Moondance, I have not thoroughly researched every page regarding Gulf Trace found in the Clerk of Court's Office. However, I did find two points of interest which you may persuit.
Found in the Declaration of Covenants and Restrictions, OR(official records) book 190 / page 17, dated 6/17/1980:
1) Page 2, par. 7, ..."The residences shall use septic tanks or sanitary sewer meeting the requirements of Walton County."...
To me, this sounds as though you, as a property owner, have a choice to use sewer.
2) page 2, par. 9, "No noxious or offensive trade shall be carried on upon any said lot or property in the subdivision nor shall anything to be done thereon which may be or become an annoyance or nuisance to the neighborhood....."
It seems to me that septic tanks polluting the beach and Gulf at Gulf Trace could certainly be deemed both an annoyance and a nuisance to the neighborhood.
I am not an attorney, not even close, but I hope this may give you some ammo.
I am sure that you, as an owner in Gulf Trace, know that, according to these same Restrictive Covenants page 3, par. 12, , "it shall be lawful for any owner of property in this subdivision to prosecute proceeds at law or in equity against such lot owner or person either to prevent the violation or to recover damages for such violation."
I wish I had more time to allocate to researching further. There may be updates or changes to these original Restrictive Covenants of which you should be aware.