2007 Ground Water Summit

Tuesday, May 1, 2007 : 10:20 a.m.

Isotope and Aqueous Chemistry Investigation of Ground Water, Pajarito Plateau and Surrounding Areas, New Mexico

Patrick Longmire, Ph.D.¹, Michael Dale², Kim Granzow² and Robert Gray³, (1)Los Alamos National Laboratory, (2)New Mexico Environment Department, DOE Oversight Bureau, (3)Daniel B. Stephens & Associates Inc.

Determining ground-water age and flow paths within aquifer systems are essential for calibrating flow and transport models. The Los Alamos National Laboratory and New Mexico Environment Department conducted an isotope and geochemical investigation from October 2004 through February 2006. The investigation evaluated ground-water flow paths and ages of samples collected from alluvial and perched intermediate zones and the upper portion of the regional aquifer primarily beneath the Pajarito Plateau and Jemez Mountains, New Mexico. Water samples were collected at 23 single-screen wells located on the Pajarito Plateau and 27 springs discharging within the Sierra de los Valles and White Rock Canyon, New Mexico. Samples were analyzed for tritium, carbon-14, noble gases (helium-3, helium-4, and neon-22), stable isotopes of carbon, hydrogen, and oxygen, and inorganic solutes. Alluvial ground water is entirely modern (recharged after 1943) based on the tritium/helium-3 dating method. Perched intermediate-depth ground water, ranging in depths up to 600 feet, within the Sierra de los Valles and beneath the Pajarito Plateau, is either entirely modern or a mixture of modern and sub-modern (recharged prior to 1943) components. The regional aquifer is either sub-modern or mixed in age. Analytical results for 100 percent modern ground water suggest that the majority of the Sierra de los Valles springs originated as local precipitation. Significant modern recharge from the Pajarito Plateau to perched intermediate zones and the regional aquifer is supported by occurrence of tritium, nitrate, uranium, chromium(VI) and/or perchlorate. The close similarity in stable isotope ratios between regional wells on the Pajarito Plateau and White Rock Canyon springs containing elevated tritium, nitrate, and/or perchlorate support the hypothesis that the perched intermediate zones provide recharge to the upper portion of the regional aquifer beneath the Pajarito Plateau. The regional aquifer is hydraulically connected to the White Rock Canyon springs.

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.

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.

Kim Granzow, New Mexico Environment Department, DOE Oversight Bureau Kim Granzow is an environmental scientist/geologist with the New Mexico Environment Department. Kim specializes in environmental monitoring for naturally occurring and anthropogenic contaminants such as perchlorate and plutonium, and utilizes Geographic Information Systems (GIS) in hydro-contaminant investigations. Kim has 11 years of experience in the field of geology and five years experience in GIS.

Robert Gray, Daniel B. Stephens & Associates Inc. Robert Gray is a senior hydrogeologist with Daniel B. Stephens & Associates and specializes in ground-water flow modeling and conducts field investigations in surface and ground-water hydrology. Mr Gray has 10 years of experience in hydrology.

The 2007 Ground Water Summit