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li law <br /> ERI 205513.05R10 Tosco76 Service Station 58K_5j&kton. alp <br /> October 27 1999 <br /> I <br /> groundwater beneath and in the vicinity of the site and submittal of a Soil and Water Investigation <br /> Report <br /> Tosco performed a well survey to identify registered wells within a '/a-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 1n the area The data indicates ten registered wells within 114-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 general 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 prumrily 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 feet bgs) <br /> identified near this site appears to be a 21-inch sewer line located approximately 70 feet south of the <br /> southern property boundary of this site Research indicated that this sewer line is a gravity drain <br /> system draining towards the west <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 Tosco <br /> received approval for implementation of the amended Work Plan (August 8, 1997) and the proposed <br /> CPT locations (provided in ERI's January 28, 1998, Quarterly Summary Report) in a letter dated <br /> January 14, 1999 <br /> During February 1999, ERI performed a soil and groundwater evaluation downgradient of the site <br /> (ERI, March 2, 1999) The scope of work included drilling three CPT borings (CPT1 through CPT3) <br /> and three continuous core soil borings (138 through B10) to depths ranging from 28 to 40 feet bgs The <br /> approximate locations of soil borings B8 through BIO are shown on Plate 2 <br /> Laboratory analyses of soil samples collected from borings B8 through B10 did not detect residual <br /> hydrocarbons or oxygenated compounds at or above laboratory method detection limits Laboratory <br /> analyses of reconnaissance groundwater samples collected from the off-site soil borings detected <br /> concentrations of toluene (up to 0 56 ppb) and/or total xylenes (up to 1 6 ppb) in borings B8 and B9, <br /> diesel range hydrocarbons in boring B10 (up to 490 ppb), MTBE in borings B8 and B10 (up to 90 <br /> ppb), and ethanol (21 ppb) and methanol (91 ppb) 1n boring B9 Data collected during this <br /> investigation and previous investigations indicate the groundwater beneath and downgradlent of the site <br /> appears to consist of a single, unconfined aquifer of variable permeability <br /> 3 <br />