Hydrogeochemical characterization of groundwater in the southern part of Quintana Roo, Mexico

In order to identify the processes controlling the geochemical evolution of groundwater in the southern part of the state of Quintana Roo, Mexico, 53 drinking water wells were sampled in the months of October and November 2012 (rainy season). Physical parameters measured in the field were pH, temperature, electrical conductivity and total dissolved solids. Chemical constituents analyzed include the cations calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+) and the anions bicarbonate (HCO3-), sulfate (SO42-), chloride (Cl-) and nitrate (NO3-). Descriptive statistics, correlation matrices, factor analysis, along with cluster analysis were used to gain an understanding of the hydrogeochemical processes operating in the study area. The study area is characterized by heterogeneity in their hydrogeological characteristics (karst), with lithological and geological-structural changes that result in water-bearing zones isolated from the aquifers of regional extent. Four predominant types of water were identified in the study area: calcium-bicarbonate type (Ca-HCO3), mixed calcium-magnesium-chloride type (Ca-HCO3), mixed Ca-Mg-Ca sulfate-calcium type (Ca-SO4) and sodium-chlorided type (Na-Cl). Through cluster analysis, seven predominant groups were identified in the study area. These groups show contrasting values for nearby sites, favored by the heterogeneity of the aquifer medium where the water flows through different rocks: limestone, dolomite and evaporite. Three factors were identified through factor analysis, accounting for 74.68% of the cumulative variance. The parameters associated to these factors indicate that the dominant hydrogeochemical processes in the study area are (1) the dissolution of limestone and dolomite and ionic exchange; (2) mixing with seawater; and (3) anthropogenic nutrient input.