The estimation of spring water discharge is of great importance from the viewpoint of using water resources. Although a number of estimation techniques have been proposed, a simple and reliable method is not yet established. The authors have developed a numerical simulator based on the nonlinear two-hole tank model. The simulator is drived by an optimizer, with which the influencing parameters are systematically searched so that the discrepancy between the measured and calculated discharge is minimized. With this procedure, reliable simulation results can be obtained. The simulator is applied to Ubako hot spring at Hakone volcano. The results showed good agreement with the measured data, in that the discharge of the hot spring is strongly influenced by precipitation, including the fact that it dries up in winter. The authors have also investigated the dynamic characteristics of the hot spring under artificial precipitation. Through various precipitation data, the nonlinear characteristics of the model are made clear.

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We studied changes in water chemistry along the groundwater flow path in the Matsumoto tunnel vicinity and estimated the origin of the groundwater and dissolued substances. The relationship between the concentration of HCO₃^-, Ca²⁺, and Na⁺, and the CO₂ gas pressure in the groundwater indicated that the HCO₃^-, Ca²⁺, and Na⁺ were produced by reaction of the CO₂ gas in the groundwater and feldspar in the rocks. The relationship between the concentration of NO₃^- and the Eh and pH values in the groundwater indicated that in an oxidative condition, some bacteria used NH₄⁺ and produced NO₃^- and H⁺ and in a reductive condition, other bacteria used NO₃^- and produced N₂ gas and OH^-. The stable hydrogen and oxygen isotopic ratios in the groundwater and precipitation indicated that the groundwater originated from precipitation fell on the area. The concentration of ³H and the stable hydrogen and oxygen isotopic ratios in the groundwater suggested that it was getting warmer for more than 60 years. The stable carbon isotopic ratio indicated that the HCO₃^- in the groundwater originated from CO₂ gas produced by organic matter in the soil except in the deep well water. The deep well water, which had a higher concentration of HCO₃^- than the other groundwater sampled was thought to have acquired HCO₃^- through contact with rocks. The stable sulfur isotopic ratio indicated that the SO₄^2- in the groundwater was of the same origin.

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A mathematical model has been presented for simulating heat transfer in a hot dry rock with a complex-shaped fracture network. In this model, the energy equation in the fracture is expressed in terms of the finite difference approach and the matrix is expressed in terms of the finite element approach. From the results calculated by this model the following conclusions are obtained: 1. The model is valid to the simulation of fluid flow and heat transfer in the complex-shaped fracture network.2. The shape of fracture network, the number of fractures and the injection rate of water into an injection well affect both the temperature of fluid from a production well and the cumulative recovery factor of heat from the hot dry rock.3. The injection rate of water may have to be determined by considering both the period of heat recovery and the available temperature of production fluid. Key words: hot dry rock, fracture network, heat transfer, finite difference approach, finite element approach

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In this paper, we describe an experimental study for the efficiency and aging of well. It is well known that the drawdown in well increases gradually and the efficiency of well is decreases over a long period of time due to pumping. This phenomenon is so-called aging of well. But, in the past, there have been very few reports on the estimation or explanation of the mechanism involved in the aging of well by pumping.
The authors have proposed an equation for the calculation of well loss. We applied this equation to field test data and obtained satisfactory results. If we can determine the relationship among the water levels inside and just outside well by pumping, the amount of discharge and the opening ratio of well screen, we can analyze the mechanism involved in the aging of well and then evaluate the degree of the aging.
In prsent report, we obtained an empirical equation for the relation described above. This experimental equation was applied to field test data and sand model test data over a long period of time (one-half year ). As the results, it was found that we can estimate the degree of the aging of well.

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In order to model the transport of fertilizer components from soil surface to groundwater in farm land, a preliminary experiment, in which a KCl solution was infiltrated through undisturbed soil columns, was carried out and cation exchange capacity (CEC) and selectivity coefficients (K_Ca/M, M: Na⁺, K⁺, Mg²⁺ ) were determined.
The soil columns consisted of two kinds of soils: a top layer of soil containing organic material and a lower layer of decomposed granite soils. The CEC values of the two soil layers were5-20 and3-7 meq/100g of dry soil, respectively. In the columns, the exchange reaction of Ca²⁺ with K⁺ was dominant. The K_Ca/K was approximated as a function of the adsorbed potassium molar fraction, whereas the K_Ca/Mg, was constant at about 1.2.

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