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August 15, 1996 . . <br /> Mr. Michael Infurna <br /> As you know, UNOCAL initiated the environmental investigation in 1985 as a result <br /> of our lease termination and anticipated station closure and demolition. Several phases <br /> of investigation have occurred since which will be discussed in more detail below. <br /> During closure and removal of the station facilities, approximately 6,000 c.y. of soil <br /> were excavated based upon information obtained during a previous site investigation. <br /> Approximately 5,800 c.y. of soil were aerated, transported and disposed offsite. The <br /> remaining 200 c.y. of soil were transported to a Class I disposal facility. Portions of <br /> the UST pit were excavated to an unprecedented depth of 53 ft. bgs, which <br /> corresponded to the groundwater table at the time. Between 1985 to 1988, and prior <br /> to excavation activities, nineteen exploratory soil borings, ten groundwater monitoring <br /> wells and seven vapor extraction wells were installed. Feasibility testing was <br /> conducted which resulted in a recommendation to perform in-situ vapor extraction <br /> with groundwater recovery. This was never implemented due to the later decision to <br /> remediate impacted soils by way of excavation which were defined by borings and <br /> well installations during the initial investigation. As a result, the need to remediate via <br /> soil vapor extraction as previously proposed was negated. <br /> Additionally, wells MWl l and MW12 were not installed until 1992 and were placed <br /> offsite in the public right of way well after the property had been redeveloped as a <br /> commercial bank. UNOCAL contends that soils containing petroleum hydrocarbons <br /> in these wells are associated with the impacted groundwater regime and capillary <br /> fringe. <br /> Based on the extensive excavation activities employed prior to property reconstruction, <br /> the need for soil remediation via soil vapor extraction is no longer warranted. This is <br /> supported by the results of sampling conducted during excavation activities. <br /> Moreover, the RWQCB agreed that soil contamination had been adequately cleaned <br /> up as stated in their letter of August 25, 1989. Consequently, UNOCAL finds your <br /> statements concerning "limits of the over-excavation" and non-removal of impacted <br /> soils in the area of wells MW l l and MW 12 to be unfounded. It is our position that <br /> the source of contamination has been effectively removed and no additional cleanup <br /> of the vadose zone is necessary. Historical soil and groundwater data are included for <br /> reference in Attachments A and B. <br /> From 1990 to 1995, site wells were routinely monitored and sampled, some of the <br /> UNOCAL wells were destroyed and/or replaced and additional wells were installed to <br /> further characterize the groundwater plume. Since 1994, the groundwater in the site <br /> vicinity appears to be rising significantly and presently most of the well screens are <br /> 2 <br />