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lene tubing Simply insert the poly tubing down the well annulus until the ' sand bridge is contacted Attach the Plastic Plug tubing to the grout machine and pump (13227) up to one gallon of clean water while moving the tubing up and down The jetting action of the water will loosen and remove the sand bridge Check r- 20140 Grade the annulus depth again The distanceIdislodge } (AT95) should be 2 to 3 feet (0,6 to 0,9 m) less than the riser length Proceed with Section 5 5 } ' 55 Bentonite Seal Above Screen 1 Bentonite is an expanding clay whichexhibits very low permeability When properly placed,bentonite prevents con- taminants from moving into the well screens from above the des ired monitor- ing interval The seal is formed either by pouring granular bentonite into the — Probe Rost string ' annulus from the ground surface, or by Void space withdrawn 3 R above r screen injecting a high-solids bentonite slurry resulting from ) directly above the grout barrier The use stable formation (Must fill with Sand placed above of granular bentonite is limited to cases sand from screen to provide in which the top of the screen ends above surface) grout barrier the water table(no water is present in the ' probe rods) Whichever method is used, at least 2 feet(0,6 m)of bentonite must be placed above the sand pack 1 Stably Formation Granular bento- nite is recommended if the following conditions are met • Top of screen interval is above the FIGURE 5 10 water table Installing Grout Barrier from Ground Surface Formation remained open when with 20140 Grade Sand probe rods were retracted • Bridging was not encountered while installing sand for the grout barrier in Section 5 4 a) Withdraw the probe rod string another 3 to 4 feet(0,9 to l m)and ensure that the PVC riser does not lift with the rods It is important that the bottom of the rod string is above the proposed seal interval if positioned too low,dry bentonite will backup into the expendable point holder Bridging then results if moisture is present inside the probe rods b) Pour bentonite between the probe rods and PVC riser as was done with the sand in Section 5 4 To ' properly hydrate the granular bentonite,it is necessary to pen odically add water through a tremie tube while installing the bentonite To accomplish this, repeat adding six inches of granular bentonite ' Standard Operating Procedure Page 17 1 0-in x 2 5 in OD Prepack Screen Monitoring Well FIGURE 4 6 Screen Deployment Using a Casing Pull Kit