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1 <br /> c, c <br />' 1 0 INTRODUCTION <br /> SECOR International Incorporated (SECOR) has prepared this report on behalf of 7-Eleven, <br />' Inc to document the findings of assessment work, well installation, oxygen injection and <br /> groundwater extraction feasibility testing, and to submit a Site Conceptual Model for the site <br /> referenced above (Figure 1) The objective of this work was to delineate the vertical and <br />' lateral extent of petroleum hydrocarbons in soil and groundwater at the site and to determine <br /> the feasibility of groundwater extraction and oxygen injection as remedial techniques The <br /> scope of work consisted of the installation of three shallow groundwater monitoring wells, two <br /> deep cone penetrometer test (CPT) borings, one groundwater extraction well, and one <br />' oxygen Injection well, as well as conducting feasibility testing This work was performed as <br /> described in SECOR's Work Plan for Additional Site Assessment and lntenm Remediation, <br /> dated March 19, 2004, and in accordance with conditions stated in a San Joaquin County <br />' Environmental Health Department (SJCEHD) approval letter dated April 13, 2004 (Appendix <br /> A) <br />' 2.0 SITE HISTORY <br /> 21 Background <br />' The site is currently an operating 7-Eleven convenience store and gasoline station Two <br /> 10,000-gallon underground storage tanks (USTs) and one 15,000-gallon UST are located in <br /> the southeastern portion of the property (Figure 2) <br /> 22 Previous Investigations <br /> In 1997, Fluor Daniel GTI conducted Phase I and Phase II assessments at the site, <br />' consisting of soil borings and grab groundwater samples No detectable concentrations of <br /> petroleum hydrocarbons, polynuclear aromatic hydrocarbons, or pesticides were found on- <br /> site A Phase I addendum was submitted by IT Corporation on September 27, 1999 <br />' Under the direction of a SJCEHD representative, ten soil samples were collected on May 2 <br /> and 3, 2003, beneath the product lines and dispensers at depths between 3 5 feet and 4 5 <br />' feet below ground surface (bgs) The soil samples collected did not contain total petroleum <br /> hydrocarbons as gasoline (TPHg) or benzene, toluene, ethylbenzene, or total xylenes <br /> (BTEX) above laboratory reporting limits Maximum reported concentrations of methyl <br />' tertiary butyl ether (MtBE) and tert-butyl alcohol (TBA) were 4 5 milligrams per kilogram <br /> (mg/kg) and 12 mg/kg, respectively (D1-4 0') (Table 1) <br /> Due to the presence of petroleum hydrocarbons and fuel oxygenates in soil and groundwater <br />' beneath the site, SECOR submitted an Underground Storage Tank Unauthorized Release <br /> with the (Leak)/Contamination Site Report to the SJCEHD and the Central Valley Regional <br /> Water Quality Control Board <br />' During fuel line and dispenser upgrade activities on May 3, 2003, SECOR personnel <br /> collected grab water samples (W1 and W2) from two tank pit observation wells (TP-1 and <br />' TP-2) Depths to bottom of wells TP-1 and TP-2 were measured between 11 feet and 12 <br /> feet bgs (Table 2) MtBE, TBA, and tert-amyl methyl ether (TAME) were reported at <br /> concentrations up to 510,000 micrograms per liter (Ng/L), 79,000 ug/L, and 1,500 ug/L, <br />' respectively (Table 3) During UST excavation dewatering activities, approximately 199,090 <br /> 32262 Assessment&Feasibility Report&SCM doc September 34 2004 <br />' 77EL 32262 04 0502 <br />