Reports
Geology and hydrologic assessment of Coastal Plain aquifers in the Waldorf area, Charles County, Maryland
1990, Wilson, J.M. and Fleck, W.B.
Report of Investigations 53
Abstract
From the stratigraphically highest aquifer to the lowest, the hydrogeologic section at Waldorf, Maryland, consists of the surficial aquifer, the Aquia aquifer, the Waldorf aquifer system, the White Plains aquifer, the La Plata aquifer system, and the Patuxent aquifer system. The Waldorf aquifer system consists of three discrete mappable aquifers- the Monmouth, Magothy, and St. Charles- that together form an interconnected hydrologic unit. Measured transmissivities range from 2,000 to 8,500 feet squared per day (ft2/d) in the Waldorf aquifer system, 20 to 2,000 ft2/d in the White Plains aquifer, and 400 to 3,500 ft2/d in the La Plata aquifer system. The Waldorf and La Plata aquifer systems are the primary sources of water to the Waldorf public-supply system.
Stratigraphic correlations show that a northeast-striking, up-to-the-east, reverse fault of the Brandywine fault system trends through the western part of the Waldorf area. The fault has up to 250 feet (ft) of throw at the preCretaceous basement. Beds within the Patuxent and Arundel Formations (undivided) and the lower part of the Patapsco Formation may be offset across the fault. The upper part of the Patapsco, Magothy, and Severn Formations, and Tertiary formations deposited prior to the Calvert Formation show dip reversals and form a west-dipping flexure. The Potomac Group in the Waldorf area has thinned by as much as 150 ft and the Nanjemoy Formation has thinned by about 70 ft on the upthrown side of the fault.
The Aquia, Monmouth, and Magothy aquifers at Waldorf contain a moderately hard to hard, calcium sodium bicarbonate-type water. The St. Charles aquifer contains a softer, more sodic-type water than the overlying Magothy and Monmouth aquifers. Water from the White Plains aquifer is a soft, sodium calcium bicarbonate-type water. The La Plata and Patuxent aquifer systems contain a very soft, sodium bicarbonate-type water. Concentrations of total dissolved solids generally increase as the depth of the aquifer increases.
A digital ground-water-flow model of the significant aquifers in the area of Waldorf in Charles County, Maryland, was constructed. The flow model consisted of 38 rows, 29 columns, and 7 layers. The seven layers represented by the model included the following units: the surficial, Aquia, Monmouth, Magothy, St. Charles, and White Plains aquifers and the La Plata aquifer system . The model cells differed in size from 0.12 square miles (mi2) in the immediate Waldorf area to 12 mi2 at the model's edge.
The model was calibrated for transient pumping conditions from 1900 to 1985. Calibration was attained by comparing simulated heads to measured heads for about 130 observation wells . Pumpage input to the model ranged from a minimum of 0.02 million gallons per day (Mgal/d) for 1900 to a maximum of 15.6 Mgal/d for 1985. Maximum modeled transmissivities for the calibrated model ranged from 3,500 ft2/d for the Aquia aquifer, to 12,000 ft2/d for the Magothy aquifer.
The ground-water-flow model was used to simulate head changes through the year 2020 for seven different pumpage scenarios. The results of these scenarios indicated that additional pump ages of 4.2 and 1.9 Mgal/d would result in 95 and 225 ft of additional drawdown in the La Plata aquifer system and White Plains aquifer, respectively. Also, an additional pumpage of about 0.90 Mgal/d from the Waldorf aquifer system would produce additional drawdowns of about 15 ft in the Waldorf area.
Three of the scenarios were devised to estimate the amount of ground water that could be withdrawn, such that a limit of 80 percent of the total available drawdown would not be exceeded. When the Waldorf aquifer system, White Plains aquifer, and La Plata aquifer system were separately stressed until the 80-percent available drawdown was reached, withdrawal rates of 6.6, 6. 1, and 15 .2 Mgal/d, respectively, were obtained.
Downloads and Data
Report of Investigations 53 (pdf, 78.1 MB)Plate 1, Report of Investigations 53 (pdf, 1.3 MB)Plate 2, Report of Investigations 53 (pdf, 0.9 MB)Plate 3, Report of Investigations 53 (pdf, 1.5 MB)Plate 4, Report of Investigations 53 (pdf, 1.2 MB)Plate 5, Report of Investigations 53 (pdf, 0.82 MB)Plate 6, Report of Investigations 53 (pdf, 1.6 MB)Plate 7, Report of Investigations 53 (pdf, 5.6 MB)Plate 8, Report of Investigations 53 (pdf, 1.2 MB)