me basic guidance: 1. Sprinkler spacing is usually equal to the radius of the wetted circle. 2. Lateral spacing along the manifold should be about equal to the radius of the wetted circle. 3. The rate of application should not exceed the capacity of the soil to absorb the water. 4. High pressure causes small drops which are more likely to be lost to wind and evaporation. The procedure for selecting a sprinkler system is to assume a sprinkler spacing and an application rate. Then review the data on various sprinkler heads to determine which to use and what pres- sure you need. Finally, check to see that the wetted diameters of these sprinkler heads conform with the spacing you had in mind. Plots irrigated with effluent (even disinfected effluent) by sprin- klers should be located well away from areas of public access. Small drops from sprinklers can travel in the wind a half mile or more. Trickle irrigation is a low flow, low pressure irrigation system that CONVENTIONAL SYSTEM MODIFICATIONS Figure 6.15 Trickle irrigation system and emitter. can be used on level or furrowed plots. The distribution is relatively even if the flow from each outlet in the distribution system is evenly spaced and each discharges effluent at the same rate. Because the application rate is far slower than the absorption capacity of the soil, the effluent soaks in where it is applied. Because of the difficulty in obtaining equal flow through holes drilled in a pipe or hose, it is best to buy premanufactured holes at your local hardware store or garden supply house (Figure 6.15). These "emitters" each have their own characteristic maximum rate of discharge, anywhere between 0.1 and 5 gal per hour, which must be taken into account in designing the distribution system. Another choice is plastic irrigation hose with small holes located every foot or ONSITE WASTEWATER DISPOSAL Distribution system Septic tank Dosing chamber Figure 6.16 Shallow subsurface irrigation system. two. These hoses emit on the order of one-third gallon per hour per foot o