n with planning SELECTION OF SITE AND SYSTEM the location of the house which these units will serve. Many home- owners have paid dearly for neglecting the planning of their liquid waste disposal system while planning and building their house. For example, a common practice is to bring the sewer pipe out from the house under the foundation. This may be because the pipes from various appliances have been "stacked" beneath the floor, necessitating a deep "stub-out," or because it just seemed easier to do (Figure 3.17). The deeper this main sewer pipe is, the deeper the septic tank must be. And the deeper the septic tank is, the deeper the drain field must be. This means that more cubic yards of dirt must be excavated, and that encroachment on ground water or bedrock may occur. In turn, such encroachment may be legally prohibited, requiring the use of an expensive alternative system. Another common practice is locating the house on a rise and the drain field in a depression. Rainwater from the house roof and surrounding land can accumulate in the depression, overload the field area, and result in a mess in the yard, a health problem, or an "inconvenience" in the bathroom. There are several general principles which should be observed when planning the location of the liquid waste system: 1. Utilize any slope, placing the septic tank downhill from the house and the drain field downslope from the septic tank. This keeps the drain field shallow, promotes evapotranspiration, utilizes the more favorable soil layers, eliminates the need for a pump to lift the effluent to the drain field, and minimizes cost. If there is a water well on the property, the drain field should be placed downhill from it. Ground water often, but not always, flows in the same general direction as would water on the surface. Only a geohydrologist could tell for sure. 2. Locate absorption trenches parallel to land contours. This allows trenches of equal depth and minimizes the chance of over- loading the trenches at the downhill end. 3. Avoid placing