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as a base on which to place the screen. A tremie pipe having an inside nominal diameter of not less than 1 inch, shall be lowered to the bottom of the annulus between the hole and well. The tremie pipe shall be cleaned with high pressure hot water/steam prior to each use. The tremie pipe shall be arranged so that water and filter pack material fed at uniform rates are discharged as the filter pack material fills the hole from the bottom up. The tremie pipe shall be raised at a rate that will keep the bottom of the pipe no more than 5 feet above the top Of the surface of the filter pack level, and no more than 2 feet below the surface of the filter pack level at all times. Dumping filter pack material from the surface of the ground and agitating the well in an effort to settle the filter material will not be allowed. The filter pack shall be installed continuously and without interruption until the filter pack has been placed as shown in the drawings. The depth to the top of the filter pack shall be directly measured, and recorded. Any water added to the filter pack material shall be obtained in accordance with paragraph Water Source. Filter pack material shall be protected from contamination prior to placement by either storing it in plastic lined bags,or in a location protected from the weather and contamination on plastic sheeting. Filter pack material shall be transported to the well site in a manner which prevents contamination by other soils, oils, grease, and other chemicals. Temporary drill casing, if installed, or auger shall be removed simultaneously with the above I operation. Lifting of the riser pipe shall be minimized when withdrawing the temporary casing/auger. Filter pack material shall be placed in no greater than 3 foot lifts prior to retraction of the temporary casinglauger. A minimum of 6 inches of filter pack shall remain in the temporary casing/auger at all times during filter pack installation. Frequent measurements shall be made inside the annulus during retraction to ensure that the filter pack is properly placed. 3.03.6 Bentonite Seal A. A minimum 3 foot thick hydrated bentonite seal shall be placed on top of the filter pack in a manner which prevents bridging of the bentonite in the annulus. The depth to the top of the bentonite seal shall be directly measured, and recorded immediately after placement,without allowance for swelling. Following placement of the bentonite, sufficient water shall be added to fully hydrate the bentonite. If the bentonite seal is located above any borehole fluid levels, a 1 foot layer of fine sand shall be placed at the top of the bentonite seal. 3.03.7 Grout Placement A. Bentonite grout shall be mechanically mixed in accordance with paragraph BENTONITE GROUT, and placed in two stages. After the bentonite seal has been placed, ad Foothill Landfill Site Improvement Project 7 GROUNDWATER MONITORING WELLS San Joaquin County Public Works Section 02522