Quarry Ponds and Borrow Pits

        Ponds may also accompany mining activity. Once excavation reaches the groundwater, excavation pits typically fill with water, which must usually be pumped out to allow further use of the site. An example is shown in Figure 15a. Maps from the late 1800s (Fig. 15b) indicate the locations of mining activity in many parts of the Brandywine watershed. As might be expected, mining was concentrated in those regions underlain by limestone or marble. Most operations were small, and have long since abandoned, but many have left behind ponds whose origins are often recognizable primarily by their steep and angular rock margins.

Fig. 15a–b.(a) Pond created during former quarry excavation in Newlin Township; note the steep rock wall on the far side. (b) Portion of Breou Farm Atlas, showing a quarry and two ponds in north-central West Whiteland Township in 1883. Owing in part to the presence of limestone bedrock underlying much of the township, quarries and lime kilns were abundant. Just how many quarries later became ponds is not known.

        Quarrying continues in the watershed today, but the operations are much bigger and fewer in number. A notable example is the Hanson Materials quarry near Exton, seen from the air in Figure 16a.
        Ponds may also be formed when the objective is the removal of soil rather than rock. The water present in these “borrow pits”, like that of quarry ponds, is typically maintained by groundwater. New Garden Township provides a number of examples of ponds resulting from the removal of clay (kaolin) for pottery manufacture (Fig. 16b).

Fig. 16a–b.(a) Image of Hanson Materials, East Caln and West Whiteland Townships, with quarry ponds visible as green/blue-green patches near the center of the photo. (b) Kaolin borrow pit in New Garden Township, also showing two co-authors of this document (C. Robinson at left, G. Coutu at right).