When you have your septic system pumped where do you suppose that material goes?  Since you say you do my job then I can only imagine you then take that sludge out of your septic system and then dispose of it in a proper manner.  Saying you do my job implies you test it (sludge pumped from your septic tank) for heavy metals, radiation, and a plethora of other things.  It would also indicate you test the percolating liquid for fecal bacteria, E. Coli, nitrates, and again a host of other things.

Go ahead I'll wait for you to tell me what your septic system has entering your lawn in regards to E Coli per L.