Arsenic behavior in natural water and its surrounding area at the earth's surface is reviewed, and the formation mechanisms of arsenic polluted groundwater are explained. The primary arsenic is derived from deep volcanic fluids such as arsine in volcanic gases and arsenic and/or arsenite ions in hydrothermal fluids. The arsenic is moved into environmental water system by direct input from the hydrothermal fluid and by oxidation/decomposition of arsenite minerals and arsenic-bearing sulfides. The arsenic in the surface waters is deposited on the sediments after adsorbance into suspended matters and/or fixation into the microorganisms. Desorption and decomposition of arsenic-fixing materials play an important roles of desolved arsenic in the groundwater. Biological activities are also one of the roles to control the arsenic release into the groundwater.
The origins of arsenic polluted waters reported in the world are not the same, and usually two or more factors are combined in the each case. Highly arsenic containing waters appear in the naturally controlled system, however, anthropogenic factors contribute to the extention of arsenic pollution. Especially, drainage of arsenic polluted waters and highly arsenic containing materials causes to serious pollution of soils and groundwaters in the areas during long time.

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Arsenic in drinking water has become a world concern in such areas like Bangladesh and West Bengal (India). Many of the problems result from mobilization of groundwater contaminated by arsenic under natural conditions. Until recently, arsenic was often not on the list of constituents in drinking water routinely analyzed by laboratories in many countries; the presence of arsenic in drinking water was not as well known as for many other drinking-water constituents. Through the international experts' efforts on understanding the causes of the problem, some of the key factors of contamination have become consensus; such efforts include the comparison of similar arsenic groundwater problems that are found all over the world. World distribution of groundwater arsenic problems is introduced in this report according to the geochemical conditions. The United Nation's synthesis report on arsenic in drinking water has been prepared as a primer to those who tackle with the problem. In arsenic problem areas, detailed studies should be undertaken to provide a sounder basis for understanding the causes of the problem and its variation in space and time, which would be helpful to promote effective mitigation measures. Further efforts of international experts are essential, including for the development of reliable field testing method.

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The groundwater contamination by Arsenic (As) becomes a serious problem for human health in Bangladesh; having more than 0.05mg/L in As concentration in widespread areas. The Research Group for Applied Geology (RGAG) carried out hydrogeological investigations at Samta village in western Bangladesh together with the Asia Arsenic Network (AAN), Bangladeshi scientists and the villagers.
The As concentration is higher in the first aquifer where most domestic wells tap, and the As content is higher in the upper muddy layer underlain by the first aquifer in Samta. The groundwater level steeply drops down in dry season when groundwater is extensively used for irrigation.
It is possible that the As contamination is accelerated by the heavy groundwater pumpage. It is necessary to make detailed investigations in the As affected areas for establishment of groundwater management system in Bangladesh. Interdisciplinary approaches with international collaboration are also needed to combat arsenic problems to be occurred in different places in the world.

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The Lluta River, located on the northern Chile, rises in the Andes and flows into the Pacific Ocean at the southern part of Arica City. The river is very precious in this drying area for the water supply source because of the perennial flow. The river water, however, is known as high concentrations of arsenic and boron.
On the lower reaches of the Lluta River, the aquifers are composed of river deposits. The hydrogeological conditions of the area suggest that the river water is only the recharge source of the aquifers. Instead of the same origin of the water, the concentrations of arsenic and boron in the groundwater and the river water are different; arsenic is higher in the river water (0.124∼0.305mg/L) than in the groundwater (0.005∼0.045mg/L), while boron is higher in the groundwater (11.9∼27.3mWL) than in the other (10.7∼16.8mg/L).
Decrease of the arsenic concentration in the aquifer from the recharged surface water must be caused by filtering process and increase of the boron by condensation.

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The subsurface was contaminated by about 3,000l, of kerosine that percolated into the ground from a corroded subsurface pipeline in M City. Along with remediation of the contaminated groundwater mainly by pump-and-treat, investigations of lithology, groundwater flow systems, and groundwater chemistry were performed. A series of pumping tests was conducted throughout a two-year remediation period and the drawdown data were analyzed using a graphical method based on Neuman's analytical solution for pumping tests in unconfined aquifers. The analysis revealed that hydraulic conductivities and storage-related parameters were highly affected by the leakage of the kerosine, in particular during the first year after the leakage occurred. The objective of this paper is to show temporal changes in these hydrogeologic properties due to clogging of aquifer pores, which are deduced to be caused by the entrapment of liquid kerosine in pore spaces, the growth of bacterial cells, and the precipitation of inorganic solids.

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Lysimeter experiments were conducted to show relationships between the movement of water and Volatile Organohalogen Compounds (VOC) in an unsaturated zone. TCE and Bromide were used in the experiments to trace respectively the behaviors of VOC and water. Soil properties such as porosity and hydraulic conductivity were measured at eight depths. Soil water potential was measured with tensiometers, while soil water contents were obtained by a neutron soil moisture meter and TDR. Water was sprinkled from the top of the lysimeter in ten experiments. At the beginning of the first experiment, pure TCE and bromide-dated water were put at the surface of the lysimeter. Soil water and soil gas in the unsaturated zone were collected and analyzed during and after rain events. Compared the velocity of infiltrating water with that of TCE, it can be concluded that pure TCE liquid did not always move straight downward, but TCE gas moved more quickly. In addition, there was a tendency to increase TCE gas concentrations with increasing water content. It can be explained either the displacement of high gas concentration downward as a result of percolation of soil water or a desorption of TCE from soil particles.

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[in Japanese]

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