What is the Piedmont Sole Source Aquifer?
Slow moving water that is located beneath earth’s land surface is known as groundwater. The body of rocks and sediment holding the groundwater is known as an aquifer. Groundwater is a vital natural resource with over 30% of Americans relying on groundwater for drinking water.
A Sole Source Aquifer (SSA) is a designation granted by the Environmental Protection Agency (EPA). SSA is given when an aquifer is the only economically viable source of potable drinking water for a community. If contamination were to occur, it would be challenging and costly to find alternative water resources. It is crucial to protect aquifers from pollution and depletion.
In Central Maryland, the Piedmont Sole Source Aquifer (SSA) extends approximately 135 square miles across parts of Carroll, Frederick, and Howard and Montgomery Counties. The largest area of the aquifer spans across upper Montgomery County between the Potomac and Little Seneca watersheds. It is a critical resource for residents, farms, and businesses particularly those in rural areas who depend on private and municipal wells for their water supply. Notably, the aquifer lies beneath the Agricultural Reserve, a 93,000-acre protected area established to preserve farmland and natural resources. The Piedmont SSA received its federal designation in 1980. It was extended with the smaller localized Poolesville SSA that was designated in 1998. The Town of Poolesville operates a system of 12 wells that provide public water directly to its residents.
Map of the Piedmont Sole Source Aquifer.
There are two main types of aquifers. The Piedmont SSA is classified as a fractured rock or unconfined aquifer, meaning it has direct interaction with the earth’s surface while confined aquifers are sealed by impermeable layers of rock. Unconfined aquifers have upper water levels known as the water table exposed to environmental factors. The water table can rise and fall depending on the amount of water entering and leaving the aquifer system. This makes unconfined aquifers more vulnerable to changes from human use, droughts, and rainfall variability. Water is replenished in the aquifer primarily through the slow process of infiltration. Rainwater and melting snow seep through soil and rock layers flowing downward filling in the gaps between rocks, soil, and sediment. This process happens over time.
Graphic illustrates the structure of an unconfined fractured rock aquifer. Image and data obtained from
Alabama Extension.
The fractured rock structure means there is no defined “container” holding the water; instead it moves and is stored within the gaps between rocks and sediment. Fractured rock aquifer systems do not have a defined capacity like underground reservoirs. Capacity is influenced by the network of fractures and porous areas that store the water. This means that while the the aquifer can support moderate growth and human activity, sustainable management and regular monitoring are essential to prevent overuse and contamination. Conservation efforts, proper land use planning, and monitoring are vital to ensuring long term sustainability of the aquifer. With proactive stewardship, this vital aquifer can continue to provide clean, safe drinking water rural Maryland for generations to come.
Residents, farmers, and business owners can explore the EPA’s Interactive Map of SSAs to see if they live or work in an area that sources its water from the Piedmont SSA.