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Last modified
8/11/2009 11:32:57 AM
Creation date
8/10/2009 4:56:06 PM
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UCREFRP
UCREFRP Catalog Number
9343
Author
Greve, A. I., N. E. Spahr, P. C. Van Metre and J. T. Wilson.
Title
Identification of Water-Quality Trends Using Sediment Cores from Dillon Reservoir, Summit County, Colorado.
USFW Year
2001.
USFW - Doc Type
Denver.
Copyright Material
NO
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<br /> <br />blank was run as part of the PAH analysis. A method <br />blank is a laboratory blank containing 125 grams of <br />sodium sulfate that undergoes extract filtration, gel <br />permeation chromatography, fraction concentration <br />and solvent exchange, and instrumental analysis <br />(Furlong and others, 1996). All PAH concentrations <br />were below the laboratory reporting limits for the <br />method blank, indicating contamination of samples <br />due to laboratory procedures was negligible. <br />Field replicate quality-control samples were <br />not run as part of the pesticide, PCB, or PAH analysis. <br />However, seven replicate samples from Dillon <br />Reservoir were analyzed for trace elements-four <br />from the longest core taken near the dam and three <br />from core samples taken in the arms of the reservoir. <br />Among the trace-element results for the seven repli- <br />cate samples, only four trace-element concentrations, <br />out of 169 possible comparisons, had a relative percent <br />difference (RPD) higher than 10 percent. RPD is <br />calculated using: <br /> <br />RP D = I (concentration 1- concentration2) x 1001 <br />(concentration I + concentration2)/ 2 <br /> <br />The concentration of sodium in the replicate <br />samples taken at the 3- to 4-cm depth in core DLN <br />differed by 0.08 Ilg/g (microgram per gram), an RPD <br />of 10.81 percent; and the concentration of the chro- <br />mium replicate samples taken from the top 2 cm in the <br />upper Snake River arm differed by 9 Ilg/g, an RPD of <br />14 percent. Samples from the core taken in the upper <br />part of the arm of the reservoir receiving water from <br />the Blue River at the 2- to 3-cm depth had chromium <br />and cobalt RPDs of 10.65 and 19.24 percent, respec- <br />tively, and differences in concentration of 9 Ilg/g and <br />3.3 Ilg/g. Of the 129 possible trace-element concentra- <br />tion comparisons between replicate samples, 103 had a <br />RPD below 5 percent, and 22 had RPDs between 5 and <br />10 percent. <br />No field replicate samples were analyzed for <br />the pesticides, PCBs, or PAHs. The variability of the <br />sampling and analysis methods can be estimated on <br />the basis of field and laboratory replicates from cores <br />collected from several other studies in different loca- <br />tions. These cores were collected and analyzed using <br />the same methods as those used to collect the cores <br />from Dillon Reservoir. Field replicates were from a <br />single core. The sample segment was split in the field. <br />Laboratory replicates were single samples which were <br />sent to the USGS National Water Quality Laboratory, <br /> <br />where they were split and analyzed in duplicate. <br />Five field replicates from other studies were available <br />for pesticides. The average RPD was equal to or less <br />than 20 percent for all compounds except chlordane <br />(24 percent) and ODD (25 percent). Among the <br />27 lab replicates available for pesticides, 5 compounds <br />had an average RPD above 20 percent: chlordane <br />(26 percent), dieldrin (23 percent), ODD (33 percent), <br />DOT (58 percent), and mirex (40 percent). <br />PAH data from other cores included 21 <br />laboratory replicates and 4 field replicates. The <br />laboratory replicates had 15 compounds with an <br />average RPD above 20 percent; 9 between 30 percent <br />and 20 percent, 4 between 40 percent and 30 percent, <br />and 2 above 40 percent. The two compounds with <br />the highest average RPD were C4-128 isomers <br />(42 percent) and C2-l66 isomers (61 percent). The <br />field replicates had 14 compounds with an average <br />RPD above 20 percent; 8 between 30 percent and <br />20 percent, 4 between 40 percent and 30 percent, <br />and 2 above 40 percent. The two compounds with <br />the highest average RPD were 1,6-dimethylnaphtha- <br />lene (44 percent) and 2,3,6-trimethylnaphthalene <br />(41 percent). <br />The results of the trace-element replicates and <br />the laboratory quality-control checks used in the PAH <br />and pesticide analysis indicate that any variability or <br />bias due to sampling, processing, and analysis did not <br />substantially affect the results of this study. <br /> <br />Stream-Water Sampling <br /> <br />One replicate and one field-blank quality- <br />control sample were collected during stream-water <br />sampling. Differences in the concentrations for trace <br />elements in the replicate samples were within I Ilg/L <br />(microgram per liter) with the exception of dissolved <br />aluminum, 2 Ilg/L (28 Ilg/L and 26 Ilg/L); total copper, <br />3 Ilg/L (17 Ilg/L and 20 Ilg/L); and total <br />iron, 10 Ilg/L (230 Ilg/L and 220 Ilg/L). Total iron <br />is reported to the nearest 10 Ilg/L. Relative percent <br />differences are not presented because they do not real- <br />istically reflect variability in data sets that span orders <br />of magnitude and are reported with different numbers <br />of significant figures. No concentrations above the <br />minimum laboratory reporting level for the trace <br />elements were found in the field-blank sample. <br />Based on these results, variability and bias as a result <br />of stream-water sample collection, processing, and <br />analysis did not substantially affect results presented <br />for this study. <br /> <br />STUDY METHODS 9 <br />
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