There were actually a lot of the organic solvents just dumped on the ground or under-ground. And it was sald that It was okay to dump organlc solvents of thes e types on the ground because they are volatile, so they would just fly away so mewhere. Nobody cared about thesc issues in those days. When we looked at the u nderground water. however, we found out that the level of contaminants were ind eed very high. This is for thc shallow well level, and then this is for the dee p well concentration. And In case of the shallow well the concentration is high and, of course, Iower fbr the deep well. And already at this lime the semicond uctor company changed the type of solvent uscd becausc thc problern was mcntion cd, but there was still no change In the concentratlon of the shallow well. Tha t means that the organic solvent did not really decompose, but rcmained in thc soil. So they just took away the polluted soil into which the organic solvent h ad melted, and then the concentration of the shallow well went down dramaticall y.

Howevcr, if you paid attention to the deep well, concentration of the solvent i n thc dcep well water had not changed at all (see Figure 12). That means that t he organic solvcnt had gradually, very slowly, immersed itself into the lower p art of the soil, and polluted the deep well. But it was impossible to remove th e soil from the deep well level because that meant for you to take a tremendous amount of soil from the surrounding area. Trichloroethylene Is said to be carc inogenic, as proved by the anlmal testing, so it is indeed a very big problem. And solvents such as these were not considered dangerous in the past but, are n ow consid-crcci dangerous products, and we should not just dump them elsewhere.

Third, I would like to talk about the problems caused by disinfecting with chlo rine (see Figure 13). And I would like to talk about trihalomethanes, whlch hav e been proven as carcinogenic by animal experiments. In 1974, in Europe and in the United States, prob-