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r,~11?7 t..;J.x.. ~.... Table 8. Bulk atmospheric-deposition sampling sites [Identification number is latitude and longitude of the site with a two-digit sequence number at the end; see figure 8 for site location] Site code PAY GRAV A B C D E F G H J K u.s. Geological Survey Identlflcallon number 394044105420200 393609105423400 392813105403200 392822105410600 393152105434701 393300105431100 393413105432700 393506105430601 393516105430701 393612105423801 394113105420000 394116105414900 QUALITY ASSURANCE USGS quality-assurance procedures are standard- ized. Equipment and water-quality meters are regularly checked and calibrated in the field. Deionized water used in cleaning and processing is monitored for purity (Horowitz and others, 1994). Cleaning procedures are rigorous and are designed to prevent contamination of samples. Prior to sample collection. all sampling equipment and materials were cleaned according to standard procedures described in Horowitz and others (1994). The procedures involve a soak and wash in non-phosphorus detergent, soak and rinse in tapwater, followed by a soak and rinse in a 5-percent hydrochloric acid solution, and a final soak and rinse in deionized water. The procedure was perfonned for all sampler parts that contact the samples, chum splitter, and the pump tubing for sample filtration. Other procedures for ensuring against sample contamination included clean sample-processing areas, two-person sampling crews, disposable capsule filters, and ultrapure concentrated nitric acid stored in teflon containers for use in sample preservation. Two field blanks were collected during the year, although the results for only one field blank were available. A field blank is produced from water that does not contain the substances in the analysis. Specific types of blank water are used for inorganic and organic blank samples. The field blank showed all analytes to be within the precision of the method, except the dissolved organic carbon sample. Methanol was being used in the field cleaning process for the fIlter apparatus and could not be Site name Green Lake paved site near Georgetown. Colorado South Clear Creek gravel site near Georgetown, Colorado Grant road site near Grant, Colorado Grant reference site near Grant, Colorado Road site below Mill Gulch near Grant, Colorado Road site above Mill Gulch near Grant, Colorado Geneva Basin Ski Area road site near Grant, Colorado Road site above Duck Lake near Grant. Colorado Road site near Duck Lake near Grant. Colorado Road site below Guanella Pass near Georgetown. Colorado Road site above Georgetown Reservoir near Georgetown. Colorado Clear Creek reference site near Georgetown, Colorado adequately rinsed from the filter cylinder when consecu- tive samples were being processed. Samples contami- nated by methanol showed up in the analytical data as dissolved organic carbon with a higher value than total organic carbon. The erroneous results were not used, and methanol was eliminated from the cleaning process. A field spike sample was prepared, in addition to a field blank, for each of the trace organic water samples collected. A field spike is prepared by adding a precise amount of a prepared solution containing several of the analytes of interest to organic blank water and analyzing the sample for the percentage recovered. The lab analysis recovered an acceptable amount of the spiked substances in all samples. The results of the field-trace organic blanks indicated that all analytes were less than the reporting limit. When questionable results for a particular analyte were received from the lab. a repeat analysis of the same sample was requested. If the second analysis was more consistent with known characteristics of the site or the particular sample, the new result was used instead of the previous result. There are several samples in which the dissolved concentration of a trace element was reported to be higher than the total recoverable concentration. These inconsistencies are within the precision of the methods used and are due, in part, to the differences in the analytical technique used for dissolved (ICP-MS) and total recoverable trace elements (GF AA or AA), and the differences between particular aliquots of sample. The analytical quality-assurance practices and procedures of the National Water Quality Laboratory are described in Friedman and Erdmann (1982). QUALITY ASSURANCE 19