The Hershey Valley, part of the Great Valley, is 9 miles east of Harrisburg, Pennsylvania. Beekmantown limestone (Ordovician), striking N. 70° E., and steeply overturned to the southeast, underlies the valley.
The Annville Stone Company mines the high-calcium Annville limestone (top of the Beekmantown) 1½ miles northeast of the Hershey Chocolate Corporation plant. For many years 3500 gpm was the normal pumping discharge. Neither industry adversely affected the other nor any of the valley residents.
Plans of the Stone Company to mine at lower levels prompted geologic studies by the Chocolate Corporation. One hundred wells and springs in the valley were systematically observed, 12 of the most critical being measured every 2 weeks. For each there was determined the water elevation; water temperature; pH value; ppm of dissolved solids; ppm of the Ca, Mg, PO4, SiO2, Al2O3, SO4, and Fe ions; and yield in gpm of the springs. Details of ground-water movement were studied by using fluorescein. Water table maps of the valley were periodically made.
When the mine began pumping 6500 gpm from lower levels in May 1949, it drastically lowered the ground-water level over an area of 10 square miles, drying up most valley springs and many wells. About 100 sink holes of all sizes developed in the area, endangering life and property. The water-table map of November 1949 showed a huge cone of depression with the apex at the mine.
Ground-water levels were successfully restored over a large area when the Chocolate Corporation recharged water to the ground, beginning December 1949.