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S EcC ® R . concentrations of TPHg and MtBE of 72,000 ppb (MW-6) and 750 ppb (MW-6), respectively (IT, 2001). In June 2002, SECOR performed a Geoprobe assessment in order to delineate petroleum hydrocarbons in soil and groundwater downgradient and cross-gradient of the site, and to determine future locations for additional off-site groundwater monitoring wells. Nine Geoprobe borings were completed at approximately 15 feet bgs. Petroleum hydrocarbons and fuel oxygenates were not detected in any soil samples above laboratory reporting limits. TPHg and constituents of BTEX were detected in borings GP-1 through GP-3, GP-8, and GP-9, with maximum concentrations of TPHg and benzene reported at 17,000 ppb (GP-1) and 170 ppb (GP-2), respectively. MtBE was detected in groundwater from borings GP-8 and GP-9 at a maximum concentration of 230 ppb (GP-8). Petroleum hydrocarbons and fuel oxygenates were not detected above laboratory reporting limits in groundwater samples from borings GP-4 through GP-7. In November 2002, six groundwater monitoring wells (MW-10 through MW-15) were installed. The groundwater plume was delineated in all directions with the exception of northeast of MW-12. In October 2003 SECOR conducted a pumping well influence study at the site to determine if surrounding wells influence groundwater flow director gradient at the site. It was determined that surrounding wells (particularly site Lathrop Grammar School irrigation well) do not influence groundwater flow direction or gradient beneath the site. In November 2003, well MW-16 was installed north east of MW-12. MtBE was reported in MW-16. SENSTIVE RECEPTORS In January 2003, SECOR performed a sensitive receptor survey which included a search of Department of Water Resource, contact of the local water purveyor, and a 500-foot door-to-door well search. Based on SECOR's receptor survey, 12 wells are present within Y2 mile of the site. Eight of the twelve well are upgradient or cross-gradient. The 4 four down-gradient wells (to the north) are located approximately 1,500 to 2,500 feet from the site. The Lathrop Grammar School irrigation well is located approximately 1,600 feet northeast of the site and is the closest of three wells identified during a 2000- foot radius receptor survey conducted at the site. t. MONITORING AND SAMPLING TRC's Groundwater Monitoring Report dated February 24, 2005 is included as Attachment A, including Tables 1- 3, Figures 1 - 5, plus field data sheets and groundwater analytical reports. Currently MW-1 through MW-16 are monitored and sampled quarterly each year. Samples are analyzed for TPPH, BTEX, and fuel oxygenates. 3 . During the first quarter 2005 groundwater flow was toward the northeast at a gradient of 0.002 ft/ft. Maximum reported concentrations of TPPH and MtBE during the first quarter r. • 2005 were 11,000 ppb (MW-7) and 580 ppb (MW-16), respectively. MtBE concentrations in wells appear relatively stable based on graphs of concentration vs. IN.