I am in the early planning stages of building a house in a rural area (well water, no county sewer service). Since I have to dig a bunch of 36" wide trenches for my septic absorption field I was thinking... Why not install the horizontal loop UNDER the septic field? At the risk of grossing some out, when we are using the house, we will be "wetting" the field regularly, which should improve the thermal conductivity of the installation. First stop, I checked with the county health dept. They gave a preliminary OK as long as I backfilled over the loop with an approved fill material (in this case a red quartz sand available from a nearby quarry in North GA). From the bottom of the trench to the top I'm looking at: - Thin layer of sand for leveling - Slinky or web of straight pipes - 12" of additional sand - ?" of gravel (for the septic field) - either septic chamber or perf pipe (not sure about septic field design yet) - additional gravel - backfill dirt Anyone ever done this before? Conceptual fatal flaws? The heat produced in the summer should improve the bacterial action of the septic field. In the winter, the cold loop will retard it somewhat, but the county engineer was not concerned about this. Either way when the house is in use the field will be wetted regularly. FYI, I am an electrical engineer with modest mechanical training, so hit me with stuff as technical as you want! thanks!