Pollution Engineering (06/10) Vol. 42, No. 6, P. 31; Zeller, Stephen N.; Ambulkar, Archis
Dredging is the process of extracting sediment material from waterway beds, and common techniques of sediment removal from lakes include draining and excavating the lake, mechanical dredging, and hydraulic dredging. The hydraulic dredging process entails removing and transporting waterways material via sediment/water slurry, and it does not require water drawdown in the lake. Instead, the dredging equipment floats on the water surface and sucks up sediment/water slurry from the lake, conveying the slurry to an offsite location via centrifugal pumps. The process primarily involves a floating barge, dredge unit, pumps, and discharge line, and sediment removal can be carried out over an entire lake or from specific locations within the lakes. Camp Yolijwa in Newville, Pa., faced the buildup of organic sediment in Lake Henrietta, which was impacting the waterfront activities that campers enjoyed. The camp selected a geotextile or filter bags option to separate the water from the sediments; slurry was pumped into polypropylene filter bags, where sediment was trapped and water allowed to filter out through the polypropylene material. The dredged sediment material was disposed offsite following filtering. Some 7,000 cubic yards of dredge material from the lake bottom was removed, and the hydraulic dredging method used a pump to lift the material deposited on the lake bottom and pump it into large filter bags. Within a week or two, the material in the bags reached a texture comparable to wet topsoil and was transported by backhoe and dump truck, and bags were sited along the lake banks so that water returned to the lake as they drained. The dredged material was expected to be compacted to less than 50 percent of its original volume, and the contractor was able to pump the material to any location within an elevation of less than 25 vertical feet of the lake bottom at no extra cost.