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SOP No. 5.0 Monitoring Well Installation <br />surged for an additional 5 minutes. Again, additional filter pack material will be placed, as <br />required, to bring the level to at least 2 feet above the screen, or as specified by the Field <br />Geologist or driller. <br />5.2.1.3 Well Seal <br />The materials used to seal the annulus between the borehole wall and casing must: prevent <br />potential contaminant migration from ground surface or intermediate zones; isolate a discrete <br />monitoring zone; preserve confining conditions; prevent intrusion of the overlying grout into the <br />filter pack; and prevent cross- contamination between strata. The bentonite seal will consist of at <br />least 3 feet, of bentonite pellets /chips between the filter pack and the casing grout. A minimum of <br />20 feet of bentonite seal will be used in the deep bedrock wells: Wax - coated sodium bentonite <br />pellets (delayed hydration) May be used to allow the bentonite to fall through the water column <br />and prevent bridging if the saturated water column is greater than 50 feet. If the bentonite seal is <br />placed above the water table, then the bentonite will be hydrated. <br />5.2.1.4 Annulus BackfilllGrout (or suitable alternative) <br />The annular space above the filter pack and seal will be grouted with a bentonite /cement mixture. <br />Grouting is used to minimize the vertical migration of water to the screened interval and to <br />increase the stability and integrity of the well casing. <br />The cement/bentonite grout mixture shall consist of Portland Cement and 3 to 5 percent <br />bentonite powder by weight, which is approximately equivalent to one 94 -pound bag of cement <br />and between 2.8 and 4.7 pounds of bentonite. Approximately 8.5 gallons of water shall be used <br />for each cement /bentonite batch. The grout mixture shall be prepared by thoroughly mixing the <br />bentonite powder with water first and then mixing in the cement (USEPA 1990). <br />The casing grout requirements are as follows: <br />o The bentonite seal will be allowed to hydrate before the grout is placed. <br />• The annular grout will extend from the top of the bentonite seal to approximately 3 feet <br />below ground surface (bgs). <br />• Grout shall be placed in the well annulus using a tremie pipe located within approximately 10 <br />feet of the top of the bentonite seal. The tremie pipe will be pulled up as the annular space is <br />filled. The tremie pipe will have a minimum inner diameter of 1.25 inches and be composed <br />of steel or PVC. <br />a Pumping will continue until undiluted grout has been returned to the surface. <br />• After grouting, the well shall not be disturbed or be developed for a minimum of 24 hours. <br />Additional grout will be added if settling occurs. <br />Alternatively, the annular space can be backfilled with a bentonite slurry if the potential exists for <br />cross - contamination of adjacent wells. This may occur when wells are installed in pairs, and the <br />grouted interval in a deep well coincides with the water bearing zone to be screened in a shallow <br />well. <br />7/28/08 5 -ti R Incorporated <br />