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_ rr SIERRA STANDARD OPERATING PROCEDURE GROUND WATER SAMPLING The following describes sampling procedures used by SES field personnel to collect and handle ground water samples. Before samples are collected, careful consideration is given to the type of analysis to be performed so that precautions are taken to prevent loss of volatile components or contamination of the sample, and to preserve the sample for subsequent analysis. Wells will be sampled no less than 24 hours after well development. Collection methods specific to ground water sampling are presented below. Prior to sampling, each well is checked for the presence of free-phase hydrocarbons Using an MMC flexi-dip interface probe. Product thickness (measured to the nearest 0.01 ft) is noted on the sampling form. Water level measurements are also made using either a water level meter or the interface probe. The water level measurements are also noted on the sampling form. Prior to sampling, each well is purged of a minimum of four well casing volumes of water using a steam-cleaned PVC bailer, or a pre-cleaned pump. Temperature, pH and electrical conductivity are measured at least three times during purging. Purging is continued until these parameters have stabilized (i.e., changes in temperature, pH or conductivity do not exceed t0.5°F, 0.1 or 5%, respectively). The purge water is stored temporarily on-site in 55-gallon Department of Transportation- approved drums pending analytic results. The drums are labeled with the date,contents,the SES field personnel initials and SES phone number. Ground water samples are collected from the wells with steam-cleaned Teflon bailers. The water samples are decanted into the appropriate container for the analysis to be performed. Pre- preserved sample containers may be used or the analytic laboratory may add preservative to the sample upon arrival. Duplicate samples are collected from each well as a back-up sample and/or to provide quality control. The samples are labeled to include the project number, sample ID, date,preservative, and the field person's initials. The samples are placed in polyethylene bags and in an ice chest (maintained at 4'C with blue ice or ice) for transport under chain-of-custody to the . laboratory.