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Page 19 <br /> land. The entire system is watertight, reducing costs from infiltration; both conveyance and treatment facility. No <br /> manholes or lift stations are required and energy consumption is minimal. <br /> Figure 1.Typical STEP system components. <br /> Relatively small diameter PVC pipe, usually Class 200, is laid with the contour of the terrain in the same manner <br /> as a water line. Heat fused high density polyethylene with directional boring is the preferred material in some <br /> existing communities with existing utilities. <br /> An effluent sewer main line will be smaller than its corresponding water main because the peak demands are <br /> much lower. Effluent sewers generally receive only 80 percent of the daily water usage and are not required to <br /> satisfy fire and peak domestic flows. The storage reserve in the septic tanks provides sufficient buffering <br /> capacity eliminating any concern for rushing the effluent away in large doses or flow rates. The use of small <br /> diameter lines is also benefited by the fact that the effluent is substantially free of solids eliminating concerns for <br /> a minimum velocity, and the lines are free of infiltration and inflow. <br /> Excavation and installation of the main lines are areas where saving in system costs is great. In normal <br /> installations install main lines at shallow depth, usually 30 inches below original grade. In colder climates bury <br /> main lines below frost depth or insulate to prevent freeze damage. Strict vertical and horizontal alignment is <br /> unnecessary; mains are laid quickly,without tedious surveying and 901 bends,are no problem. In septic tank <br /> effluent pump(STEP)systems manholes or standard cleanouts are not necessary. Pigging ports and pigging <br /> equipment facilitate line cleaning in the same manner as water lines. To date only one STEP system on the <br /> West Coast has ever required cleaning and that was the result of improper tankage design. <br /> EDUs Qaa,Rpm Pipe Sizeb,inches Head Loss°, ft/1000 ft <br /> 10 20 11/4 35+ <br /> 100 65 2 54± <br /> 500 265 4 32± <br /> 1,000 515 6 17± <br /> a.Assumed D of 15 per EPA Manual of Practice(MOP FD-12) <br /> b.Nominal diameter. <br /> c.Head loss is based on C=150 and the inside diameter of class 200 PVC pipe. <br /> Figure 2. Head loss calculations for various STEP force-mains. <br />