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Erica Crosby and Allen Sorenson - CDMG <br />November 9, 2004 <br />Page 3 <br />ENV 250.04 <br />are impacted by matrix interferences causing samples to be diluted and to be repeatedly analyzed to <br />achieve quality assurance standards. <br />A matrix interference is a systematic error in the analytical signal caused by the presence of a <br />substance other than the analyte. A common matrix interference for ICP and ICPMS is caused by the <br />sample's impact on the droplet formation in the nebulizer or droplet size election in the spray chamber. <br />When samples have different viscosities, the signal can be suppressed. In samples that contain high <br />TDS, physical properties such as surface tension and viscosity differences from sample to sample can <br />cause inaccuracies in the results. Salt build-up in the nebulizer can also affect the results. The <br />samples have to be diluted for ICP and ICPMS to reduce the TDS to < 2000 mg/L to eliminate this <br />problem. In our samples, high solids and high pH are the main interferences. <br />A comparison between the data provided for the shallow alluvial aquifer wells or the up-gradient wells <br />versus the deeper down-gradient wells shows that when the reactivity, matrix interference, and solids <br />precipitation are not a factor the data is less variable with a markedly smaller standard deviation. <br />As a result of the unique nature of many of the samples from the Yankee Gulch monitoring program, <br />the samples are batched in the lab according to the initial screening conductivity reading so standards <br />can be used that will compensated for the full range represented in the samples and so that <br />precautions can be taken to protect the instruments from the high levels of some of the constituents. <br />American Soda hopes that this response letter answers your questions regarding Technical Revision <br />#4 for modification of the ground water monitoring plan. Should you have any additional questions or <br />comments regarding this information, please contact me at (970) 285-0406. <br />Sincerely, <br />~~~~~~~ <br />Celina Akin <br />Environmental Engineer <br />