Arizona Army National Guard Camp Navajo

Location

The Arizona Army National Guard (ARNG) Camp Navajo installation (Camp Navajo) is located in the northwestern portion of the State, approximately 10 miles west of the city of Flagstaff, south of Interstate 40 at Exit 185 in Bellemont, Arizona.  The installation encompasses 28,347 acres and is situated in heavily forested to grassy, gently rolling to steep hilly terrain approximately 7,100 feet above mean sea level.

Camp Navajo was originally established as Navajo Ordnance Depot in 1942. The installation has been in continuous operation since 1942, to include the period from 1982 to present date, when it has been under the operational control of the Arizona National Guard. The facility includes 800 ammunition storage igloos, 50 administrative buildings, 227 miles of road, 38 miles of railroad track and completed utility distribution and collection systems. Open burn and open detonation (OB/OD) historically occurred in the southern part of the installation.

Contaminants of Concern

The contaminated media includes groundwater and soil. The current contaminants of concern and contaminants of potential concern (COCs/COPCs) vary at different sites within the installation but include perchlorate, heavy metals, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs) such as pesticides and herbicides, residual from explosive waste (i.e., hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)), dioxin/furans, munitions and explosives of concern (MEC), unexploded ordinance (UXO) and polychlorinated biphenyls (PCBs). Contaminants of concern may change as new data become available.

Public Health Impact

There are currently no known exposures to COCs/COPCs in excess to applicable heath based levels at the sites. The contaminated sites, such as the former OB/OD Area, are either fenced within the installation, contain warning signs and public access is prohibited. Impacted perched groundwater is limited to the installation boundaries. Groundwater monitoring is conducted in a set of regional aquifer wells downgradient of the former OB/OD Area within and near the boundary of the installation, including public drinking water supply wells. There are currently no known exceedances of health-based standards at the public drinking water supply wells.

Site Hydrogeology

The geology of Camp Navajo is characterized by unconsolidated Quaternary alluvial deposits, volcanic rocks of Quaternary and Tertiary age and Paleozoic sedimentary rocks, mostly sandstones, limestones and shales. Outcrops of the volcanic unit are predominantly basaltic and range from lava flows to cinder cones. Thirteen volcanic vents have been identified within site boundaries. Several faults have been identified cutting Paleozoic sedimentary rocks and Quaternary-Tertiary volcanic rocks. These faults are regionally important with respect to groundwater sources and recharge.

Within the former OB/OD Area, the Fossil Mountain and the Harrisburg members of the Kaibab Formation are the dominant rock units present. These units are bisected by several northeast striking normal faults and associated fracture sets that are surficially exposed in outcrop.

The Fossil Mountain member of the underlying Kaibab Formation consists of approximately 75 meters of thick-bedded limestone, sandy-limestone, and sandstone, while the overlying Harrisburg member consists of approximately 50 meters of reddish-orange to white, thinly bedded, sandy-silty limestone, and calcareous silty sandstone.

The regional water table, occurring in the Coconino-Supai sandstone aquifer (C-aquifer), is encountered at approximately 1,500 feet below ground surface. Several perched water tables, controlled by local geologic conditions, are present above this regional unconfined aquifer. These perched saturated zones have been identified at various depths to 350 feet. 

The city of Flagstaff relies on the C-aquifer for its municipal drinking water; its production wells are located at the Woody Mountain Wellfield, three miles southeast of the eastern boundary of Camp Navajo. Since 2003, Camp Navajo and the town of Bellemont have also tapped the C-aquifer. The Camp Navajo relies on a spring supplemented by a C-aquifer well as the source of drinking water. Within the C-aquifer, groundwater flow is in a northerly direction as has been determined in the Flagstaff area.

The former OB/OD Area drains towards the former White Phosphorous Detonation and burn area (a.k.a. Chemical Canyon). The former White Phosphorous Detonation and burn area canyon is a tributary of Volunteer Canyon. Volunteer Canyon joins Sycamore Canyon and Sycamore Creek approximately 5.5 miles downstream of Camp Navajo.