It is not clear whether this…

It is not clear whether this is for a new septic system to replace existing (inadequate) systems of sewage management or if it is for an additional system. Is it their intention to increase the number of trailer sites or to upgrade the sewage treatment of the existing sites? What is the basis for the proposed volume? Not enough information is presented here to validate the requested treatment system.
Are there sufficient measures being taken to protect the new system from high water levels, current and future?
With an old trailer park located lakeside on intermittently flooded sandy soil, will there be adequate phosphorus adsorption capacity to ensure that the lake is not impacted for several decades? Aquatic macrophytes are an increasing threat to residents' enjoyment of the lake, and all possible measures should be taken to limit pollution from human waste.