SITE INFORMATION AND CORRESPONDENCE_FILE 1

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GEOMATRIX Ms. Wendy Cohen Regional Water Quality Control Board - Central Valley 7 November 1994 Page 3 data provided on the large site plan submitted to RWQCB on 13 October 1994 showed that the lateral and vertical extent of petroleum-affected soil has been defined. Mr. Moody also commented that the soil samples should be screened using a photoionization detector (PID) to detect benzene, toluene, ethylbenzene, or xylenes (BTEX). Our workplan states that we will use field vapor readings to assist us in determining which samples should be sent to the laboratory for analysis (p. S, first paragraph). Field vapor readings will be obtained using a PID; each soil boring will be screened with a PID to determine stratigraphic intervals with high vapor readings. Soil samples from intervals with the highest PID readings in each boring will be sent to the laboratory for analysis. WATER QUALITY EVALUATION Mr. Moody's letter requested that a "water quality model" be developed for the site to identify the potential for hydrocarbons in the soil to migrate into the groundwater if the soil is left in place. Our submittal of 13 October 1994 provided the locations and analytical results of all soil and groundwater samples collected to date for the project. As shown on the site plan, petroleum-affected soil occurs at a depth that includes the capillary fringe and the saturated zone. We also understand that the petroleum may have been in the subsurface for at least 50 years, because the pipeline was removed from service in the mid-1940s. Consequently, the project groundwater data can be approached as results of an in-situ leaching test. Accordingly, our strategic model for the site is built on this conceptual foundation and we use the data from the site as real-time evidence of what is happening in the subsurface. The physical distribution of chemical analytical data at the site makes mathematical/chemical modeling or the extrapolation of laboratory leaching tests unnecessary. Real-time site data from the first quarterly sampling event in 1994 show that the petroleum in the saturated or unsaturated subsurface is not providing a source of dissolved petroleum constituents to groundwater. This conclusion will be confirmed via the quarterly monitoring program. As you know, the soluble constituents in petroleum weather very rapidly due to their chemical structure. Therefore, if the material is not very soluble today, it will be even less soluble in the future. We trust that this response adequately addresses the comments in Mr. Moody's letter. We have received agreement from DTSC for review of the SHRA work plan, therefore we request your approval of the stockpiled and drummed soil sampling proposal in this letter by