Identification of freshwater - saltwater interface in coastal areas using combination of geophysical and geochemical methods: A case study in Mekong Delta, Vietnam

Abstract

Saltwater intrusion is widely observed in coastal aquifers because fresh groundwater is over exploited and abstraction wells were installed too close to saltwater intrusion zone. Identification of salt/fresh groundwater interface is important for fresh groundwater protection. This study presents an application of combination groundwater investigation methods including vertical electric sounding (VES), geochemistry and geographic information system (GIS) tools for delineation of salt/fresh groundwater interface in Mekong Delta. Twenty-seven groundwater samples are collected in existing wells for chemical analysis. Vertical electric sounding (VES) method was conducted for 37 sites to delineate freshwater zone (TDS <1g/L) and saline groundwater zone (TDS>1 g/L). Two new wells are also installed after VES measurement for groundwater sampling. Result of geochemical analysis show that TDS values of groundwater samples range from 0.25 g/L to 1.3 g/L and Cl from 8.8 to 758.6 mg/L. Electrical resistivity values range from 2 to 18.4 Ωm. The electrical resistivity values less than 10.4 Ωm is well correlated to saline groundwater. The study shows that even though VES can be an effective tool for identification of fresh/saline groundwater distribution, the method could not identify the saltwater intrusion zone. Combination of geochemical and GIS methods can clearly delineate saltwater intrusion zone. The study results show that fresh groundwater is limited in a small area of upper-middle Pleistocene aquifers. The fresh groundwater is highly affected by salinization. Therefore, the area urgently needs to take proper measures for sustainable groundwater development.

Groundwater resources in Bac Lieu province, Mekong Delta: current groundwater extraction and related issues

“…The city has about 158 000 people [10] and mostly dependent on groundwater for their drinking purpose [11]. Salinization and contamination of groundwater are observed in some surrounding area of Bac Lieu Province such as Ca Mau [12], Soc Trang province [13]. Groundwater issues in the Bac Lieu Province is rarely reported, therefore, this paper aims to understand groundwater system, current groundwater extraction and groundwater problems.…”

An assessment of groundwater quality for drinking and agricultural purposes in Ca Mau peninsula, Vietnamese Mekong Delta

“…Over abstraction of groundwater induces negative effects such as land subsidence [13], saltwater intrusion [14]. Even though many groundwater geochemical issues are noticed in other provinces of the Vietnamese Mekong Delta such as groundwater arsenic contamination in An Giang, Dong Thap [14], seawater intrusion and freshening in Soc Trang Province [15] or acidic groundwater [16]; groundwater quality in Ca Mau still remains unknown. Therefore, this study aims to investigate the suitability of groundwater quality for drinking and irrigation practices for the Ca Mau province.…”

Physico-Mechanical Foundations of Theoretical and Engineering Investigation on the Development to Corrosion-Resistant Materials in Buried Structures of Coastal Zones

“…As the rising sea levels, saltwater invades the freshwater aquifer. Groundwater over-pumping can cause the land to sink, and contaminate freshwater aquifers coastal areas with saltwater [7][8][9][10][11][12]. Seawater of the world ocean contains about 3.5% of total amount of dissolved salts (the results are presented in Tables 1 and 2), namely 2,73% NaCl; 0,32% MgCl 2 ; 0,22% MgSO 4 ; 0,13% CaSO 4 ; 0,02 KHCO 3 and small amounts of CO2 and dissolved O2.…”