I can speak for PA. Around 1972, all house construction and expansions that used on-lot sewage disposal systems had to be permitted by DER/DEP-certified Sewage Enforcement Officers. A lot of houses built prior to 1972 were also so-permitted where the municipalities voluntarily participated in the program.
The SEO permitting program involves house/lot-specific design of the septic tank and drain field. The paperwork requires a hand sketch of these features, with respect to the house and any other nearby contraints such as trees, streams, outcrops and property lines. Sketch quality varies by SEO. Some are worthless, but some are quite accurate.
Unfortunately, the SEO paper trail is hard to track down in PA. The OLDS permits are not recorded at the court house or included in building permit paperwork. One copy goes to owner/builder, who often loses or discards it the first time the house is sold. Another copy is sent to a DEP regional office - good like finding that. Another copy is sent to the municipality with no archiving mandate to speak of, so finding their copies are spotty, takes a lot of work, and is not always accessible to a mere citizen. One copy goes in the personal files of the SEO, but SEOs are private contractors who drift, relocate, and retire; so there is no guaranty that a resident living in municipality XYZ can track down the SEO who permitted their house 30-years ago.
I would imagine that many states have such OLDS permitting programs. In PA, the best place to find that paperwork is in the folder of old papers/appliance manuals that are passed along during house sales. If not that lucky, go to municipality receptionist/clerk or planning department, and ask if they have a file of the OLDS permits or can identify the SEO who worked the area at the time your house was built.
Good luck.
I have a general idea where things are anyway. Much bigger than I expected.
but that's not the JUOT way!