CLEAN TECHNIQUES FOR METAL COLLECTION AND ANALYSIS: CITY OF GASTONIA WASTEWATER DIVISION

Clean Techniques for sample collection and analysis of trace metals was implemented to reduce or eliminate NPDES discharge violations. Trace concentrations, which resulted in violations, were caused by contamination of the sample during the collection or analysis process. The trace concentrations were not present in the discharge flow. This paper will highlight what we have specifically done to avoid contaminating samples and how Clean Techniques have greatly reduced metal violations. In addition, this paper will explain the relative low cost modifications in procedures and equipment in order to eliminate measurable effects from contamination.Throughout the collection, sample digestion, and analysis process, significant consideration was given to how to control contamination in the laboratory and at the sampling site. When analyzing for trace concentrations, small levels of background contamination and interference can cause problems. Sources of contamination are improper sample handling, improperly cleaned equipment and containers and dust and debris in the air. Contact with metal objects has been eliminated. Contact with glass is minimal. All materials that come into contact with the sample are carefully cleaned and acid washed. High purity nitric acid (Ultrex) is used for sample preservation and digestions. Everyone involved in handling samples uses extra clean Class 10 gloves.Our techniques have been tested by analyzing equipment blanks, grab sample blanks, and field blanks of deionized water taken at the collection site along with the samples. Digestion blanks are analyzed with sample analysis. Considering that we subtract digestion blank results from the sample results, it is much better to eliminate contamination before the digestion. Since our samples tend to be actually very low in value, a contamination is more likely to show a violation when one is not there than show no violation when an actual violation is present.With assistance from CH2M Hill, guidelines for clean technique were established. Our changes in techniques have been gradual and are ongoing. Staff from Pre-Treatment, Laboratory and Operations has been involved in this process. Split sample analyses were conducted with Battelle Pacific Northwest Laboratory, which is a Clean Metal Laboratory in Sequim, Washington.Our old techniques, used in collection and analysis of metal samples, were in compliance with regulations and standard methods, however, we were not aware of the amount of contamination contributed by old techniques. Our results have shown that changes in violations have been even more dramatic than the changes in our methods.