Septic Field and Fruit Trees

This seems the best forum for this question, apologies if it's in the wrong spot:

As I'm getting to know our new acreage, and being a city-boy, I've discovered a few fruit trees on our property. A couple of plum trees, a couple of apple trees and a cherry tree. Lots of immature, green fruit this spring. We are excited for the potential bounty.

The trouble is, all of these trees are fairly close to the septic drain field. Not directly on top, but within 25 feet or less to the field. The field is a raised field, built almost 20 years ago. I'm not worried about roots affecting the field, we had it inspected and it seems to be working well. My main question is in regards to human consumption of the fruit.

What are the guidelines/rules of thumb for eating fruit from trees near a septic drain field? How close is too close? How can one test the fruit? I've read heavy metals are a bigger worry than fecal bacteria, is this true?

It's pretty sad that the only 6 fruit trees on the whole 5 acres are right beside the septic drain field... I do have plans for future food forests, but it would be nice to be able to use the existing fruit until future plantings start to bear.

Cheers!

Short answer -- not to worry.

Longer explanation: If you are worried about human pathogens, it's simply a matter of distance. If you rank them in order of potential health hazards, root crops > leafy vegetables > fruits with a rind that lay on the ground > fruits trellised or held above ground > tree fruits > nuts. If there is healthy soil biology, the pathogenic bacteria are going to become lunch for some other soil critter long before they can build up in numbers to cause a problem. E. coli is probably the most common problematic organism, and Paul Stamets has shown that counts of E. Coli can be drastically reduced by having it flow through a mycelial mat.

What I would suggest is to mulch the fruit trees heavily, say 4-8" of wood chippings extending past the drip line of the trees (but don't mulch right at the trunk, like is commonly done). You can speed the inoculation process along by collecting any mushrooms you come across, putting them through the blender with water, and applying the mushroom smoothie to the mulch. If you use store bought fresh mushrooms, you might even have a flush of edible mushrooms from your mulch after a few months. If you want to try that route, don't use the common white variety of mushroom or its brown cousin, the portabello, you have to use shiitake or oyster or cepi mushrooms.

As far as heavy metals, they are less of a problem, because they are not likely to get translocated to the fruit. Here again, the problem is mostly with leaves and the biomass of the plant which would pick up the heavy metal. However, you are near a septic leach field, not on top of a dump of mine tailings, so you don't have much of a problem starting out. One thing you can do and that will help out in general, is to apply biochar around the trees, say a quarter to a half inch thick, for all the area under the drip line. Not only will it pick up any heavy metals in the soil, it will help with soil moisture and soil biology.