To Susan Vita... here in Ohio, a mound of whatever size and variation has the effluent filtering through the sand into the soil and down. That processing area is called the basal area directly below the heap,
Around that processing area's soil, is a 1ft wide buffer of undisturbed soil that is there to isolate the process from the surrounding topsoil, at least as deep as the freeze zone.
Further that buffer zone is surrounded by the curtain drain (freeze zone deep) which is there to clear out any ground water that rises up from the nether regions near the mound... which drain then clears out that ground water and anything else that had gone 1) through the sand then 2) through the soil down to the depth of the curtain drain and then 3) was carried upward into the pipe in the drain by rising clean ground water...
That path should be well more than any cleaning needed... the mound designers engage in so much overkill that it's amazing they don't have financial nightmares, facing the risks of foreclosures and
mortgage increases of their clients in their sleep.....
So there's quite a significant gauntlet built in to separate your processing area from the surrounding topsoil contacted by humans..... assuming the installers did everything hoyle.....
All that because the fools put solid waste into a liquid waste system...... oy.....ttyl