Septic system squirt test

A few days ago they did the "squirt test" on the septic system:



We have clay-rich soils, which water has a hard time seeping through. To compensate, the trenches are first excavated to 4', then backfilled with washed sand to 2'. The drain lines are embedded in a couple inches of drain rock. A layer of landscape fabric above that keeps out fine dirt. Then the top of filled with the spoils of excavation, back to grade.

Because our soil percolates so poorly, the drain field is oversized - double the size for good soil. This way, the soil gets 1/2 as much effluent. A problem with a very large drain field is getting water through the pipes all the way to the end. A small flow of effluent would exit the pipes near the beginning, leaving the end of the drain field dry. To make the whole drain field operate, the system waits until there's enough effluent in a holding tank, and then squirts a predetermined dose in to the drain field with a strong pump. The system is programmed not to exceed the absorbtion capacity of the soil. If you produce a lot of wastewater in a short time, it will fill the tanks and trigger the alarm, but it won't overload the drain field.

We have 6 trenches, each 50' long, for a total of 60' of drain line. There's a manifold that distributes the effluent to the 6 trenches. The manifold has adjustment valves to ensure that the effluent is evenly distributed throughout the drainfield. In the video, the designer activate the pump and observed that the water squirted to the same height across the whole drain field.

The original septic design was for a 5-bedroom system, which required a much bigger drain field. That's too big to pump to the extremities, so the design used a "ratcheting valve". This split the drain field in half, alternating the doses. Because we downsized to a 3-bedroom system, we got to skip the ratcheting valve, but we needed a bigger pump - 1.5hp, 240V 15A, hence the big wiring operation.

They did a "drawdown test" as well. They measured the height of the water in the pump's holding tank, turned on the pump for a set period, then measured again. From this they calculated that the pump can squirt out 100 gallons per minute - wow! Based on the desired size of a dose, the figured that the pump should run for 27 seconds each time. There's a minimum of 4 hours between cycles, so that's about 3 minutes per day, tops. All that wiring for 3 minutes per day?

After the test was complete, the designer and his assistant mapped out the locations of the trenches and inspection ports, which they'll draw up back at the office (for a fee). Then the builder finished filling the trenches and grading the soil. The septic system is done.

The health department will do another inspection before giving the final approval.