Reports
Preliminary analysis of geohydrologic data from test wells drilled near Chalk Point, Prince George's County, Maryland
1976, Mack, F.K.
USGS Open-File Report 76-322
Abstract
Continued growth of southern Maryland will entail demands for increases in ground-water withdrawals. State agencies responsible for the management of the ground-water resources should have the best possible understanding of the availability of ground water and the impact of its development in order to make sound decisions regarding changes in the pattern of withdrawal.
Part of the process of evaluating ground-water resources in the Chalk Point area will be the establishment of the relationship between quantities of water pumped from individual aquifers and the resulting effect on water levels in outlying areas. Pumpage data from highyielding wells in the area have been recorded since withdrawals began in 1964. Some water-level data were obtained from two of the aquifers, the Magothy and Aquia, in 1962.
As part of this project, a test hole was drilled to 1,100 ft (335 m) at a site several thousand feet north of the high-yielding wells. Utilizing data from the probe hole to determine screen positions, three observation wells were then constructed at the site to provide separate wells in the Patapsco, Magothy, and Aquia aquifers.
The water level in each of these monitoring wells is affected by barometric pressure and tidal changes in the nearby Patuxent River. Water levels in wells tapping the Magothy aquifer respond rapidly to pumping and were as much as 42 ft (13 m) lower than water levels measured in 1962. Although long-term records are unavailable, it appears that water levels in the Patapsco aquifer are also influenced by pumping at Chalk Point. Water levels in the Aquia Formation cannot be correlated directly with any pumping from that aquifer, but they are about 8 ft (2.4 m) lower than they were in 1962, possibly because of loss of water by leakage through the underlying confining bed into the Magothy aquifer.
The transmissivities of the sand in the Patapsco Formation screened from 832 to 842 ft (254 to 257 m) below sea level; the Magothy aquifer and the Aquia Formation, as determined by water-level recovery tests, are 570 ft2/day (53 m2/day), 730 ft2/day (68 m2/day), and 1,176 ft2/day (109 m2/day), respectively.
