nsion): X 7.48 1.7 = 1 in. The total volume of the tank if it were 4 ft deep would be: volume (gal) = 3 ft X 5 ft X 4 ft X 7.48 = 449 gal. Pump selection can be a rather involved process where pressure distribution systems are used, but for dosing a conventional drain field, the process is simple. You must determine how high the efflu- ent must be pumped, over what distance, and how fast. Then ask the pump dealer exactly what pump you need. A pump that is too large can cause as much trouble as one that is too small. You need to tell the dealer two basic things: the discharge head ONSITE WASTEWATER DISPOSAL Table 4.4 Head Loss Due to Friction in PVC Pipe Pipe Diameter (in.) (gpm) 1 1/4 Friction loss (ft of head per 100 ft of pipe) and the discharge capacity wanted. The discharge head is the increase in elevation from the pump to the highest point where the effluent is to be delivered, plus the loss of energy due to the friction of the effluent against the walls of the pipe (see Table 4.4). Dis- charge head is measured in feet of water. The discharge capacity is simply the flow rate in gallons per min- ute that is required at the discharge end of the pipe. WASTE PROCESS Example For example, assume that we wish to dose a conventional drain field: (a) the drain field is 10 ft higher than the dosing pump; (b) the drain field is 75 ft from the dosing chamber; (c) 1.25-in. PVC pipe is used for the delivery pipe; (d) the dosing volume is 192 gal; and (e) the percolation rate is 60 min per in. To determine the pump characteristics required, calculate: Discharge head = elevation change (ft) + friction (ft) = 10 ft + 0.39 ft (from Table 4.4) = 10.4 ft = 10 ft 5 in. Discharge rate (gpm) = dosing volume (gal) percolation rate (min per in.) = 192 gal 60 min per in. = 3.2 gal per min. But since we cannot bury this pipe deeply enough to prevent its freezing, we must add a 0.25-in. hole in the pipe inside the dosing chamber to drain the effluent pipe supplying the drain field. This adds a requirement of 2 gal per min to the pump;