a dual - tank liquid storage tank system comprises a lined primary storage tank disposed within a lined secondary tank . construction of the system involves rolling out a secondary tank liner over an engineered base course , and then laying out a primary tank liner over the secondary tank liner , with an outer portion of the primary tank liner rolled up to fit within the primary tank perimeter . the primary tank &# 39 ; s perimeter wall is then assembled from wall panels resting on the secondary tank liner , and then the primary tank liner rolled out and deployed over the primary tank wall . an outer portion of the secondary tank liner is then rolled up toward the primary tank wall , and the secondary tank &# 39 ; s perimeter wall is assembled from wall panels resting on the base course . the secondary tank liner is then rolled out and deployed over the secondary tank wall .