Comprehensive Earth Science, Geohazards, and Hydrogeology Study Guide

Fundamentals of Earth Science and Geodynamics

Basic Terminology

• Earth: The third planet from the Sun and the only known planet that supports life.

• Geology: The scientific study of Earth, including its materials, structure, processes, and history.

• Geosphere: The solid portion of Earth, including the crust, mantle, and core.

• Hydrosphere: All water on Earth, including oceans, rivers, lakes, groundwater, glaciers, and water vapor.

• Atmosphere: The layer of gases surrounding Earth.

• Biosphere: The part of Earth where living organisms exist.

• Lithosphere: The rigid outer layer of Earth consisting of the crust and uppermost mantle.

• Asthenosphere: A weak, hot, plastic layer beneath the lithosphere that allows tectonic plates to move.

• Tectonic Plate: A large rigid section of the lithosphere that moves over the asthenosphere.

• Plate Tectonics: The theory that Earth’s lithosphere is divided into moving plates.

Earth's Internal Structure

Earth is divided internally into standard layers: Crust $\rightarrow$ Mantle $\rightarrow$ Outer Core $\rightarrow$ Inner Core.

• Crust: The thin, solid outermost layer of Earth.

  • Continental Crust: The thicker, less dense crust beneath continents.

  • Composition: Mostly granitic.

  • Elementary Content: Rich in silica and aluminum.

  • Age: Older than oceanic crust.

  • Thickness: Approximately $30\text{--}70\,km$ thick.

  • Oceanic Crust: The thinner, denser crust beneath oceans.

  • Composition: Mostly basaltic.

  • Elementary Content: Rich in silica, iron, and magnesium.

  • Thickness: Approximately $5\text{--}10\,km$ thick.

  • Age: Generally younger than continental crust.

• Mantle: The thick layer between the crust and core, composed mainly of silicate minerals rich in iron and magnesium.

  • Spatial Extent: Extends to about $2,900\,km$ depth.

  • Volume: Makes up most of Earth’s volume.

  • Upper Mantle: The upper portion of the mantle, extending from beneath the crust downward.

  • Lower Mantle: The deeper, hotter, denser portion of the mantle.

• Core: Earth’s innermost layer, composed primarily of iron and nickel.

  • Outer Core: The liquid portion of Earth’s core.

  • Composition: Mainly iron and nickel.

  • Function: Fluid movement generates Earth’s magnetic field.

  • Inner Core: The solid innermost part of Earth.

  • Composition: Mainly iron and nickel.

  • State: Solid due to extremely high pressure.

Compositional vs. Mechanical Layers

Compositional Layers (Chemical Composition)

• Crust: Mostly silicate minerals.

• Mantle: Mainly iron- and magnesium-rich silicate minerals.

• Core: Mainly iron and nickel.

• Silicate: A mineral or compound containing silicon and oxygen, usually with other elements.

• Iron ($Fe$): A major element concentrated in Earth’s core.

• Nickel ($Ni$): A metallic element found mainly in Earth’s core.

Mechanical Layers (Physical Properties)

• Lithosphere: Rigid outer layer made of the crust and uppermost mantle.

• Asthenosphere: Weak, plastic layer beneath the lithosphere.

• Mesosphere: The stronger, deeper portion of the mantle beneath the asthenosphere.

• Outer Core: Liquid mechanical layer.

• Inner Core: Solid mechanical layer.

Abundant Elements in Earth's Crust

• Oxygen ($O$): Most abundant element in Earth’s crust.

• Silicon ($Si$): Second most abundant element in Earth’s crust; major component of silicate minerals.

• Aluminum ($Al$): Common element in crustal minerals.

• Iron ($Fe$): Important in Earth’s mantle and core.

• Calcium ($Ca$): Common element in many minerals.

• Sodium ($Na$): Found in many silicate minerals.

• Potassium ($K$): Common in feldspar and other minerals.

• Magnesium ($Mg$): Important in mantle minerals.

Mineralogy and Mineral Properties

• Mineral: A naturally occurring, inorganic solid with an orderly crystalline structure and definite chemical composition.

• Mineralogy: The study of minerals.

• Crystal: A solid whose atoms are arranged in an orderly, repeating pattern.

• Crystalline Structure: The organized arrangement of atoms within a mineral.

• Inorganic: Not produced by living organisms.

• Naturally Occurring: Formed by natural processes rather than manufactured by humans.

• Chemical Composition: The specific elements and proportions that make up a substance.

Diagnostic Physical Properties

• Color: The visible color of a mineral.

• Streak: The color of a mineral’s powdered form.

• Luster: How light reflects from a mineral’s surface.

• Hardness: A mineral’s resistance to scratching.

• Cleavage: The tendency of a mineral to break along flat, smooth surfaces.

• Fracture: The way a mineral breaks when it does not follow cleavage planes.

• Density: Mass per unit volume of a substance.

• Specific Gravity: The ratio of a mineral’s density to the density of water.

Mohs Hardness Scale

Scale measuring mineral scratch resistance from 1 (softest) to 10 (hardest):

1. Talc (Softest)

2. Gypsum

3. Calcite

4. Fluorite

5. Apatite

6. Orthoclase

7. Quartz

8. Topaz

9. Corundum

10. Diamond (Hardest)

Petrology and the Rock Cycle

• Rock: A naturally occurring solid aggregate of one or more minerals or mineraloids.

• Petrology: The scientific study of rocks.

• Rock Cycle: The continuous process through which rocks are formed, changed, broken down, and reformed.

Major Rock Classifications

• Igneous Rock: Rock formed when molten material cools and solidifies.

  • Magma: Molten rock beneath Earth’s surface.

  • Lava: Molten rock that reaches Earth’s surface.

  • Intrusive Igneous Rock (Plutonic Rock): Igneous rock formed when magma cools beneath Earth’s surface. Example: Granite (coarse-grained).

  • Extrusive Igneous Rock (Volcanic Rock): Igneous rock formed when lava cools at Earth’s surface. Example: Basalt (fine-grained; common in oceanic crust).

• Sedimentary Rock: Rock formed from accumulated sediments that become compacted and cemented, or from chemical/biological processes.

  • Sediment: Loose particles of rock, minerals, or organic material.

  • Lithification: The process that turns sediments into sedimentary rock, mainly through compaction and cementation.

  • Clastic Sedimentary Rock: Formed from fragments of pre-existing rocks. Examples: Sandstone (sand-sized particles), Shale (fine-grained, mud/clay).

  • Chemical Sedimentary Rock: Formed when dissolved minerals precipitate from water.

  • Organic/Biochemical Sedimentary Rock: Formed from accumulated remains or activities of organisms. Example: Limestone (composed mainly of calcium carbonate).

• Metamorphic Rock: Rock formed when existing rock is changed by heat, pressure, or chemically active fluids without completely melting.

  • Metamorphism: The alteration of existing rock due to heat, pressure, or chemically active fluids.

  • Foliation: The parallel alignment of minerals caused by directed pressure.

  • Non-foliated: Metamorphic texture without visible layering or alignment.

  • Metamorphic Rock Types:

  • Slate: Fine-grained, foliated metamorphic rock commonly formed from shale.

  • Marble: Non-foliated metamorphic rock formed from limestone.

  • Gneiss: High-grade metamorphic rock with distinct mineral banding.

  • Schist: Foliated metamorphic rock with visible aligned minerals.

Earth's Internal Boundaries (Discontinuities)

• Discontinuity: A boundary inside Earth where seismic-wave behavior changes because the material or state changes.

• Mohorovičić Discontinuity (Moho): Boundary between the crust and mantle.

• Gutenberg Discontinuity: Boundary between the mantle and outer core.

• Lehmann Discontinuity: Boundary between the outer core and inner core.

Temperature, Pressure, and Geothermal Dynamics

• Geothermal Gradient: The rate at which temperature increases with increasing depth inside Earth.

• Geothermal Energy: Heat energy originating from Earth’s interior.

• Pressure: Force exerted per unit area.

• Lithostatic Pressure: Pressure caused by the weight of overlying rocks.

• Temperature: A measure of the thermal energy of a substance.

• Depth Relationships:   $\text{Depth} \uparrow \implies \text{Pressure} \uparrow$   $\text{Depth} \uparrow \implies \text{Temperature} \uparrow$

Mantle Convection Mechanisms

• Convection: Transfer of heat through the movement of material.

• Mantle Convection: Slow movement of mantle material caused by differences in temperature and density.

• Convection Current: Circular movement of material caused by heating and cooling.

• Buoyancy: The upward force that allows less-dense material to rise.

• Density Thermodynamics:   $\text{Hot Material} \rightarrow \text{Expands} \rightarrow \text{Less Dense} \rightarrow \text{Rises}$   $\text{Cool Material} \rightarrow \text{Contracts} \rightarrow \text{More Dense} \rightarrow \text{Sinks}$

Plate Tectonics and Continental Drift

• Plate Tectonics: Theory explaining the movement of Earth’s lithospheric plates.

• Continental Drift: The idea that continents have moved over geological time.

• Alfred Wegener: Scientist who proposed the Continental Drift hypothesis.

• Pangaea: A supercontinent that existed millions of years ago when most of Earth’s continents were joined together.

• Supercontinent: A large landmass formed by the joining of multiple continents.

Plate Boundaries and Interactions

• Divergent Boundary: Where two plates move away from each other.

  • Features: Mid-Ocean Ridge (underwater mountain system), Rift Valley (continental crust pulled apart), Seafloor Spreading (creation of New Crust).

• Convergent Boundary: Where two plates move toward each other.

  • Oceanic--Continental Convergence: Oceanic plate subducts beneath continental plate.

  • Continental--Continental Convergence: Continental plates collide, forming large mountain ranges.

  • Oceanic--Oceanic Convergence: One oceanic plate subducts beneath another.

  • Associated Features: Subduction (sinking plate process), Subduction Zone, Trench (deep seafloor depression), Volcanic Arc (chain of volcanoes).

• Transform Boundary: Where two plates slide horizontally past each other.

  • Features: Transform Fault, Fault (fracture with movement), Earthquake (sudden energy release along a fault).

Lines of Evidence for Plate Tectonics

• Continental Fit: Observation that continents fit together like puzzle pieces.

• Fossil Evidence: Similar fossils found on continents separated by oceans.

• Matching Rock Formations: Similar rock sequences and structures across ocean basins.

• Paleoclimate Evidence: Ancient climate indicators showing movement across climate zones.

• Magnetic Stripes: Symmetrical patterns of magnetic polarity recorded in oceanic crust around mid-ocean ridges.

• Paleomagnetism: Study of Earth’s ancient magnetic field recorded in rocks.

• Seafloor Spreading: Physical proof of continuous creation of new oceanic crust.

Earth's Magnetic Field and Geodynamo

• Magnetic Field: The region around Earth influenced by its magnetic forces.

• Geodynamo: The process in Earth’s liquid outer core that generates the magnetic field.

• Magnetic Poles: Regions where Earth’s magnetic field lines are approximately vertical.

• Magnetosphere: The region surrounding Earth dominated by Earth’s magnetic field.

• Outer Core Movement: Convective movement of electrically conductive liquid iron generating the field.

Seismic Wave Physics and Internal Shadow Zones

• Seismic Wave: Energy wave produced by an earthquake or disturbance.

  • P-Wave (Primary Wave): Fastest wave; compressional (push/pull); travels through solids, liquids, and gases.

  • S-Wave (Secondary Wave): Shear wave; travels through solids only.

  • Surface Wave: Travels along Earth’s surface; causes severe ground structural damage.

• P-Wave Shadow Zone: Area where direct P-waves are not detected due to strong refraction at the liquid outer core boundary.

• S-Wave Shadow Zone: Area where direct S-waves are absent because they cannot pass through the liquid outer core.

Planetary Differentiation and Early Earth

• Density Stratification: Structural arrangement of planetary materials according to density.

• Differentiation: Gravitational separation of materials by density during early Earth development.   $\text{Crust (Least Dense)} \rightarrow \text{Mantle (Denser)} \rightarrow \text{Core (Most Dense)}$

• Nebular Hypothesis: Model stating the solar system formed from a rotating cloud of gas and dust (Solar Nebula).

• Accretion: Gradual growth of planetary bodies via particle accumulation.

• Planetesimal: Early solid object contributing to planet growth.

• Protoplanet: Developing planetary body formed from accumulated planetesimals.

• Heat Sources during Formation: Radioactive Decay, Primordial Heat, Impact Heat.

Essential Comparative Summaries

• Continental Crust vs. Oceanic Crust:

  • Continental: Thicker ($30\text{--}70\,km$), less dense, granitic, older, forms landmasses.

  • Oceanic: Thinner ($5\text{--}10\,km$), denser, basaltic, younger, forms ocean basins.

• Magma vs. Lava: Magma is underground; Lava is molten rock on Earth's surface.

• Weathering vs. Erosion: Weathering breaks down rock; Erosion transports material.

• Crust vs. Lithosphere: Crust is a chemical layer; Lithosphere is a mechanical layer (Crust + uppermost rigid mantle).

• Mantle vs. Core: Mantle is silicate-rich; Core is iron-nickel-rich.

• P-Wave vs. S-Wave: P-waves pass through solids, liquids, and gases; S-waves pass through solids only.

Earth Processes, Geohazards, and Risk Reduction

Primary Earth Processes

• Earth Process: A natural process that changes Earth’s surface, interior, atmosphere, or ecosystems.

• Geologic Process: A natural process that forms, changes, or destroys Earth’s materials and landforms.

• Endogenic Process: A process originating from inside Earth.

• Exogenic Process: A process occurring at or near Earth’s surface driven by external forces (water, wind, ice, gravity).

Endogenic Process Mechanics

• Tectonism: Movement and deformation of Earth’s crust caused by tectonic forces.

• Diastrophism: Deformation, uplift, sinking, folding, and faulting of the crust.

• Plate Movement: Lithospheric displacement over the asthenosphere.

• Folding: Bending of rock layers due to compressional forces.

• Faulting: Breaking and displacement of rocks along a fault zone.

• Earthquake: Sudden shaking of the ground from energy release along a fault.

• Volcanism: Movement of magma toward or onto Earth's surface.

• Magmatism: Formation, movement, and solidification of magma.

• Mountain Building (Orogeny): Tectonic processes forming mountain ranges.

• Uplift: Vertical upward movement of Earth's crust.

• Subsidence: Vertical downward movement or sinking of Earth's crust.

Exogenic Process Mechanics

• Weathering: Breakdown or alteration of rocks at/near Earth's surface.

• Erosion: Removal and transportation of weathered material.

• Deposition: Settling or accumulation of transported sediment.

• Mass Wasting: Downslope movement of soil, rock, and debris under direct gravity.

• Sedimentation: Layered accumulation of sediments.

• Denudation: Overall wearing down and lowering of Earth's surface via combined weathering, erosion, and mass wasting.

Weathering Classifications

• Physical/Mechanical Weathering: Mechanical breakdown without chemical change.

  • Freeze-Thaw Weathering: Water enters cracks, freezes, expands, and fractures rock.

  • Thermal Expansion: Repeated heating/cooling cycle causes differential expansion and cracking.

  • Exfoliation: Peeling away of outer rock layers due to pressure release or temperature change.

  • Abrasion: Scouring of rock surfaces by friction from moving wind, water, or ice particles.

• Chemical Weathering: Chemical breakdown or alteration of rock minerals.

  • Oxidation: Reaction with oxygen (e.g., iron-bearing minerals rusting).

  • Hydrolysis: Chemical reaction between minerals and water.

  • Carbonation: Reaction between carbon dioxide, water, and minerals (e.g., limestone dissolution).

  • Dissolution: Complete dissolving of minerals into water solution.

• Biological Weathering: Disintegration caused directly by living organisms.

Mass Wasting Types

• Landslide: Rapid downslope movement of rock, soil, or debris.

• Rockfall: Free-fall of rocks from steep slopes or cliffs.

• Rockslide: Rapid sliding of rock masses along planar surfaces.

• Debris Flow: Rapid movement of water-saturated soil, rock fragments, and debris.

• Mudflow: Fast-moving flow consisting predominantly of water and fine sediment.

• Earthflow: Downslope movement of fine-grained, water-saturated soil.

• Creep: Extremely slow, continuous downslope movement of soil or rock.

• Slump: Downslope movement where material rotates along a curved concave surface.

• Avalanche: Rapid downslope mass movement of snow, ice, and associated debris.

Geohazard Framework and Risk Analysis

• Geohazard: A geological process/phenomenon that can potentially cause harm to people, property, infrastructure, or the environment.

• Natural Hazard: Naturally occurring event that has potential to cause loss.

• Disaster: Serious disruption occurring when a hazard impacts a vulnerable community exceeding its coping ability.

• Risk: The potential for loss calculated through interactions:   $\text{Risk} = \text{Hazard} \times \text{Exposure} \times \text{Vulnerability}$

• Exposure: Assets, infrastructure, or people situated in hazard-prone areas.

• Vulnerability: Conditions rendering assets/people susceptible to harm.

• Capacity: Resources and capabilities used to prepare for, withstand, and recover from hazards.

Specific Geohazard Categories

Earthquake Hazards

• Focus (Hypocenter): Exact point underground where earthquake rupture originates.

• Epicenter: Point on Earth's surface directly above the focus.

• Primary Hazards: Fault Rupture, Ground Shaking, Ground Rupture.

• Secondary Hazards: Aftershocks (post-mainshock events), Foreshocks (pre-mainshock events).

• Measurement Metrics:

  • Magnitude: Quantitative measure of energy released at the source.

  • Intensity: Qualitative measure of shaking effects and damage at a specific location.

Tsunami Hazards

• Tsunami: Series of high-energy ocean waves caused by sudden large-scale water displacement.

• Triggers: Undersea earthquakes, submarine landslides, coastal volcanic eruptions, meteorite impacts.

• Run-up: Maximum vertical height reached by water onshore above sea level.

• Inundation: Horizontal extent of land flooding by seawater.

Volcanic Hazards

• Volcanic Eruption: Discharge of magma, gases, ash, and pyroclastics.

• Lava Flow: Stream of molten rock on the surface.

• Ashfall: Atmosphere-borne fine material deposition.

• Pyroclastic Flow: Superheated, high-velocity mixture of gas, ash, and rock fragments.

• Pyroclastic Surge: Highly turbulent, low-density cloud of hot gas and rock debris.

• Lahar: Volcanic mudflow or debris flow mixed with water.

• Volcanic Gases: Emissions including $\text{H}_2\text{O}$, $\text{CO}_2$, and $\text{SO}_2$

• Ballistic Projectile / Volcanic Bomb: Large blocks ejected violently through air.

• Caldera Collapse: Structural collapse over a depleted magma chamber.

Slope Failure Triggers

• Heavy Rainfall: Increases pore water pressure and reduces shear strength.

• Earthquake Shaking: Induces dynamic shear stress.

• Volcanic Activity: Ground deformation and explosive disruption.

• Human Activity: Excavation, deforestation, loading, improper drainage.

• Weathering: Pre-conditions material by reducing strength.

Hydrological Hazards and Karst

• Flash Flood: Rapid onset flooding following heavy rainfall.

• River Flood: Overtop of river banks onto the adjacent Floodplain.

• Storm Surge: Coastal water level elevation driven by tropical cyclone winds and low pressure.

• Karst: Landscape formed by dissolution of soluble rocks like limestone, featuring Caverns and Sinkholes (ground collapse over cavities).

Disaster Risk Reduction (DRR)

• Hazard Assessment: Identification and mapping of physical hazard characteristics.

• Risk Assessment: Evaluating likelihood and potential consequences.

• Hazard Map vs. Risk Map: Hazard maps show spatial extent of physical threats; Risk maps overlay exposure and vulnerability data.

• Mitigation Approaches:

  • Structural Mitigation: Physical engineering (retaining walls, levees, earthquake-resistant design).

  • Non-structural Mitigation: Land-use planning, zoning, policy, education, early warning systems.

• Management Phases: Preparedness (getting ready) $\rightarrow$ Response (immediate action) $\rightarrow$ Recovery (restoration) $\rightarrow$ Resilience (long-term adaptation capability).

Philippines Regional Context

• Pacific Ring of Fire: Circum-Pacific belt characterized by active volcanism and frequent seismic activity.

• Philippine Fault Zone: Major active strike-slip fault system traversing the archipelago.

• West Valley Fault: High-risk fault segment running through Greater Metro Manila.

• Key Monitoring Agencies:

  • PHIVOLCS: Philippine Institute of Volcanology and Seismology (monitors volcanoes, earthquakes, tsunamis).

  • MGB: Mines and Geosciences Bureau (produces national GeoHazard maps for landslides and floods).

Comprehensive Hydrogeology and Groundwater Systems

Fundamentals of Hydrogeology

• Hydrogeology: Branch of geology studying groundwater occurrence, movement, chemistry, and geological interactions.

• Groundwater: Subsurface water held in soil pore spaces and rock fractures.

• Surface Water: Open water bodies on Earth's surface (rivers, lakes, streams).

• Hydrologic Cycle: Continuous movement of water through atmosphere, surface, and subsurface.

Hydrologic Cycle Processes

$\text{Precipitation} \rightarrow \text{Infiltration} \rightarrow \text{Percolation} \rightarrow \text{Recharge} \rightarrow \text{Groundwater Storage} \rightarrow \text{Discharge}$

• Evaporation: Liquid water phase change to gas via thermal energy.

• Transpiration: Water release from vegetation foliage.

• Evapotranspiration: Total flux of combined evaporation and plant transpiration.

• Condensation: Vapor phase change to liquid.

• Precipitation: Rain, snow, sleet, or hail discharge.

• Infiltration: Initial penetration of surface water into soil.

• Percolation: Deep downward flow of water through soil/rock matrix.

• Runoff: Surface overland flow toward surface water bodies.

• Recharge: Inflow replacing groundwater supply in an aquifer.

• Discharge: Outflow of groundwater to springs, surface streams, or oceans.

Subsurface Zonation

• Unsaturated Zone (Vadose Zone): Subsurface layer above the water table where pores contain both air and water.

  • Soil Moisture: Water held strictly within the soil root zone.

• Capillary Fringe: Lower part of unsaturated zone directly above water table where water is drawn upward via capillary tension.

• Saturated Zone: Subsurface zone where all interconnected void spaces are completely filled with water.

• Water Table (Groundwater Table): Upper surface boundary of the saturated zone.

Aquifer Hydraulics and Hydrostratigraphy

• Aquifer: Geological formation capable of storing and yielding significant groundwater quantities.

  • Unconfined Aquifer: Open to surface infiltration; upper boundary is the free water table.

  • Confined Aquifer: Bound above and below by low-permeability layers; water is under hydrostatic pressure.

  • Artesian Aquifer: Confined system where pressure causes water level in a well to rise above the top of the aquifer.

  • Artesian Well: Well tapping an artesian aquifer.

  • Perched Aquifer: Localized saturated zone supported above the regional water table by an isolated low-permeability lens.

• Classification of Retarding Layers:

  • Aquitard: Low-permeability layer that transmits water slowly.

  • Aquiclude: Saturated layer that stores water but transmits negligible quantities.

  • Aquifuge: Impermeable rock body that neither stores nor transmits water.

Physical Rock and Soil Hydraulic Properties

• Porosity: Ratio of void volume to total material volume, expressed as percentage:

  • Primary Porosity: Original void space created during rock formation.

  • Secondary Porosity: Voids created post-formation (fractures, joints, solution conduits).

  • Effective Porosity: Interconnected pore volume available for fluid flow.

• Permeability: Capacity of porous material to transmit fluids.

• Hydraulic Conductivity ($K$): Measure of fluid movement capacity through porous media incorporating fluid properties.

• Intrinsic Permeability: Quantitative measure of flow capacity independent of fluid density/viscosity.

• Property Contrast: Clay exhibits high total porosity but extremely low permeability due to micro-pore sizes.

Groundwater Flow Physics and Equations

• Hydraulic Head: Total mechanical energy per unit weight of water (Elevation Head + Pressure Head).

• Hydraulic Gradient: Head change per unit distance along flow path.

• Darcy's Law: Fundamental governing equation for laminar groundwater flow:   $Q = K \cdot I \cdot A$   where:

  • $Q$ = Flow rate (discharge volume per unit time)

  • $K$ = Hydraulic conductivity

  • $I$ = Hydraulic gradient ($\frac{\Delta h}{L}$)

  • $A$ = Cross-sectional area perpendicular to flow

Quantitative Storage Mechanics

• Storage Parameter Expressions:   $\text{Total Porosity} = S_y + S_r$

  • Specific Yield ($S_y$): Volume fraction of water drained by gravity from saturated material.

  • Specific Retention ($S_r$): Volume fraction retained against gravity by molecular attraction and surface tension.

• Storativity ($S$): Volume of water released/absorbed per unit surface area per unit change in head.

• Transmissivity ($T$): Total volumetric capacity of aquifer full thickness ($b$) to transmit water:   $T = K \cdot b$

Well Hydraulics and Pumping Dynamics

• Well: Borehole constructed to access or monitor groundwater.

  • Well Screen: Perforated casing allowing water ingress while filtering sediment.

  • Well Casing: Structural pipe lining preventing borehole collapse.

  • Drawdown: Vertical drop in water level caused by pumping.

  • Cone of Depression: Three-dimensional conical depression in the water table centered around an active pumping well.

  • Static Water Level: Level prior to pumping equilibrium.

  • Pumping Water Level: Equilibrium level during active abstraction.

  • Specific Capacity: Ratio of well discharge yield to total drawdown ($\frac{Q}{\text{Drawdown}}$).

Groundwater--Surface Water Interactions

• Gaining Stream (Effluent Stream): Stream channel receiving baseflow discharge from the adjacent water table.

• Losing Stream (Influent Stream): Stream channel losing surface water by downward seepage into the unsaturated/saturated zone.

• Baseflow: Groundwater contribution sustaining perennial stream flow during non-precipitation periods.

Groundwater Quality and Contamination

• Contaminant Source Classifications:

  • Point Source: Single identifiable localized origin (e.g., leaking underground storage tank, industrial pipe).

  • Nonpoint Source: Diffuse widespread discharge (e.g., agricultural fertilizer runoff, urban nitrate leaching).

• Leachate: Contaminated fluid generated by liquid percolating through solid waste matrix (e.g., landfills).

• Saltwater Intrusion: Migration of saline water into freshwater aquifers driven by excessive coastal groundwater overdraft.

• Coastal Overdraft Hazards: Excessive abstraction induces Land Subsidence (compaction of aquitards) and persistent Groundwater Depletion.