f hose at 10 pounds per square inch (23 ft) of head. Be aware that because of the small openings, you will have to filter the effluent before pumping it into the trickle system to limit plug- ging of the openings. You will most likely have to disinfect the effluent as well to prevent the accumulation of algae in the distribu- tion system. Each emitter will have a specific discharge rate, such as 0.10 gal per min. Twenty of these would then distribute effluent at the rate of 2 gal per min. Be sure that the pump you select will have the capacity to pump slightly more than the expected total discharge rate, and that it can maintain enough pressure at the far end of the system to allow all emitters to discharge at their maximum rate. Shallow subsurface irrigation systems are designed to provide the benefits of pressure dosing (even distribution), keep sewage efflu- ent below the surface of the ground, and provide more clearance to ground water or bedrock than is normally provided with conven- tional disposal systems. Commercial subsurface irrigation systems are available. Figure 6.16 shows the components of one type of shallow subsurface disposal system. While this system is not specifi- cally designed for irrigation, in that actual flow, crop water require- ments, evaporation, and precipitation are not considered, it can serve that purpose. Simply incorporate the concepts discussed ear- lier into the design. Because shallow subsurface irrigation is also good at sewage disposal if the system is installed properly, because it can be owner-built, and because it has been extensively tested and proven, its design is presented in detail in this section. The septic tank and dosing chamber are of conventional design. The design of the distribution system is similar to that of the sand mound distribution system. The absorption trench design is new. The design flow is used to size the septic tank, dosing chamber, CONVENTIONAL SYSTEM MODIFICATIONS Maximum Loading Rate (gpd/sq.ft.) Figure 6.17 Low pressure system loading rates.