AN INTEGRATED HYDROGEOLOGICAL STUDY OF MAHENDRAGARH DISTRICT, HARYANA, INDIA

Abstract

Mahendragarh district, Haryana, located near its border with Rajasthan, is a semi-arid area and affected almost perennially by scarcity of water. The average yearly rainfall for the Mahendragarh raingauge station, recorded for the 40 years period between 1950 to 1990, is 497mm, whereas the annual potential evapotranspiration is greater than the annual rainfall and varies between 1400 and 1660mm for the district. In recent years, situation has become alarming due to the persistent decline of the water table, probably due to the over-exploitation of groundwater and deterioration in the quality of groundwater. Keeping in view these problems, the present investigations were undertaken with the following main objectives: (i) Geological and structural characteristics of the area (ii) Delineation of hydrogeomorphological characters using satellite imageries, and ground checks (iii) Evaluation of subsurface geological scenario from the available data of tube wells and Vertical Electrical Soundings (VES), newly-recorded VES profiles, identification of aquifer horizons, aquicludes and aquifuge materials (iv) Hydrogeological conditions including water table configuration, pattern of groundwater flow, fluctuation of water table and estimation of hydraulic properties like transmissivity etc. of shallow aquifers from electrical resistivity data (v) Groundwater quality and its hydrochemical chracterisation (vi) Probable origin of salinity in groundwater The rock formations of the Aravalli mountain belt belong to the Delhi Supergroup of the Precambrian age, and have been divided into the Alwar and the Ajabgarh Groups. The Alwar Group is well exposed in the northern and western parts and comprised of an immense* thickness of hard and compact quartzite, having a few bands of phyilite and mica-schist. The Ajabgarh Group is made up of calc-silicates, marbles, schists, quartzites, amphibolites, pegmatites and iron ores in the southern, southeastern and southwestern parts. The formations strike between N-S to NE-SW and steeply dip towards NW or SE. The slate and phyilite are also common in this area. The slate is vertically dipping and sometimes intruded by pegmatite bodies. The Delhi Supergroup of rocks have been subjected to tectonic stresses and therefore, suffered extensive folding, faulting and igneous intrusions. In the north, two large folds are doubly-plunging: the Sohla- Khodana-SiswatAnticline and the SSW-plunging Narnaul Syncline. The Sohla-Khodana- Siswala-Anticline trends NNE-SSW for a distance of at least 44 km. The core of this large fold is represented by an open, upright anticline, whereas the western limb of this fold is well represented by the longitudinal ridges. The Narnaul Syncline extends NNE-SSW for at least 15 km as a SSW-plunging open asymmetric syncline with westerlydipping axial plane. The eastern limb of this syncline is represented by continuous exposures, whereas its western limb shows a number of digitations. As observed on satellite imageries, and during the field study, the Ajabgarh Group have undergone intense deformation in southern parts, which has caused the development of folds, faults and joints. A series of isoclinal folds with axial 11 ABSTRACT trend in NNE-SSW direction is picked up. The present study corroborates the presence of three sets of folds (designated F«, F2 and F- in chronological order) and associated structural elements. The earliest recognisable tight, sharp-hinged isoclinal folds (Fj) trend NNE-SSW. These are superposed by open, upright asymmetrical/symmetrical F2 folds and co-axially refolded F, folds. The third deformation structures are open F3 folds, with WNW-ESE axial trend and high wavelength/amplitude rates. The rock formations exhibit characteristic jointing. The dominant directions are NE-SW (dipping 75° W) , N 130°-310° (dipping 50° NE ) and N75°-255° (dipping along 20 N). NW-SE trending fractures are open tensional joints, developed perpendicular to NE-trending fold system and are of relevance in groundwater localisation and movement. Systematic and careful visual interpretation of False Color Composites (FCC) of the IRS 1A Satellite Imageries was carried out to demarcate geomorphic/landforms, fracture traces and lineaments. The hydrogeomorphological features have been divided into following geomorphic units, (i) Depositional features comprised of alluvial plain, sand dunes, points bars, and flood plains (ii) Moderate structural denudational hills (iii) Low-lying structural denudational features, e.g., inselbergs, pediplain, valley fills and vegetation anomalies The relative hydrogeological significance of geomorphological features and NWSE- trending lineaments has been confirmed by the productive wells, drilled along the fracture traces and lineaments. in It is inferred that study of fracture traces, and lineaments along with hydrogeomorphological features are important aids in targetting and localisation of groundwater in a geologically and structurally complicated area. Subsurface distribution of different geological formations and groundwater conditions have been deduced from resistivity variations with depth along with other field geological evidences. A total of 54 Vertical Electrical Soundings (VES) including 10 no. of newly-recorded VES data, using Schulumberger electrode configuration, has been utilised in this work, while data have been interpreted by a computerised (Direct) technique with curve-matching for calibration purposes. The resistivity ranges, assigned to the different subsurface formations, are 18 to 110 ohm-m for sand, 5 to 100 ohm-m for clay-sand admixtures (depending on fraction of clay), 4 to 18 ohm-m for clay, 9 to 153 ohm-m for kankar-clay mixture, 200 to 270 ohm-m for pegmatite ,40 to 200 for quartzite (weathered and semi compact), greater than 200 ohm-m for quartzite (compact), 95 to 270 ohm-m for calc-silicate rock and 665 to 800 ohm-m for slate. However, these resistivity ranges had to be utilised judiciously, keeping in view the known geology, lest it may lead to erroneous interpretation. Depth to the bedrock is highly variable and slopes towards northeast and north in the area. As a consequence, thickness of alluvial deposits increases from south to north and from west to east. The sandy horizons in a few sections appear to be water bearing in the northwestern parts of the area. The occurrence of saline groundwaters, as witnessed by the high EC values of groundwater, is also indicated along a few sections lines. In Madhogarh area towards NW, quartzite appears to be compact. However, the decrease in the value in resistivity in deeper zones tends to indicate fractured nature of quartzite formation, saturated with freshwater. The thickness of alluvium also increases gradually. iv ABSTRACT Hydrogeological inventory and network monitoring have indicated that the principal aquifer is made up of alluvial sands, often mixed with silt, gravel and kankar. However, groundwater also occurs in fractured rocks. Data from observation wells indicate that depth to watertable is highly variable in a wide range between 8m and 38m (bgl). It is shallow in NE parts and deepest in the NW and western parts. Further, there has been a considerable decline of watertable upto 25m in the past few years, especially in the western and southern parts. Such notable decline in watertable can be explained due to low recharge during lean rainfall years and overexploitation of groundwater. The watertable elevation contour maps for the years 1991, 1992 and 1993 indicate that elevation of watertable varies between 226m (AMSL) to 295m (AMSL). In general, the watertable slopes towards north and northeast. The permeability of the aquifer is greater in the northern parts, whereas steeper hydraulic gradients occur towards south and northwestern parts indicating low permeability of the aquifer. Estimation of transmissivity and hydraulic conductivity of unconfined alluvial aquifer has been attempted, using data from resistivity soundings and relationships between aquifer transmissivity and transverse resistance. However, wide variations in salinity of groundwater tend to produce conflicting results. Computed transmissivity of the aquifer at seven localities ranges from 77 to 2 2 764.6 m /day and compares reasonably with the field transmissivities (118-360 m /day) for the corresponding locations. The RMS error in such estimates was computed to be 2 36.74 m /day, which seems to be within reasonable limits, inspite of the wide fluctuations in groundwater salinity. Groundwater samples, procured from the open and deep wells spread over five administrative blocks over three seasonal cycles of periods, were analysed to establish quality characteristics of groundwater. The samples were analysed for major ions like Ct2, Mg+2, Na+, K+, HCO3, CO3? S042 , CI and TDS, pH and electrical conductivity (EC). pH values (7-8.5) indicate the alkaline character of groundwater. Low to very high values(650 to 5500 micro mhos/cm) of electrical conductivity indicate that the groundwater quality is marginal to saline in central, northern, southern, northwestern parts. CT & Na+ are the dominant ions with concentrations varying from 60 to 2200 mg/1. Groundwater is also very hard (total hardness upto 1400 mg/1) in the northern and southern parts, whereas the alkalinity varies from 170 to 600 mg/1. The concentration of K+is also considerably high and exceeds 250 mg/1 at a few locations. However, other chemical constituents in groundwater seem to be generally in the permissible ranges, given by WHO and other Regulatory agencies. The plotting of groundwater quality data on Expanded Durov's Diagram has revealed a general Na+-CT-type of groundwater, although groundwater of deeper aguifers shows high concentration of Ca+2 and SO4 exhibiting dissolution or mixing character of the groundwater. In addition, the plotting of chemical data was also carried out in the Hill-piper diagram and Romani's modified Hill-piper diagram. Though the Hill-piper plots do not indicate a definite chemical character of groundwater, Romani's triangular diagrams seem to indicate mainly Na+ and Cftype of groundwater, followed by sodium-calcium-chloride-sulphate types. Principal Component Analysis and Factor Analysis of groundwater have also been attempted to assess the chemical characteristics, in which epm ionic values have been utilized. However, a clear picture of dominant chemical character of groundwater has not emerged from the multivariate study, due to the limitation of these techniques to bring out the main chemical attributes of groundwater. Apart from the major ions, the groundwater samples were also analysed for halides (I', F'and Br"). It has been observed that fluoride concentration in the Vi ABSTRACT groundwater from 21 wells is higher than the optimal range, mainly in the NE, NW, SW and central parts. Further, F concentration is greater in deeper aquifers when compared to the shallow ones, probably because the deeper aquifers are in the close proximity of the hard rocks containing fluorine -rich minerals. It seems that lithology of the geological formation is the major controlling factor in causing high concentration of fluoride. As the concentration of I" and Br" are related to the residence time of saline waters, the 17 Cl'ratios versus I" plots show enrichment of I in the saline groundwater. This may be attributed to longer residence time of groundwater caused due to its entrapment within the low-permeability aquifer materials receiving low recharge. Thus, the groundwater in deeper aquifers seems to be of ancient origin. The present work has demonstrated the usefulness of integrated hydrogeomorphological, remote sensing, geophysical and groundwater quality studies in the geologically-coomplicated terrains for understanding their hydrogeological and chemical attributes.