Drops of rain or snow that fall onto the land do not always wash straight into rivers or streams. Instead, precipitation can seep through the soil and into groundwater. Groundwater can become contaminated when pollutants on the land seep underground; in the Chesapeake Bay watershed, polluted groundwater often pushes nutrients and chemical contaminants into the Bay. Indeed, the slow movement of polluted groundwater into the Bay is lengthening the “lag-time” between the adoption of pollution-reducing practices and the positive effects of those practices on a particular river or stream.
Groundwater is water that can be found under the earth’s surface, stored in the cracks and spaces between particles of soil, sand and rock. Precipitation can recharge groundwater supplies, as rain and melting snow soak into the ground and travel downward to reach solid, impermeable bedrock. Here, groundwater stops moving downward and starts saturating the surrounding soil, forming an area known as an aquifer.
Groundwater comes to the earth’s surface when it flows through a spring or into rivers, streams and lakes. Scientists with the U.S. Geological Survey (USGS) have found that in an average year, almost 27 of the 50 billion gallons of streamflow that enter the Chesapeake Bay come from groundwater.
Groundwater can also be extracted from the earth by wells drilled into underground aquifers.
Much of our groundwater is used to irrigate crops, and more than half of the United States relies on groundwater for drinking water. But communities can face water shortages when groundwater is used faster than it is replenished. USGS scientists have even found that the withdrawal of groundwater in the lower Bay region has caused the land to sink, worsening the effects of sea-level rise and increasing the severity of floods along the Delmarva Peninsula and Virginia Coastal Plain.
Groundwater can become contaminated when pollutants on the land seep into underground aquifers. A number of human activities can pose a threat to groundwater, including:
Several studies have found that the slow movement of polluted groundwater into the Bay is lengthening the “lag-time” between the adoption of pollution-reducing practices and the positive effects of those practices on a particular river or stream. A U.S. Geological Survey (USGS) model showed that groundwater on the Delmarva Peninsula—and the excess nitrogen it can contain—takes an average of 20 to 40 years to flow through the area’s aquifers and into rivers and streams. This means that slow-moving groundwater could push nutrient pollution into the Bay even after we have lowered the amount of nitrogen and phosphorous we put on the land. In some parts of Delmarva, the groundwater that is now flowing into local waterways contains nitrogen linked to fertilizer used three decades ago.
For Chesapeake Bay restoration to be a success, we all must do our part. Our everyday actions can have a big impact on the Bay. By making simple changes in our lives, each one of us can take part in restoring the Bay and its rivers for future generations to enjoy.
To lower the amount of pollutants seeping into groundwater, farmers can consider planting cover crops or practicing the rotational grazing of livestock. Homeowners can lower the amount of fertilizers, pesticides and road salt applied to lawns and driveways, and ensure that storage tanks and septic systems are properly managed to avoid allowing gasoline, oil or wastewater to soak into the ground.
Case studies show best management practices have lowered pollution in the Chesapeake Bay.
Continued land subsidence could worsen the effects of sea-level rise.
The oldest body of seawater ever identified is trapped beneath the largest crater in the United States.
Research shows groundwater flow can lengthen the time it takes for a conservation practice to affect a waterway.
This watershed group is cleaning up the mess that coal mining has left behind.
Publication date: July 01, 1993 | Type of document: Report | Download: Electronic Version
The Chesapeake Bay Groundwater Toxics Loading Workshop was held April 15-16, 1992, at the U.S. EPA Chesapeake Bay Program Office. Workshop participants reviewed and discussed available information on results from groundwater studies and…