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lY 42 +4 y S E C 0 R Mr Mike Infurna October 13, 2003 Page 2 • Permitting The applicable permits for soil borings will be obtained from San Joaquin County and encroachment permits for two borings will be obtained by the City of Lathrop • prior to drilling activities ConocoPhillips will obtain an access agreement for three of the borings (borings north and northeast of MW-16) prior to their completion k • Geoprobe Soil Borings Five Geoprobe® sod borings will be drilled at the locations shown ' on Figure 1 Sod borings will be drilled until groundwater is encountered The depth of these borings is estimated to be approximately 12 to 15 feet below ground surface (bgs) Soil samples will be collected at 5-foot intervals and a grab groundwater sample will be collected from the bottom of each boring using a "hydropunch" or similar sampling device Field procedures for Geoprobe®drilling are provided as Attachment A • Sample Selection and Analysis Soil samples will be collected at 5-foot intervals, and will be sent under chain-of-custody procedures to a California State-certified laboratory Selected soil samples will be analyzed for TPHg, BTEX compounds, and MtBE by EPA Method 8260E single run At a minimum, two sod samples in each boring will be analyzed for the above constituents Groundwater samples from each boring will be analyzed for TPHg, BTEX, and fuel oxygenates (MtBE, EtBE, DIPS, TAME, TBA, EDB, 1,2-DCA, and ethanol) by • EPA Method 8260B and total lead o Groundwater Monitoring Wells After completion of the Geoprobe assessment, groundwater monitoring wells will be installed at locations determined by the Geoprobe® I assessment (SECOR will submit a letter addendum proposing the number and location of additional wells) Soil borings will be drilled using 8-inch diameter hollow-stem auger Upon w completion of drilling, a 2-inch diameter groundwater monitoring well will be installed in each boring Groundwater is anticipated to be encountered at approximately 12-15 feet below ground surface (bgs) The wells will be screened from approximately 5 feet below ground surface to 10 feet below where groundwater is first encountered Field procedures for groundwater monitoring well installation are provided as Attachment A • Monitoring Well Development and Sampling After installation, the monitoring wells will be developed by rigorously surging the well over the length of the screen interval and by purging approximately 10 casing volumes of water After well development, groundwater samples will be collected and sent under standard chain-of-custody procedures to a California State-certified laboratory The groundwater samples will be analyzed for TPHg, BTEX, and fuel oxygenates (MtBE, EtBE, DIPE, TAME, TBA, EDB, 1,2-DCA, and ethanol) by • EPA Method 8260B and total lead • Well Surveying Upon completion of well construction, the well will be surveyed by a licensed surveyor to a local benchmark relative to mean sea level In order to comply with the State Geotracker requirements, the latitude and longitude location of the well will also be surveyed Groundwater gradient will be interpreted utilizing wellhead elevations and depth- to-water measurements ,r z • Report A report will be prepared after completion of the fieldwork and will document the • installation of well well MW-16, the additional geoprobe assessment, and monitoring well installation fieldwork The report will include the following items groundwater gradient map, groundwater dissolved petroleum hydrocarbon concentration maps, soil boring logs, soil 44 1 1ConocoPhdhps\Tosco Marketing1l2051Work Plans\Addendum WPLAN Oft-Site Assmnt doe