Dig a hole 1-foot square and to the depth at which the tile is to be laid. This depth in most instances will be about 24 inches and should not exceed 36 inches. Fill the hole with water to a depth of 6 inches and observe the time required for the water to seep away; divide by 6 to get the average time for the water to fall 1 inch. The test should be repeated at three or four different points in the disposal field and the average time noted for all tests used. The data in table 1 can then be used to determine the number of tiles needed. Where 1 hour is required for the water to fall 1 inch the soil is totally unsuitable, and another site should be selected. Soil conditions at the time of the test may vary from year-round average conditions, and this factor must be taken into account. If the soil appears exceptionally dry, greater depths of water may be used or the test repeated in the same hole. In no case should tests be made in filled or frozen ground. Where fissured rock formations are encountered, advice should be sought from sanitation specialists. Table 1.--_Determining tile-disposal field requirements from percolation tests_[6] ------------+----------------------++------------+--------------------- Minutes | Effective absorption|| Minutes | Effective absorption required | area required, per || required | area required, per for water to| person, in bottom ||for water to| person, in bottom fall 1 inch | of disposal trenches ||fall 1 inch | of disposal trenches ------------+----------------------++------------+--------------------- | _Square feet_ || | _Square feet_ | || | 2 or less | 26 || 10 | 52 | 30 || 15 | 63 | 36 || 30 | 90 | 40 || 60[7] | 120 ------------+----------------------++------------+--------------------- [6] A minimum of 150 square feet should be provided, equal to 100 feet of 18-inch trench. [7] If more than 60 minutes, use special design with seepage pits or sand-filter trenches. Figure 9 suggests methods of arranging the tiles in disposal fields under varying conditions and the length of tiles needed. [Illustration: Figure 9.--Arrangements for tile-disposal fields, method of laying tile, and length of tiles needed.]