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ENGEO INCORPORATED Monitoring Well Sampling The following tasks are to be performed during groundwater monitoring well sample collection: • A decontamination, sample preparation, and support area will be set up at the wellhead. All equipment and instruments that will be placed into the well casing or come in contact with water samples will be decontaminated. Decontamination procedures are described in subsequent sections of the Workplan. All decontamination procedures will be recorded in the field logbook. • The depth to water will be measured using the water level indicator device. Water levels will be measured to an accuracy of 0.01 feet. The probe will be decontaminated before and after each use. The water level will be recorded on the Monitoring Well Purge and Sampling Form (Appendix A) and in the field logbook. Depth to water will be recorded as measured from the top of the well casing. • Calculate the volume of water in casing storage within the packed off interval. The casing storage volume is calculated using the factors for various well casing diameters provided on the Monitoring Well Purge and Sampling Form. The factors are multiplied by the water column height determined by the total depth of the well minus the depth to water. The factors are derived by the following equation: (3.14) x(well inside radius in feet)2 x(7.48 gallons/cubic foot). • A minimum of three casing volumes of water will be purged prior to sample collection, with exceptions made for wells with low recharge rates. Low recharge wells are defined as wells that cannot recharge 80 percent of the original volume within 8 hours. Low recharge wells will not be drawn down more than 50 percent of the original volume during purging. • pH, electrical conductivity, temperature, turbidity, dissolved oxygen and salinity will be monitored during the purging to check that they have stabilized within 10 percent before sampling. Ten sets of water quality measurements will be made during the purging process. • Information concerning well purging shall be recorded on the Monitoring Well Purge and Sampling Form and in the field logbook. 4943.4.640.01 April 17, 2007 7