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amec-,"', Mr. Dean Hubbard Regional Water Quality Control Board February 15, 2011 Page 2 are associated with either feature. The chromatographic pattern for the soil sample that was collected at 6 feet bgs from boring TRY-1 is similar to those of samples that were fingerprinted as Bunker C fuel. Additional fingerprinting at this location will likely not provide any additional information regarding the source of the petroleum. As discussed in our January 20, 2010, telephone conversation, AMEC does not propose any additional fingerprinting. Lateral and Vertical Extent of Impacted Soil Kennedy/Jenks Consultants collected several shallow soil samples during a previous investigation in the vicinity of TRY-1 (borings OU2-AO15-S1 through -S4). Data for this previous investigation were not presented on Figure 3 in the Investigation Report. This data is shown on Figure 3 (attached). The highest concentration of total petroleum hydrocarbons quantified as diesel (TPHd) detected in soil samples collected at 6 feet bgs in these four borings was 19 mg/kg. TPH quantified as motor oil (TPHmo)was not detected above the laboratory reporting limit in samples collected at 6 feet bgs. Based on this data, the impacts detected at 6 feet bgs at TRY-1 are laterally delineated and local in nature. Additionally, petroleum hydrocarbons were not detected in the sample collected at 18 feet bgs from boring TRY-1; therefore, the vertical extent of affected soil is defined at this location. Based on the data collected in the vicinity of TRY-1, AMEC does not propose any additional soil sampling in this area. Lateral and Vertical Extent of Impacted Groundwater The lateral and vertical extent of impacted groundwater in the vicinity of TRY-1 have not been defined. AMEC proposes to advance three additional borings for the collection of groundwater samples in the vicinity of TRY-1. Proposed boring locations are shown on Figure 4. Boring TRY-30 will be advanced to define the vertical extent of affected groundwater in this area. Groundwater samples will be collected from boring TRY-30 at approximate depth intervals of 30 to 35, 40 to 45, 50 to 55, and 60 to 65 feet bgs (approximately 10, 20, 30, and 40 feet below the depth of the know affected groundwater). Samples of first-encountered groundwater will be collected from borings TRY-31 and TRY-32, located downgradient (north-northwest) of boring TRY-1, to define the lateral extent of affected groundwater in this area. VICINITY OF TRY-29 Water Board Comment: Affected soil has been delineated in OU-5. However, impacted groundwater has not been defined in the central-eastern area of OU-5 near AMEC boring TRY-29 (5,600 ug/L [micrograms per liter] TPHd). Additional soil and groundwater investigation, including fuel fingerprint determination, is needed north-northeast of the boring.