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1 <br /> by subtracting the measured depth to water from the surveyed elevation of <br /> the top of the well casing. (Depth to water was measured for all wells on <br /> the same day.) Total well depth was then measured by lowering the sensor <br /> to the bottom of the well. Total well depth, used to calculate purge volumes <br /> and to determine whether the well screen was partially obstructed by silt, <br /> was recorded to the nearest 0.1 foot in the field logbook. <br /> Well Purging <br /> Before sampling occurred, a centrifugal pump, low-flow submersible pump, <br /> or bailer was used to purge standing water in the casing and gravel pack <br /> from the monitoring well. Monitoring wells were purged according to the <br /> protocol presented in Figure A-1. In most monitoring wells, the amount of <br />' water purged before sampling was greater than or equal to four casing <br /> volumes. Some monitoring wells were expected to be evacuated to dryness <br /> after removing fewer than three casing volumes. These low-yield monitoring <br /> wells were allowed to recharge for up to 24 hours. Samples were obtained <br /> as soon as the monitoring wells recharged to a level sufficient for sample <br /> collection. If insufficient water recharged after 24 hours,the monitoring well <br /> was recorded as dry for the sampling event. <br /> Field measurements were recorded in a waterproof field logbook. Figure A-2 <br /> shows an example of the Water Sample Field Data Sheet on which field <br /> data are recorded. Field data sheets were reviewed for completeness by <br /> the sampling coordinator after the sampling <br /> event was completed. <br /> The pH, specific conductance, and temperature meter were calibrated each <br /> day before field activities were begun. The calibration was checked once <br />' each day to verify meter performance. Field meter calibrations were <br /> recorded on the water sample field data sheet (see Figure A-2). <br /> 1 <br /> Well Sampling <br /> A Teflon bailer was the only equipment acceptable for well sampling. When <br /> samples for volatile organic compound analysis were being collected, care <br /> was taken to minimize turbulence and aeration in the sample containers. <br /> Sample Preservation and Handling <br />' The following section specifies sample containers, preservation methods, <br /> and sample handling procedures. <br /> pj010f90\0900020.3az A - 3 Rev. 0 January 27, 1993 <br /> 1 <br />