Location

West of Sierra Vista in southeastern Arizona on the western flank of the San Pedro River Valley, Fort Huachuca consists of an irregularly shaped area of 115 square-miles bisected by Arizona State Highway 90. The installation is divided into the Cantonment area, the Libby Army Air Field, and the East, West and South Ranges, where military training operations are conducted.

Status

Groundwater monitoring for the South Range Landfill continues with no exceedance reported. In January 2018 the Final Decision Document for the Minefield Near the Airport was signed.

The Eastern Artillery Range 2 in-fill transect report was submitted to ADEQ in February 2018 to support the RI amendment.  ADEQ and USACE are in discussions about the findings and acceptable risk.

The Site Characterization/Corrective Action Completion Report for the Vehicle Maintenance Facility LUST site was submitted in May 2018 for review.

The next Five-Year review will be completed in 2019 and will include groundwater monitoring for the East Range Shaft and South Range Landfill.

Contaminants of Concern

In soils at the south range landfill and east range mine shaft: organochlorine pesticides, metals, VOCs, munitions constituents and petroleum hydrocarbons; MEC may exist at a portion of EAA Range2.

Public Health Impact

Groundwater monitor wells at the south range landfill and east range mine shaft have been monitored periodically over the past two decades. Contamination detected to date appears limited to samples from shallow subsurface soil and leachate under the south range landfill. Historically, trace levels of contaminants have also been detected in regional aquifer groundwater samples near the east range mine shaft. Data collected to date indicates the regional aquifer has not been impacted above Aquifer Water Quality Standards (AWQS) near either the south range landfill or the east range mine shaft. There are no known health risks from these two sites, however, groundwater monitoring will continue to protect the regional aquifer, where Sierra Vista drinking water wells withdraw groundwater. A FS will be conducted on a portion of the Eastern Area Artillery Range 2 (MRS 2A) to address potential risk from possible MEC. No further action is necessary for the minefield near the airport.

Site Hydrogeology

Fort Huachuca Army Post lies on the west side of the San Pedro River Valley basin. The basin is formed by northwest-trending mountain blocks, and bounded to the west by the Huachuca Mountains. Alluvial deposits from the adjacent mountains and are generally composed of a mixture of conglomerate, sandstone, gravel, sand, silt and clay. The basin fill has a thickness up to 350 feet, subdivided into upper and lower units, and overlies the Pantano Formation, which is comprised of well-cemented gravel, conglomerate, sandstone and siltstone and has a very low permeability. The regional aquifer is reported by the United States Geological Survey and the Arizona Department of Water Resources to be at least 300 to 500 feet below the land surface. The general direction of regional groundwater flow is generally to the northeast toward the San Pedro River, except where influenced by groundwater pumping by the base and/or Sierra Vista. Community involvement activities: No community involvement activities are planned at this time.