Fingerprinting groundwater salinity sources in the Gulf Coast Aquifer System, USA

Chowdhury, AliH.; Scanlon, BridgetR.; Reedy, RobertC.; Young, Steve

Fingerprinting groundwater salinity sources in the Gulf Coast Aquifer System, USA | Empreintes des sources de salinité sur les eaux souterraines dans le système aquifère côtier du Golfe, Etats Unis d’Amérique Las huellas de las fuentes de salinidad del agua subterránea en el Sistema Acuífero de la Costa del Golfo, EE.UU. 识别美国海湾沿海含水层系统地下水盐分源 Impressão digital de fontes de salinidade das águas subterrâneas no Sistema Aquífero da Costa do Golfo, EUA

2018

Chowdhury, AliH. | Scanlon, BridgetR. | Reedy, RobertC. | Young, Steve

Understanding groundwater salinity sources in the Gulf Coast Aquifer System (GCAS) is a critical issue due to depletion of fresh groundwater and concerns for potential seawater intrusion. The study objective was to assess sources of groundwater salinity in the GCAS using ∼1,400 chemical analyses and ∼90 isotopic analyses along nine well transects in the Texas Gulf Coast, USA. Salinity increases from northeast (median total dissolved solids (TDS) 340 mg/L) to southwest (median TDS 1,160 mg/L), which inversely correlates with the precipitation distribution pattern (1,370– 600 mm/yr, respectively). Molar Cl/Br ratios (median 540–600), depleted δ²H and δ¹⁸O (−24.7‰, −4.5‰) relative to seawater (Cl/Br ∼655 and δ²H, δ¹⁸O 0‰, 0‰, respectively), and elevated ³⁶Cl/Cl ratios (∼100), suggest precipitation enriched with marine aerosols as the dominant salinity source. Mass balance estimates suggest that marine aerosols could adequately explain salt loading over the large expanse of the GCAS. Evapotranspiration enrichment to the southwest is supported by elevated chloride concentrations in soil profiles and higher δ¹⁸O. Secondary salinity sources include dissolution of salt domes or upwelling brines from geopressured zones along growth faults, mainly near the coast in the northeast. The regional extent and large quantities of brackish water have the potential to support moderate-sized desalination plants in this location. These results have important implications for groundwater management, suggesting a current lack of regional seawater intrusion and a suitable source of relatively low TDS water for desalination.

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