26 



Ash Lagoon 3 North. The changes observed were seen as significant although some data appeared 



anomalous. In the fall of 1994 a new piezometer series 885 was completed near series 775. Data 

 from the new piezometers suggests that, in fact, the previous results from 775B and 775D are not 

 representative of actual conditions. Piezometers 775B and 775D were decommissioned as part of 

 Ash Lagoon 3 South construction in December 1994. 



Sand lens piezometers 71 2B, 766, and 767 are located between the polishing pond and the cooling 

 water canal. Piezometer 767 is located on the top of Dyke G and 766 and 7128 are located at the 

 toe of Dyke G. These piezometers have historically been of interest as the sand lens provides a 

 preferential pathway for leachate migration. 



A review of the boron concentration for Piezometer 766 shows an increasing trend up to October 



1 988 when levels peaked at 1 2.6 mg/L. Boron concentrations decreased to 6.99 mg/L in April 1 990, 

 then began increasing again-peaking at 35.2 mg/L in June 1993 before falling to 26.7 mg/L in 

 October 1993. In October 1994, the boron concentration increased to 36.2 mg/L, the highest 

 concentration recorded to date. The chloride concentration for 766 has shown little movement since 

 1987 and remains within the 20 to 30 mg/L range, similar to the ash lagoon surface-water 

 concentration. 



Until April 1988 the boron concentration for Piezometer 767 was increasing and peaked at 

 49.4 mg/L. From this peak the boron concentration has steadily decreased to the end of 1 991 when 

 the concentration leveled off near 5 mg/L. The October 1994 result is 6.41 mg/L. The reduction in 

 boron concentrations for samples from 767 suggest the movement of a slug of leachate and not a 

 continuous plume. There has been an increasing trend in chloride for 767 ranging from 25 mg/L in 



1 989 to 75 mg/L In 1 991 . Since 1991 the concentration has remained near 70 mg/L with an October 

 1994 result of 73.4 mg/L. 



