sentences:  2,700 people work on the 1.5 km² peninsula that has about 30 companies, most of which are subsidiaries of Norsk Hydro, including Hydro's research park with 350 employees.A populated area south of the peninsula itself, which was initially housing for the Hydro employees, is also considered part of Herøya as a suburb of the city of Porsgrunn.Herøya also has a local football club, participating in the Norwegian 5th division.