Assessment of aquifer vulnerability and water quality: Validated using groundwater flow origin-based regression analysis

The Puebla Valley aquifer (PV), a volcanosedimentary system located in central Mexico, faces increasing pressure due to land use change and groundwater contamination. However, its vulnerability had not been comprehensively assessed. This study aimed to evaluate the intrinsic vulnerability of the PV aquifer using the DRASTIC methodology adapted to the characteristics of a volcanosedimentary environment and validate the results using simple linear regression analysis based on the origin of groundwater flows, correlating them with water quality indices (WQI) and contamination indices (C${}_d$).

The DRASTIC model was adjusted by modifying parameter weights to reflect local aquifer conditions, considering land use change (recharge, agricultural and urban zones) as the basis. Linear regression showed significant correlations (p$<$0.001) between vulnerability and WQI; for flows from Sierra Nevada, an 84% fit was found between these two variables, and 83% for La Malinche. The Atoyac River was identified as the main contamination source, with extreme values of WQI=35 (poor quality) and C${}_d>3$ (high health risk) in adjacent areas.

DRASTIC classified 550 km${}^2$ (25% of the area) as low vulnerability, 800 km${}^2$ (36%) as moderate, and 690 km${}^2$ (31%) as high. The most influential factors were recharge ($>350$ mm/year in critical zones), water table depth ($<$7 m) and topographic gradient ($>$5%).

These results validate for the first time a DRASTIC adapted with flow-origin-based regression for volcanosedimentary aquifers. They emphasize the need to: urgently protect recharge zones and regulate discharges into the Atoyac River. The methodology provides tools for sustainable management in subhumid environments, but under anthropogenic activities.