Unlike the Centre Region, most communities with a population of several thousand or more are located adjacent to a river or a large body of fresh water. For those communities, water management is relatively simple: “Pump it and Dump It.”
Water is pumped from the river upstream of the community, used, and after treatment, the wastewater is dumped back into the river downstream. Where the source is a lake, water drawn from the lake is treated, used and the treated wastewater returned to the lake at some point distant from the withdrawal location. In either case, natural cleansing processes and dilution minimizes the likelihood of contamination of the source by the treated wastewater.
In the Centre Region, without a lake or through flowing river, our only water source is the rain (or snow) that falls within the 175 square mile area of the Spring Creek groundwater basin. (See watershed map in the article “Why two boundaries”). Although total precipitation may vary widely from year to year, the 70-year annual average is very close to 40 inches, corresponding to a supply of roughly 333 million gallons of water per day (MGD).
Not all of this water is available for our use. More than half (about 185 MGD) is returned to the atmosphere directly by evaporation or by transpiration of trees and other vegetation. A small quantity (perhaps 25 MGD) that may be augmented by storm water, flows away in surface streams. The remainder, somewhat more than one third of the total supply (125 MGD), seeps into the ground, trickling downward through soil to fill cracks, crevices and interstices in the underlying rock. More than 20 deep wells tap this groundwater reservoir to meet the (approximately) 12 million gallon daily demand of Centre Region.
For a major producer, a well must be capable of delivering a sustained yield of several hundred gallons per minute. For a provider like the State College Borough Water Authority (SCBWA) that pumps about 5 million gallons per day, it is necessary to develop enough such wells to ensure a supply at least 7.5 MGD, 50% greater than the average daily demand. In addition, the producer must maintain standby electric generators to keep the pumps operating in the event of a power failure
The Groundwater Reservoir
The sandstones exposed on the crests of Tussey and Bald Eagle Mountains are only moderately permeable. They retain sufficient water to supply the private wells of nearby residents, but most of the precipitation that falls on the ridges flows off on the surface. Small reservoirs in the ridge-top swale capture some of this water for use by the Correctional Institute at Rockview, by Harris Township and by State College Borough, but most flows off in streams through small gaps like that at Shingletown. These surface streams may be augmented by springs on the mountain slope particularly near the contact between the sandstones and the less permeable black shale beneath.
The surface water from the mountain slopes is largely free of dissolved calcium carbonate, and is by far the “softest” water available in the region. But it is vulnerable to contamination, notably by micro-organisms like Giardia sp. and Cryptosporidium. At the base of the mountains, streams like Slab Cabin Run may merge with surface streams of the valley bottom or disappear into sinkholes in the limestone of the valley floor.
In most regions, rainwater that seeps downward through the soil is filtered and cleansed naturally. And below the water table, groundwater is distributed relatively uniformly in cracks and pores throughout the rock. In a limestone terrain, however, this is not the case. Carbon dioxide dissolves in rain as it falls through the atmosphere, making rainwater mildly acid. Because limestone is soluble in acid solutions, rainwater seeping downward toward the water table dissolves the rock, enlarging the cracks and crevices through which it moves. The enlarged channels capture increasing amounts of water, and soon grow into drains that allow potentially polluted surface water virtually free access to the groundwater reservoir. When overlying soil collapses into such drains the resulting sinkholes may present a safety hazard or cause costly damage to property. In some cases, sinkholes may capture most or all of the water in a watershed, leaving only ephemeral streams or empty channels on the surface, like Big Hollow.
Water in the groundwater reservoir is not stagnant. Like water on the surface, it is constantly moving, albeit slowly, from its source (the recharge area) toward the basin outlet. The acid solution continues to dissolve the rock, enlarging the fractures and cracks through which it moves, forming a complex of horizontal channels. Partially water-filled channels near the water table are as close to “underground rivers” as occur in nature. Nearby Penn’s Cave is an example of such a water channel.
Because groundwater in a limestone terrain is concentrated in channels, rather than distributed uniformly in pores throughout the rock, locating high yield wells presents special challenges. An ideal well would tap into one (or more) channels, but locating such channels several hundred feet below the surface is not easy. Fortunately, fractures in the rock often cause linear features on the surface (e.g., aligned trees, straight stream courses, even differences in soil type) and such traces can be seen in aerial or satellite photographs. Unfortunately, the relatively fast movement of groundwater through fractures enlarged by solution may facilitate the spread of contaminants and make locating their source difficult.
Source Water Management
We currently withdraw about 12 MGD from the ground water reservoir in the Centre Region. This represents less than ten percent of the net annual supply (total precipitation less evaporation and transpiration loss). Although this would seem to leave an ample reserve to accommodate future growth, it is important that we maintain the water table at or close to its present level. Failure to do so could cause the loss of wetlands, reduction in discharge from springs, and diminished flow in surface streams. Many people would find the consequences unacceptable. Quite aside from any potential long-term effects of a changing climate, the immediate impact of excessive groundwater withdrawal would be far-reaching, economically, recreationally, aesthetically and environmentally. (Some experts believe that groundwater withdrawn by SCBWA is already degrading Slab Cabin Run.)
If we assume that the population will grow at a conservative (1.6%) annual rate, we must prepare for at least an additional 20,000 residents in ten years, creating an additional demand for almost one million gallons of water each day. To ensure an adequate supply of water (and the facilities to treat the added wastewater) will require a comprehensive water management plan.
Population growth is considered desirable economically, but paradoxically, growth increases demand for water while diminishing the supply. Vital groundwater recharge area is lost to buildings and other added impermeable surfaces. The volume of storm water will increase as well, further reducing recharge, if not wisely managed.
Increased reliance upon water reuse may be essential; the use of potable water should be eliminated where reuse water would serve. Storm water, a significant part of the total water resource is now largely wasted; retention basins must be designed to foster recharge rather than flood control. Such basins should be sited and constructed with no less professional guidance than the selection of well sites. Changed conditions may make it necessary to re-evaluate existing laws and regulations that may foster, rather than limit unhelpful activity. Above all, it is essential that we acknowledge the fragility of our water resource, and recognize that essential measures to conserve and protect it may be costly.
Robert Schmalz is Professor Emeritus of Geology, Penn State University. His interests focus on the chemistry of natural waters. He served as a member and chairman of the State College Borough Water Authority and as member and chairman of the University Area Joint Authority. He has been a resident of State College since 1958.