14 Groundwater Hydrology-I

Anita Singh

epgp books

 

 

Objectives

 

1.   An introduction to groundwater hydrology

2.   An understanding of groundwater concept, its significance and occurrence around the globe

3.   An overview of different generic types of water and hydrological cycle

4.   The basic concepts of geological formations (aquifers), its parameters and its importance

5.   An overview of geological factors governing groundwater and its availability

6.   Understanding of basic fundamentals of groundwater flow

7.   Understanding of Darcy Law, its significance and associated limitations

 14.1    Introduction

Ground-water hydrology is a branch of hydrology that deals with the existence, movement, and quality of undergroundwater beneath the Earth’s surface.As per the U.S. National Research Council (1991), hydrology is defined as, “The science that treats the water of the Earth, and their occurrence, circulation, and distribution, their physical and chemical properties, and their reaction with the environment, including their relation to living things”. Life originated in water and depends on water. The entire living world of our planet, i.e., plants, animals and human beings depend upon water for their survival. Life is unthinkable without water. Most of the societies and cultures originated near water sources. Water is required for each and every step of life for fulfilment of their various purposeslike drinking, irrigation, transportation, and recreation. Water present beneath the land surface is counted as subsurface water or undergroundwater, which is usually differentiated into two different zones i.e. saturated zone and unsaturated zone. In most of the areas, unsaturated zone exists immediately below the land surfaceand usually found above the saturated zone. This zone of underground water contains both air and water. However, saturated zone contains interconnected openings which are saturated in water. This zone of underneath land surface actually presents true groundwater, whose existence is in pore spaces and fractures of sediments beneath the Earth’s surface. Therefore, in other sense, true groundwater is found in the open space between sedimentary materials or in fractured rocks, existed beneath the unstaurated zone, and the available water has a pressure greater than atmospheric pressure.Moreover, groundwater facilitates availability of water for human consumption. Groundwater is imitative from several sources, however, primarily rainfall and snow melting acts as precursor for the saturated zone of groundwater. The hydrological cycle is the central focus for groundwater hydrology. A part of water percolates from the land surface and infiltrate to saturated zone of groundwater through unsaturated zone. Therefore, unsaturated zone has a great importance to groundwater hydrology and usually differentiated into three different sub-zones: soil zone, intermediate zone, and capillary fringe (as mentioned in Fig. 1). The capillary fringe represents the zone exist immediately above the water table, where some or all of the interstices are filled with water at pressure lower than atmospheric pressure. This sub-zone of unsaturated zone remain continuous with water below the water table (Meinzer, 1923).

 

Some facts about groundwater (Leopold, 1974; Raghunath, 2003; Spellman, 2012):

 

  • Water is most widely occurring substance on Earth, however, only 2.8% of total water resourcesexist as fresh water. Moreover, the biggest portion of fresh water remains locked in glaciers and icebergs or lies in deep underground aquifers. Out of this 2.8%, about 0.6% is available as groundwater and only 0.3% can be extracted economically with the present drilling technologies.
  • The unseen oceans of fresh water beneath the Earth surface makes about 35 times the available water in lakes and streams at any time.
  • The available groundwater for human consumptiongenerally occurs within 800 meters from the Earth surface.
  • Currently, around one fifthof total water consumed at world level, is maintained by groundwater resources only and 80% of the total groundwater consumption is meant for irrigating agricultural lands.Moreover, entire Earth surface can be covered with a 55 meter thick layer from the volume of groundwater available beneath the Earth surface.
  • The groundwater moves with extremely slow speed underneath the Earth surface through the interparticle space or between the networks of fractures of unconsolidated material.The rate of exchangeof groundwater in 280 years is almost 1/9,000 the rate of exchange of fresh water in rivers and streams
  • The movement of groundwater generally follows the path from recharge areas, from where water percolates to the ground, to the discharge areas, from where it exits from the ground.

o   Classification of water with reference to its origin:

 

The relationship between different generic types of water is depicted in Fig. 2. Most of water resources are segregated into different generic types on the basis of their origin and occurrence which are described as under (Singhal and Gupta, 2010):

Magmatic water

 

The occurrence of water within, and in equilibrium with, a magma or water-rich volatile fluids derived from a magma, contributes to magmatic water. The term Plutonic water is applied, where the separation is deep, while water from shallow depths called volcanic water. As far as water availability is concerned, it is of only theroritical importance and can be released to the atmosphere during a volcanic eruption.

 

Juvenile water

 

This form of water is also known as new water, which has not been introduced to hydrosphere previously. The magmatic water is also a part of juvenile water, which may be either contributed from deep seated magma or shallow volcanic eruption.

Meteoric water

 

Most of the meteroric water is as a resultant of different forms of atmospheric precipitation, usually a part of present day hydrological cycle.This resource facilitates the water available in lakes, rivers, streams, wells and icemelts, which originates directly or indirectly from the precipitation. Although a large volume of precipitated water or water from melting of snow and ice, reaches the seas and oceans through the surface flows or runoffs, however, a considerable portionis also assessible to groundwater. Thewater infiltered remain continue its downward journey till it reaches to zone of saturation.

 

Connate water

 

The water retained in ancient aquifers, encountered at great depth in sedimentary rocks, either through marine or fresh water in origin, contributes to connate water. Generally, this type of water is present in hydraulic discontinuity with hydrological cycle and is also coined with a misnomer term, fossil water. Connate water is usually linked with fossil fuels including oil or gases, which are marine in origin. Sometimes, incomplete compaction may cause retention of small quantity of water with rocks like limestone, sandstone, and gravel.

 

Metamorphic water or rejuvenated water

 

This term is used for water associated with hydrous rocks like micas, clay, etc., during the process of metamorphism. This genetic type of groundwater encounter more of academic interest rather than a water resource.

 

14.2    Hydrological budget

 

The global hydrological cycle maintains the continuous churning of water on, above and below the Earth surface, supporting several life form on this planet. The system can be subdivided usually into three different subsystems, including atmospheric water system, surface water system and subsurface water system. The atmospheric system includes precipitation, evaporation, interception, and transpiration, while surface water system includes overhead flow, surface run-off and run-off to streams, seas and oceans. The subsurface water system includes infiltration, subsurface flow, and groundwater recharge and groundwater flow. Under normal conditions, the travel time of groundwater can varies from less than a day to more than a million years. The hydrological budget is very important and includes inflows, outflows, and storage of water as shown in the following equations (Todd and Mays, 2005).

 

14.3     Rock properties affecting groundwater

 

Different hydraulic properties of rocks and soil, including porosity, soil classification, and specific surface, have a considerable role towards controlling occurrence, availability and flow of groundwater.

 

Soil classification

 

The amount of groundwater recharge, storage, discharge, and the extent of groundwater contamination depends on the soil properties (like death, texture, porosity, specific yield, permeability, filtering capacity). The soil serve the purpose of attenuation on filtering solid particles, chemicals and dissolved substances. Microbial and biological processes transform such contaminants and retard such substances. The coarse-textured material (like sand), are more permeable and appears the worst for contaminant removal, whereas fine-textured soils are the best to meet the purpose due to less permeability and higher contact between soil and contaminants.

 

Specific surface and specific yield

 

The surface area depends on particle size, shape and mineral types and generally refers to the area per unit weight of the material (m2/g).In saturated zone of groundwater, water may adhere to the particles due to cohesion, or adhesion and surface tension, forming a film around particles. Such groundwater in saturated rocks or soil gives an idea about specific yield, which is the ratio of volume of water that could drain from saturated rock to the total volume of rock. The value of specific yield is always less than porosity. However, likewise porosity, specific yield is also influenced with grain size.

 

Porosity

 

The soil or rock fractions occupied spaces between the grains, which serve as space (voids, interstices, pores, or pore space) for the existence of groundwater. These such opening are of great interest for hydrologists, as these space serve as water conduits. The opening of rocks acts as a reservoir for groundwater. In unconsolidated rocks (like gravel and sand), opening occur between the particles of rocks or mineral grains, which are known with the term primary openings. Whereas, the purpose is facilitated with fractures in consolidated rocks(like basalt sandstone, granite, etc.) and is termed as secondary openings. The volume of opening in the rock or underneath soil determine the quantum of groundwater. The ratio of total volume of openings/spaces to the total volume of rocks or soil, represent the porosity (Fletcher, 1996).

 

Permeability

 

The rock particles, fracture size and shape play an important role in determining the porosity and permeability, which in turn regulate the aquifer characterstics and hydraulic conductivity of groundwater. The permeability is the parameter which determine the ability of water transmission and movement, and facilitates availability of water for human consumption. Coarse materials are generally more permeable, however, large openings may lower down the permeability beacause of filling of opening with fine grains. On other hand, grainular soil (like clay), offeres more fraction between the grains, which in turn reduce its permeability. In rock with fractures, permeability can be determined with opening size, interconnectivity between fractures and porocity. Usually, crystalline rocks are less permeable due to fewer openings and less porosity. However, volcanic rocks with broader openings enables faster movement of water.

 

14.4 Classifications of Geohydrological Characterstics

 

The geological characterstics including texture, structure and lithology of sub-surface formation has a greater influence on existance and movement of groundwater. Basically, geological formations are classified into different types depending upon the hydrological characterstics, which are described as under (as depicted in Fig. 3):

 

14.4.1  Aquifer

 

The word Aquifer originates from combinationof latin words, aquiwhich means “water” and affero (comes our from ferre) which means “to bear”. In nutshell, water bearing geological formation are known as aquifers(Todd and Mays, 2005). Lohman (1972) elaborates aquifersas geological formations which contain saturated permeable material that could yield sufficient quantity of water to ensure availablity of water in well and springs. The yield of aquifer can be determined on establising the maximum water withdrawal rate with compromising its sustainability and unacceptible decline in hydraulic head of the aquifer (Freeze and Cherry, 1979).Water saturated geological formations underneath the Earth surface, which facilitate reasonable supply of water are known as aquifers. Geological formations like unconsolidated sedimetry formations with coarse rock granules appear excellent aquifers. Moreover, fractures metamorphic and igneous rocks are also form goodaquifers. The study of aquifers characterstics and movemet of groundwater in aquifers is called as hydrogeology.Meinzer (1923) elaborated the geological concept to classify the water bodies considering different types of rocks. Few of the frequently used types of confined and unconfined aquifers are illustrated as below:

o   Aquitard

 

The term aquitard originates from the combination of two latin word i.e. aqua which means “water” and tardo which means “slow down or hinders”. Aquitard represent the water saturaed geological structures (like silt, clay, shale) having insufficient permeability and confounding it to behave like resource for water supply. However, aqiutard can permit exchange of groundwater between adjuscent aquifers due to vertical leakage but does not yield water freely to wells or springs. These sufficiently thick geological structures implies to behave like a groundwater storage zone (Todd and Mays, 2005).

 

o   Aquiclude

 

Aquiclude, like other terms, also originated from latin words Aqua means “water” and claudo which means “confines or inaccessible”. Aquicludes represent such limiting geological formation like unfractures cryatlline rocks, which are fully or nearly impermeable and favours no interchange of groundwater with other quifers. An aquiclude is solid, impermeable but porous structure underlying an aquifer and can be defined as a “water saturated geological unit that is incapable of transmitting significant quantities of water under ordinary hydraulic gradient”(Freeze and Cherry, 1979).

 

o   Aquifuge

 

Aquifuge represent relatively impermeable structures (like solid granite), which do not have any interconnected openings. Hence, such geological structures can neither store water, nor exchange/ transmit water with other aquifers. Basically, the word aquifuge is coined from combination of two latin word including aqua which means “water” and fuge which means “drive away” (Todd and Mays, 2005).

 

14.4.2 Types of aquifers

 

Aquifers are generally classified into four different categories: confined, unconfined, leaky and multiple aquifers. All the different categories of aquifers are discussed in details in below section.

 

14.4.2.1  Confined aquifers

 

Confined aquifers or artesian aquifers or pressure aquifers, are the water saturated geological formation, sandwiched between impervious or semi-pervious unsaturated zone at pressure greater than atmospheric pressure (Fig. 4a). This pressure may sometime results to rise in water level above Earth surface in wells. Generally, the existence of such aquifer systems take place in sedimentary rocks of low permeability in deep beneath the Earth surface where water get entrapped at the time of deposition. These aquifers are characterized with low groundwater circulation intensity, very large storage and inadequate replenishment. The average replenishment period for a confined aquifer could be extended up to 1000 years which is even less than 0.1% of the aquifer storage period (Margat et al., 2006). These aquifers may be recharged by rain or stream water infiltrating the pervious or semi-pervious rock at some considerable distance away from the aquifer.The water level in borehole or well installed in confined aquifers may sometimes rise above the level of the aquifer, especially in the condition when piezoelectric or potentiometric surface is above the ground surface. There may be possibility of having piezoelectric surface of confined aquifer, above the Earth surface, which resulted to the formation of flowing wells under natural pressure. The term artesian is used to depict the behavior of water rise above Earth surface in such flowing confined aquifers. The water received from these aquifers may be sometime older than thousands of years. Moreover, such aquifer systems are present in deeper layers and hence, less susceptible to natural hazards and human interferences.

The water balance in confined aquifers can be represented through the equation described below, considering negligible replenishment or recharge and loss through evaporation in one day period (Karamouz et al., 2011).

 

Where

 

Wsc,i     =Amount of water stored in the confined aquifer on day i (mm)

 

Wsc,i-1  = Amount of water stored in the confined aquifer on day i-1 (mm)

 

Wper= Amount of water percolating from the unconfined aquifer into the confined aquifer on day i (mm)

 

Wpc       = Amount of water removed from the confined aquifer by pumping on dayi (mm)

 

14.4.2.2 Unconfined aquifers

 

Unconfined aquifers or phreatic aquifers or water-table aquifers are water saturated geological formations, which is overlain by the free permeable unsaturated zone at the upper boundary of the aquifer. Unlike confined aquifers, saturated zone is open to the atmosphere through open pore spaces of the overlying permeable rock or sediments, which are interconnected vertically and laterally (Fig. 4b). The pressure of water in the unconfined aquifer is equal to the atmospheric pressure and upper groundwater surface is recognized as water-table, which is free to rise and fall. Typically, water does not rise above the water-table in such aquifers.However, depth to the water-table remain variable under various geological factors like topography, geology, season and tidal effects, and the quantities of groundwater being extracted from the saturated zone. Groundwater in such an aquifers is unconfined, threrefore, these aquifers are recognised as unconfined aquifers.Unconfined aquifers are usually replenished with rain or stream water infiltrating directly through the overlying soil. Shallow unconsolidated aquifers are located in unconsolidated glacial or fluvial deposits overlain with permeable unsaturated zone of little thickness, resulting to interface of groundwater with surface water. While, in deep unconfined aquifers exists in consolidated rocks (such as sandstones), overlaid with thick permeable unsaturated zone.

 

Perched aquifers are some special kind of unconfined aquifers where a small number of aquitard exists between Earth surface and water table. In such water saturated formations, groundwater accumulates above the impervious rocks or sediments like clay layer. In other sense, the occurrence of groundwater is separated from groundwater bodies with relatively impervious strata of aerial extent.

 

The water balance in unconfined aquifers can be demonstrated with the equation 5, described as under, considering short-term replenishment inputs and interaction of groundwater and surface water (Karamouz et al., 2011).

  

 

Where

 

Wsu,i  = Amount of water stored in the unconfined aquifer on day i (mm)

Wsu,i-1= Amount of water stored in the unconfined aquifer on day i-1 (mm)

Rr = Amount of recharge entering in the aquifer on day i (mm)

Bf = Base flow to the main channel on day i (mm)

Wsd = Amount of water moving into the soil zone in response to water deficiencies on day i (mm)

Wper= Amount of water percolating from the unconfined aquifer into the confined aquifer on day i (mm)

Wpu       = Amount of water removed from the unconfined aquifer by pumping on dayi (mm)

 

14.4.2.3 Leaky aquifers

 

Completely confined or unconfined aquifers are hard to find in nature, however, their existence is more frequently in form of leaky aquifers. These aquifers are overlain or underlain by a semi-confining layer or semi-pervious aquitards, therefore, such aquifers are also recognized as semi-confined aquifers. Generally, aquitards represents the lower permeability beds saturated or partial saturated zone which limit the movement of groundwater between the aquifers.Aquitard will be partially saturated when these extend to the land surface (Fig. 4c).On other hand, aquitard will be available in fully saturated form, when overlain with unconfined aquifers bounded above with the water table (Fig. 4d). These characteristics are reflected especially in alluvial valley plains or former lake basins. Groundwater exploration in wells or bore-wells installed in these aquifers make available water bounded in aquifers as well as in aquitards. Groundwater flows horizontally in aquifers, while movement of groundwater takes place in vertical direction in aquitards during extraction of water.

14.4.2.4  Multi-layered aquifers

 

Hydraulically, single aquifer exists infrequently in nature. Generally, aquifer is a part of multiple aquifers, which are arranged in a system. The movement of groundwater in such multi-layered aquifer system is much complex and depends upon the degree of hydraulic communication between the individual aquifers. A multi-layered aquifer system may be one of different types of aquifers available in the system. The aquifer may consists of a system containing two or more aquifers separated with aquicludes (Fig. 4e). The system of such aquifers may consist of confined aquifers or a mixture of unconfined aquifer overlain with a confined aquifer. In such an aquifer system, hydraulic characteristics like transmissivity and storativity of both the individual aquifers are maintained. This system helps to pump out the groundwater from more than one of the aquifer layer at a time, when a well fully penetrate the aquifer system. In another system of multi-layered aquifers, two or more aquifers with their own hydraulic characteristics, are separated by interfaces maintaining unrestricted crossflow of groundwater among the aquifers. The system mimics the similar response to that of a single layered aquifer, where their hydraulic characteristics including transmissivity and storativity behave collectively for the system. This system’s response to pumping will be analogous to that of a single-layered aquifer which is equal to the sum of the transmissivity and storativity of the individual layers. In third possibility for a multi-layered aquifer system, two or more aquifers are separated with aquitards, which strengthens the prospective of leaky aquifer system. This kind of aquifer system may have a measurable impact on other aquifer layer, when pumping of water is done from leaky single-layered aquifer system. However, the impacts may be negligible or measurable, depending upon pumping time.

 

14.5     Direction and speed of groundwater movement

 

The hydraulic parameters like speed and direction of groundwater in aquifers have a great significance to determine contamination of water with various components,which tends to percolate down to the saturated zone of aquifers. Filteration coefficient and speed of groundwater movement for a particular layer depict groundwater regime for a specific location. Moreover, flow of groundwater is placed under the substancial influence of pressure, hydarulic gradient, hydraulic conductivity and dynamic porosity. Though, groundwater hydraulic conductivity itself is dependent on surface characterstics like shape, size, interconnectedness and porosity. The ability of a geological material to move water is called hydraulic gradient, and generally, expressed in gallons per day per square foot (gal/d/ft2) or in feet per day (ft/d). The height of water level attained over the arbitrary level or datum level is known as hydraulic head or simply head. The movement of water follows in direction from a point of higher static groundwater elevation to lower elevation and higher to lower water head or potential, which is generally a virtue of position. Moreover, differential water level facilitate the movement of water, their speed as well a direction. Under the influence of all these parameters, groundwater moves slowly, may be less than one foot to few tens of feet per day (Harter, 2003). Unlike surface water, groundwater is restricted to flow freely and largly dependent on interconnected pores of the material. That’s why, hydraulic conductivity of sand and gravels is much larger in comparision to finely grained material like clay, whose interconnected pores are limited to support the flow of groundwater. The porosity of the material not only controls flow of water underneath but also responsible for contamination of groundwater with pollutants through percolation from land surface to groundwater. Higher percolation rate results in filteration of a significant amount of chemicals and pathogens to groundwater. The intergranular space between the particles of the material, also governs the storage capacity of aquifers. Highly porous medium like sand and gravels accommodate more water due to compartively richer intergranular space in comparsion of granite or clay.

 

14.6    Darcy Law

 

The flow of groundwater in aquifers from recharge to discharge point is a function of porous medium. For the first time, the flow of groundwater in granular or porous medium is expressed through a generalised mathematical relationship, which is known as Darcy Law, on the name of a French engineer, Henry Darcy. The empirical equation was formulated considering the prilimnary experiments conducted in 1803 to detremine the flow of groundwater through beds of porous materials like sand, rocks etc, which further formulates the basis for modern hydrogeology. He designed a transmission system for supply of safe drinking water through a porous material (sand) packed pipes from a large spring which was distant for more than 10 km from Dijon. The porous material acts as purification substrate for the supply and distribution of safe and relaibale drinking water. In 1856, he published his scientific finding and produce a empirical equation in term of Darcy Law, which indicates the fact that the rate of flow of a fluid (volume of fluid flow per unit time) between two ends is directly related to the pressure difference, distance and permeability of interconnecting pathways between the end points of connecting channel. Here, in this empirical equation (Equation 6), pressure represents the excessive pressure exerted due to gravity, underneth to the ground suface, over the normal hydrostatic fluid pressure. The experimental setup followed for Darcy Law is depicted in Fig. 5.

 

In modern sense, considering a cylindrical column of length of interest “l” and cross section area  “A”,  stoppered  on  both  the  ends  and  outfitted  with  tubes  for  inflow,  outflow  tubes  and manometer, Darcy Law can be expressed as:

 

Q = -KA dh/dl = -Ki                                                                   (Equation 6)

 

where: Q   = Rate of flow of fluid (groundwater) [volume per time or m3/d]

 

K =Hydraulic conductivity (m/d), which depends on the size and arrangement of the water-transmitting openings (pores and fractures) and on the dynamic characteristics of the fluid (water) such as kinematic viscosity, density, and the strength of the gravitational field;

A = Cross sectional area of cylindrical column (m2)

dh/dl = Loss of hydraulic head over the length of interest of cylindrical column (m/m)

 

i = Hydraulic gradient.

 

When water is introduced to the inlet channels of cylinderical pipe and allowed to flow through the porous medium, then it will take some time to get all pores filled with water and to attain flow rate equilibrium at inlet and outlet point.

 

In this sense, Darcy Law may be defined as rate of flow of fluid in porous medium or specific discharge (as shown in Equation 7) or Darcy velocity is proportional to the loss of hydraulic head and inversaly proportional to the length of path followed for the flow of liquid, or

 

Under the set of assumptions, the permeability of a medium is considered as 1 darcy, when it allows a fluid flows with a speed of 1cm3/s with viscosity 1 cP (1 mPa•s) under a pressure gradient of 1 atm/cm acting across a cross sectional area of 1 cm².

 

14.7    Limitations with applicability of Darcy Law

 

The application of Darcy Law are limited for specific circumstances and conditions, governing the flow of fluids from one zone to another and finally to assess the scope of hydraulic fracturing fluids towards fresh water zone. The extent of the law includes laminar flow of fluids in saturated granular medium under steady state conditions, assuming homogeneous, incompressible and isotherm fluids with negligible kinetic energy. In such an assumptions fluid movement is governed through viscous forces, when fluids are moving slowly along the parallel streamlines. Moreover, the speed of fluid increases on rapid extraction at the discharge point. At this point, the movement become chaotically and turbulent under the inertial forces rather than viscous forces. In such a situation, flow is computed with Reynolds number, which is the ratio between the inertial forces and viscous forces governing the flow. Specifically, Reynolds numbers are used to distinguish between the laminar flow, transition zone and the turbulent flow.

 

The validity of the law deviated when flow is turbulent, which may be identified in cavernous limestone or fractured basalt. However, averaging character considering negligible influences of factors and representative range, Darcy Law can be applicable for several circumstances in-spite of basic assumptions (Freeze and Cherry, 1979).

 

The cogency of Darcy Law is considered with few of the conditions or circumstances which are enlisted as under:

 

  • Saturated and unsaturated flow of fluids in aquifers and aquitards
  • Steady-state and transient flow;
  • Flow in granular media and in fractured rocks;
  • Flow in homogeneous systems and heterogeneous systems.

 

14.8     Steady State groundwater flow equation

 

When groundwater is stationary in a saturated porous medium under steady-state conditions, state variables became independent of time. The steady-state conditions define constant flow rate, piezometeric head and volume of stored fluid with respect to time. Moreover, the law of conservation of mass for such steady- state flow indicates the equilibrium condition of fluid flow at recharge and discharge point of any elementary control volume. In such constant conditions, flow equation for a homogenous, isotropic medium may get reduced to Laplace’s equation or potential equation.

 

Moreover, the equation may also follow the condition in shallow parts, where pore space deformation is negligible. However, in certain conditions, when flow may be incompressibleand deviate from steady-state condition, the boundary layer become time dependent with continuously rising and falling of water table. In such a generalized assumption of homogeneous hydraulic conductivity, the equation may be expressed as given below:

Summary: In this module students will able to understand basic concept of groundwater, its significance and occurrence around the globe, different generic types of water, geological formations (aquifers). The student will gain knowledge about geological factors governing groundwater and its availability, basic fundamentals of groundwater flow and Darcy Law.

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