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Abdelwahed Facility, Ultramar Site No. 13792 May 9, 2013 Stockton California NFAR Request and Well Destruction Work Plan Control Board -Central Valley Region Tri -Regional Board Staff Recommendations for Preliminary Investigation and Evaluation of Underground Tank Sites, Appendix A — Reports Table 1 -Checklist of Required Data for No Further Action Requests at Underground Tank Sites (Checklist of Required Data), and that the report also include a work plan for destruction of all wells associated with the site. Results of this investigation indicate that additional soil and groundwater remediation is not warranted and that site conditions meet closure criteria requirements. Horizon requests this site be assigned a no further action required status. The rationale for this recommendation is made on the basis of evaluations of results of previous site investigations, soil and groundwater remediation, natural attenuation of impacted groundwater indicated by nearly ten years of quarterly groundwater monitoring, a site conceptual model that indicates no threatened sensitive receptors, and soil gas analytical results that indicate that the risk to the human health to workers in the site building is below the level of concern. The residual hydrocarbon plume should continue to attenuate and groundwater will attain water quality objectives for hydrocarbons in 10 to 36 years. Checklist of Required Data The items contained in the Checklist of Required Data are addressed below in the numerical order they appear in the checklist: 1. A water supply well survey was completed for the area within a 2000 -foot radius of the site as part of a sensitive receptor survey. Two wells were identified within the 2000 -foot radius of the site as summarized in Table 4 and on Figure 8. The two wells were identified as domestic. The locations of the wells are approximately 680 feet north and 1750 feet south of the Site. The domestic wells could not be located in a field check; their status is unknown. According to Scott Bailey of California Water Service (CWS), residential customers in the survey area are supplied with potable water via CWS. 2. Scaled site location map and scaled site maps are included in all site reports. 3. Figures showing site lithology in cross section and treatment system layout and process flow have been included in previous reports and are contained Attachment G in this report. 4. No stockpiled soil remains on site. 5. Currently, there are eleven groundwater monitoring wells (MW -2 through MW -4 and MW -6 through MW -13), five vapor extraction wells (VW -1 through VW -5) and two sparge wells (SW -1 and SW -2) associated with the site as shown on Figure 3. Wells MW -6, MW -7, MW -10, MW -11 and MW -12 are located off site to the east and south. Monitoring well MW -5 was destroyed March 2008 and monitoring well MW -1 was destroyed July 2012. All wells associated with the site shall be destroyed subsequent to site closure. 1792 NFAR rpt.doc Project No. 1792.26 8 HORIZON ENVIRONMENTAL INC.