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AF/11 Ifflp WESTERN 1386 EAS r BEAMER s tRI_r t <br /> LY GEO-ENGINEERS w�Di AND CA 95776-6003 <br /> (530) 668-5300 <br /> CALM C0N11W 10R#513857 I AX(530)662-0273 <br /> RFGIS"I LRLD(ij-'m ,is rs w(,gL@)niothLr win <br /> October 9, 1998 <br /> Mr John Margowski <br /> Wickland Pioperties <br /> P O Box 13648 <br /> Sacramento, California 95853-4648 <br /> (916) 978-2485, FAX (916) 978-2428 <br /> RE REQUEST FOR SITE CLOSURE and Update Status Report 1153, Scptennbei 1998 <br /> Quaiteily fug Joiner Rcgal Station #603, 6425 Pacific Avenue, Stockton, Cahloinia <br /> Dear Mr Mai gowski <br /> INTRODUCTION <br /> • This update, STATUS REPORT 453, presents data collected fiorr► July 1, through September 30, <br /> 1998 and trrc,ludes the Quarterly Groundwater Sairipling, Vapor Extraction System Monitoring and <br /> Venting of MW8 Also included with this report is the SECOND REQUEST FOR SITE <br /> CLOSURE as outlined in Appendix B of TRI-REGIONAL BOARD STAFF <br /> RECOMMENDATIONS FOR PRELIMINARY INVESTIGATION AND EVALUATION OF <br /> UNDERGROUND TANK SITES, March 1, 1994 <br /> Site Closui a was requested in Update Status Report #52 dated July 9, 1998. Using a Risk Base <br /> Corrective Action Tier 11 model benzene needed to be reduced to below 10 ug/L. This latest <br /> sample rc%ults shows that benzene levels have been reduced to 5 ug/L in wells MW8 and <br /> MW12, to 2 ug/L in MW2 and to 0.8 mg/L in MW 13. All other wells show benzene to be <br /> below laboratory lower detection limas of 0.5 ug/L. A previous report (CONFIRMATION OF <br /> THE EFFECTS OF THE VAPOR EXTRACTION SYSTEM, for this site, dated July 31, 1997) <br /> documented our findings from the soil boring samples obtained to confirm the effectiveness of the <br /> operating Vapor Extraction System (VES) Diilling/sampling occurred oil June 4 and 5, 1997 Four <br /> borings (5134, S135, S136 and SI37) were drilled and sampled Soil sample results from these boring <br /> showed a complete removal of Benzene and Toluene, better than 97% reduction in TPI-Ig and better <br /> than 90% r ecluction in Xylenes, see Table 2 One of these borings (S137) was converted into a two <br /> inch vapor extraction/sparging well and renamed MW13 Testing for the bio-receptors DrssoIved <br /> Oxygen (02), Sulfate (SO4), Nitrate (NO,) and Ferrous Iron (Fe2) was performed during tine <br /> December 1997 quarterly sampling That report documents the ongoing effects of natural <br /> attenuation on the hydiocarbon plume, showing plume reduction and stability As requested by San <br /> Joaquin County Health the Oxygenants were sampled for all wells dui ing the December 1997 <br /> sampling All wells were below the laboratory lower detection limits with the exception of M W 1 1, <br /> i <br /> 1 8603 Update 1153/CLOSURE" 2 10/98 <br />