1、Standard Practice for Collection and Preservation of Water Samples AASHTO Designation: R 24-99 (2013) American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-5b R 24-1 AASHTO Standard Practice for Collection and Preservati
2、on of Water Samples AASHTO Designation: R 24-99 (2013) 1. SCOPE 1.1. The objective of sampling is to collect a portion of material small enough in volume to be conveniently transported to and handled in the laboratory while still accurately representing the material being sampled. This implies, firs
3、t, that the relative portions or concentrations of all pertinent components must be the same in the sample as in the material being sampled, and second, that the sample must be handled in such a way that no significant changes in composition occur before the tests are performed. Complete and unequiv
4、ocal preservation of samples, whether domestic sewage, industrial waste, or natural waters, is a practical impossibility. Regardless of the nature of the sample, complete stability for every constituent can never be achieved. At best, preservation techniques can only retard the chemical and biologic
5、al changes that inevitably continue after the sample is removed from the parent source. 1.2. The values stated in SI units are to be regarded as the standard. 2. TYPES OF SAMPLES 2.1. Grab or Catch SamplesStrictly speaking, a sample collected at a particular time and place can represent only the com
6、position of the source at that time and place. However, when a source is known to be fairly constant in composition over a considerable period of time or over substantial distances in all directions, then the sample may be said to represent a longer time period or a larger volume, or both, than the
7、specific point at which it was collected. In such circumstances, some sources may be quite well represented by single grab samples. Examples are some water supplies, some surface waters, and, rarely, some wastewater streams. 2.1.1. When a source is known to vary with time, grab samples collected at
8、suitable intervals and analyzed separately can be of great value in documenting the extent, frequency, and duration of these variations. Choose sampling intervals on the basis of the frequency with which changes may be expected, which may vary from as little as 5 min to as long as 1 h or more. 2.1.2
9、. When the composition of a source varies in space rather than time, a set of samples collected from appropriate locations with less emphasis on timing may provide the most useful information. 2.1.3. Use great care in sampling wastewater sludges, sludge banks, and muds. No definite procedure can be
10、given, but every possible precaution should be taken to obtain a representative sample. 2.2. Composite SamplesIn most cases, the term composite sample refers to a mixture of grab samples collected at the same sampling point at different times. Sometimes the term time-composite is used when it is nec
11、essary to distinguish this type of sample from others. Time-composite samples are most useful for observing average concentrations that are used, for example, in calculating the loading or the efficiency of a wastewater treatment plant. As an alternative to the separate analysis of a large number of
12、 samples, followed by computation of average and total results, composite samples of this type represent substantial savings in 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5b R 24-2 AASHTO laborat
13、ory effort and expense. For these purposes, a composite sample representing a 24-h period is considered standard for most determinations. Under certain circumstances, however, a composite sample representing one shift, or a shorter time period, or a complete cycle of a periodic operation, may be pre
14、ferable. Evaluation of the effects of special, variable, or irregular discharges and operations may require composite samples representing the period during which such discharges occur. 2.2.1. For determination of components or characteristics subject to significant and unavoidable changes during st
15、orage, composite samples cannot be used. Perform such determinations on individual samples as soon as possible after collection and preferably at the sampling point. Analyses for all dissolved gases, residual chlorine, soluble sulfide, temperature, and pH are examples of determinations of this type.
16、 Changes in components such as dissolved oxygen or carbon dioxide, pH, or temperature may produce secondary changes in certain inorganic components such as iron, manganese, alkalinity, or hardness. Use time-composite samples only for determining components that can be demonstrated to remain unchange
17、d under the existing conditions of sample collection and preservation. 2.2.2. Take individual portions in a wide-mouth bottle having a diameter of at least 35 mm at the mouth and capacity of at least 120 mL. Collect these portions each hourin some cases each half-hour or even every 5 minand mix at t
18、he end of the sampling period or combine in a single bottle as collected. If preservatives are used, add them to the sample bottle initially so that all portions of the composite are preserved as soon as collected. Analysis of individual samples may sometimes be necessary. 2.2.3. It is desirable, an
19、d often absolutely essential, to combine the individual samples in volumes proportional to the volume of flow. A final volume of 2 to 3 L is sufficient for sewage, effluents, and wastes. 2.2.3.1. Automatic sampling devices are available but should not be used unless the sample is preserved as descri
20、bed below. Clean sampling devices, including bottles, daily to eliminate biological growths and other deposits. 2.3. Integrated SamplesFor certain purposes, the information needed is provided best by analysis of mixtures of grab samples collected from different points simultaneously, or as nearly so
21、 as possible. Such mixtures are sometimes called integrated samples. An example of the need for such sampling occurs in a river or stream that varies in composition across its width and depth. For evaluation of average composition or total loading, a mixture of samples representing various points in
22、 the cross section, in proportion to their relative flows, may be useful. The need for integrated samples may also exist if combined treatment is proposed for several separate wastewater streams, the interaction of which may have a significant effect on treatability or even the composition of the mi
23、xture. Mathematical prediction of the interactions may be inaccurate or impossible, and testing of a suitable integrated sample may provide more useful information. 2.3.1. Both natural and artificial lakes often show variations of composition with both depth and horizontal location. However, under m
24、ost conditions, neither total nor average figures are especially significant in these situations. The local variations are of more importance, and the samples are examined separately rather than integrated. 2.3.2. The preparation of integrated samples usually requires special equipment to collect a
25、sample from a known depth, without contamination by the overlying water. Prior knowledge about the volume, movement, and composition of the various parts of the water being sampled is usually required. Therefore, the collection of the integrated samples becomes a complicated and specialized process
26、that cannot be described in complete detail here. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5b R 24-3 AASHTO 3. FREQUENCY AND DURATION OF SAMPLING 3.1. A reasonably accurate estimate of the comp
27、osition of a raw water piped from a large body of water, such as the Great Lakes, far enough from the shoreline to avoid variation from inflowing tributaries and waste discharges, may be made by taking individual samples at infrequent intervals, such as biweekly or monthly, sufficient to cover seaso
28、nal changes. If samples are taken from near the shoreline of such a body of water or from a river, take them at shorter intervals, for instance daily, to provide more exact knowledge of the variations in composition where these are of importance in the use to which the water is to be put. If greater
29、 variations or cycles of pollution occur, or closer surveillance of plant intake water is required, collect more frequent samples; for example, at hourly intervals. 3.2. Water undergoing continuous or intermittent treatment must be sampled with such frequency that adequate control is assured. The in
30、terval between samples is directly related to the rate at which critical characteristics can reach intolerable limits. 4. POINT OF SAMPLING 4.1. Choose the point of sampling with extreme care so that a representative sample of the water to be tested is obtained. Avoid surface scum. 4.2. Because of a
31、 wide variety of conditions found in streams, lakes, reservoirs, and other bodies of water, it is not possible to prescribe the exact point of sampling. Where the water in a stream is mixed so as to approach uniformity, a sample taken at any point in the cross section is satisfactory. For large rive
32、rs or for streams not likely to be uniformly mixed, more samples are desirable and are usually taken at a number of points at the surface across the entire width and at a number of depths at each point. Take care, when boats are used, to avoid collecting samples where the turbulence caused by a prop
33、eller or by oars has disturbed the characteristics of the water. Ordinarily, samples are taken at these points and then combined to obtain an integrated sample of such a stream of water. Alternatively, test the single grab samples, for example, to determine the point of highest bacterial density. 4.
34、3. Choose the location of the sampling point with respect to the information desired and in conformity with local conditions. Allow sufficient distance downstream, with respect to stream flow at the time of sampling, from a tributary or source of pollution to permit thorough mixing. If this is not p
35、ossible, it is better to sample the stream above the tributary or source of pollution and, in addition, to sample the tributary or source of pollution. In general, a distance of 1.5 to 5 km (1 to 3 mi) below the tributary is sufficient. 4.4. Collect samples at least 0.8 km (0.5 mi) below dams or wat
36、erfalls to allow time for the escape of entrained air. When lakes, reservoirs, or other bodies of water are sampled, it is necessary to avoid nonrepresentative areas such as those created by inlet streams, more stagnant areas, or abrupt changes in shorelines, unless determining the effect of such lo
37、cal conditions is a part of the sampling program. 4.5. It is desirable to take a series of samples from any source of water to determine whether differences in composition are likely to exist before final selection of the sampling point. 5. SAMPLE CONTAINERS 5.1. Sample containers shall be made of m
38、aterials that will not contaminate the sample and, before use, shall be cleaned thoroughly to remove all extraneous surface dirt. Chemically resistant glass and polyethylene are suitable materials for the containers. Only polyethylene containers shall be used 2015 by the American Association of Stat
39、e Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5b R 24-4 AASHTO for samples in which small amounts of hardness, silica, sodium, or potassium are to be determined. The collection, storage, and subsequent analytical determination in plastic
40、containers will result in erroneous pH values because of the permeability of plastic to gases such as CO2. Note 1New chemically resistant glass containers shall be conditioned by allowing them to stand full of distilled water for several days. Conditioning may be hastened by a preliminary treatment
41、with dilute hydrochloric acid solution. 5.2. The closures for the sample containers shall be glass stoppers that have been thoroughly washed or plastic caps with suitable liners. 5.3. Refer to Table 1 for the recommended container for individual parameters. 6. GENERAL PRECAUTIONS 6.1. For sampling o
42、f unconfined water at any specified depth in ponds, lagoons, reservoirs, etc., during which contact with air or agitation of the water would cause a change in concentration of characteristics of a constituent to be determined, use a sampling apparatus so constructed that the solution at the depth to
43、 be sampled flows through a tube to the bottom of the container, and that a volume of sample equal to 4 to 10 times the volume of the receiving container passes through it. When no determinations of dissolved gases are to be made, any less complicated apparatus may be used that will permit the colle
44、ction of a sample at a desired depth, or of an integrated sample containing water from all points in a vertical section. 6.2. Some test methods require adjustment to other than ambient temperature. Such adjustment should be carried out when indicated. 6.3. Normally, samples are taken without separat
45、ion of particulate matter. If constituents are present in colloidal or flocculent suspension, take the sample so that they are present in representative portion. 6.4. Volume of sample: 6.4.1. Collect a minimum volume of 2 L; 4 L is preferable. 6.4.2. The estimates in Table 1 cover the volume of samp
46、le required for the usual determinations that are made on a water sample as well as for several tests that are made for special purposes. 6.4.3. The sample volume required for bacteriological analysis varies greatly with the bacterial density of the water. Serial dilutions are necessary for high-den
47、sity samples. 6.5. When samples are to be shipped, do not fill the bottle entirely in order to allow some room for expansion when subjected to a change in temperature. An air space of 10 to 25 mL usually suffices for this purpose, although this does not protect against bursting of the container due
48、to freezing. 6.6. If contact with air would cause a change in the concentration or characteristics of a constituent to be determined, secure the sample without contact with air and completely fill the container. 6.7. Microbiological samples: 6.7.1. When taking a sample from a sample line or tap, all
49、ow the water to run for at least 5 min or long enough to flush, with six to ten times its volume, the entire part of the system that has been stagnant for 2 h or more. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-5b R 24-5 AASHTO 6.7.2. Turn off the sample outlet and empty it of water without touching the inside. Flame the outlet with a suitable torch or other device that will avoid the deposition of soot, which is undesirable. This flaming procedure may be omitted if the outlet
