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F4 collected The reason for this procedure is that flowing (heaving) sands have been previously encountered at this site from these depths and drilling problems in these conditions can be greatly minimized if the bottom of hollow-stem augers is plugged until the total depth is reached The wells will be constructed within the hollow stem augers using 2-inch diameter flush-threaded, schedule 80, 0020-inch slotted PVC well screen and blank casing The well casing will be lowered through the augers a n d #2/12 filter pack sand will be placed in the annular space between the well casing and the borehole from the bottom of the boring to approximately 2-feet above the screened interval The well will b e developed using a surge block and bailer to settle the sand prior t o placing the sanitary seal Well development water will be contained in 5 5 - gallon steel drums, labeled and stored on-site until proper off-site disposal can be arranged Approximately 1 to 2-feet of time release (coated) bentonite pellets will be placed on top of the sand pack prior t o placing the cement sanitary seal Cement mixed with 3 to 5 percent bentonite powder by volume will be used to fill the annular space between the bentonite layer and the surface to prevent surface water from infiltrating into the well and to prevent conduits for the migration of contamination from shallow groundwater into deeper zones The cement will be placed by tremae pipe in all situations where the seal is placed below the water table The well heads will be protected with a locking well plug beneath an at-grade, traffic-rated well box (See Figure 5 - Typical Monitoring Well) All monitoring wells will be screened with screens no longer than 15-feet in length Each monitoring well will have only one screened interval Since the CPT borings have not yet been completed, the exact well construction is not yet known but it is anticipated that the wells will be screened between approximately 55 and 70-feet bgs TASK 4 - DRILL ONE SOIL BORING AT THE SITE TO A DEPTH OF APPROXIMATELY 115-FEET BGS AND INSTALL A GROUNDWATER MONITORING WELL IN THIS BORING TO SCREEN THE WATER BEARING ZONE APPROXIMATELY 100 TO 115-FEET BGS ASE will drill one (1) soil boring at the site to approximately 115 -feet bgs using a hollow-stem auger drill rig for the installation of a monitoring well screened approximately 100 to 115-feet bgs This well will be drilled near the eastern property line (the downgradient edge of the property in the 55 to 70-foot bgs zone) to monitor the vertical extent of contamination at that location It will also be used to determine the groundwater flow Frank's One Stop Workplan — June 2000 -12-