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Former Donna Gardner Property - 3 - 12 May 2010 <br />26090 N. Thornton Rd <br />Thornton, San Joaquin County <br />Summary and Recommendations <br />The responsible parties have complied with all of the requirements in the Regional Board staff <br />letters. Concentrations of petroleum hydrocarbons have decreased significantly over <br />approximately 64 monitoring events since groundwater monitoring started in 1991. <br />On 24 May 2009, maximum groundwater monitoring concentrations were TPHg, 1,400 ug/L; <br />ethylbenzene, 6.1 ug/L; and xylenes, 3.8 ug/L. The consultant estimates groundwater will <br />reach WQGs within two years. The petroleum hydrocarbons plume has been defined both <br />laterally and vertically, and poses minimal risk to sensitive receptors, human health, or other <br />beneficial uses of groundwater in the area. <br />Based on the minimal residual contamination in soil and groundwater, lack of threats from <br />vapor intrusion and groundwater pollution to Well #2, declining soil and groundwater <br />petroleum hydrocarbons concentrations, compliance with the tasks of Regional Board <br />directives, and a well defined vertical and lateral extent of pollution, no further action is <br />warranted for the Site. Staff recommends closure of this Site. The required public <br />participation comment period was completed on 24 December 2009 with no adverse <br />comments. All remaining monitoring wells were properly abandoned on 4 May 2010 <br />Attachments: Attachment 1: Site Location Figure 1 <br />Attachment 2: Site Plan with former USTs and Well Locations Figure 2