HR: 09:18h
AN: H41K-06    [Abstracts]
TI: Trace Perchlorate in Background Ground Water and Local Precipitation, Northern Rio Grande Basin, New Mexico
AU: * Dale, M
EM: mdale@lanl.gov
AF: New Mexico Environment Department, DOE Oversight Bureau, 134 State Road 4, Suite A, White Rock, NM 87544, United States
AU: Longmire, P
EM: plongmire@lanl.gov
AF: Los Alamos National Laboratory, Group EES-6, MS D469, Los Alamos, NM 87545, United States
AU: Granzow, K P
EM: kgranzow@lanl.gov
AF: New Mexico Environment Department, DOE Oversight Bureau, 134 State Road 4, Suite A, White Rock, NM 87544, United States
AU: Englert, D
EM: david.englert@state.nm.us
AF: New Mexico Environment Department, DOE Oversight Bureau, 134 State Road 4, Suite A, White Rock, NM 87544, United States
AU: Yanicak, S
EM: syanicak@lanl.gov
AF: New Mexico Environment Department, DOE Oversight Bureau, 134 State Road 4, Suite A, White Rock, NM 87544, United States
AU: Larson, T
EM: tlarson@lanl.gov
AF: Los Alamos National Laboratory, Group EES-6, MS D469, Los Alamos, NM 87545, United States
AU: Rearick, M
EM: mrearick@lanl.gov
AF: Los Alamos National Laboratory, Group EES-6, MS D469, Los Alamos, NM 87545, United States
AU: Heikoop, J
EM: jheikoop@lanl.gov
AF: Los Alamos National Laboratory, Group EES-6, MS D469, Los Alamos, NM 87545, United States
AU: Perkins, G
EM: gperkins@lanl.gov
AF: Los Alamos National Laboratory, Group EES-6, MS D469, Los Alamos, NM 87545, United States
AB: Perchlorate occurs at detectable concentrations of 0.07 to 0.45 parts per billion (ppb) in ground water of background quality within the northern Rio Grande basin, New Mexico. Ground-water samples were collected from 47 wells and springs near Los Alamos, Santa Fe, and Taos, New Mexico. Analytical methods consisted of liquid and ion chromatography-mass spectrometry mass spectrometry (LC/MS/MS and IC/MS/MS). An upper tolerance limit (mean plus two standard deviations) of 0.40 ppb was calculated from 184 analytical results for the background samples. Six distinguishable ground-water zones were sampled based on location, age, and hydrochemistry. In the Los Alamos area, ground water within the mountain-front and mountain-block region is mostly young or modern (less than 50 years). The regional aquifer including the White Rock Canyon springs are of sub-modern age (greater than 50 years). Tritium data from springs north of Taos indicate ground water of modern and sub-modern ages. Background perchlorate concentrations within the Los Alamos area were consistently higher than those measured in the Taos area. Ground water from the Taos area contains less perchlorate and has lower δ¹⁸O and δ²H values than ground water from the Los Alamos area. The elevation at which precipitation occurs with respect to recharge and/or the amount of evapotranspiration may play a role in perchlorate concentration in ground water. Natural variability, hydrogeology, and atmospheric inputs may also affect perchlorate concentration in ground water. A linear regression through perchlorate and chloride concentrations for all stations resulted in an r² = 0. However, the r² value of the Los Alamos regional aquifer for perchlorate versus chloride was 0.66. Thirteen precipitation samples were collected in the Los Alamos area. Results from eleven of these samples showed no perchlorate greater than 0.05 and 0.009 ppb, the method detection limit (MDL). Two precipitation samples analyzed using the IC/MS/MS method detected perchlorate at 0.0210 and 0.0099 ppb with an MDL of 0.0012 ppb. These results have application for establishing site-specific background values, delineating anthropogenic impacts to ground water, measuring natural attenuation and contaminant gradients, and may aid in the process of setting drinking-water standards.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1806 Chemistry of fresh water
DE: 1818 Evapotranspiration
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2007 Fall Meeting