SITE INFORMATION AND CORRESPONDENCE_FILE 1

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Page 1 of 4 Lori Duncan [EH] From: Rosecrance, Ann [arosecrance@craworld.com] Sent: Tuesday, February 23, 2010 4:34 PM To: Lori Duncan [EH] Cc: denis.l.brown@shell.com; Neely, Joe; Filing Subject: 6131 Pacific Ave, Stockton - Former Shell Service Station - CRA 240854 Lori: We received your January 13,2010 letter in response to our proposed Corrective Action Plan and Site Investigation Work Plan (CAP/WP) of December 9,2009 and discussed it with Shell(Denis Brown and Shell's technical group in Houston). We still believe that the work we proposed in our CAP/WP is warranted and prudent. In determining the next step for this site,our initial thought was to propose a meeting with you to discuss this matter and come to a resolution. However,in the interest of moving this project along,we thought it best to first present our thoughts to you regarding this work via email. If you agree with our expanded explanation regarding our proposed work provided below,then we would not need to have a meeting and will proceed with your approval. But if you and Nuel still feel that some or all of the proposed work described below is not needed,then we would like to meet with you to discuss this further. Below is a description of the major elements of our work plan and our rationale for proposing this work. 1. We proposed one well (MW-15)north of the former USTs to provide shallow delineation along the northern portion of the site since wells MW-1 and MW-2(northern wells)have submerged screens. • MW-15 was not approved by EHD. • EHD states that MW-1 and MW-2 provide sufficient delineation(we agree with this). • We agree that MW-15 is not needed since EHD states that MW-1 and MW-2 provide sufficient delineation to the north. 2. We proposed two wells(MW-16 and MW-17) on the west side and east side,respectively, of the former UST complex. • MW-16 was proposed as a deeply screened well since we only have a shallow screened well (VEW-2) on the west side of the former USTs. • MW-17 was proposed as a shallow screened well since we only have a deep screened well(VEW- 4) on the east side of the former USTs. • EHD has not approved either of these wells and requested that we install one well in the vicinity of the former USTs that is screened deeper than our deep zone wells. EHD indicates that we have sufficient delineation at the site. We agree with EHD that we have delineated the horizontal extent of the plume at the site. But now that we are proposing remediation using ISCO,we need to better define the area where treatment is required. The existing data for the former UST area is not sufficient to make this determination for the following reasons: • The soil data is 20 years old. • Groundwater has risen>20 feet over the life of this case. • The existing wells are screened at different depths across the site. • There has been two phases of remediation and 20 years of natural attenuation that has likely 4/12/2010