The cache is not at the published coordinates
To get the correct coordinates you need to complete the "Time Traveling in the Storm Water Park" Adventure Lab
The Sebastian Storm Water Park is a 175 acre passive recreation facility with several miles of hiking/biking trails located in the beautiful city of Sebastian, Florida. There are no hours of operation posted, but I wouldn't go out there at night ... There are lots of wild critters out there! The park is also dog-friendly. Bring water and enjoy nature!