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13 submerged in the sealing material maintaining a positive displacement throughout the sealing process until the grouting material has reached the ground surface. 3)The Contractor shall take measures to ensure that the weight of the cement column does not collapse the well casing during the sealing operation. 4)Well development shall not commence until a minimum of 24 hours after placement of the seal. 2.3.8 WELL DEVELOPMENT A. Scope--This item shall consist of airlift pumping and surging of the wells. The purpose of well development is to remove drilling fluids and to develop the gravel pack and aquifer to ensure that proper ground-water samples may be obtained from the piezometers. B. Methods 1. The Contractor shall provide an air compressor, sufficient pipe, and necessary equipment used for pumping that shall be capable of pumping 25 gpm from a static water level of 100 feet during development. 2. The air compressor used during well development shall be fitted with in-line filters to prevent volatile organic compounds from entering the well casings from the compressor. A 0.3 micron pre-filter and a 0.01 micron filter run in series and verified compatible to the Contractor's compressor will be required during all phases of well development. The Contractor shall furnish the Engineer with the make and model number of the air compressor to be used and the manufacturer and model number of the proposed filters to be used prior to the construction of the wells. 3. After the placement of the gravel envelope and annular seals has been completed, the gravel envelope shall be cleaned of all fluids, cake, and substances that would impair the flow of water into the well and the quality thereof. Cleaning shall be accomplished by airlift pumping and surging until the gravel has been cleaned and consolidated. 4. Pumping will be done with a minimum 3/8-inch diameter air pipe using the well casing as the eductor pipe. The air compressor and necessary equipment used for pumping shall be capable of pumping 25 gpm from a static water level of 100 feet during development. The pumping operations will be conducted until the well is fully developed and discharging clean ground water. 5. The development shall continue until the well produces water free of sand and the following turbidity guidelines can be achieved after surging the well. For piezometers that produce less than 2 gpm, a turbidity of 10 NTU within two casing volumes of purging. For piezometers that produce at least 2 gpm, a turbidity of 5 NTU must be achieved within two casing volumes of purging. 2.3.9 SURFACE COMPLETION A. Scope -- This item shall consist of furnishing and installing an above ground or flush mount (vault) surface completion on the Plans and in accordance with State and local standards.