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FIGURE 7-3 <br /> 156 <br /> ALTERNATING TRENCH SYSTEM WITH DIVERSION VALVE <br /> Septic <br /> Tank <br /> Diversion <br /> 40 Valve <br /> • <br /> • <br /> • <br /> Q <br /> 2. In areas with severe winters, avoid areas that are kept clear <br /> of snow. Automobiles, snowmobiles, and other vehicles should <br /> not be allowed on the area. Compacted or cleared snow will <br /> . allow frost to penetrate the system, and compacted soil and <br /> loss of vegetation from traffic over the system will reduce <br /> evapotranspiration i:1 the summer. <br /> 3. Preserve as many trees as possible. Trenches may be run be- <br /> tween trees. Avoid damaging the trees during construction. <br /> Configuration: Trenches should be used wherever possible. Not only do <br /> trenches perform better than beds, but they also conform to the site <br /> more easily. Trenches do not need to be straight, but should be curved <br /> to fit the contour of the lot or to avoid trees. A multi-trench system <br /> is preferable to a single trench because of the flexibility it offers in <br /> wastewater application. <br /> On lots with insufficient area for trenches or on sites with granular <br /> soils, beds may be used. If only a sloping site exists, the bed should <br /> be constructed with long axes following the contour. However, beds <br /> should not be constructed on sites with slopes greater than 10% because <br /> the excavation becomes too deep on the upslope side. In such instances, <br /> 218 <br />