a number of years of drying before the land can be reused. This often 

 makes available upland areas hard to find. Approximately 1600 cubic 

 yards of dredge spoil occupy an acre to a depth of one foot. 



The land area required for spoil disposal is often extensive and the 

 problems of site acquisition for land disposal are difficult nationwide. 

 In urban situations the only available sites with sufficient acreage may 

 be those that are assigned to open space recreation, or other natural 

 areas. Because of disadvantages in land characteristics, spoil volumes, 

 land use, and other factors the shortage is reported to be most acute in 

 the southeastern United States [31]. 



Placing disposal areas on impermeable soil (such as clay) behind leak- 

 proof dikes, directing wastewater return weirs to saltwater habitats and 

 other methods are used to reduce impacts from this spoil method. 



Contained Disposal : Despite the high cost of dikes and water control 

 structures, disposal of spoil in containment areas in or at the edge of 

 estuaries is a common proposal. Containments range in size from less 

 than 10 acres to over 4 square miles and have life expectancies from less 

 than 1 year to over 100 years [31]. Nearly all containment areas are 

 enclosed by tight dikes and equipped with height-adjustable spillways to 

 accommodate varying filling rates. Containment areas include a detention 

 capability for the removal of suspended matter by settlement [38]. Although 

 the effluent is somewhat improved before it flows over the spillways, a 

 higher level of treatment is often required before discharge when polluted 

 spoil is involved. From Table 22, it is possible to compute flows from 

 pipelines of various sizes and therefore to determine the required size 

 of the detention facility. 



Experience has shown that polluted fine sediments (fines) accumulate 

 on the surface of the spoil mass in containment areas, particularly where 

 maintenance dredging spoils are deposited. To prevent fine material from 

 washing back to the estuary with runoff from rainstorms, it is necessary 

 to keep the spillways (stop logs, return weirs, etc.) in place and function- 

 ing after the dredging has terminated or else to cover the areas with a 

 layer of clean, coarse fill [40]. 



Retaining dikes are primarily earth embankments; however, open-water 

 containment facilities have also been constructed, and in certain cases 

 rockfill or slag has been used. Dike characteristics are largely 

 dependent upon foundation conditions and available construction materials. 

 Construction may be difficult because of generally poor organic foundation 

 conditions or the use of low-quality borrow materials. Retaining dikes 

 often require continual maintenance. Foundation and material deficiency 

 failures have occurred largely because of inadequate dike design, poor 

 construction practices, and minimal inspection of dikes during dredging 

 operations. The effects of seepage are directly responsible for or 

 contribute to the majority of retaining dike failures [41]. 



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