SITE INFORMATION AND CORRESPONDENCE FILE 2

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Rodger Liston ` Darpetro Inc. 749 E. Charter Way, Stockton, California Page 2 of 3 EHD believes the proposed shallow sample depths are appropriate for the UST system components in the immediate area of investigation , however as the deeper sampling points were proposed to assess degassing from ground water, they should all be collected from the same depth interval . As a sand unit was commonly encountered at a depth of 25 feet bsg in the general area , EHD recommends collecting the nine deeper soil gas samples from a depth interval of 23 to 27 feet bsg to include the sand interval . If your consultant concurs with this recommendation , EHD approves the WP-Soil Gas with the common deeper sampling interval . Please be sure the analytical regimen includes total petroleum hydrocarbons as gasoline (TPH-g), 1 ,2-dichloroethane (1 , 2-DCA) and ethylene dibromide (EDB). CGG proposes in WP to advance one boring of unspecified depth in the former UST pit to collect soil samples at 5-foot intervals and grab ground water samples at 10-foot intervals until two consecutive ground water samples test 'non-detect' for gasoline components, the chemical analyses to be performed by an on-site mobile laboratory. In addition , CGG proposes to install a ground water monitoring well , MW- 14, on the south side of .Charter Way for the lateral assessment of impacted ground water toward the south . CGG anticipates that an access agreement to install the proposed MW-14 will not be granted . EHD notes that it may be possible to install wells for lateral assessment immediately south of Charter Way on or near Grant Street. EHD recommends additional wells for lateral characterization in the southeast and northeast corners of the site, and on or near the northeast corner of Grant Street and Charter Way, south of MW-8 (BM-8). . The 814 E . Charter Way site has two monitoring wells near the southeast corner of Charter Way and Grant Street. MW-11 monitors the water table and MWA 11 monitors a sand interval at 50 feet bsg . Trace concentrations of toluene were initially detected in each zone , but were not detected in the second monitoring event. These wells may be suitable to monitor the southeast extent of your plume of impacted groundwater. CGG maintains that the vertical extent of the release was established by soil data from boring B-2. EHD addressed this issue in the 13 April 2004 letter, but misidentified the data obtained from boring B-2 as B-3 data in the letter. EHD's point in the 13 April 2004 letter still holds and EHD notes further that a major interest of the directed vertical assessment is the extent of dissolved contaminants, which the B-2 data would not address , even if its distance from the former UST pit were not an issue. CGG's proposed boring in the former UST pit should address these issues. EHD is concerned that the approach for determining the total depth of the proposed boring in the former UST pit is not an efficient method at this time and has discussed the issue with both the Central Valley Regional Water Quality Control Board (CVRWQCB) and with personnel of the State Water Board Cleanup Fund (Fund) . Both concur that at the current level of assessment of the site and surrounding sites that it would be more appropriate to select a target depth based on the known geology of the area and known contaminant pathways. Hydropunch water samples should be collected from each interval of potential high permeability and submitted to a non-mobile laboratory for chemical analysis. Mobil laboratories are more commonly utilized for control of excavation remedial actions.