After the Combine take over, a portal storm in city 15 sets off the nuclear reactor into total meltdown.While causing a Level 7 incident the combine did not leave. City 15 functioned as normal under combine rule, until a year later were significant reports by the civil protection members noting the high radiation level,large drops in population,and unknown creatures. That's were you come in, you are a part of Zeta Squad a group of 4 combine in for clean up and recon. but you discover more then just head crabs on your venture
we never see citizens with jobs or any thing different than the stranded clothes