ARCHIVED REPORTS XR0000286 - Laserfiche WebLink

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Maximum methyl tert-butyl ether (MTBE) concentrations of 277 and 99 µg11 have been detected in groundwater samples analyzed by EPA Test Methods 8020 and 8260, respectively Historical groundwater flow beneath the Site is directed to the east and southeast A summary of historical analytical groundwater data is tabulated in Appendix A ' In February 2000, the mass of petroleum hydrocarbons in soil was estimated at approximately 485 Pounds for TPHg and 8 pounds for benzene The mass of petroleum hydrocarbons in groundwater beneath the Site was estimated to be approximately 2 grams of TPHg and 0 7 grams of benzene The groundwater plume beneath the Site may extend beneath B Street Review of the historical soil analytical data indicates petroleum hydrocarbon impacts at intervals between 35 and 66 feet below the ground surface (bgs) with the exception of the tank removal soil samples collected between 12 and 14 feet bgs Approximate locations of the groundwater monitoring wells are depicted on Figure 2 FIELD ACTIVI'T'IES Depth to Groundwater Measurements On July 9, 2002, representatives of Geocon measured the depth to groundwater in monitoring wells MW-1 through MW-12, VW-1 and VW-2 using a battery operated water level meter The measurements were obtained from a surveyed reference point at the top of the well casing (TOC) The approximate well locations and site features are depicted on Figure 2, Groundwater Elevation Map -July 2002 ' During the Second Quarter - 2002, the depth to groundwater in wells MW-1 through MW-12, VW-1 and VW-2 was recorded between 49 50 (MW-9) and 51 17 (MW-12) feet below TOC Based on the July 2002 groundwater elevation data, the groundwater beneath the Site appears to be directed toward the southeast at an approximate gradient of 0 003 which is consistent with historical groundwater flow A summary of the TOC elevations, depth to groundwater measurements and Mean ' Sea Level groundwater elevations is presented on Table 1 Well Purging and Sampling ' Approximately three well volumes of water (31 to 62 gallons) were extracted from each well utilizing a 2-inch diameter submersible pump During the well purging activities, the groundwater ' was monitored for pH, electrical conductivity, temperature and turbidity This information is included on the Monitoring Well Sampling Data Sheets presented in Appendix B Following the purging activities, groundwater samples were collected from the wells and decanted ' into five 40-milliliter volatile organic analysis vials and one one-liter amber glass bottle The samples were sealed, labeled, placed in an ice chest containing ice, and subsequently transported to the laboratory using standard chain-of-custody protocol The extracted groundwater was placed into 14 Department of Transportation-approved, 17-H, 55- gallon drums and temporarily stored onsite pending receipt of laboratory analysis The drums were ' transported by ABCO Environmental Services to Instrat, Inc located in Rio Vista, California Project No S8475-06-24A -2- September 11,2002