- 72 - 



During 1990, approximately 3,200 metres of ash line was replaced. Most 

 of the replaced pipe was heavier walled than the pipe that was originally 

 installed. Where possible, the ash lines were placed inside the lagoon 

 dykes so that any leaks would be contained within the lagoon system. 



In November 1990, the ash dykes on Ash Lagoon No. 1 were built up to make 

 room for future operations. The discharge structure was also modified 

 accordingly. 



Seepage calculation using the methods developed by T.A. Prickett, P.E., 

 of Urbana, Illinois, were slightly modified in 1989 to address the loss 

 of piezometer series C730 associated with Ash Lagoon No. 1. The same 

 modifications which involve estimating data for C730 series piezometers 

 were used in 1990. Also, as in 1989, piezometer level measurements were 

 used rather than calculating the change in water levels per year. Re- 

 sults of the seepage calculations for Ash Lagoon No. 1, 2, and 3 and the 

 polishing pond are shown in table 9. A graph of annual seepage rates is 

 shown in Figure 61. 



TOTAL SEEPAGE 

 ASH LAGOON No. 2 

 POLISHING POND 

 ASH LAGOON No t 

 ASH LAGOON No. 3 NORTH 



Figure 61. — Ash lagoon seepage rates at the Poplar 

 River Power Station, 1984-1990. 



