Synoptic Sampling

After concentrations of the injected chloride achieved equilibrium throughout the study reach, synoptic water samples for chemical analyses were collected on August 26 in acid-washed 3-L polyethylene bottles at each sampling site. To reduce the effect of load changes caused by diel variation in streamflow, samples were collected and processed as rapidly as possible. At sampling sites where stream mixing was good, samples were collected at a single vertical near midstream. At all other sites, equal-width, depth-integrated sampling methods (Knapton, 1985; Ward and Harr, 1990) were used. Synoptic sampling was conducted by one sampling team traveling upstream. Sampling was started at 0905 hours at site 12,410 and was completed at 1513 hours at site 0.

Water-quality samples were transported to a central processing location near the middle of the study reach as soon after collection as possible. Field values of specific conductance and pH were determined on an unfiltered aliquot of each sample. A second unfiltered aliquot was drawn for analysis of total-recoverable metals. Samples for major ions and dissolved metals were filtered through a 0.1-μm plate filter. Sample processing, filtration, and preservation were performed according to procedures described by Knapton (1985), Ward and Harr (1990), and Horowitz and others (1994). Water samples were analyzed by the USGS National Water Quality Laboratory (NWQL) in Lakewood, Colo., using methods described by Fishman and Friedman (1989), Fishman (1993), Garbarino and Taylor (1996), Hoffman and others (1996), and Garbarino and Struzeski (1998). Water-quality data are reported in table 6 (at back of report). The procedure for determining the minimum reporting level was changed (Childress and others, 1999) during analysis of water samples collected for this study. Consequently, two different minimum reporting levels appear for chloride in table 6.

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