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r ' ' <br /> CAP Addendum, Former EZ Serve 100966,2531 Waterloo Rd., Stockton, CA <br /> October 21, 2009 <br /> a A comparison of pre- and post-remediation groundwater sample data indicates dissolved <br /> phase concentrations of TPH-G, benzene, and MTBE generally decreased in the <br /> majority of the wells onsite. However, concentrations of TPH-G, benzene, and MTBE <br /> significantly increased in wells MW-12 and YEAS-4. This data indicates hydrocarbons <br /> were drawn towards the extraction wells during the event and significant residual <br /> concentrations remain in the subsurface in the vicinity of these two wells. <br /> The results of the site remediation activities indicate HVDPE / GWAS are effective in removing <br /> concentrations of TPH-G, BTEX and MTBE from the soil and groundwater at this Site. <br /> RECOMMENDATIONS CONCERNING CONTINUED SITE REMEDIATION <br /> GESI is recommending an additional 30 days of HVDPE / GWAS activities be completed using <br /> a mobile system to further reduce the concentrations of petroleum hydrocarbons in the soil and <br /> groundwater. It is recommended that this work be implemented as soon as possible prior to the <br /> rainy season. <br /> Additional HVDPE activities would be focused on wells in the area of wells MW-12 and YEAS-4. <br /> Assuming an extraction rate of 4 pounds per hour during the proposed event, GESI estimates a <br /> mass of approximately 2,500 pounds of hydrocarbons would be extracted during the 30-day <br /> event. <br /> GESI concludes it would be more cost-effective to proceed with HVDPE and GWAS using a <br /> mobile system than to go through the time and expense to permit and install a fixed-based <br /> extraction system which would be operable for a limited time period. Additionally, there are <br /> space limitations onsite as the parcel size is only 10,000 square feet and contains a <br /> convenience store and customer parking area. There is no reasonable location for installation <br /> of a remediation compound. Due to the depth to water (approximately 60 feet in September <br /> 2009) other methods such as excavation, or chemical injection would be difficult to implement <br /> and would not be cost-effective. <br /> Should you have questions or comments regarding this report, please contact us at (805) 642- <br /> 1668 or email to ischaafCc)-geoenviroservices.com. <br /> Sincerely, <br /> r <br /> GeoEnviro Services, Inc. P <br /> 4 <br /> oseph P. Schaaf, P.G., C.Hg. <br /> Principal Geologist <br /> cc: Mr. Jack Ceccarelli, RPMS <br /> SWRCB Geotracker Database <br /> - 2- <br />