Excerpt from Hydrology and Water Quality of the Shallow Aquifer System, Yorktown Battlefield, Colonial National Historical Park at Yorktown, Virginia

Because of the good hydraulic connection between the streams and the Cornwallis Cave aquifer, shallow ground water generally discharges to local streams rather than flow under the streams to regional discharge areas. Therefore, the potential is limited for the transport of contaminants from recharge areas outside the battlefield through the shallow aquifersystem to the battlefield. Flow under streams to regional discharge areas most likely occurs through the yorktown-eastover aquifer, which is also the most likely pathway for the transport of contaminants from sources outside the battlefield to the battlefield. Contaminant transport through the yorktown-eastover aquifer, however, probably is limited by the low permeability of the overlying Yorktown confining unit.

The quality of ground water (represented by spring discharge) near Yorktown Battlefield depends on the aquifer from which the water discharges and the location of the spring. Concentrations of major ions were lower in water discharging from the Columbia aquifer than from the Cornwallis Cave aquifer. Concentrations of bicarbonate ions in water from two springs discharging from the Columbia aquifer, for example, were 0 and 6 milligrams per liter concentrations in water from 12 springs discharging from the Cornwallis Cave aquifer ranged from 133 to 410 mg/l. The primary source of high concentrations of bicarbonate ions in the Cornwallis Cave aquifer likely is the dissolution of aragonite in shell material in the aquifer. Concentrations of bicarbonate ions in water discharging from the Cornwallis Cave aquifer in the York River Basin generally were higher than concentrations in discharge in the James River Basin. The higher concentrations in discharge in the York River Basin can result from less precipitation of calcite from water in the York River Basin where flow paths are shorter and ground water likely is younger than in the James River Basin.

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