New Mexico Geological Society Annual Spring Meeting — Abstracts

ABSTRACT
Kirtland Air Force Base discovered a leak at the former fuel offloading rack in 1999, leading to a soil and groundwater investigation to determine the nature and extent of contamination resulting from the release of aviation gas into the environment. The majority of contamination is limited to the source area on the Air Force base with dissolved constituents extending off-base. Ethylene dibromide (EDB) is the primary risk driver for the site, with the dissolved phase plume extending approximately 7,000 feet down gradient towards the Albuquerque Bernalillo County Water Utility Authority Ridgecrest water supply wells. Depth to groundwater at the site is betwen 460 to 480 feet and flows to the north-northeast towards a cone of depression located near the Ridgecrest well field.

Utilizing geologist soil boring logs, continuous cores, and geophysical analyses, environmental sequence stratigraphy cross-sections have been developed at regional and plume scales. These cross-sections are consistent with the geologic understanding of the Abuquerque Basin synthesized by Connell (2008). Regional cross sections show that the EDB plume migrates within the portion of the groundwater system comprised of braided river deposits of the Ancestral Rio Grande, one of three primary depositional systems that filled the Rio Grande Rift Basins over time (Champion et al., 2015). Plume scale sections show that the coarse channel-fill and bar sediments are interbedded with silts and clays deposited in overbank and incipient floodplain settings (Champion et al., 2016). The depositional morphology of these fluvial deposits appears to influence plume hydraulics, resulting in the lateral spreading of the plume parallel and perpendicular to the regional hydraulic gradient.

Understanding the basin geology, specifically the orientation and extent of the braided channel deposits, at a variety of scales is critical for the design and implementation of the remediation technologies used to address EDB in groundwater. Locations of extraction wells for the ongoing EDB plume collapse interim measure were largely informed by the site stratigraphy and the simulation of plume capture using three-dimensional fate and transport models.

References:

1. Champion, Tom et al., 2015. Regional Geology and Cross Sections, Kirtland Air Force Base. Albuquerque, NM: Technical Memorandum.
2. Champion, Tom et al., 2016. Plume and Water-table scale Cross Sections, Kirtland Air Force Base. Albuquerque, NM: Technical Memorandum
3. Connell, Sean D., 2008. Preliminary Geologic Map of the Albuquerque-Rio Ranch Metropolitan Area and Vicinity, Bernalillo and Sandoval Counties, New Mexico Socorro, NM: New Mexico Bureau of Geology and Mineral Resources