Significant Developments in the Understanding of Culebra Hydrology at the WIPP Site

Understanding of the groundwater hydrology of the Culebra Dolomite Member of the Rustler Formation at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico, has significantly improved over the last decade due to the collection of additional field data, development of a more comprehensive conceptual model, and advances in numerical groundwater flow modeling. The Culebra is a 7meter-thick fractured dolomite found in the Permian Delaware Basin in southeastern New Mexico and west Texas. Although the WIPP repository, located in bedded halite of the Salado Formation, is stratigraphically more than 200 m below the Culebra, the Culebra is considered the most likely groundwater pathway for radionuclides released from WIPP due to inadvertent human intrusion. Since 1998, when the Environmental Protection Agency (EPA) accepted the initial Compliance Certification Application [1], a great deal of geologic and hydrologic investigation on the Culebra has been done to refine and enhance our understanding.