New Mexico Geological Society Annual Spring Meeting — Abstracts

Groundwater monitoring is conducted at three Environmental Restoration (ER) Operations groundwater Areas of Concern, including Technical Area-V Groundwater (TAVG), Tijeras Arroyo Groundwater (TAG), and Burn Site Groundwater (BSG) for the U.S. Department of Energy, National Nuclear Security Administration at Sandia National Laboratories, New Mexico.

The TAVG is located on the East Mesa of the Albuquerque Basin in the central portion of Kirtland Air Force Base. Groundwater occurs at a depth of approximately 500 feet within unconsolidated, alluvial fan sediments of the Santa Fe Group. Historic discharges of waste waters have impacted the uppermost Regional Aquifer with nitrate and trichloroethene (TCE). The impacted sediments have low hydraulic conductivities averaging 4 to 5 feet/day. The maximum nitrate and TCE concentrations are 15 mg/L and 19 ug/L, respectively. A treatability study of in-situ bioremediation is currently being conducted. An injection well is used to distribute the bacteria dehalococcoides and various nutrients to the aquifer.

The TAG is located on the East Mesa of the Albuquerque Basin along the northern rim of Tijeras Arroyo. Groundwater occurs in two water-bearing zones within unconsolidated, alluvial fan sediments of the Santa Fe Group: the Perched Groundwater System (PGWS) and the Regional Aquifer. The PGWS is present at a depth of 290 feet and consists of a thin zone of saturation ranging from 7 to 17 feet thick. The PGWS was primarily created by manmade activities including sewage lagoons, landscape watering, and waste-water outfalls. Most recharge inputs have been eliminated and the PGWS is dewatering. Nitrate is the contaminant of concern with concentrations occasionally exceeding 30 mg/L (as nitrogen) in the PGWS. The Regional Aquifer occurs at an average depth of 410 feet and is vertically separated from the PGWS by approximately 200 feet of unsaturated sediments over much of the TAG area. The maximum nitrate concentration in the Regional Aquifer is 4 mg/L. Remedial alternatives for the nitrate-impacted groundwater in the PGWS are currently being evaluated.

The BSG is located along the eastern margin of the Albuquerque Basin, and the terrain is characterized by large topographic relief exceeding 900 ft in deeply incised into Paleozoic strata and Precambrian basement. Groundwater occurs in granitic gneiss and metamorphic units (phyllite, schist, and quartzite). Groundwater is semiconfined and migrates in a generally westward direction through a diverse set of fractures and along near-vertical faults; the thin veneer of alluvium at the site is sporadically saturated. Releases to the environment include outdoor detonations of high explosives from 1967 to 1985, wastewater disposal from 1978 to 1988, and burn tests from 1969 to present. Nitrate is the contaminant of concern with concentrations exceeding 40 mg/L (as nitrogen). Remedial alternatives for the nitrate-impacted groundwater are currently being evaluated.

_{Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2018-2931 A.}