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Page 1 of 2 <br />From: Michael Carroll [mcarroll@sjgov.org] <br />Sent: Tuesday, February 07, 2012 11:05 AM <br />To: Robert McClellon [EH] <br />Cc: Natalia Subbotnikova [EH] <br />Subject: Gas Probe Modifications - answers to questions <br />Thanks for forwarding these questions. I have inserted my responses, which I hope will provide assurance that <br />inserting the tubes within the existing pipes does not conflict with the objectives of soil gas monitoring, and may <br />enhance our ability to do so. <br />Best regards, <br />Mike Carroll <br />W. Michael Carroll, PE <br />Senior Civil Engineer, Public Works/Solid Waste <br />1810 E Hazelton Way <br />Stockton, CA 95205 <br />Phone (Direct): 209-468-8504 <br />Phone (Office Main): 209-468-3066 <br />Fax: 209-468-3078 <br />From: Robert McClellon [EH] [mailto:RMcClellon@sjcehd.com] <br />Sent: Tuesday, February 07, 2012 8:09 AM <br />To: Michael Carroll <br />Cc: Natalia Subbotnikova [EH] <br />Subject: Gas Probe Modifications <br />Mike here are comments from Calrecycle staff: <br />Hello Natalia: Thank you for forwarding the proposed revision to County landfills gas compliance wells. We do <br />understand the Operator would like to reduce their purge time by inserting polyethylene tubes inside the existing <br />PVC pipes. <br />Perhaps this is not important, but most of our probes are W High density polyethylene (HDPE), although we do <br />have some PVC. <br />Based on Calrecycle's landfill gas monitoring procedures, we have recommended against purging the gas probes <br />and have recommended readings once steady state has been achieved. Purging might actually defeat the <br />purpose of true gas monitoring since by purging, gas that might have had the potential to migrate and accumulate <br />within the probes will be purged. <br />This method of monitoring is exactly what we planned. Perhaps "purged" was the wrong term; it is our intent <br />to clear the probe of gas pulled during the previous measurement so that we measure the current <br />concentrations. We don't intend to pull more gas from the soil than that, but gas from the previous <br />measurement could be trapped in the probe, and should be removed before making a new measurement. The <br />tubes will greatly reduce the volume needed to clear the probe for the new measurement. <br />2/7/2012 <br />