Laserfiche WebLink
_ Stantec <br /> I { 1 ^ I <br /> Mike Infurna [EH] <br /> �C " <br /> From: Chevlen, Benjamin [Benjamin.Chevlen@stantec.com] <br /> Sent: Thursday, January 21, 2010 12:01 PM \ <br /> To: Mike Infurna [EH] <br /> Cc: Grayson, Terry L (DXT Services) <br /> Subject: RE: Path forward at 76 Station 5886 in Stockton <br /> Attachments: MW-1 MTBE Concentration Trends.pdf <br /> Mike -Thanks for the response. To answer a couple of your questions, as well as to pose several new ones: <br /> e Stantec is in the process of pursuing an access agreement to perform batch extractions from well cluster <br /> MW-9 (main focus being well MW-9D). Once received, Stantec will perform three 8-hour bi-weekly batch <br /> extraction events. I'll let you know when the access agreement is completed. <br /> e No current cross sections exist for the site. During first quarter 2010, Stantec will prepare some revised <br /> cross sections. <br /> e While no groundwater data was collected from within March Lane, my understanding of the model used is <br /> that point source concentrations were used to predict future contaminant migration and dispersion. For <br /> existing contamination (presumed) between monitoring wells MW-1 and MW-9, the migration and <br /> dispersion of those contaminants is expected to be similar to those predicted for wells MW-1 and MW-9. If <br /> you have further questions regarding the hydrogeologic report, let me know and I'll discuss them with the <br /> Hydrogeologist responsible for preparing the report. <br /> t e 1 respect your comment that you would have liked to see February 2002 data from well MW-1 in the <br /> I hydrogeologic model. The reason that we limited ourselves to data collected over the past two years was <br /> I to create a model representative of current conditions. For your information, I have included a plot showing <br /> all quarterly MTBE concentrations in well MW-1 over time (data points collected during monthly sampling <br /> events performed in the second through fourth quarter of 2001 were omitted). As shown on the figure, not <br /> only have MTBE concentrations steadily declined, but the R-square value for the best-fit trendline is >0.8, <br /> indicating a high level of correlation. The graph suggests that natural attenuation (via bioremediation, <br /> adsorption,and/or dispersion) is occurring. Based on the hydrogeologic model and attached graph, is <br /> additional down-gradient delineation still warranted? <br /> e Stantec is under the impression that not only is additional lateral delineation of the dissolved-phase <br /> hydrocarbons still required, but that vertical delineation is required as well. If additional lateral <br /> delineation is not required, would additional vertical assessment of dissolved-phase MTBE still be <br /> required? Would the results of the future soil vapor sampling be incorporated into the EHD's determination <br /> if additional delineation (both lateral and vertical) is required? <br /> Benjamin Chevlen,P.G. - <br /> Senior Geologist <br /> +- Stantec <br /> 1 Ph (805)230-1266 Ext.293 <br /> Fx: (805)230-1277 <br /> Cell: (916)425-4849 <br /> benjamin.chevlen@stantee.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 /> 6 <br /> Please consider the environment before printing this email. <br /> From: Mike Infurna [EH] [mailto:MInfurna@sjcehd.com]: <br /> 1/21/2010 <br />