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STANDARD PROCEDURES Evacuation Groundwater wells are thoroughly purged before sampling to insure that the sample is collected from water that has been newly drawn into the well from the surrounding geolog- ic formation The selection of equipment to evacuate each well is based on the physical characteristics of the well and what is known about the performance of the formation in which the well has been installed There are several suitable devices which can be used for evacuation The most commonly employed devices are air or gas actuated pumps, electric submersible pumps, and hand or mechanically actuated bailers Our personnel frequently employ USGS/Middleburg positive displacement pumps or similar air actuated pumps which do not agitate the water standing in the well Normal evacuation removes three case volumes of water from the well More than three case volumes of water are removed in cases where more evacuation is needed to achieve stabilization of water parameters and when requested by the local implementing agency Less water may be removed 1n cases where the well dewaters and does not recharge to 80% of its original volume within two hours and any additional time our personnel have reason to remain at the site In such cases, our personnel return to the site within twenty four hours and collect sample material from the water which has recharged into the well case Decontamination All apparatus is brought to the site in clean and serviceable condition The equipment is decontaminated after each use and before leaving the site Effluent water from purging and on-site equipment cleaning is collected and transported to Shell's Martinez Manufacturing Complex in Martinez, California Free Product Skimmer The column headed, VOLUME OF DvMSCIBLES REMOVED (ml) is included in the TABLE OF WELL GAUGING DATA to cover situations where a free product skimming device must be removed from the well prior to gauging Skimmers are installed in wells with a free product zone on the surface of the water The skimmer is a free product recov- ery device which often prevents normal well gauging and free product zone measurements The 2 0" and 3 0" PetroTraps fall into the category of devices that obstruct normal gaug- ing In cases where the consultant elects to have our personnel pull the skimmers out of the well and gauge the well, our personnel perform the additional task of draining the accumulated free product out of the PetroTrap before putting it back in the well This Wane Tech Ser%ncm Inc 930826-W-1 Shell 7910 Lower Sacramento Rd,Stocidon page 2