SITE INFORMATION AND CORRESPONDENCE

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Beacon Station No. 3641 March 17,2011 Stockton California No Further Action Required Request 14. The additional cost to remediate the site to background levels would exceed the incremental benefit to sensitive receptors in the area. Residual hydrocarbon impacts will not unreasonably affect the current and foreseeable beneficial uses of the groundwater resource. See Updated Site Conceptual Model; Source, Nature and Extent of Soil and Groundwater Impacts, 15. The residual mass of TPHg in soil was estimated as the difference between the original mass estimated from investigation soil data and the mass removed by vapor extraction. The residual masses of TPHg, benzene, and MTBE in groundwater were estimated on the basis of the latest groundwater monitoring data (fourth quarter 2010). See Updated Site Conceptual Model; Source, Nature and Extent of Soil and Groundivater Impacts. 16. No formal risk assessment was conducted for this site. Results of a soil gas investigation_indicated the risks of vapor intrusion and inhalation to the human health to Workers in the site building, and to a hypothetical resident at the site, are below the level of concern. No exposure pathways from current residual hydrocarbons in soil or groundwater are likely to become a public health concern in the future. See No Further Action Required Request. 17. No formal fate and transport modeling was conducted for this site. Current groundwater monitoring data indicate that residual hydrocarbon in groundwater are limited to the immediate UST basin area. Concentrations of MTBE in groundwater extend off site to the west and south. However, the MTBE is expected to attenuate by natural processes to background levels in a reasonable period of time. See Updated Site Conceptual Model; Source, Nature and Extent of Soil and Groundwater Impacts. 18. The site conceptual model indicates that the hydrocarbon groundwater plume is decreasing in extent and concentration. Soil gas analytical results indicate that the site does not pose a threat to the public via the vapor intrusion exposure pathway. There is no reasonable expectation that residually-impacted site groundwater will be accessed for water supply purposes. There are no known complete exposure pathways to sensitive receptors. See No Further Action Required Request. 19. A list of technical reports include subsurface investigation, soil sampling and quarterly monitoring documents. See Appendix B. 20. Site investigations at the site were conducted and associated documentation were submitted in compliance with RWQCB and EHD requirements. NFAR CvrLttr FebI I Project No. 1641.26 3 HORIZON ENVIRONMENTAL INC.