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(18)OS04 AND (18)OH20 AS PROSPECTIVE INDICATORS OF ELEVATED ARSENIC IN THE GOOSE RIVER GROUND-WATERSHED, MAINE
Citation:
Sidle*, W C. (18)OS04 AND (18)OH20 AS PROSPECTIVE INDICATORS OF ELEVATED ARSENIC IN THE GOOSE RIVER GROUND-WATERSHED, MAINE. LaMoreaux, P.E. (ed.), ENVIRONMENTAL GEOLOGY. Springer-Verlag, New York, NY, 42(4):350-359, (2002).
Description:
Anomalous geogenic arsenic occurs in drinking water from the Goose River crystalline ground-watershed in mid-coastal Maine. Isotope investigations were useful in understanding release areas of arsenic into affected water wells. The isotope composition of sulfate associated with probable arsenian pyrite oxidation is described. Correlation of 18OSO4 enrichment (+4.57 o/oo to +7.46 o/oo Vienna Standard Mean Ocean Water) is discussed with specific and recurring areas of elevated arsenic (10 g l-1 - 52 g l-1). While arsenic concentrations were highly variable over two years per well, 18OSO4 values were always consistent and suggested a specific and consistent risk for elevated arsenic occurrences for each well. The 18O values in the water molecule (-12.07 o/oo to -8.81 o/oo VSMOW) and the 18OSO4 values may serve as prospective indicators of prominent zones of aeration at depth in discrete fracture zones. The 18O values in the water molecule and sulfate ion appear to indicate that more than 60 % of O2 incorporated into the SO42- ion is from dissolved oxygen and belong to distinct fractured areas. These aeration zones or oxidation fronts as outlined by oxygen isotopy are sentinels for high arsenic risk in groundwater.