12-12-1987 Planning Packet - Laserfiche WebLink

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T%bie 1. Soil characteristics and required areas for sewage treatment Percolation rate, minutes per inch Soil texture Soil treatment area in square feet per gallon of waste per day^ Table 2. Estimated sewage flows in gallons per day Faster than 0.1^ 0.1 to 5 6 to 15 16 to 30 31 to 45 46 to 60 Slower than 60^ Coarse sand Sand Sandy loam Loam Silt loam Clay loam Clay Soil too coarse for sewage treatment^^ 0.83 1.27 1.67 2.00 2.20 Use sewage treatment mounds or alternative systems ^For uenches only, the bottom areas may be reduced if more than 6 inches of rock is placed below the distribution pipe: for 12 inches of rock below the distribution pipe the bottom areas can be reduced by 20 percent: a 34 percent reduction for 18 inches: and a 40 percent re* duct ion for 24 inches, ^Soil is unsuitable for standard soil treatment units. Use sewage treatment mounds ot alterno' tive systems. Number of bedrooms Type of residence® 1 II III IV 2 300 225 180 60% 3 450 300 218 of 4 600 375 256 values 5 750 450 294 in 6 900 525 332 Type I.* 7 1,050 600 370 11, or III 8 1,200 675 408 Columns The estimated percolation rate is used to determine the absorption area (table 1) and the estimated sewage flow rate of the residence is determined from table 2. While soil texture is not an absolute indicator of the pcrcola* tion rate, it can provide helpful prelim inary information. The "feel method" is commonly used to evaluate soil tex ture which should be evaluated every 12 inches on a site or whenever the tex ture changes noticeably to the touch. The first soil boring conducted on this lot indicated mottling at a 12 inen depth (figure 4). Alternative waste treatment site 1 was rejected on the basis of a high water table although at the time of the boring there was no water apparent in the hole. Soil boring 2 was made in the center of alternative waste treatment site 2. Thdre was no indication of soil mot tling to a depth of more than 5 feet. Soil texture was estimated using the "feel method." The texture was a loam at the depth of the proposed system. On this basis the percolation rate was estimated at from 16 to 30 minutes per inch (mpi) (table 1). U ing Toivn and Country Sewjge Treatment, Extension Bulletin 304 as a reference, a soil with a percolation rate in the 1C> to 30 mpi range would require 1.67 'iquare feet of trench bot tom area per gallon of waste per day (table 1). However, if 12 inches of rock are placed under the distribution pipe in the trench, a recommendation where trees are present or likely to be present, the bottom area can be reduced by 20 percent to 1.34 square feet per gallon per day. Since a four bedroom, type I house was being installed on the lot. the estimated sewage flow was 600 gal lons per day which required 600x 1.34 =* 800 square feet of trench bottom area (table 2). The trenches were 30 in ches wide, so a total of 320 lineal feat was required. This could be accom plished with four 80-foot runs. The trenches were to be spaced approxi mately 8 feet on centers with total width required of approximately 32 feet. ^Type I: The total floor area of the residence divided by the number of bedrooms is more than 300 square feet per bedroom: no more than two of the following water use appti* ances are installed: automatic washer, dish* washer, water softener, garbage disposal or self-cleaning humidifier in furnace. Type II: More than 500square feet of total residence floor area per bedroom and no more than two of the water-use appliances. Type III: Less than 500square feet of total residence floor area per bedroom and no more than two of the water-use appliances. Type IV* Type I, II, or III but with no toilet wastes discharged into the sewage system. Figure 4. Final location of improvcinentsafter che site has been properly evaluated. l