64 

 7.7 Interceptor Trench 



When Ash Lagoon No. 3 North was built, two separate interceptor trenches were also 

 constmcted along the toe side of Dykes "H" and "I". Each interceptor trench consists of 

 two legs that drain into a manhole. The west interceptor trench's manhole (designated 

 DG1 ) is at junction of Dykes "D" and "H". One leg extends south from the manhole along 

 Dyke "D" to the end of the dyke. The other leg extends east to about the half way point 

 along Dyke "H". 



The second manhole is located at the junction of Dykes "H" and "I", (designated DG2). 

 One leg extends west along Dyke "H" and stops before it hits the west interceptor trench. 

 The second leg goes northeast along Dyke "I". 



Draining of the interceptor trenches is expected to keep the area downstream of Ash 

 Lagoons No. 2 and No. 3 North from becoming saturated. This is desirable because this 

 area will eventually become Ash Lagoon No. 3 South. It will be easier and less 

 expensive to build this lagoon if the soil is not saturated. 



During the summer of 1989, electric pumps and discharge piping were installed in each 

 manhole. The west manhole discharges in Ash Lagoon No. 2 and the east manhole into 

 Ash Lagoon No. 3 North. Both pumps are activated by level controllers. The pumps 

 were commissioned and put into service in December 1989. 



