SITE INFORMATION AND CORRESPONDENCE_FILE 2

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15 May 2009 AGE-NC Project No. 95-0103 Page 4 of 6 were to determine the mass in areas previously under assessed. All soil sample collected under the building were non-detect for petroleum hydrocarbons from a depth of 5 feet to 14 feet bsg. Most of the soil samples collected were impacted at 17 feet to24 feet; while one sample collected at 30 feet demonstrated minor impact (1.3 mg/kg - TPH-g). Of the analytical results for samples under the building, eight sample had concentrations below ten mg/kg(1.1 mg/kg to 8.3 mg/kg)and four had concentration above 100 mg/kg (210 mg/kg to 550 mg/kg). The average concentration, in soil between 17 feet and 24 feet was 216 mg/kg.These values were used to prepare a mass estimate for soil impacted under the building in 2003;which was reviewed by the EHD and received a comment letter dated 27 April 2004. The EHD asserted that the mass was underestimated and thickness of impacted was greater than the laboratory data indicated;when compared to non-detected soil samples within a range of ten feet tick(more samples not impacted then impacted).A statical analysis of the soil sample data set indicates the average TPH-g concentration prior to remediation was 612.8 mg/kg and median value 80 mg/kg; while the average value was 177.8 mg/kg following air-sparging remediation and 106 mg/kg following first ground water extraction cycle. BTEX concentrations in soil also averaged lower following remediation. The first paragraph of the second page points out the EHD conjecture of Chapin Petition assertion the mass of dissolved contamination`rebounds'following the termination of remediation.The more important factor was noted by the EHD was decline caused by remediation. The most significant declined was caused by air-sparging of the ground water within the installation of one main sparge well and seven air-sparge implants screens, designed to create smaller air bubbles, installed to a depth of 30 feet bsg. This mechanical air-sparging likely desorbed and remediated the northern portion of the soil plume.The second most significant declined in the dissolved concentrations may have been the natural attenuation contaminates between 1997 and 2000,prior to active ground water remediation. Bio-degrading bacteria were detected from two wells in 1998. The third most significant declined in the dissolved concentrations may have been the ground water extraction regimes implemented on the site at the direction of the Regional Board; first at the western edge of the site and most recently in the northern portion of the site. Extraction well EW-4 ground water remediated rapidly, which is the location for 8,000-gallon UST release area. The first paragraph of the third page points out the EHD conjecture of Chapin Petition assertion that reduction of adsorbed mass at the site has not been equal to the dissolved mass reduction following remediation cycles. The EHD argument consists of the rising ground water from 21 feet (ground water was detected at 24 fee bsg in 1990) to 10 feet at the maximum level in the spring of 1998; which occurred during the El Nino cycle not typical to California. The majority of the subsurface soils,from 15 feet to 25 feet are sand and may have a greater thickness near the former 8,000-gallon UST area.This type of soil is generally conducive to remediation;as air-sparging and ground water extraction proved by lowering dissolved concentrations rapidly. The letter states that only natural attenuation and soil washing from ground water extraction have influenced the adsorbed soil and omitted the years of air-sparging in the area of the most significantly impacted soils.These soils were Advanced GeoEnvironmental,Inc.