DISSOLVED CARBON DIOXIDE IN THERMAL SPRINGS IN SWEET CREEK VALLEY, NEAR GAP MILLS, WV

Thermal springs occur in clusters in the Appalachian Valley and Ridge and often have high dissolved CO₂ concentrations. A study of the Sweet Springs Valley of Virginia and West Virginia illustrates the geologic and geochemical complexity in one such setting. The study area includes 5 springs over 3-km in the Sweet Springs Creek Watershed. Surface deposits of travertine attest to the long-term discharge of CO₂ in the area and the mineral characteristics of the springs. The St. Clair’s Thrust Fault and associated splays outcrop adjacent to the major travertine deposits and one splay maps along lineations in a travertine terrace. Layered travertine deposits are evident throughout the valley. The fault splay truncates Devonian-aged shales such as the Millsboro and thrusts Silurian and lower Devonian aged sandstones and carbonates over the Devonian units.

Spring geochemical data have been collected in conjunction with CO₂ measurements. All springs have calcium carbonate waters but fall into three distinct groupings. Spellman Spring has cold water (~12°C), low CO₂ (~5 mg/L), and electrical conductivity (EC) (~ 450 μS/cm); all parameters are similar to other karst springs in the region. The 3 springs of group two have similar chemistries to each other, with temperatures 19-23°C, EC at 1400-1900 μS/cm, and CO₂ ranging from 220-440 mg/L; at two of these springs Fe hydroxide precipitates at the spring emergence but this does not occur at the third spring in the group. The fifth spring, which emerges from a cave, is cold (~10°C), but has moderate CO₂ (~80 mg/L) and EC (~ 900 μS/cm) between the values determined at the other two groups of springs. The fifth spring is also notable for H₂S concentrations in excess of 1,500 mg/L. The springs illustrate the geochemical variability that can occur within structurally complex geology and localized high CO₂ systems. Additional work is focusing on the kinetic barriers present in the system that may retard the precipitation of CaCO₃.