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ERI 205513 QS7 Tosco 76 Service Station 5886 Stockton California January 29 1999 <br /> groundwater beneath and in the vicinity of the site and submittal of a Soil and Water Investigation <br /> Report To date, Tosco has not received a response and/or approval of the Work Plan addendum from <br /> the County <br /> Tosco performed a well survey to identify registered wells within a 114 mile radius of the site The <br /> purpose of this survey was to identify wells that may provide conduits for potential vertical migration <br /> of dissolved hydrocarbons and oxygenated compounds and to provide information regarding sensitive <br /> receptors in the area The data indicates ten registered wells within 1/4-mile of the site, seven of these <br /> wells are cathodic protection wells and three are water supply wells The closest water supply well is <br /> approximately 1,000 feet northeast of the site in the generally upgradient direction of interpreted <br /> historical groundwater flow <br /> In July 1997, Triangle Environmental, Inc performed a tightness test to evaluate the integrity of the <br /> existing fuel distribution system The results indicate the system passed within allowable tolerances <br /> During third quarter 1997, Tosco performed an underground utility search to Identify locations and <br /> orientations of utility trenches and to evaluate whether these facilities may provide conduits for the <br /> potential lateral off-site migration of dissolved hydrocarbons and oxygenated compounds The results <br /> of this utility search indicated that utilities are primarily located within the March Lane right-of-way <br /> and are oriented east to west Lateral utility trench lines servicing specific sites are oriented <br /> perpendicular to the main utility lines The deepest utility trench (approximately 10 5 ft bgs) Identified <br /> near this site appears to be a 21-Inch sewer line located approximately 70 feet south of the southern <br /> property boundary of this site Research indicated that this sewer line is a gravity drain system <br /> draining towards the west The locations of the underground utilities are shown on Plate 2 <br /> On January 28, 1998, Tosco submitted the fourth quarter 1997 Quarterly Summary Report which <br /> included proposed off-site cone penetrometer (CPT) locations to further evaluate the extent of dissolved <br /> MTBE detected in groundwater during ongoing quarterly groundwater monitoring and sampling The <br /> proposed CPT locations are shown the Plate 2 <br /> FOURTH QUARTER ACTIVITIES <br /> Based upon previous work completed at the site and In accordance with the correspondence and request <br /> from the County, Tosco performed the following tasks during the fourth quarter 1998 <br /> • Gettler-Ryan, Inc (GRI) of Dublin, California performed groundwater monitoring and <br /> sampling at the site on December 3, 1998 The draft results and data are attached (Attachment <br /> A) The finalized GRI Fourth Quarter 1998 Groundwater Monitoring and Sampling Report <br /> will be provided by GRI under a separate cover The results of the quarterly monitoring and <br /> sampling event indicate the following <br /> Groundwater was measured at approximately 6 1 to 9 1 feet bgs (an elevation <br /> increase of approximately 0 5 to 0 8 feet since the third quarter 1998 groundwater <br /> monitoring and sampling event) in the groundwater monitoring wells During <br /> December 1998, groundwater flow direction was towards the west-southwest at a <br /> 3 <br />