the underground gas storage project in the Blue Ridge Tunnel between Charlottesville/Waynesboro was not completed, but caverns at Saltville are operational
Map Source: Color Landform Atlas of the United States, Virginia - county map
There are many above-ground natural gas storage facilities scattered across the state, managed by the 10 investor-owned and municipal Local Distribution Companies in Virginia such as Roanoke Gas and Atmos Energy.
There are also above-ground propane storage facilities. Propane can be trucked to those sites, far from pipelines. Rural houses often have a propane storage tank, and many backyard grills rely upon small propane cylinders that can be replaced at a 7-11, Home Depot, etc.
Virginia Natural Gas operates three propane-air plants, two in southern Virginia and one in Northern Virginia. Four other such plants are operated by other companies in Virginia. Those facilities blend propane with compressed air, creating a synthetic natural gas that can be used during periods of peak demand to ensure supplies are not interrupted. Virginia Natural Gas also has a connection to the Columbia Gas Transmission Company's Chesapeake Liquefied Natural Gas (LNG) facility in Chesapeake, which provides another backup to meet peak demand.1
Underground natural gas storage comes in two versions: natural and artificial. Different sedimentary rock formations in Virginia contain natural gas, including coal beds in the Appalachian Plateau, Oriskany sandstone in Rockingham County, and the Triassic sandstones in the Taylorsville Basin northeast of Fredericksburg. These formations have been natural storage reservoirs for millions of years.
Several underground natural gas reservoirs in Virginia are far more recent; they were created in the 20th Century. The attempt during the 1950's to store natural gas in an old railroad tunnel near Charlottesville failed. The natural gas storage field at Saltville was successfully completed in the 1990's, and the depleted natural reservoir at Early Grove is also utilized as a storage field.
During the 1940's, the Claudius Crozet's railroad tunnel under the Blue Ridge was repurposed to serve as an artificial storage cavern for natural gas. The original Blue Ridge Tunnel had been constructed in 1858, then abandoned in 1944 when a new tunnel was bored through the mountain parallel to it.
Concrete bulkheads 14' thick were constructed in the 1950's to create an artificial storage tank, but the project was not finished.27
Over 300 million years ago, in what geologists would later classify the Mississippian subperiod of the Carboniferous period, modern Smyth County was located at the edge of an ocean. Salt water washed into a basin and evaporated, in a repeating cycle that created beds of "evaporites" later named the Little Valley and the Maccrady Shale. The ocean later covered the deposits. Various layers of limestone, shale, and other rocks ended up on top, then eroded away, while the layers were faulted and cracked by tectonic forces.3
Since at least the Ice Age, groundwater circulating through those deposits has emerged at the surface in springs. The groundwater reaching the surface was enriched in salt, and the naturally-occurring brine has attracted animals to salt licks.
In the 1780's, investors from Tidewater (including the husband of Patrick Henry's sister) started digging shallow wells to extracted the brine. The King family floated salt down the North Fork of the Holston River to Tennessee, creating a settlement at Kingsport and sending product further down the Tennessee River to the developing city of Chattanooga. During the Civil War, brine was evaporated in kettles to produce salt for preserving meat and other food.
In the 1890's, deeper wells were used to pump brine to the surface. Instead of evaporating it for production of table salt (sodium chloride), the brine was processed to create chlorine and caustic soda chemicals for various industrial uses. The industrial operations spurred the creation of a company town, Saltville in Smyth County. In 1972, the Olin Corporation shut down its operations at Saltville. The chemical plant became a Superfund site requiring extensive cleanup due to pollution caused by mercury used in the chlorine production process.4
Throughout eight decades of extensive pumping of brine, voids were created underground as the fluid with dissolved salt was carried to the surface for processing. Twenty years after 1972, the empty space underground were more valuable than the remaining salt; it could be used to create storage caverns for natural gas.
The demand for salt-related products did not justify the new investment in the 1990's. The reason for extracting more salt was to create larger voids underground. That effort cost over $70 million and created about 150 new local jobs.5
In 1996 the Environmental Protection Agency issued Underground Injection Control permits so the caverns created by earlier salt mining could be expanded. Water was pumped 2,000-4,000 feet underground (below the dept of the drinking water aquifer) to dissolve more salt, and the brine was forced to the surface to create additional storage capacity. This time, the brine was simply evaporated to create commercial products for agriculture and swimming pool maintenance.6
During the summer months when demand for home heating is low, gas is carried by the East Tennessee Natural Gas pipeline north from the Gulf Coast, from nearby coalbed methane wells in Appalachian coal fields, and from natural gas wells drilled into Appalachian shales (such as the Marcellus formation) and hydraulically fractured. The surplus gas is injected underground during the low-demand periods, the pressure displaces any remaining brine, and gas molecules fill the spaces once occupied by salt crystals and brine.
When the weather cools and demand increases during the winter, the stockpiled natural gas is extracted and piped to customers when there is a surge in demand. The Saltville caverns offered 5.5 billion cubic feet (Bcf) of natural gas storage capacity when Spectra purchased the underground storage system in 2008. It can deliver 300 million cubic feet of natural gas daily to customers, supplementing delivery from the East Tennessee Natural Gas pipeline.7
To put that into context, all Virginia customers in 2012 used nearly 400Bcf of natural gas, and:8
Creating an above-surface storage reservoir would have been more expensive than utilizing the Maccrady Shale, but the underground geology was not ideal. Because the original horizontal salt bed deposits were disrupted by tectonic faulting and broken up into underground blocks, the solution caverns ended up being smaller than anticipated. After determining that at least one was 70% filled with rubble, the natural gas storage company reduced its estimate of volume by 30%.9
Spectra, owner of the East Tennessee Natural Gas pipeline, stockpiles gas during periods of low demand in salt caverns at Saltville
Source: Spectra, Saltville Gas Storage
Natural gas was produced from the Early Grove anticline, in Scott and Washington counties. It was first drilled in 1931, and gas was transported to Bristol through a 4-inch pipeline. The field was revitalized by new drilling in 1980, but production was limited.10
The withdrawal of natural gas did not result in compaction of the reservoir; the voids between the rock particles remained. After the East Tennessee Natural Gas pipeline was constructed through southwestern Virginia, the depleted field was converted into Virginia's first storage reservoir in 1990.11
By 2009, it had a "working capacity" of 1.4 Billion cubic feet (Bcf) of natural gas. It could deliver from storage 20,000 Million cubic feet/day (Mcf), adding pressure to the pipeline when customer demand was high.12
the Early Grove depleted gas storage field is managed by Spectra in synch with operations of the Saltville gas storage facility and demand on the East Tennessee Natural Gas pipeline
Source: Spectra Energy, Saltville Gas Storage Company, LLC
annual natural gas withdrawals from the Saltville and Early Grove reservoirs match annual injections, since storage is designed to balance summer and winter demand
Source: US Energy Information Administration, Underground Natural Gas Storage by All Operators
gas storage capacity in the caverns at Saltville was expanded from 1 billion cubic feet in 1999 to 6.2 billion cubic feet in 2006
Source: Energy Information Administration, Virginia Natural Gas Underground Storage Salt Caverns Capacity