Ground Water in Virginia

the original source of groundwater - rainfall
the original source of groundwater: rainfall
Source: Virginia Water Resources Research Center - The Threat to Virginia's Groundwater

When it rains... where does the water go? In urbanized areas, where pavement and roof tops cover the natural ground surface, raindrops might run down a gutter or off a paved road into a stormwater pond, then drain from the pond's outlet into a creek.

Runoff from parking lots occurs even in natural areas, such as state parks. When it rains at the marina in Leesylvania State Park, water runs directly from the impervious parking lot asphalt directly into the Potomac River, while much of the rainwater hitting the entrance road (Daniel K. Ludwig Drive) first flows into Powell's Creek before reaching the river. The surface runoff will absorb dirt particles (and fluids that have dripped from cars and trucks), making the roads and parking lots look clean after a storm - but carrying the dissolved pollution downstream towards the Chesapeake Bay.

In undeveloped areas within the park, water hits tree leaves, soaks into the soil, and goes underground. On a hot summer day, the water under the surface may stay only briefly in the pore spaces between soil particles, before evaporating directly back into the atmosphere or indirectly after being sucked into the root system of plants ("evapotranspiration").

Virginia soils can keep water for up to two weeks, before evapotranspiration sucks all the moisture from near the surface. Suburban gardeners and farmers across the state are well aware of the days between rains. As one farmer put it:1

We're only 10 to 14 days away from the last rain to a drought.

underground, water can accumulate during the winter, but groundwater levels drop during the summer as evapotranspiration peaks
underground, water can accumulate during the winter, but groundwater levels drop during the summer as evapotranspiration peaks
Source: US Geological Survey, Groundwater Watch - Glasgow, Virginia

If rainfall is sufficient, however, raindrops may seep below the root zone and accumulate under the surface in a layer of soil or rock, to become groundwater rather than surface runoff or transpiration. Water seeping underground does not create a lake or pond under the surface; instead, the drops fill up the pores between particles of rock. Rock underground is rarely so solid that there are no pores, and there are normally many connections between pores that make the subsurface permeable. Even igneous rocks typically have fractures or joints through which water can move, though slowly and in limited quantities.

water molecules can be trapped in pores between particles underground
water molecules can be trapped in pores between particles underground
Source: US Geological Survey, Ground Water in Freshwater-Saltwater Environments of the Atlantic Coast (Figure 3)

groundwater measuring well at Nottoway Park At Nottoway Park (near the Vienna Metro station), the depth to groundwater averages 16 feet - so plant roots are sucking up the water trapped only temporarily in the soil between rains, while the groundwater in the completely-saturated zone can be much deeper.2

Underneath the Fairfax campus of George Mason University, the metamorphic bedrock has weathered and become a rotted "saprolite" through chemical weathering as feldspars (such as NaAlSi3O8, KAlSi3O8, CaAl2Si2O8) and other minerals have absorbed water and altered to clay. In the Piedmont bedrock of Fairfax County, between Centreville and I-95, the igneous rocks have decomposed to great depth, creating pores between the particles and making it easier to drill a well to the unweathered bedrock.3

The average depth of weathering, estimated from the depth to which well casing can be driven, is about 100 feet on uplands, 95 feet on hilltops, 90 feet on hillsides, and 60 feet in gullies.

A zone of water-saturated rock is called an aquifer if enough water accumulates underground in the pores between rock particles to supply a natural spring or an artificial water well. Depending upon the rock type, aquifers can absorb and release a lot of water... or just a little.

After a rainstorm in Northern Virginia, the sandstone bedrock west of Centreville (the Mesozoic Basin that formed when the Atlantic Ocean first opened) will absorb substantial water between the grains of sandstone. However, the soil that formed above basalt intrusions in the basin stay relatively dry, because the igneous rock is not very porous. The grains of iron, calcium, and other minerals in the basalt are packed tightly together, without gaps for water molecules. In addition, the basalt has few fractures, so water does not seep into many cracks.

different types of bedrock affect aquifers in Northern Virginia
different types of bedrock affect aquifers in Northern Virginia
Source: US Geological Suvey - National Atlas

The quality as well as the quantity of groundwater is significant to users. In densely-settled areas such as Alexandria, utilities treat raw water so it meets Safe Drinking Water Act standards and then pipe drinking-quality water to customers. Most people living in the Rural Area of Prince William County, away from water and sewer services provided in the Development Area, drill individual wells to obtain drinkling water for widely-separated houses - and rarely treat the water, except to replace calcium with sodium (salt is used to soften the water, reducing its "hardness") and occasionally to remove excessive dissolved iron.

For water quality purposes, water wells supplying drinking water to rural houses are sealed (cased) for the top 30 or so feet. An iron pipe inserted into the well is not perforated in the top 30 feet, blocking the surface water with its load of diossolved fertilzer, dog poop, oil from cars, etc. from entering the well. Drinking water wells must also be located a certain distance away from septic tanks, where human waste flushed away from rural homes is converted by bacteria into harmless gases and fluids.

Locating where to drill a well requires an understanding of local geology, as well as local/state requirements for distance from structures and septic systems. Some owners of rural lots even hire people with a reputation for "dowsing" or "witching" where water will be encountered underground. In theory, a forked branch or other tool, when held correctly by a skilled dowser as he/she walks over a property, will bend towards the ground whenever there is a strong signal of water below the surface.

All bedrock is not the same; rainwater does not flow quickly through the surface into all sediments, or through fractures in all bedrock. Wells drilled in the Blue Ridge crystalline rocks in western Fauquier county, or in a basalt flow in the Triassic Basin, may generate less than the 3-5 gallons/minute usually required to obtain a mortgage on a new house. In contrast, limestone in the Shenandoah Valley is porous, and some wells there can flow at hundreds of gallons/minute. (Before building a house away from municipal water systems, it is wise to drill a well and make sure there is enough water...)

dowsing for groundwater
dowsing for groundwater
Source: US Geological Suvey - Water dowsing

most rainfall returns to the atmosphere through direct evaporation and transpiration through plants, rather than sinking down into the saturated zone
most rainfall returns to the atmosphere through direct evaporation and transpiration through plants, rather than sinking down into the saturated zone
Source: US Geological Survey Sustainability of Ground-Water Resources (Circular 1186)

Groundwater is stratified underground in a pattern similar to a sponge that has not been used for a day. Typically, such a sponge will be dry at the top, where pores are filled with air. Further down, water molecules saturate the spaces between the pores. In soil (and in caves), the dry zone at the top is the vadose zone. The area of an aquifer where pores are filled with water is the phreatic zone. In a cave, the surface of an underground lake will show very clearly the beginning of the phreatic zone.

When you drill a well down into an aquifer and cross from air-filled to water-filled pores between soil particles, you are crossing the "water table." The water table is the top level of the soil where a well fill with water. A simplistic explanation - above the water table, soil is dry. Below the water table, soil is wet. Reality is more complicated, of course. There is a capillary fringe above the water table, where small pores may be wet and large pores may be dry due to the physics of surface tension and capillary action.

wells drilled to intercept aquifers
wells drilled to intercept aquifers
Source: USGS Water-Supply Paper 1539-L, Geology and Ground-Water Resources of the Fairfax Quadrangle

A well driller might encounter the water table at 20 feet, but typically wells intended to supply single family residences are drilled 70-400 feet deep. To supply the town (now city) of Fairfax before it implemented a water supply system based on surface water (Goose Creek and Beaverdam Creek, in Loudoun County), municipal wells were drilled from 165 to 809 feet deep and yielded 15 to 125 gallons/minute.4

Drilling deep allows drillers to intersect multiple layers of water-soaked rock, or to intersect enough vertical distance in one aquifer to supply the minimum required. With enough water oozing from the ground into the well through holes in the well casing, a typical well is designed to supply at least five gallons/minute - enough water for for multiple showers/cooking in the morning without emptying the well completely. A deep well also serves as a storage tank. In the course of a day, a well will recharge with water from adjacent rock formations before a family comes home in the evening and pumps water from the well into the house again.

Drinking water from most wells is not chlorinated or disinfected with ultraviolet light, and well water is not flouridated either. Well water has fewer non-natural chemicals, which is a benefit if you keep fish in an aquarium. Well water may include so much calcium (creating "hard water") or sulfur that homeowners need to buy water conditioning systems. The cost of a water softening system, requiring several bags of salt each month, can be equal to the cost of municipal water.

relationship of springs and groundwater
relationship of springs and groundwater
Source: USGS - Ground Water and Surface Water: A Single Resource

Where a stream valley has eroded down to the level of the water table at the top of the aquifer, water emerges at a spring. If the water table drops during the summer, when evapotranspiration increases, a spring may dry up, only to re-appar in the winter once the water table rises again. Water levels can fluctuate 15 feet. Water that goes into the ground may also be pumped back to the surface through artificial wells drilled down into an aquifer - and if the well is not deep enough, it too may go dry in late summer:5

In a normal year the groundwater levels begin to rise in November and continue to rise until April or May, when the growing season begins. During the growing season much of the rainfall... is returned to the atmosphere by evapotranspiration and never reaches the water table. In April or May the water table begins a steady downward trend, interrupted only by short periods of heavy rainfall in some years, until killing frosts in the fall terminate the consumption of water by plants. In dry years the downward trend may continue into the winter, and unless winter precipitation is sufficient to cause recharge, there is little rise before the next growing season begins.

USGS graphic of groundwater
how rainfall recharges aquifers
Source: USGS - GROUND WATER ATLAS of the UNITED STATES: Delaware, Maryland, New Jersey,
North Carolina, Pennsylvania, Virginia, West Virginia
, HA 730-L

Groundwater that emerges from springs/wells started as surface water. Whatever the raindrops absorbed in their travels through the atmosphere and into the ground will be carried underground. The aquifer may be contaminated with gasoline or heavy metals from automobile brake particles on pavement, or from bacteria from animal feces - but in many cases, the soil particles will trap the contaminants.

For organic contaminants, bacteria, ultraviolet rays, or other natural factors may decompose the molecules and clean the groundwater before it emerges at a spring/well. In limestone karst areas, however, the pores and permeability underground may be sufficient for contaminants (even items as large as corn cobs) to migrate underground. If a sinkhole is used as a garbage dump, then the waste is likely to reappear at a spring nearby.

Government agencies now encourage developers to direct runoff to seep into groundwater rather than to surface streams. The Chesapeake Bay Preservation Act regulations ("Ches Bay regs") require a 100-foot wide buffer on either side of perennial streams in most of Tidewater Virginia. Buffers of undisturbed vegetation along streams allow sediment to be trapped by grass/leaves on the ground before runoff carries the particles to the stream. Without buffers, sediment clogs streams while also carrying excessive amounts if nutrients (nitrogen and phosphorous) into waterways.

stripping vegetation from soil surface while developing land opposite McCoart Administrative Center (Prince William County)
stripping vegetation from soil surface while developing land opposite McCoart Administrative Center (Prince William County)

Low Impact Development (LID) projects are now designed to minimize surface runoff, by diverting and retaining rainfall so it soaks into the ground. Depressions filled with permeable soil or even rock (french drains) trap runoff from roofs and parking lots. If LID projects are designed correctly and maintained, the runoff soaks into the ground slowly rather than flows to a nearby stream. LID projects can fail where there is too much clay in the soil, or silt/debris accumulating in a depression blocks rainwater from seeping into the ground.

One potential long-term impact of diverting surface water underground: modern pollution may be pushed into the groundwater, polluting underground aquifers. Plumes of polluted groundwater from leaking underground storage tanks at gas stations, or from improper disposal of hazardous waste in deep wells, can create serious environmental impacts for many, many years.

idealized flow of rainwater across surface and underground
idealized flow of rainwater across surface and underground in Coastal Plain physiographic province
Source: US Geological Survey, Ground Water in Freshwater-Saltwater Environments of the Atlantic Coast (Figure 3)

East of the Blue Ridge, some of the sediments deposited over the last 145 million years still remain. During the Cretaceous Period, freshwater rivers flowed on top of the exposed crystalline bedrock of various "terranes," the chunks of igneous/metamorphic crust that had been added to the North American continent as the Iapetus Ocean closed. Dinosaurs were wandering through the basins that had first formed in the Triassic Period, and their heavy feet crushed some of the early flowering plants evolving on the Cretaceous soils.

The rivers carried eroded sediments down from the west. They formed deltas and sandbars that extended the coastline further east, comparable to the way the Mississippi River has deposited sediments along the Gulf Coast. The largest grains of sand stayed where the crust was warped upward at the Norfolk Arch along today's Peninsula, while smaller clay particles moved to the lower-energy waters in depressed embayments to the north (Salisbury Embayment in Maryland) and south (Albemarle Embayment in North Carolina).

coarse-grained sand deposited in river channels during the Cretaceous Period created porous sediments that transmit water, while fine-grained clay particles that settled out in floodplains and slow-moving environments now block water flow in underground aquifers
coarse-grained sand deposited in river channels during the Cretaceous Period created porous sediments that transmit water, while fine-grained clay particles that settled out in floodplains and slow-moving environments now block water flow in underground aquifers
Source: Randy McBride, US Geological Survey, The Potomac Aquifer of the Virginia Coastal Plain

Today, the Cretaceous sediments above the Norfolk Arch form an unconsolidated aquifer with patches of impervious clay. The Cretaceous Period deposits underneath the Potomac River and Chowan River include broader layers of clay, creating confining units that separate aquifers.

above the Norfolk Arch, coarse-grained sediments now form a continuous aquifer without confining units that form separate aquifers
above the Norfolk Arch, coarse-grained sediments now form a continuous aquifer without confining units that form separate aquifers
Source: Randy McBride, US Geological Survey, The Potomac Aquifer of the Virginia Coastal Plain

During the Paleocene, Eocene, Oligocene, Miocene and the Pliocene epochs (formerly called the Tertiary Period), sea levels rose and fell, alternately drowning and exposing the eastern part of Virginia. Marine sediments covered the freshwater sediments of the Cretaceous Period until the Pliocene Period, 3 million years ago. Sedimentary deposits were fragmented during both freshwater abd marine deposition; there are no hydrogeologic units today that stretch across the entire Coastal Plain.6

the aquifers on the Coastal Plain are in sediments deposited in the last 145 million years
the aquifers on the Coastal Plain are in sediments deposited in the last 145 million years
Source: Randy McBride, US Geological Survey, The Potomac Aquifer of the Virginia Coastal Plain

The geologic formations deposited since the Cretaceous vary in their capacity to store water and serve as aquifers for human use:7

[U]nconsolidated sands and gravels, sandstones, and limestones commonly are major sources of ground-water supplies (aquifers), whereas beds of silt and clay function primarily as confining units...

Ground water in the Atlantic coastal zone occurs in confined and unconfined aquifers. Where water completely fills the pore spaces of an aquifer that is overlain by a confining unit, the aquifer is referred to as confined (or artesian). In contrast, where water only partially fills the pore spaces of an aquifer, the upper surface of the saturated zone (which is called the water table) is free to rise and decline, and the aquifer is referred to as unconfined (or as a water-table aquifer).

aquifers can be separated by confining units of less-permeable clay, and can have water of different quality (especially salinity, if near the Chesapeake Bay/Atlantic Ocean)
aquifers can be separated by "confining units" of less-permeable clay, and can have water of different quality (especially salinity, if near the Chesapeake Bay/Atlantic Ocean)
Source: Technical Analysis and Justification for Ground Water Ordinances on the Eastern Shore of Virginia (Figure 1-1)

One description of the Mid-Atlantic Coastal Plain noted:8

Most of the sediments...are derived from the erosion of the hard rocks of the Piedmont and the Blue Ridge and Appalachian Mountains.

Coastal Plain geologic units form a vertical series of alternating aquifers and leaky confining units... Most ground water is recharged to an unconfined surficial aquifer and discharges to a nearby surface-water body. A small percentage (approximately 3 percent) of ground water from the surficial aquifer recharges confined aquifers and follows long regional flowpaths with accordingly long travel times to discharge to larger rivers, estuaries, or the ocean

typically, deep groundwater is older than shallow aquifers
typically, deep groundwater is older than shallow aquifers
Source: US Geological Survey (USGS), Water Supply Paper 2220, Basic ground-water hydrology

West of the Fall Line, the recharge area (the source of the groundwater, where raindrops seeped below the surface) will be located close to a natural spring or human-drilled well. In the Piedmont's decomposed soil/bedrock near the surface known as "saprolite," groundwater moves as it does in the Coastal Plan between the pores of the sediment grains. In the crystalline bedrock of the Piedmont, however, groundwater is found in the fractures and is not evenly distributed.

Even in the Blue Ridge, igneous rocks are sufficiently fractured to allow surface waters to seep into the ground, and be pumped back to the surface wherever a well intercepts a fracture. If the elevation of the recharge area is higher than the elevation of a well, then water will flow under pressure out of an artesian well without requiring any pumping.

Of the 43" of rain that falls annually on the Coastal Plain, 10" infiltrates underground - but only 1" reaches the deep layers of the aquifer. Due to the slow flow of groundwater through most porous and permeable rock formations (10' per year above the Norfolk Arch, but as slow as 0.1' per year through the clay-rich sediments above the Salisbury Embayment), a raindrop may spend decades or even thousands of years underground before re-emerging at the surface. Water soaking underground from the surface may re-emerge much quicker, however. Groundwater extracted at Indian Head, Maryland (across the Potomac River from Quantico Marine Corps Base in Prince William County) had been underground only about 35 years.9

water entering the Potomac Aquifer at the Fall Line, in the recharge zone of Cretaceous Period freshwater sediments, can spend a million years underground as it moves eastward - while infiltration from the surface into the younger marine sediments may emerge in less than 100 years
water entering the Potomac Aquifer at the Fall Line, in the recharge zone of Cretaceous Period freshwater sediments, can spend a million years underground as it moves eastward - while infiltration from the surface into the younger marine sediments may emerge in less than 100 years
Source: Randy McBride, US Geological Survey, The Potomac Aquifer of the Virginia Coastal Plain

groundwater that seeps into the deep sediments takes longer to re-emerge at the surface
groundwater that seeps into the deep sediments takes longer to re-emerge at the surface
Source: Randy McBride, US Geological Survey, The Potomac Aquifer of the Virginia Coastal Plain

Folk tales of long-distance underground transport are overstated:10

...an erroneous belief prevails that ground water in the Washington-Fairfax region originates at a considerable distance, such as in the Blue Ridge or even the Pennsylvania mountains. This cannot be true, because no single water-bearing structural feature in this region extends more than a few miles. The water from wells in the Fairfax quadrangle originates as precipitation in or near the local drainage basin.

The Northern Neck Bottling Company, located in Montross in Westmoreland County, used to claim the Carver's Original Ginger Ale were special in part because:11

The water originates in the Blue Ridge Mountains of Virginia and is drawn from a 650-foot deep artesian well at the plant.

Perhaps... but water that seeped into Piedmont formations would emerge at springs when encountering low elevations at the Fall Line. For mountain raindrops to get 650 feet under the Northern Neck, raindrops falling on the Blue Ridge would have to flow down the Potomac/Rappahannock rivers, then seep underground near the Fall Line. However, there is a grain of truth to the claim that Northern Neck wells may draw from sources far away.

outcrops of Potomac Formation near Fall Line
outcrops of Potomac Formation near Fall Line
Source: US Geological Survey (USGS, Bulletin 1556, Engineering Geology and Design of Slopes for Cretaceous Potomac Deposits in Fairfax County, Virginia, and Vicinity (Figure 1)

Aquifers in the Coastal Plain may be recharged from as much as 20-50 miles away, at the Fall Line. Rainfall can seep into the Potomac Formation and other geologic units where they are exposed to the surface near the Fall Line. Raindrops from Richmond can flow eastward, downward - and slowly - to end up in an aquifer hundreds of feet beneath the surface at Hampton Roads.

Coastal Plain aquifers
Coastal Plain aquifers in Virginia
Source: US Geological Survey (USGS), Aquifer Susceptibility in Virginia, 1998-2000 (Water-Resources Investigations Report 03-4278)

Much of the water in the Lower Potomac Aquifer was trapped when the sediments were first deposited in the Cretaceous Period. At Suffolk and Newport News, for example, the Upper/Middle/Lower Potomac aquifers will be largely isolated from the surface; recharge by modern rainwater will be difficult.

Recharge rate is a significant policy issue. If deep aquifer isolation is complete, then groundwater pumped to the surface from such sources will not be replenished. If groundwater is not renewable, then pumping from deep aquifers should be managed as a one-time mining process, comparable to extraction of coal or quarrying/crushing basalt for construction projects.

Southeastern Virginia Aquifer System
Southeastern Virginia Aquifer System
Source: City of Franklin Comprehensive Plan, Franklin 2010 (Figure 4-3)

Obviously the municipal and industrial wells in Hampton Roads, the Peninsula, the Middle Peninsula, the Northern Neck, and the Eastern Shore do not dry up quickly once pumping starts. Some recharge must be occurring, either via transport from the Fall Line exposures or directly from the surface.

conceptual model of shallow aquifer recharge and underground flow in southern part of Virginia Beach, showing how
conceptual model of shallow aquifer recharge and underground flow in southern part of Virginia Beach showing how "confining units" can be fragmented and allow rainwater to soak underground through Columbia aquifer into Yorktown-Eastover aquifer... and how saltwater can intrude and affect shallow wells
Source: US Geological Survey (USGS), Conceptual Hydrogeologic Framework of the Shallow Aquifer System at Virginia Beach, Virginia, Water-Resources Investigations Report 01-4262 (Figure 13)

Confining units in the Coastal Plain are not 100% impervious. Some fluids do migrate vertically between layers, so rain that falls on the Coastal Plain could end up in the aquifers under the surface. However, the confining units do limit the speed and volume of "leakage" between different aquifers. So long as rainfall exceeds withdrawal, and the ground surface remains pervious, then freshwater will move underground due to gravity. The freshwater is lighter than saltwater, so freshwater will "float" on top of saltwater underground.

sediments form aquifers and confining layers, with saltwater underneath freshwater typically
sediments form aquifers and confining layers, typically with heavier saltwater underneath freshwater
Source: US Geological Survey (USGS), Effects of Withdrawals on Ground-Water Levels in Southern Maryland and the Adjacent Eastern Shore, 19802005 (Scientific Investigations Report 20075249, Figure 3)

However, if wells pump freshwater out of an aquifer faster than that aquifer is recharged from the surface or adjacent freshwater zones, then saltwater or brackish water in the Chesapeake Bay estuaries may intrude further into aquifers underneath the Coastal Plain.

saltwater could intrude the aquifers on the Coastal Plain as freshwater is pumped out for human use
saltwater could intrude the aquifers on the Coastal Plain as freshwater is pumped out for human use
Source: Randy McBride, US Geological Survey, The Potomac Aquifer of the Virginia Coastal Plain

Drinking water/industrial wells also can be affected if freshwater recharge is altered by stormater systems that carry rain quickly to streams, rather than allow the rainwater to soak into the ground:12

In the humid climate of Virginia Beach, the periodic recharge of freshwater through the sand units of the shallow aquifer system occurs often enough to create a dynamic equilibrium whereby freshwater flows continually down and away from the center of the ridges to mix with and sweep brackish water and saltwater back toward the tidal rivers, bays, salt marshes, and the Atlantic Ocean.

Fresh ground-water recharge to deeper units is hindered in some areas by semi-confining and confining sediments beneath the water table aquifer, particularly those of the Yorktown confining unit. Pockets of saline water may be trapped within impermeable sediments in some areas. Where recharge of fresh ground water is inhibited, saline water is at shallower depths. The fresh ground water that does recharge the deeper sediments of the shallow aquifer system flows over and above the heavier saltwater beneath the city.

Ground Water Management Areas in Virginia
Ground Water Management Areas in Virginia
Source: Virginia Department of Environmental Quality, Ground Water Withdrawal Permitting Program

Groundwater may be a renewable resource, but an aquifer can be drained faster than it recharges naturally. Based on legislation passed by the General Assembly in 1992, the Virginia Department of Environmental Quality (DEQ) has designated two Ground Water Management Areas, one on the Eastern Shore and one west of the Chesapeake Bay. State permits are required to withdraw more than 300,000 gallons/month from wells in a designated Ground Water Management Area.

There is plenty of water in the Atlantic Ocean and Chesapeake Bay to recharge aquifers in the area, but salt water is less desirable for drinking, irrigation, or industrial uses. In Virginia's two Ground Water Management Areas, DEQ has the authority to denying or limit requests for large groundwater withdrawals. That allows the state officials to minimize the potential of salt water from the Chesapeake Bay/Atlantic Ocean intruding into an aquifer.

Brackish groundwater is converted to drinking water quality by desalination plants in James City County, Gloucester County, and the cities of Chesapeake, Newport News, and Suffolk. Desalination is typically the most expensive way to generate drinking water from seawater, which is why desalination plants built during droughts in Australia and California were monthballed after rains returned, but desalination is cost-effective when the groundwater is contaminated by just a small percentage of salt.13

near the Atlantic Ocean, saltwater can intrude different confined aquifers at different rates, as freshwater is pumped out from different depths
near the Atlantic Ocean, saltwater can intrude different confined aquifers at different rates, as freshwater is pumped out from different depths
Source: US Geological Survey, Ground Water in Freshwater-Saltwater Environments of the Atlantic Coast (Figure 5)

In southeastern Virginia, there is a natural inland saltwater wedge where groundwater far west of the Atlantic Ocean is unexpectedly salty. One theory presumed the aquifers were just slow to flush out saltwater from the past, when sea levels were higher and all of the groundwater underneath that part of the Coastal Plain was seawater.

inland saltwater wedge in southeastern Virginia
inland saltwater wedge in southeastern Virginia, with line of equal dissolved-solids concentration (in milligrams/liter)
Source: US Geological Survey, Ground Water in Freshwater-Saltwater Environments of the Atlantic Coast (Figure 15)

In the 1990's, the discovery of a 35-million year old impact crater in the lower Chesapeake Bay provided a new explanation. The inland saltwater wedge was created when a meteor/comet (bolide) dug a 6,000-foot deep crater. Seawater instantly vaporized, creating a brine (1.5 times as salty as normal seawater) that was trapped as debris flung up by the impact quickly re-filled the hole. The impact also cracked the confining layers in sedimentary formations for some distance, providing channels today for seawater to intrude vertically and inland.14

how impact altered sedimentary layers in southeastern Virginia
how impact altered sedimentary layers in southeastern Virginia
Source: US Geological Survey, Ground Water in Freshwater-Saltwater Environments of the Atlantic Coast (Figure 17)

In addition to potentially-excessive groundwater withdrawals by municipal drinking water wells, primary concerns in Ground Water Management Area include industrial water use by paper mills at Franklin and West Point, and by chicken processing plants or facilities supporting offshore energy development on the Eastern Shore. Groundwater withdrawal at the West Point paper mill has lowered groundwater levels as much as 100 feet, and created a "cone of depression" with a radius of about 29 miles around the withdrawal point. At Franklin, the land itself has subsided an inch, as sediments compacted after water was extracted.15

lowered groundwater levels, resulting from industrial use by paper mills at Franklin and West Point
lowered groundwater levels, resulting from industrial use by paper mills at Franklin and West Point
Source: US Geological Survey, Simulation of Groundwater Flow in the Coastal Plain Aquifer System of Virginia, Scientific Investigations Report 20095039 (Figure 32b)

lowered potentiometric surface of groundwater caused by withdrawals for paper mill at West Point
lowered "potentiometric surface" of groundwater caused by withdrawals for paper mill at West Point
Source: US Geological Survey, Potentiometric surface map for the Cretaceous aquifer, Virginia Coastal Plain, Water Resources Investigations Open-File Report 80-965

impact of groundwater withdrawals for International Paper mill in Franklin, Virginia before 2009 shutdown
impact of groundwater withdrawals for International Paper mill in Franklin, Virginia before 2009 shutdown
(reductions from projected "normal" level, measured in feet)
Source: Hampton Roads Planning District Commission, International Paper Closure: Impact on Groundwater Resources

pumping groundwater faster than natural recharge will cause the surface to drop (land subsidence)
pumping groundwater faster than natural recharge will cause the surface to drop (land subsidence)
Source: US Fish and Wildlife Service, Vanishing Lands - Sea Level, Society, and Chesapeake Bay (Figure 21)

Caves and Springs in Virginia

Thermal Springs in Virginia

The Chesapeake Bay "Bolide" That Shaped the Groundwater in Southeastern Virginia

Links

Thomas Jefferson described Falling Spring in Augusta County as the only remarkable Cascade in this country
Thomas Jefferson described Falling Spring in Augusta County as "the only remarkable Cascade in this country"16
Source: painted by Samuel Colman, Library of Congress, Falling Spring, Virginia

References

1. "Southeast corn yields trending lower," Southeast Farm Press, July 18, 2012, p.18, http://southeastfarmpress.com/grains/southeast-corn-yields-trending-down-soybeans (last checked August 3, 2012)
2. "Groundwater Watch," Site Number: 385305077162101 - 52V 24, US Geological Survey, http://groundwaterwatch.usgs.gov/AWLSites.asp?S=385305077162101 (last checked August 3, 2012)
3. Paul M. Johnston, Geology and Ground-Water Resources of the Fairfax Quadrangle, USGS Water-Supply Paper 1539-L, 1962, p.L-12, http://pubs.usgs.gov/wsp/1539l/report.pdf (last checked June 18, 2012)
4. Paul M. Johnston, Geology and Ground-Water Resources of the Fairfax Quadrangle, p.L-2
5. Paul M. Johnston, Geology and Ground-Water Resources of the Fairfax Quadrangle, p.L-40
6. Carl H. Hobbs, III, David E. Krantz, Geoffrey L. Wikel, "Coastal Processes and Offshore Geology," submitted as a chapter for The Geology of Virginia, Chuck Bailey (ed.), p.4, http://www.eeescience.utoledo.edu/Faculty/Krantz/download_files/Virginia_Coast.Hobbs_Krantz_&_Wikel.2008.pdf; Andrew A. Meng III, John F. Harsh, "Hydrogeologic Framework of the Virginia Coastal Plain," U.S. Geological Survey Professional Paper 1404-C, 1988, pp.C7-C9, ; E. Randolph McFarland, "Sediment Distribution and Hydrologic Conditions of the Potomac Aquifer in Virginia and Parts of Maryland and North Carolina," U.S. Geological Survey Scientific Investigations Report 20135116, 2013, p.6, http://pubs.usgs.gov/sir/2013/5116/pdf/sir2013-5116.pdf (last checked October 20, 2014)
7. Paul M. Barlow, "Ground Water in Freshwater-Saltwater Environments of the Atlantic Coast," US Geological Survey Circular 1262, p.6, http://pubs.usgs.gov/circ/2003/circ1262/pdf/circ1262.pdf (last checked July 27, 2012)
8. Scott W. Ator, Judith M. Denver, David E. Krantz, Wayne L. Newell, Sarah K. Martucci, "A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain," US Geological Survey Professional Paper 1680, 2005, p.5, http://pubs.usgs.gov/pp/2005/pp1680/pdf/PP1680.pdf (last checked July 27, 2012)
9. Steven N. Hiortdahl, "Changes in Ground-Water Quality Caused by River-Water Intrusion in the Potomac Group Aquifer System of North western Charles County, Maryland," p.391, http://info.ngwa.org/gwol/pdf/900156679.PDF; E. Randolph McFarland, "Sediment Distribution and Hydrologic Conditions of the Potomac Aquifer in Virginia and Parts of Maryland and North Carolina," U.S. Geological Survey Scientific Investigations Report 20135116, 2013, p.7, p.14, p.61, http://pubs.usgs.gov/sir/2013/5116/pdf/sir2013-5116.pdf (last checked October 20, 2014)
10. Paul M. Johnston, Geology and Ground-Water Resources of the Fairfax Quadrangle, p.L-29
11. Carver's Original History, www.realgingerale.com/history.htm (as posted on July 14, 2002, but no longer online. See "Northern Neck Ginger Ales Still Made," Newport News Daily Press, December 02, 2002 http://articles.dailypress.com/2002-12-02/news/0212020011_1_bottles-blue-ridge-mountains-e-mail (last checked September 30, 2011)
12. Barry S. Smith, George E. Harlow, Jr., "Conceptual Hydrogeologic Framework of the Shallow Aquifer System at Virginia Beach, Virginia," US Geological Survey Water-Resources Investigations Report 01-4262, 2002, p.33, http://va.water.usgs.gov/online_pubs/WRIR/01-4262/wrir_01-4262.htm (last checked February 7, 2013)
13. Tamim Younos, "The Feasibility Of Using Desalination To Supplement Drinking Water Supplies In Eastern Virginia," Virginia Water Resources Research Center, VWRRC Special Report SR25-2004, June 2004, p.61-63, http://vtechworks.lib.vt.edu/bitstream/handle/10919/49471/VWRRC_sr200425.pdf; "Nation's largest ocean desalination plant goes up near San Diego; Future of the California coast?," San Jose Mercury News, May 29, 2014, http://www.mercurynews.com/science/ci_25859513/nations-largest-ocean-desalination-plant-goes-up-near (last checked August 22, 2014)
14. "The Chesapeake Bay Bolide Impact: A New View of Coastal Plain Evolution," USGS Fact Sheet 049-98, http://pubs.usgs.gov/fs/fs49-98/index.html (last checked July 27, 2012)
15. Paul M. Barlow, "Ground Water in Freshwater-Saltwater Environments of the Atlantic Coast," pp.22-24 (last checked July 27, 2012)
"Chapter II - Natural Conditions," 2003 Comprehensive Plan Update - King William County, Virginia, p.II-15, http://www.kingwilliamcounty.us/Assets/G_Chapter_II_Natural_Conditions_final.pdf; Jason P. Pope and Thomas J. Burbey, "Characterization and Modeling of Land Subsidence Due to Ground-Water Withdrawals From the Confined Aquifers of the Virginia Coastal Plain," in U.S. Geological Survey Subsidence Interest Group Conference, Proceedings of the Technical Meeting, Galveston, Texas, November 2729, 2001, US Geological Survey Open-File Report 03308, p.49, http://pubs.usgs.gov/of/2003/ofr03-308/pdf/OFR03-308.pdf (last checked July 27, 2012)
16. Thomas Jefferson, "Query 5: 'Cascades' Its Cascades and Caverns?", Notes on the State of Virginia, http://web.archive.org/web/20080914030942/http://etext.lib.virginia.edu/toc/modeng/public/JefVirg.html (last checked August 11, 2014)

a bolide impact 35 million years ago fractured groundwater aquifers in what is now Hampton Roads/Eastern Shore
a bolide impact 35 million years ago fractured groundwater aquifers in what is now Hampton Roads/Eastern Shore
Source: Hampton Roads Regional Water Supply Plan (Map 3-6)


Rivers and Watersheds
Eastern Shore
Virginia Places