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' Work Plan Page 11 <br /> Former Manna Pro Site <br />' Projeo No 207 3 <br /> August 16, 1999 <br />' The proposed screened interval of 20 to 50 feet is greater than usual for a vapor extraction <br /> well The reason for this is to enhance the ability to remove sparge air which may <br />' become trapped in the sub-surface As air is introduced into expelled from the pilot <br /> sparge well, it will tend to rise toward the surface If rising air encounters a relatively <br /> impermeable clay layer, however, it may tend to become trapped against the clay By <br />' having the nearby vapor extraction well screened deeper, any such trapped air should tend <br /> to migrate toward the extraction well, where it may be removed along with any entrained <br /> hydrocarbons <br /> 4.2.2 Air Sparge Well Construction <br />' This well, designated SPW-1, will be located approximately 15 feet up-gradient from the <br /> vapor extraction well VEW-1 The following table describes the construction of the air <br /> sparge well <br />' Casing 2" Schedule 40 PVC <br /> Screen 0 010 Slotted Schedule 40 PVC <br />' Screened Interval 50-55 feet below ground surface (bgs) <br /> Filter Pack 48-55 feet bgs <br /> Filter Pack Material #3 Monterey sand <br /> Bentonite Transition Seal 45-48 feet bgs <br /> Annular Seal 0-45 feet bgs <br /> The sparge well will be screened to expel air near the bottom or slightly below the main <br /> mass of the contaminant This placement will allow several fee of vertical space in which <br /> the air may penetrate deeper into the native formation before beginning to rise and spread <br /> through the main contaminant mass <br /> 4.2.3 Air Monitoring Well Construction <br /> These two wells, designated OB-4 and OB-5, will be located at about 15 and 30 feet <br /> down gradient from the vapor extraction well The following table describes the <br /> construction of the combination air momtonng/shallow air recharge well <br />' Casing 2" Schedule 40 PVC <br /> Screen 0 010 Slotted Schedule 40 PVC <br /> Screened Interval 20-30 feet below ground surface (bgs) <br /> Filter Pack 18-30 feet bgs <br /> Filter Pack Material #3 Monterey sand <br /> Bentonite Transition Seal 15-18 feet bgs <br /> Annular Seal 0-15 feet bgs <br /> 2937 Veneman Ave,#B240 Geo-Phase Environmental Inc Phone(209) 569-0293 <br /> Modesto, CA 95356 Fax(209) 569-0295 <br />