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Geologic and Hydrologic Factors Controlling Radon‐222 in Ground Water in Maine
Author(s) -
Brutsaert Willem F.,
Norton Stephen A.,
Hess Charles T.,
Williams John S.
Publication year - 1981
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.1745-6584.1981.tb03488.x
Subject(s) - geology , chlorite , metamorphic rock , sillimanite , groundwater , mineralogy , overburden , geochemistry , radon , pegmatite , geomorphology , biotite , mining engineering , quartz , geotechnical engineering , paleontology , physics , quantum mechanics
High Radon‐222 ( 222 Rn) concentrations exist in ground water from most granitic rocks in Maine. Some values exceed the suggested limit of 500 pCi/1 (E.P.A., 1976) by more than 100 times. Although high values (x̄= 22,100 pCi/1) are conclusively linked with the granites, high values are also present in ground water in metasedimentary rocks from sillimanite‐ (x̄= 13,630 pCi/1) and sillimanite‐orthoclase zone metamorphic terrains. Metamorphic (anatectic) pegmatites with hydrothermally introduced uranium are thought to be the source of radon in high grade terrain. At lower grade (chlorite to staurolite), no relationship exists between 222 Rn content and metamorphic grade, although each rock formation has a somewhat characteristic 222 Rn range from ground water, ranges which overlap. Considerable local 222 Rn variations exist within the same rock body, reflecting local geologic and hydrologic conditions. Data on well depth, type of well, well yield, overburden type and thickness, and water chemistry show that 222 Rn may increase slightly with well depth up to 50 to 75 m and is essentially constant thereafter. Low yield wells, generally associated with areas of thin overburden, tend to have higher 222 Rn values than high yield wells, normally associated with thick sand and gravel overburdens. 222 Rn concentrations decrease with increasing sodium concentrations, suggesting that low 222 Rn wells are closely linked with surface waters. No other chemical parameter (Na, K, Ca, Mg, Fe, Mn, Zn, and Cu) correlates with 222 Rn content within a single rock unit.