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fi)r;r:;~ q .oj '. ", 1993a). The USGS hydrologic data-collection network is in the area surrounding the industrial facilities of the Site (fig. I). EXPLANATION OF THE SURFACE-WATER DATA The surface-water quantity data consist of daily mean discharge and daily total precipitation collected by the USGS in water year 1996. A detailed explana- tion of how the discharge data were collected, ana- lyzed, computed, and arranged for presentation in this report is provided in Appendix I ("Discharge Data Collection and Computation") at the back of this report. Definitions of hydrologic terms used in this report are provided in Appendix 2 ("Glossary") at the back of this report. The surface-water quality data consist of ana- lytical results for all samples collected by the USGS in water year 1996. Field water-quality measurements (water temperature, pH, and specific conductance), chemical-quality samples, and suspended-sediment , samples (concentrations and sand breaks) were col- lected by the USGS. Analyses of all chemical-quality samples were conducted by the National Water Qual- ity Laboratory in Arvada, Colorado (or one of its con- tractors), according to standard USGS analytical methods. Analyses of all suspended-sediment sam- ples were conducted by the Cascades Volcano Obser- vatory Sediment Laboratory in Vancouver, Washington, according to standard USGS analytical methods. Surface-Water Gaging-Station Identification Numbers Each gaging station identified in this report was assigned a unique site number (for example, GSO I) by EG&G Rocky Flats, Incorporated, as part of previous studies at the Site. The USGS also assigned a 15-digit station identification number to each gaging station for use in the USGS data base. The station identification number usually is the latitude and longitude of the gaging station with a sequence number (00) at the end. Discharge The USGS gaging stations are designed to provide continuous records of discharge at each gage. Gaging stations operated at the Site by the USGS in water year 1996 are listed in table I, and their loca- tions are shown in figure 1. Continuous records of discharge are obtained using a continuous stage- recording device and a rating curve to convert observed stage values to discharge. Records of stage, recorded at 15-minute intervals, can be used to com- pute instantaneous discharge (at a given 15-minute interval) or daily mean discharge (mean for 24 hours). Daily mean discharges are presented in this report. Daily mean discharge data for each gaging sta- tion are listed in tables 2-17 in the "Surface-Water Data" section; data are ordered by site number (GSOI, SW027, and so forth) as listed in table I. Much of the gaging-station descriptive information at the begin- ning of each table was provided by EG&G Rocky Flats, Incorporated (1993b) and was reviewed by the USGS prior to publication in this report. Precipitation Precipitation gages were installed at seven gag- ing stations (GS02, GS03, GS04, GS05, GSIO" SW029, and SW998) in water year 1996 to determine the areal distribution of rainfall at the Site. Because the precipitation gages were not heated, the period of data collection was April to September 1996; precipi- tation from snowfall was not recorded. Daily total precipitation data are listed in tables 18-24 in the "Surface-Water Data" section. Water Quality The USGS collected surface-water quality (chemical and suspended-sediment) data at seven gaging stations (GSOI, GS02, GS03, GS04, GS05, GS06, and SW134) in water year 1996; some sus- pended-sediment samples also were collected at gaging stations GSIO, GSII, and GSI6. Chemical- quality constituents sampled by the USGS in water year 1996 were radionuclides (plutonium, americium, Explanation of the Surface-Water Data 3