An Emergency Isolation and Treatment Shelter (EITS) deck system is constructed from a multiple of deck unit modules. Each deck unit module includes four adjustable leg assemblies attachable together by a lower truss between each leg assembly so as to support a deck surface panel. The size of the deck unit module defines the modularity of the EITS. Each leg assembly includes a primary leg, an intermediate leg, and a screw foot each in telescopic relationship. Each leg assembly may be telescoped independently to provide a level deck surface irrespective of the underlying terrain.