Sub-aqueous placement of water-based suspensions and method of manufacture and use

A suspension (10) having a specific gravity greater than 1.0 that contains one or more reactive materials, said suspension containing a biopolymer that decomposes over time, thereby releasing the contaminant reactant for contact with the contaminants in the waterway bottom sediment or waterway floor material. In one embodiment, the suspension (10) includes a water-buoyant material, that can be placed underwater over a sub-aqueous waterway bottom or floor (12) that contains a contaminant to be treated or confined and remains in place for treatment and/or confinement. After the suspension is placed, it may be stabilized against movement by applying a confining or weighting layer, such as sand or a water-permeable or water-impermeable geotextile, thereover.