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Prior to collection of water-quality samples, all sampling equipment was thoroughly cleaned with a labomtory-grade detergent, rinsed sequentially with tap water, a dilute hydrochloric acid solution, and deionized water. The cleaned sampling equipment was placed into two clean, clear plastic bags between sampling events to avoid environmental contamina- tion. Sampling equipment was thoroughly rinsed with river water prior to sampling. All personnel involved in sampling-equipment preparation and sample collec- tion and processing wore latex gloves to minimize sample contamination. Water-quality samples generally were collected using the equal-width increment method (Edwards and Glysson, 1988). The equal-width increment method provides a sample that is discharge weighted both vertically and laterally and whose volume is propor- tional to the discharge in the sampled zone. The equal-width increment method results in a representa- tive constituent concentration for the entire river cross section. A US-DH--81 water-quality sampler was used when the river was wadable, and a US-D--77 water-quality sampler was used from the cableway when the river was not wadable (Edwards and Glysson, 1988). Both of these samplers use plastic components in their design; therefore, the potential of trace-element contamination resulting from sample contact with metal surfaces is minimized. After the samples were collected, aliquots of mw water for total or total-recoverable (whole-water) analyses were collected into a clean plastic bottle and acidified, using nitric acid, to a pH less than 2; additional aliquots were collected for dissolved-constituent analyses. These aliquots were filtered through a 0.45-~m filter into a clean plastic bottle and acidified using nitric acid to a pH less than 2. After the samples were collected, preserved, and processed, the samples were sent using chain-of-custody procedures to a U.S. Environmental Protection Agency contract laboratory. The samples were analyzed for dissolved (filterable through 0.45-~m filter) and total aluminum, antimony, arsenic, barium, beryllium, boron, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, mercury, molybdenum, nickel, potassium, selenium, silver, sodium, titanium, vanadium, and zinc by using either inductively coupled plasma (ICP) or graphite furnace atomic absorption (GFAA) methods. 4 Quality-controllquality-assurance samples represented about 10 percent of the total samples. These included replicate samples and equipment blanks. Quality-controllquality-assurance samples were analyzed for concentrations of dissolved and total metals. Results from quality-control sample analyses indicated that cleaning procedures were acceptable and that cross contamination was not a problem. Transport of metals entering Terrace Reservoir was evaluated using data collected at site AR34.5, AlamoBa River above Terrace Reservoir (fig. I; table I). From late April 1994 through March 1995, 52 water samples were collected at site AR34.5 for total-metal analyses, and 34 water samples were collected for dissolved-metal analyses. Because previous investigations (Ortiz and others, 1995) indicated that substantial metal transport occurred in the AlamoBa River Basin during minfall runoff, samples were collected using an automatic sampler at a single point within the river cross section at site AR34.5 during a few rainfall-runoff events (table I). These samples were analyzed for total or total-recoverable (whole-water) concentration of trace elements. In general, discrete samples collected during a runoff event were flow weighted the following day into a single composite sample by using guidelines described by the U.S. Environmental Protection Agency (1991) so an event-mean concen- tration could be determined. Additionally, selected discrete samples collected during a few runoff events were analyzed separately to provide information on the variability of metal concentrations that occurs during a rainfall-runoff event. To relate the metal concentration of point samples to a concentration that is representative of the entire cross section, an additional 22 point samples were collected concur- rently with equal-width increment samples collected at various streamflows. Transport of metals out of Terrace Reservoir was evaluated using data collected at site AR31.0, AlamoBa River below Terrace Reservoir (fig. I; table I). From late April 1994 through March 1995, 25 water samples were collected at site AR31.0 for dissolved- and total-metal analyses. Four samples collected from November 1994 through March 1995 were collected at this site during the period when the reservoir outlet was closed. As_sment 01 Metal Trsnsport Inlo snd Oul 01 Tsrracs R...rvolr, Con.jos County, Coloredo, V'I Ul3161 April 1994 Through March 1995