32 



disagreement between triplicates for ammonia. The results for TOC ranged from 8.4 to 9.8 mg/L, 



with none of the reporting labs agreeing with each other. Three labs showed very good interagency 

 consistency for sulphate while the fourth lab was biased low. One lab has consistently been biased 

 high for TDS, however this is due in part to differing methodology. If that is considered, the TDS 

 results are comparable. Total zinc results shown some disagreement, with three labs reporting "less 

 than" results and one reporting significantly higher results. Vanadium showed a large variability 

 between labs, with a 1 times difference in reported results. The two labs which reported dissolved 

 iron had good reproducibility within their respective lab but not with each other. Two of the four labs 

 reporting mercury had good agreement, one reported "sample contaminated," and the other 

 reported results ranging from <0.005 to 0.03 ^.g/L (micrograms per liter). The Interagency boron 

 results were comparable for three of the four labs. One lab was biased a little low. The remaining 

 metals results were either near or below the analytical detection limit. 



The evaluation and interpretation of interagency data can be difficult and sometimes impossible, 

 therefore one must do more than just compare raw data in these types of quality-control exercises. 

 It is up to each agency to decide if their results are acceptable with respect to the other participant's 

 results. 



