With regard to the requirement to connect to regional sewer system it is usually just boiler plating and becomes a sort of sword of Damocles hanging over the park. Many permits dont even have it but I think if you dug through the regulatory code it would probably be there. The assumption is the the regional sewer systems provides better treatment. It is usually brought up if the system fails or is struggling with compliance. Then out come the large connection and tap fees.
As far as well contamination goes microbial and nitrates as usually a function of either shallow well depth, faulty well surface seal, contaminated aquifer , geology or all four. Im looking at a park with all four. No surface seal, shallow depth 100 feet deep, drainfield to close, aquifer is contaminated to 300 feet based on geology of area. I like the fun ones . Well construction is the key a 600 foot well could have a faulty surface seal and be contaminated. However contaminates like arsenic or uranium are generally from the formation and if you have it it will have showed up already. Areas with oil well fracking might be the exception to what I said above.
As far as insurance for regulatory risk I have yet to see it but I will leave that answer to the experts.