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I <br /> Ground Water Sampling <br /> of the well, it is sealed on one or both ends by some mechanism The ground- <br /> water sample is subsequently transferred into sample containers from the bailer <br /> Bailers are relatively inexpensive to purchase or fabricate (especially the single <br /> and double check valve bailers), easy to clean, portable, simple to operate, and <br /> require no external power source(U S EPA, 1983). Disadvantages are that their <br />' use can be time consuming and labor intensive and that the transfer of water to a <br /> sample container may significantly alter the chemistry of ground-water samples <br /> due to degassing,volatilization or aeration Use of a bailer may also result in an <br />' increase of turbidity that may affect analysis results The four main varieties of <br /> bailers are the single check valve, double check valve, messenger, and syringe <br /> bailers <br />' Recent research focusing on the comparison of different types of ground-water <br /> sampling equipment demonstrates that significant loss of volatile organic <br />' compounds may occur when bailers are used to sample ground water(Pearsall and <br /> Eckhardt, 1987;Yeskis et al , 1988,Tax et al , 1991). Bailers should not be used <br /> to sample ground water that will be analyzed for volatile organic compounds, <br /> unless a bailer is the only available method for sampling an LNAPL or DNAPL <br />' or the use of a bailer is approved by the lead regulatory agency <br /> Bailers used to collect ground-water samples for inorganic analyses should be <br />' constructed of either fluorocarbon resin or PVC Bailers used to collect ground- <br /> water samples for organic analyses should be constructed of stainless steel The <br /> cable used to raise and lower the bailer should also be an inert material or coated <br /> with an inert material Ideally the bailer should be easy to disassemble to facilitate <br /> cleaning and decontamination <br />' Bailers should never be dropped into a well and should be removed from the well <br /> in a manner that causes as little agitation to the sample as possible For example, <br /> the bailer should not be removed in ajerky fashion or be allowed to continually <br /> bang against the well casing as it is drawn u To eensure consistent samples, <br />' Cal/EPA recommends that the bailer be submerged only to a depth necessary for <br /> filling, except when the bailer is being used to sample a DNAPL When <br /> transferring the sample from a bailer to a container,it is preferable to use a bottom <br />' emptying device with a valve to allow the water to slowly drain from the bailer <br /> The sample should be allowed to run down the sides of the collection bottle to <br /> avoid excessive agitation of the sample <br />' Wigle Check Valve Bailers <br />' A single check valve bailer has a check valve at the bottom of the sample <br /> chamber to seal the bailer when it is withdrawn from a well A ball and <br /> seat arrangement is most common In operation, the single check valve <br /> bailer is slowly lowered into the well annulus, water enters the chamber <br />' through the bottom, and when the bailer is withdrawn, the ball <br /> immediately seats with little or no sample loss through the check valve <br /> Single check valve bailers provide a portable and simple means for <br />' collecting a water sample Limitations include difficulty in ascertaining <br /> the point the sample represents within the water column, oxidation near <br /> the sample surface, and possible disturbance of the water column by the <br /> 11 <br />