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Work Plan for Soil and Groundwater i vestigation E C O R Former ARCO Service Station#0760 December 13,2006 Page 4 Groundwater Monitoring Well Installation In order to evaluate the current extent of fuel-related hydrocarbons the installation of three groundwater monitoring wells (MW-6 through MW-8) are proposed at the approximate locations shown on Figure 2. Locations of proposed wells may require modification due to field conditions (obstructions). It is also possible that the locations of some wells may be moved for space constraints and/or to accommodate drilling equipment. Each boring will be advanced to approximately 70 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 or Engineer. 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 the boring logs. All down-hole drilling equipment will be steam-cleaned following the completion of each soil boring. Down-hole sampling equipment will be 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 placed from approximately 50 to 70 feet bgs. 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 well will be secured with a locking well cap, and completed with a watertight traffic-rated well box installed at grade. Monitoring Well Development/Sampling/Analysis The newly installed groundwater monitoring wells will be developed by vigorously surging the well over the length of the screen interval and by purging approximately 10 casing volumes of water. Groundwater samples will be collected and analyzed for the presence of TPHg, BTEX, MtBE, ethanol, TBA DIPE, ETBE, TAME, 1,2-DCA and EDB using EPA Method 8260B. Soil Vapor Probe Installation In order to evaluate the vapor intrusion pathway, SECOR proposes to install three soil vapor probes at the approximate locations shown on Figure 2. The vapor probes will be installed using 3-inch diameter hand-auger borings or air knife to a depth of approximately 6 feet bgs. Tygon®tubing will be placed into each open boring with the tubing bottom at approximately 5'/4 feet bgs. A 6-inch long section of 1-inch diameter, machine slotted PVC(or stainless steel)will extend from approximately 5 '/4 to 5 3/4 feet bgs. A filter pack consisting of#3 Monterey Sand (or the equivalent)will be placed in the annular space surrounding the entire screened interval from 5 feet to 6 feet bgs. The sand pack will be covered with 1 foot of dry granular bentonite followed by hydrated bentonite to 1 foot bgs. Each probe will then be completed with cement and/or grout from the top of the seal to the ground surface. The tubing will be capped with a gas-tight cap (such as Swagelok® cap) at the ground surface to prevent the potential for barometric pressure fluctuations to induce vapor transport between the subsurface and atmosphere. The excess length of Tygon®tubing with the Swagelok® type valve will be coiled up inside the well box. The probe will be secured in a watertight traffic-rated well box installed at grade. A typical vapor probe detail is included as Figure 3 ARCO 00760 Soil and Groundwater Investigation WP.doc