2.3.1.1. Mechanical vs. Hydraulic Dredging

Dredging is used for land reclamation; a lot of dredging occurs here. Environmental remediation dredging is different because one of the problems in dredging is following.

Dredging is a process often utilized to reclaim land, which means making more land available by removing sediment from underwater locations. Among the various types of dredging, environmental remediation dredging specifically focuses on cleaning up contaminated areas. The key point here is to understand that while dredging is done for many purposes, when concerning the environment, it becomes a critical remediative action due to the contaminants involved.

Think of dredging like cleaning out a messy garage. In some cases, you remove everything to find and fix the damaged areas (like contaminants in water); in other cases, you're just moving things around without really cleaning up.

The mechanical regime uses a bucket head dredge. It goes in, hooks up, and comes out; it retains the solids very effectively.

Mechanical dredging employs machines known as bucket head dredges. These machines scoop up the sediments and remove them effectively from the water. The essential aspect of mechanical dredging is that it separates solids from water, which is advantageous because it helps in retaining the sediments needed for remediation. However, the downside is that this method can create cloudiness or turbidity in the water, which can result in additional environmental issues.

You can compare this to using a vacuum cleaner to clean a carpet. The vacuum effectively picks up dirt and dust, but in doing so, it stirs up some of that dust into the air, which can temporarily make your room dusty.

The hydraulic dredging uses a kind of drill. It is like a screwdriver that gently drills and creates a slurry, which is pumped out, generating much lesser resuspension.

Hydraulic dredging operates differently from mechanical dredging. Instead of scooping out sediments, it utilizes a drilling mechanism that creates a slurry of soil. This slurry is less disruptive to the surrounding water because it minimizes resuspension, meaning it doesn't disperse contaminants throughout a larger area. Although this method generates less immediate disturbance, it produces a contaminated slurry that requires further handling and processing.

Imagine using a blender to mix a smoothie. You wouldn’t create a mess because the blender is contained; however, once you pour it out, you need to clean the blender. Similarly, hydraulic dredging creates a slurry that, while less messy while created, still has associated cleanup.

When you are dredging, chemicals can release into the water. This can lead to desorption and re-suspension.

During dredging operations, there is a risk that contaminants trapped in the sediment can be released back into the water. This occurs via a process called desorption, meaning that the contaminants detach from the sediments and re-enter the water column. This can contribute to water pollution and adverse effects on aquatic life, leading to additional concerns for environmental protection during dredging activities.

Think of it like removing a sponge soaked with dirty water from a bucket. When you lift the sponge out, some of that dirty water will leak back into the bucket, causing it to remain contaminated despite your efforts to clean up.

What happens to dredge material when it leaves a dredging site? It has to go somewhere; usually, it is placed in a confined disposal facility.

After dredging, the sediments—often contaminated—need to be managed carefully. They are typically transferred to a confined disposal facility, similar to a landfill specifically designed for dredged materials. This step is crucial as it prevents the contaminants from spreading, but it presents challenges as the dredged material can still release pollutants over time, requiring proper monitoring and management.

Imagine cleaning out your garage and removing all the junk to a designated storage space where it’s contained. While the area looks cleaner, you might find that some of that junk needs to be taken care of later to avoid any potential hazards that could arise from it being stored away improperly.

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