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} Y Case Closure Summary Page 2 <br /> Baking Underground Fuel Storage Tank F.. yarn <br /> III. Release and Site Characterization Information continued i <br /> Maximum Documented Contaminant Concentrations --Before and After Cleanup <br /> Contaminant Soil Soil refto <br /> Water Contaminant Soil Soil Water Water After <br /> Before After After Before After Before <br /> (Ppm) (ppm) (ppm) <br /> TPH (Gas) 3,800 <1.0 93 <0.050 MTBE NA i 0.095 0.56 0.080 <br /> TPH(Diesel) 45 <1.0 32 X0.050 TBA NA ,� <0.025 NA <0.005 <br /> Benzene 5.9 <0.005 6.5 <0.0005 EDB NA 1 4:0.005 NA <0.0005 <br /> Toluene 46 <0.005 35 <0.0005 1,2-DCA NA i; <0.005 NA <0.0005 <br /> Ethylbenzene 23 <0.005 4.5 <0.0005 Oxygenates NA <0.005 NA <0.005 <br /> Xylenes 150 <0.005 25 <0.0005 <br /> Water Before results are from SB5 on 12112196. Soil Before results are from over-excavation sampling 8129195. { <br /> Water After results reflected the latest round of MW sampling in April 2003 and CPT-investigation in July 2003, Soil <br /> samples reflected the last time soil samples were collected during installation of MW16, 7, and 8 in November 2000. The <br /> presence of MTBE in the soil samples most likely comes from cross-contamination of dissolved MTBE: Concentrations of <br /> all contaminants in groundwater in the latest sampling were not detect except MTBE" <br /> The MTBE plume is mobile in a down gradient direction, but the concentration has declined since 1996. The extent of the I <br /> plume has been defined, with the vertical extent at less than 100 ft bsg (from CPT samples). The dissolved MTBE appears <br /> to be in a sand layer at approximately 60 feet to 85 feet bsg, as consistently indicated by the results of the deepest well on <br /> site MW-9 which was screened 70 to 75 feet bsg. <br /> The consultant calculated an attenuation by dispersion time of 1260 days for the plume,which translates to a transport <br /> distance of less than 100 feet beyond the furthest down-gradient wel(MW-10. They also plotted a Non-Steady State <br /> Spreadsheet Analytical Model,which estimated a period of 4.3 years for the MTBE plume to reach a concentration of 4.96 <br /> ugh of MTBE at a projected distance of 1,700 feet and model velocity of 0.07 ft/day. With the exception of one 53.7-foot i <br /> monitoring well located 1,600 feet southeast of the site, no other wells were identified in a 2,000-foot well survey. The <br /> remaining mass of dissolved MTBE was calculated at 1.4 pounds. Beneficial uses of groundwater are protected, now and <br /> in the future. <br /> IV. Closure t <br /> Does completed corrective action protect existing beneficial uses per the Regional Board Basin Plan? Yes <br /> I t <br /> Does completed corrective action protect potential beneficial uses per the Regional Board Basin Plan? Yes <br /> Does corrective action protect public health for current land use? Yes <br /> Site management requirements: none <br /> Should corrective action be reviewed if land use changes?Yes <br /> Monitoring wells decommissioned: No Number Decommissioned: 0 Number retained: 10 <br /> List enforcement actions taken: NOR sent Il. <br /> �i <br /> List enforcement actions rescinded: None <br /> V. Local Agency Representative Data <br /> Name: Margaret Lagorio Title: Supervisor REHS/Site Mitigation/LOP Unit IV <br /> i <br /> Signature: ln=ft� Date: <br /> E <br /> VI. Central Valley Regional Water Quality Control Board RB) Notification i <br /> Date Submitted to RB: Response Date: 1 i <br /> RB Staff:Jaynes L. Barton Response: <br /> Title: Assoc Eng Geologist I <br /> VII. Additional Comments, Data, etc. i <br /> This document and the related CASE CLOSURE LETTER,Shall be retained by the lead agency as part of the <br /> official site file. (08124193) Exhibit N Page 2 of 2 <br />