SITE INFORMATION AND CORRESPONDENCE_FILE 2

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11-07-1996 1 : 13PM FROM P_ 6 en virus,, Request to Install Ground Water Monitoring Wells in lieu of Geoprobes We concur with SJCPHS that installation of ground water monitoring wells and the ability to collect reproducible samples is necessary for delineation of petroleum hydrocarbons in ground water. However, Shell does not wish to install additional wells which do not serve to complete delineation of the plume (i.e. install additional wells from which ground water is not non-detect). Use of the geoprobe is proposed as a reconnaissance tool to determine whether the limits of the plume have been reached. Upon receipt of the ground water chemical analytical data from the geoprobes, if data indicate that ground water conditions are non-detect (ND)for constituents of concern, installation of ground water monitoring wells will be completed If ground water conditions are not ND in the locations of the geoprobes, revised locations will be proposed in a"step-out"manner. Drilling activities in these locations will proceed upon approval and receipt of permits from SJCPHS and acquisitions of encroachment and/or right-of-entry agreements. Request for Additional Monitoring Well to the Southwest of MW-3 The geoprobe locations proposed in the work plan were selected based on SJCPHS December 13, 1996 letter which stated that"additional ground water investigation is necessary west of Geo3, and south of GeoI and Geo4,"and the south/southeasterly ground water flow direction which has been observed. If SJCPHS feels that investigation west of MW-3 is necessary, we would propose that the gcoprobe planned to the west of Geo3 be moved south, to the location shown on the attached Plate 2. It would then address investigation cross-gradient of both Geo3 and MW-3- Request for Additional Soil Investigation in the Former Dispenser Island Area Discussions held with the former consultant regarding the need for investigation in the former dispenser island area were apparently not communicated to Enviros during the transfer of the project. We apologize for this lack of communication. We have noted from the site file that results from the sampling done during the tank and line replacement were submitted to you by Fugro on December 11, 1995. A review of the laboratory data sheets shows that Table 3B "Soil Analytical Results-Product Line Trenches,"contains errors in reporting of benzene and toluene for sample TR-1 and in benzene for sample TR-2. Corrected results are as follows: Smple Benzene Toluene TR-1 0.021 0.008 TR-2 3.7 ----- (results in parts per million) Full documentation of sampling in the former dispenser island areas is provided in Aegis Environmental's "Preliminary Subsurface Investigatiou/I'ank Closure Report," dated June 18, 1990. Geoprobe borings are proposed in the locations shown on Plate 2 to delineate the lateral and vertical extent of petroleum hydrocarbons in soil. The proposed depth of these boring. is 10 feet below grade(fbg). Borings adjacent to sample locations TR-4 and TR-2 will be drilled to depths as necessary to delineate the vertical extent of petroleum hydrocarbons in soil. 2