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Work Plan for Additional Assessment S Z C 0 R ARCO Service Station No.2133 and Chevron Service Station No.9-4275 Stockton,California Page 3 I. ' I well box and several feet of casing. The former well will be capped with appropriate materials to match existing grade. The well box will be contained and disposed of offsite. Well construction details are included as Table 1. Task 3— Groundwater Monitoring Well Installation i As previously proposed and in order to evaluate the current extent of fuel-related hydrocarbons and MTBE the installation of one offsite groundwater monitoring well (MW-10) is proposed at the approximate location shown on Figure 2. The location of the proposed well may require modification due to field conditions (obstructions). It is also possible that the location may be moved for space constraints and/or to accommodate drilling equipment. MW-10 boring will be advanced to approximately 20 feet bgs using a hollow-stem auger drill rig equipped with 8-inch diameter continuous flight augers. During advancement, soil samples for chemical analyses will be collected at five-foot intervals using a California-modified split-spoon sampler driven approximately 18 inches using a 140-pound hammer falling 30 inches (blow count). Soil contained in the sampler will also be classified according to the Unified Soil Classification System (USCS) by a geologist under the direction of a State of California 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. i At the terminal depth of the boring, a groundwater monitoring well will be installed within the annulus of the auger. The 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 placed from approximately 5 to 20 feet bgs. A filter pack consisting j of sand will be placed in the annular space surrounding the entire screened interval, and will i extend approximately one foot above the top of the screen interval. A bentonite pellet annular seal will be placed above the filter pack, and the well will be completed with cement and/or grout { from the top of the seal to the ground surface. The well will be secured with a locking well cap, i and completed with a watertight traffic-rated well box installed at grade. i Task 4— 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 the 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 Teflon® sheets and plastic end caps, and j 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, i MTBE, ethanol, TBA DIPE, ETBE, TAME, 1,2-DCA and EDB by using Environmental Protection Agency (EPA) Method 8260B. j Task 5—Well Development The newly constructed monitoring well 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 11 f I