USGS: TWRI BK 5 CH1 (Susp Sed Conc):  Suspended-sediment concentration in water by filtration or evaporation

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Official Method Name
 Procedure for determining suspended sediment concentration
Current Revision
1969
Media
 WATER
Instrumentation
 Gravimetry
Method Subcategory
 Inorganic
Method Source
  USGS
Citation
 Guy, H.P., 1977, Laboratory theory and methods for sediment analysis: U.S. Geological Survey Techniques of Water-Resources Investigations, book 5, chap. C1, 64 p.
Brief Method Summary
 This method describes the analysis of water samples for suspended-sediment concentration using either filtration or evaporation methods.

Filtration is used for samples with less than 10,000 mg/L of sand or 200 mg/L of clay. If samples contain concentrations higher than these values, evaporation methods are used, due to the possibility of clogging filters. The evaporation method also works well if the sediment readily settles to the bottom of the sample container because of its coarseness or because of the natural flocculation of the suspended clay.

For both methods:Record the gross and tare weights to the nearest gram for each sample. Store the weighed bottles on a convenient rack or table for several hours, or overnight, to assure that the sediment settles from suspension. In the event that the sediment does not settle, filtration tubes or flocculating agents may be used. Samples to be analyzed for particle-size distribution should be separated from those to be analyzed for concentration only.
Record the conductance of the supernatant water for each sample set. This is not published but is used as a control on the person taking the samples and as an aid in finding and correcting errors made in recording the field and lab data.
Decant most of the sediment-free water using care not to disturb or remove sediment. If a dissolved-solids correction is necessary when using the evaporation method, then the amount of supernatant liquid left with the sediment should be approximately equal to one of the aliquots. Use distilled water to wash the remainder into a previously weighed evaporating dish or filtration crucible, depending on the method used.

Filtration method: Pass the sample through a Gooch crucible (a small porcelain cup of approximately 25 ml capacity with a perforated bottom) in conjunction with glass-fiber filter disk or Whatman #934-AH glass filter.

For both methods: Dry the evaporating dishes or crucibles and, after loss of all visible water, heat at about 110o C for 1 hour. The evaporating dishes must be dried at a temperature low enough to prevent "spattering" of sediment from the dishes by boiling action. Cool the containers in a desiccator at room temperature. Weigh the containers to the nearest 0.0001 g on an analytical balance. The tare weight of the evaporating dish should be obtained before each use because of the loss of weight caused by small chips, frequent washing, and slight differences in washing or cleaning methods. The tare weight of the crucible must be obtained before each use because of differences in weights of the filtering mats, especially when the asbestos mats are used. If sediment concentrations are greater than 1,000 mg/l, then it may not be necessary to obtain a new tare weight each time a crucible with a glass-fiber filter mat is used.

Compute the net weight of sediment in the container and deduct, if necessary, the dissolved-solids correction. Compute the concentration of the sample in parts per million determined on the basis of one million times the ratio of the net weight of sediment to the net weight of the water-sediment mixture. The computed parts per million can then be expressed in the common units of milligrams per liter by application of the conversion factor given in the method report. Usually concentrations are less than 16,000 parts per million in which case parts per million equals milligrams per liter. However, when the concentration does exceed 16,000 ppm the appropriate conversion factor should be penciled plainly below the concentration on the form as a reminder to the data user that milligrams per liter is different from parts per million.
Scope and Application
 This method is applicable to the determination of suspended-sediment concentration in water samples. Water samples may vary from containing minute quantities of sediment of very small particle sizes to samples containing large quantities of sediment in a wide range of particle sizes. It is important that the method used is appropriate for the concentration and character of the sediment being analyzed.
Applicable Concentration Range
 Filtration method: applicable to samples with less than 10,000 mg/L of sand or 200 mg/L of clay

Evaporation method: applicable concentration range is undetermined
Interferences
 For samples with suspensions of naturally dispersed clay, the settling time may make the evaporation method impractical; in these cases, special procedures using filtration tubes or flocculating agents can be incorporated into the method.
Quality Control Requirements
 Not available
Sample Handling
 Store sample bottles on a rack or table so that the sediment settles from suspension.
Maximum Holding Time
 Not applicable
Relative Cost
 Less than $50
Sample Preparation Methods
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