The affection in groundwater by leachate produced in La Mina landfill has been controlled during a 600 days period by means of hydrochemistry monitoring in springs, wells and piezometers. Hydrochemistry diagrams and statistical tools allow (1) a differentiation between points affected by leachate infiltration, from those others belonging to the non-contaminated groundwater and (2) to separate groups of waters with different grades of affection. The contaminated waters are of chloride-sodium type, but several points presents a mixed bicarbonate-chloride sodium type of water. Evolution of chloride, as a conservative parameter, permits to follow the contamination trend. In the non-affected groundwater, chloride concentration is always below 20 mg/l, with a natural fluctuation due to the dry and wet seasons of the year