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SOP No. 5.0 Monitoring Well Installation <br />least 3 feet, but not more than 5 feet, of bentonite pellets between the filter pack and the casing <br />grout. A minimum of 20 feet of bentonite seal will be used in the deep bedrock wells. Wax- <br />coated sodium bentonite pellets (delayed hydration) may be used to allow the bentonite to fall <br />through the water column and prevent bridging if the saturated water column is greater than 50 <br />feet. If the bentonite seal is placed above the water table, then the bentonite will be hydrated <br />using deionized or distilled water. <br />5.2.1.4 Annulus BackfilllGrout <br />The annular space above the filter pack and seal will be grouted with a bentonite/cement <br />mixture. Grouting is used to minimize the vertical migration of water to the screened interval <br />and to increase the stability and integrity of the well casing. <br />The cement/bentonite grout mixture shall consist of 95 to 97 percent Type V or Type II-V <br />Portland Cement and 3 to 5 percent bentonite powder by weight (equivalent to one 94-pound bag <br />of cement and between 2.8 and 4.7 pounds of bentonite). Approximately 8.5 gallons of water <br />shall be used for each cement/bentonite batch. The grout mixture shall be prepared by <br />thoroughly mixing the bentonite powder with water first and then mixing in the cement (USEPA <br />1990). <br />The casing grout requirements are as follows: <br />• The bentonite seal will be allowed to hydrate for a minimum of 1/2 hour before the grout is <br />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 side-discharge tremie pipe located within <br />approximately 10 feet of the top of the bentonite seal. The tremie pipe will be pulled up as <br />the annular space is filled. The tremie pipe will have a minimum inner diameter of 1.25 <br />inches and be composed of steel or PVC. <br />• No single lift of grout will exceed 100 feet and each lift will be allowed to set before the next <br />lift is placed. <br />• 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 <br />for cross-contamination of adjacent wells. This may occur when wells are installed in pairs, and <br />the grouted interval in a deep well coincides with the water bearing zone to be screened in a <br />shallow well. <br />5.2.1.5 Surface Seal Installation <br />Groundwater monitoring wells will be constructed with above-ground completions. A concrete <br />surface seal will be placed around the annulus of the well to a minimum depth of one foot or to <br />the top of the bentonite/cement grout, whichever is deeper. Twenty-four hours should elapse <br />between grout emplacement and installation of the surface seal to allow the grout to cure and <br />7/28/08 Page 6 of 8 R Squared Inc. <br />Attachment A