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Montana 



Seventeen samples were collected in Montana south of the 

 international boundary during August, 1987, for purposes of 

 characterizing ground water levels and quality. The samples do not 

 show any major changes from prior years. 



The data for this year's samples are included with previous years 

 data in Table 6 . The sample from GWQQC Well 14 is not included 

 because the polyphosphate solution, used to develop the well after 

 1986 sampling, had not been adequately purged from the well. In 

 almost all cases for all constituents, the current year's data fall 

 within the range established by prior values. Some exceptions 

 occur with the newer wells which only have two or three analyses, 

 however, the most striking aspect of the data is their similarity 

 to the results from prior years. One does not see any indications 

 of a systematic change with one possible exception. The exception 

 is mercury, which is discussed below. 



Mercury data for most of the older wells show the highest values in 

 the years 1981 and 1986, while the 1987 data have no concentration 

 above the detection limit of 40 parts per trillion. If next year's 

 samples show the same low values (verified by referee laboratory 

 results on two or three of the statistically high valued wells), it 

 is recommended that the low sulphate wells completed in the coal 

 seam have the mercury determinations discontinued, and that the 

 other wells be reviewed two years later to evaluate the 

 continuation of mercury analyses. 



There is a sound theoretical reason for not expecting to have 

 detectable mercury in the water from the deeper coal horizons. 

 These waters are typically reduced from their contact with organic 

 matter and much of their sulphate has been reduced to sulphide. 

 Inorgamic mercury is exceptionally insoluble in the presence of 



