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S ECOR Work Plan for Additional Site Assessment and Interim Remediation Addendum 7-Eleven Store#32262 March 31, 2005 Page 3 REPORTING SECOR will prepare a report summarizing the fieldwork completed and data collected including: • Details of field procedures and operations • Tabulated results of the groundwater sample analyses • Results of the groundwater pumping test • Recommendations for future work. SJCEHD COMMENTS In the February 14, 2005 letter from the SJCEHD, SECOR was requested to address the following comments: • Please provide to SJC/EHD a copy of the chromatogram, as well as documentation of which pipe dope product lists this compound [2-ethyl-9- hexanol] as an ingredient, and an explanation of how SECOR considers it to be likely that pipe dope is the source of the detected contamination. SECOR stated that 2-ethyl-1-hexanol is "commonly associated with pipe dope" based on information provided by Joel Kiff of Kiff Analytical in Davis, California. A copy of the chromatogram and a statement from Mr. Kiff regarding the 2-ethyl-1- hexanol are included in Attachment B • Before SECOR dismisses oxygen injection as a remedial option at this site, SJC/EHD considers that the test should be conducted as proposed and approved, or a justification and validation for the test method employed should be presented to SJC/EHD for further evaluation. Please demonstrate the test design as conducted provided adequate response time for dissolved oxygen to migrate through fine grained soil to the observation wells. SECOR will conduct an additional oxygen injection test as outlined in the original Work Plan for Additional Site Assessment and Interim Remediation. Post-injection dissolved oxygen injection readings will be monitored 24 hours after injection. • Analytical results indicate that the lateral extent of the shallow plume has not been defined. In addition, increasing concentrations of MtBE in MW-2 indicate that further investigation must be done to define the lateral extent of the plume towards the west. MtBE concentrations in groundwater samples collected from monitoring well MW-2 have decreased from 2,900 micrograms per liter (Ng/L) in July 2004 to 220 pg/L in January 2005 (Table 1 and Figure 2). MtBE concentrations in groundwater monitoring well MW-8 (installed July 2004) have decreased from 210 lag/L to 42 pg/L during the same period of time. 1:17-Eleven\7-11 Stores\32262\WorkplansM262 Addendum to Offsite well install and interim remediation workplan.doc