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at the current time. They provide a sample that represents the characteristics of the liquid <br />being sampled at a particular point in space and time. Discrete samples are used where: <br />• The flow of liquid may not be continuous (e.g., batch discharges or intermittent flows) <br />• The characteristics of the liquid are known to be fairly constant <br />• The samples are to be used for parameters with characteristics that are likely to change <br />significantly with time (e.g., dissolved gases, bacterial decay, hydrolysis reactions, <br />oxidation/reduction reactions) <br />• The recharge rate is slow or where the wellbore volume to be purged would be excessive <br />• The compositing process would significantly affect the concentration of an analyte. <br />Interpretation of results depends upon knowledge of groundwater flow direction and formation <br />transmissivity, lithology sampled, and a properly collected, preserved, and uncontaminated <br />sample. See Table 5 through Table 10 for advantages and disadvantages of different sampling <br />devices. A description of the depth of monitoring wells and a depth to the sample interval is <br />necessary before proper sampling strategies can be chosen. <br />B.6.4. Material Considerations <br />The quality of the analytical data can be greatly affected by interactions between the sample <br />and the sampling device. These interactions include chemical attack, microbial colonization, <br />sorption, and leaching effects. To ensure the integrity of the sample and maximize the <br />analytical quality, the sampling device shall be constructed of a nonreactive material. <br />The materials listed below are generally used in construction of sampling devices and sampling <br />containers. <br />B.6.4.1. Rigid materials: <br />• Teflon <br />• Stainless steel <br />• Polyvinyl chloride (PVC) <br />B.6.4.2. Flexible materials: <br />• Teflon <br />• Polypropylene <br />• Linear polyethylene <br />• Flexible PVC <br />• Viton <br />• Conventional polyethylene <br />• Tygon <br />• Silicone/neoprene <br />The choice of materials used shall be considered with respect to the parameter being sampled. <br />The factors to be considered are: <br />Daub & Associates, Inc. <br />Page B-13 Natural Soda LLC 2015 S A P <br />