Groundwater resource degradation in coastal plains: the example of the Cecina area (Tuscany -Central Italy).

The paper describes the degradation of the groundwater resources in the Cecina area, where seawater intrusion, B contamination
and NO3 pollution are all affecting the heavily exploited Pleistocene aquifer. Over-pumping has brought water
levels to about 0 m.a.s.l. as far as about 7 km from the shore line, thereby promoting the seawater intrusion. The intrusion,
which is characterized by cation exchange phenomena and Ca-Cl type waters, enters the plain mostly through the shallower
horizons. The saline front, which advanced from 0.5 to 1 km in 4 a, has by now reached the foot of the hills to
the east of the town, where it is also affecting wells of the local aqueduct. Boron contamination, linked to past discharge
of industrial waste transported downstream by the river, reached concentrations as high as 3.5 mg/L in the mid-1980s.
Although a decreasing trend is now under way, B content is still close to 1 mg/L. The presence of high NO3, which,
together with the seawater intrusion, represents a major issue for groundwater management in the area, is linked to the
widespread utilization of fertilizers. Nitrate concentration, which reaches a maximum of about 300 mg/L in the shallow
aquifer horizons and then decreases rather regularly with depth, is strongly influenced by precipitation. However, irrigation
also contributes significantly to transporting the NO3 contamination to depth, as clearly shown by d18O data. The
severe decline in the quality of the groundwater resource in the Cecina area is further compounded by an overall decrease
in water availability in the region of Tuscany, as evidenced by long-term monitoring of precipitation and fluvial discharge.
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