Soil conditions may very well be the determining factor as to whether one can build a regular septic drain field. One option here is to have a septic tank, but rather than a drain field, have it drain into a septic lagoon. If the percolation of the soil is insufficient to allow for a good drain field, this can be much cheaper that building, for instance, a sand hill. The lagoon is supposed to be more-or-less water tight....as in water tight as a pond. They are lined with clay, and as I said before, typically have a sufficient volume so that the septic effluent does not dominate the aroma. The bioactivity of the lagoon should be sufficient to allow the effluent to degrade without marked stink. I've been around quite a few lagoons which could easily be mistaken for normal ponds. That said, I would also prefer a standard septic system with a tank and a drain field, just so as not to have the fenced and wasted space of the lagoon. I can, however, imagine wanting a particular property badly enough that I would go for the lagoon if that was the only way to put in a system. I certainly wouldn't want a lagoon on a one acre lot, but with more space it is usually possible to place one such that it is not particularly intrusive. Properly built and sized, they don't usually stink any more than the area over a drain field. It should never smell like the typical waste treatment plant because the volume of waste should always be a small fraction of the volume of the lagoon. If Mechanic is unfamiliar with lagoons, he might want to "visit" some to see for himself. I would imagine there are a few his installer could recommend for scenic, and olfactory, visits!
Chuck