Concurrent Disposal and Consolidation of Dredged Sediment Using Horizontal Drains and Vacuum Loading

A method of remediating a submerged contamination site containing a total volume VT of contaminated sediment comprising a larger percentage by volume of water than fine-grained solids, comprising the steps of:

• a. establishing a submerged pond near the contamination site by:
• i) installing a water barrier structure around an area;
• ii) removing any water from the area;
• iii) removing any contaminated sediment from the area and temporarily storing it outside the pond;
• iv) removing a sufficient volume of non-contaminated earthen materials from the area to create a volumetric capacity sufficient to contain the consolidated volume of the total contaminated sediment and storing the excavated clean material separately out of the pond for later use;
• and,
• v) installing a liner system in the interior of the area;
• b. dredging and discharging a first volume portion V1 of the contaminated sediment into the pond as a slurry;
• c. allowing the first volume portion V1 to separate into a lower, settled solids portion and upper liquid portion;
• d. installing a plurality of parallel, coplanar horizontal drains in the lower solids portion intermediate the bottom of the pond and the top of the solids portion, to form a first level of horizontal drains within the first level of solids;
• e. sequentially repeating steps b-d with a plurality of additional volume portions Vn until the total volume VT of the contaminated sediment is removed from the contamination site, wherein each successive level of horizontal drains is installed within the lower solids portion intermediate the horizontal top of the solids portion and the level of horizontal drains below it;
• f. applying vacuum pressure to each of said horizontal drains to extract water from the solids portion until the total volume VT of contaminated sediment is consolidated in the pond;
• and,
• g. closing the pond by covering the consolidated, contaminated sediment with a layer of excavated clean material.

A system for dewatering and consolidating a total volume VT of sediment having a mixture of water and fine-grained solids, comprising:

• a. a disposal pond near the contamination site for containing the sediment;
• b. a plurality of coplanar drains arranged in parallel, vertically-spaced levels relative to the bottom of the pond,
• c. a vacuum pressure source connected to each said drains;
• and,
• d. a barge for traversing the pond and installing said drains in the sediment

A method of dewatering and consolidating a total volume VT of sediment having a mixture of water and fine-grained solids, comprising the steps of:

• a. establishing a disposal pond near the site of the sediment;
• b. transferring a first volume portion V1 of the sediment from the site to the disposal pond;
• c. allowing the first volume portion V1 to separate into a lower, settled solids portion and upper liquid portion;
• d. installing a plurality of parallel, coplanar horizontal drains in the lower solids portion intermediate the bottom of the pond and the top of the solids portion, to form a first level of horizontal drains within the first level of solids;
• e. sequentially repeating steps b-d with a plurality of additional volume portions Vn until the total volume VT is transferred to the pond, wherein each successive level of horizontal drains is installed within the lower solids portion intermediate the horizontal top of the solids portion and the level of horizontal drains below it;
• f. applying vacuum pressure to each of said horizontal drains to extract water from the solids portion until the total volume VT of contaminated sediment is dewatered and consolidated in the pond.

A method of dewatering and consolidating a total volume VT of sediment having a mixture of water and fine-grained solids, comprising the steps of:

• a. establishing a submerged disposal pond near the site of the sediment by:
• i) installing a silt curtain enclosing a disposal area to minimize migration of suspended sediment out of the area;
• ii) removing a sufficient volume of non-contaminated earthen materials from the area to create a volumetric capacity sufficient to contain the consolidated volume of the total contaminated sediment and storing the excavated clean material separately out of the area for later use;
• and,
• iii) installing a submerged liner on the bottom of the area to minimize migration of contaminants after completion of sediment disposal and pond closure;
• b. dredging and discharging a first volume portion V1 of the contaminated sediment into the pond as a slurry;
• c. allowing the first volume portion V1 to separate into a lower, settled solids portion and upper liquid portion;
• d. installing a plurality of parallel, coplanar horizontal drains in the lower solids portion intermediate the bottom of the pond and the top of the solids portion, to form a first level of horizontal drains within the first level of solids;
• e. sequentially repeating steps b-d with a plurality of additional volume portions Vn until the total volume VT of the contaminated sediment is removed from the contamination site, wherein each successive level of horizontal drains is installed within the lower solids portion intermediate the horizontal top of the solids portion and the level of horizontal drains below it;
• f. applying vacuum pressure to each of said horizontal drains to extract water from the solids portion until the total volume VT of contaminated sediment is consolidated in the pond;
• and,
• g. closing the pond by covering the consolidated, contaminated sediment with a layer of excavated clean material.