Maryland Department of Natural Resources

Charles County Patuxent Aquifer Study

Project Details

This project involves evaluating the water-supply potential of the Patuxent aquifer (the deepest Coastal Plain aquifer in Charles County) in north-central Charles County (Waldorf vicinity), through the drilling, construction, and testing of up to four test wells. The study, supported with funding from Charles County, is expected to be completed by June 2013.

Background


In 2010, Charles County Department of Utilities pumped on average approximately 1.78, 2.5, and 0.29 million gallons per day (Mgal/d) from the Magothy-Upper Patapsco, Lower Patapsco, and Patuxent aquifers, respectively, to supply the Waldorf and Bryans Road service areas. Water levels in the Magothy and Upper Patapsco aquifers generally show a flat to slightly declining trend. Rising water levels in the Lower Patapsco aquifer were observed as of 2010 for the third consecutive year in wells in the far north and northwestern parts of the county. Water levels in the Lower Patapsco aquifer at Douglas Point continue to decline, while levels at St. Charles, La Plata, and Chapel Point Woods show a flat trend. Water levels in the Patuxent aquifer generally continue to decline at rates of up to approximately 3 to 4 feet per year. Ground-water modeling and optimization studies identified scenarios that could reduce drawdown in the Lower Patapsco and Patuxent aquifers while meeting projected water demands. The results of those studies indicate that optimizing withdrawal rates and shifting withdrawals to the southeast and to the deeper Patuxent aquifer can reduce drawdown. Aquifer tests and ground-water flow models of the Patuxent aquifer in the Bryans Road area indicate that the Patuxent aquifer is capable of supplying approximately 3 Mgal/d before waters levels fall below the management level.

Location of test wells

Currently, information regarding the hydraulic characteristics of the Patuxent aquifer is concentrated in the up-dip area at Indian Head and Bryans Road, and in a few outlying locations. Little is known, however, regarding the hydraulic characteristics and water-supply potential of the Patuxent aquifer in north-central Charles County. One test well was constructed in the Waldorf area at Smallwood West (CH Be 57) in 1985. Total sand thickness in the Patuxent aquifer at that location is about 80 feet, and the transmissivity is relatively low (although this may be in part attributed to incomplete well development and partial penetration of the aquifer in the test well). To adequately evaluate the water-supply potential of the Patuxent aquifer in north-central Charles County, additional test wells are needed to better define the aquifer’s thickness, extent, and hydraulic properties. In addition, the test wells will provide water-level data for assessment of withdrawals, and for future model calibration. Test wells should be constructed in the Waldorf area where potential future Patuxent production wells are more likely to be located.

Study Objectives

The objectives of this study are to investigate the hydrogeologic characteristics (lithology, sand thickness, extent, and hydraulic properties) of the Patuxent aquifer in north-central Charles County through construction of up to four test wells to help evaluate the water-supply capacity.

Methods of investigation


Drill up to four holes to basement rock. Drilling depths will vary from about 1,450 to 2,000 feet. Collect and describe drill cuttings.

Run geophysical logs (gamma, self-potential, resistivity, and multi-point resistance) in each borehole.

Construct a 4-inch test well at each site, screened in the Patuxent aquifer. Screened intervals will vary from about 1,150 to 1,950 feet below land surface.

Conduct 24-hour, continuous-rate aquifer tests in each test well.

Analyze water quality at each well; test for major ions, trace elements, radionuclides and other selected constituents.

Install pressure transducers to record water levels for up to 3 weeks to determine short-term water-level responses.

Prepare a Maryland Geological Survey (MGS) Open-File Report describing well construction and results of geologic and hydrologic data.