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- L , <br /> Mr. Jim Barton <br /> RWQCB <br /> March 29, 2013 <br /> Page 2 <br /> construction workers that might work in site soil (e.g., soil contact in utility <br /> trenches). <br /> • Use additional data to update the mass remaining of the CSM. <br /> • Obtain the necessary data needed to allow the RWQCB to evaluate the site for <br /> low threat closure. <br /> Media of Concern <br /> The media of concern are soil vapor(soil gas) in the unsaturated zone, soil, and shallow <br /> (first encountered) groundwater underlying the site. <br /> BACKGROUND <br /> The following subsections summarize the history,previous investigations, geology, and <br /> hydrogeology of the site. <br /> Previous Investigations <br /> Assessment activities conducted at the site by Advanced GeoEnvironmental, Inc. (AGI) <br /> and MACTEC Engineering and Consulting, Inc. (MACTEC) in 2004 and 2005 reported <br /> soil and/or groundwater impacts at three locations on the site. These areas of concern <br /> included the northwest, southwest and southeast corners of the site, as discussed below. <br /> See Attachment B for a summary of results from previous investigations. <br /> In September 2012, URS conducted additional site assessment activities at the southwest <br /> and southeast corners of the site. Boring locations from historical and the URS 2012 <br /> investigation are shown on Figure 2. Soil and groundwater sample.depths and results are <br /> shown in Attachment B. <br /> Northwest Corner <br /> In 1986, eight underground storage tanks (USTs) were removed from the. northwest <br /> corner of the site. These USTs reportedly contained isopropyl acetate, isopropyl alcohol, <br /> toluene, normal-propyl acetate, acetone and waste ink. As a result of site activities, this <br /> portion of the site was impacted by toluene and is being investigated and remediated by <br /> Dopaco,Inc. <br /> The northwest corner was not part of this investigation. <br /> Southwest Corner(Boring B-7 Area) <br /> In August 1985, two 4,000-gallon diesel USTs-were removed from the southwest corner <br /> of the site. No confirmation samples were collected following removal. Drilling and <br /> sampling activities conducted in 2005 reported elevated concentrations of total petroleum <br /> hydrocarbons as gasoline (TPHg) and TPH as diesel (TPHd). The highest concentrations <br />