DESIGN AND CONSTRUCTION OF

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Government of India & Government of The Netherlands

DHV CONSULTANTS &

DELFT HYDRAULICS with HALCROW, TAHAL, CES, ORG & JPS

MANUAL

DESIGN AND CONSTRUCTION OF

LITHOSPECIFIC PIEZOMETER

September 2002

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Preface

With the commencement of World Bank Assisted Hydrology Project in nine Peninsular States of the country, a sizeable programme for establishing groundwater monitoring network has been taken up. The main objectives were to augment the existing network of observation wells by construction of dedicated piezometers for monitoring groundwater levels and quality. Many of these piezometers have been provided with Digital Water Level Recorders (DWLRs) enabling recording of high frequency water level data. These piezometers are intended to serve as primary stations for monitoring purposes. This has necessitated formulation of guidelines for location and siting of piezometers, their construction and design so that the primary stations truly reflect the groundwater regime behaviour of the aquifer under monitoring. Besides, there is a need to lay down the precise practices for the design and collection of data during drilling. The hydrogeological setting of the Peninsular India represents a varied environment with differing lithological settings, especially in consolidated formations, which are predominant in the HP States. The different lithological environment in conjunction with climatological and land forms call for a separate procedure to follow. Hence the manual is considered essential for reference to the field workers and practicing Hydrogeologists.

A Manual on ‘Guidelines for Implementation of piezometers’ has already been released by the Hydrology Project, during July 1998. The present Manual seeks to present the practices, which should be followed during selecting the location of the piezometer, drilling, construction and design in the different geological formations commonly encountered in a typical hydrogeological environment. The Manual also deals with the methods of sensitizing the piezometer to respond to the aquifer inputs and out puts; maintenance and rehabilitation of the piezometers.

One of the main aims of the Hydrology project is to install scientifically designed and correctly installed piezometers to monitor piezometric head of shallow unconfined and deeper confined aquifers. Though the design criteria and field operations are well known to all the field practitioners, certain aspects need to be well understood and assimilated into the practice of implementing a piezometer. The manual gives the guidelines, which are expected to assist the professionals in realising the necessary reorientation of their drilling experience and expertise.

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Scope of the Manual

An earlier Manual on “Guidelines for the Implementation of piezometers” was prepared and released by the Consultants in July 1998. The Manual dealt with the optimal network design and the details of piezometers in unconsolidated and consolidated formations. However, as majority of the participating HP States fall in hard rock areas of the country, a need has been felt to deal with various aspects of piezometers in different lithologies along with methods of drilling, design and pumping test of piezometers.

The manual is intended to serve as a practical guide to the groundwater field workers and as a tool to visualise the hydrogeological situations and ground realities of the piezometer site and what results could be expected. And remedial measures to be adopted to revitalise a piezometer.

This Manual seeks to highlight the concept of lithospecific Piezometers, criteria for prioritisation of areas for location and site selection using Remote Sensing and other methods. The procedures of Drilling and Design of Piezometers along with an account of methods of analysis of pumping test data of the piezometers for different types of aquifers have been described. Also topics on Development of piezometers and their Maintenance have been discussed using inputs from various sources. Finally selection and installation of appropriate type of water level recorders in tune with the requirements for litho specific piezometers has been discussed in the manual. It is hoped the manual will meet the guidelines for hydrogeologists engaged in planning, execution and field operations and data retrieval from piezometers as per their requirements.

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1 Introduction

1.1 General

Groundwater monitoring is an essential tool to obtain the information on groundwater quantity and quality data through representative sampling. This helps in recording the response of groundwater system to a natural or artificial input and out put. Any planning for groundwater development should be guided by regime monitoring indicators such as water levels and quality changes over a period. Groundwater is a dynamic resource requiring continuous monitoring of its quantity and quality data for updating and assessment of available resource potential. Such an updating can be made possible by using a sound observational database from a scientifically well established network monitoring system.

Groundwater observation monitoring network stations or piezometers are constructed to record the response of groundwater regime to the natural and artificial recharge and discharge conditions. Keeping in view the regional and local requirements, the planning and design of such a network depends upon hydrogeologic, physiographic and climatic situations, purpose of the study, stage of development, as well as political and social demands (UNESCO, 1977). The various types of observation networks can be setup depending on the objectives e.g., hydrogeological, water management, baseline water quality and for specific purposes. In the ongoing Hydrology Project, the objectives of the observational network mainly include high frequency groundwater level and groundwater quality monitoring.

A few of the salient features of the groundwater monitoring system are as under:

– Strengthening of the existing network through construction of purpose built observation wells (piezometers) through identifying gaps in the data.

– Ensuring integration of networks of Central and State Groundwater Organisations avoiding any duplication.

– Achieving optimum observation network density in the given area.

– Installation of high frequency water level measuring devices like Digital Water Level Recorders (DWLR’s) on piezometers at key /nodal locations.

– Establishment of Data Centres at Unit level, Regional level and National level to handle, storage, validation, synthesis, retrieval and dissemination of data generated to user agencies

– Development of Hydrological Information System (HIS)

– To ensure transparency in the availability of ‘demand driven’ groundwater data required by the User community.

– Ascertain the data needs, data type (historical, real time etc.), parameters of data requirements of user community through Hydrology Data User Group (HDUG) meetings.

For implementation of the observation network monitoring, CGWB and the State Groundwater Agencies of the participating States have constructed a sizeable number of purpose built observation wells (piezometers) with the provision to install DWLR’s at key locations and suitable pumps for water sampling. Some of the piezometers constructed are replacement to old, defunct existing open wells, due to de-saturation of aquifer, disuse, and aging, among other factors.

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The observation wells/piezometers are usually of small diameter so as to accommodate the water level measuring device and the water-sampling pump. In unconsolidated formations, piezometers are provided with screens tapping the zone of interest; where as in the consolidated rocks, piezometers are left open ended (uncased) beneath the loose soil/loose over-burden where the hole has to be provided with a casing. Up-gradation/strengthening of the observation well network is a continuous process which would require replacement of non performing open wells with dedicated piezometers as well as construction of deep piezometers to cover aquifers that have not been previously monitored. Improvement in the density of the network would also arise with time. All this would involve construction of many more piezometers. The present manual aims to serve as a reference guide during piezometer construction. It is expected that this manual would also help the different agencies to formulate ‘Protocols and Procedures’ for construction of piezometers. The detailed piezometer construction procedure must contain number of elements plus any additional site-specific elements, which may be required. This manual describes the significance of different elements in the piezometer construction

1.2 Characteristics of geological formations

The unconsolidated geological materials are generally composed of sand, gravel, and clay in various proportion as alternate layers and are characterised by occurrence of primary (interstitial) pore spaces which provide the main loci for storage and movement of groundwater in the saturated zone. These materials are often assumed to behave as homogeneous and isotropic media. Yet, the homogeneous aquifers seldom occur in nature, with most aquifers being stratified to some degree. Due to this, the hydraulic conductivity is found to differ in horizontal and vertical directions.

Rock

group Rock types Mode of occurrence Main features

important for groundwater occurrence Crystalline

rocks Non-volcanic igneous and metamorphic rocks, viz.

Granites, gneisses, schists, slates and phyllites, etc.

Large size massifs and plutons; regional metamorphic belts

Weathered horizon, fractures and lineaments with secondary porosity Volcanic

rocks Basalts, andesites and

rhyolites Lava flows at places

interbedded with sedimentary beds

Fractures, vesicles and inter-flow sediments Carbonate

rocks Limestones and dolomites Mostly as chemical precipitates with varying admixtures of clastics in a layered sedimentary sequence

Fractures and solution cavities

Clastic

rocks Consolidated sandstones

and shales Interbedded sedimentary

sequence Inter-granular pore

spaces and fractures Table 1.1: Hydrogeological Classification of Consolidated Rocks

(after Singhal & Gupta, 1999)

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The consolidated geological formations dominate the Peninsular India. These formations are devoid of primary porosity and permeability, but tend to acquire some hydraulic conductivity through joints, fracturing, weathering and other geological processes. From hydrogeological point of view, these are classified into Crystalline rocks, Volcanic rocks, Clastic rocks and Carbonate rocks. Groundwater occurrence in these rocks is mainly dependent upon the degree of weathering and consolidation of fractures and fissures, which form the main flow conduits. Table 1.0 gives chief rock types and brief mode of occurrence of groundwater along with main features of occurrence of groundwater in each such formations.

The table shows that in contrast to the dominant primary porosity as a main feature for groundwater storage and movement in the unconsolidated formations, distinctly different hydrogeological frame work and flow features characterise the consolidated formations. The location and depth of the network observation wells and/or piezometers in such formations solely depends on the factors like the thickness of weathered zone, occurrence and characteristics of fractures and related hydrological features. In the case of uniformly and densely fractured rocks, the site selection and construction of such piezometers can be more or less similar to that in unconsolidated aquifers. However, in case of non-uniform fracturing, or in weathered zones of crystalline rocks, in carbonate aquifers with solution cavities and in basaltic aquifers with lava vesicles and tubes, the decision on the placement and depth of piezometers may require detailed studies of the hydrogeological situation. The hydrogeological framework of peninsular India is described in details in Annexure-I.

1.3 Significance of lithology in the construction of piezometers:

Groundwater occurs in the aquifers either as an individual horizon or as multiple layers. For proper accounting of resources and judicious planning of exploitation, it essential to monitor the water levels which are indicators of its potential at different times. The quantity and quality of water occurring in the aquifers depend upon its mineralogical and geochemical conditions at the particular level. For this independent observation wells are constructed known as ‘piezometers’.

All water level monitoring programs depend on the design of piezometer. Decisions made about the design of the piezometer and its location are crucial to water data collection program. Ideally, the piezometer constructed as part of the monitoring network need to provide data representative of the different geology, lithology and groundwater development environments. Decisions about the real-areal distribution and depth of completion of piezometers should take into consideration the physical boundaries and geological complexity of the aquifers under study.

Water level monitoring in complex geological and lithological environment may require measurements of water levels in multiple piezometers (nested) constructed at different depths tapping different aquifer units representing varied lithological and geological units in the area. Large geological/lithological units that extend beyond the state boundaries require a network of piezometers that have representation beyond the states distributed among one or more states. One of the purpose of a network is to monitor ambient groundwater conditions or the effects of natural, climatic-induced hydrologic stresses, the piezometer network will require monitoring structures that are representative of regional geological, lithological units that have lateral and vertical continuity and represent the horizontal groundwater flow regime without any major gaps. The aim should be to ensure that there are no mixing up of information due to improper piezometer design. These and many other technical considerations pertinent to the design of a piezometer focussing on lithological and geological units is discussed in detail.

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Commonly overlooked is the need for study of geological map and available reports of the area giving details on the mineralogical and lithological information before deciding about the location and design of the piezometer. Good understanding of the lithology of the area help in designing the appropriate piezometers that enable collection of accurate, authentic and precise water level data, which will reflect true conditions in the aquifer being monitored and provide data that can be relied upon for many intended uses. Therefore field and office practices that will provide the needed levels of quality assurance for water level data should be carefully thought out and consistently employed. In the construction of piezometers the principal objectives should be:

– to monitor the water levels and water quality of independent aquifer

– to understand the relationship between different aquifers

– to understand the hydraulic characteristics of different aquifers.

– to evaluate groundwater regime characteristics

– to understand the regional flow characteristics

– to refine groundwater resources assessment

The procedure and protocol for design and construction of piezometers shall be dictated by a number of factors including the geology, hydrogeology, lithology, aquifer geometry not forgetting the objectives of the monitoring network. Thus prioritisation of the piezometer site as well as their design and construction should have a clear bearing and perception of the geology, lithology and aquifer type. A geological map, lithological cross section, structural map, geomorphological map and geophysical survey reports are the important tools that will help in understanding the regional geological control on the groundwater system which is an important consideration for the piezometer design. This brings to the fore the need to consider different lithologies separately for hydrological studies necessary for identification of

‘representative’ piezometer sites. This has lead to introduction of the concept of lithology- specific-piezometers, commonly referred to as ‘Lithospecific Piezometers’.

1.4 Groundwater monitoring in India- an historical perspective

The Central Groundwater Board in 1968 started groundwater monitoring as part of its activities with one observation well for each toposheet over the entire country. In all 68 observation stations were established. Gradually with the need more number of stations with lithological representation were also added. Mostly existing open wells owned by farmers or utilized for drinking water were included in such monitoring systems. With the operation of groundwater exploration and resource evaluation projects under UNDP and other added projects many observation network stations were established tapping shallow as well as deeper aquifers and amalgamated in the regular groundwater monitoring system.

These were mostly on the basis of availability of wells as a sort of compromise and not on the basis of requirements at the specific locations. The water levels were measured initially twice, pre-monsoon and post monsoon period, which subsequently was converted to five times in a year falling in the months of January, March, May, August and November months.

From 1986 onwards 4 times in a year is measured in the months of January, May, August and November. The data collected is utilised in specific reports for reporting on fluctuations and assessing water resources for the administrative divisions.

By 1972 the State Groundwater departments also came into establishment and gradually groundwater monitoring was taken up. The density of network observation wells in alluvium was about one well per 100 sq. km on an arbitrary basis, while in hard rock it was more than

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that mostly in localized areas with groundwater development. Also in exploratory areas with possible scope for groundwater development, monitoring was enhanced with addition of piezometers constructed for well field studies both in soft rock as well as hard rock areas under various national /international added projects in the country. At best these monitoring network stations served as indicators on baseline water level and water quality data. The information emanating from such networks has generally permitted conceptualisation of the groundwater system and its resource evaluation. These were in essence need-based piezometers rather than scientifically required for country monitoring system.

The data generated was mostly utilised for use in the internal report preparation by the departments and evaluation of groundwater resources for administrative units for the country as a whole. The depth to water level maps were prepared and interpreted for response of aquifers to various natural inputs from rainfall and canal/irrigation returns in terms of maps both for pre-monsoon and post-monsoon season. Also maps on water quality covering electrical conductivity and iso-chloride and total dissolved salts were prepared and interpreted.

The data generated were with certain inaccuracies as the monitoring wells were one those used for drinking as well as irrigation, as a result exact water levels were not possible.

Subsequently, with the advent of tube wells and bore wells in hard rock areas which were fitted with electrically operated pumps, the water levels started declining and many of the dug wells went dry during summer period. As a result, lowest water level data could not be recorded. Some of the old wells went into disuse or were dumped with garbage and as such data collection was not possible, leading to data gaps.

Topics include in this document are: network review, site investigations, piezometer construction, development, discharge measurement, performing aquifer tests, and water quality sampling.

1.5 Updating the existing network- based on current objectives

The first task before construction of new piezometers is to review the existing monitoring network at the micro level i.e; drainage basin, geological basin and in limited circumstances, considering only the administrative boundary as a unit. The review has to integrate the monitoring wells of all the agencies involved with water level and water quality monitoring.

The review has to be necessarily be aquifer wise. The review should be based on all available data. The evaluation should lead to identification of the data gaps (spatial and vertical).

The review has to be based on the data available from the networks related to; aquifer wise density, depth of the aquifers and water level plus water quality. The review should also evaluate the areas where the data generated from the existing network has been used i.e.;

• groundwater resource assessment,

• understanding the groundwater flow dynamics,

• delineation of recharge/discharge areas,

• regional groundwater quality variations over space/time

Based on the review the adequacy of the network has to be evaluated; areas showing gaps in understanding have to be identified; areas showing more than adequate numbers of observation wells have also to be identified and duplicate observation wells, if any, have also

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to be considered for elimination or reducing the monitoring frequency. In case an existing network (with respect to a specific aquifer) is found to be inadequate, additional piezometers, tapping that specific aquifer, need to be provided.

The first step towards planning to the enhancement shall comprise of macro-level planning, i.e., estimating the required number of additional piezometers and their location at a macro- level (say on a map of scale 50,000). The subsequent step shall involve pinpointing the sites for the additional piezometers on the ground, i.e., micro-level allocation.

1.6 Macro-level planning

Depending upon the intended use of the data from the network, the macro-level planning of the network enhancement can be accomplished using the statistical tools in the dedicated software

1.6.1 Coefficient of variation method

The method requires the user to specify the maximum permissible error in the estimate of the mean water level. Subsequently, based upon an analysis of the data from the existing network, the required number of the piezometers is computed, from which the additional number of the piezometers are derived.

The following procedure is adopted for locating the additional piezometers within the specified area.

• Employing the concurrent data from the existing network, draw contours of water level at a uniform interval.

• Divide the entire area into zones, each zone representing an area falling between two successive contours.

• Divide the required number of piezometers equally among all the zones. This will ensure a greater density of the piezometers in the regions of steeply sloping piezometric head and vice versa.

• Count the number of existing piezometers in each zone and hence estimate zone-wise, the required number of additional piezometers.

• Locate the additional piezometers in each zone in such a way that the piezometers (existing and additional) are uniformly distributed within the zone.

1.6.2 Kriging

Kriging is a powerful tool for evaluating an existing network. It also assists in the macro-level location of additional piezometers, in case the existing network is found to be inadequate.

The steps involved are as follows:

• Specify the level of permissible interpolation error.

• Conduct kriging on the concurrent piezometric data from the existing network. This shall yield contours of piezometric head and of the interpolation error.

• Study the error contours and hence identify the regions where the error is in excess of the specified permissible level. Additional piezometers are to be allocated to these regions.

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• Locate additional piezometers in the identified regions tentatively, generally ensuring that the increase in the network density is consistent with the error excess.

• Conduct kriging on the tentatively enhanced network and plot contours of the error. It may be noted that kriging permits generation of such contours, even though the data from the newly introduced piezometers do not yet exist.

• Study the modified error contours and check whether the error everywhere falls below the specified limit and the enhancement has not been over-done. An over enhanced network shall display interpolation errors far less than the prescribed limit.

• Modify the network further, if necessary by repeating the relevant steps 1.7 Micro-level planning

After having decided the location of the piezometer sites on the map, it is essential to pinpoint the site exactly on the ground. Certain micro-level deviations may be necessary to accommodate various hydrogeological and logistical considerations.

1.7.1 Hydrogeological considerations

These considerations originate from the primary expectation out of a piezometer, i.e. it should record harmonized natural behaviour of groundwater rather than local micro-trends.

This can be ensured by keeping in mind the following:

• The site should show no impact of any external inputs such as from canal, tank, perennial river and irrigation return flows, except in special cases where interest is the study of the influence of these parameters on groundwater system.

• The site should not fall within the radius of influence of a well, which is under pumping;

but it should be capable of recording the effects of the pumping as a regional phenomenon.

• The piezometric head/water quality at the site should not be influenced by local recharge/pollutant sources.

1.7.2 Logistical considerations

There could be many general as well as area-specific logistical considerations such as:

• No other agency is considering constructing a piezometer tapping the same aquifer, in the vicinity.

• The site is approachable by the rig and support vehicles.

• Adequate space is available at the site for setting up drilling equipment, digging mud pit and draining the discharge, while the site should be clear of trees, overhead electric cables, under ground cables/ pipelines/ drainage lines etc.

• The ownership of the site is clear and agreements have been made for drilling the piezometer and for continued monitoring.

• The site should be safe from vandalism, as a costly DWLR will be installed.

• The site should be neither too close nor too far off from the road.

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1.8 Desk studies

Based on the network review and identification of the area where additional informations are required piezometer site selection has to be initiated. Desk studies need to be carried out in the office through review of topographical maps, geological maps, geophysical surveys data, geological cross sections, drilling data, water table/piezometer maps, water quality maps etc.

Data emerging from the desk studies should be systematically organised, location wise, for carrying to the field for field review and investigations.

1.8.1 Remote sensing interpretation map

The Hydrology Project has been involved in the creation of GIS data sets in which the thematic maps are generated using satellite data. The thematic maps, should be used during the desk review for the locating the appropriate sites for the piezometers. The Remote sensing maps have to be the basis for delineating the faults, lineaments, study the geology, hydrogeology, land use etc. Using the GIS capabilities different themes should be overlaid to zero on the most appropriate location. Based on the GIS studies and remote sensing interpretations inference on the subsurface soil moisture, recharge potentialities need to be estimated. The Remote sensing interpretations should be used to interpret features like karst topography, dykes, reefs, unconfirmities, buried channels, salt encrustations, tide levels, alluvial fans and abandoned channels etc.

In the hard rock terrain's the remote sensing studies should help in understanding the spatial distribution of rock out-crops, the catchment characteristics, the presence of structures and drainage systems influencing the groundwater movement, the nature of the land form and the slope based on which interpret is the likely thickness of regolith/overburden, the general groundwater potentiality and the most preferbale location for constructing the piezometer.

For this purpose, the GIS datasets related to geology, its structures, geomorphology, drainage and soil should be integrated and interpreted.

The satellite imageries provide a good idea of drainage network for computing drainage density. Drainage density exhibits a very wide range of values in nature depending upon the relief, climate, and resistance to erosion and permeability of rock material. In general, low drainage density (1.9-2.5 km-1) is characteristic of region of highly resistant or highly permeable surface and low relief. High drainage density (12.5 – 19.0 km-1) is found in regions of weak or impermeable subsurface materials, sparse vegetation and mountainous relief. In areas of low relief, drainage density may be more indicative of permeability of surface material and therefore, could be used as a criterion for the selection of suitable sites for piezometers. The drainage analysis is utilized to differentiate the terrains into highly dissected plateau (HDP), moderately dissected plateau (MDP) and poorly dissected plateau (PDP) (see figure 1.1).

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Figure 1.1: Map showing lineaments in the hardrock area in Salem area, of Tamil Nadu

Study of lineament is the most important aspect of satellite image interpretations for groundwater studies in the hard rock terrains. It has been established that the groundwater structures constructed close to fractures of tensional origin, or close to their intersections, have proved extremely successful. Siting of piezometers near such favourable structures should be considered and such areas clearly marked on the toposheet of 50,000 scale and inspected in the field.

On the satellite imagery, the lineaments can be easily identified by digital image processing as well as visual interpretation, using tone, colour, texture, pattern, and association. The automatic techniques of digital edge (or line) detection can be applied for lineament detection (Singhal and Gupta, 1999). However, fracture traces having low dips, which have more potential for groundwater may not be very easily deciphered. Staff with extensive field experience would be able to make such interpretations easily.

1.9 Field investigations

The Field investigations consists of a number of elements including, geological, hydrogeological, geomorphological and hydrological investigations

1.9.1 Geological investigations

Geological map of the area on 1: 50,000 or 1:250,000 scale prepared by national agencies like Geological Survey of India or State Mines and Geology departments which has been converted to digital format as part of the GIS data set preparation should be printed and carried to the field these maps help to visualize the occurrence of rock formations, their disposition, sequences and structures, faults, dykes etc. Surfacial distribution of rocks and

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their regional continuity should also be visualized. The different lithological and structural features like joints, lineaments, foliation, discontinuities, degree of susceptibility of rocks to weathering, from Dug well sections need to be studied.

Field investigations should also include information about the orientation and density of fractures, although their subsurface distribution may be different which can be deciphered from subsurface investigation. A kinematic analysis of fracture pattern and lineaments is often useful in delineation of their tectonic origin. Whereas, plotting of the dip and strike of joints on Schmidt's Stereo net and as rose diagrams can bring out synoptic, structurally weak zones.

Data about the thickness and composition of the weathered zone (regolith) is particularly important in crystalline rocks. The minerological composition of weathered products, particularly presence of interstial clay matrix or its absence is important. The texture of quartz grains with respect to their roundness, sphericity, angularity and abundance of will indicate in-situ deposition or transported deposition. The abundance of orthoclase, anorthosite minerals give clue to the extent of weathering in the rock as these are most dissoluble minerals. Similarly, mica is also unstable. The recharge, discharge zones with geomorphic locations and drainage system help greatly in identifying the suitable location.

In volcanic rocks presence of vesicular basalts, its thickness and geomorphic locations are important from the view point of groundwater occurrence. The vesicular and amygdloidal basalt is most susceptible to weathering. The vesicles with tubular structures form good water conduits in basalt. Added to this, fractures and lineaments enhance the potential of the rock unit. The hard basalt with fractures underlying the vesicular basalt also forms potential water bearing zones in basalt. Attention should also be paid to the palaeodrainage, characters of individual flow units including their dips and inter-flow formations. The surface drainage plays an important role in basaltic rocks. The recharge-discharge zones should also be identified. The above mentioned details will help greatly in identifying suitable location of a piezometer in basalts.

In carbonate rocks, mapping of various solutions (karst) features are of special importance.

In carbonate rock areas, the geological map with occurrence of karstified and dolomitic type of rock disposition, better groundwater potential can be visualized better. Presence of sinkholes and valley depressions form main recharge zones. Presence of springs gives clues of solution channels. However, flaggy and bedded disposition of lime stone with monotonous topography display low potential zones.

In unconsolidated and semi-consolidated formations nature of deposits are important. Valley fill deposits tend to be of assorted nature, river/fresh water deposits are likely to be with frequent variations in textures of grains, even though there may be continuity in sequence of bed, but will be with variations in lateral porosity. Sudden truncation or swelling of aquifers are common. This needs to be properly visualized through lithological cross sections, prepared on the basis of existing drilling data.

Based on exploratory drilling and well log data, following subsurface maps and sections are prepared viz. fence diagrams, isopach maps, structural contour following maps etc. This is done to able to project the subsurface distribution and configuration of aquifers, aquitards and aquicludes. Water table/piezometric contour map if available should also be studied for identifying gaps and location of suitable site for piezometer.

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1.9.2 Hydrological Investigations:

Drainage pattern is the spatial arrangement of streams and is, in general, very characteristic of rock structure and lithology. These drainage patterns reflect the hydrogeological characteristics of the area and therefore can be useful in the location of piezometer sites.

Figure 1.2 gives common drainage patterns in consolidated and unconsolidated formations.

Figure 1.2:

Common drainage patterns (A.D. Howard)

The drainage maps have been created as part of the GIS data set perpetration. The drainages have been digitised from the toposheet of 50,000 scale and updated using the thematic maps. The drainage maps have also been used in delineating the different drainage order, from the major basins, down to watershed units.

During the field investigations the position of the piezometer location has to be ascertained with respect to recharge area/run off zone/discharge area.

1.9.3 Geomorphological investigations

Geomorphological map of the area on 1: 50,000 or 1:250,000, scale available as part of the GIS data sets, should be printed and taken to the field for visualizing the various landforms.

Genetically, the landforms are divided into two groups: erosional, and depositional landforms. Erosional landforms are typically associated with the resistant hard rock terrains.

They comprise: (a) residual hills, (b) inselbergs, (c) pediments, (d) buried pediments with weathered basements, and (e) valley fills. Depositional landforms, developed by depositional processes of various natural agencies, (e.g. river and wind) are typically made up of unconsolidated sediments and may occur in the regional setting of hard rock terrains.

Favourable landforms that contribute significantly to groundwater recharge should be

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identified in the field. The possibility of locating the piezometer in such areas should be examined.

1.9.4 Geophysical Surveys:

Geophysical surveys need to be carried out as a standard procedure for getting a clear understanding of the following depth to bed rock, thickness of weathered zone, extent of saturated zone, approximate quality of water in the saturated zone, thickness of different layers in layered formations and type of layered formations. Influence of structures like fault, unconfirmities and dykes can also will be evaluated. Occurrence of saline and fresh water layers with probable depth of occurrence also will be indicated.

Electrical resistivity survey is the most commonly used method to identify the vertical lithological layering distribution in an area. New approaches using the VLF method, Electro- Magnetic methods, Gravity Methods have to be used wherever possible. The main objectives of geophysical surveys are to provide information on:

– Depth, thickness and extent of aquifers in stratified formations.

– Depth, thickness and extent of weathered and fractured zones.

– Depth to water table.

– Selecting the site of a piezometer, out of the several target areas.

– Gross Salinity distribution and contamination.

1.9.5 Hydrogeological investigations

Hydrogeological investigations should include detailed well inventory of 2-4 sq.kms around the proposed area. All the groundwater abstraction structures need to be inventoried and the information to be collected should include the depth of the well, aquifer position, rate of pumping, pumping duration, drawdown, rate of recuperation, area irrigated, lithology encountered while construction, static water level, water quality details etc. Collect water sample and carry out field analysis for pH and EC. Collect two sets of representative sample for detailed laboratory analysis.

The existing monitoring wells/piezometer around the proposed site needs to be visited and the variations if any with the proposed site understood. Examine the water level hydrograph.

Examine the water table elevation contour maps and depth to water table maps generated using two sets of data (pre-post monsoon).

Prepare lithological cross section/ fence diagram using the data from the inventoried wells, delineate the prominent aquifers in the area with their thickness and areal extent. Carry out pumping tests/ geophysical downhole logging where adequate information cannot be gathered during well inventory.

1.10 Finalisation of piezometer location

Based on all the studies and keeping in mind the logistical and safety considerations the potential site has to be identified. Where more than one site is considered then a joint team of hydrogeologists should visit the area and identify the most favourable location. The site selected should be verified for its true representation of the area specific lithology and

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regime system. The interference from pumping wells, surface water sources, polluting sources, seepage from return flows should be avoided at all costs.

1.11 Reporting of field investigations

Based on the field investigations a feasibility report has to be prepared. The following information must be documented as a file giving details of the procedures followed in deciding the piezometer site. The report should include:-

• A sketch showing the identified site and important landmarks in the vicinity. The sketch should incorporate the north direction and the distance of the site from the landmarks.

• Locate the site on the toposheet of 1:50,000 scale. Record its longitude, latitude and the reduced level as read from the toposheet. Use the hand held GPS wherever available for getting the geographical co-ordinate values.

• A narrative of the geographic setting of the piezometer site with administrative details.

Details pertaining to sites adjacent to or in the vicinity of school, sub station, police station, floodplains, wetlands should given.

• A narrative describing the regional lithologic, stratigraphic, structural, and hydrologic settings of the area.

• A narrative must be provided which describes field procedures used to characterize geologic and hydrologic conditions of the site. Standardized field procedures may be referenced. Details of the site-specific geology and hydrology based on data collected should be explained. The narrative must describe the proposed piezometer design.

Interpretations of results must be presented in a clear and concise manner. All published information sources used in the compilation of the hydrogeologic investigation must be listed.

• Appendices of the report must include:

– Compiled logs of all borwells and piezometers.

– The raw data for any and all tests (e.g., geophysical survey, bore hole logging, water quality analysis, pumping tests).

– Water level hydrographs of monitoring wells in the neighbourhood

– Water table elevation contour maps

– Hydrometerological data of the area

– All additional information that may facilitate the clearance of the proposed site.

The exact location should be marked on the ground with paint. Lithologic cross-sections must be constructed or inferred. At least one cross-section must be constructed parallel to groundwater flow. The subsurface conditions of the site must be illustrated in these cross- sections. Where more than one interpretation may be reasonably made, conservative assumptions must be used. A clear picture has to be given of the thickness, depth and lateral extent of the aquifers in the area with a clear definition of the aquifer to be monitored and the geo-hydrologic conditions. The type of monitoring required and the need if any for a DWLR and sampling pump should be brought out. The report should clearly bring out the need for the Piezometer at the proposed site with a justification for the expenditure to be made in establishing and running the network. The utility of the information emerging from the piezometer should be highlighted.

An estimate should also be prepared which should include site preparation, drilling, casing/

screen installation, gravel pack, sealing, development, pump test, platform and well head construction.

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1.12 Approval for piezometer construction

The site selection report from the field offices should be forwarded to the head quarters for approval and clearance. It is expected that the justification for the construction of the piezometer would be reviewed by a committee of senior officers at the head quarters, who will look at the requirement from a national/state perspective as well as from a local perspective. The location of the piezometer should be superposed on the existing network and its utility assessed. The aquifer to be monitored has to be verified on the cross section.

The added value from the new piezometer should be verified from a technical, management and financial perspective. On complete satisfaction of the utility of the piezometer the financial estimate has to be examined. While standard rates should be the norm, deviations should also be considered on case by case basis. The sanctions for depth of drilling, casing depth, screen position should be based on the field report, which should come up for ratification after completion of drilling. In the case where drilling contractors are to be hired for drilling the piezometers the procedure for hiring drilling contractors should follow the established norms. The tender document for inviting the drilling contractors should clearly mention that a qualified Hydrogeologist should be part of the drilling team and his/her CV should be part of the enclosures. The utility of hiring more than one contractor when the piezometer locations are far part should be examined seriously. Drilling Contractors when used the terms of the contract should clearly specify the obligations of the contractor as well as the department. Drilling being a seasonal task the procedures for selection of contractors should not be cumbersome. Acceptance of State Govt Approved Rates can reduce the process of selection. Since rain, water and mud are major hindrances, it is normally recommended that the most difficult holes be drilled first if they are accessible, saving the most convenient holes for last or to drill when the others can't be reached.

1.13 Discussion and interaction with local community

On obtaining the clearance for construction of the piezometer from head quarters, a meeting shall be convened in the village where the piezometer site is proposed. The invitees should include the village elected representatives, village officials, elders, farmers, women, schoolteachers and youth. The services of NGO groups active in the area should be used for conducting the meeting. The meeting should address the local groundwater issues and the need for groundwater monitoring. The proposed plan for establishment of the piezometer and the most favourable site location identified need to be discussed. Any suggestions from the community should be considered and animated in detail. The agency should also promise the community to make available the interpretations of the data collected. As a follow up to the discussions, an agreement should be obtained from the community to make available the required co-operation for safeguarding the piezometer as well as upkeep of the area.

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2 Drilling preparation

2.1 Planning

Successful piezometer construction requires careful advance planning to be conducted in the most expedient manner. Proper drill site selection and preparation are essential to avoid drilling at wrong site, minimise wastage of drill time and other associated costs. Land clearance is an essential item that cannot be taken lightly or ignored. Disputed lands can result in a tremendous litigation and liability to the department. The following are some detailed items to consider prior to commencing drilling of piezometer.

2.1.1 Site Preparation

Drilling sites need to be prepared prior to arrival of the drilling rig. The site has to be levelled in order to drill a vertical hole. Inclined bores considerably reduce the diameter and depth calculations become enormous. Prior to extensive site work, the driller must visit the site and clearly place his requirements. Overhead area must be clear of obstructions. Sites with trees and overhead power line should be avoided. If it is necessary to work closer to power lines, the drill crew should inform the electrical authorities either to shut down the power supply or to make the working environment safe. Underground laid infrastructure such as water lines, sewer lines, electrical/telephone cables, if any, should be checked before commencing work.

Roots are a major problem, they force their way into the piezometers,. In such areas proper preventive care should be taken by increasing the casing depth or identifying the root path and treating them.

It has to be ensured that the drilling rig has access to the site upon arrival. Problems have arisen in the past from hostile villagers and uncooperative landowners, which can be avoided if the village meetings are conducted and local communities are taken into confidence. Bridges/culverts to be crossed must be inspected to check whether they have the required width/ soil strength and have the capacity to take the weight of the rig, along with the spares.

2.1.2 Supervision of drilling

It is important to monitor the drilling and ensure that all procedures adopted should help in constructing a quality piezometer. The piezometer on completion should be providing the true picture of the water level and water quality without any bias. The drilling of the piezometer, geophysical down hole logging, development and pumping test need to be carried out under the supervision of an on site hydrogeologists. Where the work is subcontracted to a drilling contractor, then the drilling contractor should be responsible for employing the site hydrogeologist who will be available at all times till the piezometer construction is complete. The site hydrogeologist shall be responsible to record the drilling details, examine and interpret the drill cuttings, describe and record the physical and lithological characteristics of the geological material, supervise the well design, well development, measure the discharge and collect the water samples.

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2.1.3 Essential tools for field hydrogeologist

Field tools assist the field hydrogeologist in giving an accurate description of the drill cuttings. It is recommended the field hydrogeologist have these basic items (see Figure 2.1) which include:

• Pocket knife to cut the samples for testing hardness and exposing fresh surfaces Millimeter scale to determine the size of the particles

• Dilute hydrochloric acid to aid in recognizing calcium carbonate materials such aslimestone, chalk, or dolomite

• Magnifying glass (a 10x) to make a better identification of materials by enabling closer inspection

Figure 2.1:

Field tools for drill cuttings examination

2.1.4 Field notes

Field logs and notes on drilling should be prepared at the drill site itself.

The field description of drill cuttings should be simple and orderly so that the use of the terminology is uniform. A good field description of the drill cuttings is very important for the design and preparation of vertical sections. The site hydrogeologist and the drill crew are the only people who witness the drilling and the material obtained. Therefore a reasonable amount of accurate information must be logged. At a minimum, the field hydrogeologist must, in the field, note on a descriptive log the following: The field hydrogeologist must make sure to note the following on descriptive log:

• Start and stop times for drilling

• Names of field personnel

• Drill cuttings details-Colour, Texture , shape, mineral assemblage, rock type

• Diameter of drill bits

• Depth at which water encountered and discharge variations with depth

• Drilling rate

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• Casing depth

• Drill completion depth

• Screen position

• Gravel pack position

• Well completion depth

• Water bearing zones

• Development time

• Discharge after development

• Water quality details pH, EC

• Depth to water upon completion

A Standard data collection format should be adopted. All field data should be computerised systematically as soon as the drilling is complete and the field data brought to the District/Regional Data Centre.

2.1.5 Description of drill cuttings

The descriptions of the drill cuttings should be as simple as possible (see table 2.1). Every small variation does not necessarily warrant description on the log. The description should include:

Principal constituent: First determine the major constituent in the sample. If a significant portion (greater than five percent) of a secondary material is present then describe and identify it.

Colour: Describe the primary color and restrict description to one colour. If one main colour does not exist in a sample, make a simple description of the multicolouration.

Texture: Mention the texture of the primary material under three to four main cateogories such as Coarse-grained, medium grained, Fine-grained, Highly organic etc.

Shape: Cateogorise the most dominant shape of the drill cuttings under rounded, sub rounded or angular.

Hardness: should be mentioned with respect to Mohs 'Hardness Scale

5.5 – 10: Rocks that will scratch the knife: Sandstone, Chert, Schist, Granite, Gneiss, some Limestone

3 - 5.5: Rocks that can be scratched with the knife blade: Siltstone, Shale, most Limestone 1 – 3: Rocks that can be scratched with fingernail: Gypsum, Calcite, Evaporites, Chalk, some Shale

Cementation: Identify the degree of cementation if any.

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Descriptive adjectives: Use any descriptive adjectives that might further aid in the understanding.

Log form: To promote consistency, use the standard log form which is consistent with the data entry system.

Depth to (m)

Lithoological

description Colour Texture Shape Remarks

0.2 Laterite red hard subangular-subrounded

6.5 Laterite verigated/

wuggy red medium subangular to angular

17.1 Lateritic clay red fine rounded

17.5 Basalt weathered black medium subangular-subrounded 29.5 Basalt weathered/

fractured

black coarse subangular to angular

51 Basalt hard black fine subangular-subrounded

52 Clay black fine rounded

83 Basalt hard black fine subangular-subrounded

83.9 Basalt weathered/

fractured black coarse subangular to angular Water touched discharge 0.2cum/hr

86 Clay Ash fine rounded

87 Sand White fine subangular-

subrounded

Table 2.1: Sample description of a drill cuttings during the construction of piezometer

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3 Construction of piezometer

The purpose of constructing a lithospecific piezometer is to obtain complete lithological data and not just to drill a monitoring well. In order to obtain data of maximum accuracy, the field hydrogeologist must work closely with the driller and consult with him whenever changes are noticed in penetration rate, slow returns, change in colour of samples, reduction in discharge etc. The hydrogeologist must recognize the reasons for such changes. The difficulties in drilling, such as caving, boulders, caverns, etc. Whenever encountered, must be clearly recorded.

Construction of lithospecific piezometers must ensure that the piezometers meet the design criteria for water level and water quality monitoring. Factors to be considered for piezometer construction shall include the following aquifer to be monitored, nature of materials that make up and overlie the aquifer (for example, unconsolidated or consolidated materials; if consolidated materials whether fractured or have cavities caused by dissolution); the depth to water, the type of drilling equipment required; access to the site; well casing and screen materials, length, and diameter, and cost. In unconsolidated deposits, the piezometer design, including the well screen, casing, annular space, back fill, gravel and surface seals.

Specific aspects of design however, can vary depending on specific requirements to meet local variations, site conditions encountered, and the drilling method used.

3.1 Selecting the appropriate drilling technique

Drilling technique for construction of piezometer will depend upon the type and nature of formations likely to be encountered below at the selected site. The technique to be adopted for soft and unconsolidated sediments shall be rotary, with bentonite mud or any other biodegradable mud as the drilling fluid. In the hard rocks, DTH drilling rigs are best suited.

The DTH drilling technique uses air to bring the cuttings to the surface, as well as cleanses the hole. Availability of high-pressure compressors makes drilling very fast. In such situations the fines get deposited in the fractures. The drilling in such cases should be followed up systematic development. In the soft rocks, with poor accessibility and in river alluvium, hand rotary drilling can be adopted as in parts of Orissa, Tamil Nadu and Andhra Pradesh. In hard rocks, with heavy overburden having boulders the drilling has to be done using a combination of rotory and DTH rigs.

The drilling should ensure that it is capable of recording faithfully the harmonized areal behaviour of groundwater of the targeted aquifer in the area, instead of a local micro trend.

The piezometer should not be effected by wrong drilling techniques which can bring in external contaminants such as, poor quality water used in the mud pit, thick bentonite mud, drilling oil etc.

3.2 Deciding the depth of piezometers

The depth and diameter of piezometers are two important factors, which not only decide their best suited design, but may also affect the cost/economics of the piezometer installation.

In the unconsolidated formations, the aquifer horizon for construction of piezometer has to be based on good understanding of the different vertically distributed aquifers, and the

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specific aquifer of interest. In case all the aquifers need to be monitored, piezometer nests have to be constructed. Systematic collection of drills cuttings and recording of drill time log, followed by electrical logging of the borehole, is very important in delineating the exact thickness of the aquifer. In the event of construction of nests, the deepest aquifer should be drilled first. The identified zones should be correlated with the regional aquifer system, distributed in the sub-basin or basin, and accordingly the piezometer depth is then decided.

In crystalline rocks, the depth of the piezometer should be decided on the basis of occurrence of aquifer(s) to be monitored in a given hydrogeological environment. Three rypical situations are discussed

Case i: Weathered zone is made up of quartz and the fractured rock immediately underlying it. The weathered zone acts as a good storage zone with its inter-granular connection, while the underlying fractured zone forms the main flow/conduit zone. In such a case the overlying permeable zone recharges the fractured zone and hence the two zones can be considered as part of the same aquifer. The piezometer should be then drilled down to the fractured zone.

Case ii: Fractured zone is overlain by clayey weathered zone. The weathered and fractured zone exhibit different permeabilities. In such situations both the weathered and fractured zone are to be considered as independent zones. The monitoring should be done independently for the weathered as well as the fractured zone. The shallow weathered zone can be monitored using an existing open dug well while the fractured zone is monitored by constructing a piezometer.

Case iii: Weathered zone is clayey and impermeable, the recharge to deeper fracture zone may be from a distant recharge area. In such case the piezometer has to be installed against the fractured zone only. The extent and thickness of the fractures do not follow a systematic fashion, hence the need for greater care in identifying the fractured zone by thoroughly monitoring the drilling.

In case of basaltic rocks, occurrence of multiple aquifers is common. Generally, the upper weathered zone in such rocks is totally clayey and impervious and the first aquifer in such formations may occur at different depth as vesicular zones. Each vesicular flow should be tapped by an independent piezometer. In areas where more than one vesicular flow has to be monitored, piezometer nests or a group of piezometers within a limited area (village, watershed) need to be installed, tapping different aquifers. Care has to be taken in properly sealing the upper aquifers while tapping the deeper zones. Typically, contractors who drill drinking water wells are not the best suited for drilling such piezometers. Departmental drilling rigs should be mobilised for taking up such drilling.

In the case of hard sedimentary rocks, good understanding of the stratigraphy is critical in understanding the different potential aquifers. Sandstone, shale and limestone occur in sequences. The sandstone in many cases have copious supplies. The limestone rocks possess both primary and secondary porosity in the form of fractures, solution cavities and cavernous zones. Shale have limited discharge. Good understanding of the startigarphy, combined with judiciously used geophysical surveys and profiling, the depth of the aquifer to be monitored can be inferred. Confined aquifers when met with produce artesian free flowing wells, should be, anticipated at the design stage itself. Methods to monitor the pressure changes should be part of the design.

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The depth has to be accurately measured after the piezometer construction is complete by using a weighted tape. The measurement should also be compared with the total number of drill rods used during the piezometer construction.

3.3 Diameter of piezometer

A piezometer is a non-pumping well and ideally needs to be as small in diameter as possible. The diameter should be such that it shall facilitate measurement of water table using a variety of measuring devices and collection of water sample. The diameter will also be dictated by the diameter of the measuring device, such as the probe of the Digital Water Level Recorder, diameter of the water quality sampling pump. Piezometers having a diameters of 100 mm are the most suitable. Shallow piezometers having diameter of 50 mm are also uncommon. The utility of the piezometers, to carry out pumping tests, geophysical down hole logging and hydrofracturing should also influence the diameter of the piezometer.

In the case of deep tube wells (>100 mtrs) in the alluvial areas, the cost will be a major consideration in deciding the diameter of the piezometer. In such situations telescopic design of 100-150mm down to 30 mtrs followed by 50mm dia till the bottom should also be seriously considered. Inclined piezometers can reduce the diameter considerably and cause major problems during lowering of DWLR probe or the sampling pump etc.

The diameter of the hole is often critical and is recorded based on the diameter of the drilling bit. The hole diameter is best measured using a calliper log.

The piezometer is intended to be vertical, however it does not always stay vertical but drifts from verticality. To understand the drift use of a mirror should be made to reflect sunlight down the hole to enable a visual check on the straightness of a hole. Visibility of half hole is an indication of loss of verticality. The exact point of deviation can be checked by measuring the depth with a tape, while reflecting light down the hole.

3.4 Actions to be taken prior to drilling

• Confirm landowner's/concerned government agencies, permission to enter the property for drilling.

• If the location is within a school/office/hospital discuss with the authorities to confirm the appropriate time when the drilling can be carried out without disturbing their functioning.

• Check the marking at the site and confirm with the geographical co-ordinates.

• Locate any subsurface power lines, waters lines, telephone cables, sewer etc.

• Locate water sources for drilling purposes and secure permission for their use.

• Prepare the drainage channel for draining of water.

3.5 Piezometer construction in unconsolidated formations

Unconsolidated formations in peninsular India are largely localised to coastal tracts composed of beds of sand and clays, and sedimentary beds of Gondwana and Tertiary formations made of alternate layers of sandstone and shales. Piezometer construction in these areas is through rotary drilling. In the unconsolidated formation, rotary drilling has to be adopted. Rotary drilling makes use of viscous bentonite mixed fluid as medium of drilling.

The mud fluid acts as coolant to the rotating drilling bit as well as a medium for bringing out drill cuttings outside the borehole. Use of bentonite clay has been banned for water well

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drilling in many countries, as they are not bio-degradable. Organic materials like guar gum are replacing bentonite clay as popular bio-degradable drilling fluid.

The main components (see figure 3.1) of a piezometer in an unconsolidated formation are:

Borehole: This is the primary component of a piezometer and acts as a host to the other components.

Well assembly: This is essentially the hardware of the piezometer and is accommodated in the borehole and also protrudes above the ground. Depending upon location of the aquifer in the vertical section, it may comprise one or more of the following parts:

Figure 3.1:

Piezometer components in unconsolidated rocks

Blank casing pipe: A blank casing pipe is provided to serve one or more of the following objectives:

• To prevent caving-in/sloughing of the drilled formation.

• To prevent a hydraulic connection between the piezometer and the drilled formation other than the aquifer to be monitored.

• To collect the fines entering into the screen. As debris sump.

Screen: A screen provides a hydraulic connection between the piezometer and the aquifer to be monitored.

Gravel pack and seal: Gravel is provided in the annular space between the borehole and the well assembly around the screen and beyond, extending preferably over the entire thickness of the aquifer to be monitored. The gravel pack serves the following purposes:

• inhibits the entry of the fines into the screen.

• enhances the hydraulic connection between the piezometer and the aquifer

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Cement seal:is provided just above and just below the gravel pack to preempt any hydraulic connection between the piezometer and the overlying/ underlying formations, through the gravel pack and screen perforations.

Sanitary seal: A 50cm thick concrete seal is provided at the ground surface to prevent the entry of surface water into the piezometer. The seal should be in the form of a cone around the casing to drain the water away from the well. The seal is underlain by a clay fill/packing for a more effective isolation of the aquifer to be monitored.

3.6 Sampling procedures during drilling

Examination of drill cuttings is very critical part of piezometer design in the un-consolidated formations. Some formations are better aquifers than others. Grain size have to be interpreted during the examination of the lithology (see figure 3.2).

Clean gravel have large pores and hold large quantities of water.

Sand and gravel mixture are very good aquifers. When percentage of gravel to sand is very high the aquifer will permit copious discharges.

Coarse sand are potential aquifers

Figure 3.2:

Grain size classification

Fine sand are poor aquifers

Clays hold lot of water but cannot flow. In some situations the clays when tapped can yield poor quality water.

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Sandy aquifers when overlain by thick impermeable clay and when penetrated by the piezometer can result in flowing wells.

Standarised sampling procedures have to be adopted by all agencies:

• Collect the samples for every meter.

• Lay the samples in succession, as obtained, and mark the depth

• Dry the samples for accurate identification and classification.

• Describe the samples precisely before and after washing and record any additional information.

• Look out for fossils and identify them

• Compare all samples with previous samples.

• Place the samples in plastic wrap and label legibly for any future identification/test.

• Sample boxes with pigeon hole windows are best suited to transport and for preserving the samples.

3.7 Down hole inspection

In order to take a decision on the design the piezometer assembly, downhole geophysical logging needs to be carried out. Logging should be used for providing additiona information than gained from examination of drill cuttings. Th details to be collected shall include the formation penetrated, formation characteristics modified as a result of drilling, condition of the hole, the exact depth and thickness of the aquifers and water quality of the aquifers. The standard probes to be used shall be electric, SP, Gamma, calipper, temp and fluid conductivity (refer Annexure-II). The geo-physical logging, examination of drill cuttings and the objective of monitoring should form the basis for finalising the piezometer design.

3.8 Piezometer Completion

Piezometer completion should ensure that the hydraulic head measured in the piezometer is that of the aquifer of interest. Ensures that only the aquifer of interest contributes water to the piezometer and prevents the annular space from being a vertical conduit for water and contaminants. Such completion steps are critical to the long-term goals of groundwater monitoring. It has to be remembered that the investments made in the construction of piezometers are part of network monitoring programme that have to last for decades. Well completion in unconsolidated deposit rocks consists of installing the well casing and screen, filling and sealing the annular space between the well casing and piezometer wall.

3.8.1 Piezometer Design

Good design and careful well construction can only ensure good hydraulic flow characteristics in the aquifer. The screens should be lined up exactly with the permeable portion of the aquifer. The screens should provide the same hydraulic conductivity of the aquifer. The design should prevent entry of fines and sand particles into the piezometer.

The piezometer should completely seal the aquifer which are not to be monitored. The well assembly should be able to withstand any corrosion or physical damages during pumping and logging.

DESIGN AND CONSTRUCTION OF

MANUAL

DESIGN AND CONSTRUCTION OF

LITHOSPECIFIC PIEZOMETER

September 2002

Table of Contents

Preface

Scope of the Manual

1 Introduction

2 Drilling preparation

3 Construction of piezometer