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11age 1 01 1 <br /> Stantec <br /> Mike Infurna [EH] <br /> From: Chevlen, Benjamin[Benjamin.Chevlen@stantec.com] <br /> Sent: Tuesday, January 19, 2010 10:27 AM <br /> To: Mike Infurna[EH] <br /> Subject: Path forward at 76 Station 5886 in Stockton <br /> Mike-Stantec is currently working on the Fourth Quarter 2009 Quarterly Status Summary Report for the above- <br /> referenced site. In an attempt to be proactive, Stantec will be including several recommendations in the report to <br /> move the site towards case closure. The recommendations and justifications for each recommendation are as <br /> follows: <br /> • Perform periodic batch extractions from off-site monitoring well cluster MW-9. Stantec proposes <br /> performing three bi-weekly batch extraction events in an attempt to decrease the concentration of MTBE in <br /> off-site groundwater. Based on the results of a Sensitive Receptor Survey performed by Stantec in <br /> November 2009 (report dated December 3, 2009), no down-gradient sensitive receptors were identified <br /> within 1,000 feet of the site. Based on hydrogeologic modeling performed for the site(report dated <br /> January 6, 2010), further migration of the off-site MTBE plume is not expected to be significant. Rather <br /> than being performed to protect human health, the batch extraction events would be performed as a <br /> proactive action performed due to ConocoPhillips' desire to remediate environmental impact whenever <br /> feasible. <br /> . Perform on-and off-site shallow soil vapor sampling. Stantec proposes performing on-and off-site <br /> shallow soil vapor sampling activities to evaluate the potential risks associated with vapor intrusion of <br /> vapor-phase hydrocarbons in the subsurface. Due to the shallow depth to groundwater, the soil vapor <br /> samples would likely be taken from a depth of approximately 4 feet bgs, as opposed to the more typical <br /> depth of 5 feet bgs. <br /> . Install one off-site monitoring well cluster, including a well set into a fourth, deeper water-bearing <br /> zone. Stantec proposes installing a set of four monitoring wells down-gradient of well cluster MW-9 <br /> (beyond the TransAmerica property). The purpose of the well cluster is to achieve both lateral and <br /> vertical delineation of the dissolved-phase MTBE plume. At this time, ConocoPhillips will cease pursuing <br /> an access agreement with TransAmerica to install the previously-proposed well cluster/soil borings on the <br /> TransAmerica property. <br /> If there are any other actions that the SJCEHD will need to have performed prior to granting case closure <br /> (assuming favorable results of the three activities proposed above), please let me know. Thank you. <br /> Benjamin Chevlen, P.G. <br /> Senior Geologist <br /> Stantec <br /> Ph: (805)230-1266 Ext. 293 <br /> Fx: (805)230-1277 <br /> Cell:(916)425-4849 <br /> benja min.chevlenr✓a@stantec.com <br /> stantec.com <br /> The content of this email is the confidential property of Stantec and should not be copied, modified, retransmitted, or used for <br /> any purpose except with Stantec's written authorization. If you are not the intended recipient, please delete all copies and <br /> notify us immediately. <br /> Please consider the environment before printing this email. <br /> 1/19/2010 <br />