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- h site, ASE estimates that the well will be screened between approximately 4 and 18-feet bgs. The well casing will be lowered through the augers and #2/12 filter pack sand will be placed in the annular space between t h e well casing and the borehole from the bottom of the boring to approximately 1-foot above the screened interval. Approximately 0.5-feet of bentonite pellets will be placed on top of the sand pack prior to placing the cement sanitary seal. Since the bentonite sea] will be placed in the unsaturated zone; the bentonite will be hydrated with potable water prioz- to placing the cement sanitary seal. Cement mixed ti�iih 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. The seal will be placed by simply pouring the seal into the boring. The well head will be protected with a locking well plug beneath an at-grade, traffic-rated well box (See Figure 4 - Typical Monitoring Well). .. TASK S -INSTALL AN AIR SPARGING WELL In order to conduct an air sparging test, an air sparging well will have to be constructed. This well will be placed near monitoring well MW-2 �..• (Figure 3). The well will be constructed using a drill rig equipped with 8- inch diameter hollow-stem augers. The well will be constructed within the I hollow stem augers using 2-inch diameter flush-threaded, schedule 40, 0.020-inch slotted PVC well screen and blank casing. The well will be screened between approximately 14 and 16-feet bgs. The well casing will be lowered through the augers and #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 1-foot above the screened interval. Approximately 0.5-feet of coated bentonite pellets will be placed on top of the sand pack prior to 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 1� zones. The cement seal in this well will be placed using a tremie pipe. The well head will be protected with a locking well plug beneath an at- grade, traffic-rated well box (See Figure 5 - Typical Air Sparging Well). TASK 6 - DRILL TWO SOIL BORINGS TO APPROXIMATELY 6-FEET BGS AND CONSTRUCT VAPOR EXTRACTION WELLS IN's BORINGS ASE will drill two soil borings to approximately 6-feet bgs at the site using a drill rig equipped with 8-inch diameter hollow stem augers (Figure 3). 574 West Grand Line Road, Tracy, CA Workplan — April 2001 -8-