Applying the theory of log-normal-probability distribution, we obtained the theoretical equation showing the relationship between alA and D as listed in Eq. (3), and we referred to this equation as the depth-area-curve equation. We also used Eq. (6), Eq. (7) and Eq. (8) to calculate the values of Dmode, Dmedian and Dmean, respectively. The values calculated by the theoretical equation were compared with the values observed. The results were as follows;
1) The deviation of the theoretical values of Dmode from the observed ones (that were calculated by Eq. (9)) was 41.5% at the maximum value and 1.6% at the minimum one.
2) The theoretical values of a/A at Dmode agreed closely in practice with the values observed.
3) For the values of Dmedian, the theoretical values agreed well with the values observed.
From these results, we concluded that we would be able to use the theoretical equations obtained here to estimate the depth-area curve or the relationship between the water-table depth and its corresponding area, Dmode. Dmedian and Dmean for a given region for a given period. References

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The utilization of natural tritium plays the most important role in surveying large areas for the development of groundwater resources.
The flow velocity and flow distribution of the groundwater in a large water system could not be directly calculated by other methods in the past.
In the study reported here, bomb-produced tritium was used as a tracer to estimate mean groundwater velocities by the distance of seepage from the groundwater recharge zone.
At present, the concentration of natural tritium is obtained by the following: 10 1-groundwater in the deep layer intercepted from the shallow water by clay layer is concentrated into one-hundreds ml by 2-step electrolysis after distillation its tritium concentration is measured by the liquid scintillation spectrometer.
The tritium unit (T. U. ) of the groundwater in the Kanto plain showed 2 to 406 T. U.
Natural tritium content of levels is less than 5 T. U. Therefore, the 1954 front are estimated to have moved 40 km along the basin of the River Tone and 48 km along the basin of the River Kinu. The groundwater velocities were computed 9 mid and 11 mfel respectively. It was clarified that the deep groundwater in the Kanto Plain is strongly followed by the geological structure of the Kanto structural basin and flow out towards the Tokyo Bay according to the past results.

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(1) The nature of the ground around Dangyo Mineral Waters is composed of the rhyolitic tuff and dacitic tuff of the volcanic activitiy in cretaceous period.
(2) Powerful mineral waters in this area gush out from the intersecting point between the joint in NE side and the one in NW side of pyroclastic rock mass.
Mineral Waters contain a large quantity of CO₂ gas, and rgister 14-15°C in the temperature.
(3) Electric resistivities in this area was indicative of 450∼5 Ω-m.
(4) γrays in the soil in this area was indicative of 350∼820 CPM. The soils which lie at the depth of 0.4 meters in the point indicating the highestγrays intensity, are analysed by theγrays spectrometer concerning theirγrays energy. From the result of analysis, the presence of U or Th system radioactive nuclide and K⁴⁰can be inferred.
(5) From the result of aquifer test of the well, transmissibility coefficient was indicative of 2.108×10^-5m²/sec.

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