that includes the LANL and the adjacent communities of Los Alamos and White Rock, San Ildefonso Pueblo The Pajarito Plateau is an important source of abundant potable land west of the Rio Grande, and a northern outlying groundwater for Los Alamos National Laboratory (LANL) and the part of Bandelier National Monument (Fig. 3). Areas communities of Los Alamos and White Rock. Geologic investigations were undertaken as part of a plateau-wide hydrogeological investiga-of the southern Pajarito Plateau in Bandelier National tion to develop conceptual models of the groundwater system as a Monument are not discussed because there are no hyframework for numerical simulations of groundwater flow. The Pajadrogeologic data from wells in this area. The northern rito Plateau is located in the western part of the Españ ola basin where plateau is not discussed because hydrogeologic data for rocks of the Jemez and Cerros del Rio volcanic fields overlie and the Santa Clara Pueblo is not available to the public. interfinger with Neogene basin-fill sedimentary rocks. The vadose Groundwater drawn from beneath the plateau is the zone is about 200 m (600 ft) thick beneath mesas on the east side of primary source of municipal and industrial water used the plateau and more than 375 m (1245 ft) thick on the west side. by LANL and by adjacent communities. Water supply Groundwater occurs as shallow groundwater in canyon-floor alluvium, wells on the plateau are 600 to 950 m (2000-3110 ft) moderately deep groundwater perched in bedrock units of the vadose zone, and groundwater associated with the regional saturated zone.deep (Purtymun, 1995;Koch and Rogers, 2003), andThe most productive rocks of the regional aquifer occur in a westward-they tap the western-central part of the Españ ola basin thickening wedge of coarse-grained, Miocene and Pliocene volcaregional aquifer in Miocene and Pliocene sedimentary niclastic rocks derived from the Jemez volcanic field. Eastern aquifer and volcanic rocks. Although numerous wells penetrate rocks consist of fine-grained, somewhat less productive Miocene sedithe upper part of the regional saturated zone, none fully mentary deposits derived from highland sources to the east and north.penetrate the aquifer.
Intermediate and mafic lavas interbedded with the Miocene and Plio-Water quality is typically good, but the effects of cene sedimentary deposits are components of the regional aquifer LANL operations can be detected in parts of the locally. The hydrogeology of the Pajarito Plateau is probably typical groundwater system. Locally, shallow and intermediate of groundwater systems along the margins of the Rio Grande rift where arid to semiarid, sediment-filled basins receive most of their perched groundwater systems of the vadose zone conrecharge from adjacent mountainous areas.