A sealant product to form a reactive seal in a subsurface or intermittently subaqueous environment includes a reactive medium and a hydratable material that when hydrated forms the seal. For example, the reactive medium may be a zero-valent metal, a reduced metal, shredded tires, and any combinations thereof. A method of forming a reactive seal comprising applying a sealant product in a subsurface or intermittently subaqueous environment to form the seal.