Groundwater Geol 1110 Newell guest lecture 3/28/16

The Hydrosphere

The water cycle

Water Cycle Precipitation Precipitation Infiltration Infiltration Runoff Runoff Evaporation Evaporation Transpiration Transpiration Evapotranspiration Evapotranspiration

Groundwater: Outline 1. What is groundwater? Terms. 2. Darcy’s Law and groundwater movement 3. Groundwater extraction and contamination problems

Surface water – groundwater connection

Porosity – percentage of rock or sediment volume that consists of void space (pores) 30 % 15% Porosity isolated – pores not connected

Permeability – rocks ability to transmit fluid Depends on - grain size/arrangement - interconnectedness of pore spaces High permeability: gravels, sands, limestones with dissolution channels, fractured rocks Low permeability: clays, unfractured metamorphic and igneous rocks, limestones without dissolution Possible to have high porosity and low permeability: Example: Clays

Aquifer : geologic unit that stores and is capable of transmitting significant water; moderate to high permeability (both permeable and porous) Aquaclude: rock formations that slow but do not prevent flow of water to or from an adjacent aquifer (low permeability)

Unconfined Aquifer At shallow depth Water table is the top boundary Recharged by precipitation infiltrating Confined Aquifer Deeper Confined on top by a less permeable layer Recharged slowly

Perched water table Above the main water table In unsaturated zones Due to lenses of less permeable rocks (e.g., shales or clays)

Springs

Hot Springs

Groundwater: Outline 1. What is groundwater? Terms. 2. Darcy’s Law and groundwater movement 3. Groundwater extraction and contamination problems

Groundwater movement Hydraulic gradient Hydraulic gradient – the groundwater elevation (or pressure) difference over a given distance – groundwater moves from high elevation (high pressure) to low elevation (low pressure)

Groundwater Movement High P to low P results in curved flow-paths in subsurface High P to low P results in curved flow-paths in subsurface

Groundwater Movement

Quantifying Flow: Darcy’s Law Henri Darcy – mid 1800’s Expression describing the discharge of groundwater flowing through an aquifer Q = k*A*(h2-h1)/d hydraulic conductivity (k)* cross sectional area (A) * hydraulic graient

Wells

Flowing Well Pressure surface elevation above ground surface Pressure surface elevation above ground surface

Groundwater: Outline 1. What is groundwater? Terms. 2. Darcy’s Law and groundwater movement 3. Groundwater extraction and contamination problems

Environmental Aspects of Groundwater Groundwater depletion Groundwater depletion Subsidence due to Groundwater (and other fluid) extraction Subsidence due to Groundwater (and other fluid) extraction Salt Water Intrusion Salt Water Intrusion Groundwater contamination Groundwater contamination

Groundwater extraction and subsidence

San Joaquin Valley USGS, 1984

Groundwater decline and subsidence, Tucson, AZ

If pumping > recharge Subsidence due to groundwater withdrawal in Pahrump Valley, Nevada

Earth Fissures – Cedar City, UT In addition to groundwater decline and damage to surface structures…subside nce can result in pathways for contaminated water to aquifers

Extraction of Hydrocarbons Signal Hill, Long Beach, CA: 1930’s (those are oil well derricks)

Subsidence – Oil Extraction Oil extraction caused subsidence Water flooding started in 50’s

Salt Water Intrusion

Contamination

Other Groundwater Features – Caverns and Karst Topography

Karst Topography and Sinkholes

Flow Systems