[The scientific collaboration on a hydrogeological mapping project between the Geological Survey of Italy (ISPRA) and the China Geological Survey]

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Geochemical characterization of groundwater and saltwater intrusion processes along the Luy River, Binh Thuan, Vietnam

<p>KEYWORDS: Saltwater intrusion, Geochemistry, Groundwater extraction  </p><p>ABSTRACT: With an average annual rainfall of 800-1150 mm/year, the Binh Thuan province is one of the driest places in Vietnam. The quantity and quality of groundwater play a significant role in the agriculture, aquaculture development and daily life of the local communities. In 2012, the national center for water resources (Nawapi, 2012) delineated the seawater intrusion extent in Binh Thuan based on the total dissolved solids (TDS) content of water samples taken from shallow boreholes. The threshold of 3g/L and 1.5g/L were exceeded in the estuaries of the Luy, Long Song and Ca Ty rivers. In recent years, the prolonged droughts combined with the sea level rise and the over-extraction of groundwater during the dry season increased dramatically the seawater intrusion process especially in the estuaries of the province.</p><p>The geochemistry of groundwater in the Luy River catchment was studied to investigate the contamination of the aquifers and identify the processes taking place. From 1991 to 2015, 98 water samples had been taken from the wells in the area in both dry and rainy seasons. 71% of the water samples were fresh while 21% and 5% were lightly saline and moderately saline respectively. In summer 2020, 110 new water samples from both shallow and deep wells were collected in the Luy river catchment in wells from 3m to 40m. The TDS values are ranging from 105 to 23080 mg/L and can be classified into 4 groups: freshwater (48%), slightly saline (40%), moderately saline (8%) and very saline (4%). The samples show that the seawater intrusion expands not only horizontally at shallow depth along the river but also deeper down the aquifer in most of the study area, what is also confirmed by geophysical data. Freshwater samples were mostly collected at a depth lower than 10m. The chemical composition of water samples were analyzed showing evidence of seawater intrusion, but also the occurrence of freshening processes within the study area. Together with the presence of saltwater at larger depths, this points towards a situation more complex than previously thought. Saltwater intrusions are likely not only related to interaction with the river estuary, but also to the presence of fossil saltwater in the aquifer, and to groundwater pumping and irrigation practices.</p><p>REFERENCES</p><p>NAWAPI. 2012. Hydrogeological mapping at scale 1:50000 in Ninh Thuan and Binh Thuan provinces. In Vietnamese. </p><p> </p><p>*Corresponding Author. Email: [email protected]</p>

The Applicability of an Inverse Schlumberger Array for Near-Surface Targets in Shallow Water Environments

We investigate the applicability of offshore geoelectrical profiling in the littoral zone, e.g., for archaeological prospection, sediment classification and investigations on coastal ground water upwelling. We performed field measurements with a 20 m long multi-electrode streamer in inverse Schlumberger configuration, which we used to statistically evaluate measurement uncertainty and the reproducibility of offshore electric resistivity tomography. We compared floating and submerged electrodes, as well as stationary and towed measurements. We found out that apparent resistivity values can be determined with an accuracy of 1% to 5% (1σ) depending on the measurement setup under field conditions. Based on these values and focusing on typical meter-scale targets, we used synthetic resistivity models to theoretically investigate the tomographic resolution and depth penetration achievable near-beach underneath a column of brackish water of about 1 m depth. From the analysis, we conclude that offshore geoelectric sounding allows the mapping of archaeological stone settings. The material differentiation of low-porosity rock masses < 15% is critical. Submerged wooden objects show a significant resistivity contrast to sand and rocks. Distinguishing brine-saturated sandy sediments from cohesive silty-clayey sediments is difficult due to their equal or reversed resistivity contrasts. Submarine freshwater discharges in sandy aquifers can be localized well, though difficulties may occur if the seafloor encounters massive low-porosity rock masses. As to the measurement setups, submerged and floating electrodes differ in their spatial resolution. Whereas stone settings of 0.5 to 1 m can still be located with submerged electrodes within the uppermost 4 m underneath the seafloor, they have to be >2 m if floating electrodes are used. Therefore, we recommend using submerged electrodes, especially in archaeological prospection. Littoral geological and hydrogeological mapping is also feasible with floating electrodes in a more time-saving way.

Faecal contamination in groundwater and its association with population density: a study in coastal areas of Semarang

Increased population density causes the supply of clean water to be unable to meet the requirements. The coastal area of Semarang is also faced with a tidal problem. While good sanitation is a top priority in improving health, nutrition and productivity (6th SDG target), the cause of water borne disease must be considered. This research was conducted in May 2019 at 30 points in the coastal area of Semarang, covering 9 sub-districts. Assessment of microbiology is carried out on coliform parameters and the presence of Eschericia coli. Data on septic tank type, depth, distance of the septic tank to the sample points and drainage frequency were collected. Population data are based on data from BPS. Hydrogeological mapping was used to describe the distribution of faecal contamination and other factors. Around 73.3% of the groundwater samples exceeded the coliform parameter limit and 86.7% of the samples were found to have E. coli. Only 37.5% of the septic tank is cemented and 66.7% with a safe distance from the water source. Population density was not significantly related to poor groundwater quality, because even though the area is less densely populated, E. coli is found positive in ground water.

The hydrogeological mapping of the southwestern part of Serang Regency, Banten, Indonesia

The development of Serang City as the central government of Banten Province leads to persistently increasing demand for clean water in the area and its surroundings. This study aimed to perform the hydrogeological mapping of the southwestern part of Serang Regency. The study area covered four districts, namely Baros, Padarincang, Paburuan, and Ciomas. These four districts are the clean water source of Serang City that also functions as a buffer zone designed for the development of freshwater fishery and wetland agriculture. Hydrogeological mapping in the study area is expected to be one of the inputs in planning the use of water resources. The method used in this research included analyses of drill data, geophysical measurement results, the findings of previous studies, hydrological map scale 1:250000, and geological map scale 1:100000, as well as geomorphological mapping and field survey. This research produced six classes of hydrogeological units that covered areas with scarce groundwater productivity up to those with high groundwater productivity.