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. S ECOR • Work Plan for Monitoring Well Installation July 31, 2007 Former ARCO Service Station No. 4932 Stockton, California Page 7 Permitting The required monitoring well installation and abandonment permits (Attachment C) will be obtained from San Joaquin County Environmental Health Department (SJCEHD). Task 2 —Soil Boring Advancement, Soil Sampling, and Monitoring Well Installation Seven off-site soil boring/groundwater monitoring wells (DMW-4, DMW-5, DMW-6, DMW-7, DMW-8, DMW-9, and DMW-10) are proposed at the approximate locations shown on Figure 2. The locations of the proposed wells may require field modification due to unforeseen conditions such as obstructions or space constraints to accommodate drilling equipment placement, etc. DMW-4, DMW-5, DMW-6, DMW-7, DMW-8, DMW-9, and DMW-10 will be advanced using a sonic drilling rig equipped with 8-inch diameter heavy-walled down-hole casing to a total depth of 75 feet bgs. During advancement, soil samples will be collected continuously using a 20-foot core barrel. An attending geologist will log cuttings and sample in accordance with American Society for Testing and Materials (ASTM) D-2488 — Standard Practice for Description and Identification of Soils (Visual-Manual Procedure) under the direction of a State of California Professional Geologist (PG) or Professional Engineer (PE). Soil cores will be screened in the field for the presence of volatile organic compounds (VOCs) using a photoionization detector (PID). All down-hole drilling equipment will be decontaminated with high pressure steam following the completion of each soil boring. Down-hole sampling equipment will be decontaminated between samples using an Alconox detergent solution and a tap water rinse. If groundwater is encountered in the B' zone (45-75 feet bgs) a groundwater monitoring well will be installed within the annulus of the auger. Any monitoring well installed will have ten feet of l screen to delineate the groundwater encountered in the B' zone (from approximately 55 to 65 feet bgs) and will be constructed of 2-inch diameter, flush-threaded, schedule 40 PVC well casing and 0.020-inch factory-slotted well screen. A sand filter pack will be placed in the ' annular space surrounding the entire screened interval, and will extend approximately three feet above the screen interval. A two to three foot thick bentonite annular seal will be placed above Al the filter pack and hydrated. The remainder of the annular space will be filled with neat cement a and/or grout from the top of the bentonite seal to within 12 inches of the surface. The well will j be secured with a locking well cap, and completed with a watertight traffic-rated well box installed at grade. Task 3 — Laboratory Analyses for Soil Soil samples will be collected at five foot intervals for possible chemical analyses. Soil samples selected for chemical analyses will be contained in 2"-diameter by 6"-long brass or stainless steel sleeves, which will then be sealed on each end with Teflon tape and plastic end caps. The i soil samples selected for chemical analyses will be based on visual observations and PID measurements. The selected samples will be placed on ice in an insulated cooler until 1 relinquished, under documented chain-of-custody control, to a California certified analytical laboratory. Selected soil samples will be analyzed for GRO — (C6-C12), BTEX, MTBE, di- isopropyl ether (DIPE), ETBE, TAME, TBA, ethanol, DIPS, 1,2-DCA, and 1,2-dibromoethane (ethylene dibromide or EDB) by Environmental Protection Agency (EPA) Method 826013, Task 4—Well Development Following well installation, the monitoring well seals will be allowed to cure for at least 48 hours prior to development. Development (to clean the filter pack and stabilize the aquifer materials 4932 WP for MW Installation 2007.doc SECOR International Incorporated