Design and Construction

Three septic tanks, of approximately 5,678 liters (1,500 gal) each, were connected to the downspouts of three homes using 10 cm (4 in) diameter plastic corrugated pipe in July of 2005.  A plastic corrugated “T” connection was fitted onto the downspout (Figure 1).  Plastic corrugated pipe was connected to the “T” at the downspout and run below the surface to the septic tank (Figure 2).  The corrugated pipe was connected to a PVC pipe fitting at the inlet of the septic tank (Figure 3).The “T” connection was used so that if the septic tanks were to exceed capacity, the overflow would exit in the same manner as with the standard gutter system.  The baffle, present in the septic tank prior to the retrofit, was removed or punctured in each of the tanks in order to maximize the capacity of the tank and to ensure that overflow would reach the drain field. The water level in each of the tanks was recorded using INFINITY™ continuous water table recorders installed in a 10 cm (4 in) diameter PVC pipe (Figure 14).  Precipitation was recorded at the site using a manual rain gauge and an automated Davis Rain Collector tipping bucket recorder with a 0.25 mm (0.01 inch) capacity bucket (Davis Instruments, Hayward CA, Model 7852).  The rainfall was logged using a HOBO® data logger (Onset Computer Corporation).   

Figure 1                                                                      Figure 2
 

Figure 3

A drainage area of 78.5 m2 (845 ft2) from the adjacent home was connected to tank 1.  Tank 1 was fitted with a 186 Watt pump so that the homeowner could use the rain water to water her garden and greenhouse.  A 3.2 cm (1.25 in) PVC pipe was connected to the pump, inserted through the top of the tank, and fitted with a spigot (Figure 4).  Figure 5 shows the irrigation system in action