Reports
Ground water in Prince George's County
1966, Mack, F.K.
Bulletin 29
Abstract
This report is an appraisal of ground-water resources in a rapidly developing area of the Maryland Coastal Plain. It has been prepared to guide County and State planners in effectively supplying the water requirements of new industries, commercial establishments, and public water systems.
Bounded on the west by Washington, D. C., Fairfax County, Virginia, and Montgomery County, Maryland; on the east and north by the Patuxent River; and on the south by Charles County; Prince Georges County includes an area of 486 square miles of land. It is situated on a part of the Atlantic Coastal Plain adjacent to the Piedmont province. Altitudes of the land surface range from 0 to about 420 feet. About 75 per cent of the County lies between 100 and 200 feet above sea level and only about 1 per cent (5 square miles) is more than .500 feet above sea level. The climate is humid and temperate with a mean annual temperature of 550 F and an average annual precipitation of about 45 inches.
The County is underlain by a wedge-shaped mass of unconsolidated Coastal Plain sediments of Cretaceous, Tertiary, and Quaternary age which overlie much older crystalline rocks. The wedge of sediments is less than a foot thick in the northwestern part of the area but thickens to 2,500 to 3,000 feet in the southeastern part. The four major artesian aquifers—the Patuxent, Patapsco, Magothy, and Aquia Formations—dip gently toward the southeast.
An average of 44 mgd (million gallons per day) of water was used in the County in 1963. About 25 per cent of that quantity was from ground-water sources within the County and 75 per cent was from surface-water sources of the Washington Suburban Sanitary Commission—mainly the Patuxent River but including some water from the Potomac River. Ground water is used mainly to supply the many scattered rural homes but does supply a few public water systems.
Artesian aquifers of Prince Georges County function both as reservoirs capable of storing large quantities of water and as conduits capable of transmitting water from recharge areas. Quantities of water stored in the aquifers are adequate to supply water far into the future at the current rate of usage. Aquifer characteristics indicate that under optimum conditions, as much as 50 mgd of additional water may be available on a continuing basis through recharge from the outcrop areas. Shallow aquifers will undoubtedly receive an additional large increment of recharge water by infiltration of precipitation through the surface deposits.
A systematic appraisal of the ground water available from each of four localities in the County shows that the details of ground-water conditions vary from place to place. The thinness of the unconsolidated sediments in the northwestern part limits the amount of drawdown available and thus the amount of water available from individual wells. Geologic conditions will permit the withdrawal of large quantities of water from some aquifers in the eastern part of the County. Waterbearing properties of the major geologic formations, which seem to be most favorable in the northeastern part of the County, become progressively less favorable toward the southwestern part.
Piezometric maps show that the main area of recharge for most of the artesian aquifers is in the northwestern part of the County. The maps show that large cones of depression have formed in the area along the Potomac River south of Washington, D. C., as a result of heavy pumping from aquifers in both the Patuxent and Patapsco Formations. Water levels in many wells in that area are substantially below sea level. Concern about the possibility of salt-water contamination of aquifers by intrusion is justified only in the small portion of County adjacent to the lower Patuxent River
Water from the western and southern part of the County requires little or no treatment before general use, whereas water from the northern part of the County generally needs treatment for high iron content and low pH.
