Shannon Road/El Camino del Cerro | Site Hyrdogeology

The western portion of the site is located within the Cortaro Basin, a block fault subbasin of the Tucson Basin. The eastern portion of the site is located within the Tucson Basin. The Tucson Basin is a broad, northwest sloping alluvial valley surrounded by mountain ranges and can be divided into four geologic units: the Pantano Formation, Tinaja Beds, Fort Lowell Formation, and recent alluvial deposits. The lower portion of the Ft. Lowell Formation and the upper Tinaja Beds comprise the regional aquifer at the site.

The Tucson Basin is drained to the northwest by the Santa Cruz River and the Rillito Creek, one of the major Santa Cruz River tributaries. The Santa Cruz River and Rillito Creek are ephemeral, which are streams that flow as a result of seasonal storm events. Effluent released from the Roger Road Wastewater Treatment Plant provides a perennial source of flow in the Santa Cruz River adjacent to the site.

Depth to groundwater ranges from 120 to 135 feet below ground surface (bgs) in the western portion of the site, and at approximately 130 to 135 feet bgs in the eastern portion of the site. Groundwater flow direction is generally toward the north-northwest. While regional groundwater flow direction is generally toward the north-northwest, the local flow is influenced by extraction from local wells and is towards the north-northeast.