161st Air National Guard

161st Air National Guard

Location

The 161st Air National Guard (ANG) Base is located on the southwest corner of a 50.7 acre site at the  Phoenix Sky Harbor International Airport (PSHIA) in Phoenix, Arizona between the south runway and the Salt River Channel. The facility was relocated in 2001 for the expansion of the runway network at PSHIA.

Contaminants of Concern

Contaminants are to be determined based on results of the 2018 site investigation of soil and groundwater.

Public Health Impact

Public health impacts are to be determined based on results of the 2018 site investigation of soil and groundwater.

Site Hydrogeology

The site is located in the West Salt River Valley sub-basin of the Phoenix Active Management Area.  Valley-filled deposits lie beneath the West Salt River Basin and these deposits are underlain by metamorphic, granitic, and extrusive rocks that form an impermeable hydrologic barrier. The valley-fill deposits are the main sources of groundwater. Based on lithology, the valley-fill deposits can be divided into three water bearing strata. The top layer is the Upper  Alluvial Unit. Beneath this layer is the Middle Fine-grained Unit. The bottom layer is the Lower Conglomerate Unit.

The Lower Conglomerate Unit can be divided into two sub units based upon grain size, clast type, and stratigraphy. The lower part of this unit is moderately to well-cemented mudstone or siltstone that may be evaporitic; sand; gravel conglomerate, and massive deposits of gypsum, anhydrite, and halite. Course grains may appear locally in the lower part of the unit, and wells drilled to these areas may yield up to 2,100 gallons per minute. The upper part of the Lower Conglomerate Unit Consists of weakly to moderately cemented clay, silt, mudstone, gypsiferous mudstone, gypsum, sand, and finely grained gravel.

The Middle Fine-grained Unit consists of weakly consolidated silt, sand, gravel and clay and ranges in thickness from 100 to 800 feet throughout the sub-basin. It is made of mostly unconsolidated silt, sand and gravel. The unit ranges from 400 feet thick to less than 200 feet thick.

The primary source of water in the valley-fill deposits is the Upper Alluvial Unit. This unit consists mostly of unconsolidated silt, sand, and gravel. Groundwater is usually unconfined, but semi-confined conditions may occur locally where there is an increase of finer grained materials. Perched conditions are also known to occur. Groundwater flow is usually to the west-northwest direction and occurs from 70 feet to 80 feet below ground surface.

Status

The Air National Guard developed a Work Plan to investigate the potential presence of Per- and Polyfluoroalkyl Substances (PFAS or PFCs) in site soils and groundwater.  The field investigation for this project will commence in early 2018.