Water Extraction >> Water Extration Prices

Chemical analyses included radionuclides, majorand trace elements, and organic compounds. Qualityassurance samples were analyzed with each set of environmental samples for all constituents except radionuclides (table 2, atend of report), Water Extration Prices which used different quality-assurance methods. 

Each sample set number can be used to match the sampleset with the corresponding quality-assurance results grouped atthe bottom of tables 3–7 (at end of report). Descriptions of the Water Extration Prices analytical methods follow.

RadionuclidesSelected freeze-dried sediment samples were analyzedfor radionuclides (table 2) at the USGS National Research Program laboratory in Menlo Park, Calif. Cesium-137 (137Cs),lead-210 (210Pb), Water Extration Prices and radium-226 (226Ra) were measured toestimate sediment accumulation rates. 

The short-lived radionuclides beryllium-7 (7Be) (53.3-day half-life) and thorium-234(234Th) (24.1-day half-life) were measured as indicators of sediment mixing Water Extration Prices and recent deposition. 

Activities of total 137Cs,210Pb, 226Ra, 7Be, Water Extration Prices and 234Th were measured simultaneously by gamma spectrometry on the basis of American Society of Testing and Materials standards C 1402-98 and E 181-98,similar to methodology described by Robbins and Edgington(1976), Baskaran and Naidu (1995), and Fuller and others(1999). 

Subsamples of freeze-dried sediment samples were Water Extration Prices counted using a high-resolution intrinsic germanium detector gamma spectrometer. Two spectrometers were used, eachwith different detector geometry: (1) well detector, in which the sample is placed in a borehole in the detector; and (2) axialdetector, in which the sample is place on top of the detectorhousing. 

Samples were sealed in 7-milliliter polyethylenescintillation vials or in 30- or 60-milliliter polypropylenewide-mouth jars. The supported 210Pb activity, defined bythe 226Ra activity, Water Extration Prices was determined on each sample from the352- and 609-kiloelectronvolt gamma emission lines oflead-214 (214Pb) and bismuth-214 (214Bi), respectively, shortlived daughters of 226Ra. 

The supported activity of 234Th, Water Extration Prices defined by its parent uranium-238 (238U), was determined by reanalyzing samples after 5 half-lives or more have elapsed.

Self-absorption of the gamma emission line for each isotope Water Extration Prices was accounted for using an attenuation factor for each counting container calculated from an empirical relation between self-absorption and bulk density developed for this geometryon the basis of the method of Cutshall and others (1983).

Self-absorption of the 214Pb, 214Bi, and 7Be and Water Extration Prices the 661.5-kiloelectronvolt gamma emission lines of 137Cs was negligiblefor the well detector samples. Detector efficiency for eachisotope except 7Be was determined from National Institute ofStandards and Technology (NIST) traceable standards. 

NIST and International Atomic Energy Agency (IAEA) reference Water Extration Prices materials were counted monthly to check detector calibration.Because of the short half-life of 7Be, calibration standardsare not readily available. 

Instead, the detector efficiency forthe 477-kiloelectronvolt emission line of 7Be was determinedusing the actinium-228 emission at 463 kiloelectronvoltfrom an IAEA thorium ore certified reference material. This Water Extration Prices approach assumes no substantial difference in detector efficiency over this narrow energy range. 

The reported uncertaintyin the measured activity, calculated from the random countingerror of samples Water Extration Prices and background spectra at 1 standard deviation, typically was within ±10 percent. The measured activitiesof replicate analysis of material from the same sample agreedto within ±15 percent. 

Measured activities of 7Be were decaycorrected for the period between sample collection Water Extration Prices and analyses. Decay correction for unsupported 234Th was not necessarybecause the samples had no measurable unsupported activityas determined by reanalysis of samples after 5 half-lives ormore had lapsed.

Major and Trace ElementsFreeze-dried sediment samples were analyzed for a suiteof major Water Extration Prices and trace elements, total carbon, total organic carbon,and total nitrogen (table 3). The analyses of all elements,except total carbon, total organic carbon, and total nitrogen,were done following modifications of the procedures ofHorowitz and others (1989). 

For all elements except antimony,arsenic, mercury, Water Extration Prices and selenium, 250- or 500-milligramaliquots were digested with a combination of hydrofluoricacid/perchloric acid/aqua regia in Teflon beakers at 200degrees Celsius (°C); the resulting salts were solubilized using50 milliliters of 0.5-percent nitric acid. 

Cadmium, lead, andsilver concentrations were determined by flame atomic absorption spectrometry (AAS) using a flame ionization tube, Water Extration Prices mixed salt standards, and background correction. All other elementswere analyzed by simultaneous inductively coupled plasmaatomic emission spectroscopy (ICP–AES) with an axial torch,using inter-element correction factors. 

Aliquots from thesame digestion solutions were used for the determination ofantimony, arsenic, Water Extration Prices and selenium, but final solutions were madeup in 50-percent hydrochloric acid. Selenium was determinedon the digestate (in 50-percent hydrochloric acid); antimonyand arsenic were determined after the addition of an oxalicacid/hydroxylamine solution with subsequent reduction.

Determination of selenium was by hydride generation AAS,whereas antimony and arsenic were by hydride generationICP–AES. Mercury was Water Extration Prices analyzed using separate 250- or 500-milligram aliquots digested with LeFort aqua regia at 100 °Cwith quantitation by cold vapor employing an AAS as thedetector.

Total carbon and total nitrogen were determined on 100-to 200-milligram sample aliquots by the evolution (combustion) of both carbon dioxide Water Extration Prices and mixed nitrogen oxides using acarbon/nitrogen analyzer with a thermal conductivity detector.

Total organic carbon was determined by analyzing sample aliquots pretreated with 10-percent hydrochloric acid to remove inorganic carbonates prior to the analysis, Water Extration Prices by the evolution(combustion) of carbon dioxide using a carbon/sulfur analyzerwith an infrared detector.

Analytical precision and bias were monitored by the replicate analyses of 10 percent of the samples (precision) andby the concomitant digestion and analysis of various NIST Water Extration Prices and USGS reference materials (precision and bias), and foundto be similar to those reported in Horowitz and Elrick (1985),Elrick and Horowitz (1985, 1987), and Horowitz and others(1989). 

Precision typically was ±10 percent or better; no biaswas detected. However, Water Extration Prices when sediment-associated elementalconcentrations approached the laboratory reporting levels,precision could be as low as ±100 percent.

Organic CompoundsAnalyses included organochlorine pesticides, polychlorinated biphenyls (PCBs) (table 4), polycyclic aromatichydrocarbons (PAHs) (table 5), urban waste indicator (UWI)compounds (table 6), Water Extration Prices and current-use pesticides (table 7). Insome cases, compounds were quantified by more than onemethod.

Chlorinated Hydrocarbons and Polycyclic Aromatic Hydrocarbons Organochlorine pesticides, PCBs, PAHs, and alkylsubstituted PAHs (alkyl-PAHs) were extracted, isolated, Water Extration Prices and analyzed using the procedures of Noriega and others (2003)and Olson and others (2003).

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