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1 56 Grouting the well annulus Geoprohe Grout The placement of grout material within Machine ' the remaining well annulus provides ad- Plastic Plug (Gstoflo) chtional protection from vertical contami- — (13227) nant migration Most grout mixes are ' composed of neat cement, high-solids bentonite slurry,or a combination of ce- ment and bentonite Such mixes must 0 t be delivered with a high-pressure grout pump When stable formations exist,the well may be sealed by pouring dry granu- lar bentonite directly into the annulus from the ground surface Consult the appropriate regulatory agency to deter- mine approved grouting methods This Trem,e Tuttle ' section presents the procedure for grout- pumped (F 299) Tubing ing the well annulus with the Geoprobe Bentonite slurry 14298) Model GS500 or GS1000 Grout Ma- fills void as rods chine Refer to Figure 5 12 as needed withdrawn { 1 Mix an appropriate amount of grout High solids Bentonite slurry material and place it in the hopper of forms well seal Grout Barrier the grout machine — (20140 Grade sand or Natural Formation) NOTE It is recommended that an addi- tional 20 to 25 percent of the calculated annulus volume be added to the total grout volume This additional amount allows for grout that either remains in the grout hose or moves into the formation during pumping Including the additional ' 20 percent, it will take approximately FIGURE 511 0 54 gallons(2,0 L)of grout for each foot Installing Bentonite Seal with of riser below ground surface Geoprobe G51000 Grout Machine ' 2 Insert tremie tube into the well annu- lus until the end of the flexible tubing reaches the top of the bentonite seal Ensure that at least 25 feet(8 m)of tubing extends from the top of ' the rod string This extra length allows rod retraction with the tubing attached to the pump 3 Attach the tubing to the grout machine and begin pumping If the bentonite seal was below the water ' table(deep well installation),water will be displaced and flow from the probe rods as the annulus is filled with grout Continue operating the pump until undiluted grout flows from the top probe rod ' 4 Reposition the probe unit and prepare to pull rods 5 Begin pulling the probe rods while continuing to pump grout Match the pulling speed to grout flow so that the rods remain filled to the ground surface This maintains hydraulic head within the probe rods and ensures that the void left by the withdrawn rods is completely filled with grout ' Standard Operating Procedure Page 19 1 0-in x 2 5-in OD Prepack Screen Monitoring Well