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Equation No. 6 (0.436 in/day) x (1 ft/12 in) x (7.48 gal/ft ) = 0.272 gpd/ft2 To determine the required filter bed area, first the daily household flow needs to be stated. The following flow is to be used for the project: Design Flow Rate 4 bedroom residence: 500 gallons per day The filter bed area is found by dividing the design flow rate by the sewage loading rate. Calculated Filter Bed Area For 4 bedroom: 500 gpd / 0.272 gp6j/ft2 = 1838 ft2 (about 42 ft x 42 ft) Factor of Safety 1838 ft2 x 1.5 = 2757 ft2 (about 53 ft x 53 ft) A factor of safety of an additional 50 percent (1.5) was added to insure spill-over protection. Extra disposal capacity in the system is required to absorb the flow from occasional periods of heavy rain combined with the lower pan evaporation rates (later converted to evapotranspiration rates). Essential Design Requirements: The following items are important to the performance of the ETA Septic Systems. Some of the items have been cited directly or modified from Otis and Boyle(1980) and San Joaquin County (1996). The filter bed can be either a square shape or rectangular shape, or several smaller beds connected in series or parallel. 1) The septic tank capacity shall be composed of one 1600 gallon septic tank. A lift station will be required to pump the wastewater into the filter bed. 2) See the engineered septic system drawing for thickness of filter material (sand). 3) The bed bottom should be level to promote even loading. Great care should be made during excavation to remove smearing of clay. The entire site was found to be composed of clayey type soils. The final cleaning and preparation of the bed should occur when the clay has dried to a point where further smearing will not occur during cleaning. The percolation capacity of the clayey soil is a significant factor and was incorporated in the design of the system. An inspection of the cleaned native soils is required by our office. —Calculations,Page 3—