Stone & Pipe Conventional Drainfield

A stone and pipe conventional is the oldest of all septic systems. This type of conventional is constructed by digging a series of trenches. How many trenches and the length of the trenches are dependant on the loading rate of the soil and the gallons/day produced by the structure attached to the septic system. For example, let’s use a three bedroom house with a soil test that has a loading rate 0.5. Most commonly, the stone and pipe conventional for this house would have two trenches 6 feet wide and 75 feet long.

stoneand1First, trenches or cells are dug to install the conventional component. The bottom of each trench is dug level so the effluent is evenly distributed in the cell. Most of the time, all the trenches are dug at the same level. However, some trenches are dug at different elevations because of a shallow limiting factor and a sloped contour. Once the trench is dug, it is filled with at least 6 inches of 1.5 inch washed stone (sometimes called aggregate). The stone acts as a buffer and a reservoir between the pipe and the soil. Once the stone is placed, four inch perforated pipe is placed over the stone. This is the distribution lateral. It is not pressurized and contains pitch to let the effluent travel to the end of the trench. Another 2 inches of stone is placed over the lateral. Geotextile fabric is than placed over the entire trench to keep soil out of the stone. Two observation wells are also placed inside the trench for monitoring purposes. Finally, the trench is backfilled.

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