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• i <br /> Jim Pinasco <br /> January 4, 1995 <br /> Page 4 <br /> possible sequence is installation of dedicated equipment in <br /> designated wells with a sampling team following after <br /> installation of the bladder pump. For cost effectiveness, it is <br /> also recommended that the sampling study coincide with a <br /> scheduled ground water sampling event. Low-volume purging and <br /> low-flow rate sampling should precede standard purging and <br /> sampling to allow comparison of data collected from different <br /> purge volumes from the same well during the same sampling event. <br /> 4 . Number of Wells To Be Sampled <br /> The Report states that initially 30 wells will be included <br /> in the low-flow rate sampling study. Later, 10 of the 30 wells <br /> will be selected for sampling with all three sampling methods <br /> (conventional purging and sampling with a bailer, low-volume <br /> purge and low-flow rate sampling with dedicated bladder pump, and <br /> standard purging and sampling with dedicated bladder pump) . As <br /> discussed in comment 1, sampling with a bailer provides more data <br /> but from a sampling method that is no longer used at the <br /> facility. It does not make sense to remove dedicated pumps to <br /> collect samples with a bailer, especially because bailers are no <br /> longer used for sampling at DDRW Tracy. <br /> Recommendations <br /> It is recommended that the low-flow rate sampling study be <br /> conducted on the same 30 wells for two sampling events rather <br /> than only 10 wells for the second event. The additional costs <br /> for adding 20 wells to the second event should be more than <br /> offset by savings from deleting sampling with a bailer and <br /> analyzing those samples. Thirty samples from two sampling events <br /> with differing hydrostratigraphic zones, well screen lengths, <br /> contaminant concentrations, and physical locations in the plume <br /> will provide a better set of data from which to- draw comparisons. <br /> The improved comparison will also provide a better basis for <br /> determining which sampling protocol to adopt basewide. Ground <br /> water sampling protocol should be consistent basewide to provide <br /> comparable data. <br /> MS.mk <br /> MS4.015/5 <br />