SITE INFORMATION AND CORRESPONDENCE

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Geweke Land Developmen*d Marketing - 4 - • 18 October 2010 16 S. Cherokee Lane Lodi, San Joaquin County Sensitive Receptor Survey The Closure Summary Report identified 1 irrigation well and 1 inactive municipal well within 2000' of the site, and one active municipal well located 900' southeast of the site. The nearest surface water body, the Mokelumne River, is over 2000' north (upgradient) of the Site. The consultant determined that sensitive receptors are not threatened by residual groundwater contamination. Site Geology and HydrogeologV The Closure Summary Report listed Site soils as inter-fingered beds of gravels, sands, silts and clays down to 145' bgs, the total depth investigated. From 1985 to 2008, depth to water varied from approximately 42' bgs to 63' bgs, with water table elevations ranging from approximately 17' below mean sea level (msl) to 2 feet above msi. The downgradient groundwater flow direction was predominantly to the south. The groundwater gradient varied from 0.001 ft/ft to 0.002 ft/ft. Residual Mass Calculation Initial estimates for TPHg in soil were 3,554 gallons, prior to Bio remediation and 5 gallons of TPHg in groundwater, prior to ozone injection. The Closure Summary Report estimated 315 gallons of TPHg remain in soil, and 1 .8 gallons of TPHg remain in groundwater. Summary and Recommendations Geweke has complied with all of the requirements in CAO 93-701 and in the Regional Board staff letters. Concentrations of petroleum hydrocarbons have decreased significantly over approximately 70 monitoring events since groundwater monitoring started in 1985. On 30 June 2009, maximum groundwater monitoring concentrations were TPHg, 3,300 ug/L; ethylbenzene, 18 ug/L; and xylenes, 92 ug/L. The consultant estimates groundwater will reach WQGs within twenty three years. The City of Lodi Public Water Service office was contacted on 15 December 2009; and there are no current plans to use the groundwater prior to reaching WQGs. Moreover, the City installs sanitary seals to between 200' and 250' depth to lessen communication between the primary drinking water aquifer and shallow groundwater. 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 enforcement orders and directives, and a well defined vertical and lateral extent of pollution, no further action is warranted for the Site. Staff recommends rescission of CAO 93-701 and closure of this Site. The required public participation comment period was completed, including the nearby Lodi Adult School, on