SITE INFORMATION AND CORRESPONDENCE

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ARCO Station #0960 • - 3 - • 24 November 2009 225 S. Cherokee Lane Lodi, San Joaquin County approximately 54' bgs to 66' bgs, with water table elevations ranging from approximately 8 ' to 1' below mean sea level. The downgradient groundwater flow direction varied from southeast to west. The groundwater gradient varied from 0.0005 ft/ft to 0.018 ft/ft. Residual Mass Calculation At the conclusion of the soil remediation in 1997, the consultant estimated the remaining residual contaminant mass in soil as 1,730 gallons of TPHg and 1,390 gallons of TPHd. The NFAR estimate is approximately 2 gallons of TPHg/MTBE/1 ,2-DCA remain in groundwater. Summary and Recommendations ARCO has complied with all of the requirements in the Regional Board staff letters. Concentrations of petroleum hydrocarbons have decreased significantly over approximately 25 monitoring events since groundwater monitoring started in 1991. On 3 October 2008, maximum groundwater monitoring concentrations were TPHg, 300 ug/L; MTBE, 11 ug/L; and 1,2-DCA, 1.1 ug/L. The consultant estimates groundwater will reach WQGs within one year. The petroleum hydrocarbons plume has been defined both laterally and vertically, and poses minimal risk to sensitive receptors, human health, or other beneficial uses of groundwater in the area. Based on the minimal residual contamination in soil and groundwater, lack of threats from vapor intrusion, declining soil and groundwater petroleum hydrocarbons concentrations, compliance with the tasks of Regional Board directives, and a well defined vertical and lateral extent of pollution, no further action is warranted for the Site. Staff recommends closure of this Site. The required public participation comment period was completed on 24 July 2009 with no adverse comments. All remaining monitoring wells were properly abandoned on 29 October 2009 Attachments: Attachment 1: Site Location Figure 1 Attachment 2: Site Plan with former USTs and Well Locations Figure 2