Assessment of Physicochemical Groundwater Quality and Hydrogeochemical Processes in an Area near a Municipal Landfill Site: A Case Study of the Toluca Valley.

Sanitary landfills are considered one of the main sources of contamination of water resources due to the generation of leachate with a high content of dissolved organic matter (DOM), inorganic material, and toxic elements. This study aimed to determine the influence of leachate on the physicochemical quality and hydrogeochemical processes which determine the chemical composition of groundwater in an area near a municipal sanitary landfill site. In situ parameters (pH, temperature, electrical conductivity, dissolved oxygen, ORP), physicochemical parameters (HCO3-, PO43-, Cl-, NO3-, SO42-, NH4+, Ca2+, Mg2+, Na+, K+), and dissolved organic matter were analyzed. The content of dissolved organic matter (DOM) was determined by 3D fluorescence microscopy. The presence of Cl-, NO3-, NH4+, PO43-, BOD, and COD indicated the presence of contamination. The significant correlation between NO3- and PO43- ions (r = 0.940) and DOM of anthropogenic origin in the 3D fluorescence spectra confirm that its presence in the water is associated with the municipal landfill site in question. The type of water in the area is Mg-HCO3, with a tendency to Na-HCO3 and Na-SO+-Cl. The water-rock interaction process predominates in the chemical composition of water; however, significant correlations between Na+ and Ca2+ (r = 0.876), and between K+ and Mg2+ (r = 0.980) showed that an ion exchange process had taken place. Likewise, there is enrichment by HCO3- and SO42- ions due to the mineralization of the organic matter from the leachate. The groundwater quality that supplies the study area is being affected by leachate infiltration from the sanitary landfill.

Assessment of contamination by anthropogenic dissolved organic matter in the aquifer that underlies the agricultural area.

The use of wastewater for agricultural irrigation is a common practice worldwide; long-term use of wastewater can have adverse effects, such as the migration of the anthropogenic dissolved organic matter into the aquifer. Three-dimensional fluorescence spectroscopy (EEM) was used to investigate the characteristics of dissolved organic matter (DOM) in groundwater and irrigation wastewater, to establish the effect of intensive irrigation on the water quality from the aquifer that underlies the area. The fluorescence spectra showed the presence of humic and fulvic acids and anthropogenic organic compounds similar to aromatic proteins and soluble microbial products in wastewater resources. The significant fraction of DOM in groundwater samples are aromatic proteins and soluble microbial products, identical to wastewater. Chlorides and nitrate ion concentrations suggest a local flow system. High levels of TDS are associated with intensive irrigation with residual water and the return irrigation associated with a gradual increase in salts of CO32-, NO3-, HCO3-, Cl-, and SO42-. The anthropogenic DOM is a useful indicator of water quality management in groundwater based on origin tracking of DOM and changes in organic pollutants. Fluorescence spectroscopy can be used to investigate groundwater pollution characteristics and monitor DOM dynamics in groundwater.