USGS-OWQ: NFM 6.7.3.A: Turbidity, electrometric benchtop determination on water subsamples
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Official Method Name
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Turbidity, Static (Benchtop) Determination |
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Current Revision
| Version 2.1, Sept. 2005 |
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Media
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WATER |
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Instrumentation
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Turbidity |
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Method Subcategory
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Physical |
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Method Source
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Citation
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Brief Method Summary
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This on-site measurement method provided requires a turbidimeter using white-light nephelometry (that meets USEPA drinking-water measurement specifications) and other static measurement procedures that do not meet USEPA specifications, such as ISO 7027. Static, or benchtop, determination involves removal of the water sample from its source and immediate measurement. Correct sample-collection and handling techniques, and correct use and calibration of the turbidimeter, are critical to a meaningful measurement. |
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Scope and Application
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Method describes turbidity-sampling techniques from surface-water and ground-water sources, with specific instructions for samples with less than 40 turbidity units and with greater than 40 turbidity units. This method applies to turbidity determination using a portable field turbidimeter on-site at the time of sample collection. The reporting units vary, depending on the instrument type. Sample that is poured into the measurement cell (cuvette)must be well-mixed and bubble-free. This method does not yield an accurate result if coarse materials are present that settle within 3 to 5 seconds. For measurements of drinking water, the turbidity instrument must conform to the specifications detailed in EPA Method 180.1 or GLI Method 2. |
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Applicable Concentration Range
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instrument-dependent |
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Interferences
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Color and/or gas bubbles in the water sample; biologic activity; precipitation of humic acids and minerals; particle settling; condensation, scratches, or dirt on the sample cell. |
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Quality Control Requirements
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Cleaned and calibrated equipment is essential. Record the very first reading after placing sample cell into the measurement chamber. Unstable readings may indicate particle setting. Record a minimum of three readings over a defined time interval; repeat the measurement process with a fresh sample at least two times until three or more sample values fall within +/- 10 percent. |
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Sample Handling
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Sample that is poured into the measurement cell (cuvette) must be well-mixed and bubble-free. This method does not yield an accurate result if coarse materials are present that settle within 3 to 5 seconds. |
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Maximum Holding Time
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24 hours |
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Relative Cost
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Unknown |
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Sample Preparation Methods
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Fresh sample, well-mixed, no bubbles |
