Use of Geotube Dewatering Containers in Environmental Dredging
Type:
Presented during:
WODCON XVIII - 2007 Orlando, Florida, USA
Authors:
Mastin, Lebster
Abstract: Confined Placement Areas (CPAs) are not always a viable containment and processing option for fine grain residuals produced during environmental rehabilitation and maintenance dredging. A suitable upland or underwater placement area may not be economically or operationally available, an operations timeline for solids removal prompts onsite dewatering, and residuals may be contaminated with polychlorinated biphenyls (PCBs), metals (e.g., Cu, Fe, Hg, Ni, Pb, Zn, etc.), polycyclic aromatic hydrocarbons (PAHs), nutrients, and pesticides. Several mechanical dewatering options (e.g., belt filter press, centrifuge, etc.) are available as short-term or long-term remedies for onsite dewatering but are capital intensive for facilities and contractors that already operate on competitive budgets. The objective of this study was to evaluate Geotube® containers as a dewatering option for several environmental dredging projects including cost effectiveness, ease of operation, solids and contaminant retention, solids handling time, flow and volume rates, and seasonality. Geotube® containers, typically with the aid of dewatering polymers, were recommended to and implemented by several project engineers into which materials were dredged and pumped directly from storage lagoons, retention basins, and waterways. After inline flocculation, the permeable geotextile that forms the Geotube® container allows efficient dewatering while containing the fine grain solids. For containment and dewatering of dredging residuals, use of Geotubes® (including dewatering polymer and feed equipment) cost less than $3.65 per cubic yard, required minimal technical assistance to install and operate, retained greater than 95-percent solids (including contaminants), solids were only handled once they were dried sufficiently for hauling and disposal (20 to 80-percent cake solids), and did not interfere with facility operations. In addition, mobilization, additional onsite facility infrastructure, energy consumption, and restrictive production rates prohibited the use of mechanical dewatering on a variety of project sites. Overall, this dewatering methodology greatly reduced the volume and mass of residual solids and costs associated with hauling and disposal while allowing continual operation of facility lagoons and waterways. If time and space are available for Geotube® operations, Geotube® applications are 80 to 90-percent less capital intensive compared to these alternative onsite dewatering techniques.
Keywords: dewatering, liquid residuals, polymers, belt filter press, confined placement area.