Davis-Monthan Air Force Base

Davis-Monthan Air Force Base

Location

Eastern Tucson, Ariz. The northern boundary gradually descends to the south from Golf Links Road to Irvington Road. The eastern boundary is Harrison Road and the western boundary is Alvernon Way. The southern-most boundary is Valencia Road on the east side of the site.

Contaminants of Concern

Contaminants of concern for sites where petroleum was released include petroleum hydrocarbons and BTEX in soils. The capped landfill contaminants of concern includes methane gas, volatile organic compounds (VOCs) and metals in soil. Per and polyfluorinated alkyl substances (PFAS) in concentrations below the EPA Health Advisory levels were found on-site at various locations in the soil, sediment and groundwater.

Public Health Concerns

There currently are no known risks to human health at this time, however an SI for PFAS is currently being conducted and expected to be completed in 2019. All other exposure pathways have been eliminated through remediation or restricted access/use.

Site Hydrogeology

Davis-Monthan Air Force Base (DMAFB) is located within the Tucson basin, a northwest trending alluvial valley. The Santa Cruz River flows northwesterly and provides the main drainage for the Tucson basin and is located approximately 4.6 miles west of the base. DMAFB is located in the Sonoran Desert which has an arid climate with a low precipitation rate of 12 inches per year and a high evaporation rate of 65 inches per year.

Groundwater occurs within the unconsolidated alluvial deposits consisting of interfingering sand, gravel, silt, and clay. The saturated thickness of these sediments is extremely variable, being thin (less than 200 feet) toward the mountains and thickening (greater than 5,000 feet) toward the center of the basin. These deposits were distributed laterally over time by a constantly changing stream course.

In the vicinity of DMAFB, the Pantano Formation, Tinaja Beds, and Fort Lowell Formation are the primary water bearing units. Groundwater is encountered at approximately 350 feet below ground surface near DMAFB, and groundwater generally flows in a northwest direction.

Action Taken

Petroleum contaminated sites ST-35, ST-36, and ST-52 were treated with soil-vapor extraction (SVE). An additional petroleum contaminated site ST-55 was proposed for risk-based closure. The low-level radioactive material waste storage area RW-16 was excavated and remediated. Geophysical surveys and limited excavations were conducted at the three Munitions Response Sites (MRS) TM553, TM553a, and TM554a. The closed base landfill LF-01 had a methane control system and landfill cap installed in 1999. A Preliminary Assessment Report (PA) for PFAS was completed in September 2015 and a site investigation (SI) is in-progress.

Status

For site LF-01 the USAF continues operation and maintenance of the landfill cap, the methane collection system, and are preparing to issue the Annual Inspection Report. For site ST-36 the USAF is currently working on a well closure work plan in preparation for site closure. ADEQ agrees with the USAF recommendation to close site ST055 with no further action. The public comment period for the Final Proposed Plans for MRS sites TM553, TM553a, and TM554a ended October 4, 2018. USAF is currently reviewing the public comments and preparing RODs. Excavation is complete at site RW-16 and the USAF is currently working on closure documentation. Final RODs for sites ST-35 and ST-52 were completed in December 2018 so remediation for these two sites are complete.

Community Involvement Activities

DMAFB is currently working with Tucson Water to evaluate elevated PFAS in Tucson Water wells outside of the base property.