CONFINED AQUATIC DISPOSAL (CAD)
MPA identified the need to investigate Confined Aquatic Disposal (CAD) as an alternative dredged material management option when there is a pinch point in MPA’s primary dredged material management methods, which are upland placement sites and innovative reuse.
What is CAD?
Confined Aquatic Disposal is an internationally recognized method for managing dredged material, involving the placement of sediment into specially engineered underwater depressions designed for safe containment. Designs are site-specific and tailored to the geotechnical and environmental conditions of the proposed construction area. The selected location must meet defined criteria to be considered for this method.
Below, please find more detailed information about CAD.
Final Report
Report Webinar
Newsletter
Spotlight Series
Fact Sheet
FAQs
How Does CAD Work?
The construction of a CAD cell begins by identifying a location that meets criteria for stable containment, accessibility, minimal environmental impact and ideally has sufficient quantities of sand that can be used for innovative reuse or beneficial use. A thin layer of material (sand, silt, and clay) is dredged from the river bottom and placed in a dredged material containment facility. Next, a layer of sand and gravel is removed to deepen the cell, but only in the areas that have a relatively thick, impervious clay layer. Finally, the resulting cell (or depression) is filled with sediment dredged from the shipping channel. The thick clay underneath the cell creates a barrier, effectively eliminating the potential for deposited sediments to interact with aquifers that lie still deeper beneath the surface. The sand that is removed is stockpiled for use in a future innovative reuse or beneficial use project.
CAD Has Three Stages:
A depression (or cell) is excavated into the sand layer of the river bottom.
Excavated sand is used in a beneficial or innovative manner; such as wetland creation or structural fill.
The depression is then filled in with dredged material.
The enormous volume of dredged material generated each year to maintain safely navigable Port waterways means MPA is always searching for the best possible storage options for this sediment.
MPA identified the need to investigate CAD as an alternative dredged material management option when there is a pinch point in MPA’s primary dredged material management methods, which are upland placement sites and innovative reuse.
With limited dredged material placement capacity at MPA Harbor Dredged Material Containment Facilities (DMCF), exploring innovative new approaches to dredged material placement in Baltimore Harbor is necessary to maintain the water channels of the Port of Baltimore at depths and widths that modern ships can safely and efficiently navigate.
CAD in Baltimore Harbor
In 2016, MPA constructed its first CAD cell in Baltimore Harbor and began an extensive 2-year study of this new approach in Maryland. CAD has been used successfully in other areas of the United States, including Boston and Newark Bay.
The 2016 CAD pilot project identified planning goals to be taken into consideration while exploring a second CAD project: evaluate different site conditions that may influence other locations within Baltimore Harbor; operate a larger capacity cell with multi-use or multiple cells within an established area, and determine cost effectiveness.
Following the 2016 CAD Pilot Project, MPA created a technical advisory group involving experts from state and federal agencies, local governments, NGOs, and community stakeholders to evaluate and guide the development of a second CAD pilot project in Baltimore Harbor with a focus on site selection, environmental impact, and public benefits.
Preliminary site analysis for a second pilot project included an environmental assessment, hydrodynamic modeling, and geotechnical investigations. The additional evaluations provided additional information to fill in data gaps to assist in future site selection.
In addition to input from committee members, the CAD Subcommittee conducted a comprehensive outreach campaign to solicit broad community input on the proposed CAD pilot project.
The results of the CAD Subcommittee’s work have been released in a report that outlines the next steps for evaluating the viability of future CAD efforts and reflects the subcommittee’s consensus that current data gaps prevent MPA from proceeding with any design, engineering, or construction activities, including selecting a specific pilot location.
Next Steps
A CAD project cannot and will not move forward until data gaps are filled. MPA may begin conducting studies to fill these identified data gaps once sufficient funding is available. Currently, MPA has other strategic priorities and lacks the funding to pursue low priority projects, which includes CAD. Any changes to this will be communicated through the DMMP committee process. However, at this time, all CAD-related activities, including preliminary planning, investigations, engineering, and design remain on hold.
