Hydromorphogeological Microzonation to Infer Groundwater Potential and Quality in National Capital Region

Abstract

Multi-sensor satellite data integrated with Global Positioning System enabled geophysical and geochemical information has the potential to infer the availability and quality of groundwater in metamorphic Aravali formation of National Capital Region. Surface manifestation of satellite data has the potential to infer subsurface geology as well as soil moisture in weathered aquifer material. Normalized Difference Vegetation Index computed from the vegetation above the inferred lineament has the potential to infer groundwater quality. Electrical resistivity, X-Ray diffraction (XRD) and Induced Couple Plasma Emission Spectrophotometer (ICPES) analysis further support the spectral reflectance anomaly in litho units. Deep seated fractures with interconnected morphological manifestation have been inferred by using Proton Precession Magnetometer anomaly data. Although it was not possible to infer very deep seated potential fractures by using satellite data but the accurate ground truthing by geophysical investigations has been used to provide a clear hydromorphogeological attribute of potential aquifers. Drilling litho logs supported by thin section petrography suggests that high grade metamorphism is suggestive of good fractures in quartzite-schist-granite-pegmatite terrain of Aravali formation of Research and referral Hospital and Jawaharlal Nehru University areas.

ICPES and XRD analysis of these metamorphic litho-units, weathered material, soil and groundwater confirms that groundwater quality improves with the grade of metamorphism of the Precambrian formation. Eleven deep tube wells were drilled in this terrain down to 150 meter to 185 meters below ground level (bgl) are showing five to seven sets of potential aquifer zones from 25 meter to 165 meter bgl. In most of the cases the shallow aquifer zone ranging from 25 meter to 32 meter bgl were dried up due to over pumping and improper land use practices. After successful tapping of multiple fracture zones in this unconfined aquifer, the piezometric head has shown a substantial rise. Raised groundwater level has laterally recharged the dried aquifers in the water starved Aravali terrain. NDVI attributes further confirm good health of vegetation, which is suggestive of the quality and quantity of groundwater in this area.

Introduction

The National Capital Region (N.C.R) falls in the Western zone of the country. It gets an average rainfall of 632mm/year. Moreover, National Capital Territory (NCT) is situated on the banks of Yamuna which is a tributary of Ganges. Yamuna’s water has been channelized to other areas. By the time Yamuna reaches Delhi, it does not remain a river but turns into a drain. The water problem in National Capital Territory is well known. Unprecedented growth of urbanization in the area has resulted in the destruction of the traditional surface water structures for constructing buildings. This has resulted in the scarcity of water for various uses. With the rising population of NCR and the declining availability of water due to industrial pollution & destruction of surface tanks and pond, the water scenario of NCRis alarming. Frequent failure of monsoons, increasing demand and over exploitation leads to depletion of groundwater resources in many parts of the country. Groundwater is not only an important component of the hydrological cycle but also an important source of drinking water. Comparative estimation indicates that probably at least two hundred times the volume of annual run off from the world’s river is stored as groundwater beneath the land surface( Maning, 1987).Therefore detailed investigation regarding the occurrence and renewal of groundwater has become necessary. Safe use, tactical exploration and management of groundwater resources require good knowledge and proper understanding of the groundwater regime and its control.

Material and Methodology

Multisensor satellite data were georeferenced for interpretation and delineation to infer potential zones for groundwater exploration and assessment of its quality. Based on theanomalous attributes of satellite data, groundwater exploration sites were selected. Interconnected fracture zones in the Quartzites and Pegmatites shows anomalous NDVI values. Resistivity and magnetic surveys were conducted in these places to recommend sites for drilling. NDVI values of satellite data were further correlated to infer the quality of groundwater. Deep rooted vegetation extracts groundwater from the interconnected fractures. ICPAES study of the groundwater in some areas of Pegmatite and quartzite friction zone shows higher concentration of dissolved ions, which was correlated with the higher attribute of near infrared reflectance. The hydromorphogeological information were interpreted in GIS format to infer the microzonation of units showing qualitative and quantitative character of groundwater.

Software Used(i) Arc/Info GIS Workstation version 9.1
(ii) Arc View GIS 3.1
(iii) Auto CAD Map 2000
(iv) ERDAS Imagine Image Processing Software Version 8.4
(v) Rockworks 6.9.8
(vi) Geoimage
(vii) SPSS 14 for Windows

Pre-Processing of Satellite Images

The LISS- III image was obtained from NRSA for the year 2005.
• Satellite image from IRS-1D, LISS-III sensor, on a scale of 1:50,000(geo-coded) representing synoptic view of earth’s surface at 25mX25m ground resolution in three spectral bands have been procured. The details of the IRS data used to accomplish the study are given below (Flowchart.1).

• Data product –Standard FCC (False colour composite), bands 1, 2 and 3 in the range of (0.52-0.59 microns) B2, (0.62-0.68microns) B3 and (0.77-0.86microns) B4 respectively.

• Projection: The image was projected to Lambert Conformal Conic Projection, Spheroid and datum Everest.

The SRTM data were processed to transform it into product usable in GIS:-

• Conversion of raw data: the image was converted from the DTED Level-2 format to ESRI grid format (resolution 79.6m X 79.6 meter).

• Mosaicking: the individual tiles were mosaicked and then was clipped using shapefile of study area.

• Projection: The final output of step b was projected into Lambert Conformal Conic projection, spheroid and datum Everest.

The Resourcesat-1 (PAN and LISS III merged) satellite image was projected in the same manner. This ultimately helps in increasing the spatial resolution which helped to determine the lineaments in the area easily.

Geophysical Investigation

Delhi ridge lineaments were inferred using RESOURSESAT-1 (IRS-P6) Sensor-AWIFS data show a strong trend in NE-SW direction only (Figure.1) Further, the area was studied using IRS-1D Panchromatic and LISS-III sensor data(Figure.2) has shown detailed lineament which passes though Asola Bhati sanctuary, J.N.U. Sports Complex (stadium), RR Hospital and extends up to Bahadurgarh in Haryana (adjacent to north west Delhi). Panchromatic sensor shows detailed land use patterns of Delhi area, which are useful information in water resource management (Figure.3). Measurementswere taken along this lineament, which is inferred as sudden decrease in resistivity andmagnetic values (average magnetic value of Delhi region is 47,000 gammas).

Groundwater recharge map of whole Delhi and specifically ridge area has been prepared by using multisensor satellite data and geophysical investigations. Based on the spot magnetic values in and around NCR region, 20 profiles were done. Contour maps were made along the profile. Contour lines were drawn at every ten gammas interval; Low magnetic values were noticed in lineaments intersections which were showing low resistivity on ferruginous quartzite. Selections of drilling sites were based on the points inferred by magnetometer showing low magnetic values and interconnected lineaments.

X- Ray Diffractometer: - Bulk mineral composition and concentration of the various elements in the drill cuttings were analyzed using the X-Ray diffractometer. Model used is PW 3040/60 X/ Pert PRO Console (Philips, The Netherlands). Interpretation of modern x-ray diffractograms requires several steps

1. Completely drying the samples
2. The rocks (drill cuts) samples were crushed – 200 mesh in agate pestle and mortar for analysis.
3. Slides are prepared from the meshed samples and put in the X-ray diffractometer to get the xray diffractometer in the rd, dat and udf format.
4. The results were then analyzed on X-Pert High Score software.

ICP-AES Analysis: - Multielement Analysis by BRGM Procedure

The geological materials such as rocks, soils and stream sediment samples were crushed – 200 mesh in agate Pestle and mortar for analysis. The geological samples were digested with mixed acid (HF, HCI, HNO₃ and HCIO₄).

Methodology adopted for ICPAES analysis
Alkaline and acid fluxes are also very effective for the decomposition of refractory minerals. Basic Fluxes efficiently decompose complex silicate and minimize volatilization of minerals. Among these Fluxes, Sodium Hydroxide, Carbonate, Peroxide and their mixtures have been used. Sodium Peroxide is very effective for decomposing materials containing Sn, W, Cr and Mo. The flow sheet scheme for sample treatment, decomposition and dissolution for multi element analysis of rocks, soils and stream sediments by ICP-AES is shown in the figure. BRGM program for the determination of major, minor and trace elements, special wavelengths and limits of detection in solid materials, for geotechnical exploration samples, based on l gm sample in 100 ml (Figure.4).

Soil Particle Size Analysis

The particle size analysis of soil estimates the percentage sand, silt and clay contents of the soil and is often reported as percentage by weight of oven dry and organic matter free soil. The analysis is usually performed on air-dry soil. Based on the proportion of different particle sizes, a soil texture category may be assigned to the sample. The first stage in a particle size analysis is the dispersion of the soil into individual particles - sand (>1000μm - 600μm - 37μm). The hydrometer method of silt and clay measurement relies on the effects of particle size on differential settling velocities within a water column. Theoretically the particles are assumed to be spherical and have a specific gravity of 2.65. If all other factors are constant, the settling velocity is proportional to the square of the radius of the particle in accordance with stoke’s law.

Drilling details

Based on the Remote sensing and Geophysical investigation, exploratory drilling were carried out in 7 locations at JNU and 4 locations in RR Hospital in NCR in 2006-2007. The details of wells drilled in JNU are shown in Table:1.

Yield Description

Groundwater occurs in Aravaliis in confined aquifer at various levels in JNU area (24mbgl to 185mbgl). After drilling on scientifically selected suitable sites, 100% success was achieved in this water starved, metamorphic terrain. Based on the lithologs prepared by Remote Sensing Application Laboratory, SES, JNU, slotted pipes were lowered down to scientifically corrected accurate depth zones. The compressor test was carried out. In this process a pipe of diameter inch with orifice diameter of 2.5inch was fitted in the discharge pipe. Head of the orifice was measured through a transparent rubber tube. Table.2 Shows discharge of groundwater in Lt/hr from circular orifice.



The lithology of primary drilling Sites Site 1 (JNU1) and Site 2 (JNU2) within JNU shows excellent aquifer has been encountered from 60mbgl down to 96mbgl. The litholog (Table.3) as well as compressor test in the field has further confirmed the high potential aquifer in this area. X-Ray and ICPAES a result shows that at a deeper level water quality remain excellent as in the upper level. At the depth 108.5mbgl the mineral peak shows mainly quartz with some accessories of calcium carbonate. Down to 146.34mbgl the fractured quartzite further shows another good layer of aquifer (Figure 5 and Figure.6). Beyond ferrugenous quartzite at depth of 146 to 150mbgl the compact mica schist shows some garnet crystals in thin section petrography. The presence of garnet in mica schist is suggestive of high grade metamorphism which is further supported by X-Ray and ICPAES investigations. The presence of Barium is decreasing from 4.57mbgl to 77.74mbgl which is suggestive of the selective chemical mobility of the ions during metamorphism leading to pegmatisation.

The presence of different mineral studied in thin section under the petrological microscope, ICPAES and X-Ray diffraction confirms the presence of zoned pegmatite in this area. Groundwater quantity and quality in this area is dependent on grade of metamorphism i.e. pegmatisation and its structural anomaly. Presence of Barium Feldspar forms a weak zone through which the fractures have been developed down to 4.57 to 77.74mbgl(Table.4). Groundwater estimation in this area is highly depend on mineral paragenesis and induced structural anomaly in this area.

Drilling at Site 2 (JNU 2) went up to 182.92metres depth. Here also upper layers up to 9metres depth (approx.) were composed of silt and clay. This was followed by several layers of sand and ferruginous quartzite. Zone around 36-40 metres depth marked the transition to mica schist dominant layers (Figure.7).

Sub-surface lithological information was used to generate a lithology solid model for drilling sites predicting the possible sub-surface lithological connections and extrapolating the information to the whole region apart from primary drilling sites. The software (Rockworks) determines the lithology types along each borehole in the project, and assigns certain values to those nodes along the wells. It then uses the “lithoblending” method to assign lithology to nodes lying between wells(Figure.8). Finally, it will reset those nodes above the ground surface to a value of 0.

Three dimensional fence diagrams generated for the part of study area covered by 7 drilling locations shows that top layers in most parts are predominantly composed of Weathered/Fractured Ferrogenous Quartzite. On the other hand the lower layers throughout this part of study area are mostly composed of Mica Schist and Compact Quartzite.

Summary and Conclusion

The land use of National Capital Region in general and Delhi in particular has gone under drastic change. Change in land use, population growth and seismic instability have all contributed in changing the hydrgeomorphology of NCR. Besides water resources, the growing awareness about the mountain ranges and the alarm of environmental degradation has forced the administration of NCR to arrest the deteriorating environment. The present work can help contribute its mite in mitigating looming ecological crisis. As has been said earlier that this work aims at hard rocks, colluvial and alluvial aggregates for exploration, exploitation and management of water resources. It required a geoscientific database of water resources for generation of development plans for optimal use of potential resources. Although it is difficult to make all information relating to subsurface water available at one place, nevertheless the present study attempts to give a clear evaluation of a part of National Capital Region.

To achieve above a systematic approach of understanding the terrain characteristic at a regional level and then going for detailed mapping by using geological, geophysical, drilling and analysis of drill cuttings and groundwater samples have been adopted. Remote sensing and GIS is used here which has emerged as the most optimal means for monitoring and management of water resources on global, regional and local scale. Being at higher elevation of NCR region with such condition i.e. fault zones, groundwater bearing fracture system and buried pediment plains, major part of the study area has become ideal recharge zone for better groundwater conditions. At higher elevations drainage system which follows the structural lineament and fault zone limit the capacity to hold and retain surface runoff of the rainwater.

An approach was made by drilling in Aravalli in seven locations in a part of JNU and four locations in Research and Referral Hospital. Information from the drilled litholog was correlated with resistivity, magnetic and attributes of NDVI from satellite data. Analysis of drilled logs and groundwater samples from different zones were done to correlate these data with remote sensing geological and geophysical information. These data along with ancillary information were analysed in Arc/GIS software for attribute data creation, derivation of secondary maps of groundwater prospects and quality zonation.

For the present investigation satellite data IRS 1C, IRS 1D (LISS III), Resourcesat and Landsat were used. For geo-referencing Survey of India toposheets and NATMO maps has been used. The data collected from different sources have been used as ground truth information for the preparation of various thematic maps. Detailed ground truthing has been carried out in some selected points of study area. These ground truthing includes resistivity and magnetic surveys and drilling by Down the Hole Hammering (DTH) rig. This process involved following steps:

• Interpretation of data available (Geophysical, Geological, Geochemical, Soil texture andDrilling) for locating suitable groundwater exploration points.
• Interpretation of IRS, Resourcesat, SPOT, and Landsat data for demarcation of groundwaterzone including its quality.
• To identify the structural control of the area through Digital Elevation Model generated ShuttleRadar Terrain Mission (SRTM).
• Interpretation of lineament and fracture system in the NCR region.
• Collection of samples for detailed geochemical and petrological analysis.
• Confirmation of recently identified groundwater zone based on distinct vegetation anomaly andlineament fabrics depicted on satellite images.
• Identification of possible groundwater zones based on drilling data.
• Identification of groundwater quality based on NDVI attributes.

It has been observed through field investigations that the interconnected fracture in Aravalli quartzite has been found to have potential for groundwater exploration. Within Aravalli quartzite the ferrugenous variety was found more fracture prone. Pegmatites, Aplite and Quartz vein intercalated with schistose rocks has multiple fracture system. Thin section analysis of rocks from different depth zones shows that the grade of metamorphism has relevance with groundwater quality and potentiality (Figure.8,Figure.9,Figure.10 Figure.11 and Figure.12).

It has been observed that from Aravalli quartzite to river Yamuna there are three prominent watershed boundaries in existence. The buried pediment plains and alluvial plain boundary is demarcated by a very thick layer of fine grained sediments. Hydrogeomorphologically this boundary is not suitable for groundwater exploration.

Elemental composition (rock analysis) of the selected rock samples were analysed by ICPAES. The rock sample represents potential fracture zones encountered during groundwater exploration. The analytical data reveals the following features.

• In all the drilling sites silica content increases with depth which is suggestive of good to excellent groundwater quality at depth.
• Concentration of Al2O3 decreases with depth which is also suggestive of excellent groundwater quality.
• Concentration of Zr is found higher in upper zone (245ppm) which reduces to bare (
The conclusions inferred from the research work more than eloquent i.e. it was found that wherever the lineament density were high there were also resistivity and magnetic anomaly with lower values. At all those places groundwater available in large quantity. If Normalized Differential Vegetation Index is high, the vegetation is thick due to high moisture laden lineament which is suggestive of high mineral availability and hence the groundwater availability. Wherever there has been excessive use of land, it is difficult to find out the contours of the lineaments. Whereas the lineaments of the unperturbed lands can be easily brought to light.

Resistivity survey threw light on the different levels of water availability. One could infer from photomicrograph of rock shreds obtained during drilling that high grade metamorphism which has not disturbed the aquifers. Since all the aquifers are situated at great depth, they are beyond anthropogenic perturbations. On the other hand alluvial aquifers are more prone to anthropogenic pollution as they are shallow and therefore not potable. Further, it was found that wherever there has been change in the landuse the natural recharge potential too has declined. Digital Elevation Model (DEM) could tell us about the course of water run-off and it will help in recharging the aquifer. Thestudy also came to the conclusion that wells may not be directly recharged. There can be indirect method of recharging them. Recharging the lateral dry wells can be done by the lateral homogeneity. In view of total area of study in JNU which is approximately 5sqkm the number of tube wells were restricted to seven based on the delineation of micro-watershed. As per the National Water Policy there should not be more than one tube well in one micro-watershed.

The research work carried out recommends that there should not be further drilling in JNU area for sustainable performance of the aquifers. Although the discharge of the tube wells are ranging between 24,475 Lt/hr to 34,125 Lt/hr with less than 10mts draw down in 72hrs of pumping but it is recommended that the groundwater can be pumped from the tub wells for 8Hrs then it should be allowed to recover for 5hrs. In this area most of the drilling site fractures are interconnected with high transmissitivity, it has been observed that 80% recovery of draw down takes place within 1hr, if surrounding tube wells are also stopped. Remaining 20% recovery takes 4hr due to elastic nature of the aquifer. Hence it will be safer if the tube wells are not pumped together with more than 8hrs. If the above recommendations are not followed and tube wells are operated continuously then it may result in permanent decline of groundwater level.

Similar work has been done from Remote Sensing Laboratory, SES, JNU in Humanyun Tomb, IGNOU and Research and Referral Hospital areas. The result and effect is arrest of lowering down of the water level in the areas mentioned above further supports the lateral recharge hypothesis in confined aquifers.

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Saumitra Mukherjee, Satyanarayan Shashtri, Chander Kumar Singh, Amit Singh
School of Environmental Sciences, JNU, New Delhi