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analyzed for the same range of analytes. <br /> • Explain the rationale for the analytical process being <br /> proposed. <br /> 28. Section 4 . 2.4 states that soil samples will be collected by <br /> inserting a fine-mesh sieve beneath the discharge port of <br /> the drill rig. Considering the travel time in the borehole <br /> and the destruction caused by the drill-bit itself, accuracy <br /> in estimating the depth of samples collected in this manner <br /> does not appear to be likely. <br /> • Explain how an accurate depth of the sample can be <br /> estimated with this collection method. <br /> • If an accurate depth cannot be assured, DLA needs to <br /> propose depth discrete sampling. <br /> Pages 4-4 to 4-6 . Section 4 . 3 <br /> 29. It is stated that groundwater sampling will be performed if <br /> the wells are found to be "structurally sound. " <br /> • Explain how it will be determined if the well is <br /> "structurally sound" . <br /> • If geophysical logging will be performed prior to <br /> sampling, explain who will make the final determination <br /> as to whether a well is "structurally sound" (i.e. , <br /> DDRW-Tracy, WCC, EPA, or the geophysical contractor?) <br /> 30. If Wells No. 1 and 2 are not to be purged prior to sampling, <br /> it will not be possible to retrieve representative samples <br /> of the aquifer water present in the wells since the original <br /> abandonment. Drilling to reopen the well and the addition <br /> of compressed air, potable water, or drilling fluids will <br /> have disturbed the well to the point that no representative <br /> aquifer water will be available for sampling. Purging is <br /> necessary if there is to be any credibility to the data. <br /> • A controlled purging of the wells is recommended, using <br /> standard monitoring parameters such as pH, Eh, specific <br /> conductance and temperature. A method will need to be <br /> found to purge the well without damaging the casing. <br /> If duplicate samples are to be retrieved, the RWQCB <br /> requires a post-sampling purge to remove the water <br /> column present during the first sampling, in order to <br /> get a sample which is independent of the first sampled <br /> water column. <br /> 31. The sampling plan includes retrieval of groundwater samples <br /> from four different wells, with a total of seven samples <br /> 9 of 12 <br />