Hydrogeology

Geochemical Assessment of the Evolution of Groundwater under the Impact of Seawater Intrusion in the Mannar District of Sri Lanka.

2023-01-01T00:00:00Z

Geochemical Assessment of the Evolution of Groundwater under the Impact of Seawater Intrusion in the Mannar District of Sri Lanka. Athauda, S.; Wang, Y.; Hao, Z.; Indika, S.; Yapabandara, I.; Weragoda, S.K.; Liu, J.; Wei, Y. Groundwater is an important drinking water resource in the coastal regions of island countries and has suffered from heavy seawater intrusion. However, the areas specifically affected by seawater intrusion and their groundwater hydrogeochemical compositions and evolution processes remain unclear. This study analyzed the hydrogeochemical compositions, water quality, and evolution processes of groundwater in the Mannar district, Sri Lanka, during the dry season. A total of 56 samples were collected from shallow wells and tube wells across the region, and about 64.28% of groundwater samples had good quality (WQI< 100). Geochemical compositions and water quality parameters had a high level in the north and south mainland regions, where they severely suffered from seawater intrusion with a high content of Cl− and Na+. The geochemical compositions of groundwater in the Mannar district were predominantly affected by rock weathering and/or evaporation processes. Cl-Na and HCO 3-Ca facies were the main hydrochemical types, and the corresponding ions were mainly from silicate and halite dissolution. The reverse cation exchange process mainly occurred in seawater intrusion areas. The study highlights the impacts of seawater intrusion on the hydrogeochemical compositions and evolution processes in Mannar region groundwater, which will enhance the understanding of the local water quality and seawater intrusion situation and aid in protecting drinking water safety by routinely monitoring the groundwater quality and implementing targeted desalination techniques in the key areas.

Hydrocarbon Prospectivity of Shallow Water Areas in the Northern Mannar Basin, Offshore Sri Lanka .

2014-01-01T00:00:00Z

Hydrocarbon Prospectivity of Shallow Water Areas in the Northern Mannar Basin, Offshore Sri Lanka . Upul Premarathne; Noriyuki Suzuki The Gulf of Mannar is located between the southeastern coastline of India and the western coastline of Sri Lanka. It is a failed rift associated with the breakup of East Gondwana. The Sri Lankan jurisdiction of the Gulf of Mannar is frequently referred to as the Mannar Basin, which extends over 45, 000km2 in shallow to ultra deep-water setting. Shallow water areas of the northern Mannar basin, which is the southern extension of the adjoining Cauvery Basin, extend over 3,000 km2. Pearl-1 has been the only exploration well drilled in the shallow water areas of the northern Mannar Basin. It has penetrated around 2,902m thick Recent to Late Cretaceous (Maastrichtian-Late Turonian?) sediments overlain by an igneous rock. Gulf of Mannar has a wider distribution of igneous rocks interbedded with Late Cretaceous sediments. The Pearl-1 well has not penetrated the synrift sediments underneath the igneous rock. Except for a few thin stratigraphic sections, which have total organic carbon (TOC) ranging from 0.5% to 1.0%, most sediments penetrated by the Pearl-1 well has less than 0.5% TOC indicating poor source potential. Organic matter in these sediments is predominantly composed of type III kerogen. Paleogene and Late Cretaceous claystones with relatively high TOC have hydrogen index values ranging 50-100 mg HC/g TOC, which indicates gas potential. Tmax for a claystone at 2,920m yield 454 oC showing the sediment to have been in the oil window for type III kerogen. Accordingly, the Production Index (PI) for this sediment yield 0.43%, which indicates the generation and expulsion of hydrocarbons. However, the stratigraphic section of the Pearl-1 well does not have sufficiently thick organic-rich sediments to produce economically viable hydrocarbon deposits. The shallow water area of the Mannar Basin has had higher heat flows in the past. As per the current geothermal gradient, source kitchen in this area should lie in Early Cretaceous synrift sediments. Synrift claystone penetrated by wells drilled in the deepwater Mannar Basin as well as in the adjacent Cauvery basin are relatively rich in organic carbon compared to postrift sediments. The Thermal and burial history of the area suggests that the northern Mannar basin could have two phases of economically significant hydrocarbon generation, which is associated with the juxtaposition of Reunion hotspot during the Late Paleocene and the Early Eocene and rapid burial during the Neogene period. Pearl-1 well has penetrated around 900m thick reservoir quality sandstone deposited in bathyal to outer bathyal environments. In addition, the Paleogene section has clastic and carbonate potential reservoir rocks interbedded with fine-grained sediments, which could act as potential seals. Seismic data show the Mannar basin to have multiple play types including stratigraphic pinchouts, rotated fault blocks and anticlinal traps. Fault systems could provide sample pathways for vertical hydrocarbon migration. Therefore, the probability of finding hydrocarbon deposits in Late Cretaceous and Paleogene sections in the shallow water areas of the northern Mannar basin could be relatively high.

Hydrogeochemical characterization of Jaffna’s aquifer systems in Sri Lanka.

2013-01-01T00:00:00Z

Hydrogeochemical characterization of Jaffna’s aquifer systems in Sri Lanka. Thushyanthy, M.; Vithanage, M.; Pathmarajah, S.; Arasalingam, S.; Ariyaratne, R.; Manthrithilake, H.

Preliminary study on geochemical classification of groundwater: A case study from water supply wells

2009-01-01T00:00:00Z

Preliminary study on geochemical classification of groundwater: A case study from water supply wells Barathithasan, T.; Thushyanthy, M.; Saravanan, S.; Carmelita Nishanthiny, S. Regional classification of groundwater has useful applications in agriculture, ecology and human health investigations. It is important for the development of civilization and to establish database for planning future water resources development strategies. The hydro chemical study reveals quality of water that is suitable for drinking, agriculture. Presence of excessive quantities of sodium and chloride in groundwater are one of the major constrains in agriculture. Groundwater prospecting techniques and investigations are directed mainly at locating groundwater resources and also at understanding the formations of ground water systems with respect to the environment in which it occurs. The aim of the study was to present the detailed chemical facies of groundwater of water supply wells. The chemical quality of groundwater is related to the geology of the area. Major cations; Na", Ca, Mg",K", and Fe" and major anions; CSO, HCO, CO,, and NO were determined for nine water supply wells from October 2008 to January 2009 based on the Sri Lankan standard. The results of these analyses were plotted on piper diagram. Water samples were grouped into two major types, namely Ca and Na types. The results revealed that Chunnakam, Nilawari and Allappiddi water samples fall into Ca - HCO, type which is due to the influence of calcium carbonate rock. The water supply well at Valveddithurai, Puttur, and Velanai fall into Ca-Cl type and the Karavedddy, Arali and Vaddukkodai water samples fall into Na - CI type water. Sodium and Calcium are the major cations in groundwater. The groundwater from central part of Jaffna peninsula; Chunnakam and Nilawarai shows high bicarbonate water. Wells near the shore-lines areas, Valveddithurai, Arali, Velanai and Allappiddi, the quality changes to the chloride type due to sea water intrusion. However, some supply wells at Karaveddy, Vaddukoddai, and Puttur also shows higher chloride contents which could be due to mixture of recharging water and salt water up corning.