From Longman Dictionary of Contemporary Englishon-siteˈon-ˌsite adjective [only before noun], adverb at the place or on the area of land that you are talking about OPP off-site on-site car parking Accommodation is provided on-site.
Examples from the Corpuson-site• on-site medical treatment for the accident victimson siteon siteat the place where people work, study, or stay There’s a bar, restaurant, and gym on site. → site
Examples from the Corpuson site• An engineer will be on site to supervise the construction.From Longman Business Dictionaryon-siteˌon-ˈsite adverb at a particular place of work or a place where something is being built, rather than away from itThe waste is treated on-site. → compare off-site —on-site adjectiveon-site staff training