Groundwater Basics

Everyone can and should do something to protect groundwater. Why? We all have a stake in maintaining its quality and quantity.
Groundwater Basics - Articles


Ninety-nine percent of all available freshwater comes from aquifers underground. Additionally, most surface water bodies are connected to groundwater so how you impact surface water matters too.

Furthermore, many public water systems draw all or part of their supply from groundwater, so protecting the resource protects the public water supply and influences treatment costs. If you own a well to provide water for your family, farm, or business, groundwater protection is critical to you.

So what is groundwater? Precipitation that does not quickly run off into streams, is not evaporated by the sun, or does not get taken up by plant roots, slowly infiltrates through layers of soil and rock to become groundwater feeding the springs, streams, and wells of Pennsylvania. Most of this recharge occurs from rain and melting snow during early spring and late fall when the soil is not frozen and plants are not actively growing. This infiltrating water eventually reaches a saturated layer of sand, gravel, or rock called an aquifer. Aquifers may occur a few feet below the land surface, like in Florida, but in Pennsylvania they are more commonly found at depths greater than 100 feet.

Groundwater does not simply remain stagnant under the ground. Rather, it moves underground from upland to lowland areas. The direction of groundwater flow underground can be determined by looking at how surface water flows. Flowing groundwater eventually reaches a discharge point where the water table meets the land surface. Springs are a classic discharge point where groundwater bubbling to the surface can be seen. However, streams and lakes are the most likely points of discharge for groundwater.

Groundwater in Pennsylvania is a vast resource and is estimated to be more than twice as abundant as the amount of water that flows annually in the state's streams. Pennsylvanians have tapped into this important resource and each day more than one billion gallons of groundwater are pumped from aquifers throughout the state for various uses. More than half of this groundwater is used for domestic drinking-water supplies, which demand high-quality, uncontaminated water.

Groundwater is especially vital to rural areas of the state. Pennsylvania has more than one million private water wells supplying water to more than three million rural residents. An additional 20,000 new private wells are drilled each year around the state.

People from many parts of Pennsylvania are concerned about the future availability of adequate groundwater supplies for meeting home and business needs. In some cases, these concerns are due to increasing local use of groundwater that exceeds the amount of recharge that supplies the aquifer. More often, groundwater supplies are threatened by increasing impervious cover of the land surface. Each year, more land area is being covered with roofs, sidewalks, driveways, parking lots, and other surfaces that do not allow rainwater to recharge the underlying groundwater aquifers. Every acre of land that is covered with an impervious surface generates 27,000 gallons of surface runoff instead of groundwater recharge during a one-inch rainstorm. Without recharge water feeding the aquifer, groundwater mining or water removal from the aquifer more quickly than it can be recharge, may occur.

Groundwater mining has been documented in parts of southeastern Pennsylvania, where impervious cover has increased rapidly and groundwater withdrawals have also increased. Water resources planning efforts initiated in Pennsylvania in 2003 aim to document areas where groundwater resources are currently or will be overused. With this information, local government planning officials can more adequately guide future development based on existing water resources.

The quality of groundwater is also a concern in many areas of the state. Contrary to popular belief, natural groundwater is not always free of pollutants and impurities. Some pollutants occur naturally when water interacts with impurities in the rock layers encompassing an aquifer. Human activities can also pollute groundwater aquifers.