What is an aquifer?
An aquifer is a body of rock or sediment that stores and transmits
large amounts of groundwater. An aquifer typically consists of
sands and gravels with interconnected pore spaces, or rocks with
numerous interconnected fractures or cavities. Groundwater flows
through these pore spaces and fractures, and the amount and rate of
water flow is determined by the size and “connectedness” of the
fractures and spaces. Contrary to popular belief, water rarely
flows in underground streams.
Geology affects the groundwater availability. West of the I-95 corridor, most of Maryland is underlain by rocks, while to the east and south, the Maryland Coastal Plain is underlain by sediments. Layers of sand and gravel form the aquifers that are the primary source of water supply in the Coastal Plain; these are separated by layers of less permeable silts and clays.
In Maryland, most groundwater originates as rain or snow that falls directly within the state and then seeps downward to replenish the aquifers. During a drought, the shallowest aquifers are most likely to experience reduced water levels.
In the Coastal Plain, where most wells withdraw water from deeper aquifers, a drought is less likely to cause a well to go dry; however, some areas have experienced long-term declines in water level due to increased groundwater withdrawals.
The Maryland Geological Survey (part of the Department of Natural Resources), the Maryland Department of the Environment and the U.S. Geological Survey are currently working together on a regional assessment of the Maryland’s Coastal Plain aquifers that will provide the information needed to properly manage Maryland’s groundwater resources.
- David Bolton and Heather Quinn, Geologists
Schematic of the Atlantic Coastal Plain
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