This estimate of the average concentration of settled material 

 is based on a sediment concentration at the interface between 

 the supernatant and settled layer of 50 g/£. The concentration 

 increases with increasing depth at a rate, of 25 g/£/ft. 



Volume of settled material 

 = 1.19 * 10 7 g/62.5 g/£ 

 = 190,212 I 

 = 6,718 ft 3 or 0.15 acre-ft 



c. Required area based on storage. 

 Area = 0.15 acre-ft/1 ft 



= 0.15 acre 



d. Volume of ponding based on retention time. 

 Ponded volume = 3 cfs x (150 min)(60 sec/min) 



= 27,000 ft 3 or 0.62 acre-ft 



e. Required area based on ponding. 

 Area = 0.62 acre-ft/3 ft 



= 0.21 acre 



Since the surface area is the larger of the two areas required, 

 the surface area is then 0.21 acre. A detailed procedure is 

 outlined in Schroeder (1983). 



Polymer feed system 



57. The polymer feed system should be designed to handle a liquid poly- 

 mer of low viscosity. This type of polymer will minimize handling, pumping, 

 and any dilution problems that occur. A more detailed discussion of this is 

 given in EM 1110-2-5027. 



58. Storage. For a 100,000-cu yd site containing 64,000 cu yd of sedi- 

 ment, 685 gal of polymer would be required to be stored onsite in thirteen 

 55-gal drums (see calculations below) . The polymer will be pumped directly 

 from the drums to an in-line static mixer by a polymer pump. These drums will 

 have to be protected against freezing. 



59. The volume of polymer required is based on the assumption that 

 192,000 cu yd of effluent from the primary CDF will be treated. The optimum 

 polymer dosage is 15 mg/Jl. The specific weight of the polymer is 8.5 lb/gal. 

 Thus, 



38 



