THE LOS ALAMOS NATIONAL LABORATORY REGIONAL GROUNDWATER MODEL

The Los Alamos National Laboratory (LANL) regional groundwater model (LRGM) simulates flow and transport beneath the Pajarito Plateau, the location of the town of Los Alamos, New Mexico, and LANL. This model has evolved significantly since its initial development as a groundwater flow model for the entire 6,000 km² Espanola Basin. The original basin model was developed in 1998 in order to simulate groundwater flow along the major basins of the Rio Grande Rift. The U.S. Geological Survey and other researchers contributed to the effort of defining the initial conceptual model and provided the supporting datasets. Numerous papers have been presented and published in the past nine years documenting the evolution of this model. This presentation describes the latest developments with the LRGM, including: the development of new boundary conditions including a new infiltration map that is used for recharge; model calibration; and analyses of flow paths by forward and reverse particle tracking using geochemical tracer data. Although there is a thick unsaturated zone above the regional aquifer, the infiltration map is applied as a recharge map directly to the water table. Model calibration uses multi-scale datasets and is the subject of a companion paper in this conference (Dai et al., Session T27). Flow path analyses indicate that flow paths to Los Alamos water supply wells rarely originate at the water table, but rather, originate in deeper groundwaters at the western boundary of the model due to extreme stratigraphic anisotropy. However, there are some flow paths from the water table to deep water supply well screens indicating the existence of a vertical component of flow. LANL has been an active participant in the Espanola Basin Technical Advisory Group (EBTAG), and continues to work with collaborators from other agencies to ensure consistency and defensibility in groundwater modeling approaches. Future work planned for the LRGM includes the extension of the regional model boundaries using the latest geological data to include the Buckman well-field, an important water supply source for the city of Santa Fe, New Mexico. The extension of the model boundaries will be conducted in collaboration with EBTAG members in order to evaluate the potential impact of LANL activities on water supplies at the Buckman well-field.