Figure 3-13. Filter grease trap.
d. Evaporation Beds. In places where clay soil prevents the use of standard
soakage pits, evaporation beds (see Figure 3-14) may be used if climate is hot and dry.
(1) Construction. Sufficient 8 by 10 feet beds are constructed to allow 3
square feet of surface area per person per day for kitchen waste and 2 square feet per
person per day for wash and bath wastes. The beds are to be spaced so that the
wastes can be distributed to any one of the beds. In the construction of a bed, the top
soil is first scraped off and piled up to form a small dike. Then the scraped earth within
the bed is spaded to a depth of 10 to 15 inches and raked into a series of rows. The
ridges are approximately 6 inches above the depression. These rows may be formed
either lengthwise or crosswise as deemed desirable for best distribution of water.
(2) Operation. In operation, one bed is flooded during one day with liquid
waste to the top of the ridges, which is equivalent to an average depth of 3 inches over
the bed. The liquid waste is then allowed to evaporate and percolate. After 3 or 4 days,
this bed is usually sufficiently dry for respading and reforming. The other beds are
flooded on successive days with the same sequence of events being followed.
(3) Sanitation. Careful attention must be given to proper rotation,
maintenance, and dosage of evaporation beds. It is also essential that the kitchen
waste be run through an efficient grease trap (para 3-7) before it is allowed to enter the
evaporation beds. If these beds are used properly, they create no insect hazard and