The rural residents that flocked to the PA countryside, built massive homes with 20,000L septic tanks and drainage fields with zero regard for the ground water and thus creating gas pockets in the water table they extract from?
Those rural residents?
I wasn't aware you needed both. I assume the sewage is collected and taken to the country or nearest city sewage treatment plant. I'm going to hazard that the trenching method is expensive and only approved in areas where pumping out a septic tank would be overly expensive for the places that are more 'remote'.
Since you have to go below the frost line for either wouldn't that be a good starting location for the 'geo-thermal alternative heating/cooling system'.
If I was to build something new and 'rural' or 'remote' I think one system would work in both cases. It it a self contained sewage treatment system that extracts the gases and solids for burning and the 'gray water' is used for plants, including garden areas or fruit trees I believe. The only waste product would be a bit of ash and that is a natural solid sterilizer and/or weed killer. There is a company in Edmonton that has them in production if you would like me to find it I probably can. (it was being attached to a well site trailer as they no longer just dig a hole and fill it in later. Pretty much a start and forget kind of system)
If anything needs fixing in the the rural applications that come under term 'barns' should be using the latest types of systems that cities are adopting less toxic ways such as ozone and an MMS type of treatment as being just as effective but less long term problems. That would include a air-tight tarp over the lagoons and the gas collected could be collected and used or removed and sold as a usable product to somebody.