Estimating the Isotopic Composition of Meteoric Water Index in Geothermal Fields in the Philippines

Abstract

Meteoric Water Index (MWI) is a set of numbers that may represent the composition of all the meteoric waters in a certain area. The MWI, together with the Local Meteoric Water Line (LMWL) is often established by collecting monthly rain samples for two to five years. In areas with no intensive sampling of rainwaters, a simple methodology of estimating the composition of MWI is proposed. One can use isotopic compositions of the rivers, groundwaters, sulphate springs and chloride springs to estimate MWI. The convergence of the lines produced by the data points and slopes of each type of waters often points to the MWI. Several cases in the geothermal fields in the Philippines are presented.