TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Method: The charcoal is used as a porous material. The volume ratio of volume of micropores of the porous material having pore size permitting the bacteria to enter into the micropores and colonize in it, to a total volume of micropores of the porous material is equal to or larger than 10 %. ACTIVITY - Soil Improver.    MECHANISM OF ACTION - None given.    EXAMPLE - A soil percolation technique to control groundwater pollution were as follows: Artificial microhabitats containing enriched simazine-degrading bacteria were applied to soil at a golf course continuously using simazine, and the ground water pollution-controlling functions of the artificial microhabitats were compared using artificial microhabitats with or without enrichments of simazine-degrading bacteria. The conditions of the experiments were as follows: Standard product of simazine was tested. Soil of a golf course continuously using simazine, sieved to soil material having a size of 2 mm or less. Chitosan-treated charcoal formed by normally baking a wood of broad-leaved tree and fragmenting to pieces of 5-10 mm, in which enrichment of the simazine-decomposing bacteria was carried. Charcoal formed by normally baking a wood of broad-leaved tree and fragmenting to pieces of 5-10 mm, in which the simazine-decomposing bacteria were enriched. Mixing ratio of artificial microhabitats to the soil to be tested. Inorganic salt medium containing only 5 mg/l of simazine as carbon and nitrogen sources was used. The above experimental conditions substantially realize conditions under which agricultural chemicals were regularly sprayed in golf courses at time intervals of several days. The results showed changes in the concentrations of simazine, Cl- and NO3- in the circulating solutions in the experiments concerning the respective artificial microhabitats. When attention was paid to the simazine concentration, this showed that in the artificial microhabitat with enrichments of simazine-decomposing bacteria, simazine was nearly completely decomposed or degraded in about a week after the experiment started, while the artificial microhabitat without enrichments of decomposing bacteria as a comparative example, decomposition or degradation of simazine does hardly proceed even after 3 weeks. The same applied to the artificial microhabitat with enrichments of decomposing bacteria and the artificial microhabitat without enrichments of decomposing bacteria. From these findings, it was understood that by burying artificial microhabitats with enrichments of decomposing bacteria in soil for the emergence of decomposing activities of the bacteria, groundwater was prevented from being contaminated by agricultural chemicals.