the Archaean basement, rocks of  Aravalli and Delhi super groups, Erinpura granite, Malani igneous suite, Marwar super group rocks.(Paliwal et al., 1997). Malani igneous suite of rocks viz, rhyolite and granite are exposed in the Eastern part of the district near Degana and Didwana. The diverse geological formations found in the Degana block range from Archaean Basement to Recent Alluvium (Table-1). The Pre Cambrian phyllites spread in 69.38 sq. km area in the SSE area of the block, the granites and Gneisses cover 115.34 sq km area in the central part of the block, Tertiary Sandstone covering 252.50 sq km area in the western part of Degana block and the Recent Alluvium covering 1025 sq km area in the block (Soni et al, 1999).

Hydrogeologically the whole district can be classified into three formations viz. consolidated formation, semi-consolidated formation and unconsolidated formation.  Hydrogeological formations identified in the Degana block include Older alluvium, Tertiary Sandstone, Phyllites, Granites, and Gneiss. Groundwater generally occurs under water table conditions in the alluvium and schist but under semi confined to confined conditions in sandstones due to presence of overlying argillaceous beds in the study area (Vyas, 1999; Vyas and Paliwal, 2001; Vyas, 2010; Chauhan and Vyas, 2021). Depth of groundwater measured during pre and post monsoon seasons varies considerably in the open wells of Degana block (Figure-2). Groundwater level recorded in Pre and Post Monsoon seasons during 2016 and 2021 were analyzed and given in Table- 2. Abnormal values recorded in villages – Degana and Rewat for Pre to Post Monsoon season-2021. Water level depletion recorded in almost all key well stations except Bachhwari and Thata for Pre monsoon-2016 to Pre monsoon-2021 seasons.

Figure 2 : Measuring groundwater level of open well in Degana block

Table-2: Groundwater fluctuations in Degana block of Nagaur district for period 2016 and 2021 (values of Groundwater level are below ground level; in meters)

In Degana block in older alluvium average depth to water is 40 meters below ground level. Yield of wells and tube wells from these aquifers varies from 36 to 540 m3/day and groundwater having electrical conductivity between 4000-8000 micro-siemens /cm. at 25° c. Average depth to water in Tertiary Sandstone is 50 meters below ground level and the yield from these resources varies from 18 to 540 m3/day.  Other water bearing formation schist located in the northeast part of the Degana block, in these aquifers groundwater is available only in weathered zone and yield from these is low to moderate (Gouran and Vyas, 1998; Vyas, 2010; Chauhan and Vyas, 2021).

Status of groundwater in Degana block of Nagaur district for period 1990-2020 as per State groundwater Department is given in Table- 3. Degana block was categorized in White category during year 1990 but later on since 1993; due to overexploitation of the groundwater in the block it is categorized as Dark/Over exploitation. Static groundwater reserves i.e. the groundwater that occurs permanently within saturated zone of the groundwater reservoir; are computed, considering the average thickness of the zone of saturation, specific yield of the formation and its areas extension. The formation-wise static reserves of the Degana block have been calculated in the Degana block of Nagaur district are given in Table- 4 (Gouran and Vyas, 1998).

Table- 4. Static groundwater reserves, formation-wise, in Degana block of Nagaur district of Rajasthan, India (after Gouran and Vyas, 1998).

Note: Non Potential Older Alluvium {Saline (Ao)} area of 260.00 sq.km. of the Degana block is not included.

Hydrochemistry

To study the groundwater quality of Degana Block groundwater samples were collected from different 22 villages during Pre-monsoon - 2018 season. Chemical analysis reveals that groundwater quality of the Degana block show high concentration of fluoride, nitrate, chlorides and total dissolved solids much higher than the limit prescribed by the Bureau of Indian Standards (1992). Results of groundwater samples analyzed are given in Table- 5. 

Nitrate in groundwater is an important factor for judging the portability of water. High concentration of nitrate in groundwater shows its pollution by extraneous sources and renders its quality unfit for drinking use. Indiscriminate use of nitrogenous fertilizers, unorganized way of sewage disposal and decay of organic matter in surface water bodies contributing nitrate in groundwater significantly. 65% of the Groundwater sources in the Degana block falls in the desirable limit of the Nitrate (i.e. <45 mg/l), 15% of groundwater source having the high values of Nitrate (i.e. 46-100 mg/l) while remaining 20% of the groundwater showing very high values of Nitrate (i.e. >100 mg/l). Kiroda and Kawal villages in the Degana block reported high Nitrate values up to 178 mg/l and 182 mg/l respectively. (G.W.D. Report, 2018).

 Nitrate concentration in groundwater within desirable limit lies only in seven villages. All other samples show nitrate in the groundwater exceeding 45 mg /litre. Over all 31.81% samples (07 villages) in the block have nitrates exceeding the emergency limit i.e.100 mg /litre. Nitrate concentration ranges from 04 ppm (Akeli-B) to 375 ppm (Jakhera). (Chauhan and Vyas, 2021).

The Chloride in groundwater imparts a salty taste to the water when it is present in concentration more than 200 mg/l. The Bureau of Indian Standards (1992) suggested chlorides in drinking water to the extent of 250 mg/l in general and up to 1000 mg/l in emergency to be good for the human health. The high chloride concentration in the Degana block confirms that groundwater of the block is hard and saline water having Chloride type of character. Only 13% of the Groundwater sources in the Degana block falls in the desirable limit of the Chloride (i.e. <250 mg/l), 8.7% of groundwater source having the high values of Chloride (i.e. 251-1000 mg/l) and remaining 78.3% of the groundwater showing very high values of Chloride (i.e. >1000 mg/l). Jalsoo Nanak village in the Degana block reported high Chloride value up to 3829 mg/l (G.W.D. Report, 2018). Chemical analysis of samples of 22 villages has shown that about 95.45% villages in the block have Chlorides in the groundwater more than 250 mg/l. Chlorides concentration ranges from 150 ppm (Luniyas) to 4050 ppm (Chudiyas). (Chauhan and Vyas, 2021).

The behavior of water's salinity is indicated by total dissolved solids (TDS). More than 500 mg/l of TDS in water is not regarded as good for drinking purposes. An average TDS content that was discovered to be higher than the permitted limit may be the result of different pollutants seeping into the groundwater. This can reduce the water's portability, irritate human gastrointestinal tracts, and have laxative effects. High TDS levels may not be aesthetically pleasing for bathing and washing. Only 4.3% of the Groundwater sources in the Degana block falls in the desirable limit of the TDS (i.e. <500 mg/l), 17.4% of groundwater source having the high values of TDS (i.e. 501-2000 mg/l) and remaining 78.3% of the groundwater showing very high values of TDS (i.e. >2000 mg/l) Achojai village in the Degana block reported high TDS value up to 7620 mg/l (G.W.D. Report, 2018).  Over all 77.27% samples (17 out of 22 villages) in the block have T.D.S. in the groundwater exceeding the emergency limit i.e. 2000 mg /liter. Values of T.D.S. range between 485 ppm (Luniyas) to 9500 ppm (Chudiyas). (Chauhan and Vyas, 2021).

Nearly 13% of the Groundwater sources in the Degana block falls in the salinity level fresh to slightly saline (i.e. E.C.< 2000 µS/cm), 8.7% of groundwater source are moderately saline (i.e. E.C. 2000-4000 µS/cm), 47.8% of groundwater source are highly saline (i.e. E.C. 4000-8000 µS/cm) and remaining 30.4% of the groundwater are very highly saline (i.e. E.C .>8000 µS/cm) Achojai village in the Degana block reported highest E.C  value up to 12700 µS/cm (G.W.D. Report,2018). Groundwater in Degana block is alkaline. pH value of groundwater samples ranges from 7.5 (Thata) to 8.5 (Kitalsar and Sanjoo).(Chauhan and Vyas, 2021).

Fluoride Problem in the Region

Fluoride presence in groundwater has drawn attention of society due to its impact on human physiology. Deficiency of fluoride (<0.6 mg/lit) causes dental carries and excess amount (>1.5 mg/lit) causes skeletal fluorosis and other manifestations (W.H.O.,1971, Bureau of Indian Standards. 1992). Higher concentration of fluoride affects metabolic activities of an individual which may cause skeletal fluorosis, dental fluorosis, non-ulcer dyspepsia, polyurea (to urinate more frequently), Polydipsia (excessive thirst), muscle weakness, repeated abortions/still birth due to hampering of blood flow to fetus on account of hardening and calcification of blood vessels, oligospermia (deficiency of spermatozoa in semen), azoospermia (absence of supermatozoa in semen), low testosterone level, discoloration of teeth enamel (Underwood, 1977; W.H.O., 1984; Singh and Seimbi, 1988: Machoy et.al., Susheela, 1999. Maanju et.al. 2003).

Due to arid climatic condition and scarcity of surface water resources inhabitants of Rajasthan are dependent largely on groundwater for drinking and agriculture purposes; 30 districts (out of 32 districts) of the State are facing the fluoride problem. Around 20% of the fluoride-affected villages of the world are in India. Out of 33211 fluoride affected villages in the country, Rajasthan has 16560 villages (>50%) (UNICEF, 2001). About 64% villages of the Nagaur district are endemic to fluoride related problems. High concentration of fluoride (i.e. > 4.00 mg/l) in a particular belt lying in south eastern part of the district covering parts of Parbatsar, Makrana and Degana blocks is so remarkable that people call that area as Banka Patti (Banka – Distorted, Patti – Belt; the term used for a strip of land where deformed people reside).

A study by Hussain et al. (2007); on distribution of fluoride contaminate in groundwater performed in 750 villages of Nagaur district of Rajasthan by collecting 871 water samples. Fluoride concentration in the district varied from 0.1-19.0 mg/lit. 510 (68%) villages had a fluoride concentration above 1.5 mg/lit. 142 villages (18.93%), were in category I, in which the fluoride concentration was below 1.0 mg/lit, the maximum desirable limit of standards for drinking water. Out of 750 villages of Nagaur districts, 98 villages (13.06%) had a fluoride concentration between 1.0-1.5 mg/lit and fell in category II. The maximum permissible limit of fluoride in the standard for drinking water is 1.5 mg/lit. About 44% of the population of 322 villages (42.93%) consumes water with a fluoride concentration between 1.5-3.0 mg/lit, which is above the maximum permissible limit as recommended by BIS. In 22 villages (2.93%) the fluoride concentration in the groundwater was above 5.0 mg/lit. The fluoride concentration in Nagaur district is not uniform due to variations in the presence and accessibility of fluoride bearing minerals to water and the weathering and leaching process.

All types of aquifer in Nagaur district have shown a high concentration of fluoride in the groundwater (Vyas, 2015). Fluoride in groundwater is contributed by minerals like, Fluorite, Apatite, Topaz, Fluorspars, Metamorphic and Sedimentary rocks. Concentration of high fluoride in some part of the study area (part of Banka Patti belt)  causes Dental and Skeletal Fluorosis and other diseases like mottling of teeth, bamboo spine, deformation of bones and stunted growth in human beings as well as livestock.

Fluoride Dilemma in Degana Block

On the basis of the fluoride concentration in the study area Soni et al. 1999; have classified the area of Degana block in to central zone (highly problematic, >5 mg/lit), intermediate zone (problematic, 2 to 5 mg/lit), and peripheral zone (safe, 0-2 mg/lit) covering 46.80, 942.23 and 474.24 sq km area respectively. The general groundwater flow direction in the area is north-west and the hydraulic gradient in the central zone is low as compared to intermediate and peripheral zones. High concentration of fluoride in the groundwater is present along the groundwater flow direction, where the hydraulic gradient is also comparatively less and it is also contributed by the groundwater of Banka Patti area, north-east to the Degana block area. The granites, gneisses and pegmatites present in the central part of the area also contribute to the fluoride contents in groundwater (Soni et.al. 1999).        

8.6% of the Groundwater sources in the Degana block falls in the desirable limit of the Fluoride (i.e. <1.50 mg/l), and remaining 91.3% of groundwater source having the high values of Fluoride (i.e. >1.50 mg/l). Kitalsar village in the Degana block reported highest Fluoride value (G.W.D. Report, 2018).

72.72% samples (total 16 out of 22 villages) were found to have groundwater with fluoride content exceeding the prescribed permissible limit. Groundwater in 31.81% samples    (07 villages) has fluoride content ranging between 1.6 to 3.00 mg/l. About 36.36% (8) villages have fluoride in the groundwater ranging between more than 3 to more than 5.00 mg/l. Fluoride concentration ranges from 0.54 ppm (Rajod) to 6.81 ppm (Kitalsar).(Chauhan and Vyas, 2021).

Fluoride’s presence in groundwater may be associated with the sedimentation processes, since quaternary sediments of the Degana block area are rich in micaceous minerals, which contain fluoride. Eastern most area of the Degana block having high concentration of fluoride in groundwater. Excess fluoride prone areas of the Degana block are given in Table- 6.

Figure 3: Dental Fluorosis affected person in Degana block

Figure 4: Skeletal Fluorosis affected person in Degana block

The "water" is about to be designated as a rare resource. India has a 2461 Cu. M./person/year available water supply. The most valuable and commonly used resource on the earth is groundwater, which is a gift from nature to all life. The time has come for everyone in every hamlet to recognize groundwater as a valuable resource that requires care, collection, storage, and management so it may be used again at the time of scarcity. The availability of groundwater resources, which are found below the surface of the ground, is crucial for the survival of life. Due to arid climatic condition and scarcity of surface water resources, inhabitants of Rajasthan State are largely dependent on groundwater for drinking agriculture and industrial purposes.

Groundwater of the study area of Degana block has quality problems. Groundwater quality varies widely in the study area; it is saline in northern and central parts of Degana blocks. Depth to water varies considerably in the block. High concentrations of T.D.S., nitrate and fluoride are major quality problems associated with groundwater (Vyas, 1999). The effects of high fluoride concentration in groundwater in the study area are very severe; have causing fluorosis problem in the region. High concentration of fluoride is present along the northwest flow direction of groundwater where hydraulic gradient is comparatively low and also near the rocks, which are enriched in fluoride contents. Granites, gneisses and deluvial placer deposits in the area of Degana block contribute the fluoride concentration in groundwater. Occurrence of high fluoride in the groundwater of the area is a serious health hazard for drinking water (Vyas, 2010). Remedial steps suggested for the area include-micro level survey by developing number of piezometers at different locations in study area and its regular periodical monitoring, and study of fluctuation of fluoride content vis-a-vis rise or fall of water table. Detailed studies are to be carried out to know the exact source of fluoride in the area. Grass root education should be imparted to the rural uneducated section of society about the severe effects of high fluoride on health (Vyas, 2010). Due to its effects on human physiology, the presence of fluoride in groundwater has attracted the attention of society. The suffering of the locals is made worse by the dry to semi-arid climate, poor, inconsistent rainfall, lack of surface water supplies, frequent famines, and decrease of the water table. Therefore, it is advised that the research region adopt suitable methods for groundwater resource conservation and judicious management.

Over exploitation of groundwater in the Degana block coupled with limited groundwater recharge has resulted in depletion of water table, desaturation of aquifers and deterioration in groundwater quality. Therefore, it is recommended that adequate measures for conservation and judicious groundwater management schemes be adopted. Artificial recharge methods need to be implemented on large scale for augmenting groundwater resources by roof top rain water harvesting and other important viable water harvesting systems practiced in the region include Talab, Nadi, Tanka, Pond, Bawari, Percolation tanks and other suitable recharge structures at appropriate locations (Figure-5 and 6). Use of surface water for drinking and irrigation purposes by developing a lift canal from main Indira Gandhi Canal, in the high fluoride concentrated groundwater area will be the next alternative in near future (Chauhan and Vyas, 2021).

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