GROUNDWATER www.google.com en.wikipedia.org Thompson Higher Education 2007; Monroe, Wicander, and Hazlett, Physical Geology
GROUNDWATER is one of the most important geological resources for humans Worldwide 50% of people obtain their water from the ground. 70 times more abundant in the subsurface than in surface reservoirs. Moves so slowly it is stored in the earth and remains availableeven in dry periods. In some places it flows from humid environments to dry ones, making water available. It serves as an underground reservoir of water that eventuallyruns into streams and lakes.
Groundwater and Porosity and Permeability Groundwater and Porosity and Permeability The Water Table Water Wells Borehole Geophysics Groundwater Movement Recharge and Discharge areas, Springs and Artesian Systems Groundwater Erosion and Deposition Modifications of the Groundwater System And Their Effects Hydrothermal Activity
Groundwater is that water which occupies pore spaces and other cavities within subsurface rocks and unconsolidated materials. Groundwater by volume is only about 1% of the of the hydrologiccycle but constitutes approximately 22% of the world's fresh water supply.
Porosity is the percentage volume of rock, sediment or soil which consists of pore space
Porosity Soil is about half pore space, much of which is filled with water. The rest is stored in unconsolidated sediments, or cracks and joints in rocks.
Porosity
Permeability refers to the transmissibility of fluids through rock, sediment,or soil. Connected pores gives rock permeability Transmissibility is the ease with which water moves through rock A rock can have abundant pore space but if these spaces are not connected, groundwater can not move through it. The pore spaces have to be big enough and interconnected to move water. Affected by: number of available conduits size of the conduits straightness of the conduits
Groundwater Movement mostly occurs by the work of gravity (water flows down hill) but generally occurs very slowly (cm to meters/day)
Groundwater Zones and the Water Table The aeration zone contains both air and water in the pore spaces of rock, soil or sediment. The water table surface separates the aeration zone from the saturated zone. The saturation zonehas all pore spaces occupied by water.
The Water Table is an important concept called a potential surfaceand can not be seen directly. Water Table mimics surface topography. Water table coincides with level of water in wells. Water table is important in explaining the flow of springs and streams, and water levels in lakes.
Water Table Maps When the depth to the water table is measured in wells at multiple points in the same aquifer, the elevations can be contoured to show the groundwater flow direction The groundwater flow direction is always normal to the potential-surface contours
Water Table Fluctuates by Season
Water Table and Streams When the water table is higher in elevation than a stream, ground water flows into the steam called gaining stream (usually in humid climates). When water table is below a stream it is called losing stream and supplies water to the ground (usually in desert climates).
Aquifers, Aquitards, Aquicludes, and Confining Units An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, or silt) from which groundwater can be extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Anaquitardis low permeability material along an aquifer that retards the flow of groundwater. An aquiclude is a solid, impermeable area underlying or overlying an aquifer. When anaquicludeoverlies an aquifer under confined pressure, thesrtatare called a confining unit overlying a confined aquifer.
Water Wells are devices similar to drinking straws that help people to remove water from the zone of saturation. Wells must be below the water table because during pumping the water table is lowered in elevation (this is calleddrawdown). Once a well is pumping, a conical depression forms in the watertable called a cone of depression.
Springs occur where an aquifer and water table intersect the ground surface A Perched Water Table is when anaquitardblocks the downward movement of water, and two water table levels can form with the upper being a perched water table. They can form springs on hillsides and in road cuts.
Groundwater moves slowly through aquifers, from areas of high pressure to areas of lower pressure such as streams, lakes, and swamps. Municipal water systems commonly have well water pumped to elevated holding tanks where gravity maintains pressure to the recipients When groundwater in an aquifer is confined by aquicludes and is under hydrostatic pressure as the result of an elevation difference between the zone of recharge and lower portions of the aquifer, an artesian system exists.
Groundwater Flow Rates are dependant upon the permeability of the material and the hydraulic gradient Flow rates are typically 10-100 cm/day, or 40-400 m/yr
Karst Topography is characterized by sinkholes, solution valleys, and disappearing streams, and results from groundwater weathering and erosion.
Caves form when groundwater weathers and erodes soluble rock such as limestone in the zone of saturation. cave
Karst Topography Of the Irish Barren Uplands
Karst Topography As groundwater percolates through the zone of aeration and flows through the saturated zone, it dissolves the carbonate rocks and gradually forms a sytem of passageways. Horizontal passageways carry water to streams and allows the local base level to drop, creating cave and cavern systems.
Cave Deposits Buchan Cave, Victoria, Australia
Cave Deposits
Aquifer Systems consists of aquifers andaquitards.
Aquifers and Confining Units of New Jersey
The Great Artesian Basin in Australiais arguably the largest groundwater aquifer in the world (over 1.7 million km²). It plays a large part in water supplies forqueenslandand remote parts of South Australia. Queensland
Groundwater Depletion and Ground Subsidence When withdrawal from wells exceeds the rate of recharge, dry wells, loss of hydrostatic pressure, saltwater encroachment and ground subsidence may result. Aquifer depletion is a problem in some areas, and is especially critical in northern Africa.
Groundwater Depletion and Ground Subsidence New methods of groundwater management such as artificial recharge and injection of surface waters during seasonal wet periods has extended the life of many freshwater aquifers, especially in the United States. But there are other places like the arid southwest USA where 10s of meters of land subsidence is directly related to groundwater depletion. 9 m in 52 years
The Ogallala Aquifer of the central United States is one of the world's great aquifers, but in places it is being rapidly depleted by growing municipal use, and continuing agricultural use. This huge aquifer, which underlies portions of eight states, contains primarily fossil water from the time of the lastglaciation(10-85 Ka). Annual recharge, in the more arid parts of the aquifer, is estimated to total only about 10 percent of annual withdrawals.
Saltwater Incursion Freshwater is less dense than saltwater and will form a lens floating atop the salty groundwater If excessive pumping occurs, a cone of depression develops in the fresh groundwater, which may result in saltwater contamination of the well. Pumping water back into the fresh groundwater system through recharge wells can help lower the freshwater-saltwater interface and reduce saltwater incursion.
The Edwards Aquifer in central Texas is a carbonate aquifer has historically been providing high quality water for nearly 2 million people, and even today, is full because of tremendous recharge from a number of area streams, rivers and lakes. The primary risk to this resource is human development over the recharge areas.
Dollars and Ground-water Quality The Environmental Protection Agency estimates that communities in the United States need $12.1 billion in funding immediately to protect the nation's drinking water supplies and to meet minimum health-based standards. The agency also estimates that $138.4 billion will be needed over the next 20 years to upgrade or replace the water infrastructure (2007).
Dollars and Ground-water Quality The agency also estimates that $138.4 billion will be needed over the next 20 years to upgrade or replace the water infrastructure. $263 billion gap (2013)
Groundwater Pollution Groundwater contamination can be natural or anthropogenic (man-derived) Contamination from anthropogenic and animal sewage, landfills, and toxic waste is becoming a serious problem. High-density housing with water wells and septic very bad.
Arsenic in Groundwater can be either natural or anthropogenic
red black gray red
Arsenic in Groundwater
Septic Systems have a life expectancy of about 20 years, but regular maintenance and best management practices can extend the life. Minimize the amount of solid material, water, and chemicals like solvents, paint, etc., that goes in. Pump solids from the tank regularly (minimum evry 4 years) Keep leach field free of rooted plants Divert surface water away from the field
Groundwater Pollution commonly occurs as plumesthat show concentration gradients having constituents concentrations decreasing away from the source area. A common saying: The solution to pollution is dilution In New Jersey, parties that are determined to be responible for groundwater contamination are required to delineate the horizontal and vertical limits of pollution plume, usually by drilling test, observation, and monitoring wells.
Bacteria and Groundwater Pollution In the future, naturally occurring bacteria may provide solutions for many groundwater pollution problems. Bacteria have been shown to convert uranium in contaminated waters to a highly insoluble form. Some microbes living in oxygen-free sediments can break down derivatives of hydrofluorocarbons, which are among the compounds under consideration to replace ozone-destroying chlorofluorocarbons (CFCs). And, microbes which degrade toxic carcinogenic aromatic hydrocarbons like benzene and toluene can be boosted to work in anaerobic conditions commonly found in heavily polluted aquifers. EOS, July 19,1994.
Hydrothermal Systems Geysers and hot springs develop where groundwater is heated by hot subsurface rocks or the geothermal gradient. Geysers are hot springs which periodically eject hot water and steam.
Hot Springs Deposits, Yellowstone, National Park, Wyoming, USA
Hydrothermal Systems and Early Biological Evolution Hydrothermal systems are considered primary targets in the search for fossil evidence of early life forms. These environments are favorable for the generation of organic compounds necessary for life. They may also have provided sanctuaries for heat-loving microorganisms during catastrophic earth events. High rates of mineralization would favor preservation. GSA Today, July, 2000. Some scientists believe that hydrothermal vents were the cradle of life, that may have began well before 3.2 billion years ago. They argue that the mix of high heat and cold seawater in the vent environment led to the formation of the first organic compounds, and that the formationof pyrite in ancient vents from sulfur and iron could have produced energy to force organic compounds to combine, leading eventually to the creation of life. In this context it has been proposed that metal sulfides of black smokers (one type of deep sea vent) could act as catalysts in the first step toward building organic molecules. Using electron ionization mass spectroscopy, they found few differences when they compared organic compounds from current vents with biologically diverse vents fossilized in 3.2-billion-yearold greenstone from South Africa.
Geysers Old Faithful, Yellowstone Old Faithful is a cone geyser located in Wyoming, in Yellowstone National Park, USA. N, it was the first geyser in the park to receive a name. It is also considered to be the most predictable geographical feature on Earth erupting almost every 91 minutes. The Geysers, Sonoma County, California Geothermal Systems ~ 120 mi North of San Francisco is piped directly to electricity-generating turbines to produce electricity for regional distribution
Geothermal Energy is formed from the steam and hot water which resides in Earth's crust. Geothermal energy It provides a relatively clean source of energy for heat and electricity. In New Jersey, a study of the geophysical parameters needed to design geothermal systems shows that the efficiency of geothermal systems in this region increases as geological materials become more consolidated and hardened into rock. Substrate in southern New Jersey consists of sand, silt, clay, and gravel, which are less efficient at storing and diffusing heat than are the igneous, metamorphic, and compacted sedimentary rocks of higher latitudes.
Dowsing, Divining, Water-Witching, and Doodlebugging Dowsing is the GOD-given talent of finding subsurface features of interest without using scientific instruments. Employed in attempts to locate ground water, buried metals or ores, gemstones, oil, gravesites, and many other objects and materials, as well as Earth currents. Dowsing or water-witching for water Doodlebugging for oil There is no accepted scientific rationale behind divining, and there is no scientific evidence that it is effective.
Fractured Bedrock Hydrogeology Profile diagrams illustrating the relationship between topographic grade and direction of cross flows in wells under natural (nonpumping) conditions. A. Upward cross flows occur in wells that penetrate deep aquifers with strata dipping in the same direction as topographic grade over long distances. B. Downward cross flows occur where strata dip in a direction opposite to long topographic grades. C. Wells that penetrate strata intersecting both recharge areas on hilltops and hill slopes and discharge areas in valleys can have both upward and downward cross flows. In general, cross flows can be expected to coincide with the direction of leakage in thick sequences of poorly conductive stratathat confine bed-parallel water-bearing units.