SITE INFORMATION AND CORRESPONDENCE

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3� (4aking Underground Fuel Storage Tank Proam `yIII Release and Site Characterization Information (continued) L)RAFT I Maximum Documented Contaminant Concentrations --Before and After Cleanup i II l Contaminant Soil Beforel After2 Water Before After Contaminant SbIlBeforel After2 Water Before After (Ppm) (Ppm) (Ppm) (Ppm) iE (PPm) (Ppm) (Ppm) (Ppm) ' TPH (Gas) 3,800 <100.0 <0.05 <0.05 Ethylbenzene 10!0 <0.5 <0.0005 <0.0005 k TPH (Diesel) 130,000 6,700 0.2103 <0.057Xylene i 54'!0 3.8 0.00065 <0,00056 Benzene X2.0 <0.005 <0.00053 <0.00056 l Toluene 2.0 0.93 0.006624 <0.00056 MTBE NA NA NA NA I Comments l 1. Soil before sample collected at 15' below grade during the installation of MW4 on 10114192. 2. Soil after sample collected from the sidewall following the excavation attempt at 14' below grade on 511/95: 3. Water before sample collected from MW6 on 817195. 4. Water before sample collected from MW4 on 8/5193'15. Water sample collected from MW4 on 10121192. 6. Water after sample collected from MW4 on 1111195. 7. Water atter sample collected from MW4 on 6130197. The soil sample, RF2, that was collected at the time of the 6126186 tank removal that was anaylzed for chlorinated hydrocarbons evidenced 0.058 ppm chlorobenzene, 1.227 ppm 1.2 dichlorobenzene, 23-447ppm 1,3, dichlorobenzene and I 100.087 ppm 1,4 dichlorobenzene. Subsequent soil and groundwater sampiing'I`events failed to confirm the presences of { these contaminants. 1V. Closure k Does completed corrective action protect existing beneficial uses per the'Redional Board Basin Plan? Yes. Does completed corrective action protect potential beneficial uses per the Regional Board Basin Plan? Yes. { Does corrective action protect public health for current land use? Yes. Site management requirements: None. Should corrective action be reviewed if land use changes? Yes. '1 Monitoring/Vapor wells decommissioned: Number Decommissioned: Number retained: List enforcement actions taken: NOR sent on 3127190 and 1114191 I List enforcement actions rescinded: None it V. Local Agency Representative Data J; Name: Donna Heran Title: Director'&Environmental Health ,t Signature: Date: VI. Central Valley Regional Water Quality Control Board (RB) Notification/! I [[RB ate Submitted to RB: Response Date: Staff: J. Brathovde Response: tle: Assoc Eng Geologist t{ e I VII. Additional Comments, Data, etc. I� Dan B. Wynne, Certified Engineering Geologist#EG1569 recommended that the site br certified as requiring no further corrective action. He stated that the excavation of approximately 330 cubic yards resulted in a reduction of at least 67 percent of the TPH as diesel mass at the site and that the maximum residual mass of 160 gallons of TPH as diesel could be present in the 70 foot thick vadose zone at the site. The remaining mass was estimated to comprise 17,030 cubic feet of contaminated soil with a log-normal distribution of TPH as diesel concentrations'�anging from < 1 mg/kg to 130,000 mg/kg. The mathematical modeling (VLEACHSM Model) of TPH as diesel at the site estimated that the maximum average (area- we g ted TPH as diesel concentration in groundwater from leachate would be 44 gg/L. He also stated that bioassessment test results indicated that intrinssic bioremediation was likely taking place and contributing to the observed decreasing soil and groundwater TPH as diesel concentrations. This document and the related CASE CLOSURE LETTER, Shall be retained by the lead agency as part of the official site file.