optimized to a particular project having site specific issues demands and conditions an important feature of the ag layer 24 88 is that it must be more permeable than both the underlying sediment 16 and the overlying ab and bb layer 22 90 so that the ag layer creates a long preferential flow path 25 and or provides sufficient contact and residence times to enable reactions e g sorption complexation destruction and or precipitation to occur to facilitate the capture and removal of contaminants from pore fluids e g groundwater and or gas as the contaminated pore fluid preferentially flows into and through the ag layer 24 88 the contaminated pore fluid is actively treated until it daylights at the leftmost extent of the ag layer 24 and enters into the overlying water column 10 or surface water the exposed section of the ag layer also facilitates the dissipation of positive pore water pressure associated with upwelling pore fluid active reactive sediment capping systems have been described above in connection with fig1 in particular the reactive capping systems of aquablok ltd utilize a composite particle comprising a core or aggregate material in combination with various amendments such as sorbents in accordance with the present invention the reactive layer portion or material within such systems may employ a self regenerating reactive material as described below as described herein combinations of materials may be used in forming either of the two major layers of a capping system for example the bb layer of the bb ag system is itself a blend of ab composite particles with aggregate other materials such as slag clays sand mortars binders etc might be used in combination with ab particles for the impermeable layer which should have a hydraulic conductivity of 1.