Surficial aquifer
Encyclopedia
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
s typically less than 50 feet (15m), but thicknesses of about 60 feet (18.3 m) have been mapped.
Composition
Surficial aquifers system consists mostly of beds of unconsolidated sand, cavity-riddled limestoneLimestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
and shells, sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
, sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
, and clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
sand with minor clay or silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
from the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
to Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
periods.
In most cases the flow system is undivided, though in places, clay beds
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
are sufficiently thick and continuous to divide the system into two or three aquifers. Complex interbedding of fine and coarse-textured rocks is typical of the system. These rocks range from late Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
to Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
periods.
In Georgia
Georgia (U.S. state)
Georgia is a state located in the southeastern United States. It was established in 1732, the last of the original Thirteen Colonies. The state is named after King George II of Great Britain. Georgia was the fourth state to ratify the United States Constitution, on January 2, 1788...
and South Carolina
South Carolina
South Carolina is a state in the Deep South of the United States that borders Georgia to the south, North Carolina to the north, and the Atlantic Ocean to the east. Originally part of the Province of Carolina, the Province of South Carolina was one of the 13 colonies that declared independence...
, unnamed, sandy, marine terrace
Marine terrace
A marine terrace, coastal terrace, raised beach or perched coastline is a relatively flat, horizontal or gently inclined surface of marine origin, mostly an old abrasion platform which has been lifted out of the sphere of wave activity . Thus it lies above or under the current sea level, depending...
deposits of Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
age and sand of Holocene age comprise the system. These sandy beds commonly contain clay and silt.
In Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
, these aquifers are shallow beds of sea shells and sand that lie less than 100 feet (30.5 m) underground. They are separated from the Floridan Aquifer
Floridan Aquifer
The Floridan Aquifer is a portion of the principal artesian aquifer that extends into Florida and is composed of carbonate rock and located beneath the coastal regions of the Southeastern United States and is one of the world's most productive aquifers. It is under all of Florida as well as ...
by a confining bed of soil. Some have been contaminated by saltwater, yet they provide most of the public freshwater supply southwest of Lake Okeechobee
Lake Okeechobee
Lake Okeechobee , locally referred to as The Lake or The Big O, is the largest freshwater lake in the state of Florida. It is the seventh largest freshwater lake in the United States and the second largest freshwater lake contained entirely within the lower 48 states...
and along the Atlantic coast north of Palm Beach
Palm Beach, Florida
The Town of Palm Beach is an incorporated town in Palm Beach County, Florida, United States. The Intracoastal Waterway separates it from the neighboring cities of West Palm Beach and Lake Worth...
.
In surficial aquifers, the groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
continuously is under unconfined and moves along the hydraulic gradient from areas of recharge to streams
STREAMS
In computer networking, STREAMS is the native framework in Unix System V for implementing character devices.STREAMS was designed as a modular architecture for implementing full-duplex I/O between kernel or user space processes and device drivers. Its most frequent uses have been in developing...
and other places of discharge. Surficial aquifers are recharged locally as the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
fluctuates in response to drought
Drought
A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...
or rainfall. Therefore, the temperature and flow from water-table springs varies.
Important surficial aquifers
The Biscayne Aquifer
Biscayne Aquifer
The Biscayne Aquifer, named after Biscayne Bay, is a surficial aquifer. It is a shallow layer of highly permeable limestone under a portion of South Florida...
is a surficial aquifer located in southeast Florida. It covers over 3000 square miles (7,770 km²), and is the most intensely used water source in Florida, supplying water to Dade County, Broward County
Broward County, Florida
-2000 Census:As of the census of 2000, there were 1,623,018 people, 654,445 households, and 411,645 families residing in the county. The population density was 1,346 people per square mile . There were 741,043 housing units at an average density of 615 per square mile...
, Palm Beach County
Palm Beach County, Florida
Palm Beach County is the largest county in the state of Florida in total area, and third in population. As of 2010, the county's estimated population was 1,320,134, making it the twenty-eighth most populous in the United States...
and Monroe County
Monroe County, Florida
Monroe County is a county located in the state of Florida. As of 2000, the population was 79,589. The U.S. Census Bureau 2006 estimate for the county was 74,737....
. The aquifer lies close to the surface and is extremely vulnerable to pollutants that leach through the shallow limestone bedrock. In some areas, it has been contaminated by fuel spills, industrial discharge, landfills, and saltwater.
The Sand and Gravel Aquifer stretches 2400 square miles (6,216 km²) across the panhandle of Florida and is replenished with rainfall. Over the years water levels have dropped due to water-well use by pumping, and it has been contaminated by industrial waste
Industrial waste
Industrial waste is a type of waste produced by industrial activity, such as that of factories, mills and mines. It has existed since the outset of the industrial revolution....
and saltwater instrusion.
The Chokoloskee Aquifer is surficial aquifer that covers 3000 square miles (7,770 km²) in southwest Florida. It is recharged by rainfall. It is believed that artificial drainage canals have lowered water levels and increased saltwater intrusion.