Origin
of Arsenic in Groundwater from the Multilayer
Aquifer in Cremona (Northern Italy)
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Abstract
An
analysis of 70 wells that tap groundwater from depths of up
to 260 m in and around the town of Cremona, N. Italy, shows that 50
of them contain more than 10 μg/L of arsenic. Concentrations
of As >10 ppb are accompanied by concentrations of Fe ranging from
<0.1 to 6 mg/L and high concentrations of NH<sub>4</sub> and Mn
(<19 and <1.3 mg/L, respectively). The associations suggest
that the mechanism of mobilization of As is the reductive dissolution
of Fe oxides driven by the degradation of peat, which is commonly
found in the aquifer system. Groundwater in the aquifer has a component
of downward flow via leakage through aquitards and flow through lateral
discontinuities in them. Along these flow paths, As is released by
reductive dissolution of Fe oxides in shallow and intermediate aquifers
(0–85 m below surface), reaching up to 183 μg/L, and
is attenuated (<95 μg/L) at greater depths (100–150
m). Coprecipitation in iron sulfides could play an important role
in As attenuation at these depths. The lower As concentration (<37
μg/L) in the deepest aquifer (160–260 m) is less related
to the As concentration of the overlying aquifers because the groundwater
here has a component of upward flow
