28 



Ground-water quality in the vicinity of the ash lagoons can potentially be affected by leachate 

 movement through the ash lagoon liner systems. The piezometers listed in the Technical Monitoring 

 Schedules are used to assess leachate movement and calculate seepage rates. Piezometric water level, 

 boron and chloride are the chosen indicator parameters to assess leachate movement. 



The ground-water monitoring program was expanded in 1 994 as a result of Ash Lagoon #3 South 

 construction. In total, 20 new pneumatic piezometers and 28 new standpipe piezometers were 

 completed within their target zones. Testing of these piezometers began in 1 995. The limited data so 

 far do not show any unusual or unexpected values. 



Piezometers C867A, C868A and C87 1 A are completed immediately above the liner system, within the 

 ash stack of Ash Lagoon # 1 . The 1 999 monitoring results continue to suggest confirmation of the trend 

 first observed in 1993 that the boron concentration decreases with depth within the ash stack. The 

 effect of ash thickness on leachate quality is, however, not completely understood. 



The chemistry of water immediately above the liner systems is therefore expected to differ from the 

 chemistry of surface water in the lagoons. Meaningfiil information is only available from piezometers 

 installed within Ash Lagoon #1 where ash has been deposited for many years. New piezometers 

 C886A, C887A, C890A and C893A have been completed above the liner system of new Ash Lagoon 

 #3 south and are now being monitored. Future monitoring of all piezometers completed above the 

 lagoon liner systems will continue with the purpose of confirming the boron trend noted above and to 

 improve the understanding of leachate quality and flow from the ash lagoons. 



The piezometric surface measurements for the oxidized till continue to show the presence of a ground- 

 water mound beneath the ash lagoons. The mound extends from the west side of the polishing pond 

 to the east side of Ash Lagoon No. 2. Isolated ground- water mounds have developed within the area 

 of the oxidized ground-water moimd. Piezometers located in the oxidized till suggest limited leachate 

 activity. No seepage activity is evident in the unoxidized till. 



The greatest changes in chloride and boron concentrations within the oxidized till have occurred 

 where piezometric levels have changed the most. Although increasing levels do not automatically 

 suggest that the water affecting the piezometers is leachate, changing piezometric levels do suggest 



