Maryland Department of Natural Resources

Frequently Asked Questions

What is groundwater?
(1) Water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper surface of the saturated zone is called the water table. (2) Water stored underground in rock crevices and in the pores of geologic materials that make up the Earth's crust.
Where does groundwater originate?
Groundwater originates from rainfall that slowly percolates through layers of soil and rock. Most recharge to aquifers in Maryland is relatively localized, occurring within the outcrop areas of the aquifers. A common misconception is that the aquifers are recharged at great distances (far out-of-state).
Who should I contact for information about my well?
You should contact your local County Health Department environmental health office for information about your well. Maryland State regulations require that well drillers obtain a permit to drill a well, and on completion of the well, submit a report to the local county health department. The completion report includes a log of the sediment that was encountered during drilling, well construction information such as well screen depth and casing diameter, and information on well yield. Your well permit number will be needed to obtain your well record. The well permit number is stamped on a metal tag affixed to the well casing.
What aquifer is my well in?
There are many aquifers that occur in Maryland. The Maryland Geological Survey over many years has conducted investigations which have mapped the extent of most of the major aquifers. The determination of which aquifer your well is completed in can be made by referencing those investigations (see Data and Publications) with knowledge of the well depth and land surface elevation. The Survey is developing an interactive, web-based utility that will aid in this process. In the meanwhile, please contact the Survey's Hydrogeology Program for assistance (Andrew Staley: or call 410.260.8818).
Is my water contaminated? What should I have it tested for?
Groundwater in Maryland overwhelmingly is clean and safe to drink. Most groundwater in the Coastal Plain (the part of Maryland south and east of I-95) is withdrawn from relatively deep artesian aquifers that are protected by overlying clay layers. In some areas of the Coastal Plain, naturally-occurring arsenic and radium may exceed drinking-water standards established by the U.S. Environmental Protection Agency. Shallow groundwater (from water-table aquifers), however, is more at risk from contamination from the surface. Shallow water-table wells in urban settings may become contaminated by road salt (sodium chloride), fertilizer (nitrate) and pesticides. Other chemicals may be present if located near commercial or industrial areas. Shallow water-table wells in rural areas may become contaminated by septic systems (nitrates), fertilizer (nitrate) and pesticides. If you suspect that your well may be contaminated, contact your local County Health Department for information on how to have it tested.

Groundwater frequently contains naturally-occurring constituents that are a nuisance aesthetically but do not pose a health risk. Some examples include white scale or residue caused by excessive calcium and magnesium derived from dissolved fossil-shell material, iron-staining from excessive dissolved iron and manganese, and "rotten-egg" smell from hydrogen sulfide gas derived from the activities of sulfur-reducing bacteria that feed on small amounts of sulfur in low-oxygen environments common in many aquifers. Hydrogen sulfide gas can also be produced in low oxygen environments in plumbing systems.
How old is groundwater?
In Maryland, groundwater can range from days old to as much as a million years old.
Why is my basement wet?
The water table varies in depth both spatially and seasonally. Areas with a relatively shallow water table can pose problems with infiltration into basements. This problem is accentuated following major rainfall events, or during the spring and early summer months when the water table is typically at its highest. The majority of wet basements, however, are likely not caused by rising groundwater, but attributed to improper treatment of the house foundation, landscaping issues, improper grading, etc.
Is land subsiding due to groundwater withdrawals?
In the unconsolidated sediments of the Coastal Plain, large groundwater withdrawals can potentially result in land subsidence. The Maryland Geological Survey has monitored land subsidence surrounding three major well fields in Anne Arundel County since 1994. To date, no subsidence has been detected. In the future, the Survey will expand the monitoring effort to other areas of the Coastal Plain with different geologic conditions.
Does groundwater occur as underground streams?
In Maryland, groundwater does not occur as underground streams, rather it flows through small pore spaces between sand grains in unconsolidated sediments (eastern and southern Maryland) or through fractures and faults (central and western Maryland). In the Ridge and Valley Province (western Maryland), limestone formations may form relatively large solution cavities that result in limited open channel flow.