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installed by gravity through the rod and PVC pipe annulus, forms a barrier above the prepacked screen <br /> (Fig 2 2) This sand or natural formation barrier prevents bentonite grout from penetrating into the <br /> screened interval Granular bentonite or bentonite slurry is then installed in the annulus to forma well <br /> ' sea] A high-pressure grout pump (Geoprobe Model GS1000 or GS500) may be used to pump high- <br /> solids bentonite slurry or neat cement grout to fill the well annulus as the probe ro:L are retracted (Fig <br /> 2 3) The grout mixture must be pumped from the bottom up to accomplish a tight seal and to meet <br /> regulatory requirements <br /> In certain formation conditions, the prepacked screens may bind inside the probe rods as the rods are <br /> retracted This is most common in sandy formations that produce conditions sometimes referred to as <br /> ' Flush Mount Concrete Pad <br /> Well Cover <br /> Thickness ?4 0 in <br /> ' J Plug PVC Pipe <br /> (Locking Plug) 2 0 in Sch 40 <br /> 24-an length <br /> Plastic Plug <br /> ' (13227} <br /> PVC Riser <br /> 1 Nn Sch 40 <br /> 5-ft lengths <br /> (12876) <br /> High Solids 8entomte Slurry <br /> or Neat Cement Grout <br /> ' Bentonite Well Seal <br /> Thickness ?2 feet <br /> Grout Bamer <br /> (20140 Sand or Collapsed <br /> Natural Formation) <br /> ' Thickness >2 feet above top <br /> of screens <br /> 1 0-in Pipe x 2 5-in OD <br /> Prepack Well Screen <br /> PVC Bottom Plug <br /> (12881) <br /> Expendable Pant 3 fi in OD <br /> (AT3215) <br /> FIGURE 2 2 <br /> Installed Geoprobe 1 0-in x 2 5-in OD Prepack Screen Monitoring Well <br /> Standard Operating Procedure Page 4 1 0-m x 2 5-m OD Prepack Screen Monitoring well <br /> r <br />