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2072 | Geof%u00edsica Internacional (2026) 65-21. IntroductionDuring the last decade, arsenic (As) contamination has been identified in groundwater of various regions of the world. The highest levels of As have been determined in Asia and Europe, followed by Africa, North America, South America, and Australia (Shaji et al., 2021). This metalloid is widely known due to its extensive use in science, medicine, and technology, as well as its toxicity (Armienta et al., 1995). Since its health risk includes both carcinogenic and non-carcinogenic effects (Singh et al., 2021), the World Health Organization (WHO) establishes that the permissible limit for arsenic in drinking water is 0.01%u00a0mg/L (World Health Organization, 2011; Jha et al., 2023). The presence of arsenic in Mexico has been known since the 1960s, with various health effects reported in the Comarca Lagunera region of northern Mexico (Cebrian et al., 1983; Armienta et al., 2008).Therefore, NOM-127-SSA1-2021, is the Mexican Standard for Water for Human Use and Consumption, which defines the permissible limit for arsenic in drinking water as 0.025%u00a0mg/L for all localities and will be adjusted according to the gradual compliance schedule, until reaching a maximum value of 0.01%u00a0mg/L (Secretar%u00eda de Salud, 2022).Since 1992, high concentrations of arsenic have been detected in the water sourced from drinking water wells in the municipality of Zimap%u00e1n, posing an environmental hazard. Armienta et al.(1997a; 2001) based on hydrogeological, hydrogeochemical, mineralogical and chemical determinations (rocks, tailings, soils) and geological studies identified three primary sources of contamination in the aquifer system:a) Natural from water interaction with mineralized limestone rock and iron oxides/hydroxides in the deep fractured limestone aquifer, with arsenic concentrations exceeding 1.09%u00a0mg/Lb) Mine tailings releasing arsenic up to 0.437%u00a0mg/L to the shallow aquifer.c) Arsenic-laden vapors that permeated the soil, producing water concentrations of 0.10%u00a0mg/L in shallow wells.Arsenic contamination is associated with mineral deposits enriched in metallic sulfides such as pyrite and arsenopyrite, as well as minerals like scorodite. Arsenic release into groundwater is mainly driven by arsenopyrite oxidation near mineralized zones, an exothermic process that lowers pH and increases sulfate and temperature, releasing arsenic into the water (Dove & Rimstidt, Figure 1. Lithology and structural geology of Zimap%u00e1n, Hidalgo (Derived and modified from INEGI, 2002, 2010; Servicio Geol%u00f3gico Mexicano, 2002; Ramos Leal, 1996).455000 460000 465000 470000 Zimap%u00e1n LITOLOGY AGE(MA) o Alluvium 0.01 o o 1-' w*t o o o < :::, F. Daxi: \\(.) o Polymict 1.68 N N conglomerate N N 5.1 s o SPFM N Las .Espinas >- desrhc - rt'lyoliti o a:: ,.; ,,.',-_ lavas <( I # I .. ~ .,%u00a1 z : : ~-~%u2022 ~ '#,.': Rhyolitic deposits 1-a:: .a%u2022 ( '.> F.EIMorro: o w 24 \, .: %u2022 '_,... e o w %u00ba.o o, o o (.) (.) 1-