Analysis and Modeling of Carbon-14 in Ground Water Beneath the Pajarito Plateau, Los Alamos, New Mexico

2007 Ground Water Summit

Tuesday, May 1, 2007 : 10:40 a.m.

Analysis and Modeling of Carbon-14 in Ground Water Beneath the Pajarito Plateau, Los Alamos, New Mexico

Edward M. Kwicklis, Hydrogeologist¹, Michael Dale², Patrick Longmire, Ph.D.¹ and Jennifer Teerlink, M.S.¹, (1)Los Alamos National Laboratory, (2)New Mexico Environment Department, DOE Oversight Bureau

Los Alamos National Laboratory (LANL or the Laboratory) and the New Mexico Environment Department (NMED) are in the midst of a two-year project to investigate the sources, flow paths, flow velocities and mixing of groundwater in the vicinity of LANL from groundwater geochemical and isotopic data. Central to this investigation are groundwater carbon-14 (¹⁴C) data collected by the NMED from over 80 springs and wells in the LANL area. These data are being used to calculate groundwater travel times and residence times in the underlying regional aquifer. To sort out the relative impacts of water/rock interactions, groundwater mixing, and radioactive decay on the groundwater ¹⁴C activities, groundwater ¹⁴C data are being examined in conjunction with other groundwater geochemical and isotopic data from the study area. These supporting data can help provide evidence of the source of the groundwater and its history of water/rock interaction, and thus aide in the interpretation of the ¹⁴C data.

Ongoing analyses suggest that only deep groundwater from the regional aquifer production wells and groundwater from some springs on the east side of the Rio Grande have undergone significant interactions with calcite. Based on their uncorrected ages, most of the groundwater in the regional aquifer appears to have a residence time of between 2,500 and 7,500 years, except for deep groundwater from production wells near the Rio Grande, where the apparent groundwater residence times exceed 10,000 years. However, even this groundwater may be younger than 10,000 years based on the age corrections using DIC and δ¹³C. Scatter plots and maps of the supporting geochemical data are being used to formulate conceptual and numerical geochemical models to calculate travel times in the regional aquifer.

Edward M. Kwicklis, Hydrogeologist, Los Alamos National Laboratory Ed has over 20 years experience working on groundwater studies. His past experience includes analyzing groundwater flow systems in complex geologic areas in Nevada using groundwater chemical and isotopic information.

Michael Dale, New Mexico Environment Department, DOE Oversight Bureau Michael Dale is a hydrogeologist with the New Mexico Environment Department. Michael conducts hydrogeochemical investigations including measuring naturally-occurring perchlorate and delineating ground-water flow paths using isotopic and chemical tracers. Michael has 13 years experience in the fields of hydrochemistry and hydrogeology.

Patrick Longmire, Ph.D., Los Alamos National Laboratory Dr. Patrick Longmire is an aqueous geochemist at Los Alamos National Laboratory specializing in the fate and transport of radionuclides and inorganic contaminants in ground-water systems. Patrick has been investigating the use of permeable reactive barrier technology to remediate ground water contaminated with perchlorate, nitrate, metals, and radionuclides. Dr. Longmire has 30 years of experience in the field of aqueous environmental geochemistry. Patrick has been teaching short courses on ground water geochemistry for NGWA since 1986.

Jennifer Teerlink, M.S., Los Alamos National Laboratory Jennifer Teerlink is currently working as a geochemist through Los Alamos National Lab's student programs. She recently completed a Master of Science degree at University of Maryland and is in the process of applying to PhD programs for Fall 2007.

The 2007 Ground Water Summit