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Ms. Devra Lewis June 7,2001 Page 7 The Middle Zone borehole locations (MW-10, MW-12, and MW-14) will be advanced to a depth approximately 5 feet below the lowest sand of the Upper Zone, approximately 40 feet bgs,using 12-inch diameter hollow stem augers. The 12-inch augers will be left in place to serve as a temporary casing while the borehole is advanced to total depth using 8-inch diameter hollow-stem augers inserted inside. The monitoring well will be constructed within the hollow stem of the augers using approximately 10 to 15 feet of two-inch diameter,flush-threaded Schedule 40 PVC,0.020-inch machine slotted screen extending from the bottom of the borehole and completed with blank casing to ground surface. A graded sand filter pack will be placed in the annular space from the bottom of the borehole to approximately one foot above the top of the well screen. One foot of bentonite pellets will be placed above the filter pack and hydrated. The remainder of the annular space above the bentonite pellet seal will be filled with a cement-bentonite(5%) grout mixture. The Lower Zone borehole location (MW-15) will be advanced to approximately 60 feet bgs using 12-inch diameter hollow stem augers. The 12-inch augers will be left in place to serve as a temporary casing while the borehole is advanced to total depth using 8-inch diameter hollow-stem augers inserted inside. The monitoring well will be constructed within the hollow stem of the augers using approximately 10 to 15 feet of two-inch diameter, flush-threaded Schedule 40 PVC, 0.020-inch machine slotted screen extending from graded sand filter pack the bottom of the borehole and completed with blank casing to ground surface. A g p will be placed in the annular space from the bottom of the borehole to approximately one foot above the top of the well,screen. One foot of bentonite pellets will be placed above the filter pack and hydrated. The remainder of the annular space above the bentonite pellet seal will be filled with a cement-bentonite(5%) grout mixture. All wells will be completed at the surface inside of a 6-inch diameter or 4-inch by 6-inch rectangular steel conductor casing which will extend approximately 2 feet above grade and 2 to 3 feet below grade. The conductor casing will be fitted with locking covers. Steel guard posts consisting of 6-inch diameter steel casing filled with concrete will be placed on three sides of the wells. The posts will extend approximately three feet above grade and three feet below grade. The posts and metal conductor casings will be painted yellow for visibility. 3.4 TASK 4—GROUNDWATER SAMPLING Following installation, the top of casing elevations for each monitoring well will be surveyed by a licensed land surveyor to allow groundwater elevations to be calculated. Groundwater samples will be collected from the newly installed wells approximately one week after installation. Subsequent sampling of the wells will be on a quarterly basis, in conjunction with the current Monitoring and Reporting Program (Order No. 5-00-846, November 17, 2000). Samples from wells MW-9 through MW-15 will be analyzed for VOCs by EPA Method 8260B with a reporting limit of 0.5 micrograms per liter(µg/L). 3.4.1 Sample Collection Procedures Prior to well development,depth-to-groundwater and the total depth of each well will be measured using an electronic water-level indicator and recorded on a Hydrologic Data Sheet. Each well will be developed by alternately surging and bailing until the purged groundwater is relatively free of sediment. Well development will be accomplished by utilizing a 2-inch diameter surge block and a PVC bailer. During well development,pH,temperature, and conductivity will be measured and color and turbidity will be visually inspected. These measurements and observations will be recorded on Groundwater Sample Field Data Sheets. SECOR anticipates purging approximately ten casing volumes from each wellbore. HAPioneer-Tracy\WorkP1an200 I\workplan.doc SECOR International Inc.