Empirical relationships between recharge elevation and the oxygen and hydrogen isotopic composition of spring discharge have been developed for the Jemez Mountains of northern New Mexico (Vuataz and Goff, 1986, JGR, v. 91, no. B2, p. 1835-1853.)  These relationships have been used to reconstruct recharge elevations for waters located beneath the Pajarito Plateau located on the eastern flank of the Jemez Mountains.  The Pajarito Plateau is the location of Los Alamos National Laboratory, and therefore, accurate determinations of recharge elevations are necessary for contaminant flow and transport modeling.

The empirical relationships developed by Vuataz and Goff are only calibrated to a lower elevation of 2260 m, whereas it has been speculated that recharge may occur at lower elevation on the Plateau itself.   To determine the validity of extrapolating the recharge elevation – isotope relationships to lower elevation it is necessary to understand the isotopic controls that lead to those relationships.  These could include, but are not limited to, 1) the classic temperature dependent altitude effect, 2) the pseudo-altitude effect, 3) the relative importance of different precipitation sources with different isotopic signatures over an elevation gradient, and 4) variation in the location and timing of infiltration at different elevations.

A model will be presented which examines the relative importance of these various isotopic effects in yielding the observed isotopic relationships.  This model will be constrained to recent GIS-based models of infiltration for the eastern edge of the Jemez Mountains and the Pajarito Plateau and to measurements of the isotopic composition of local precipitation.  This will allow for a determination of the likely nature of recharge elevation—isotope relationships extended to the Pajarito Plateau itself.