Sandy

I copied the last paragraph for you, as it is the only portion that specifically addresses vegetable gardens, but the entire article is worth reviewing:

"Vegetable Gardens and Drainage Fields
Sometimes the ideal place to put a vegetable garden
seems to be over the leach field, raising the question of bacterial and viral contamination from the effluent. Soils vary a
great deal in their ability to filter viruses and bacteria. Clay
soils work best, eliminating bacteria within a few inches of
the drain trenches, but sandy soils may allow bacterial movement for several feet. A properly operating system will not
contaminate the soil with disease-causing organisms, but it is
very difficult to determine if a field is operating just as it
should. If at all possible, use your septic drain field for ornamentals and plant your vegetables elsewhere. If you must
plant vegetables, take the following precautions. Do not plant
root crops over drain lines. Leafy vegetables could be contaminated by rain splashing soil onto the plant, so either
mulch them to eliminate splashing or don't grow them.
Fruiting crops are probably safe; train any vining ones such
as cucumbers or tomatoes onto a support so that the fruit is
off the ground. Thoroughly wash any produce from the garden before eating it. Do not construct raised beds over the
field; they might inhibit evaporation of moisture."

Although the drain field may seem to be the ideal place to have a vegetable garden, it is not recommended. Even though different soil types differ in their ability to filter contaminants out of the effluent, there is no way to be absolutely sure that everything is being filtered out. Therefore it is not recommended to plant vegetables in a septic drain field because of the health risks associated with bacterial contamination. Also, vegetable gardening requires frequent cultivation of the soil, supplemental watering and fertilization. None of these practices are recommended for a drain field. Using a raised bed is also not recommended. The additional soil over the drain field reduces the effectiveness of the system to filter the effluent because it interferes with evaporation of soil moisture.

Short and direct from Perdue:

Never place plants meant to be eaten (fruits or
vegetable plants) over septic systems.

Also would a deep taproot plant like comfrey be dangerous to grow over a leach field?