ARCHIVED REPORTS XR0008711 - Laserfiche WebLink

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` August 30, 2000 Mr. Ed Ralston Page 2 Michael Infurna of San Joaquin County Public Health Services, Environmental Health Division (SJCPHS/EHD). Additional excavation and sampling was completed on April 15, 1999 to remove the unidentified piping discovered on April 8, 1999. Over-excavation in the southern portion of the site was terminated to protect the structural integrity of the station canopy supports. Following removal of the former station canopy, canopy footings and kiosk, additional over- excavation excavation was completed on June I and 2, 1999. An additional 960 tons of soil were rcnioved to a maximum depth of 31 feet bgs. Over-excavation was terminated Mien, the structural integrity of the sidewalk was endangered and groundwater was encountered. Groundwater was encountered during additional over-excavation activities at a depth of approximately 31 feet bgs. One water grab sample was collected from the excavation. The grab water sample contained elevated TPH-g and BTEX concentrations. Four groundwater monitoring wells (MW-1 through MW-4) were installed on December 9 and 10, 1999 at the locations shown on Figure 2. The wells were screened from 5 feet above to 15 feet below the current water level. Initial depth to water in MW-I was 36 feet, therefore the well was set at 50 feet bgs. Groundwater rose to approximately 30 feet bgs after well completion. Groundwater sampling events identified low intermittent concentrations of benzene and MtBE. SCOPE OF WORK The scope of work completed for this investigation included the installation of four Geoprobe borings to delineate the vertical extent of hydrocarbons in the soil and groundwater. Geoprobe borings locations were based upon results of previous overexcavation and assessment activities and are shown in Figure 1. As required by the Occupational Health and Safety Administration (OSHA) Standard "Hazardous Waste Operations and Emergency Response" guidelines (29 CFR 1910.120), and by California Occupational Health and Safety Administration (Cal-OSHA) "Hazardous Waste Operations and Emergency Response" guidelines (CCR Title 8, Section 5192), IT has prepared a Site-Specific Health and Safety Plan (SSP). Prior to the commencement of fieldwork the SSP was updated with appropriate field personal and subcontractor information. The field staff and contractors reviewed the SSP before beginning field operations at the site. The specific scope of work is discussed below: • Geoprobe Borings. Four Geoprobe borings (GP-1 through GP-4) were driven using a CPT rig in the general locations shown on Figure 1. GP-1 through GP- 3 were advanced until refusal at approximately 60 feet bgs. GP-4 was advanced to first groundwater at approximately 30 feet bgs. Once selected depth was reached a discrete water sample was collected. Soil samples were Wrandp 11Proj ectsTrojects1911\01111 A101021911011 rpt.doc