Hydrogeological Evaluation of the Edwards Air Force Base Air Force Research Laboratory Area, Antelope Valley, California

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In cooperation with Air Force Civil Engineer Center (AFCEC), the U.S. Geological Survey (USGS) is evaluating the hydrogeology of the Air Force Research Laboratory (AFRL) and Site 25 areas of Edwards Air Force Base (EAFB) and the adjacent North-Muroc groundwater subbasin to help determine regional groundwater movement and the possible long-term movement and pathways of contaminated water from the AFRL into aquifers used for groundwater supply. 

In 1980, as part of the Air Force Installation Restoration Program, a preliminary base-wide assessment of known and suspected hazardous substance sites was initiated at EAFB (Tetra Tech, 2014). In 1989, the U.S. Environmental Protection Agency (USEPA) listed EAFB on the National Priorities List under the Comprehensive Environmental Response, Compensation, and Liability Act, identifying the area as a site for long-term cleanup with oversight of the restoration activities provided by the USEPA, the California Department of Toxic Substances Control, and the California Regional Water Quality Control Board-Lahontan Region.

The USGS has been conducting hydrogeologic research in the Antelope Valley area since 1911.  In 2017, the USGS entered a cooperative agreement with the AFCEC to combine the information from these previous studies with new data to provide a broader, regional understanding of the hydrogeology of the transition from the AFRL to the alluvial flow system.

Data collected by the USGS in federal fiscal year (FFY) 2017 included -geophysical surveys of 11 wells, water-quality sampling of nine wells, and gravity data from survey points throughout the AFRL, as well as water-level measurements in 34 off-base wells. Additionally, the USGS compiled water-level data and borehole lithologic data from other sources. The complete dataset was used to prepare preliminary versions of the hydrogeologic framework conceptualization that would then be revised using data collected in subsequent years.

In FFY 2018, the USGS collected surface geophysical data at the AFRL to help characterize the hydrogeologic structure of the area; specifically, the depth and structure of the basement material, the thickness and layering of the alluvial material, and the location and other structures such as faults. Multiple geophysical techniques were implemented to improve the resolution of the results, including gravity, direct-current (DC) resistivity, and transient electromagnetic (TEM) surveys. Gravity data were collected to provide information on the structure of the basement material and the thickness of the alluvial deposits (alluvial thickness model). DC resistivity data were collected to provide information on the structure of the basement material, the thickness and layering of the alluvial deposits, and water-table elevation.

a lone Joshua tree stands out amongs desert scrub and fluffy clouds in a blue sky

Joshua trees dot the desert landscape on Edwards Air Force Base in Antelope Valley, CA.  (Public domain.)

In 2019, light detection and ranging, or LiDAR, data was collected by the U.S. Interagency Elevation Inventory project to identify potential surface expressions of fault traces around the EAFB area. A variety of techniques were used to study whether wells in the Site 25 area of EAFB were acting as conduits for vertical flow of contaminates to different depths. To determine ambient flow conditions, single borehole dilution tests (SBDT) were conducted on 8 wells. SBDTs involve placing frozen food dye in the well and tracking its movement. Colloidal borescope data, which calculates the velocity and direction of flow of water and areas of cross-flow in wells, was gathered from 6 wells. Water quality samples were taken from 8 well to analyze for volatile organic compounds (VOCs).  LiDAR imagery was collected and analyzed by USGS Geology, Minerals, Energy, and Geophysics Science Center to identify linear features on land surface which could potentially be faults.

Research and data collection in FY2020-21 will help to refine fault locations and describe fault structure in areas where the faults may act as impediments, or conduits, to groundwater flow. Results of this work will be used to guide further data collection by EAFB remedial project managers, help develop the hydrogeologic framework conceptualization that is underway, and develop a new, detailed (>=1:24,000-scale) surficial geologic map of the AFRL area.

The Air Force Research Laboratory occupies approximately 80,000 acres (AECOM, 2014) southeast of Boron, California, and east of the North-Muroc groundwater subbasin, in Antelope Valley, CA.  The AFRL was constructed for the Apollo Program and consists of 12 facilities for testing full-size rocket engines, engine components, and liquid and solid propellants (Tetra Tech, 2014).

 

References

AECOM, 2014, 2012 Groundwater Modeling Report for the Northeast AFRL, Air force Research Laboratory, Detachment 7, Operable Units 4 and 9, Edwards Air Force Base, California: AR File Number 4795.

Tetra Tech, 2014, Basewide Groundwater Monitoring Sampling and Analysis Plan, Volume I – Long-Term Monitoring Optimization Work Plan: AR File Number 4799.