SITE INFORMATION AND CORRESPONDENCE

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STATE OF CALIFORNIA-Environmental ProtectioNmo6ency PETE WILSON Govemor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD CENTRAL VALLEY REGION 14n�_„I ,,��oF4 3443 Routier Road, Suite A ' 4Z I,% Sacramento,CA 95827-3098 § PHONE:(916)255-3000 �j ✓ L-C ' P � !: 2 1 FAX(916)255-3015 L+ t: - 27 November 1996 Ms. Katie Hower Chevron Pipeline Company P.O. Box 5059 San Ramon, CA 94583 REMEDIAL ACTION WORK PLAN, CHEVRON PIPELINE COMPANY, CORRAL HOLLOW AND GRANT LINE ROADS, TRACY, SAN JOAQUIN COUNTY I have reviewed the 15 November 1996 Remedial Action Work Plan prepared by Geomatrix Consultants for the Chevron Pipeline leak site at Corral Hollow and Grant Line Roads. Geomatrix proposes to begin implementing dual-phase soil and groundwater remediation at the site. I have the following comments regarding the site status and remedial action work plan(RAP). Although the lateral extent of soil and groundwater contamination is fairly well defined,the vertical extent of groundwater contamination still needs to be better defined by monitoring at least one relatively deep groundwater monitoring well placed in an appropriate location. ASW-1 is an appropriate well for monitoring the vertical extent of contamination directly below the most affected area,but I am concerned that vertical migration downward may not occur until some further distance away from the source. An appropriate location for an additional relatively deep monitoring well would be in the approximate location of former grab groundwater sampling point S-17. The well should be screened from approximately 16 to 18 feet below the ground surface. The RAP states that the extent of soil contamination is defined to the north by boring locations S-16 and S-17. However, S-16 showed contamination and S-17 was not sampled. Another p onion of the RAP states that there has been little migration of affected groundwater away from the source. MW-10 has recently shown 96 jLg/l of benzene and 220 lcg/1 of TPH as gasoline and is approximately 200 feet away fiom the source area. These apparent discrepancies need to be explained. The plan to install a dual-phase remedial system is hereby approved. The monitoring network after wells MW-6, MW-7, MW-12 and MW-13 are converted to extraction wells will consist of seven wells (not six as was stated in the RAP). These wells are MW-3, MW-5, MW-8, MW-9, MW-10, MW-11 and MW-14. One additional shallow monitoring well will need to be installed to replace the loss of wells MW-7 and MW-12 . This well could be place to the north and in between these two wells. MW-3 no longer needs to be sampled. Therefore,with the addition of a deep monitoring well as discussed above, a total of eight wells will need to be monitored. This monitoring network is needed to show whether the remediation system is effective at removing contamination from the subsurface. Soil sampling will be needed sometime after the remediation system begins operating to confirm that soil contaminants are being removed. This sampling plan needs to be developed and submitted for approval-