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• A purge rate should be selected as to stabilize drawdown. If the.well is able to sustain a 0.5 gallon per minute (gpm) purge rate, then once temperature, pH;and specific conductance parameters have stabilized, as listed above, well purging is considered complete. All purge rates and volumes removed will be recorded on Groundwater Sampling Logs. • If the well is unable to sustain a 0.5 gpm purge rate and the well is pumped dry, then groundwater samples will be collected once the well has recovered a sufficient amount of water to bail. A disposable or properly decontaminated TeflonTM bailer should be used to sample. If the well is purged dry a note will be recorded on the Groundwater Sampling Log. 4` Techniques for conventional /modified well purging include: • Acceptable purge/sampling'devices for this project shall.be submersible positive- displacement type pumps, bailers, and bladder pumps for purging and sampling. It is recommended to purge and sample at similar rates. • Purging should be accomplished with as minimal disturbance to the surrounding formation as 1 possible. fi • Purge water is containerized on-site and stored as directed by the Project Manager. The following formula may be used to determine the volume of any well: V = 5.875xC2xH where: V= volume in gallons C =casing diameter, in feet H=height of water column, in feet Using this formula, the volume`per linear foot of well easing of common casing sizes is listed below: Casing Diameter Volume per inches Linear Foot (gallons) 1.5" 0.092 2.0" 0.163 4.0" 0.563 6.0" 1.469 Well Sampling ' After purging has been completed groundwater samples should be collected either directly from the new or properly decontaminated pump tubing or from a disposable or properly decontaminated Teflon TM bailer equipped with a bottom-emptying device. Appropriate gw sampling.SOP Page 3 Of 5 February 2005