Estimating Soil Water Susceptibility to Salinization in the Mekong River Delta Using a Modified DRASTIC Model

Saltwater intrusion risk assessment is a foundational step for preventing and controlling salinization in coastal regions. The Vietnamese Mekong Delta (VMD) is highly affected by drought and salinization threats, especially severe under the impacts of global climate change and the rapid development of an upstream hydropower dam system. This study aimed to apply a modified DRASTIC model, which combines the generic DRASTIC model with hydrological and anthropogenic factors (i.e., river catchment and land use), to examine seawater intrusion vulnerability in the soil-water-bearing layer in the Ben Tre province, located in the VMD. One hundred and fifty hand-auger samples for total dissolved solids (TDS) measurements, one of the reflected salinity parameters, were used to validate the results obtained with both the DRASTIC and modified DRASTIC models. The spatial analysis tools in the ArcGIS software (i.e., Kriging and data classification tools) were used to interpolate, classify, and map the input factors and salinization susceptibility in the study area. The results show that the vulnerability index values obtained from the DRASTIC and modified DRASTIC models were 36–128 and 55–163, respectively. The vulnerable indices increased from inland districts to coastal areas. The Ba Tri and Binh Dai districts were recorded as having very high vulnerability to salinization, while the Chau Thanh and Cho Lach districts were at a low vulnerability level. From the comparative analysis of the two models, it is obvious that the modified DRASTIC model with the inclusion of a river or canal network and agricultural practices factors enables better performance than the generic DRASTIC model. This enhancement is explained by the significant impact of anthropogenic activities on the salinization of soil water content. This study’s results can be used as scientific implications for planners and decision-makers in river catchment and land-use management practices.

Anthropic Pollution Impacts on Groundwater Vulnerability Based on Modified DRASTIC-FAHP

In arid and semi-arid regions such as Iran, groundwater is more important for humans and ecosystems than surface water. Different models of groundwater vulnerability assessment can be used to better manage water resources. The purpose of this study is to evaluate the qualitative vulnerability of groundwater resources in the Birjand Plain aquifer using the DRASTIC model and 7 hydrogeological components. DRASTIC model was also modified by adding a land use component (MDRASTIC) based on Analytical Hierarchy Process (AHP) and Fuzzy Analytic Hierarchy Process (FAHP) methods. After calculating the vulnerability index, the vulnerability of each method was mapped and the final index obtained from each method was classified into 4 different categories. Nitrate concentration was used to confirm the results and to analyze the sensitivity of a single parameter. Sensitivity analysis showed that the groundwater vulnerability is mainly affected by water depth and land use. To validate each of the models, their correlation with nitrate concentration was calculated and compared. To determine the correlation coefficient, simple linear regression method was performed and the Pearson and Spearman methods were used. According to the obtained Pearson correlation results, the DRASTIC, MDRASTIC, MDRASTIC-AHP, and MDRASTIC-FAHP models resulted in values of 0.550, 0.680, 0.778, and 0.794respectively. The results show a good correlation between the modified DRASTIC-FAHP model and nitrate concentration as an indicator of groundwater pollution.

Vulnerability Assessment of Water in Landfill Site and Environs: A Case Study of Olusosun in Lagos, Nigeria

This study assessed the vulnerability of landfill site in Olusosun, Lagos Nigeria using modified DRASTIC (DRASTIC L) model in a geographical information system environment. It also analyzed water samples with a view to determining the amount of trace metals concentrate present. Water samples were collected from different Boreholes and Wells with a radius of 500m to the landfill site. The modified DRASTIC (DRASTIC L) based on eight parameters such as Depth to water, Net recharge, Aquifer media, Soil media, Topography, Impact of vadose zone, Hydraulic conductivity and Distance to landfill site. The vulnerability index was calculated using a sum overlay of the eight parameters. ArcGIS 10.2 software was used to integrate all these parameters together to obtain Boreholes and Wells vulnerable zones I areas. The results showed that out of a total of 228.38 hectares, only about 47.46 hectare was observed to be within the low vulnerable zone having a DRASTIC index range between 113 – 136; while about 130.65 hectares were found to be in the moderately vulnerable zone with a DRASTIC index ranging between 136 and 144. About 50.28 hectares were within the high vulnerability zone having a DRASTIC index range between 144 and 163.Atomic Absorption Spectroscopy (AAS) was used for to test the concentrations of the heavy metals in the water samples collected and found that aside the presence of other heavy metals, Chromium was found to be present in most Wells and Boreholes measuring between 0.08 mg/L and 0.43 mg/L which is above the World Health Organization Standard of 0.05 mg/L for drinking water. This study concluded that the groundwater is contaminated and the level of pollution is directly related to the distance from the landfill.