Where some see fear and goblins, others see opportunity. If the site truely has great potential, AND the purchase price is right, why not go for it. Just a few caveats: 1. It will help tremendously if you have already operated a wash, preferrably with reclaim. 2. Expect to spend a lot more time monitoring the site for things like oil changes, RV holding tank dumps, and my favorite, carpet cleaning vans. A camera setup will be real helpful. 3. Run the place in an above average condition. Keep records of pit pumping and anything else environmental. 4. Plan on running it for two to three years and sell it to recoup your investment.
You might also check with the city master planner to see when they plan to run sewer linew to that area. Also see if other washes are operating legally on a drain field. If they are, then you can not be denied permission also.