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Work Plan for Additional Assessment S E C O R ARCO Service Station No. 548 1 Stockton, California Page 4 of 6 Professional Geologist (PG) or Professional Engineer (PE). Soil will be screened in the field for the presence of volatile organic compounds (VOCs) using a photoionization detector (PID) . Soil classifications, PID measurements, sample intervals and other pertinent geologic information will be recorded on boring logs. All down-hole drilling equipment is steam-cleaned following the completion of each soil boring . Down-hole sampling equipment is washed in an Alconox solution between samples. At the terminal depth of each boring , a groundwater monitoring well will be installed within the annulus of the auger. Each well will be constructed using 2-inch diameter, flush- threaded, schedule 40 polyvinyl chloride (PVC) well casing with approximately 20 feet of 0. 020-inch factory-slotted well screen. A filter pack consisting of sand will be placed in the annular space surrounding the entire screened interval, and will extend approximately one foot above the top of the screen interval . A bentonite pellet annular seal will be placed above the filter pack, and each well will be completed with cement and/or grout from the top of the seal to the ground surface. The wells will be secured with a locking well cap, and completed with a watertight traffic- rated well box installed at grade. Task 3 — Laboratory Analyses Soil samples collected will be selected for chemical analyses based on visual observations and PID measurements. A minimum of two soil samples will be analyzed from each boring . Soil samples selected for chemical analyses will be contained in 2"-diameter by 6"-long brass or stainless steel sleeves, capped at each end with Teflone sheets and plastic end caps, and placed on ice in an insulated cooler until relinquished under chain-of-custody to a certified analytical laboratory. Selected soil samples will be analyzed for the presence of GRO, BTEX, fuel oxygenates (including MTBE), and 1 ,2-DCA according to USEPA Method 8260B, Task 4 — Well Development The newly constructed monitoring wells will be developed a minimum of 48 hours following well construction . Development will be accomplished by alternately surging each well with a vented surge block followed by bailing to remove accumulated sediment. Final purging will be performed with either a submersible pump or bailer, and pH , temperature, and conductivity will be measured at regular intervals during purging . Development will be considered complete when either 1 ) 8 well volumes have been removed and physical- chemical parameters trends have stabilized over three consecutive measurements (<0. 05 pH , 3% conductivity, and 10% temperature), 2) 10 well volumes have been removed , or 3) until the well has been purged dry (if the well does not sustain flow or is slow to recover) . Task 5 — Waste Handling and Disposal All investigation derived waste (IDW), including soil cuttings and purge water from well installation and development will be stored on-site in Department of Transportation- approved 55-gallon drums and/or roll off bins pending the results of chemical analyses. Analytical results will be used for waste profiling and disposal. After profiling , IDW will be transported and disposed at an appropriate State-certified disposal facility. Task 6 — Surveying Once all proposed wells are installed, a California-licensed land surveyor will survey the location and top of casing elevation of newly installed wells relative to a known benchmark according to the North American Datum of 1983 (NAD83) and the National Geodetic Vertical Datum of 1929 (NGVD29) . The new wells will be surveyed relative to the same benchmark used for the existing wells on-site.