A & E’s Speciality Dredge Technology
The term “Environmental Dredging“ has come into common use for describing the process for removal of contaminated aquatic bottom sediments.
Major considerations for environmental dredging include; sediment volume removal rates, precision of sediment removal cuts, over dredging, slumping or erosion of material back into the cut, resuspension of sediments which include the residual and fallback layer (spillage) of contaminants, releases of dissolved contaminants throughout the water column, plume transport and volatilization of contaminates into the air.
Mechanical Dredges remove bottom sediment using conventional Clamshell Buckets and Enclosed Buckets through the direct application of mechanical forces to dislodge and excavate the material. They are capable of removing hard packed materials and recovering debris.
Hydraulic Dredges remove and transport bottom sediments with entrained water in the form of a slurry with assorted forms of rotating mechanical devices called cutterheads, augers, specialty dredges, etc. They provide an economical means of removing large quantities of sediments on a continuous basis, without timed cycles, directly by pipeline to a collection facility. They are designed to dislodge, grind, shear and entrain and direct the sediment toward a suction intake pipe.
Environmental Lunch Box Dredge (ELB) is a specialty form of hydraulic dredging. It is designed for a specific purpose related to environmental dredging of contaminated sediments. The ELB “unit” provides sampling, viewing, sonar locating, monitoring, separating, testing, treating, injecting, removing or replacing silt, sediment and materials from a containment unit positioned on water bottoms.
The ELB works when its open bottom containment structure forms a seal with the water bottom materials then uses “agitators” for suspending the sediment and materials within the confines of the unit. The agitators are water/air jet nozzles, flexible water/air whips and variable speed impellers used for directing streams of water and/or air at variable pressures capable of suspending, cutting, pulverizing and shredding materials within the unit.
The ELB unit provides outlets through which the sediments, materials, contaminates, fluids and invasive species may be withdrawn from the unit for harvesting, separation, replacement or treatment all the while monitoring for natural or manmade materials, toxins, contaminants, elements, gases, nutrients, organisms and such.
A closed loop piping system design includes a forward and reverse pumping and mixing system for exterior and/or in-situ treatments of additives, reducers, catalysts, microbes, stabilizers, adhesives, charged particles, gases or other elements. Once treated “clean” separated materials maybe returned via the ELB to fill the voids created from the dredging process and if mixed with “Green Peas” packets, it will advance the Habitat Restoration Process. The Green Plant Energy Aid System (Green Peas) is a biodegradable packet filled with plants, (cuttings, roots, tubers, seeds, etc.) along with nutrients and soil organisms necessary to accelerate plant growth in a greenhouse development setting that shelters the new growth from the forces of nature over a controlled period of time.
Environmental Lunch Box Dredge (ELB) Advantages:
Greater sediment volume removal rates than for comparably sized Clamshell dredges,
Provides an economical means of removing large quantities of sediments on a continuous basis by pumping directly by pipeline to a collection facility without the cycle times of Bucket dredges,
Effective for removing sediment overlying clay, hardpan, rock bottoms, uneven bedrock, bedrock cracks and crevices, logs, etc.
Effective in both hard packed and soft sediment bottoms,
Nominally close to 100% effective at suppressing sediment resuspension, releases and residuals at the water bottoms, throughout the water column and at the water surface,
Recovers biogenic gas escaping from the disturbed dredged bed,
Reduces the amount of volatilization of contaminants into the air,
No slumping or erosion of material back into the cut,
No effects that allow for dislodged sediments to be dispersed throughout the water column and subject to plume transport like those from Clamshell buckets or rotating Cutterheads,
No failed bucket closures allowing for sediment releases,
No sediment releases from bucket exterior “wash off” throughout the water column or above of the water,
No sediment released from plowing action, over burial, or excessive rotating speed that would result in sediment releases, which are likely to be concentrated in the lower portion of the water column,
No leaving “windrows” of materials on the sediment bottoms that operation of conventional Hydraulic dredges tends to leave,
No shearing action through the sediment,
No fallback layer (spillage) generating a residual layer due to the positioning of the suction pipes of Standard Hydraulic Dredges,
According to the Army Corps of Engineers Technical Guidelines for Environmental Dredging of Contaminated Sediments, “as a rule of thumb, the thickness of the spillage layer for a Conventional Cutterhead Hydraulic dredge can be 0.2 times the cutterhead diameter (example; 0.2 x 24 inch cutter head = 4.80 inches spillage layer) or 0.5 times the discharge pipe diameter (example; 0.5 x 24 inch discharge pipe = 12 inches spillage layer)”,
No plume generation, travel and recontamination of non-contaminated clean areas,
No multiple cleanup passes,
No barges needed for transport of dredged sediment,
No second handling of dredged sediments again at the barge unloading site,
Conclusions: The Environmental Lunch Box (ELB) dredging process addresses all major considerations for environmental dredging, including: sediment volume removal rates, precision of sediment removal cuts, over dredging, slumping or erosion of material back into the cut, resuspension of sediments, which include the residual and fallback layer (spillage) of contaminants, releases of dissolved contaminants throughout the water column, plume transport and volatilization of contaminates into the air.
ELB Advantages Summary: The ELB is:
- More efficient at removing most types of bottom materials,
- More efficient at sediment material removal on a continuous basis,
- More efficient at controlling sediment and contaminate re-suspension, releases, residual buildup, plume formation and transport.