We put in a new Tank and Leach Lines on an old house 4 years ago. We had to pull permits for the entire process. All the work done had to be approved before any actual digging was done. We wanted it done legally due to resale at some point. I took one set of plans down to San Bernardino, dropped them off and they were approved by someone a week later. I then took that approved set to Victorville to another Dept. and they were approved there too.
In Wrightwood, the leach lines have to be longer due to our rocky soil that does not absorb waste water as well as the soil down in Phelan area. Having longer leach lines costs more-it's a lot of hard work to dig leach lines in WW, therefore the costs are absorbed by you. You can't put a new leach field on an old one, must create a whole new path. It sounds like you may not have a lot of room in your yard? Or they had no other place to lay the lines? Is your front yard small? No matter the case, they are required to plan it and dig it according to the plans and requirements set forth in this County for WW.
Once all our work was done by the contractor, the leach lines, tank and distribution box were left uncovered. This whole system had to be approved, or written off, by the County Inspector. He comes up here about 3 times a week to check off all the projects going on in WW. It took him more than 3 visits to approve the system. Our contactor was required to fix everything before signing off. Once that was done, he covered it all up. We wanted to pour a concrete driveway and NO WAY could it be poured over the tank, lines or dist. box!! Everthing works peachy now!!
I'm thinking that no permits were pulled for your system. I think you should ask to see all the paperwork and the nitty gritty of how it got signed off. You are entitled to the driveway you thought you were purchasing.
I have a friend who experienced almost your same exact problem down in the Lake L. A. area. When it was all said and done, the seller and the realtor split the costs of the repair. They created this, not you.
It comes down to dishonesty and greed and you have a few in your story not playing by the rules and that is causing Chaos- which all stems from the broken promises you got going there.
Hang in there and this will all be behind you in a few months!!