54 



Total seepage rates and permeabilities of the liners are in the same order of magnitude 



as originally calculated by T.A. Prickitt. 



7.6 Lagoon Water Quality 



During the last two years, test results for many parameters have changed significantly 

 with most sharing a common pattern of declining and then increasing. An investigation 

 has not revealed a specific factor as to the cause of the changes but rather has indicated 

 a series of events that may have influenced the changes. By the end of 1991, tests 

 results were moving towards pre-1990 levels. 



The graphs contained in this section illustrate the results of thirteen parameters for the 

 polishing pond from 1983 to 1991. On many of the graphs, polishing pond volume and 

 pH have been added for reference. Figure 7.2 illustrates polishing pond conductivity and 

 displays the overall general condition of the polishing pond from 1983 to 1991. 

 Historically, there has been an inverse relationship between polishing pond conductivity 

 and polishing pond volume. An increase in polishing pond levels resulting from the 

 addition of supply or melt-water normally results in an improvement in water quality. 

 From 1985 to 1988, conductivity was consistent at about the 3000 ^is/cm level. In mid- 

 1988, conductivity increased as volumes within the lagoons decreased due to very high 

 evaporation rates that year. Over the winter of 1990 and 1991, conductivity reached 



historic levels of 6000 |is/cm before decreasing sharply in early 1991 in response to 

 supply water being added to the lagoon system. At the end of 1991, polishing pond 



