A thought...if the septic system is yours, then what's in it is already "personal", so it is doubtful that the groundwater 25-feet away horizontally and adjacent to the field contains ruminants which could make you sick. The bacteria in the tank and in the soil is pretty darn efficient at eliminating nutrients. Also, across the larger field of the yard and neighborhood, rainfall washes the upper soil layers deeper into the ground vertically. Bacteria and viruses are always present in the environment. A healthy person has many defenses.

Percolation is primarily vertical with some leachate spreading out horizontally by capillary attraction, at the elevation of the lowest holes in the system's pipes, or vault, or gravel pit, etc., already deeper than 12-inches below the surface.

The rate of dosing in an on-site septic system is also very small and the bulk of it IS NOT sanitary waste although 7-gallons per flush, if an older toilet, and 1.5 gallons per flush if water saving. Multiply that by the inhabitants of the house, estimated number of times they flush, wash hands in bathroom sinks, take showers, run water through the kitchen sink, wash clothes, etc., and the septic system dosing is designed for 100-gallons per person per day (conservative to preclude overdosing).

The design dosing is distributed across (guesstimate and soil percolation dependent) four (4) or six (6) 4-inch drainpipes on the order of 15 to 20-feet in length, each leg, for a French drain system. The actual dosing is a tiny amount per pipe per day and insufficient to drive the "head" (groundwater gradient) to the sides, even after years of use.

It wasn't nice and it wasn't pretty when I helped my brother dig up his system (with small backhoe) to install a vault system in its place. We got FILTHY. When it was done, we threw our shoes, gloves, and clothes away, the dirt washed off with soap and water (to "seed" the new system), and not one of us got sick or infected, just tired.