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R;1 <br /> IYOIYZOI�T EiTVY2QIT1► 1lT <br /> Specidlls15 rn Sii srnent;Remedial'iestini�.Design Ope�ahgia - <br /> fJaca�iaey 29 2008 <br /> Kit:;fl olnds Sexton <br /> tllti'illll3i'�:�1hC.. . �Y ' <br /> 5:West ThirdSireef- <br /> [1a11ford Califortaia 9320 <br /> Sllb"£GtE <br /> ). Qu ttfetJy Ct ourdwatctr Nlnnt[o"i itg/Win edtatt4 j,_ <br /> y sfen>;•I2ei"ort <br /> C°ou1 th Q•uar ter 20t)7 I <br /> Beacon Stattoii No.3G4:1 l <br /> 1210 East Hairinier'1 ane;St,ckton,.Caltfaiiia <br /> Conclusions and Recommendations <br /> Results of fourth quarter groundwater monitoring indicate continued decreasing hydrocarbon <br /> concentration trends in response to the ongoing remedial actions. Hydrocarbon <br /> concentrations in groundwater in the immediate vicinity of the vapor extraction and air <br /> sparge wells have decreased by one to two orders of magnitude since the initiation of <br /> remediation systems operation, <br /> Horizon completed Installation of anaddtttanal monitoring well MW 14 in August_2006 <br /> according to the approved letter.Work Plan dated April 21,2006. Three rounds of quarterly, <br /> sampling of monitoring well MW-14 since August 2006 indicate -no groundwater <br /> hydrocarbon impacts. Horizon submitted Additional. Monitoring .Well Installation.'and <br /> �} rj Updated Site Conceptual Model on December 7,2006. <br /> Horizon recommends that a proundwater concentration.rebound test be conducted during first <br /> 1 uarter 2008. The VES shall be shut in during January 2008 and remain non-operational <br /> until after the first quarter groundwater monitoring event tentatively planned for March 2008. <br /> Continued non-operation or re-start of the VES shall be evaluated on the basis of results of <br /> l the first quarter 2008 groundwater monitoring. <br /> Horizon further recommends destruction of deep monitoring wells MW-11 through MW-l3 <br /> (screened between 127t and 135 fectdeep)and monitoring well MW-14(screened from 95 to <br /> 100 feet deep). hese wells were ins a e o e ineate t e,vertica extent o -petroleum <br /> hydrocarbon-impacted groundwater. Analytical results of groundwater.samples from these <br /> wells indicate that groundwater at the screened depths is not impacted by petroleum <br /> hydrocarbons and will not be impacted by the initial release that precipitated this remediation <br /> project. <br /> 641gmrQ407.doc. <br /> Project No.1641.410 3 HORIZON ENVIRONMENTAL INC. <br /> e <br /> SAN JOAQUIN CD <br /> 60MONMENTAL HEALTH C � <br /> 6W E. MAIN ST.X ; <br /> 61 I ON Cil 91iW <br /> ❑ APPMved: . <br /> qpm, :80P4"Wft / <br /> �$BPpf�11n djISM ftroWki <br /> telb <br /> ^" /VOY AVAJO C - <br /> zzwlw4y �_#gatA__WS NO 11 1110111 <br /> em tm of aft�I no autiorin or aw M <br /> 1 . <br />