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Third Quarter 2002 Status Report 4 7-Eleven Inc Store#17647 1046 West Yosemite Avenue Manteca CA October 22 2002 DO levels ranged from 1 3 milligrams per liter(mg/L) In well MW-3 to 19 mg/L In well MW-1, Indicating relatively uniform depleted DO conditions Purge Water Transportation and Disposal ' All purge water collected during this quarterly monitoring and sampling event was stored onsite In 55-gallon Department of Transportation (DOT)-approved drums pending characterization and proper disposal at a licensed recycling facility Waste documentation will be forwarded If requested Residual Mass Calculation ' The residual mass of MTBE at the site was calculated for sod and groundwater(Shaw Environmental, July 2002) Based on the calculation, it Is assumed that there are 0 022 pounds of residual MTBE in the soil This number is an average of data collected between December 12, 1998, and June 18, 1999 The ' dissolved mass for MTBE is calculated at 0 005 pounds Calculations are included in Attachment 5 ' Closure Documentation Groundwater monitoring data continue to Indicate that this site is low risk, based on 1) sustained levels of low-level to non-detectable dissolved hydrocarbon concentrations In all of the monitoring wells during at least seven consecutive quarterly monitoring events, 2) non-detectable soil and groundwater hydrocarbon concentrations in the latest downgradient soil borings, 3) no nearby sensitive receptors within 4,000 feet downgradient of the site, and 4) estimated low residual MTBE mass In soil and groundwater ' Groundwater flow at the site occurs most consistently to the northwest, with MW-3 lying furthest downgradient from the former tank/pump island locations Dissolved MTBE concentrations In well MW-3 have declined since the first quarter 2000, from 108 lag/L to a current concentration of 1 9 lag/L Recent data substantiates previously documented MTBE concentration trends Declining DO levels in MW-3 possibly indicate that natural attenuation/biodegradation Is occurring Data from the monitoring wells indicate that dissolved 1,2-DCA is not present in levels of over 1p9/L and dissolved EDB Is not detected In addition, groundwater samples for downgradient assessment ' borings GP-6 and GP-7 were non-detectable for dissolved 1,2-DCA Based on the above-mentioned site conditions, Shaw Environmental, Inc requested site closure in July 2002 SJCPHS has requested a workplan for destruction of onsite monitoring wells, pending confirmation of closure based on the most recent (third quarter)2002 results Data indicate closure is appropriate The ' workplan for well demolition will be submitted prior to the end of the 2002 calendar year 17647Q23 doc