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• S E C 0 R Mr. Cervantes Response Letter March 14, 2008 Page 2 soil and groundwater contamination at the Unocal OU. The RDA recently issued a requestfor proposal(RFP) for further work at the Unocal OU. Based on a review of historical data and the RFP,and based on SECOR's experience with excavation activities in areas where the City of Stockton previously performed site decommissioning activities,the likelihood of buried tanks and pipelines with residual product at the Unocal OU is high. It is our opinion that source removal activities and further assessment activities in soil and groundwater are needed at the Unocal OU, although such request should be directed to the RDA. • The monitoring wells located in the parking lot on the north side of Weber Avenue (see area identified in Attachment 2) continue to exhibit high levels of separate phase hydrocarbons. Monitoring wells 19,43,47,48,and 49 were not sampled due to the presence of"Sheen"or"SPM'. It is apparent that additional remedial measures need to be implemented in that area to more quickly and efficiently remove the separate phase product. A work plan for implementing additional remedial activities in the parking area is required to be submitted by 14 March 2008. A work plan for additional groundwater assessment is included in Attachment A. Following completion of those activities and review of the data obtained from the proposed additional assessment,SECOR will provide recommendations for further action in the area north of Weber Avenue. In the interim, the periodic SPH removal events currently performed in this area will continue. Response to Specific Comments: • Monitoring wells 18, 20,42,and 51 were not previously sampled due to "No Access Agreement". The City of Stockton owns the property in which those wells are located. Please coordinate with the City in advance of your sampling events such that you can obtain access. We are more than willing to discuss this issue with the City if there is a continuing problem. Access agreements are and have been in place between the L&M Group and the City of Stockton. The access agreement issues described above were with the Waterfront Office Towers Owners Association. The renewal of a previous agreement, unfortunately,took longer than anticipated. Access has since been secured and quarterly monitoring and sampling has resumed in these wells. • Please delineate clearly the boundary lines of L&M Operable Unit on all figures in future monitoring reports(Figures 1-22 in 3' quarter 2007 report). SECOR has added the boundaries of the L&M OU, Morton-Alco OU, and the Unocal OU to the figures provided in the 4`h quarter report. SECOR will also show these boundaries in future monitoring reports for the site. CRWQCB Response Letter.rinal.doc SECOR International Incorpomted