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Abdelwahed Facility, Ultramar Site No. 13792 May 9, 2013 "Stockton California N.FAR Request and Well Destruction Work Plan 6. Depth -to -groundwater and groundwater elevation data are summarized in Table 1. 7. Results of ' groundwater and soil analyses are summarized in Tables 1 and 2, respectively. 8. Lateral and vertical extents of hydrocarbon impacts -to soil and groundwater are shown maps and cross sections contained in Attachment G. 9. Zones of vapor extraction and air sparge influence were evaluated by pilot test field data.; a figure showing influence zones are contained in Attachment G. 10. The release was reported in July 2002. All reports are on file at EHD. 1-1. Best Available Technology (BAT), vapor. extraction and air sparging, were utilized. 12. Background is attainable through the BAT utilized followed by a reasonable period of natural attenuation. 13. In 2005, the pre -remediation volumes of the constituents of concern (COCs) TPHg, benzene and DCA in soil and groundwater were estimated as follows: Soil: 1182 gallons (7494 pounds) TPHg 1.1 gallons (8.0 pounds) benzene 0.02 gallons (0.2 pound) DCA Groundwater: 37 gallons (234 pounds) TPHg 4.1 _gallons (30 pounds) benzene 0.23 gallons (2.3 pound) DCA Approximately 40;300 .pounds of TPHg were removed by vapor extraction and air sparge systems operations. Fourth, quarter 2012 groundwater monitoring data indicate TPHg, benzene and DCA plumes in groundwater as shown ori Figures 4, 5 and 6 contained in Attachment G. The current retaining volumes of constituents of concern in groundwater were estimated as follows: 1.5 gallons. (9:5 pounds) TPHg U07 gallon (0.5 pound) benzene 0.02 gallon (0.2 pound) DCA 14: Historical groundwater concentration data from former well MW -i were used to estimate conservative attenuation rates for the COCl. The estimated attenuation rates were applied to COC concentrations -in -wells MW_6 and MW -13 to estimate times to reach WQOs utilizing the first order attenuation equation. 15. The source of hydrocarbons to soil and groundwater has been stopped and the secondary soil arid .groundwater sources have been remediated to the full practical extent. The groundwater hydrocarbon plume will further attenuate at a rate that will protect the. usable groundwater resources of the State and allow concentrations of COCs to reach WQOs in a reasonable period of time. Soil gas investigation results 1792 NFAR rpt.doc Project No. 1792.26 9 HORIZON ENVIRONMENTAL INC.