Groundwater recharge and flow on Montserrat, West Indies: Insights from groundwater dating

Study region: Montserrat, Lesser Antilles, Caribbean. Study focus: Analysis of δ²H and δ¹⁸O isotopes, and chlorofluorocarbon (CFC) anthropogenic tracers in Montserrat groundwater provides insights into the age and provenance of the spring waters. New hydrological insights: δ²H and δ¹⁸O analysis indicates uniform recharge elevations for groundwaters on Montserrat. CFC-11 and CFC-12 analysis reveals age differences between isotopically similar, high elevation springs and low elevation aquifer waters. Low CFC concentrations within a confined low elevation aquifer suggest water ages of ~45 years. High CFC concentrations in the northern and western springs are explained by rapid infiltration of cool (high CFC concentration) rainfall into saturated compartments, with flow through the vadose zone to the phreatic zone dominated by compartment flow. Lower CFC concentrations in a number of aligned warmer springs suggest a contribution from older, warmer waters from depth. Temperatures and CFC concentrations indicate older component supply rates of up to 8L/s to the highest yielding spring on Centre Hills, with contributions of up to 75% in the warmest spring waters.