Changes in the calcocarbonic system of karst groundwaters by infiltration of leachates from a USWL (La Mina landfill, South of Spain)

Leachates from La Mina landfill are degrading the natural quality of a karstic aquifer. The chemical composition of waters from wells, piezometers and main springs has been analyzed and hydrochemical calculations have been performed with the aid of the EQ3NR software package. Water closer to the landfill shows that reactions take place in an open system, with constant and high P_CO2 (log P_CO2 = -1.40), what provokes an “extra” dissolution of carbonated minerals. The results are lower pH’s and higher calcium, magnesium and bicarbonate contents, compared to unaffected groundwaters. Samples coming from piezometers located far away from the landfill show a higher pH, lower calcium, magnesium, and bicarbonate than that of the background, and present a lower P_CO2 than the atmosphere (log P_CO2 < -3.50). The calcocarbonic reactions take place within a closed system and CO₂ is being consumed without further replenishment.