Waste Programs Division
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.
In 2009, the Army Military Munitions Response Program (MMRP) began a remedial investigation (RI) of the practice minefield near the airport (FTHU 007). In March 2012, the result of the final RI report for the minefield near the airport was that No Department of Defense Action Indicated (NDAI), deeming no further action necessary at this site to address potential risk from munitions of explosive concern (MEC) or munitions constituents (MC). The Eastern Artillery Area Range (FTHU 013), also known as EAA Range 2, was used as a buffer zone for training involving 105mm mortars. A RI was completed in August 2012. Fragments from 105mm mortars were found. The RI recommended a feasibility study for the southeastern portion of the munitions response site near the installation fence line. The South Range Landfill (FTHU 010) environmental restoration program (ERP) site remains under long-term monitoring. The south range landfill had three groundwater monitoring wells and two leachate monitor wells that were sampled annually. Mid- to late-2014, fieldwork was conducted at the East Range Mine Shaft as part of the second Five-Year Review to ensure that the remedy in place is protective of human health. Mid-2015, the Draft Final Second Five-Year Review Report was submitted to ADEQ for review.
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.
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.