24 



started increasing again, and peaked at 23.7 mg/L at the end of 1991. In 1992, the boron 



concentrations remained stable at about 25 mg/L. 



Until April 1988, the boron concentration for samples from C767 was increasing and peaked at 49.4 

 mg/L. From this peak, the boron concentration has steadily decreased. By the end of 1991 the 

 boron concentration had leveled off t>elow 4 mg/L and remained at this concentration through 1992. 

 The reduction in boron concentrations for samples from C767 to background concentrations suggest 

 a leachate plume and not a continuous front. 



Piezometer C712B has been monitored for several years. Historically, boron concentrations have 

 been below 1 mg/L. In mid-1987, increasing boron concentrations were noted with the concentration 

 peaking in April 1992 at 26.6 mg/L. 



Chloride concentrations trended down in samples from C712B to 50 mg/L in 1988 from over 200 

 mg/L in 1984. Since 1988, chloride concentrations have changed little with the exception of a spike 

 over 125 mg/L in 1991 . There is an increasing trend in samples from piezometer C767, increasing 

 from about 25 mg/L in 1989 to 75 mg/L in 1991. Since 1991, the chloride concentrations in samples 

 from C767 have remained about 75 mg/L. The chloride concentrations for samples from C766 have 

 shown little change since 1987 and remain between 20 and 30 mg/L, similar to ash-lagoon chloride 

 concentrations. The lag time for the boron concentration to increase when compared to chloride is 

 expected because boron moves slower through soil than an element like chloride. The higher boron 

 concentrations in samples from C767 than in samples from the other two piezometers are much 

 closer to the boron concentrations in the Polishing Pond. 



The total calculated seepage from the ash lagoon was determined to be 1.51 Us. This is an 

 increase over the 1991 calculated value of 1.267 Us. 



The increase can mostly be attributed to the increase in calculated seepage rates for Ash Lagoon 

 No. 1 from 0.245 L/s in 1991 to 0.417 L/s in 1992. The piezometric levels in the new piezometers 



