Laserfiche WebLink
Second Quarter 2002 Monitoring and Sampling Report and Request for Closure 4 <br /> 7-Eleven Inc Store#17647-1048 West Yosemite Avenue Manteca CA July 25 2002 <br /> DO levels ranged from 1 3 milligrams per liter(mg/L)in well MW-3 to 1 9 mg/L in well MW-1, indicating <br /> relatively uniform depleted DO conditions <br /> ' Purge Water Transportation and Disposal <br /> All purge water collected during this quarterly monitoring and sampling event was stored onsite in <br /> ' 55-gallon Department of Transportation (DOT)-approved drums pending characterization and proper <br /> disposal at a licensed recycling facility Waste documentation will be forwarded if requested <br /> ' Residual Mass Calculation <br /> The residual mass of MTBE at the site was calculated for soil and groundwater Based on the <br /> calculation, it Is assumed that there are 0 022 pounds of residual MTBE in the soil This number is an <br /> average of data collected between December 12, 1998 and June 18, 1999 The dissolved mass for <br /> MTBE is calculated at 0 0048 pounds Calculations are included in Attachment 5 <br /> Request for Closure <br /> Groundwater monitoring data continue to indicate that this site Is low risk, based on 1) sustained levels <br /> M of low-level to non-detectable dissolved hydrocarbon concentrations in all of the monitoring wells during <br /> seven consecutive quarterly monitoring events, 2) non-detectable soil and groundwater hydrocarbon <br /> concentrations in the latest downgradient soil borings, 3) no nearby sensitive receptors within 4,000 feet <br /> ' downgradient of the site, and 4) low residual MTBE mass in soil and groundwater <br /> Groundwater flow at the site occurs most consistently to the northwest, with MW-3 lying furthest <br /> ' downgradient from the former tank/pump island locations Dissolved MTBE concentrations in well MW-3 <br /> have declined since the first quarter 2000, from 108 pg/L to a current concentration of 9 5 pg/L <br /> ' Declining DO levels in MW-3 continue to indicate that natural attenuation/biodegradation Is occurring <br /> Data from the monitoring wells indicate that dissolved 1,2-DCA is not present in levels of over 1 pg/L, <br /> and dissolved EDB is not detected In addition, groundwater samples for downgradient assessment <br /> borings GP-6 and GP-7 were non-detectable for dissolved 1,2-DCA <br /> ' Based on the above-mentioned site conditions, Shaw Environmental and Infrastructure, Inc requests site <br /> closure <br /> 1 21756g4 rpt <br />