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Groundwater level lowering in the North China Plain (NCP) has been developing during past several decades by overuse in populated cities and industrial districts as well as by irrigation. To interpret groundwater level lowering in terms of aquifer-bearing beds having relatively high porosity, contour maps and cross sections of water level lowering based on monitoring data are compared with subsurface Quaternary geologic map. The comparison revealed that the extents of productive shallow and deep aquifers are generally restricted in specifi c regions where sand and gravel occur in lenticular form. The groundwater resources are regarded as fossil resource because groundwater of deep aquifer is dated as older than 10,000 years BP. Therefore, if overproduction of groundwater continues at the same rate as at present, it should result in depletion or severe lowering of water level and induce ground subsidence and water quality deterioration. To overcome the problems, effective use of irrigation and recycling of used water from industrial and domestic uses by water purifi cation are essential.

Abstact:In east Asia, where significant economical growth in this century is expected, intensive installation of geothermal heat pump (GHP) system may be important from both energy security and environmental protection aspects. Detailed underground temperature survey is essential for its promotion. Possibility of geothermal heat-pump application in tropical Asia is studied based on groundwater temperature data. Although generally geothermal heat-pump system may not have thermal merit for space cooling in tropics because subsurface temperature is generally higher than average atmospheric temperature, there may be some places in tropical regions where underground can be used as "cold heat-source". In order to confirm this possibility, groundwater temperature surveys were widely conducted in the Chao-Phraya plain, Thailand and Red-river plain, Vietnam to compare with atmospheric temperature data. As a result, regional variation of subsurface temperature at depths from 20 to 50 m of 3.4 K was observed in the whole Chao-Phraya plain while that of 2.0 K was observed in the Red-river plain. In some cities, subsurface temperature lower than monthly mean maximum atmospheric temperature for 5 K or more over four months was identified. Thus underground may be used as cold heat-source even in parts of tropical regions.

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