Water Quality Data for the Arkansas River Basin 1990-93

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03 8. The chemical constituents presented in this report were analyzed at the U.S. Geological Survey National Water Quality Laboratory (NWQL) in Arvada, Colo., using methods listed in Fishman and others (1994). The inorganic constituents, including dissolved solids, major nutrients, and trace elements, were analyzed using methods described by Fishman and Friedman (1989) and Fishman (1993). Pesticides were periodically collected at five surface -water stations (table 1) and were analyzed using methods described by Wershaw and others (1987) and Fishman (1993). Radiochemical constituents were collected at eight surface -water stations (table 1) and were ana- lyzed using methods developed by Thatcher and others (1977). The nitrogen data presented in the "Water - Quality Data' section at the back of this report indicate a change in the reporting of total nitrite plus nitrate as nitrogen and total ammonia as nitrogen after January 1, 1993. Following a thorough laboratory evaluation of the analytical method used to generate data for the above constituents on unfiltered and filtered samples, the NWQL concluded that "no valid basis exists for distinguishing between unfiltered and filtered determinations of nutrient species" using the current (1992) method, and "concentrations for the identified nutrient species are statistically indistin- guishable" (U.S. Geological Survey, written commun., 1992). As a result, nutrient samples collected for the analysis of total nitrite plus nitrate as nitrogen and total ammonia as nitrogen were replaced by the analyses of the dissolved fraction in 1993. The analysis of total phosphorus was not affected by this change. Suspended- sediment samples were periodically collected at 15 surface -water stations (table 1) using methods described by Guy and Norman (1970). The samples were collected using a DH--48 (hand -held sampler) or a D-74 (cable- and -reel sampler) depth - integrating sampler and the equal- width - increment method described by Sylvester and others (1990). Suspended- sediment samples were analyzed at the U.S. Geological Survey Sediment Laboratory in Cheyenne, Wyo., using methods described by Guy (1969). Samples containing sufficient suspended - sediment concentration were analyzed specifically for the percentage of suspended sediment finer than sand size (less than 0.062 mm). Quality- Assurance Procedures Standard U.S. Geological Survey techniques were used during field collection and preservation of all water - quality samples to ensure that representative environmental samples were obtained for analysis. Standard field procedures included checking equip- ment operation and instrument calibrations before collecting onsite measurements. In addition to stan- dard field procedures, specific quality- control proce- dures for the collection, treatment, and analysis of water samples were followed (Sylvester and others, 1990). The quality- assurance data presented in this report include laboratory analyses of source- solution blanks and field- equipment blanks. Source - solution blanks are samples obtained from the deionized water supply that is considered free of analytes of interest and that was used for rinsing and to develop field - equipment blanks. Field - equipment blanks consisted of deionized water that was passed over all the surfaces of decontaminated sampling and processing equipment to evaluate the adequacy of field cleaning and rinsing procedures. Laboratory quality assurance included procedures described by Friedman and Erdmann (1982). The data generated from quality- assurance samples were reviewed by appropriate U.S. Geological Survey personnel associated with the investigation to identify potential sample contamination problems. Deficiencies in the quality- assurance data were documented and corrective actions were taken when required. The cleaning and rinsing procedures described in the preceding "Methods of Data Collection and Analysis" section were designed to decrease the likeli- hood of equipment- caused contamination between surface -water sites. In an effort to evaluate field - equipment cleaning procedures, a field- equipment blank was collected for laboratory analysis during each sampling trip. During the first year of sampling (1990), measured concentrations of some analytes in the field - equipment blanks were higher than expected. These results prompted a reexamination of the collection process for the field - equipment blanks. It was deter- mined that deionized water that passed over some metal equipment surfaces, which were not in contact with the environmental sample, could have biased the results of the field- equipment blanks. As a result, collection procedures for field- equipment blanks were modified in 1991 to better simulate the contact that occurs between native river water and sampling - equipment surfaces during collection of the environ- mental sample. Subsequent concentrations of analytes determined in the quality- assurance samples were within acceptable levels throughout the remainder of the study. TYPES OF WATER - QUALITY DATA 7