Subaqueous capping is typically less expensive than full dredging and upland disposal, particularly on large contaminated areas where the volume of material to be dredged, transported, and disposed of is significant. The cost comparison depends heavily on site-specific factors — the extent of contamination, water depth, site access, and the regulatory cleanup goals — so a direct comparison requires site-specific evaluation. What capping offers in addition to cost is a lower-disturbance approach that avoids resuspension and spread risks associated with dredging in active aquatic environments.

Reactive core mats can be engineered to target a range of priority contaminants commonly found in harbor and waterway sediments, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), heavy metals, and certain pesticides. The reactive material within the mat is selected based on the specific contaminants of concern at the site — which is why site-specific sediment characterization data is essential before reactive core mat specifications can be finalized. FTG works with the project’s environmental team to match mat specifications to the site’s contaminant profile.

A properly designed and maintained subaqueous cap can remain effective for decades. Long-term effectiveness depends on cap integrity — whether the cap remains in place and undisturbed over time — and on the natural attenuation processes that continue to reduce contaminant bioavailability beneath the cap. Most regulatory frameworks for subaqueous capping require a long-term monitoring and maintenance plan to confirm cap performance and detect any areas where integrity may be compromised. FTG’s role is in the conceptual design and installation of the cap system; long-term monitoring is typically managed by the project’s environmental team.

Capping is not well-suited to sites where the contaminated sediments are actively mobile — subject to significant scour from currents, propeller wash, or storm-driven wave action that would displace or erode the cap over time. It is also less appropriate where navigation requirements preclude adding any material to the bottom, where the contaminants are too mobile or volatile to be effectively contained by a physical or reactive layer, or where regulators require mass removal of contamination as the cleanup standard. In those situations, dredging or other active remediation approaches are more appropriate, and hydraulic dredging, polymer flocculation, and TITANTube® dewatering may be applicable. FTG can help in this case as well.

Yes — combined approaches are common. In many remediation projects, dredging removes the most heavily contaminated material from areas where removal is feasible and where the risks of dredging are manageable, while capping addresses areas where dredging is impractical — too deep, too close to navigation infrastructure, or with sediments too thin or diffuse for cost-effective mechanical removal. FTG can provide capping field services within a broader remediation scope that includes dredging by others and possible treatment and dewatering of contaminated sediments in TITANTubes®.

Reactive core mat panelizing is completed before underwater installation begins, so FTG’s preparation work can run in parallel with other site mobilization activities. Placement sequencing is developed in coordination with the underwater placement contractor and the project’s environmental team — typically proceeding from the upgradient or most heavily contaminated areas outward, with careful attention to water quality monitoring during placement. FTG provides the prepared mat panels staged for placement; the underwater placement contractor is responsible for mat positioning and confirmation of coverage.