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WESTERN 1386 EAST BEAMER S'1REFT <br /> ! W(MLAND CA 95776-6003 <br /> .. W,,�'O '+ GEO-ENGINEERS (530) 668-5300. <br /> CALIF.CONTRAC'T'OR 4513857 FAX(530)662-0273 <br /> CiLA <br /> REGISTERED GEOLOGISTS Wege(q-)mother.com <br /> July 9, 1998 <br /> Mr. John Margowski <br /> Wickland Properties <br /> P.O. Box 13648 <br /> .Sacramento, California 95853-4648 <br /> (916) 2485, FAX (916) 978-2428 <br /> RE: REQUEST FOR SITE CLOSURE and Update Status Report #52, May 1998 Quarterly for <br /> former Rcgal Station 11603, 6425 Pacific Avenue, Stockton, California. <br /> 1 <br /> Dcar Mr. Margowski: <br /> INTRODUCTION <br /> �. <br /> This update, STATUS REPORT #52, presents data collected from March 31, through July 2, 1998 <br /> and includes the Quarterly Groundwater Sampling, Vapor Extraction System Monitoring and <br /> Venting of MW8. Also included with this report is the REQUEST FOR SITE CLOSURE as <br /> outlined in Appendix B of TRI-REGIONAL BOARD STAFF RECOMMENDATIONS FOR <br /> PRELIMINARY INVESTIGATION AND EVALUATION OF UNDERGROUND TANK SITES, <br /> March 1, 1994. <br /> A previous report (CONFIRMATION OF THE EFFECTS OF THE VAPOR EXTRACTION <br /> SYSTEM, for this site, dated July 31, 1997) documented our findings from the soil boring Samples <br /> obtained to confirm the effectiveness of the operating Vapor Extraction Systcni (VES). <br /> Drilling/sampling occurred on June 4 and 5, 1997. Four borings (SB4, S135, 5136 and SB7) were <br /> drilled and sampled. Soil sample results from these boring showed a complete removal of Benzene <br /> and Toluene, better than 97% reduction in TPHg and better than 90% reduction in Xylenes, see <br /> 'rabic 2. One of these borings (S137) was converted into a two inch vapor extraction/sparging well <br /> and renamed MW13. Testing for the bio-receptors Dissolved Oxygen (02), Sulfate (SO4), Nitrate <br /> (NO3) and ferrous Iron (Fe2) was performed during the December 1997 quarterly Sampling. That <br /> report documents the ongoing effects of natural attenuation on the hydrocarbon plume, showing <br /> plume reduction and stability. As requested by San Joaquin County Health the Oxygenints werc <br /> sampled for all wells. All wells were below the laboratory lower detection limits with the exception <br /> of MW11, which contained 30 ug/L MTBE. MW1l is offsite and cross gradient of the R603 <br /> hydrocarbon plume and may represent the leading edge of other MTBE plumc(s) in the area. <br /> 1 12603 Update H52/CLOSURE RV 7198 ' <br />