| Summary |
Twenty nine wells in eastern North Carolina were sampled and analyzed for HCO₃̄, pH, Eh, O₂, S²̄, SiO₂, SO₄²̄, PO₄³̄̄, Ca²⁺, Na⁺, Fe²⁺, Clʹ, NO₃²̄, NH₄(B+, F̄, TOC, [delta]¹⁸C, and [delta]¹³C from the Yorktown, Pungo River, Upper Castle Hayne (UCH), Lower Castle Hayne (LCH), Beaufort, and Peedee aquifers. Estimated residence times for the UCH indicate that groundwater in the easternmost wells was recharged during the 1 R last glacial period (LGP). Groundwater from the UCH and LCH displays high [delta]¹⁸O relative to modem water, [delta]¹⁸O values increase from west to east, which could be a result of mixing with LGP seawater, isotopic exchange during water/rock interaction, and the reservoir effect. The cone of depression associated with PCS Phosphate Mine lowers heads in the UCH and could be inducing flow from aquifers containing groundwater with lower [delta]¹⁸O. [delta]¹³C in the UCH and LCH increases from west to east. The carbon isotopic signatures of groundwater in the western part of the study area largely reflect the contribution of biogenic CO2 in the recharge zone. Higher [delta]¹³C groundwater in the east could be a result of mixing with seawater as indicated by [delta]¹⁸O and chloride and a result of water/rock interaction. |
