however, the construction of the holding basin will be an added cost. As an approximation, total 

 costs of the mechanical fillet mining system would be at least as much as the semifixed 

 alternative system and possibly higher, due to the added cost of dragline/scraper equipment 

 discussed above and construction of the holding basin. For simplicity (and because the negatives 

 discussed previously are significant enough to eliminate this alternative regardless of cost), the 

 costs used for analysis will simply duplicate those of the semifixed alternative. 



Summary 



Annual costs of each of the five alternatives are summarized in Table 22. The relative higher 

 cost of the floating plant alternative is initially somewhat surprising. However, when one 

 considers that these costs are for relatively small volumes of material using the more expensive 

 hopper dredge, then the costs seem reasonable. Additionally, many beach nourishment projects 

 obtain their sand from channel maintenance projects where the cost of dredging is borne by the 

 navigation interests and the cost of placement by the entities desiring sand on the beach. 



Table 22 



Cost Summary for Shinnecock Inlet Bypass Alternatives 



Alternatives 



First Cost/Mob & Demob 

 (S) 



Annual Cost ($)' 



1 -Floating Plant 2 

 Nearshore Placement 



Onshore Placement 



500 to 750 K 

 500 to 750 K 



712 K (3-year cycle) 

 866 K (2-year cycle) 

 1.039 M (1 -year cycle) 

 996 K (3-year cycle) 

 1.165 M (2-year cycle) 

 1 .354 M (1-year cycle) 



2--Semi-fixed Plant 3 



3.765 M 



764 K 



3~Crawldog* 



6.361 M 



1.328 M 



4-Punaise? 

 Fillet Scenario 

 Downdrift Scenario 



250 K 

 250 K 



1.310 M 

 1.310 M 



5-Mechanical Scraper/ Dragline 



3.765 M 



764 K 



'Includes amortized first/mob-demob costs. 

 2 Assumes lease/rental. 

 3 Assumes purchase. 



This cost is usually the difference between traditional lowest cost disposal options and beach or 

 nearshore placement. 



Among the intangibles associated with the semifixed alternative are concerns about line 

 plugging and possible water hammer. The possibility of plugging the discharge line is a real 

 danger, and every attempt to prevent plugging, including operating at a lower solids production 



Chapter 5 Bypassing Alternatives 69 



