12-12-1987 Planning Packet - Laserfiche WebLink

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to highlight a certain portion of the outdoor living area. While the mound must be functional for sewage treatment, the location and shape should also be functional in the landscape plan. Pages 8, 9» 10 and 11 explain the design and construction procedure for a sewage treatment mound. Some design considerations are under consideration for change by the ISTS Advisory Committee. The most significant changes are with respect to using basal width rather than having a slope restriction as presented in the table on page 8. The changes to Chapter 7080 proposed for mound design are explained on pages 21 and 22. Page 12 shows a layout of perforated laterals to provide pressure distribution of effluent over the rock layer of a mound. The length of the perforated lateral is measured from the point where the effluent enters to the end cap. All connections in the pressure distribution system must be tight in order to prevent leakage and to withstand pressure. The pipe from the pump can enter at the center of the manifold system or at the end as is shown on page 15. The laterals can be connected to the manifold as shown on page 12 or with a tee-to-tee lateral construction as shown on page 14. Also as shown on page 14, there should be a perforation drilled horizontally into the end cap of the perforated lateral near the top or crown. Page 13 presents required lateral lengths and pumping rates for three perforation sizes and spacings. For example, if 1/4-inch perforations are spaced 36 inches apart, a pumping rate of 7.5 gpm is required for each 100 square feet of rock layer area. The total pumping rate for the mound designed for the four-bedroom, type I home would be 500 sq ft x 7.5 gpm/100 sq ft = 37.5 gpm. With 1/4-inch perforations spaced 36 inches apart, the maximum length that a 1-inch perforated lateral could extend would be 27 feet, the maximum length of a 1-1/4-inch lateral would be 42 feet, and the maximum length of a 1-1/2-inch lateral would be 54 feet. Using 1 inch or 1-1/4 inch diameter pipe would require that the manifold be located in the center of the rock layer. With the 1-1/2 inch size for the perforated laterals, the manifold could be located on one end as shown on page 15. On page 13 note that as the lateral diameter increases, the maximum allowable length increases. Also, as the perforation size gets smaller, the maximum allowable length increases. The required pumping capacity is greater for a perforation spacing of 30 inches than 36 inches because there are more perforations. Also, the required pumping capacity increases as the perforation diameter increases. Another technique for determining the pumping capacity required for the perforated lateral system is to determine the number of perforations and multiply by the dischar'go per perforation. Assuming a 36-inch pcrfo»-ation spacing and a rock layer that is 50 feet long, a total of 16 perforations will be required per perforated lateral. The last perforation should be placed in the end cap of each lateral. There will bo 3 laterals and a total of 48 perforations. For a residential system, the head on the perforation should be at least 1.0 foot. The table of perforation \ -iv-