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STANDARD PROCEDURES <br /> Evacuation <br /> Groundwater wells are thoroughly purged before sampling to insure that the sample is <br /> collected from water that has been newly drawn into the well from the surrounding geologic <br /> formation The selection of equipment to evacuate each well is based on the physical <br /> characteristics of the well and what is known about the performance of the formation in <br />' which the well has been installed There are several suitable devices which can be used for <br /> evacuation The most commonly employed devices are air or gas actuated pumps, electric <br /> submersible pumps, and hand or mechanically actuated bailers Our personnel frequently <br /> employ stainless steel positive air displacement pumps or similar air actuated pumps which <br /> do not agitate the water standing in the well <br />' Normal evacuation removes four case volumes of water from the well More than four case <br /> volumes of water are removed in cases where more evacuation is needed to achieve <br /> stabilization of water parameters and when requested by the local implementing agency <br /> Less water may be removed in cases where the well dewaters and does not recharge to SO% <br /> of Its original volume within two hours and any additional time our personnel have reason to <br /> remain at the site In such cases, our personnel return to the site within twenty-four hours <br /> and collect sample material from the water that has recharged into the well case <br /> Bailers: A bailer, in its simplest form, is a hollow tube that has been fitted with a check <br /> valve at the lower end The device can be lowered into a well by means of a cord When the <br /> bailer enters the water, the check valve opens and liquid flows into the interior of the bailer <br /> The bottom check valve prevents water from escaping when the ballet is drawn up and out of <br /> the well <br /> Two types of bailers are used in groundwater wells at sites where fuel hydrocarbons and/or <br /> solvents are of concern The first type of bailer is made of a clear material such as acrylic <br /> plastic and is used to obtain a sample of the surface and the near-surface liquids, in order to <br /> detect the presence of visible or measurable fuel hydrocarbon floating on the surface The <br /> second type of bailer is made of polyethylene, Teflon, or stainless steel, and is used as an <br /> evacuation and/or sampling device Disposable bailers are made of polyethylene plastic, <br /> decontaminated by the manufacturer, individually packaged for one-time only use, and are <br /> inexpensive Teflon and stainless steel bailers are relatively easy to clean and are considered <br /> reusable with proper decontamination <br /> Because bailers are manually operated, variations in operator technique may have a greater <br /> influence on performance than would be found when using more automated sampling <br /> equipment Also, in cases where fuel hydrocarbons are involved the bailer may include near- <br /> surface contaminants that are not representative of water located deeper in the well <br /> Maine Tech Services,Inc 040E3 i-RM-i Western Farm Service @ 35110 S Hwy 33,Vemalxs,CA page 2 <br /> r <br />