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1 1 encountered below the water table and is found not to contain elevated levels of petroleum hydrocarbons 1 using field screening methods (e.g., PID meter), then the vertical continuity of this clay layer will be verified by sampling and advancing the borehole 4 Meet. If the clay layer is found to be greater than 4'/: feet thick, the clay will be considered a continuous confining layer and the borehole will be plugged 1 with bentonite or cement grout to the top of the clay. The monitoring well will be completed in the portion of the saturated zone overlying the clay layer. If the clay layer is found to be less than 4'/z feet thick, the clay will be considered a localized clay lens and the borehole will be advanced to the designed depth. ] Well Construction Procedures Two-inch diameter, Schedule 40 PVC casing and screen will be used to complete the groundwater ] monitoring wells (see Figure 6, Typical Monitoring Well Construction Details). The proper lengths of screen and blank casing will be steam-cleaned and threaded above ground prior to lowering inside the ] hollow-stem augers. The bottom of the screened interval will be fitted with an end plug and the top of the well casing will be equipped with an expandable, water-tight, locking cap. The well screen will intersect ] the water table and account for anticipated seasonal variations within the aquifer. It is anticipated that the well screen in these wells will extend from a depth of about 5 to 20 feet. No glue will be used in this ] assembly. The annular space between the well screen and the wall of the borehole will be filled with clean sand to provide filtration capacity and impede movement of sand or silt into the well. The sandpack will extend from the bottom of the well to about 1 to 2 feet above the top of the well screen. A 2-ft thick plug of hydrated bentonite will be placed above the sandpack and the remaining annular space will be backfilled with a neat cement grout with 5%powdered bentonite. The monitoring wells will be protected from vandalism or the entry of surface fluids. Each of the off-site wells will be finished with a locking standpipe and four concrete-filled steel bollards to prevent wellhead disturbance due to farming activities in the orchard. The on-site wells will be finished with a watertight, security traffic box. Well Development The monitoring wells will be partially developed during well completion by surging and bailing water from l the wells after installation of the sandpack but prior to installing the well seal. The purpose of this partial 1 i cca/03/10/95 09:38 AM(0688brpt.doc/ntw12) 4-5