Land use impact on groundwater quality and 2D resistivity Applications
Faculty of Science, Kasetsart University

Groundwater quality could be impacted from various local land uses and human activities. Case studies of different land uses which play significant effect on groundwater quality, may be classified into three types at different regions of Thailand i.e. agricultural activity at the western part, industrial estate site at the eastern part and mining region at the central-northern part of Thailand. Resistivity imaging approach was introduced to investigate subsurface geology and geo-hydrology aspects.. This technique can help to illustrate groundwater system and contaminated groundwater management.

Case of agricultural area, Kanchanaburi and Suphanburi Provinces (located in the west of Thailand). The hydro-geological features of this region are mainly fracture in hard rock aquifer and unconfined (shallow) alluvium aquifer. Due to overusing fertilizer and agriculture chemical substances in vegetable plantation areas, high nitrate content are widely found in groundwater –shallow aquifer (exceed standard). The study of chemical parameters and heavy metals pollutant in soil and groundwater at the specific example area of Tambon Dan Makham Tia, Amphoe Dan Makham Tia, Kanchanaburi Province was performed where agricultural activities arranged for asparagus field. The result show amount of arsenic was found at 6.3-17.0 mg/kg (exceed the standard of 3.9 mg/kg). High content of nitrate (49-159 mg/l -exceed the standard) was found in 8 shallow wells (from 30 wells). 2D resistivity imaging was applied to identify groundwater system and aquifer characteristics (colluviums and Permian Carboniferous meta-sediment bedrock aquifer)

Case of Industrial (and agriculture) land use of Rayong and Chonburi provinces located in the eastern part of Thailand. Topography the area appears as mountains and coastal plains close to the Gulf of Thailand. To study the quality of groundwater and soil, aquifer contamination risk assessment can be done from selected 20 severe contamination sources i.e. waste collection sites and landfills, gas station and industrial estate sites. 25 parameters were used to identify the quality of groundwater including volatile organic compounds (VOCs) and heavy metals. The result shows parameter of groundwater quality from at least 10 selected sites exceed the standard. Laem Chabang sanitary landfill of Chonburi province is an example site that found total Fe, Mn, As, Pb, Se, Hg in groundwater. The hydro-geological setting of this area consisted of weathering granite and clay. The site is located in the area of Huay Sapan and Nhong Klang Dong reservoir. There is a brook, Huay Klabok, flow through this area. The groundwater model shows the contamination from landfill to the north-westward where the local villages (Baan Nern Sai and Baan Nern Krabok) are suggested to be a sensitive area. 2D resistivity imaging was conducted cross landfill. The result shows low resistivity zone that may present leaking portion from landfill into groundwater system.

Case of gypsum mining of Nakhon Sawan - Phichit Gypsum deposit region at central- northern part where there are more than 45 gypsum mines including abandoned mines and mining license areas. Due to open pit gypsum mining activities, surface water and groundwater were contaminated from dissolved gypsum ore. The quality of enclosed surface water and groundwater effected as high hardness > 2000 mg/l or high conductivity > 2000 μs. Calcium. 2D resistivity and IP measurements imaging techniques were conducted at known subsurface geological ore deposit feature and contaminated groundwater boundary which can manage groundwater for community and agriculture uses in the future.
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