A dye test answers one question that nothing else answers cleanly: where is the water actually going. Traced dye either appears where it should not, or it does not, and both results are useful.
Two contractors can stand on the same lawn and disagree about whether it is wetter than it should be. Add traced dye and a measured volume of water, and the disagreement ends: either coloured water appears at the surface, in a ditch or at a break-out point, or it does not. That is why it is the first test run before anyone quotes a bed replacement.
That makes a dye test the tool of choice when a replacement has been quoted and the owner wants a second opinion, and when a buyer needs something firmer than an impression during a real estate inspection.
It also has a limit worth being honest about: a negative result on a dry week is weaker than a negative result after rain, because a bed near the end can still absorb a single test load. We say which conditions the test ran in, and pair it with probing from drain field failure signs.
Traced dye
How it works
How a dye test is run
Set the conditions
Recent rainfall, water use and whether the tank has just been pumped all change the result, so all three are noted first.
Introduce the dye
Tracer dye put into the system at a fixture or the tank, followed by a measured volume of water to move it.
Walk the ground
The bed, the downslope, any ditch or watercourse and the break-out points checked over the following period.
Record either result
Dye seen, where and how long it took, or dye not seen with the conditions stated. Both go in the report.
What a dye test cannot tell you
It shows the symptom, not always the cause
If dye surfaces, the bed is not accepting flow. That is established. What is not established is why, and the answer changes the bill by an order of magnitude. A tipped distribution box overloading one trench produces surfacing that looks exactly like total failure.
So a positive dye test is the start of the diagnosis, not the end. The box gets opened, the trenches get probed, and often part of the bed turns out to be working fine, which turns a replacement into a repair.
Where the question is about the line between house and tank rather than the bed, dye is the wrong tool and a camera inspection is the right one.
Where water from the system is going. If traced dye appears at the surface, in a ditch or at a break-out point, effluent is not staying in the bed. If it does not appear, under the stated conditions, it is.
Anywhere from minutes to hours depending on how far the water has to travel and how saturated the ground already is. The time to appearance is part of the finding.
Tracer dyes used for this are non-toxic and designed for the purpose. They colour water strongly at very low concentration, which is the whole point.
Yes, on a dry week with a single test load, which is why conditions are recorded alongside the result. A negative result after heavy rain is much stronger evidence than one in August.
That is exactly what a dye test is for, and it protects you as much as them: a clean result is evidence in your favour, recorded with conditions and timing.
Not necessarily. A tipped distribution box produces the same result and is a day's work. The box gets opened and the trenches probed before anyone quotes a bed. See drain field.
