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7-Eleven Store #32262 <br /> Extended Groundwater Pumping Test and Oxygen Infection Feasibility Study-Addendum <br /> 12/28/2005 <br /> • Page 2 <br /> MtBE concentrations verses groundwater elevation for wells MW-2, MW-5, MW-6D, and MW-8 <br /> that graphically document the declining MtBE concentrations in groundwater samples collected <br /> from on and offsite wells The concentration verses groundwater elevation plot for downgrad lent <br /> well MW-9 document the MtBE concentrations have been stable,fluctuating between 130 to 590 <br /> micrograms per liter (pg/L) In addition, the dissolved MtBE concentrations in the Shell Oil <br /> Products US (SOPUS) wells MW-4(s) and MW-3(s), located downgradient from the 7-Eleven <br /> site, have also been stable (Figure 2 and Attachment B) The dissolved MtBE concentrations in <br /> well MW-3(s) have fluctuated between <0 50 to 2 9 ug/L and in well MW-4(s) have ranged from <br /> 8 9 to 150 ug/L (Attachment B) The concentration of dissolved MtBE in the deep groundwater <br /> monitoring well, MW-6D, has been attor below 5 ug/L for the last five quarterly sampling events <br /> The current groundwater monitoring array effectively defines the MtBE migrating from the 7- <br /> Eleven Site <br /> RECOMMENDATIONS <br /> Since the dissolved MtBE plume associated with the 7-Eleven Site is stable and declining, <br /> SECOR recommends continued quarterly monitoring and sampling for one year to document <br /> dissolved MtBE plume stability and the declining concentration trend <br /> If you have any questions regarding the contents of this submittal, please contact the <br /> undersigned at (916) 861-0400 <br />• Sincerely, <br /> SECOR International Incorporated <br /> NAZ � <br /> JAFFREY S !n <br /> l !/U AIfCHfIMLO�fIE <br /> Damon Brown Jaff Auchterlonie, P G a +' <br /> Project Geologist Senior Geologist * 4t �O ° <br /> Na 7816 <br /> OF CA1-�F <br /> Attachments Figures <br /> Tables <br /> Attachment A— Regulatory Correspondence <br /> Attachment B — Shell Station — 2375 W Grant Line Road, Tables <br /> cc John Wainwright, SECOR/Ken Hilliard, 7-Eleven Inc <br /> Mr James L Barton, CRWQCB—Central Valley Region <br />• <br />