Laserfiche WebLink
1 Stantec Page 3 of 4 <br /> I -`• II <br /> I ! do in another 250 feet? and what concentrations you would expect in 5 years when <br /> i <br /> it gets there? <br /> I think the batch extraction is a good idea and should go online ASAP, assuming <br /> you can adequately remove enough gw with the access restrictions there. <br /> Adequate volume extraction could aide migration control and mass removal. a hail <br /> Mary.... <br /> so do what you think is best. get me a work plan for:MWs....and access from the <br /> property owner where you think the new wells will be. let me know if you're waiting <br /> for EHD approval/comments to the batch extraction. <br /> thanks for your input. I appreciate COP and Stantec's approach.... <br /> From: Chevlen, Benjamin[mailto: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 <br /> above-referenced site. In an attempt to be proactive, Stantec will be including several recommendations in <br /> the report to move the site towards case closure. The recommendations and justifications for each <br /> recommendation are as follows: <br /> • Perform periodic batch extractions from off-site monitoring well cluster MW-9. Stantec <br /> proposes performing three bi-weekly batch extraction events in an attempt to decrease the <br /> concentration of MTBE in off-site groundwater. Based on the results of a Sensitive Receptor Survey <br /> performed by Stantec in November 2009 (report dated December 3, 2009), no down-gradient <br /> sensitive receptors were identified within 1,000 feet of the site. Based on hydrogeologe modeling <br /> performed for the site (report dated January 6, 2010), further migration of the off-site MTBE plume is <br /> not expected to be significant. Rather than being performed to protect human health, the batch <br /> extraction events would be performed as a proactive action performed due to ConocoPhillips'desire <br /> to remediate,environmental impact whenever feasible. <br /> • Perform on-and off-site shallow soil vapor sampling. Stantec proposes performing on-and off- <br /> site shallow soil vapor sampling activities to evaluate the potential risks associated with vapor <br /> intrusion of vapor-phase hydrocarbons in the subsurface., Due to the shallow depth to groundwater, <br /> the soil vapor samples would likely be taken from a depth of approximately 4 feet bgs, as opposed <br /> to the more typical depth of 5 feet bgs. <br /> • Install one off-site monitoring well cluster, including a well set into a fourth, deeper water- <br /> bearing zone. Stantec proposes installing a set of four monitoring wells down-gradient of well <br /> cluster MW-9 (beyond the TransAmerica property). The purpose of the well cluster is to achieve <br /> both lateral and vertical delineation of the dissolved-phase MTBE plume. At this <br /> time, ConocoPhillips will cease pursuing an access agreement with TransAmerica to install the <br /> previously-proposed well cluster/soil borings on the 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 /> 1/21/2010 <br /> r <br />