The Delaware Geological Survey undertook a drilling operation to obtain continuous core samples through the confined aquifers of the Milford area.
With the cooperation of Delaware Nature Society and the Delaware Division of Fish & Wildlife, they selected a site at Abbott’s Mill Nature Center that was ideally located for this purpose. In June, a DGS research team drilled a 630-foot-deep hole during a two week period with the DGS’s CME 55 truck-mounted drill rig. The operation recovered hundreds of feet of sediment core that yield insights into the geological characteristics of the aquifers and the history of their formation. Wireline coring requires specialized drilling equipment and knowledge by the driller to maintain an open hole while making progress and recovering core.
The DGS team had the opportunity to demonstrate this drilling technology and discuss earth science and drinking water with students from Seaford’s Frederick Douglas Elementary School, allowing them to examine and touch a new core sample that was retrieved from more than 300 feet underground.
Preliminary results indicate that the Miocene-age — 10 to 25 million years old — sediments were deposited on the sea bottom as the ancient Atlantic Ocean repeatedly flooded and retreated from the area that is now southern Delaware. The succession of alternating sea-bottom sands and muds deposited six aquifers and intervening confining beds. The new cores provide insights into the geological factors that affect how much groundwater these aquifers can yield.
In addition, this new borehole helps the DGS to better understand the connection of aquifers — essentially the underground plumbing of the groundwater system — between Milford and parts of Kent County to the northwest and Sussex County to the south.
The cores are now housed in the laboratories of the DGS on the campus of the University of Delaware and will be the focus of additional analyses in the coming months. The new geological data will be compared to results from similar cored boreholes at Bethany Beach and Marshy Hope Wildlife Area and will be documented in future Delaware Geological Survey reports.
Groundwater is the sole source of drinking water and the main source of freshwater for agriculture and industry in central and southern Delaware. Groundwater is pumped from sediment layers under the Delaware Coastal Plain. In the areas of southeastern Kent County and northeastern Sussex County near Milford, the principal groundwater sources include the near-surface, water-table aquifer and a series of deeper aquifer sands. The deeper aquifer sands are of special interest because they store groundwater in “confined aquifer” layers that are isolated from the land surface by less permeable, muddy horizons that are referred to as “confining beds.”