Hydrologic and water-chemistry data from the Cretaceous-aquifers test well (BFT-2055), Beaufort County, South Carolina

Abstract

Test well BFT-2055 was drilled through the entire thickness of Coastal Plain sediments beneath central Hilton Head Island, South Carolina, and terminated in bedrock at a depth of 3833 feet. The well was drilled to evaluate the hydraulic properties of the Cretaceous formations beneath Hilton Head Island as a potential source of supplemental water to supplies currently withdrawn from the Upper Floridan aquifer. The intervals tested include sediments of the Cape Fear and Middendorf Formations. Results from aquifer tests indicate that the transmissivity of the formations screened ranges from 1300 to 3000 feet squared per day and an average hydraulic conductivity of about 15 feet per day. Formation-fluid pressure tests indicate that the potential exists for upward ground-water flow from higher fluid pressures in the deeper Cape Fear and Middendorf Formations to lower fluid pressures in the Black Creek Formation and shallower units. A flowmeter test indicated that greater than 75 percent of the natural, unpumped flow in the well is from the screened intervals no deeper than 3100 feet. Water-chemistry analyses indicate that the water sampled from the Middendorf and Cape Fear has about 1450 milligrams per liter dissolved solids, 310 to 1000 milligrams per liter sodium, and 144 to 1600 milligrams per liter chloride. Because these chloride concentrations would render water pumped from these aquifers as nonpotable, it is unlikely that these aquifers will be used as a supplemental source of water for island residents without some form of pretreatment. Similar chloride concentrations are present in some wells in the Upper Floridan aquifer adjacent to Port Royal Sound, and these chloride concentrations were the primary reason for drilling the test well in the Cretaceous formations as a possible source of more potable water.