ARTÍCULO

Mixing processes between thermal waters and non?thermal waters: a case study in Mexico

Esteller, M.V., Martínez-Florentino, A.K., Morales-Reyes, G.P., Cardona, A., Expósito, J.L.
Environ Earth Sci (2019) 78: 295. https://doi.org/10.1007/s12665-019-8311-3, ISSN: 1866-6280 (Print) 1866-6299 (Online), 2019.

ABSTRACT:

The high content of toxic elements, such as As, in thermal water can cause water-quality problems when thermal water mixes with groundwater and/or surface water destined for human consumption. The objective of the study was to evaluate the mixing process between thermal and non-thermal waters in the Ixtapan de la Sal-Tonatico region of Mexico and to determine the resulting impacts on the quality of water for human consumption. The thermal springs of the study area had an average temperature of 35 °C and 5 g/L of total dissolved solids (TDS). The dominant ions were Cl? and Na+. The concentrations of As (1.7 mg/L), Fe (2.2 mg/L), and Mn (0.15 mg/L) and the water hardness (2087 mg CaCO3/L) exceeded the permissible limits for drinking water. Non-thermal springs, well water, and surface water were characterized as Ca–Na–Cl–HCO3, Ca– Mg–HCO3, and Na–Ca–Cl types, respectively, and had TDS values of 0.8, 0.2, and 0.4–3.9 g/L, respectively. The percentages of mixing were calculated based on the concentrations of conservative ions, such as Cl, B, Sr, and Li. The percentage of thermal water spring mixed with non-thermal spring water was around 11% and with surface water ranged from 10 to 30%. This variability is likely related to the proximity of surface water sources to the discharge points of thermal springs. As a result of mixing processes, the non-thermal water (non-thermal springs and surface waters) presents TDS, Cl?, Na+,hardness, As, Fe, and Mn values above those permitted by Mexican regulations for drinking water.