The Papago Park Military Reservation (PPMR) is situated within the West Salt River Valley, an integral part of the Phoenix Active Management Area. This designation reflects the importance of water resource management in the region.

Hydrogeological Context

The general hydrogeology of the area has undergone notable alterations since 1947. Over this time, variations in groundwater depth near the PPMR have significantly influenced, and caused changes in, the direction of both local and regional groundwater flow. Historically, the prevailing direction of groundwater movement was primarily westward, following the natural gradient toward the Salt River channel. Currently, the regional groundwater flow is directed to the southwest toward the Motorola OU1 Superfund site. This shift in flow direction is a consequence of increased groundwater withdrawal, which has lowered the water table in the unconsolidated alluvial sediments.

Site-Specific Conditions

A critical factor influencing the presence of groundwater directly beneath the PPMR is its underlying geological structure. The PPMR is located on what are considered bedrock highlands, and it is largely underlain by crystalline, relatively impermeable rock. Due to this geological composition, very little water, if any, is able to saturate the material in the immediate vicinity of the bedrock base.

While the PPMR is characterized by a bedrock base, groundwater is present in the overlying alluvial deposits in some areas. The depth to groundwater beneath the site where it is present ranges from a shallow 6 feet to a maximum of 42 feet below grade. However, it is important to note that the groundwater table is discontinuous, meaning that groundwater does not exist uniformly or everywhere beneath the entire PPMR area.