Characteristics of the Coastal Groundwater of Celestún, Mexico on the West Coast of the Yucatan Peninsula for Extreme Conditions During the Dry Season
Date:
Abstract:
Yucatan, Mexico relies entirely on groundwater due to the absence of suitable surface water. Overconsumption of groundwater puts the region at risk of seawater contamination, jeopardizing the drinking water source. This study investigates groundwater-seawater interactions at a beach near Celestún, Mexico. Its goal is to contribute local knowledge regarding Celestún’s water resources which would broadly advance understanding of the coastal hydrogeology of the Yucatan Peninsula. Knowledge of the groundwater flow patterns, water table dynamics, and saltwater intrusion near the coast will provide information useful for water resource management. Water sampling and water table mapping were conducted using 15 piezometers along a 300 ft-long beach-perpendicular transect. The water table was measured using water level meters and pressure transducers, and the transect was surveyed with a total station. Chemical measurements were performed in the field and the lab to determine pH, conductivity, oxidation-reduction potential, sulfide, and major ion concentrations. Saturated hydraulic conductivity of sediment samples as well as electrical resistivity imaging (ERI) was measured along the transect.The hydrological, geophysical, and geochemical observations revealed that the beach transect is saltwater-dominated with a relatively thick vadose zone around 4.5 m. The site has an upper unconfined aquifer composed of sand, a caprock confining layer, and a lower confined aquifer. There was pronounced variability in the permeability of the surface sands ranging from 0.026 m/day to 50.3 m/day, as well as in topography and vegetation, which caused differences in infiltration rates. The tidally influenced unconfined coastal aquifer showed that groundwater flow is primarily landwards, with seawater mostly infiltrating, likely due to the dry season. Geochemical data from the wells are comparable to that of seawater and provide evidence of intrusion. The ERI data indicate that the caprock plays a role in protecting the deeper aquifer from local seawater intrusion. Thus, the shallow, unconfined aquifer at the beaches of Celestún may not be optimal for domestic use, but the deeper aquifer may host substantial fresh groundwater and should be further explored. However, no samples were collected in the confined aquifer.