Investigation of groundwater salinity using geophysical and geochemical approaches: heuningnes catchment coastal aquifer. Western Cape Province, South Africa

Abstract

Seawater intrusion is recognised as a major factor affecting the quality of groundwater in coastal aquifers around the world. To determine the occurrence and extent of saline groundwater intrusion prevailing in the Heuningnes Catchment, a 2D resistivity imaging survey was carried out in three sites within the catchment. Eleven resistivity profile lines were conducted using the multi-electrode ABEM SAS resistivity meter system, employing the Wenner Array to map the extent of saline groundwater. A 2D resistivity image was acquired for these resistivity profile lines and the data were processed using Res2DINV software to produce the 2D inverse resistivity models. The interpretation of the resistivity models revealed three resistivity zones. The first zone is characterised by low resistivity (1-3 Ω.m); this represents an aquifer filled with saline water. The second resistivity zone has values ranging from (3-30 Ω.m); this represents a brackish saturated formation. The third resistivity zone denotes a sandy layer/sandstone saturated with freshwater having high resistivity values above 30 Ω.m. Geochemical analysis results of water samples at 11 locations along the electrical resistivity profile lines also suggest high salinity, indicated by high levels of Cl − , Na + , Total Dissolved Solids, and Electrical Conductivity. It is concluded that some parts of the study area are impacted by seawater intrusion, based on the lower resistivity of < 3 Ω.m and ionic ratios which were close to the standard seawater ratios for Na + /Cl − and SO 4 2− /Cl − . In addition, the high ionic ratios of Na + /Cl − and SO 4 2− /Cl − suggest that salinity in the area is a result of dissolution of evaporates and dilution of marine clays rich in sodium. Therefore, salinization in the study area is the result of combined processes. Integration approach proved to be significant in mapping saline groundwater in coastal aquifers. Integrated assessment of resistivity data, ionic analysis and chemical interpretation indicate that the study area is a transition zone from freshwater to saltwater and only few locations are actually impacted by seawater intrusion. The overall groundwater quality is not apt for human ingestion.

Toward Contamination in Coastal Regions for Groundwater Quality, Fluoride, Nitrate and Human Health Risk Assessments Within Multi-aquifer Al-Hassa, Saudi Arabia

“…A recent study on coastal groundwater in Bhola District, Bangladesh, reported an average EC of 588.15 µS/cm [46], indicating a notable difference between the two reports. However, the EC values observed in this study align with those found in coastal aquifers of Southern Kenya [47], Western Cape Province, South Africa [48], and South [49]. Typically, fresh groundwater unaffected by saltwater intrusion exhibits mild salinity and, thus, low EC values.…”

Characterisation of Hydro-Geochemical Processes Influencing Groundwater Quality in Rural Areas: A Case Study of Soutpansberg Region, Limpopo Province, South Africa

“…This finding is similar to those in Tshikondeni, which is part of the Soutpansberg Basin, that indicated that the Na + + Cl − /(Na + + K + + Ca 2+ ) ratio was greater than >0.5 (ion exchange) and the weathering of rocks influenced the groundwater chemistry [21]. In this study, the classification used in [47] was adopted, where parameters with a correlation coefficient >0.7 were considered to be strongly correlated. Parameters with correlation coefficient >0.5 to <0.7 were considered to have a moderate correlation and a correlation coefficient less than 0.5 indicated that there was no relationship between the parameters.…”

“…A strong correlation (r = 1) between Na + and Cl − indicates that these parameters originated from the same source. The correlation coefficient between TDS and In this study, the classification used in [47] was adopted, where parameters with a correlation coefficient >0.7 were considered to be strongly correlated. Parameters with correlation coefficient >0.5 to <0.7 were considered to have a moderate correlation and a correlation coefficient less than 0.5 indicated that there was no relationship between the parameters.…”

Qualidade de águas superficiais e subterrâneas para irrigação em um município do semiárido do estado do Rio Grande do Norte

“…Em adição, Carvalho & Souza (2022) discutem a influência do clima em águas superficiais e subterrâneas no município de Carnaúba dos Dantas/RN, evidenciando o papel que a irregularidade das chuvas tende a exercer na distribuição iônica tanto em águas superficiais quanto subterrâneas. Comumente, as águas associadas a reservatórios em unidades aquíferas fissurais submetidas a um regime de chuvas irregular, se encontram salinizadas, impactando seu eventual uso na irrigação (Nogueira et al, 2019;Mokoena et al, 2021). Geralmente, essas águas apresentam quantitativos de sólidos totais dissolvidos elevados e que as tornam inadequadas ao consumo humano e uso agrícola, ou no limiar entre a possibilidade de seu uso ou descarte (Batarseh, 2017;Qaisar et al, 2018;Batarseh et al, 2021).…”