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Chlorine‐36 in Ground Water Containing Low Chloride Concentrations
Author(s) -
Davis Stanley N.,
FabrykaMartin June,
Wolfsberg Laura,
Moysey Stephen,
Shaver Robert,
Alexander E. Calvin,
Krothe Noel
Publication year - 2000
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.2000.tb00691.x
Subject(s) - chloride , chlorine , bromide , groundwater , groundwater recharge , evaporite , iodide , environmental chemistry , chemistry , environmental science , mixing ratio , hydrology (agriculture) , mineralogy , geology , aquifer , atmospheric sciences , inorganic chemistry , carbonate , geotechnical engineering , organic chemistry
Analyses of ground water from wells and springs in the United States indicate a broad regional trend in preanthropogenic ( 36 Cl/total Cl) ×10 15 ratios in potable water. Coastal areas influenced by marine chloride have ratios less than 100. These ratios increase inland and reach a maximum of about 1400 in the central and northern Rocky Mountains. However, the magnitude of these regional variations is greatly exceeded at a local level if water samples are considered regardless of age or origin. Most local departures from regional trends can be attributed to mixing of ground water recharge with either 36 Cl from nuclear fusion tests to produce higher ratios or mixing with sources of old chloride such as from evaporite minerals to produce lower ratios. A useful interpretation of 36 Cl data is difficult unless the origin of the chloride is understood. The interpretation is an unusually difficult problem for water having low chloride concentrations. The assumption that low concentrations originate primarily from wet and dry atmospheric deposition can be questioned even for some dilute waters with less than 2.0 mg/L chloride. Chloride/bromide ratios in ground water can help decipher the origin of the chloride. The presence of nonatmospheric chloride can be identified in part by its association with chloride/bromide mass ratios greater than about 200 in coastal areas and 100 in inland areas. Accurate chloride and bromide analyses are recommended for virtually all studies of 36 Cl in natural waters, and particularly those with low concentrations of chloride.