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I7, f1 . qP22 November 2006 AGE-NC Project No. 95-0167 ff. Page 3 of 15 ku� 3.0. ASSESSMENT OF HYDROCARBON-IMPACTED SOIL AND GROUND WATER t Seven soil probe borings (PI through P3 , P5 through P8) were installed near the former location of UST. Petroleum hydrocarbons were detected in soil samples from P2 to a depth of 20 feet, P3 to a [ ! depth of 25 feet, and P7 to a depth of 15 feet. P3 experienced the highest concentration of TPH-g at 10 feet at a concentration of 230 mg/kg. One soil probe boring (P4) was advanced in the City of Stockton right-of-way on Fremont Street and no hydrocarbons were detected. TPH-g was detected Jin four of six grab ground water samples (P5 , P6, P7, and P8) at concentrations as high as 94,000 micrograms per liter (µg/1) in boring P6. AGE estimated a volume of approximately 775 cubic yards of impacted soil in the vicinity of the former UST. Analytical results of soil samples are presented in Table 1 . Analytical results of grab ground water samples are presented in Table 2. ` From June 1999 to November 2000, six pilot soil borings (MW4 through MW-6) were advanced for the construction of ground water monitoring wells and collection of soil samples. TPH-g was detected in one of the soil samples analyzed (MW 1 - 15) at a concentration of 990 mg/kg. MW- 1 is j 1 located directly east of the former dispenser. _ In November 2000, three soil probe borings (P9 through P 11 ) were advanced at the site. Boring P9 was advanced to a depth of 35 feet bsg, boring P10 was advanced to a depth of 40 feet bsg, and boring Pl l was advanced for collection of a grab ground water sample to 20 feet bsg. TPH-g was detected in soil samples collected from P9 at 15 feet and 20 feet at concentrations of 11 µg/1 and `� 76 µg/1, respectively. TPH-g was detected in all three grab ground water samples (P9 through Pl l) at concentrations as high as 35 ,000 µg/1 in P9 (Table 4). On 20 September 2004, two additional ground water monitoring wells (MW7 and MW-8) were installed at the site. A total of seven soil samples were collected from the borings and no analyzed Lq constituents were detected at or above laboratory reporting limits. Figure 4 illustrates the petroleum impacted soil cross section and the estimated extent of impacted soil in the vicinity of the UST. Analytical results of all soil samples collected at the site are summarized on Table 1 . ' Quarterly ground water monitoring commenced at the site in July 1999; to date, twenty-five ground water monitoring events have been conducted at the site. Ground water flow direction at the site has been consistently towards the northwest. Petroleum hydrocarbons have been detected consistently only in wells MW- 1 and MW-2 ; the highest concentration of dissolved hydrocarbons continues to be in the area of the former UST; TPH-g, BTEX constituents and 1 ,2-DCA are present in significant concentrations in monitoring well MW- 1 . The vertical extent of dissolved petroleum hydrocarbon contamination was defined by the cone ' I Advanced GeoEnvironmental, Inc. i