In 2263, he and around 150 other colonists departed Earth for Omicron Ceti III hoping to establish an agricultural colony where they could "return to a simple life." After landing on the planet in 2264, Sandoval and the others were taken over by spores that protected them from the deadly berthold radiation bombarding the planet. The spores provided a constant feeling of contentment, and also perfect physical health. Sandoval's lung scarring from his bout with pneumonia disappeared, and his appendix returned.
When the USS Enterprise investigated the Omicron colony in 2267, Sandoval conspired with colony Botanist Leila Kalomi to infect the starship with the spores. Though he was intially successful in converting the entire crew to his colony, Enterprise Captain James T. Kirk used a subsonic transmitter to destroy the spores. Freed of their influence, Sandoval realized he had accomplished nothing he had set out to do. He planned to try to start a new colony once the Enterprise evacuated the Omicron colonists to Starbase 27. (TOS: "This Side of Paradise")