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Page 2of3 <br /> --=- <br />' <br /> From: Michael Carroll [nla|lto:nmcarnzU@ ' ov.org] <br /> Sent: Tuesday, February 07, 2O1211:O5AM <br /> To: Roberty4cCle|hon [EH] <br /> Cc: Natalia Gubbotnikova [EH] <br /> Subject: Gas Probe Modifications - answers toquestions <br /> Good morning Robert, <br /> Thanks for forwarding these questions. | have inserted mnyresponses,which | 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 todoso. <br /> Best regards, <br /> Mike Carroll <br /> vv.Michael Carroll,ps <br /> Senior Civil Engineer,Public Works/Solid Waste <br /> zDzOEHazelton Way <br /> Stockton,Cx95ZO5 <br /> Phone(Di,ect):2O9-4G8-8504 <br /> Phone(Office K8ain):2U9'458'3O66 <br /> Fax:209-468-3078 <br /> From: Robert MnC|eUon [EH] Fnnai|to:RMcC|eUon@ 'cehd.connl <br /> Sent: Tuesday, February O7, 2O128:O9AM <br /> To: Michael Carroll <br /> Cc: Nata(ia8ubbotnihova [EH] <br /> Subject: Gas Probe Modifications <br /> Mike here are comments from Cm|reoyo|ootaff. <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 isnot important, but most ofour probes are WHigh density polyethylene (HDPE),although m/edo <br /> have some PVC. <br /> Based on Calrecycle's landfill gas monitoring procedures,we have recommended againstpur8ingtho0aopnoboa <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 bopurged. <br /> This method ofmonitoring iaexactly what vveplanned. Perhaps "purged"was the wrong term; i1isour 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 betrapped inthe probe, and should beremoved before making anew measurement. The <br /> tubes will greatly reduce the volume needed to clear the probe for the new measurement. <br /> In fact, reducing the amount of gas needed to clear the probe (by using much smaller tubes to carry the sampled <br /> gas)will reduce the potential for the problem brought up by CalRecycle staff—that we do not want to remove <br /> so much gas from the soil that we introduce air from the surface,thus diluting the soil gas. <br /> 2/22/20l2 <br />