15 Environmental Geochemistry and Health Impacts

This session welcomes research on contaminant occurrence, fate and transport, and impacts on human and environmental health. Interdisciplinary contributions with implications for environmental remediation and natural resources management are encouraged.

Monday, 18 May 2026
1:30 PM - 4:00 PM
Alvarado G

Fire Retardant - An Inadvertent Tracer Study for Groundwater Recharge

Paper number: 15-6
Program: Technical Sessions
Time: 3:05 PM – 3:25 PM

Authors

Abstract

The Hermit's Peak/Calf Canyon Fire of 2022 was the largest wildfire in New Mexico's history burning over 350,000 acres in the state's north. A commercial fire retardant containing Sb and other metals was widely applied to the fire area by the USFS using aerial suppression in conjunction with ground operations. Well-water monitoring at 18 locations within the burn scar was begun in 2023 to evaluate fire effects on groundwater quality. Initial results indicated an increase in P and N, indicators of elevated OM content. The sample size has increased to approximately 74 wells by 2025. Wells were sampled annually in July in 2023 and 2024, then biannually in 2025. In 2025, summer water levels in a subset of wells increased between <1in (2.5cm) to >4.5 ft (1.2m). 2025 also saw the appearance of Sb, As, Mn and other metals in well-water samples from a large subset of the sampled wells. Concentrations varied from trace amounts to significantly higher than EPA MCL levels. Sb concentrations are virtually ubiquitous in wells within the burn scar and levels above MCL are widespread. Sb as Sb2O3 is a major component of fire suppressants but occurs only in sub-ppm concentrations in rocks that comprise the Sangre de Cristo Mountains. Measured static water levels (SWLs) in sampled wells define an approximate minimum phreatic zone depth and range from <10 to 250 ft (3.05 to 76.25m). SWLs greater than ~115 ft (35m) are in Paleozoic shale and limestone and/or fractured Precambrian basement whereas shallower SWL depths are largely in alluvium. If sourced from retardant applied in 2022, the early occurrence of P and N and the presence of Sb in shallower wells indicate relatively rapid groundwater recharge by local surface water in alluvium that fills intermontane valleys. Fluvial and atmospheric depositional pathways for fire retardant are considered along with transport timing based on local tritium data to explain observed metal concentrations.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410656

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