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Parts of Thar Desert, Rajasthan
Groundwater Studies
In this area, groundwater occurs under unconfined to confined conditions in the alluvium of Recent Age and sedimentary rocks of Tertiary and Mesozoic Age. Exploratory drilling in Jaisalmer district shows that the aquifers are encountered in the depth range of 45 to 70 m and 125 to 160 m.
The aquifers in Sam Block have been classified into several ground water potential zones based on the average discharge and water level conditions. The broader classification is: Alluvium (A1, A2), Tertiary Sandstone (T1), Parwar Sandstone (P1), Badesar Sandstone (Bd), Lathi Sandstone (L1, L2) and Granite (G). There are further bifurcations within these potential zones based on the criteria mentioned above and also quality of ground water.
Figure 5.7: Aquifer system in and around study area.
Source : CGWB
Water level
Ground water levels are monitored four times in a year by CGWB as well as by the State Ground Water Department. Monitoring wells, in and around the study area shown in the following map, are monitored for observing ground water regime. Some more observation wells are proposed to be established including dedicated piezometers.
Figure 5.8: Location of ground water monitoring wells.
Source : CGWB
The data, recorded from some of the monitoring wells representing different aquifer zones in Sam Block, during the period 1999 – 2008, is presented in the following ground water hydrographs. Depth to ground water levels vary from 15 to 55 m bgl in the A1 & A2 aquifers, from 60 to 98 m bgl in T1 aquifer, 104 to 110 m bgl in P1 aquifer, 70 to 105 in Bd aquifer, 87 to 107 m bgl in L1 & L2 aquifers and 58 to 68 m bgl in Ss1 aquifer.
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Source: CGWB
Geophysical studies
Vertical electrical soundings (VES) and electrical logs of the boreholes drilled under exploration program, in and around the study area, indicate different lithological groups and fresh – saline ground water interface. Depth to interface varies from 80 to 270 m bgl in Jaisalmer district.
Figure 5.24: Location of geophysical survey sites.
Source: CGWB
Boreholes, drilled in and around the study area, for estimating ground water potential and its quality, have revealed the presence of number of aquifer zones and chemical quality of ground water in them.
Figure 5.25: Location of exploratory wells.
Source: CGWB
Groundwater quality
Ground water in some parts of the area is contaminated with high salinity. The Electrical Conductivity of ground water ranges from 1500 to 9500 µ Siemens / cm.
Ground water is also affected with high fluoride content due to geogenic sources. It is higher than the permissible limit of 1.5 mg/l in some parts of the district, viz., Miazler, Phulia, Fatehgarh, Hamira, Awai and other places. The observation well, at Renau, just north of the study area has recorded fluoride content up to 7.0 mg/l.
It is planned to generate more information on the chemical quality variation in the study area.
Groundwater resources
The dynamic ground water resources have been estimated by Central Ground Water Board and the State Ground Water Board of Rajasthan for the year 2009.
As per the estimation, the annual replenishable ground water resources in Sam Block is 28 million cubic metres (MCM). The net annual ground water availability in the Block is 26 MCM, out of which 16 MCM is used at present for various purposes. The Sam Block is categorised as ‘Safe’ area for ground water development.