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x amec-i Mr. Dean Hubbard Regional Water Quality Control Board February 15, 2011 Page 3 Response Source Determination/Fingerprinting Chevron Energy Technology Environmental Analysis Laboratory (CETEAL), conducted hydrocarbon fingerprinting on the groundwater sample collected from boring TRY-29 identified it as a weathered Bunker C fuel.' AEMC does not anticipate that additional fingerprinting would provide new information, and fingerprinting may not be possible due to the low concentration of petroleum hydrocarbons detected in soil in this area. As discussed in the January 20, 2010, AMEC does not propose any additional hydrocarbon fingerprinting is proposed in this area. Soil Sampling The Water Board comment states that soil has been delineated, but requests additional soil sampling. During the January 20, 2011, phone conversation, you confirmed that additional soil sampling is not requested in this area; however, a soil sample should be collected if affected soil is observed during drilling additional activities. Lateral and Vertical Extent of Impacted Groundwater The lateral and vertical extent of impacted groundwater in the vicinity of TRY-29 have not been defined. AMEC proposes to advance four additional borings for the collection of groundwater samples in the vicinity of TRY-29. Proposed boring locations are shown on Figure 5. Boring TRY-33 will be advanced to define the vertical extent of affected groundwater in this area. Groundwater samples will be collected from boring TRY-33 at depths 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-34 through TRY-36, located downgradient (north-northwest) of boring TRY-29, to define the lateral extent of affected groundwater in this area. METHODOLOGY The same field and analytical methods employed by AMEC, as described in the Investigation Report, will be used for the proposed investigation. To reach the sampling depths proposed, a cone penetrometer test (CPT) rig will be used to advance borings, and groundwater samples will be collected using a Hydropunch-style tool. Therefore, a continuous core cannot be recovered and lithology will not be logged during drilling activities. Groundwater samples will be analyzed for TPHd, TPHmo, polynuclear aromatic hydrocarbons, and benzene, ethylbenzene, toluene, and xylenes. The two deeper groundwater samples collected from borings TRY-30 and TRY-33 will be placed on hold pending results from the shallower groundwater samples at these locations. ' 2010, CETEAL, Project Summary, Project No. 2010.0020, Date Completed: April 5.