Hydrogeologic characteristics of the Waste Gate Formation, a new subsurface unit of the Potomac Group underlying the eastern Delmarva Peninsula
1984, Hansen, H.J.
Information Circular 39
The Lower Cretaceous Waste Gate Formation (Hansen, 1982) is a new name proposed for a subsurface unit of the Potomac Group occurring beneath the eastern Delmarva Peninsula; the top of the unit occurs at depths ranging from about 3,500 feet at its up-dip edge to 5,670 feet at the Coast. It consists chiefly of unconsolidated to moderately lithified, light gray to whitish, arkosic to sub arkosic sandstones and drab, often finely laminated silty shales (or clays). It ranges up to 1,500 feet thick at the Coast with sand percentages characteristically 50 to 70 percent. The unit is tentatively dated Neocomian (Berriasian to Hauterivian (?)) on the basis of limited palynological data. An apparent absence of Clavatipollenites and other Zone I (mid-Barremian to early Albian) palynomorphs implies that the Waste Gate Formation is older than the Patuxent Formation, which comprises the basal beds of the outcropping Potomac Group.
Sandstone porosities of the Waste Gate Formation, estimated from geophysical logs, range between 19 and 27 percent. Analysis of production test data for a Waste Gate sandstone in the DOE Crisfield Airport No. 1 well yielded permeabilities in the 75 to 118 millidarcy (3 to 5 gallons/ day / foot2) range. The formation waters of the Waste Gate are of the sodium-calcium chloride type. The Crisfield Airport well produced salty water with a chloride concentration of 42,000 mg/l (71,000 mg/l total dissolved solids). Elsewhere on the Peninsula, geophysical log estimates of NaCl salinity range from 53,700 mg/l to 97,000 mg/l. Below 3,000 feet Waste Gate fluid pressures increase under a hydrostatic pressure gradient of about 0.44 to 0.46 psi/foot. Temperature gradients appear to fall between 1.3° and 1.75° F/100 ft. Waste Gate formation temperatures range from about 124° F in up-dip areas to about 172° F near the base of the formation at the Coast; temperatures as high as 190° F are possible, but are less likely.
Possible utilization of the Waste Gate aquifers include extraction of chemical commodities from brines, low-temperature geothermal heat production, and disposal of liquid wastes.