West Van Buren | Site Hydrogeology

The WVB is within the basin and range physiographic province and is generally characterized as a series of extended terrains. The basin and range province consists of high-angle normal faulting which created broad basins and surrounding mountain ranges. Historically, the Gila, Salt and Aqua Fria River system influenced the WVB. However, due to upstream reclamation projects, these streams are no longer perennial and the river system influence has declined.

The aquifer is divided into three sections: the upper alluvial unit (UAU), middle alluvial unit (MAU) and the lower alluvial unit (LAU). Contamination in the site to date has been limited to the UAU and the MAU.

The UAU is composed primarily of coarse-grained sediment deposited by the ancestral Salt River. The UAU extends from the surface to approximately 200 feet below ground surface (bgs) in the eastern portion of the site and to approximately 400 feet bgs in the western portion of the site.The MAU is composed of thick sequences of clay, silt and sand with some interbedded gravel and cobbles lens. The MAU is approximately 100 feet thick in the eastern portion of the site and approximately 500 feet thick in the western portion of the site.

As of Sept. 2006, the water level in the aquifer was approximately 98 feet bgs in the eastern portion of the site and 130 feet bgs in the western portion of the site. As of March 2013, the water level in the UAU aquifer was approximately 95 feet bgs in the eastern portion of the site and 105 feet bgs in the western portion of the site. Water levels are influenced by pumping and drought conditions. Multiple sources are responsible for the commingled plume of contaminated groundwater. Contaminated groundwater also enters the site from the north and the east.