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Well Purging <br /> Before sampling commences, well casing storage water and interstitial water in the artificial <br /> sand pack shall be purged from the well using: (1) a positive displacement bladder pump <br /> constructed of inert non-wetting Teflon and stainless steel; (2) a pneumatic-airlift pumping <br /> a <br /> system;(3)a centrifugal pumping system;or(4)a PVC,Teflon or stainless steel bailer. Methods <br /> of purging will be assessed based on the well size, location, depth, accessibility, and known <br /> chemical conditions. Individual well purge volumes are calculated from the casing volumes. In <br /> general, a minimum of 3 to 5 casing volumes will be purged. Wells which dewater or <br /> demonstrate slow recharge capacities (i-e., low yield wells which only recover to 70 percent of <br /> initial water column height after 1 hour) during purging activities may be sampled after fewer <br /> than 3 to 5 purging cycles. If a''low yield well is to be sampled, sampling shall not take place <br /> until at least 70 percent of the previously measured water column has been replaced by <br /> recharge- Monitoring wells shall be purged according to the protocol flowchart presented in <br /> Plate A-3. Water removed from the wells will either be disposed or stored in 55-gallon DCT <br /> drums for future disposal according to proceedures outlined for contaminated,soil cuttings in the r <br /> Soil Sampling Protocol section above. Where appropriate, physical parameters (pH, specific <br /> conductance, and temperature)'will be monitored by HETI field crew during well purging <br /> operations. If necessary, purging may continue until all three physical parameters have <br /> stabilized. Stability shall be defined,as a change of less than 0.2 pH units, less than 10 percent <br /> in micro mhos,and less than 1.0 degree Centigrade. The pH meters shall be read to the nearest <br /> ±0.1 pH units. Specific conductance meters shall be read to the nearest±10 micro-mhos per <br /> centimeter. Both types of meters shall be calibrated daily to manufacturer's specifications. <br /> Temperature shall be read to the nearest ±0.1 degree centigrade. Field data collected while p <br /> developing,purging and sampling the wells will be entered onto the HETI Purge/Sample Sheet <br /> (Plate A-2). Copies of the Purge/Sample Sheets will be reviewed for accuracy and <br /> completeness for each well sampled.; <br /> } <br /> i <br /> k <br /> ' r <br /> ,I! <br /> I} <br /> . I <br /> Ai <br /> I <br /> 10 <br /> i <br />