Water Is Life
By Wil Orndorff, DCR Natural Heritage Program
Water is life, or so goes a proverb common to many cultures around the world. When Europeans first arrived in the Americas over 500 years ago, they may have been in search of silver and gold, but it was a reliable supply of water that determined if and where they could stay. In the mountains and valleys of the Appalachians, springs by far supplied the vast majority of water to the pioneers, many of the same springs relied on by generations of earlier Americans. Visit a colonial-era house in western Virginia and you will almost always find the spring responsible for its location. Early forts and blockhouses were commonly built around springs to secure water supplies in the event of a siege. Not only did springs provide water for drinking, but also for irrigation, manufacturing, and food processing. Mills throughout western Virginia were powered by spring runs flowing over water wheels, and spring ponds were the site of early aquaculture, yielding trout and watercress.
A spring is defined as a place where water flows from the ground. To many people, springs seem magical. Ponce de Leon was but one of many people throughout history who believed certain springs were the “Fountain of Youth,” and searched relentlessly for these places. But over the centuries man has come to realize that springs are simply a part of the natural hydrological cycle, and form in a variety of ways when precipitation finds its way underground and returns to the surface. Springs can be found flowing from the base of ancient landslides along mountainsides, at the intersections of fractures in igneous or metamorphic rocks, or from sand and gravel deposits from ancient rivers. However, the vast majority of the world’s large springs—and the ones most important to our ancestors—are karst springs. Springs producing more than a million gallons per day are not uncommon in Virginia. The flow in Bath County’s Coursey Springs, one of Virginia’s largest, rarely dips below five million gallons per day!
Karst springs form when precipitation has worked its way through soluble limestone and dolostone, dissolving some of the rock along the way and returning to the surface as cold, clear, mineral-rich water. Precipitation can enter the subsurface either as diffuse flow percolating through soil, or as sinking streams where flowing surface waters are captured by underground drainage.
As water makes its way from the subsurface to a karst spring, it passes through a network of conduits and fissures formed by the dissolving of bedrock. Many of these are large enough to crawl, walk, swim, or rappel through and are thus considered caves. Caves as long as 30 miles and up to a quarter mile deep have been documented behind Virginia’s karst springs. Cave divers have entered springs and descended to depths of over 250 feet below the water level, and sometimes have resurfaced in air-filled passages that have no other access. Many cave systems have what are termed “vadose” streams above the water table that terminate in “phreatic” or water-filled passages extending beneath the water table. The spring where this water reappears at the surface is called the “resurgence” of the cave.
Settlers not only obtained water from springs proper, but also directly from the cave streams behind them. Throughout much of southwestern Virginia to this day, hydraulic ram pumps, which require no electricity to move water, are not an uncommon sight in underground streams near cave entrances.
Determining where the water from a particular spring originates is no easy feat. While caves provide windows into the plumbing behind springs, only rarely do they show the whole picture. To complicate matters, subterranean flow quite commonly passes underneath surface drainage divides. Hydrologists rely on a variety of methods—geologic mapping, chemical analysis, and pump testing among them—to determine the watershed or recharge area of a particular spring. One particularly powerful technique is dye tracing, in which nontoxic, fluorescent dyes are introduced into groundwater inputs or cave streams, then absorbed by receptors in cave streams, springs, or even wells. By connecting the dots between places where a particular dye was introduced at a particular time and the locations and dates where it was recovered, maps showing subterranean flow paths can be generated. With enough dye tracing, the recharge area of many springs can be accurately determined. However, because there are so many springs in Virginia and very limited resources to perform dye tracing, we do not know the recharge areas of the vast majority of our springs.
A recent technique for evaluating spring water is determining its age, or how long it has been underground. To do this, geochemists use a variety of chemical tracers present in the water. Some of these are naturally occurring compounds, while others such as chlorofluorocarbons and tritium are the result of specific human technological advances that introduced these chemicals into the atmosphere at specific times. In many springs the ages are complicated and not always consistent depending on which chemical age is considered. However, consistent patterns emerge. Water from springs connected to known cave systems is generally very young, from a couple of weeks to a few years in age. By contrast, water from some of the larger springs in places like the Shenandoah Valley, with few or no known caves known behind them, can range from 10 to 50 or more years in age. These older springs are believed to represent flow paths extending to great depths through thick limestone deposits, sometime resulting in elevated temperatures as well.
In some places, like Virginia’s Warm Springs Valley, the karst waters circulate deep enough to produce true hot springs. Because of radioactive decay and the insulating properties of rock, the temperature of bedrock increases systematically with depth. As a result, the temperature of spring water reflects the depth to which it circulates. Precipitation falling on the north slope of Warm Springs Mountain sinks into the limestone along its flank, and slowly descends to depths of a few kilometers, absorbing warmth from the surrounding rock before rising rapidly along the handful of dissolved fractures that lead to the valley’s thermal springs. The same phenomenon occurs elsewhere in the mountains of Western Virginia, but not to a great enough extent to produce true hot springs.
Oddities among Virginia’s springs are not limited to thermal springs. A spring just north of Harrisonburg is termed the “tide spring,” which repeatedly flows then stops every hour or so, as it has for millennia. DCR scientists have recently discovered that similar water level oscillations occur in at least three caves along this belt of limestone four miles long, suggesting it is more than a local curiosity. Bath County’s Muddy Run is fed by a spring that always flows milky due to suspended solids within the water. Sweet Chalybeate Spring in Alleghany County is naturally carbonated.
Virginia’s springs have long been a popular destination for folks in search of the waters’ therapeutic values and for others just looking for a good soak. During the 19th and early 20th centuries, over a dozen karst springs in Western Virginia were home to resorts where Virginians from the flatlands to the east retreated during the summer to enjoy the clean water, relatively cool air, and a markedly lower number of biting insects. The names of communities such as Orkney Springs and Rockbridge Baths pay homage to this history.
The economic and social roles that karst springs play extend well beyond resorts, however. Numerous communities across western Virginia rely on karst springs as their primary or secondary water supplies. Some counties use a combination of several springs as their primary water supplies. In addition, towns and counties own water rights to many more springs in case their flow is needed to meet future capacity. In the droughts of the early 2000s, several of these springs were brought on line to compensate for historically low reservoir levels and stream flows. And of course, thousands of Virginia’s citizens continue to rely on spring water for domestic water supplies. When offered the opportunity to connect to municipal water supplies, the response is typically “No thanks.” Everyone knows the best-tasting water flows from clean karst springs.
It would be easy to take for granted that Virginia’s karst springs will always remain reliable sources of clean water. That would be a mistake. Springs may be complicated, each with its unique plumbing, but they are not magic. Every spring has a recharge area, and the land use activities that take place within recharge areas affect both the quality and quantity of spring water. Contaminants introduced by septic tanks, confined animal feeding operations, land application of biosolids, industrial discharges, and storm water runoff all find their way to karst springs. For example, in studies of karst waters in the Shenandoah Valley, all samples tested for atrazine, an herbicide commonly used prior to seeding crops, have turned up positive. In a case from Warren County, fluorescent dye flushed down a toilet turned up in the owner’s tap water drawn from a karst spring!
Perhaps even more ominous than the risk of contamination is the reduction in spring flow itself. Every well drilled within the recharge area of a spring reduces its flow, because the well is tapping the same subterranean reservoir that feeds the spring. Another factor placing the flow of karst springs at risk is global warming. Cooperative studies by DCR and Virginia Tech scientists have shown that the amount of recharge to a karst aquifer is related to evaporation and the length of the growing season. As the Earth continues to warm, both will probably increase, reducing the amount of water reaching the karst aquifer. The aquatic systems relying on karst waters will be stressed with significant effects on multiple species as base flow in late summer continues to reduce.
Karst springs are clearly a significant component of Virginia’s Natural Heritage, one long taken for granted yet critical to our natural systems. An ancient Chinese proverb offers wisdom to guide us: when drinking the water, remember the spring. Let’s hope it’s not too late.