SITE INFORMATION AND CORRESPONDENCE

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li eaking Underground Fuel Storage Tank Dram F III Release and Site Characterization Information (continued) Maximum Documented Contaminant Concentrations --Before and After Cleanup i 1! II Contaminant Soil Beforel After Water Before After Contaminant SoilBbforel After2 Water Before After (ppm) (ppm) (Ppm) (Ppm) i; (Ppm) (Ppm) (ppm) (Ppm) TPH (Gas) 3,800 <100.0 <0.05 _<_050_53 Ethyibenzene 10.0 '' <0.5 <0.0005 <0.0005ti TPH (Diesel) 130,000 6,700 0.2103 <0.057 Xylene 54.0 3.8 0.00065 <0.00056 Benzene <2.0 <fl.005 <0.00053 <0.00056 Toluene 2.0 0.93 0.006624 <0.00056 MTBE !'. NA NA NA NA i Comments 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 511795. 3! Water before sample collected from MW6 on 817195. 4. Water before sample collected from MW4 on 815193. 5.1 Water sample collected from MW4 on 10121192. 6. Water after sample collected from MW4 on 1111195. 7. Water after sample collected from MW4 on 6130197. The soil sample, Ri=2, 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 100.087 ppm 1,4 dichlorobenzene. Subsequent soil and groundwater sampling events failed to confirm the presences of these contaminants. i IV. Closure Does completed corrective action protect existing beneficial uses per the Regional"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. .i Should corrective action be reviewed if land use changes? Yes. MonitoringNaporwe/ls decommissioned: 7 , Number retained: 0 List enforcement actions taken: NOR sent on 3127190 and 1114191 List enforcement actions rescinded: None o V. Local Agency Representative Data ; a Name: Don a Heran Title: Director of'Environmental Health ii Signature: Date: � )vh_� VI. Central Valley Regional Water Quality Control Board (RB) Notification } Date Submitted to RB: 7118197 Response!Date: 8128197 and 1011197 ;1 RB Staff. J. Brathovde Response: No Further Action Concurrence Title: Assoc Eng Geologist ,i it VII. Additional Comments, Data, etc. ' 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 ranging 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- weighted) TPH as diesel concentration in groundwater from leachate would be 44 µg/L. He also stated that bioassessment test results indicated that intrinssic bioremediation was likely taking place and contributing to the observed decreasing soil 1 and groundwater TPH as diesel concentrations. This document and the related Cl' CLOSURE LETTER, Shall be retained h•-,the lead agency as part of the official site file. i!