I live in a 60+ year old rural home. The septic and greywater systems both drain into the roadside ditch. This seems to be a common occurrence in this county. We get bad smells when the wind is wrong and I think that tells me the situation should be improved.
I would estimate the ditch falls around 5 feet over the next 300 feet. I'm looking for some reasonable suggestions. Thanks
I bought land that has a legal sewer lagoon on it, which is a fairly vile thought. It basically works like your ditch, just a place stuff goes. I plan to install between the house and the lagoon, a worm composting area and a series of plant filtration beds for the water to be processed through. After all that, any left will go to the lagoon. So basically the lagoon is just for problems and overflow, not for the main sewage. It should be done before it gets there. This is something like the sewage systems used in earthships.
Same concept can be used for your ditch. Look up earthship sewage systems (can't find the link I wanted to show you) and reed bed filtration systems (Reed bed article and see what you can put between the house and ditch.
The best way to update a system like you have may be to do what we call a "One Piper" here. As the name suggests, a lot of people here lack the cash to build a legal system so they semi cheat by making a "one piper". Basically it is as the name implies...using one pipe off the end of their septic tank. All you have to do is dig up the pipe, place crushed rock under the pipe and place in new perforated pipe. This helps distribute the gray/black water over a much broader area instead of just draining it to the roadside ditch.
It is not as good as an engineered system of course, but it is hard to spend some $7000 on a new leach field type system versus that of a one pipe system that costs a few hundred bucks. Because it is leaching over a broad area, it is hard to knock it too hard.
As for the Grandfathered status, I know of some towns here that require a new permit if more then two sections of pipe need to be replaced. However if you do 2 sections of pipe per year, you will still be grandfathered. In your case though, just doing the last two sections of pipe (20 feet) with perforated pipe and crushed rock in the trench underneath covered with hay as a filter, might really slow the drainage into the ditch. By going back a length or two at a time, you will soon get the greatest area of leaching so you do not foul one area of your property with gray/blackwater.
Is it ideal? No, but it may be a reasonable way to improve what you do have.
We've got plenty similar situations in Ireland too. What you call "Grandfathered" we probably call "Legacy Sites" - sites where there is an existing system that either has planning permission but doesn't work, or predates planning (and still doesn't work).
A cost effective solution that I've found works well on clayey soils with an existing problem like yours is to build a soil based constructed wetland between the septic tank and the drain. In Ireland the recommended size is 5m wide x 20 or 30m long, depending on how clean you want the final effluent. Just excavate the area so that you're down c.6-12" below the septic tank outlet pipe. Backfill with c.2-4" of clean, weed free topsoil, and plant with a selection of wetland plants such as Typha, Phragmites, Sparganium and Iris (or plants with similar physical characteristics that grow locally in your area). Ideally the overall wetland depth from ground surface down to the wetland base would be <1m for safety. Set the water depth using an outlet pipe on an elbow. Twist the elbow of the pipe to hold back water to a depth of c.1" until the plants are well established, and then 4" thereafter.
Legally you will probably need planning permission. We certainly do here. I know of some people who have just gone ahead and built the system without permission and although that's not legally permitted, it does have the advantage of getting the water cleaner quicker. In some cases, local authorities have demanded that the unauthorised wetland be removed again and replaced with a mechanical system. But then again, the opposite has happened too, where conventional systems need to be replaced with a wetland...
I've another alternative that may or may not need permission. Take Travis' one piper; but instead of gravel and a perforated pipe, split a 1' couri pipe (twin walled courigated plastic pipe) down the middle to make 2 gutters. Dig 2 or 3 trenches between the tank and the polluted drain (a few inches deeper than the existing discharge pipe) and lay your gutters face down on the trench base. Cover with soil and plant willow cuttings over the top. The willows are voracious feeders and will mop up liquid, nitrogen and phosphorus. They may mop up enough to eliminate any discharge at all, certainly in drier times of the year. The pipe set up will prevent willow roots blocking your pipes (whereas perforated pipes would block in sort order).